Symposium Organizers
Elena A. Rozhkova, Argonne National Laboratory
Haifeng Ding, Nanjing University
Miguel Angel Garcia, Institute for Ceramic and Glass, CSIC
Carlos Rinaldi, University of Florida
Symposium Support
The Center for Nanoscale Materials – Argonne National Laboratory
MD9.1: Magnetic Materials—From Fundamentals to Applications I
Session Chairs
Dhirendra Bahadur
Elena A. Rozhkova
Monday PM, March 28, 2016
PCC North, 100 Level, Room 121 C
2:30 PM - *MD9.1.01
The Intricacies of the Transduction Mechanism in Giant Magnetoresistive Biosensors with Magnetic Nanoparticle Labels
Shan Wang 1,Jung-Rok Lee 1,Daniel J.B. Bechstein 1
1 Stanford University Stanford United States,
Show AbstractGiant magnetoresistive (GMR) biosensors consisting of many rectangular stripes are being developed for high sensitivity medical diagnostics of diseases at early stages, but many aspects of the sensing mechanism remain to be clarified. Using e-beam patterned masks on the sensors, we showed that the magnetic nanoparticles with a diameter of 50 nm located between the stripes predominantly determine the sensor signals over those located on the sensor stripes. Based on computational analysis, it was confirmed that the particles in the trench, particularly those near the edges of the stripes, mainly affect the sensor signals due to additional field from the stripe under an applied field. We also demonstrated that the direction of the average magnetic field from the particles that contributes to the signal is indeed the same as that of the applied field, indicating that the particles in the trench are pivotal to produce sensor signal. Importantly, the same detection principle was validated with a duplex protein assay. Also, 8 different types of sensor stripes were fabricated and design parameters were explored. According to the detection principle uncovered, GMR biosensors can be further optimized to improve their sensitivity, which is highly desirable for early diagnosis of diseases.
The GMR biosensors require well-tailored magnetic particles as detection probes, which need to give rise to a large and specific biological signal while showing very low nonspecific binding. This is especially important in wash-free bioassay protocols, which do not require removal of particles before measurement, often a necessity in point of care diagnostics. We show that magnetic interactions between magnetic particles and magnetized sensors dramatically impact particle transport and magnetic adhesion to the sensor surfaces. The dynamics of magnetic particles’ biomolecular binding and magnetic adhesion to the sensor surface is revealed in microfluidic experiments. We elucidate how flow forces can inhibit magnetic adhesion, greatly diminishing or even eliminating nonspecific signals in wash-free magnetic bioassays, and enhancing signal to noise ratios by several orders of magnitude. Our method is useful for selecting and optimizing magnetic particles for a wide range of magnetic sensor platforms.
This work is supported in part by NIH through the Center for Cancer Nanotechnology Excellence (U54CA151459) and the Autoimmunity Center of Excellence (ACE) at Stanford (U19AI110491).
References:
1. Jung-Rok Lee, et al., “Experimental and theoretical investigation of the precise transduction mechanism in giant magnetoresistive biosensors,” Sci. Rep., in press.
2. A.D. Henriksen, et al., “On the importance of sensor height variation for detection of magnetic labels by magnetoresistive sensors,” Sci. Rep., 5, 12282, 2015.
3. D.J.B. Bechstein, et al., “High performance wash-free magnetic bioassays through microfluidically enhanced particle specificity,” Sci. Rep., 5, 11693, 2015.
3:00 PM - *MD9.1.02
Development of Magnetic Nanoparticles for Simultaneous Imaging and Therapy
Yuping Bao 1
1 Univ of Alabama Tuscaloosa United States,
Show AbstractMRI is a widely used and valuable imaging tool for non-invasive clinical diagnosis and disease monitoring. In particular, in combination with therapeutic agents, MRI can offer in in-vivo tracking of drug delivery and release. To enable in-vivo MRI therapy tracking, efficient contrast agents are critical for resolution and tracking time. In this presentation, the development of effective contrast agent for MRI tracking will be presented, mainly T1 contrast agents based on the size and shape variation. For any biomedical application, the surface properties are key to defining the interfacial interactions. This talk will also address the facile method developed in our lab to attach various molecules onto nanoparticle surfaces for hydrophilicity and desirable functionality. Subsequently, drug encapsulation and release will be discussed.
4:00 PM - MD9.1.03
In Vivo Tissue Targeted Magnetic Particle Imaging (MPI)
Hamed Arami 2,Haydin Bradshaw 1,Eric Teeman 1,Alyssa Troska 1,Kannan Krishnan 1
1 Materials Science University of Washington Seattle United States,2 School of Medicine Stanford University Palo Alto United States,1 Materials Science University of Washington Seattle United States
Show AbstractMagnetic particle imaging (MPI) is a real-time, quantitative and clinically safe imaging technique, potentially applicable for future clinical applications such as cancer imaging, cardiovascular imaging or stem cell labeling and tracking. MPI performance (i.e. spatial resolution and sensitivity) is highly dependent on nanoparticles (NPs) size distribution, magnetization and environment. Therefore, NPs MPI signal is different after distribution into tissues or binding to the cells. Here, using in vitro and in vivo studies, we present the potential capabilities of MPI for tissue targeted imaging applications such as cancer and atherosclerosis imaging. To do this, first we used two preliminary experimental models to predict the performance of the tracers in a tissue equivalent environment and an acidic lysosome-like solution. For efficient targeting and specific binding of the NPs to the cells we need to conjugate additional biomolecules that can be recognized by receptors on the cells membranes. Therefore, as the next step, we introduced functional groups to the surface of the optimized NPs that can be used for bonding of the targeting peptides for imaging of the cancers or heart lesions. We also conjugated near infra-red fluorescent (NIRF) molecules to these functional groups and evaluated NPs performance as multimodal MPI tracers. This additional modality enabled us to study the targeting ability, biodistribution and pharmacokinetics of the NPs in mice more accurately, since NIRF has a high tracer mass sensitivity and reveals more details of microstructural distribution of the NPs in cancer, heart lesions and other organs. In addition, we investigated the pharmacokinetics and biodistribution of these NPs after their intravenous injection and evaluated their MPI performance after their accumulation in reticuloendothelial system (RES) organs (e.g. liver and spleen). We also present preliminary results of our in vivo cancer and atherosclerosis imaging in mice models (i.e. glioma xenografts in nude mice, prostate cancer in trabsgenic mice and heart lesions in C57BL6 LDL receptor mice). These results pave the ways for future applications of MPI for pre-clinical tissue-targeted magnetic imaging and diagnostic applications.
Acknowledgements:
This work was supported by NIH grants 1RO1EB013689-01 (NIBIB), 2R42EB013520-02A1 and 1R41EB013520-01.
4:15 PM - MD9.1.04
Magnetoresistance, Electrically Detected Magnetic Resonance, and Spin-Transport in a Variety of Amorphous Semiconductor and Insulator Thin-Films
Michael Mutch 1,Patrick Lenahan 1
1 Pennsylvania State University University Park United States,
Show AbstractSpin-dependent transport is of interest for spintronic applications.[1-3] Novel experimental techniques for the study of spin-dependent transport include near-zero field magnetoresistance (MR)[1-3] and electrically detected magnetic resonance (EDMR).[2,4,5] EDMR has been used to study a variety of defects in organic[1,3] and inorganic[2,4,5] semiconductors and dielectrics. We demonstrate a ubiquitous nature of MR and EDMR phenomena. We use EDMR, which can be used to study defect chemistry and energy levels, to link defects to MR phenomena in a variety of semiconductor and insulator systems. We complement the aforementioned methods with an analysis of EDMR and MR in inorganic materials as a means of understanding the relationship between spin-dependent transport and quantum effects such as electron-nuclear hyperfine interactions and spin-orbit coupling.
Films in our study include a-C:H, diamond-like carbon (DLC), a-B:H, a-SiC:H, and a-Si:H, and range in thickness between 10 and 500 nm. Films are grown on p-Si with Ti gate contacts. In all cases, strong EDMR and MR responses are observed. The EDMR responses, which we later link to MR responses, are believed to be a result of spin-dependent recombination (SDR) and/or spin-dependent trap-assisted tunneling events (SDTAT) through point defects. These transport phenomena have been observed in a variety of organic and inorganic systems.[1.4,5] Responses in this study are almost always broad and featureless, making defect identification via EDMR somewhat difficult. However, we circumvent this problem, to some extent, by making line width comparisons of spectra at high and low EDMR field/frequency combinations. As will be explained, these comparisons allow for an elementary understanding of line width contributions from defect hyperfine interactions and spin-orbit coupling. We also perform EDMR and MR measurements as functions of heterojunction bias, and compare with calculated band diagrams. Variable bias measurements allow for a rough calculation of defect energy levels. We find, via variable bias EDMR and MR comparisons, that defect energy levels are very similar in both cases. This provides a strong circumstantial connection between the nature of EDMR and MR phenomena. Finally, we make EDMR and MR measurements as functions of temperature. We find that the EDMR and MR versus temperature responses to be similar. This provides more evidence linking the underlying EDMR and MR phenomena.
[1] J. M. Lupton and C. Boehme, Nature Materials 7, 598 (2008).
[2] C. J. Cochrane et al. J. Appl. Phys. 112, 123714 (2012).
[3] N. J. Harmon et al., Phys. Rev. B 85, 075204 (2012).
[4] D. Kaplan et. al, J. Phys. Lett. 39(4), L51-L54 (1978).
[5] J. T. Ryan et al., J. Appl. Phys. 108, 064511 (2010).
4:30 PM - MD9.1.05
First-Principles Study of Magnetic Anisotropy in Cu-doped Nd-Fe-B Magnets
Yasutomi Tatetsu 1,Shinji Tsuneyuki 3,Yoshihiro Gohda 2
1 ESICMM, The University of Tokyo Tokyo Japan,1 ESICMM, The University of Tokyo Tokyo Japan,3 The Institute for Solid State Physics Kashiwa Japan1 ESICMM, The University of Tokyo Tokyo Japan,2 Materials Science and Engineering Tokyo Institute of Technology Yokohama Japan
Show AbstractStrong magnets are required to be installed in high efficiency motors for energy conservation. Nd-Fe-B magnets are known as the strongest permanent magnets and widely used in various kinds of materials, for example hybrid vehicles, wind turbines, hard disk drives, and cell phones. However, thermal stability of these magnets, especially at high temperature, is a known issue that is challenging for material designs. Recent experiments examining the microstructures of Nd-Fe-B magnets show that controlling the structural and magnetic properties of interfaces between subphases and main phases is important to improve the coercivity. As in Ref. [1], Nd-Fe-B magnets can be actually improved by the Nd-Cu grain boundary diffusion process and there is a relationship between the Cu concentration at the grain boundary and the coercivity improvement[2].
To understand this coercivity improvement we simulated Cu-doped Nd2Fe14B/NdOx systems, which were discovered around triple junctions in annealed Nd-Fe-B magnets and Cu is thought to be around main-phase (Nd2Fe14B) grains[1]. We used the computational code OpenMX within density functional theory[3]. We simulated various model structures containing more than 200 atoms each and checked their stability by comparing their total energies after structural optimization. For computational costs we used the open core pseudopotential of Nd atoms in which well-localized 4f electrons are treated as spin-polarized core electrons. From the total energy analysis we found that substituting the Nd site with Cu at the main-phase interface gives a structure that is more stable than the one obtained by substituting at the subphase (NdOx) interface. We analyzed the anisotropy of Nd atoms by calculating the crystal field parameters (CFP) of Nd atoms from first principles since the coercivity of Nd-Fe-B magnets is basically related to the anisotropy of Nd atoms. In addition, the anisotropy of Fe atoms were calculated in the manner determined by T. Zahra et al.[4]. We found the anisotropy of Nd and Fe atoms at the interface are basically negative as reported in a previous study of the surface case for Nd atoms[5]. Considering these negative anisotropy and the total energy analysis, we conclude that Cu substitution works effectively in terms of improvement of the coercivity.
[1] H. Sepehri-Amin, et al., Acta Mater. 61, 6622 (2013).
[2] A. Yasui, et al., J. Appl. Phys. 117, 17B313 (2015).
[3] http://www.openmx-square.org
[4] T. Zahra, T. Ozaki, S. Tsuneyuki, and Y. Gohda, Appl. Phys. Lett. 104, 242403 (2014).
[5] S. Tanaka, et al., J. Appl. Phys. 109, 07A702 (2011).
Symposium Organizers
Elena A. Rozhkova, Argonne National Laboratory
Haifeng Ding, Nanjing University
Miguel Angel Garcia, Institute for Ceramic and Glass, CSIC
Carlos Rinaldi, University of Florida
Symposium Support
The Center for Nanoscale Materials – Argonne National Laboratory
MD9.2: Magnetic Materials—From Fundamentals to Applications II
Session Chairs
Tuesday PM, March 29, 2016
PCC West, 100 Level, Room 105 B
2:30 PM - *MD9.2.01
Spin(calori)tronics with Magnetic Insulators
Gerrit Bauer 2
1 Tohoku University Sendai Japan,2 Kavli Institute of NanoScience Delft University of Technology Delft Netherlands,
Show AbstractSpintronics based on magnetic and non-magnetic elemental metals generated functionalities that are employed in nanoscale devices such as switches, memories, and sensors. Ferrimagnetic electric insulators such as man-made yttrium iron garnets form another class of versatile materials with high magnetic quality. K. Uchida, E. Saitoh c.s., demonstrated that they can be actuated thermally and electrically and thereby integrated into conventional electronics and thermoelectric devices, raising the hope for a new and green spintronics. After an elementary introduction into the basic physical concepts, I will review a number of recent theoretical insights and experimental evidence on magnetic insulators and its bilayers with non-magnetic metals.
3:00 PM - MD9.2.02
Coalescence Driven Magnetic Order of an Uncompensated Dilute Antiferromagnetic Oxide
Verena Ney 1,Bastian Henne 1,Katharina Ollefs 2,Fabrice Wilhelm 2,Andrei Rogalev 2,Andras Kovac 3,Andreas Ney 1
1 Johannes Kepler University Linz Austria,2 ESRF Grenoble France3 Forschungszentrum Juelich GmbH Juelich Germany
Show AbstractCo:ZnO films with Co concentrations of up to 60% of the cationic lattice have been grown by reactive magnetron sputtering. The wurtzite crystal structure was maintained even for these high dopant concentrations beyond the coalescence limit [1]. By measuring the x-ray absorption at the near edge and the linear and circular dichroism of the films at the Zn and Co K-edge it could be shown that Co substitutes predominantly for Zn in the lattice. No hints of metallic Co have been found in the samples. At low Co concentrations the films are paramagnetic, but with increasing Co content the films show antiferromagnetic next neighbor interaction [2] and develop magnetic order with increasing characteristic temperature. Uncompensated spins interact with the antiferromagnetic configurations and lead to a vertical exchange bias like effect. In addition, the single ion anisotropy [3] is lost with increasing Co percentage and the effective magnetic moment is strongly reduced.
[1] B. Henne, V. Ney, K. Ollefs, F. Wilhelm, A. Rogalev, A. Ney, Scintific reports, in revision (2015)
[2] A. Ney, V. Ney, F. Wilhelm, A. Rogalev, K. Usadel; Phys. Rev. B, Volume 85, 245202/1-8 (2012)
[3] A. Ney, T. Kammermeier, K. Ollefs, S. Ye, V. Ney, T. C. Kaspar, S. A. Chambers, F. Wilhelm and A. Rogalev; Phys. Rev. B 81, 054420 (2010
3:15 PM - MD9.2.03
Interplay of Anisotropy, Strain and Microstructure in α″-Fe16N2 Bulk Magnet
Md Mehedi 1,Yanfeng Jiang 2,Matteo Cococcioni 1,Jian-Ping Wang 2
1 Chemical Engineering and Materials Science University of Minnesota Minneapolis United States,2 Electrical and Computer Engineering University of Minnesota Minneapolis United States
Show AbstractSince its discovery in 1970s, α″-Fe16N2 has drawn the attention of the scientists for its high saturation magnetization and uniaxial magnetocrystalline anisotropy.[1-2] However, due to the discrepancies between the results reported by several groups, its potential application was always debated and scientists couldn’t find a common ground till 2010.[3-6] Nian Ji et. al. proposed a cluster model for the first time to describe the high moment of α″-Fe16N2, which was widely accepted in the scientific world.[7-8] However, the exact value of magnetocrytalline anisotropy of α″-Fe16N2 was also reported differently in different papers.[1,6,9] In our lab, we calculated the magnetocrystalline anisotropy of α″-Fe16N2 by using DFT calculation and validated the result from experimental results. Due to its high magnetocrystalline anisotropy, α″-Fe16N2 has a potential application as a rare-earth-free permanent magnet.[10-11] Thus, we analyzed the potential coercivity mechanism of the bulk α″-Fe16N2 magnet and proposed a model based on random anisotropy model with some extension. We also calculated the effect of grain size, stress annealing and composite phase mixture in the coercivity of α″-Fe16N2 bulk magnet. Finally, we analyzed the effect of nanostructure on the magnetic properties by using analytical equations.
References:
1.Kim, T. K., and Minoru Takahashi,
Applied Physics Letters 20.12 (1972): 492-494.
2.Annual Conference on Magnetism and Magnetic Materials, 1996 (Session on Fe
16N
2)
3.Sugita, Y., et al. ,
Journal of applied physics 70.10 (1991): 5977-5982.
4.Coey, J. M. D. ,
Journal of Applied Physics 76.10 (1994): 6632-6636.
5.Huang, M. Q., et al. ,
Journal of Applied Physics 75.10 (1994): 6574-6576.
6.Ji, Nian, et al. ,
Physical Review B 84.24 (2011): 245310.
7.Ji, N., X. Liu, and J. P. Wang. ,
New Journal of Physics 12.6 (2010): 063032.
8.Wang, Jian-Ping, et al. ,
Magnetics, IEEE Transactions on 48.5 (2012): 1710-1717.
9.Uchida, S., et al,
Journal of Magnetism and Magnetic Materials 310.2 (2007): 1796- 1798.
10.Wang, Jian-Ping, Shihai He, and Yanfeng Jiang. , U.S. Patent Application 14/238,835.
11.Ogawa, Tomoyuki, et al,
Applied Physics Express 6.7 (2013): 073007.
3:30 PM - MD9.2.04
Antiferromagnetism in RuO2
Paul Snijders 2,Tom Berlijn 1,Paul Kent 1,Thomas Maier 1,Haidong Zhou 2,Huibo Cao 1,Olivier Delaire 1,Yang Wang 1,Hanno Weitering 1,Michael Koehler 3
1 Oak Ridge National Laboratory Oak Ridge United States,2 Dept. of Physics and Astronomy University of Tennessee Knoxville United States,1 Oak Ridge National Laboratory Oak Ridge United States2 Dept. of Physics and Astronomy University of Tennessee Knoxville United States2 Dept. of Physics and Astronomy University of Tennessee Knoxville United States,1 Oak Ridge National Laboratory Oak Ridge United States3 Dept of Materials Science and Engineering University of Tennessee Knoxville United States
Show AbstractRutile RuO2 is a metallic 4d transition metal oxide with applications in electrochemistry, catalysis, and as diffusion barriers and strip-line connectors in microelectronics. Its electronic and chemical properties have therefore been studied extensively. However, its magnetic properties have received little attention.
We have theoretically and experimentally investigated the magnetic properties of RuO2. DFT+U calculations show that for modest local interactions the moments within the Ru2O4 unit cell strongly prefer to align antiferromagnetically, while leaving the electronic structure metallic. Magnetic susceptibility measurements show an approximately linear increase over a large temperature range, with a broad maximum near 925 K, suggesting a surprisingly high Neel temperature. This is confirmed with single crystal neutron diffraction experiments revealing structurally forbidden Bragg peaks that are absent in X-ray diffraction data. These magnetic peaks gradually disappear above 925 K, in agreement with the susceptibility data. This establishes RuO2 as a 4d binary oxide exhibiting itinerant antiferromagnetism at temperatures far surpassing the ordering temperatures of elemental Cr or doped pnictides.
This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
4:15 PM - *MD9.2.05
Graphene as a Spin Tunnel Barrier in MTJs and Silicon
Berend Jonker 1
1 Naval Research Laboratory Washington United States,
Show AbstractGraphene has been widely studied for its high in-plane charge carrier mobility and long spin diffusion lengths. In contrast, the out-of-plane charge and spin transport behavior of this atomically thin material have not been well addressed. Tunnel barriers to date have relied upon oxides which often exhibit defects, trap states and interdiffusion which compromise performance and reliability. We show here that while graphene exhibits metallic conductivity in-plane, it serves effectively as an insulator for transport perpendicular to the plane. We fabricate graphene-based magnetic tunnel junctions, and demonstrate electrical spin injection/detection in silicon and graphene using graphene as a tunnel barrier.
Graphene is grown by chemical vapor deposition and incorporated as the tunnel barrier by physical transfer and standard lithographic processes to form Co / graphene / NiFe magnetic tunnel junctions (MTJs) [1]. Non-linear I-V curves and weak temperature dependence of the zero-bias resistance provide clear evidence for tunneling. The magnetic field dependence exhibits the classic signature of an MTJ, and the structures exhibit tunneling magnetoresistance to 425 K, in good agreement with theory [2].
Graphene successfully circumvents the classic issue of conductivity mismatch between a metal and a semiconductor for electrical spin injection / detection. Hanle spin precession measurements performed on non-local spin valve (NLSV) devices with NiFe / single layer graphene / Si contacts exhibit the classic Lorentzian lineshape due to spin injection and dephasing in Si. The spin lifetimes correlate with Si carrier concentration, and the contact resistance–area products are 2-3 orders of magnitude lower than those achieved with oxide barriers [3]. This reduction of contact resistance enables NLSV spin transport and Hanle measurements of spin lifetimes in Si nanowires [4].
Finally, we demonstrate homoepitaxial tunnel barrier structures in which graphene serves as both the tunnel barrier and the transport channel [5,6]. We fluorinate the top graphene layer to decouple it from the bottom layer, so that it serves as a tunnel barrier for spin injection into the lower graphene channel. We demonstrate lateral transport of spin currents in NLSV structures, high spin injection efficiency with record tunneling spin polarization >45%, and determine spin lifetimes with the Hanle effect. Similar effects are observed with hydrogenated graphene [6].
[1] Cobas, Friedman, van’t Erve, Robinson, and Jonker, Nano Letters 12, 3000 (2012).
[2] Karpan et al, Phys. Rev. Lett. 99, 176602 (2007); Phys. Rev. B 78, 195419 (2008).
[3] van’t Erve, Friedman, Cobas, Li, Robinson and Jonker, Nature Nano. 7, 737 (2012).
[4] van ‘t Erve, Friedman, Li, Robinson, Connell, Lauhon and Jonker, Nature Comm. 6, 7541 (2015).
[5] Friedman, van ‘t Erve, Li, Robinson and Jonker, Nature Comm. 5, 3161 (2014).
[6] Friedman, van ‘t Erve, Robinson, Whitener and Jonker, ACS Nano 9, 6747 (2015).
4:45 PM - MD9.2.06
PT Symmetry-Breaking in Non-Equilibrium Magnetic Systems
Alexey Galda 1,Valerii Vinokur 1
1 Argonne National Laboratory Lemont United States,
Show AbstractMost of natural processes occur under out-of-equilibrium conditions. However, the lack of general principles governing non-equilibrium behavior only allows to treat it in a few special cases. We introduce generalized non-Hermitian Hamiltonian approach for description of out-of-equilibrium phase transitions in the exemplary context of dissipative non-equilibrium dynamics of an open quantum spin system. The imaginary part of the proposed Hamiltonian describes effects of damping and the applied Slonczewski spin-transfer torque (STT). In the classical limit, our approach reproduces Landau-Lifshitz-Slonczewski dynamics of a large macrospin. We reveal the STT-driven parity-time (PT) symmetry-breaking transition corresponding to a phase transition from precessional magnetization dynamics to controlled switching. Micromagnetic simulations for nanoscale ferromagnetic disks demonstrate the predicted effect. Our findings break ground for a general quantitative description of out-of-equilibrium phase transitions.
5:00 PM - *MD9.2.07
Exchange-Dominated Pure Spin Current Transport in Alq3 Molecules
Di Wu 1
1 Department of Physics Nanjing University Nanjing China,
Show AbstractThe use of organic semiconductors (OSCs) in spintronics has aroused considerable interests, owing to their much longer spin-relaxation times of OSCs than those of inorganic counterparts. The most studied example is the organic spin valve (OSV), in which magnetoresistance (MR) effect is frequently reported. However, studies on pure spin current injection and transport in OSCs are scarce. Recently, the pioneering work by Watanabe et al. demonstrated that pure spin current can be pumped into and propagates in semiconducting polymers (Nature Phys. 10, 308 (2014)). In the present work we extend the study to small molecule OSCs, and demonstrate that pure spin current can be injected into Alq3 from the adjacent magnetic insulator Y3Fe5O12 (YIG) by spin pumping. The pure spin current is detected by inverse spin Hall effect (ISHE) in Pd after propagation through Alq3. An unusual angular dependence of the inverse spin Hall effect is found. It, however, only appears when the microwave magnetic field is neither fully perpendicular to nor fully within the sample plane, excluding the presence of the Hanle effect. Together with quantitative temperature-dependent measurements, these results provide compelling evidence that the pure spin current transport in Alq3 is dominated by the exchange-mediated mechanism.
5:30 PM - MD9.2.08
Spin-Orbit Torque Induced Reversible Coercivity Change in Co/Pd Multilayer Thin Films
Sandeep Kumar 1
1 Univ of California-Riverside Riverside United States,
Show AbstractIn this work we report reversible reduction in coercivity of Co/Pd multilayer thin films under high-density direct current biasing. We carried out in-situ focused magneto optic Kerr effect based hysteresis measurement while the specimen was under DC bias. The experiments show a reversible reduction in coercivity during the application of direct current. We propose this reduction occurs due to the spin-orbit torques (Rashba) generated at high current densities. Using an in-situ transmission electron microscope biasing experiment, we also showed the presence of dissymmetric lattice structure of Co/Pd multilayers. Our results suggest that the Rashba torque is the dominant spin-orbit torque since coercivity change is a bulk phenomenon as compared to spin Hall effect.
5:45 PM - MD9.2.09
Thermal Dependence of Helicity Independent All-Optical Switching
Richard Wilson 1,Jon Gorchon 1,Yang Yang 1,Jun-Yang Chen 3,Li He 3,Mo Li 3,Jeff Bokor 2
1 Electrical Engineering and Computer Sciences University of California Berkeley Berkeley United States,2 Lawrence Berkeley National Lab Berkeley United States,1 Electrical Engineering and Computer Sciences University of California Berkeley Berkeley United States3 University of Minnesota Minneapolis United States1 Electrical Engineering and Computer Sciences University of California Berkeley Berkeley United States,2 Lawrence Berkeley National Lab Berkeley United States
Show AbstractIrradiation of ferro- and ferri-magnetic metals with high-energy femtosecond laser pulses leads to ultrafast heating induced changes to the magnetization. In ferrimagnetic metals such as GdFeCo or TbFeCo, reversal of the magnetization can occur if heating of the electrons is sufficiently large and fast. Ultrafast magnetic switching via heating of the electrons opens the possibility to generate ultrafast switches for memory and logic. However, a comprehensive and quantitative description of all optical switching (AOS) remains elusive due to the complexity of the problem. Following laser irradiation, energy and angular momentum is rapidly exchanged between numerous subsystems that cannot all be simultaneously probed, e.g. thermal electrons at the Fermi level, 4f spins, majority and minority 3d spins, and phonons. In this work, we perform a combination of single shot and time-resolved magneto optic Kerr effect (TR-MOKE) measurements of ferri-magnetic GdFeCo and TbCo alloys as a function of laser fluence and ambient temperature. At low absorbed laser fluence, e.g. less than 0.4 mJ/cm2, the demagnetization rate as a function of ambient temperature of the FeCo sublattice is qualitatively similar to that of a single element ferromagnet such as Ni, Fe, or Co. Additionally, the demagnetization rate of the CoFe sublattice displays a dependence on ambient temperature consistent with the predictions of a simple thermal model. For absorbed fluences greater than ~1 mJ/cm2, the magnetization dynamics of the FeCo sublattice show dramatic differences from our low fluence experiments. These differences include magnetization reversal for fluences above a critical value, e.g. ~2 mJ/cm2 at room temperature. The critical switching fluence decreases substantially with increasing ambient temperature. The speed of both the initial switching and subsequent magnetization recovery depend strongly on the ambient temperature of the sample. Finally, we experimentally determine the peak electron and lattice temperatures required for AOS to occur.
MD9.3: Poster Session: Magnetic Materials—From Fundamentals to Applications
Session Chairs
Wednesday AM, March 30, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - MD9.3.01
Effect of Heat Treatment and Average Crystallite Size on MnBi Magnetic Behavior
Alfredo Carranco 1,Carlos Rodriguez 2,Maricruz Rocha 2,Jose Elizalde Galindo 1
1 Physics and Mathematics Universidad Autonoma de Ciudad Juarez Juarez Mexico,2 Universidad Tecnologica de Ciudad Juarez Juarez Mexico
Show AbstractThis work shows how the magnetic properties of intermetallic MnBi nanocomposite are influenced by effect of heat treatment and crystallite size controlled by mechanical milling. MnxBi100-x (x= 45, 50, 55) compounds with 5%, 10% and 15% of Bismuth excess were synthetized by arc melting technique, and annealed under Ar atmosphere at temperature T equal to 573 and 623K for 12 and 10h. Another nanocomposite of MnxBi100-x (X= 45, 50, 55) were synthetized in the same way, grinded during 4 and 8 hours in a high energy mill and annealed at 1073 K for 10 minutes and quenched. X-Ray Diffraction patterns confirmed the presence of MnBi phases. The microstructure were characterized by Scanning Electron Microscopy. Hysteresis loops collected by Vibrant Sample Magnetometer (VSM) showed an increment of coercive field from 5 KOe (freshly melted) to 10 KOe after the annealing for no-grinded samples. Grinded samples showed and increment to 16KOe in coercive field due to the small size of crystallite. So, samples with small average crystallite size reduced my milling have better magnetic properties than samples just synthetized and annealed.
9:00 PM - MD9.3.02
Inducing Coercivity in Coherently Strained [Fe-Co/Au-Cu]n Multilayers
Georgios Giannopoulos 1,Ruslan Salikhov 2,Ludwig Reichel 3,Imran Khan 5,Anastasios Markou 4,Ioannis Panagiotopoulos 6,Michael Farle 7,Sebastian Faehler 8,J Hong 9,Vasilis Psycharis 10,Dimitrios Niarchos 11
1 NCSR Demokritos Greece Athens Greece,2 Fakultät für Physik and Center for Nanointegration (CeNIDE) Duisburg Germany3 IFW Dresden Dresden Germany5 Pukyong National University Busan Korea (the Republic of)4 University of Ioannina Ioannina Greece6 University of Ioannina Ioannina Greece7 Fakultät für Physik and Center for Nanointegration (CeNIDE) Duisburg Germany8 IFW Dresden Dresden Germany9 Pukyong National University Busan Korea (the Republic of)10 NCSR Demokritos Greece Athens Greece11 NCSR Demokritos Greece Athens Greece
Show AbstractFor a permanent magnet, high magnetocrystalline anisotropy, high magnetic moment and coercivity are required. Fe-Co alloy is proposed as an alternative to rare earth permanent magnets, as it is proposed to exhibit both, a high magnetocrystalline anisotropy energy [1] along with a high magnetization.
In this work we present our approach of inducing magnetocrystalline anisotropy and coercivity in Fe-Co/Au-Cu multilayer films, produced by magnetron sputtering. The main idea is the stabilization of metastable tetragonal phases and the induction of anisotropy by straining the FeCo unit cell [1]. We also doped FeCo with Carbon since by this way, we can stabilize strain and increase the magnetocrystalline anisotropy [2, 3]. However, with increasing thickness of the films, a partial strain relaxation is expected [4]. In order to induce strain from both sides in the FeCo layer and thus prevent the strain relaxation, we deposited Fe-Co/Au-Cu multilayers on single crystalline MgO (100) substrate. The thickness of the layers varied between 1-3nm for FeCo and 1-2nm for AuCu.
X-ray,SQUID and FMR measurements were performed. The multilayer films grow epitaxially. A peak shift of 0.5o was observed in the XRD patterns compared to the theoretically expected value for FeCo-C alloys, which is a strong indication of tetragonal distortion. A high magnetocrystalline anisotropy value of about 0.4 MJ/m3 was measured using FMR for the [Fe45Co55(3 nm)/Au30Cu70 (1 nm)]12 system. Theoretical calculations have also been performed using full potential linearized augmented plane wave method (FLAPW) with generalized gradient approximation (GGA). An anisotropy value of 0.43MJ/m3 was estimated according to the computational results for the AuCu/FeCo/AuCu system.
In our multilayers, the up-sclaing of the thickness, a reduced strain relaxation, along with the induction of coercivity in the order of 900 Oe, is a first promising step towards rare earth free permanent magnets.
Acknowledgements
We acknowledge funding of the EU through FP7-REFREEPERMAG
References
[1] T. Burkert, L. Nordström, O. Eriksson, and O. Heinonen , Physical Review Letters 93, 027203 (2004)
[2] E. K. Delczeg-Czirjak, A. Edstrom, M. Werwinski, J. Rusz, N. V. Skorodumova, L. Vitos, and O. Eriksson, Physical Review B 89, 144403 (2014)
[3] G. Giannopoulos, R. Salikhov, B. Zingsem, A. Markou, I. Panagiotopoulos, V. Psycharis, M. Farle, and D. Niarchos, APL Materials 3,041103 (2015)
[4] L. Reichel, G. Giannopoulos, S. Kauffmann-Weiss, M. Hoffmann, D. Pohl, A.Edstroem, S. Oswald, D. Niarchos, J. Rusz, L. Schultz, and S. Fähler, Journal of Applied Physics 116, 213901 (2014)
9:00 PM - MD9.3.03
Increase of Magnetic Sensitivity of Magnetically Controlled Mems Switches
Sergey Karabanov 1,Dmitriy Suvorov 1,Gennadiy Gololobov 1,Dmitriy Tarabrin 1,Evgeniy Slivkin 1
1 Ryazan State Radio Engineering University Ryazan Russian Federation,
Show AbstractMagnetically controlled MEMS switches, the functional analogue of small reed switches and Hall sensors, are highly competitive products. The important target is to increase the switches lifetime and sensitivity on condition of keeping inertial stability.
In present work for the study of magnetic sensitivity in COMSOL program package a number of 3D models of magnetically controlled MEMS switches for 3 design options has been developed: with a fixed beam, with a torsion bar beam, with the magnetic concentrator. The models are based on the equations of magnetic field distribution, action of magnetic field force on ferromagnets, on equations describing mechanical stresses. The properties of electrodeposited permalloy (75% Fe, 25 % Ni) as ferromagnetic material of the magnetic beam, magnetic concentrators and torsion levers have been investigated in the models.
In the course of modeling the following results were received: 1) profiles of mechanical stresses distribution, magnetic field inside MEMS switch design and dynamics of geometry change of moving parts during commutation are defined; 2) dependences of magnetic sensitivity and shock tolerance at various design geometries are received; 3) it is established that the use of magnetic concentrators is an effective method of MEMS switch sensitivity increase. 4) It is established that the use of elbowed torsion bars for fastening is an effective method for magnetic sensitivity increase. 5) It is shown that electrodeposited permalloy consisting of 75% Fe and 25 % Ni is the suitable material for production of basic ferromagnetic materials of MEMS switches.
The results of the completed calculations show that the design including a traveling magnetic ram and fixed magnetic concentrator provides 2 times increase of magnetic sensitivity. The use of magnetic concentrators is the effective method for improvement of operational characteristics of magnetically controlled MEMS switches. It is shown that the use of elbowed torsion bars is the effective way of magnetic sensitivity increase providing the possibility of considerable decrease of mechanical stresses appearing at commutation.
The obtained results are used for the development of new MEMS switches types.
9:00 PM - MD9.3.04
Structural, Magnetic Properties and Mossbauer Analysis of Dy2Fe17-(x+y) Nbx Siy (x= 0, 0.25,0.50 and y =0, 1, 2, 3) Prepared by Arc-Melting
Hitesh Adhikari 1,Dipesh Neupane 1,Syed Ali 2,Sanjay R Mishra 1
1 Univ of Memphis Memphis United States,2 Department of Science John Tyler High School Tyler United States
Show AbstractThe R2Fe17 compound is the most iron-rich phase in the binary R-Fe alloy system. The main drawbacks of these materials are low Curie temperature (Tc) and magnetic anisotropies which restrict the possible applications of these materials as high temperature permanent magnets. The substitution of non-magnetic atoms (C, N, H) in Fe sites increases ferromagnetic coupling which in turn increases the Tc and magneto-crystalline anisotropy but the nitrogen and carbon materials are not stable at high temperatures.
Furthermore, Unless removed by a homogenization treatment, the iron reduces the coercivity of the subsequently fabricated magnets.Thus 2:17 alloys are subjected to long isothermal annealing of several days, in order to remove the free iron. This makes the production less cost effective. In an attempt to reduce the manufacturing costs additional elements such as Nb, and Si have been added to the ingot to create an alloy without free iron.These additions lead to the formation of a eutectic mixture consisting of the 2:17 phase, Nb-Si phase and the DyFe3 paramagnetic Laves phase. Majority of the work on 2:17 pure and substituted intermetallics are limited to single atom substitution but in The doubly substitution improves the Tc at lower level doping without much deterioration in magnetization. Interestingly, Nb and Si doped compounds are light-weighted and corrosion resistant, which are desired in many potential applications of permanent magnet.
In this study the effects of double substitution of nonmagnetic metallic atom Nb and Si for Fe on the structural and magnetic properties of Dy2Fe17-(x+y)NbxSiy compounds were investigated. A series of Dy2Fe17-(x+y)Nbx Siy (x= 0, 0.25,0.5 and y =0, 1, 2, 3) compounds were prepared by arc melting in an argon atmosphere. The structural and magnetic properties of these compounds have been studied via XRD,VSM and 57Fe Mössbauer spectroscopy. The substitution of Nb and Si in Dy2Fe17-(x+y) compound was found to have an important effect on their structure and magnetic properties. An increase in unit cell volume with the increase in Nb and Si content is observed in Dy2Fe17-(x+y)Nbx Siy. Rietveld analysis of XRD patterns show that these compounds form the hexagonal Th2Ni17 structure. The saturation magnetization of Dy2Fe17-(x+y)Nbx Siy shows an approximately linear increase with the increase of x (for y=0) up to 95.86 emu/g for x=0.25 and y=0. However, lower magnetization values were obtained for Dy2Fe15.75Nb0.25 Si1 (51.99 emu/g) and Dy2Fe14.75Nb0.25 Si2 (24.36 emu/g). The room temperature Mössbauer analysis showed that the hyperfine field values decreased with Nb and Si substitution due to magnetic dilution upon substitution.
Thus, the present study clearly demonstrates Dy2Fe17-(x+y) Nbx Siy compounds achieve high Tc in low level doping of Nb and Si without much reduction in Ms. This magnet may find application in the industry for its high Tc, high energy product,and corrosion resistance properties.
9:00 PM - MD9.3.05
Effect of Boron Addition on Magnetic Domain Structure of Rapidly Quenched Zr2Co11-Based Nanomaterials
Lanping Yue 1,Yunlong Jin 2,David Sellmyer 2
1 Nebraska Center of Materials and Nanoscience University of Nebraska Lincoln United States,1 Nebraska Center of Materials and Nanoscience University of Nebraska Lincoln United States,2 Department of Physics and Astronomy University of Nebraska Lincoln United States
Show AbstractZr2Co11-based nanomaterials are promising candidates for the development of rare-earth-free permanent magnets with strong magnetocrystalline anisotropy energy, high Curie-temperature, and hard magnetic performance. Addition of suitable external element Mo, Si, or B into Zr2Co11-based alloys has shown significant improvement in the magnetic properties, such as a significant increase in coercivity and energy product [1-4]. Although Boron element doping favors the formation of the hard-magnetic phase and increases the coercivity of melt-spun Zr-Co alloys, how B addition affects magnetic microstructure and what is the correlation of magnetic microstructure and magnetism are still unclear. The investigation of the magnetic microstructure and property relationship is important for the understanding of these improvements and further for the development of high-performance magnets. The effect of B addition on magnetic domain structures of nanocrystalline Zr16Co82.5−xMo1Bx (x = 0, 1, 2, 3 and 4) melt-spun ribbons was investigated by Magnetic Force Microscopy (MFM). We find that element addition is a feasible way to modify magnetic domain structure and enhance coercivity for Zr2(Co, Mo, B)11 nanocrystalline alloys. The best magnetic properties were obtained with a significant increase in coercivity Hc and isotropic maximum energy product (BH)max for the x = 1 sample with Hc = 5.4 kOe and (BH)max = 4.1 MGOe . A detail MFM image analysis of the B-content dependence of magnetic domain structures in this class of non-rare-earth Zr16Co82.5−xMo1Bx (x = 0, 1, 2, 3 and 4) nanocrystalline ribbons is provided to further advance the insight into the underlying microscopic mechanisms. Surface roughness analysis of the melt-spun ribbons was also performed by Atomic Force Microscopy (AFM). This research was supported by DOE/Ames under Grant no. DE-AC02-07CH11358 and SC-15-423. The research was performed in part in the Nebraska Nanoscale Facility: National Nanotechnology Coordinated Infrastructure and the Nebraska Center for Materials and Nanoscience, which are supported by the National Science Foundation under Award ECCS: 1542182, and the Nebraska Research Initiative.
9:00 PM - MD9.3.06
A Flexible Magnetically Responsive Film for Remote Manipulation of Droplets
Hangil Ko 1,Hoon E. Jeong 1
1 UNIST Ulsan Korea (the Republic of),
Show AbstractThe manipulation of droplets is of significant interest for a broad range of applications from lab-on-a-chip devices to bioinspired functional surfaces. To manipulate a droplet, micro- or nanopatterned surfaces have been suggested as a passive approach, in which unique structural features or chemical gradients enable liquid wetting and spreading in a specific direction. Although these approaches enable control over liquid wetting and spreading without external forces, they are typically slow and not reversible, presenting inherent limitations. A set of active droplet manipulation techniques have also been proposed, including electrowetting, dielectrophoresis and thermocapillary force. Compared with the passive approaches, these active techniques provide enhanced control over droplet position and motion in a fast and reliable fashion. Nonetheless, the electrowetting platform requires electrodes formed on a substrate, as well as an external power source, for the manipulation of liquid droplets, which limits the scalability and applicability of the technique.
To this end, magnetically actuating surfaces with micro- or nanoscale structures have considerable potential to be used for the active and dynamic manipulation of droplets because of their reversible and instantaneous structural tunability in response to a remote and non-destructive magnetic field. However, previous droplet manipulation techniques based on magnetic force are mostly limited to irreversible transitions of wetting states without the ability to control the position and motion of discrete droplets. Although some studies reported positional control of droplets based on using a magnetic field, they utilized a droplet mixed with magnetic nanoparticles, which significantly limits broad application of the techniques.
Here, we report a novel technique that enables active and dynamic control over the position and motion of a pure discrete droplet by utilizing a magnetically responsive flexible film comprising reversibly actuating hierarchical pillars on the surface. In this approach, a discrete droplet of water can be rapidly manipulated to arbitrary target locations on the flexible film with only the use of a permanent magnet. The flexible film with actuating hierarchical pillars is simply fabricated by a mouldless self-assembly of a solution comprising precured polymers and magnetic particles under a magnetic field. This magnetically responsive surface exhibits reliable actuating capabilities with immediate field responses and maximum tilting angles of ~90°. Furthermore, the magnetic responsive film exhibits superhydrophobicity regardless of the tilting angles of the actuating pillars. Using this novel magnetically responsive film with a superhydrophobic nature, we demonstrate highly precise and dynamic manipulation of a discrete droplet in an active and instant manner using only a permanent magnet.
9:00 PM - MD9.3.07
Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe4N, and Half-Metallic Ferromagnet: Systematic Analysis and Intuitive Explanation
Satoshi Kokado 1,Takuya Ito 1,Ryutaro Wada 1,Masakiyo Tsunoda 2
1 Graduate School of Integrated Science and Technology Shizuoka Univ Hamamatsu Japan,2 Graduate School of Engineering Tohoku University Sendai Japan
Show AbstractThe anisotropic magnetoresistance (AMR) effect is a phenomenon in which the electrical resistivity depends on the relative angle between the magnetization direction and the electric current direction [1-9]. The AMR ratio, which is the efficiency of the effect, is defined by (ρ∥-ρ⊥)/ρ⊥, where ρ∥ (ρ⊥) is a resistivity for the case of the electrical current parallel to the magnetization (a resistivity for the case of the current perpendicular to the magnetization). The AMR ratio has been experimentally measured for various ferromagnets since about 150 years ago. Systematic analyses for their AMR ratios, however, have been scarce so far. In addition, the intuitive explanation about the AMR effects has seldom been reported.
In this study, we first derived a general expression of the AMR ratio [3,4]. We here used the two-current model with all the s-d scattering processes. The d states were obtained by applying the perturbation theory to a Hamiltonian with the exchange splitting and spin-orbit interaction VSO. Using the expression, we next analyzed the AMR ratios of Fe, Co, Ni, Fe4N, and half-metallic ferromagnet. We found that Fe, Co, and Ni exhibit the positive AMR ratio, while Fe4N and half-metallic ferromagnet show the negative AMR ratio. Such a tendency agreed with the experimental results. In addition, their AMR effects could be intuitively explained by using the d orbitals, which were distorted by VSO. We finally showed that the negative AMR ratio is a necessary condition for half-metallic ferromagnet [3-6]. Details will be reported in our presentation.
[1] Masakiyo Tsunoda et al., Appl. Phys. Express 2, 083001 (2009).
[2] Masakiyo Tsunoda et al., Appl. Phys. Express 3, 113003 (2010).
[3] Satoshi Kokado et al., J. Phys. Soc. Jpn. 81, 024705 (2012).
[4] Satoshi Kokado et al., Adv. Mater. Res. 750-752, 978 (2013).
[5] Fujun Yang et al., Phys. Rev. B 86, 020409 (2012).
[6] Yuya Sakuraba et al., Appl. Phys. Lett. 104, 172407 (2014).
[7] Kazuki Kabara et al., Appl. Phys. Express 7, 063003 (2014).
[8] Satoshi Kokado et al., phys. stat. solidi (c) 11, 1026 (2014).
[9] Satoshi Kokado et al., J. Phys. Soc. Jpn. 84, 094710 (2015).
9:00 PM - MD9.3.08
Characterization of (Ferromagnetic)/(Normal Metal or Insulator) Multilayer Thin Films
Sandeep Kumar 1,Paul Lou 1
1 Univ of California-Riverside Riverside United States,
Show AbstractIn this work, we present the experimental results on magnetic behavior and thermal transport behavior of ferromagnetic multilayer thin films. We have developed a unique micro-electro-mechanical systems (MEMS) based experimental setup that has freestanding specimen and allows us to measure electrical and thermal conductivity of thin films. We measured the thermal conductivity using 3ω method. We also investigated the ferromagnetic behavior under high density current using magneto-optic Kerr effect measurement and transmission electron microscope. The techniques presented in this work allows us to have a comprehensive characterization of the multilayer ferromagnetic thin films.
9:00 PM - MD9.3.09
Au@CoFe2O4 Yolk-Shell Nanoparticles: An Efficient MRI Contrast Agent, Magneto-Hyperthermal and Drug-Delivery Armada for Cancer Theranostics
Ravichandran Manisekaran 1,Goldie Oza 1,Velumani S 1
1 Centro de Investigación y de Estudios Avanzados del Instituto Mexico City Mexico,
Show AbstractAn iterative-seeding based magneto-plasmonic Au@CoFe2O4 yolk-shell nanoparticles using ascorbic acid and cobalt ferrite as reducing nanotemplates has been designed. We have proposed a novel aspect of site-specific targeting of Doxorubicin using iterative Au coated CoFe2O4 yolk-shell nanoparticles as a nanopayload and folic acid as a targeting agent for cancerous cells. The multiple iterations and different shell size and shapes have been well explained using XRD and HRTEM. One single layer of Au on Cobalt ferrite nanoparticles enhances the capability of binding drugs, but multiple coating further augments the physiological stability and tunes surface plasmon resonance as well as dielectrics for proficient loading of drugs as well as pH-dependent release in specific microenvironment. The functionalization of folic acid and Doxorubicin was confirmed by FTIR and TGA. SQUID explained the efficacy of iterative method by confirming that even after 5 Au iterations, Au@CoFe2O4 was highly superparamagnetic. MRI showed that the yolk-shell possess enhanced T2 contrast for imaging both normal and cancer cells. Magnetic Hyperthermia studies exhibited an overwhelming augmentation in the temperature rise for yolk-shell nanoparticles. Doxorubicin release kinetics profile has been fit based on Zero-order, First Order, Higuchi and Hixson-Crowell model. This nanocarrier as an efficient MRI contrast agent, Magneto-hyperthermal and drug-delivery nanofleet is a step ahead towards the success of cancer theranostics. This drug delivery system can act as an efficient nanocarrier in the cancer micromilieu for synaphic targeting and assassination of the cancer cells, thus rescuing the life of patients.
9:00 PM - MD9.3.10
Surfactant Assisted Synthesis of Single Phase BiFeO3: Structural, Magnetic and Mossbauer Study
Dipesh Neupane 1,Sanjay R Mishra 1,Lijia Wang 1
1 Univ of Memphis Memphis United States,
Show AbstractMultiferroics are the materials in which two or more than two ferroic orders(ferroelectric, ferromagnetic and ferroelastic) occur in the same phase. Among these compounds, ABO3 perovskites where A = Bi and B = transition metal of the first row, i.e., Fe, deserve much attention because of their multiferroic possibilities, where spontaneous magnetic order and ferroelectric polarization might be combined in a single phase material. These materials offer wide potential applications in information storage and sensors. It has been already reported that during the synthesis of BiFeO3, results in the appearance of phases. Many alternative strategies have been (are being) attempted to prepare pure BiFeO3. In order to obtain a pure phase, a temperature and heat treatment are critical.
Single particle 40 to 60 nm of the multiferroic rhombohedral structure BiFeO3 were synthesized via co-precipitation method using cetyltrimethyl ammonium bromide(CTAB) as a surfactant, and different heat treated in air (at 550°C, 6000C and 6500C) for 2 hrs. The effects of CTAB contents (0, 3, 6 and 9 wt.%) on formation, structure, morphology and magnetic property of the BiFeO3 particles were investigated. Pure phase Multiferroic BiFeO3 powder were obtained in the existence of CTAB surfactant at 5500C, whereas secondary phase Bi25FeO39 was detected for the sample without presence of CTAB and in the samples with CTAB annealed at higher temperature.
Our vibrating sample magnetometer results suggest that a saturation magnetic response in BiFeO3 can be initiated when the size of the system is less and coerivity increases with increasing of particle size due to the uniaxial crystalline anisotropy.
The Mossbauer study of BiFeO3 gives quadrupole splitting of sample with increased sample size, which could suggest a change in atomic displacement accompanied by modified polarization properties. At room temperature, a superposition of quadrupolar (doublet) and magnetic (sixplet) absorption spectra is observed. The spectra become progressively more magnetic with increasing annealing temperature. The collapsed quadrupolar spectra are associated with the subset of smallest particles within the size distribution synthesized within a given sample. Least-square fits of our experimental data to theoretical spectra give values for the isomer shift (δ), quadrupole splitting (ΔEQ), and magnetic hyperfine field (Hhf) consistent with the presence of high-spin ferric ions . BiFeO3 has been reported to exhibit a single doublet with a quadrupole splitting of about (ΔEQ) 0.08 mm/s, indicating a slightly distorted octahedral symmetry at the Fe3+ site above Neel temperature. For larger particles, two inequivalent magnetic subsites are observed with slightly different values of magnetic hyperfine fields (Hhf1 ) 471.9 kOe and (Hhf2 ) 494.7 kOe for the 50 nm, 600 °C annealed sample. These result implies that CTAB may act as a crystalisation master, controlling the nucleation and growth of the crystal of BiFeO3.
9:00 PM - MD9.3.11
Geometrical Confinment and Spin Vortex Resonance
Valentine Novosad 1
1 Argonne Nat'l Lab Lemont United States,
Show AbstractSince the demonstration of magnetic vortex oscillators [1] driven by a spin-polarized current, there has been an increased interest in the dynamic properties of geometrically confined spin vortices. The frequency of the gyrotropic mode of the vortex core depends on the geometry (circular vs. elliptical dots) and the dot dimensions [2] Apart from this, it has been reported that the intrinsic film defects may affect the dynamics of magnetic vortices [3]. In this work, we demonstrate that a relatively small alteration to the dot topography could also serve as an artificial pinning site for the vortex core, and thus significantly influence the resonant properties. The pinning sites were introduced by inserting a concentric nonmagnetic disk under the magnetic element. The experimental microwave absorption spectra clearly indicate that the behavior of the vortex core is significantly modified due to the presence of the vortex barrier. A stepwise jump upwards in frequency (~0.2 GHz) of the vortex mode is observed in the modified dot structure when the field magnitude is decreased, while the reference dot demonstrates a very weak field independence, as expected. The stepwise jump in the frequency can be attributed to the change in the vortex core position. The micromagnetic simulations are in good agreement with the experiment, suggesting that the frequency difference between the remanent state and the displaced vortex could be further increased with the increase of the aspect ratio of the barrier. The described approach can be used to design spintronic devices with distinct magnetic field dependence of the resonant response.
This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
[1] V.S. Pribiag, I.N. Krivorotov, G.D. Fuchs, P.M. Braganca, O. Ozatay, J.C. Sankey, D.C. Ralph, and R. a. Buhrman, Nat. Phys. 3, 498 (2007).
[2] [2] V. Novosad, F. Fradin, P. Roy, K. Buchanan, K. Guslienko, S. D. Bader, Phys. Rev., B 72, 024455 (2005).
[3] R.L. Compton and P. a. Crowell, Phys. Rev. Lett. 97, 137202 (2006).
9:00 PM - MD9.3.12
Room-Temperature Ferromagnetism in Co-Implanted MoS2 Single Crystals
Li-Ting Tseng 1,Sean Li 1,Jiabao Yi 1
1 School of Materials Science and Engineering University of New South Wales UNSW Sydney Australia,
Show AbstractManipulating the spin state of electrons has driven much interest due to the potential applications of spintronics devices. Diluted magnetic semiconductor is one of the promising candidates to combine both semiconducting and magnetic properties into spintronic devices. Recently, MoS2 has attracted much attention because of its unique semiconducting properties with an indirect bandgap of 1 eV for the bulk form and a direct bandgap of 1.8 eV for the monolayer. It has been widely explored due to its potential applications in transistors, sensors and energy materials. Theoretical calculations have indicated that MoS2 are diamagnetic and transition-metal-doping could result in ferromagnetic coupling. However, only a few experimental works have been conducted to study the magnetic properties of transition-metal-doped MoS2. In this work, Co doping is performed by ion implantation. Co ions with a dose concentration of 1.65×1016 ions/cm2 are implanted into a MoS2 single crystal and produce a 15nm-thick surface layer doped with 4 at% of Co. The effect of Co doping on the magnetic properties of MoS2 is investigated in detail. XRD and Raman analysis indicate that the MoS2 single crystal has a hexagonal structure and no secondary phases are detected in the Co-implanted sample. The temperature dependent M-H loops show that the pure MoS2 single crystal is diamagnetic. Furthermore, the addition of Co ions in MoS2 single crystal turns its magnetic behaviour into ferromagnetic at room temperature. ZFC and FC curves also confirm the ferromagnetic ordering beyond room temperature. Our theoretical results based on first principle calculation elucidate that the Co substitution in the crystal lattice is the origin of ferromagnetism.
9:00 PM - MD9.3.13
Electronic and Magnetic Properties of Co Doped Monolayer MoS2: A First-Principles Study
Yiren Wang 1,Sean Li 1,Jiabao Yi 1
1 UNSW Kensington Australia,
Show AbstractMoS2 is one of the 2D materials that have shown great potential for the new generation low-dimensional transistors, photo-emitting devices and spintronics devices due to their unique structural and electronic properties. Monolayer MoS2 (1H-MoS2) has drawn much attention due to the unique properties from its bulk counterpart. Previous researches have shown that pristine bulk MoS2 is nonmagnetic; however recent theoretical and experimental results indicate a likelihood of magnetism in 1H-MoS2.
In this work, we carefully investigate the structural, electronic and magnetic properties of Co doped monolayer MoS2 by considering a variety of defects including all the possible defect complexes using first-principles calculations. A 4×4 MoS2 monolayer supercell structure containing 32 S and 16 Mo atoms is adopted in this study. For comparing the size effect of the supercell on the electronic and magnetic properties and simulating different doping levels, 3×3 and 5×5 MoS2 monolayer supercells with the same lattice constants and calculation details are also employed.
The results indicate that pristine 1H-MoS2 is nonmagnetic. The materials with the existence of S vacancy or Mo vacancy alone are non-magnetic either. Further calculation demonstrates that Co dopants can induce robust magnetic moment in this system and the magnetization originates from the d orbitals of the Co, NN Mo atoms and the p orbitals of the NN S atoms via p-d hybridization. The magnetic moment is strongly dependent on the doping concentration. 1H-MoS2 with lower doping concentrations (4 at% or 6.25 at%) has a stable magnetic moment of 3 μB, which is higher than that at higher doping level (8 at%, or 11.1 at%, or 12.5 at%). The substitutional CoMo defects tend to cluster at higher doping concentration. Subsequently the substitutional CoMo defects will not result in magnetic state. However, if Mo vacancies exist in the system, the dopants tend to separate from each other with a particular distance and the system shows ferromagnetic state. In addition, this tendency is energy favorable.
Based on our calculations, we find that the magnetism in Co-doped 1H-MoS2 system can only be obtained when the dopants are rather dispersed and uniform, suggesting intrinsic ferromagnetism of a new kind of diluted magnetic semiconductor. The work may pave ways for achieving intrinsic diluted magnetic semiconductor based on MoS2 semiconductors.
9:00 PM - MD9.3.14
Electrospun Magnetic Iron/Polyaniline Nanofibers for Application in Magnetic Hyperthermia Therapy
Shu-Chian Yang 1,Su-Hua Chang 1,Ta-I Yang 1
1 Chung Yuan Christian Univ Chung Li Taiwan,
Show AbstractCancer is among the major causes to human deaths. Magnetic hyperthermia therapy is one of the promising technologies to treat cancer. Therefore, the goal of this research is to develop electrospun magnetic iron/polyaniline nanofibers for application in hyperthermia therapy. In this study, we synthesized metallic iron (Fe0) nanoparticles at room temperature with assistance of polyvinylpyrrolidone to tailor their particle size. The Fe nanoparticles were subsequently incorporated with conducting polyaniline (PANI) to form Fe0 / PANI nanofibers using electrospinning technique. The PANI shells prevent the possibility of Fe0 oxidation and further improve the hyperthermia effect, benefiting from the high conductivity of the PANI polymer. The method developed in this study could provide a new method to design magnetic nanocomposites with enhanced hyperthermia effect to treat cancers.
9:00 PM - MD9.3.15
Study of Co Additive on Magnetic Property of Mn-Zn Ferrites and Related Thin Layer Formation by Thermal Spray Coating and Its Properties for Megahertz Frequency Range for Wireless Power Transfer Applications
Myong Jae Yoo 1
1 KETI Seongnam Korea (the Republic of),
Show AbstractWireless power transfer(WPT) involves various technologies and one of the crucial elements is the use of magnetic materials. Various magnetic materials can be used for WPT or wireless power charging. Currently Fe based metallic materials are employed in various devices but regardless of the high permeability the use of Fe based metallic materials is limited to a few kHz due to low resistivity and large eddy current losses. Thus in order to provide high permeability with use in higher frequency range such as megahertz(MHz) range the use of ferrites is necessary. In this study Mn-Zn ferrites with high permeability is fabricated with Co as primary additive and their properties investigated in MHz range. Also the formation of thin layers using thermal spray coating process and its properties with regard to MHz range is studied.
9:00 PM - MD9.3.16
Synthesis and Study of Magnetic Properties of Hard-Soft SrFe12-xAlxO19/Ni0.5Zn0.5Fe2O4 Ferrite Nanocomposites
Dipesh Neupane 1,Abdellah Lisfi 2,Sanjay R Mishra 1
1 Univ of Memphis Memphis United States,2 Department of Physics Morgan State University Baltimore United States
Show AbstractA considerable amount of research has been carried out on Ni-Zn ferrites because of their innumerable applications in non-resonant devices due to their high magnetization Ms. Similarly, Al doped SrFe12-XAlXO19 has their distinct magnetic properties such as their high Tc, high coercive force, have made them popular for industrial application such as microwave device in recording media.
Energy product as a combination of magnetization and coercivity essentially determines the quality of the permanent magnets. But unfortunately, magnetic materials tend naturally to have one rather both; soft magnetic materials usually have relatively high magnetization, while most of hard magnets have high coercivity, but quite low magnetization. Exchange spring principle can identify a route to provide the possibility for improving remanence and energy product of the permanent magnets by making the composite of suitable material. The present study is to obtain Pure phase exchange-coupled nanocomposites of hard-soft magnetic oxides, (hard) SrFe12-XAlxO19 - (soft)Y Ni0.5Zn0.5Fe2O4 with X=0, 0.5, 1, 1.5 and 2 and Y=wt.10%, wt.20%, wt.30%, wt.40% and wt.50% were prepared via autocombution method. The X-ray powder diffraction (XRD) patterns of as prepared nanocomposite peaks are in good agreement with the hexagonal and cubic phases and their peaks are broadened due to their nanometer sizes. VSM measurement report that a ~19% increase in Ms value for nanocomposite with x=0 (69.5 emu/g) for hard and 50 Wt.% of the soft phase. A linear increase in Mr /Ms with soft-phase content indicates the presence of enhanced exchange-coupling between hard and soft phases of the nanocomposite. The highest Mr /Ms ratio of 0.60 was obtained for nanocomposite containing wt. 10.% of the soft-phase with X=1.5 Al doped sample which is significantly larger than the value of 0.5 predicted for non-interacting permanent magnet. This indicates the existence of intergrain exchange coupling between hard and soft phases. The observed reduction in coercieve field values of the nanocomposite with increase in soft-phase content is explained on the basis of competition between exchange and dipolar interaction between hard-soft and soft–soft phases of the nanocomposite.
[i]. P . Ravindernathan and K. C. Patil, J. Mater. Sci. 22 (1987) 3261.
[ii]. H. Igarash and K. Ohazaki, J. Amer. Ceram. Soc. 60 (1997) 51.
[iii]. A. Goldman, Am. Ceram. Soc. Bull. 63 (1984) 582.
[iv]. A. C. F. M. Costa, E. Tortella, M. R. Morelli, M. Kaufman and R. H. G. A. Kiminami, J. Mater Sci. 37 (2002) 3569 – 3572.
[v]. H. Luo, B.K. Rai, S.R. Mishra, V.V. Nguyen, J.P. Liu, Journal of Magnetism and Magnetic Materials 324 (2012) 2602–2608.
[vi]. N. Dishovske, A. Petkov, I.V. Nedkov, IEEE Transactions on Magnetics, 30 (1994), p. 969
[vii]. O. Kubo, T. Ido, H. Yok, IEEE Transactions on Magnetics, 18 (1982), p. 1122.
[viii]. M.A. Radmanesh, S.A. Seyyed Ebrahimi, j. magnetism and magnetic materials 324 (2012) 3094.
Symposium Organizers
Elena A. Rozhkova, Argonne National Laboratory
Haifeng Ding, Nanjing University
Miguel Angel Garcia, Institute for Ceramic and Glass, CSIC
Carlos Rinaldi, University of Florida
Symposium Support
The Center for Nanoscale Materials – Argonne National Laboratory
MD9.4: Magnetic Materials—From Fundamentals to Applications III
Session Chairs
Wednesday AM, March 30, 2016
PCC West, 100 Level, Room 105 B
9:45 AM - *MD9.4.01
Synthesis and Assembly of Barium-doped Iron Oxide Nanoparticles and Nanomagnets
Shouheng Sun 1
1 Brown Univ Providence United States,
Show AbstractWe report a facile organic-phase synthesis of monodisperse barium-doped iron oxide (Ba-Fe-O) nanoparticles (NPs) through thermal decomposition of Ba(stearate)2 and Fe(acac)3 in 1-octadecene with oleic acid and oleylamine as surfactants. The Ba/Fe composition (from 0.04 to 0.095) is controlled by the Ba(strearate)2/Fe(acac)3 ratio or by the oleylamine and 1-octadecene volume ratio. The as-synthesized Ba-Fe-O NPs, especially the Ba0.082-Fe-O NPs, can be easily converted into hexagonal barium ferrite (BaFe) by annealing in O2 atmosphere at 700 °C for 1 h, showing strong ferromagnetic properties with Hc reaching 5260 Oe and Ms of 54 emu/g. More importantly, these monodisperse Ba-Fe-O NPs are well dispersed in hexane and can be easily assembled into densely packed 2D arrays and further converted into oriented BaFe magnets. Our reported synthetic method and self-assembly approach can also be extended to Sr-Fe-O and ferromagnetic SrFe NPs, providing a unique way of fabricating ferromagnetic ferrite arrays that may be important for magnetic energy storage and data storage applications.
10:15 AM - MD9.4.03
Atomic Scale Structure and Properties of Highly Stable Antiphase Boundary Defects in Fe3O4
Keith McKenna 1,Zhongchang Wang 3,Vlado Lazarov 1,Yuichi Ikuhara 3
1 University of York York United Kingdom,3 WPI-AIMR Tohoku University Sendai Japan2 University of Tokyo Tokyo Japan,3 WPI-AIMR Tohoku University Sendai Japan
Show AbstractThe complex and intriguing properties of the ferrimagnetic half metal magnetite (Fe3O4) are of continuing fundamental interest as well as being important for practical applications in spintronics, magnetism, catalysis and medicine. There is considerable speculation concerning the role of the ubiquitous antiphase boundary (APB) defects in magnetite, however, direct information on their structure and properties has remained challenging to obtain. Here we combine predictive first principles modelling with high-resolution transmission electron microscopy to unambiguously determine the three-dimensional structure of APBs in magnetite. We demonstrate that APB defects on the {110} planes are unusually stable and induce antiferromagnetic coupling between adjacent domains providing an explanation for the magnetoresistance and reduced spin polarization often observed. We also demonstrate how the high stability of the {110} APB defects is connected to the existence of a metastable bulk phase of Fe3O4, which could be stabilized by strain in films or nanostructures.
[1] K. P. McKenna, F. Hofer, D. Gilks, V. K. Lazarov, C. Chen, Z. Wang and Y. Ikuhara, Nature Communications 5, 5740 (2014)
10:30 AM - MD9.4.04
Strain Effect in Epitaxial FePt Films on Different Single Crystal Substrates
Sung Hun Wee 1,Sebastian Wicht 3,Shikha Jain 1,Olav Hellwig 1,Bernd Rellinghaus 2
1 HGST, a Western Digital Company San Jose United States,2 IFW Dresden, Institute for Metallic Materials Dresden Germany,3 TU Dresden, Insitut für Werkstoffwissenschaft Dresden Germany2 IFW Dresden, Institute for Metallic Materials Dresden Germany
Show AbstractHeat assisted magnetic recording (HAMR) technology based on L10-ordered FePt magnetic media is a promising magnetic recording technology to overcome the areal density limit of current perpendicular magnetic recording technology and thereby, extend the areal density beyond 1.5 Tbit/in2. To develop high performance HAMR media, it is essential to have granular structured FePt media layers with good L10 chemical ordering and strong (001) texture. In this work, we systematically investigate the influence of the lattice mismatch between FePt and the substrate crystal on the structural and magnetic properties of FePt films. Granular structured, ~10 nm thick, epitaxial FePt films with and without carbon segregant were prepared on different single crystal substrates of (La,Sr)(Al,Ta)O3 (LSAT), SrTiO3 (STO), MgAl2O4 (MAO), and MgO, causing an in-plane lattice mismatch (LM) with FePt to vary from 0.4% up to 9.6%. The films on STO, MAO, and MgO show strong (001) texture with no misoriented FePt grains while the film on LSAT, the least lattice-mismatched substrate, additionally has FePt grains with (110) orientation. Although all of the films are in-plane tensile-strained, X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) confirm that the strain level and the related interface defect density impacting the texture, L10 chemical ordering, and magnetic properties are significantly affected by the degree of LM. Detailed quantitative and statistical XRD and HRTEM results on the FePt strain state and interface defect structure and their impact on the ordering and magnetic properties will be presented in this talk.
10:45 AM - MD9.4.05
Exchange-Coupled Ferromagnetism in Co0.4Pt0.6 Nanochessboards: Role of Lengthscales and Morphology
Eric Vetter 1,Priya Ghatwai 1,William Soffa 1,Jerrold Floro 1
1 Materials Science and Engineering University of Virginia Charlottesville United States,
Show AbstractEutectoid decomposition of A1 Co-Pt alloys near 60% Pt can result in formation of the unique nanochessboard structure. The nanochessboard represents a self-assembled 2+1D-periodic stacking of magnetically hard L10 nanorods embedded in a soft L12 matrix, all separated by coherent interfaces. Lateral lengthscales of the chessboard of order 20 nm. As such, the chessboard is a fascinating structure in which to examine exchange coupling, of intermediate complexity between epitaxial bilayers and nanocrystalline aggregates. Two key process parameters that govern chessboard formation are the thermal cooling rate used to pass through the A1—L10+L12 eutectoid, and the final temperature reached during the ramp, prior to rapid quenching. At slower cooling rates, 40 oC/day, we varied the final temperature, and measured both M-H loops and first order reversal curves (FORCs). Formation of the hard L10 phase is clearly evident in both the major-loop susceptibilities and in the FORC density plots. The data suggest incomplete exchange coupling between the hard and soft phases, including residual A1, likely due to lengthscales that are slightly too large relative to the hard-phase domain wall thickness. At higher cooling rates, 80 oC/day, however, single-phase behavior is obtained, even though x-ray diffraction confirms the presence of both hard and soft phases. Increases in both coercivity and remanence ratio are observed, relative to the slower-cooled specimens. This results from a reduction in chessboard lengthscale by more rapidly cooling through the eutectoid, resulting in rigid exchange coupling. FORC density plots from chessboards can show rich substructure indicating significant local and mean field interactions. Some aspects resemble “paradigmatic” features observed in idealized systems, but with interesting and non-trivial differences arising from the more complex structure of the chessboard. Support of the National Science Foundation through grant DMR-1105336 is gratefully acknowledged.
11:30 AM - MD9.4.06
Fine-Tuning the Magnetic Properties of Cobalt Ferrite Thin Films by Controlling the Nanoscale Architecture
Shauna Robbennolt 1,Abraham Buditama 1,Hyeyeon Kang 1,Paul Nordeen 1,Laura Schelhas 2,Gregory Carman 1,Sarah Tolbert 1
1 UCLA Los Angeles United States,2 SSRL Palo Alto United States
Show AbstractAdvances in nanoscience have allowed us to tune material properties by controlling the nanoscale architecture. Here, we report that by controlling film porosity, annealing temperature and building blocks (i.e. nanocrystals and sol-gel precursors) we are able to tune the static magnetic properties of cobalt ferrite (CoFe2O4) thin films over a wide range. Bulk cobalt ferrite is a magnetically hard material with a coercivity around 3600 Oe. However, its coercivity can be lowered by making it nanocrystalline, mesoporous or both. Furthermore, the magnetic properties can be fine-tuned by varying the annealing temperature of the films. By combining these methods, we have shown that thin films of cobalt ferrite can be made with coercivities ranging from 3200 Oe down into the superparamagnetic regime. In addition to controlling the coercivity, the saturation field, and thereby effective permeability, can be controlled by changing size and spacing in nanocrystal based films. Finally, we find that despite the large change in static properties, the dynamic properties, as probed by ferromagnetic resonance (FMR) studies, remain unchanged over the measureable samples. These results suggest that by precisely controlling the nanoscale structure, the magnetic properties of thin films can be easily tuned and tailored toward a variety of device applications. Of particular interest is the possibility of using cobalt ferrite and other hard magnetic materials in areas such as high-frequency applications where their use has traditionally been limited
11:45 AM - MD9.4.07
Magnetic Tunnel Junctions from Alkanethiol Self Assembled Monolayers
Sophie Delprat 4,Marta Galbiati 4,Michele Mattera 3,Sergio Tatay Aguilar 3,Samuel Manas Valero 3,Alicia Forment Aliaga 3,Cyrile Deranlot 4,Sophie Collin 4,Karim Bouzehouane 4,Pierre Seneor 4,Richard Mattana 4,Frederic Petroff 4
1 Unité Mixte de physique CNRS-Thales Palaiseau France,2 Université Pierre et Marie Curie Paris France,4 Université Paris Sud Orsay France,1 Unité Mixte de physique CNRS-Thales Palaiseau France,3 Instituto de Ciencia Molecular (Universitat de Valencia) Paterna Spain,4 Université Paris Sud Orsay France3 Instituto de Ciencia Molecular (Universitat de Valencia) Paterna Spain1 Unité Mixte de physique CNRS-Thales Palaiseau France,4 Université Paris Sud Orsay France
Show AbstractMolecular spintronics, an emerging research field at the frontier between organic chemistry and spintronics, has opened novel and exciting opportunities in terms of functionalities for spintronics devices. Beyond, plasticity and low cost, carbon based materials were first seen as very promising for spintronics devices due to their expected long spin lifetime and potential for spin transport. It was only very recently that new spintronics tailoring opportunities that could be brought by molecules and molecular engineering were unveiled. Among them, it was shown that spin dependent hybridization at the metal/molecule interface could lead to a radical tailoring of spintronics properties [1,2]. In this direction Self-Assembled Monolayers (SAMs) appear to be a very promising candidate thanks to their impressive molecular scale crafting properties. Despite all the promising possibilities to build molecular spintronic devices, up to now less than a handful of experiments on the use of SAMs as spin-dependent tunnel barriers have been reported [3], still already highlighting promising potential at low temperatures [4]. In an effort to achieve room temperature spin signal, we have developed magnetic tunnel junctions based on alkanethiol (C12 to
C18) and conventional “3d” ferromagnets (such as Co,NiFe…). In this direction, we have developed a novel process to recover the oxidized ferromagnet from oxidation [5].
We will present NiFe/alkanethiol SAMs/Co devices and discuss electerical transport properties.
[1] C. Barraud et al., “Unravelling the role of the interface for spin injection into organic semiconductors,” Nat. Phys., vol. 6, no. 8, pp. 615–620, 2010.
[2] M. Galbiati et al., “Spinterface: Crafting spintronics at the molecular scale,” MRS Bull., vol. 39, pp. 602–607, 2014.
[3] W. Wang et C.A. Richter, “ Spin-polarized inelastic electron tunneling spectroscopy of a molecular magnetic tunnel junction”, Applied Physics Letters, 89, 153105 (2006)
J.R. Petta et al., “Spin-Dependent Transport in Molecular Tunnel Junctions”, Phys. Rev. Lett., 93, 136601
[4] M. Galbiati et al., “Unveiling Self-Assembled Monolayers’ Potential for Molecular Spintronics: Spin Transport at High Voltage,” Adv. Mater., vol. 24, no. 48, pp. 6429–6432, 2012.
[5] Marta Galbiati, Sophie Delprat et al. “Recovering ferromagnetic metal surfaces to fully exploit chemistry in molecular spintronics“, AIP advances 5, 057131 (2015)
12:00 PM - MD9.4.08
Longitudinal Domain Wall Formation in Elongated Nanoparticle Assemblies
Miriam Varon 1,Marco Beleggia 2,Jelena Jordanovic 1,Jakob Schiotz 1,Takeshi Kasama 3,Victor Puntes 6,Cathrine Frandsen 1
1 Department of Physics Technical University of Denmark Kgs. Lyngby Denmark,3 Center for Electron Nanoscopy Technical University of Denmark Kgs. Lyngby Denmark,2 Helmholtz-Zentrum-Berlin fuer Materialen und Energie Berlin Germany3 Center for Electron Nanoscopy Technical University of Denmark Kgs. Lyngby Denmark4 Catalan Institute of Nanoscience and Nanotechnology Bellaterra Spain,5 Vall d’Hebron Institut de Recerca (VHIR) Barcelona Spain,6 Institut Català de Recerca i Estudis Avançats (ICREA) Barcelona Spain
Show AbstractMagnetic nanoparticle systems may be considered a new class of magnetic materials, since their properties may be very different from conventional magnetic materials and can be tailored by means that are not easily accessible in other systems. Magnetostatic (dipolar) interactions between nanoparticles may open new ways to design nanocrystalline magnetic materials and devices if the collective magnetic properties can be controlled at the nanoparticle level. Dipolar interactions are sufficiently strong to sustain magnetic order at ambient temperature in assemblies of closely-spaced nanoparticles with magnetic moments of ≥ 100 µB.
Through evaporation of dense colloids of ferromagnetic 13 nm ε–Co particles onto carbon substrates, anisotropic magnetic dipolar interactions can support formation of elongated “rope-like” nanoparticle structures with aggregate widths of 100–400 nm and lengths of up to some hundred microns [1]. We have observed that unusual domain structures arise in these systems [1]. The domain structures are deemed “unusual” because, unlike conventional/continuous materials, there is no exchange energy cost proportional to the cross-sectional area of a domain wall, thus walls can be very long in dipolar-coupled magnetic materials. They can also feature a 180-degree magnetization rotation between neighboring particle chains corresponding to zero wall width.
We have verified that longitudinal domain-walls can be stabilized by dipolar inter-particle interactions in elongated nanoparticle assemblies with aspect ratios (length/width) of 2–7, in the absence of inter-particle exchange coupling. The energy of transverse/vortex walls is comparable in continuous film and nanoparticle assemblies while the energy of longitudinal walls is very large (proportional to the wall length) in continuous films and very low in nanoparticle assemblies. We find that the propagation of longitudinal domain walls occurs in the transverse direction with reverse field and that domain structures are stabilized during reversal by imperfections and packing disorder.
The domain behavior has been captured visually by electron microscopy experiments, and the results interpreted on the basis of numerical simulations, providing a coherent and consistent physical picture that highlights how the domain behavior of nanoparticle-materials does not involve transverse (or vortex) domain walls typically observed in thin film strips of Co of comparable dimensions.
[1] Scientific Reports 5, Article number: 14536 (2015)
12:15 PM - MD9.4.09
Structural and Magnetic Properties of YIG/ZnO Multilayers Grown by PLD
Joynarayan Mukherjee 1,Ramachandra Rao 1
1 IIT Madras Chennai India,
Show AbstractIn recent years, research on interfaces of various oxides has gained considerable interest because of some exciting spin-dependent phenomena1. Due to very low magnetic damping, ferrimagnetic yittrium iron garnet (YIG) is a promising material for spin injection2. The magnetic property of YIG thin film can be tuned by introducing a non-magnetic layer on top of the YIG layer. In this work, we show the structural and magnetic properties of bilayer and multilayers consisting of a ferrimagnet (Bi doped YIG) and a non-magnetic (Ga doped ZnO) layers. 10% bismuth was doped in YIG, in order to lower the sintering temperature of YIG compound to prepare the target for pulsed laser deposition (PLD).
Bi:YIG/Ga:ZnO multilayers have been grown on YAG substrate by PLD. Structural analysis was carried out using high resolution XRD (Rigaku, Smartlab).Thickness and roughness of each layer has been calculated from X-ray reflectivity (XRR) measurement. Magnetic properties were studied using SQUID VSM (Quantm Design). ZFC and FC have been recorded on the samples in the temperature range from 300 K to 20 K by applying a field of 500 Oe. Compared to the only Bi:YIG layer, the multilayers (repetitive YIG/ZnO layers (1 to 5)) show two transitions at ~ 45 K and ~110 K. The separation between ZFC and FC curve increases with the number of interfaces and this may be due to some interesting scattering phenomenon occurring at the interface. Results will be discussed in detail.
References:
Sujit Das et. al., Phys. Rev. B. 91, 134405 (2015).
Matthias Althammer et. al., Phys. Rev. B. 87, 224401 (2013).
12:30 PM - MD9.4.10
Morphology Control and Associated Magnetic Properties of Metal/Carbon Hybrid Electrospun Nanofibers for Flexible EMI-Shielding Layer
Jiwoo Yu 1,Dae-Hyun Nam 1,Young-Joo Lee 1,Young-Chang Joo 1
1 Seoul National Univ Seoul Korea (the Republic of),
Show AbstractAs humans in recent years undergo frequent RF exposure from electronic devices, the development of electromagnetic interference (EMI) shielding layer that is flexible, thin, and effective is now in high demand. Conventional metal coatings or polymer/nanoparticle composite layers are not suitable for flexible uses in concerns of delamination and agglomeration. To optimize the EMI shielding effectiveness (SE) and increase flexibility, the magnetic metal nanoparticles dispersed evenly in carbon (C) conducting path is considered to be one of the best forms of EMI shielding material, which we targeted for. We have developed a novel fabrication method, which is simple and cost effective, to control the size and distribution of transition metals inside C fibers through oxygen partial pressure (PO2) controlled calcination. The resulting SE was higher than the required commercial level of 90%. Amongst common magnetic metals, nickel and cobalt were applied due to their high permeability that enables greater shielding effectiveness. The greatest advantages of our material not only lies on its effectiveness but also on that we minimized coercivity to eliminate local heat produced when EM field is applied and, at the same time, optimized to achieve anisotropic thermal conductivity in plane direction for heat sink.
Ni/Co/C hybrid nanofibers were prepared by electrospinning followed by heat treatment technique under PO2 ranging from 0 to 1.3 Torr at 700°C. The Ni/Co ratio in weight was kept to be 5:5, and Ni/C and Co/C fibers were also prepared for comparison. The static magnetic properties of nanofibers were determined using vibrating sample magnetometer (VSM). Vector network analyzer (VNA) and 4-point probe technique were used to measure permeability, permittivity, and sheet resistance to analyze the EMI-SE in the EM frequency range of 300 MHz- 8GHz.
FE-SEM and HR-TEM results showed that the average size of metal nanoparticles grows from 5nm to 52nm as PO2 increases. Applying PO2 to combust C out to leave pores, but not enough O2 to oxidize the metal composite, enables the diffusion of metal particles into the C pores through certain mechanisms, which allowed us to control morphology of the nanofibers. XRD and Raman confirmed phases and crystallinity of the fibers, respectively. The permeability, which could be judged by the slope in M-H curve, was optimized at PO2=0.4 Torr, yet the coercivity was kept at a negligible level with the enlarged metal particles. This result is meaningful in that the increase in coercivity had been unavoidable when the nanoparticle size increases due to the loss of superparamagnetic behavior, however, for this heat treatment technique under the mechanism in which nanoparticles diffuse to agglomerate, the metal particle forms multi magnetic domain that results in a low coercivity. Calculating from the permeability and permittivity over the X-band EM frequency range, we obtained the EMI-SE of at least 93% throughout the whole range.
MD9.5: Magnetic Materials—From Fundamentals to Applications IV
Session Chairs
Wednesday PM, March 30, 2016
PCC West, 100 Level, Room 105 B
2:30 PM - *MD9.5.01
Novel Magnetic Materials in the Spotlight of Polarized X-Rays
Peter Fischer 2
1 Lawrence Berkeley National Lab Berkeley United States,2 Physics Department University of California Santa Cruz United States,
Show AbstractNanomagnetism research which aims to understand and control magnetic properties and behavior on the nanoscale through proximity and confinement, is currently shifting its focus to emerging phenomena occurring on mesoscopic scales. New avenues to control magnetic materials open up through enhanced complexity and new functionalities, which can impact the speed, size and energy efficiency of spin driven applications.
Magnetic soft X-ray spectro-microscopies [1] provide unique characterization opportunities to study the statics and dynamics of spin textures in magnetic materials combining X-ray magnetic circular dichroism (X-MCD) as element specific, quantifiable magnetic contrast mechanism with spatial and temporal resolutions down to fundamental magnetic length and time scales.
I will review recent achievements and future opportunities with magnetic x-ray spectro-microscopies. Examples will include the dynamics of magnetic vortex structures [2,3] with potential application to novel magnetic logic elements [4], magnetic spectromicroscopy of domain walls [5], and approaches to image the 3dim magnetic domain structures in rolled-up thin films with x-ray tomography [6].
This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy Contract No. DE-AC02-05-CH1123.
[1] P. Fischer, and H. Ohldag, Report on Progress in Physics 78 094501 (2015)
[2] R. Streubel, et al. Appl Phys Lett (2015) accepted
[3] M.-Y.Im, et al. Nature Communication 5 5620 (2014)
[4] H. Jung, et al., ACS Nano 6 3712 (2012)
[5] M.J. Robertson, et al., J Appl Phys 117 17D145 (2015)
[6] R. Streubel, et al. Nature Communication 6 7612 (2015)
3:00 PM - MD9.5.02
Nanoscale Magnetization Dynamics Studied by a Combination of Scanning Transmission X-Ray Microscopy and X-Ray Detected Ferromagnetic Resonance
Andreas Ney 1,Ralf Meckenstock 2,Detlef Spoddig 2,Katharina Ollefs 2,Christian Schoeppner 2,Taddaeus Schaffers 1,Stefano Bonetti 3,Hendrik Ohldag 3
1 Johannes Kepler Univ-Linz Linz Austria,2 University of Duisburg-Essen Duisburg Germany3 Stanford Synchrotron Radiation Lab Menlo Park United States
Show AbstractRecently a scanning transmission x-ray microscopy (STXM) setup has been combined with a novel microwave synchronization scheme for studying high frequency magnetization dynamics in the GHz regime [1] enabeling spatially resolved x-ray-detected ferromagnetic resonance (XFMR) studies on magnetic micro- and nanostructures. Compared to other spatially resolved detection schemes based on conventional ferromagnetic resonance (FMR) [2] the novel STXM-XFMR setup features element-selective detection as well as a high temporal and spatial resolution of down to 18 ps and 35 nm, respectively [1]. Here we will briefly present the detection scheme which allows us to probe the high-frequency transverse component of the precessing magnetization down to precession angles of 0.1° [1]. In addition, first results derived for coupled magnetic microstripes and heterostructures will be discussed and compared to conventional spatially resolved FMR [3]. We are able to directly image the magnetic excitations and identify the contributions of the respective constituents to complex conventional FMR spectra. The relative phases between microwave excitation and standing spinwave can furthermore serve to separate groundstate from coupling modes.
[1] S. Bonetti et al., Rev. Sci. Instrum. 86 (2015) 093703
[2] R. Meckenstock, Rev. Sci. Instrum. 79 (2008) 041101
[3] T. Schaffers et al. (in preparation, 2015)
3:15 PM - MD9.5.03
“Superdiamagnetism” in Materials with Coexisting Ferromagnetic and Antiferromagnetic Interactions
Mona Jani 1,R.R. da Silva 1,B. Camargo 1,D. Pedreira 1,Y. Kopelevich 1
1 Instituto de Física “Gleb Wataghin”, Universidade Estadual de Campinas (UNICAMP) Campinas Brazil,
Show AbstractApparent diamagnetic response has been reported for various materials that possess both ferromagnetic (FM) and antiferromagnetic (AFM) components of the spin ordering, e. g. [1, 2]. However, origin of the anomalously large diamagnetic moment is not yet clarified. In the present work we report the “superdiamagnetic” response measured for single-phase pyrite FeS2, NiS2 and CuCl powders. Magnetization measurements revealed a giant diamagnetic response in zero-field-cooled (zfc) regime below the transition temperature Tc = 60 K (FeS2), 30 K (NiS2) and 20 K (CuCl). The field-cooled (fc) magnetization Mfc(T) revealed a characteristic for FM materials behaviour for T
3:30 PM - MD9.5.04
Fe-Cr: Magnetic Properties and Crystal Structure under High Pressure
Itzhak Halevy 1,Amir Broide 1,Silvie Maskova 2,Matthew Lucas 3
1 NRCN Beer Sheva Israel,2 Charles University in Prague Prague Czech Republic3 Caltech Pasadena United States
Show AbstractThe Fe-Cr system was selected for experimental study in part owing to previous inelastic neutron-scattering studies of phonons in Fe-Cr alloys. The present investigation will use the technique of neutron diffraction under high-Pressure. This method gives the crystallographic structure, symmetry and the unit cell parameters combined with the magnetic structure. In preliminary measurements made on disordered bcc solid solutions of Fe-Cr we noticed the effect of the Cr concentration on the unit cell parameter. There is a known phase transition from bcc the hcp at 13GPa in the elemental iron. The transition pressure is increasing with the Cr concentration /1/. Fitting the result for Vinet EOS shows the different in Bulk Modulai at the different phases below and above the transition. The magnetic properties are also changing as we showed in previous publication. The neutron diffraction measurements complete the previous measurements of the magnetic and crystallographic properties of that system. The Fe-Cr disordered solid solutions and thin films have similar lattice parameters bcc Fe and Cr have lattice parameters of 2.87Å and 2.88Å, respectively.
At low temperatures, Fe-Cr solid solutions exhibit chemical unmixing over a broad range of compositions around the equiatomic compositions. Much experimental work on the Fe-Cr system has addressed this “spinodal decomposition” owing to its correlation with thebrittleness of ferritic stainless steels.
The thermodynamics of Fe-Cr solid solutions is an important starting place for understanding the metals physics of this unmixing. It is now known, for example, that the critical temperature is lowered by the relatively large Sph of the solid solution. Fortunately, the high-temperature disordered state of Fe-Cr is not difficult to preserve at low temperatures by rapid cooling and it is possible to prepare alloys of Fe-Cr of all compositions as bcc solid solutions with similar lattice parameters.
We use the spallation sourceneutron powder diffraction measurementstaken at ambient and high pressure using a Paris Edinburgh anvil cell. The pressure was calibrated by known oil pressure, a Pt rode was used as internal calibrator.
Alloys of Fe1−xCrx for x=0-1 were prepared by arc melting under an argon atmosphere. The alloys were enriched to contain approximately13 at. % of the 57Fe isotope for magnetic measurements by conventional Mössbauer effect. There was negligible mass loss after melting, so the compositions are expected to be accurate to 0.1 at. %. The samples were cold rolled to final thickness, sealed in a quartz tube under an argon atmosphere, and then annealed at 1100°C for 72h for magnetic measurements.
Transmission Mössbauer spectrometry was performed on all samples at room temperature with a conventional constant acceleration spectrometer, using a source of 50 mCi of 57Co in Rh. Mössbauer spectrometry has been used extensively to characterize bcc Fe-Cr alloys and the sigma-phase compound.
4:15 PM - *MD9.5.05
Synchrotron Radiation Analysis of Nd-Fe-B Sintered Magnet
Tetsuya Nakamura 2
1 JASRI / SPring-8 Sayo, Hyogo Japan,2 ESICMM/ NIMS Tsukuba Japan,
Show AbstractSince their invention in 1984 [1], Nd-Fe-B permanent magnets have been the best magnets and have become an indispensable material for electric products, hybrid vehicles, and power generators, which are key technologies for energy sustainability. Associating with the problem of critical elements, improvement in coercivity without reduction of magnetization is desperately needed for Dy-free Nd-Fe-B magnets. Generally, the grain size/orientation of Nd2Fe14B crystals in the sintered magnet and the chemical/magnetic properties of a grain boundary phase are the dominant factors determining the coercivity. Since the microstructure is intimately related to the coercivity, controlling the microstructure may bring a solution to developing a high-performance Dy-free Nd-Fe-B sintered magnet.
From a micro-magnetic point of view, a thin-film-like grain boundary (GB) phase (existing between neighboring Nd2Fe14B grains) prefers to be paramagnetic so as to prevent reversed magnetic domains from expanding into neighboring grains. Although the GB phase had been believed to be paramagnetic for a long time, a recent study using soft X-ray magnetic circular dichroism (MCD) showed that the GB phase is ferromagnetic [2] and that the Curie temperature is lower than that of the Nd2Fe14B crystal by about 50 K. This result implied that decreasing the Curie temperature could improve the coercivity. Since the post-sintered annealing process forms the GB phase effectively, the material forming the GB phase seems to be carried from the intergranular Nd-rich grains. Although the Nd-rich phases have been investigated by means of scanning electron microscopes and transmission electron microscopes, it is hard to evaluate their volume fractions from these techniques, which is crucial to improving the manufacturing process by adjusting the composition and annealing temperature, etc. Synchrotron X-ray diffraction experiments not only provide the compositions of the Nd-rich phase, but also their phase transitions at elevated temperature. In addition to the synchrotron studies above, a magnetic domain imaging technique based on soft X-ray MCD under high magnetic field (8 T, max.) has been developed at SPring-8 in order to observe magnetic domain evolution.
Acknowledgements
A part of this work is supported by the Elements Strategy Initiative Center for Magnetic Materials under the outsourcing project of MEXT.
References
[1] M. Sagawa, S. Fujimura, N. Togawa, H. Hashimoto, and Y. Matsuura, J. Appl. Phys. 55, 2083 (1984).
[2] T. Nakamura, A. Yasui, Y. Kotani, T. Fukagawa, T. Nishiuchi, H. Iwai, T. Akiya, T. Ohkubo, Y. Gohda, K. Hono, and S. Hirosawa, Appl. Phys. Lett. 105, 202404 (2014).
4:45 PM - MD9.5.06
Domain Wall Manipulation in Cylindrical Nanowires
Iurii Ivanov 1,Andrey Chuvilin 2,Jurgen Kosel 1
1 KAUST Thuwal Saudi Arabia,2 EM Lab CIC nanoGUNE Consolider San Sebastian Spain
Show AbstractA key role for the development and production of novel nanoelectric devices is the nanoscale characterization of the local magnetic and electric fields in the materials. Out of the existing TEM methods the Differential Phase Contrast (DPC) is the most useful one for fast switching between objects with tens of µm down to a few nm in size. However, the conventional DPC also requires a specially designed position sensitive detector; thus, significantly limiting a wider use of the method. Recently, we developed a simple generalization of the DPC imaging method, the Virtual Bright Field DPC (VBF-DPC), to extend the capabilities of the majority of existing TEM systems (without modifications) [1]. Here, we report the study of field-driven domain wall manipulation in cylindrical magnetic nanowires by VBF-DPC.
Cylindrical magnetic nanowires (NWs) are promising candidates for biomedical applications, sensors or to realize new types of 3D magnetic memory devices. In context of the later, it is crucial to have a possibility for controlled manipulation of domain walls (DWs) by periodic energy potentials. In order to realize such potentials, multisegmented NWs Co(hcp)/Ni(fcc) with 50-80 nm in diameter have been prepared by the electrodeposition of Co and Ni into anodic alumina membranes. Electron diffraction confirmed a very good crystal quality of the NWs. A sharp heteroepitaxial interface without the presence of oxygen between Co and Ni segments has been confirmed by electron energy loss spectroscopy (EELS) mapping.
To study the DW propagation, the multisegmented NWs were dispersed on the holy carbon grid. Our VBF-DPC imaging revealed the presence of strong periodic stray fields at the Co/Ni interfaces. In order to nucleate and manipulate the DWs, we applied an external magnetic field by tilting the sample together with the objective lens partially excited in a controlled way. Typically, to build a complete picture of the local magnetic field, the combination of 4 images from 4 VBF detectors are needed. But for monitoring the magnetic state at different fields, one detector (in that case the one which detects the component of the field perpendicular to the NW magnetisation) was enough. The DW nucleation and propagation was identified by observing a reversal of the periodic stray fields at the interfaces. Moreover we found that the stray field from the DW itself is larger then ones produced by the NW tips and interfaces.
During the propagation along the NW the DW stops only at the interfaces, proving the effectiveness of the Co/Ni interfaces for DW pinning We also were able to image the spin structure of the 3D vortex DW with a Bloch point with resolution of less than 4 nm (diffraction limit for the conditions used).
These findings open a new perspectives towards developing 3D magnetic memory devices. In particular, the experiments on current driven domain wall motion in cylindrical NWs are in progress.
[1] S. Lopatin, et al. submitted (2015)
5:00 PM - MD9.5.07
Structural and Magnetic Properties of Well-Ordered Inverted Core-Shell α-Cr2O3/α-MxCr2-xO3 (M=Co, Ni, Mn, Fe) Nanoparticles
Mohammad Delower Hossain 1,Sonal Dey 3,Robert Mayanovic 1,Mourad Benamara 2
1 Physics Astronomy and Materials Science Missouri State University Springfield United States,1 Physics Astronomy and Materials Science Missouri State University Springfield United States,3 Colleges of Nanoscale Science and Engineering SUNY Polytechnic Institute Albany United States2 Nanoscale Material Science and Engineering University of Arkansas Fayetteville United States
Show AbstractMagnetic core shell nanoparticles (NPs) have potential for applications in magnetic random access memory, spintronic devices, and drug delivery systems. Our investigations are focused on the synthesis of inverted core shell nanoparticles and characterization of their structural and magnetic properties. By using our hydrothermal nano-phase epitaxy technique, we are able to synthesize well-ordered α-Cr2O3/α-MxCr2-xO3 (M = Co, Ni, Mn, Fe) inverted core-shell nanoparticles. This typically results in the formation of novel phases of α-MxCr2-xO3 shells having ferromagnetic/ferrimagnetic (FM/FiM) spin ordering and an antiferromagnetic (AFM) α-Cr2O3 core structure. The combined results from XRD and high-resolution TEM (HRTEM) provide evidence of the presence of corundum phase both in the shell and in the core regions. HRTEM results also show a sharp interface exhibiting epitaxial atomic registry of shell atoms over highly ordered core atoms whereas TEM-EDX analyses show that the M atoms reside predominantly in the shell regions. The XPS analyses of the NPs indicate the M transition metals incorporated in the shell are in the +2 oxidation state. Magnetic measurements show well developed hysteresis loops: The field cooled hysteresis loops reveal horizontal shifts in the applied field axis and vertical shifts in the magnetization axis, relative to the zero-field cooled hysteresis loops. This provides direct evidence for the exchange bias effect between the AFM α-Cr2O3 core and the FM/FiM α-MxCr2-xO3 shell. The XPS data are consistent with oxygen vacancy formation in order to maintain charge neutrality upon substitution of the M2+ ion for the Cr3+ ion in the α-MxCr2-xO3 shell. The FM/FiM ordering in the shell may at least partially result from the F-center exchange coupling between the oxygen-vacancy induced bound magnetic polaron and nearby cations.
5:15 PM - MD9.5.08
Improving Hard Magnetic and Magnetocaloric Properties of Nanocrystalline R-Fe-M (R=Sm,Pr M=Ga,Si)
Lotfi Bessais 1,Rim Guetari 1,Karim Zehani 1,Jacques Moscovici 1,Najeh Mliki 2
1 ICMPE - CNRS-UPEC Thiais France,2 University of Tunis El Manar Tunis Tunisia
Show AbstractStructure and magnetic properties of nanocrystalline P6/mmm R(Fe,M)9C are presented. Their structure is explained with a model based on the R1−s(Fe,M)5+2s formula (s = vacancy rate) where s R atoms are statistically substituted by s transition metal pairs. The interpretation of the Mössbauer spectra is based on the correlation between the isomer shift and the Wigner-Seitz Cell volumes, calculated from the refined structural parameters. The specific behavior of the Ga/Si site isomer shift evolution corroborates the structure model. The maximum coercivity is obtained for low Ga/Si content for auto-coherent diffraction domain size ∼30 nm. This controlled microstructure might lead to hard permanent magnet materials. Furthermore, the influence of small amount of Dy substitution on magnetocaloric properties of R-Fe système is reported. The potential for using these low-cost iron based nanostructured RFe9 powders in magnetic refrigeration at room temperature is also discussed.
Symposium Organizers
Elena A. Rozhkova, Argonne National Laboratory
Haifeng Ding, Nanjing University
Miguel Angel Garcia, Institute for Ceramic and Glass, CSIC
Carlos Rinaldi, University of Florida
MD9.6: Magnetic Materials—From Fundamentals to Applications V
Session Chairs
Johan Akerman
Chia-ling Chien
Thursday AM, March 31, 2016
PCC West, 100 Level, Room 105 B
9:15 AM - *MD9.6.01
Dynamic Magnetic Solitons in Spin Torque and Spin Hall Nano-Oscillators
Johan Akerman 1
1 University of Gothenburg Gothenburg Sweden,
Show AbstractNano-contact spin-torque nano-oscillators (STNOs) [1] and spin Hall effect nano-oscillators (SHNOs) [2] provide excellent playgrounds for the study of highly non-linear and nano-scopic spin wave modes. While originally studied for their potential as highly broadband microwave signal generators, these devices now attract a rapidly growing interest as spin wave generators in magnonic devices [3,4] and as skyrmion injectors in magnetic nanowire based memories [5]. In my talk I will give an overview of a wide range of STNO and SHNO spin wave modes, including propagating spin waves [6-8], self-localized spin wave bullets [6,7] and droplets [9], as well as the recently suggested dynamical skyrmion [10]. I will also describe how these spin wave modes can interact and mutually synchronize [11,12].
[1] R. K. Dumas et al., IEEE Trans. Magn. 50, 4100107 (2014).
[2] V. E. Demidov et al., Nature Materials 11, 1028 (2012)
[3] S. Bonetti, J. Åkerman, Top. Appl. Phys. 125, 177 (2013)
[4] R. K. Dumas, J. Åkerman, Nature Nanotechnology 9, 503 (2014)
[5] J. Sampaio et al., Nature Nanotechnology 8, 839 (2013)
[6] S. Bonetti et al., Phys. Rev. Lett. 105, 217204 (2010)
[7] R. K. Dumas et al., Phys. Rev. Lett. 110, 257202 (2013)
[8] M. Madami et al., Nature Nanotechnology 6, 635 (2011)
[9] S. M. Mohseni et al., Science 339, 6125 (2013)
[10] Y. Zhou et al., Nature Communications, 6, 8193 (2015)
[11] S. R. Sani et al., Nature Communications 4, 2731 (2013)
[12] A. Houshang et al, Nature Nanotechnology, accepted (2015)
9:45 AM - *MD9.6.02
Manipulating Room Temperature Magnetic Skyrmions
Axel Hoffmann 1
1 Argonne National Laboratory Lemont United States,
Show AbstractMagnetic skyrmions are a perfect example for the ensuing complexity of mesoscale magnetism stemming from competitions between interactions crossing many lengthscales [1]. The interplay between applied magnetic fields, magnetic anisotropies, as well as symmetric and antisymmetric exchange interactions, can stabilize topologically distinct spin textures known as magnetic skyrmions. Due to their topology magnetic skyrmions can be stable with quasi-partcile like behavior, where they can be manipulated with very low electric currents. This makes them interesting for extreme low-power information technologies [2], where data is envisioned to be encoded in topological charges, instead of electronic charges as in conventional semiconducting devices. Towards the realization of this goal we demonstrated at room temperature stable magnetic skyrmions in magnetic heterostructures, which can be manipulated using spin Hall effects [3]. Furthermore, using inhomogeneous electric charge currents even allows the generation of skyrmions in a process that is remarkably similar to the droplet formation in surface-tension driven fluid flows [4].
This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division. Lithographic patterning was carried out at the Center for Nanoscale Materials, an Office of Science user facility, which is supported by DOE, Office of Science, Basic Energy Sciences under Contract No. #DE-AC02-06CH11357.
References
A. Hoffmann and H. Schultheiss, Curr. Opin. Solid State Mater. Sci. 19, 253 (2015).
A. Hoffmann and S. D. Bader, Phys. Rev. Appl. 4, 047001 (2015).
A. Hoffmann, IEEE Trans. Magn. 49, 5172 (2013).
W. Jiang, et al., Science 349, 283 (2015).
10:15 AM - MD9.6.03
Spin Wave Beam Mediated Driven Synchronization of Nano-Contact Spin Torque Oscillators
Afshin Houshang 2,Philipp Duerrenfeld 1,Ezio Iacocca 1,Sohrab Sani 3,Johan Akerman 3,Randy Dumas 2
1 University of Gothenburg Gothenburg Sweden,2 NanOsc AB Kista Sweden,1 University of Gothenburg Gothenburg Sweden3 Royal Institute of Technology Kista Sweden1 University of Gothenburg Gothenburg Sweden,2 NanOsc AB Kista Sweden,3 Royal Institute of Technology Kista Sweden
Show AbstractThe synchronization of multiple nano-contact spin torque oscillators (NC-STOs) [1-3] is mediated by propagating spin waves (SWs). While it has been shown that the Oersted field generated in the vicinity of the NC can dramatically alter the emission pattern of SWs [4], its role in the synchronization behavior of multiple NCs has not been considered. We investigate the synchronization behavior in multi NC-STOs oriented either vertically or horizontally, with respect to the in-plane component of the external field. NCs with nominal diameters of 100 nm and a center-to-center spacing ranging from 300-1500 nm are defined on top of an all metallic Co/Cu/NiFe pseudo spin valve. Synchronization is promoted (impeded) by the Oersted field landscape when the NCs are oriented vertically (horizontally) due to the highly anisotropic SW propagation. Not only is robust synchronization between two oscillators observed for separations up to 1000 nm, but synchronization of up to five oscillators, a new record, has been observed in the vertical array geometry. Furthermore, the synchronization can no longer be considered mutual, but driven, in nature as the final frequency is enforced by the NC-STO from which the SW beam originates [5].
This work was supported by the European Commission FP7-ICT-2011 contract No. 317950 “MOSAIC” and the ERC grant 307144 “MUSTANG”. Support from VR, SSF, and the Knut and Alice Wallenberg Foundation is also gratefully acknowledged.
[1] S. Kaka, et al., Nature 437, 389 (2005)
[2] F.B. Mancoff, et al., Nature 437, 393 (2005)
[3] S.R. Sani, et al., Nat. Comm. 4, 2731 (2013)
[4] R.K. Dumas, et al., Phys. Rev. Lett. 110, 257202 (2013)
[5] A. Houshang, et al., Nature Nanotechnology, in press.
10:30 AM - MD9.6.04
Large Electric-Field Control of Perpendicular Magnetic Anisotropy in Strained [Co/Ni] / PZT Heterostructures
Daniel Gopman 1,Cindi Dennis 1,P. Chen 1,Yury Iunin 2,Robert Shull 1
1 NIST Gaithersburg United States,2 Russian Academy of Sciences Institute of Solid State Physics Chernogolovka Russian Federation
Show AbstractThe high energy required to reverse the magnetization of ultrathin films with large perpendicular magnetic anisotropy (PMA) presents a challenge to the development of energy-efficient data storage and spintronics applications. Magnetoelectric strain coupling has emerged as a promising method to lower the energy cost in operating these devices. Previous work has yielded a proof of concept for lowering the coercivity and the PMA of films (Co/Pt, CoFeB, Co/Pd) coupled to piezoelectric materials (PZT/PMN-PT) under applied electric fields [1-3].
Here we present a new combination of piezoelectric/ferromagnetic heterostructure with PMA - a Co/Ni multilayer sputtered directly onto a Pb[ZrxTi1-x]O3 (PZT) substrate. Due to its high spin-transfer torque efficiencies and spin-polarization relative to Co/Pt and Co/Pd, the Co/Ni multilayer is a more promising candidate material for spin-valve and domain wall devices [4-5], but until now has not been explored as part of a ferromagnetic/piezoelectric heterostructure. Chemical-mechanical polishing was used to reduce the roughness of PZT plates from hundreds of nm to below 2 nm rms, enabling optimal magnetoelectric coupling via the direct interface between PZT and high-quality sputtered Co/Ni films with large PMA (Keff = (95 ± 9) kJ/m3), as determined by vibrating sample magnetometry and ferromagnetic resonance spectroscopy. The following layers were sputtered directly on PZT: Ta(3)/Pt(2)/[Co(0.15)/Ni(0.6)]x4/Co(0.15)/Pt(2)/Ta(3); numbers in parentheses indicate thicknesses in nm. We found that applied electric fields up to +/- 2 MV/m to the PZT generated 0.05% in-plane compression in the Co/Ni multilayer, enabling a large electric-field reduction of the PMA (ΔKeff ≥ 2 kJ/m3) and of the coercive field (35%). These results demonstrate that: (i) heterostructures combining PZT and Co/Ni exhibit larger PMA (Keff ~ 105 J/m3) than previous magnetoelectric heterostructures based on Co/Pt and CoFeB [1-3], enabling future thermally stable hybrid magnetoelectric/spintronic devices only tens of nm in diameter and (ii) substantial electric-field control of the PMA is promising for more energy efficient switching of spintronic devices.
References:
[1] Lei et al., Phys Rev B, 84, 012404 (2011)
[2] Shepley et al., Sci Rep, 5 7921 (2015)
[3] Yu et al. Appl. Phys. Lett. 106, 072402 (2015)
[4] Mangin et al., Nat. Mater. 5, 210 (2006)
[5] Ryu et al. Nat Comm, 5 3910 (2014)
11:15 AM - *MD9.6.05
Dynamic Control of Interacting Spin Vortices
Valentine Novosad 1
1 Argonne Nat'l Lab Lemont United States,
Show AbstractManipulation of the magnetization is a key problem in applied magnetism. Herewith a method of controlling the ground state using two interacting vortices as a model system will be presented. A spin vortex consists of an in-plane and out-of-plane (core) regions of magnetization. Control of an in-plane magnetization has been demonstrated previously, whereas manipulation of the vortex cores remained challenging. In our work this is achieved by driving the system from the linear regime of constant vortex gyrations to the non-linear regime of vortex-core reversals at a fixed excitation frequency of one of the coupled modes [1]. Subsequently reducing the excitation field to the linear regime, stabilizes the system to a polarity combination whose resonant frequency is decoupled from the initialization frequency. The transition of the state from one polarity combination to the other is clearly evident from the contrast in the microwave absorption amplitude obtained by gradually increasing the rf-field to higher magnitudes at the resonant frequency of one of the modes and subsequently decreasing it. The transition from one state to the other has been quantified in the form of hysteresis observed in the absorption amplitude of the output signal as a function of varying rf-power. The difference in the absorption amplitudes before and after the transition provides a measure of the coupling strength between the excitation frequency and the coupled mode. A corresponding phase diagram has been constructed that provides a summary of the excitation frequency and amplitudes required to attain a specific ground state in the system [2]. The resonant phenomena applied to a connected double-dot geometry can also be extended to a many-particle system for its potential applications, such as, spin-torque nano-oscillators, vortex-based magnonic crystals, or logic devices.
This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division.
[1] S. Jain, F. Y. Fradin, J. E. Pearson et al., Nature Comm., DOI: 10.1038/ncomms2331 (2012).
[2] S. Jain, V. Novosad, F. Y. Fradin, et al., Appl. Phys. Lett., 102, 052401 (2013).
11:45 AM - *MD9.6.06
Pure Spin Current Phenomena and Devices
Chia-ling Chien 1
1 Johns Hopkins Univ Baltimore United States,
Show AbstractPure spin current phenomena and devices are new advents in spin electronics. A pure spin current has the unique attribute of delivering spin angular momentum without a net charge current thus more energy efficient. A pure spin current can be generated by a few mechanisms, including spin Hall effect, spin pumping, longitudinal spin Seebeck effect, and lateral spin valves. The inverse spin Hall effect in a metal with strong spin-orbit coupling can detect a pure spin current by converting it into a charge current. We describe several recent advances including pure spin current phenomena in ferromagnets and antiferromagnets, spin orbit switching of ferromagnetic layers, and enhancement of pure spin current
12:15 PM - *MD9.6.07
Interface-Driven Chiral Spin Textures in Ultrathin Magnetic Films
Geoffrey Beach 1
1 MIT Cambridge United States,
Show AbstractSpin orbit coupling at interfaces in ultrathin magnetic films can give rise to chiral magnetic textures such as homochiral domain walls and magnetic skyrmions, as well as current-induced torques that can efficiently manipulate them [1-3]. This talk will describe interface-driven spin-orbit torques and Dzyaloshinskii-Moriya interactions (DMIs) in ultrathin ferromagnets adjacent to nonmagnetic heavy metals. We show that the DMI depends strongly on the heavy metal, differing by a factor of ~20 between Pt and Ta [2], and describe the influence of strong DMI on domain wall dynamics [1,2] and spin Hall effect switching [3]. We then present high-resolution x-ray microscopy and scanning probe imaging of chiral magnetic skyrmions and their dynamics in multilayer films that allow the relevant energy terms to be engineered [4]. Finally, we will describe how SOTs can be enhanced through interface engineering [5] and tuned by a gate voltage [6] by directly controlling the interfacial oxygen coordination at a ferromagnet/oxide interface [7].
[1] S. Emori, et al., Nature Mater. 12, 611 (2013)
[2] S. Emori, et al., Phys. Rev. B 90, 184427 (2014)
[3] N. Perez, et al., Appl. Phys. Lett. 104, 092403 (2014)
[4] S. Woo, et al., arXiv:1502.07376 (2015)
[5] S. Woo, et al., Appl. Phys. Lett. 105, 212404 (2014)
[6] S. Emori, et al., Appl. Phys. Lett. 105, 222401 (2014)
[7] U. Bauer, et al., Nature Mater. 14, 174 (2015)
12:45 PM - MD9.6.08
Current-Induced Rashba-Edelstein Field in Permalloy Interfaced with an Oxide
Satoru Emori 1,Tianxiang Nan 3,Amine Belkessam 2,Xinjun Wang 2,Alexei Matyushov 2,Christopher Babroski 2,Yuan Gao 2,Hwaider Lin 2,Nian Sun 2
2 Northeastern University Boston United States,1 Stanford University Stanford United States,2 Northeastern University Boston United States,3 University of Winsconsin-Madison Madison United States2 Northeastern University Boston United States
Show AbstractCurrent-induced torques due to spin-orbit interactions enable efficient control of magnetization in thin-film heterostructures. Most studies so far have focused on spin-orbit torques in bilayers consisting of a ferromagnet interfaced with a nonmagnetic heavy metal. In these bilayers, the torques may originate from the spin Hall effect within the heavy metal or the Rashba effect at the ferromagnet/metal interface.
We show the presence of a spin-orbit field-like torque in permalloy (Py) thin films capped by Al2O3 by using a second-order planar Hall effect voltage technique [1] and spin-torque ferromagnetic resonance [2]. The effective field from this torque is significantly larger than the maximum possible Oersted field. Its magnitude scales inversely with Py thickness, and its direction is transverse to the current axis and independent of the magnetization orientation in Py. Furthermore, inserting an atomically thin, strong spin-scattering layer of Pt at the Py/Al2O3 interface suppresses this field-like torque. These findings point to a Rashba-Edelstein effect at the interface between a 3d transition metal and an oxide, with the resulting interfacial spin accumulation generating an effective field on the adjacent magnetization. This Rashba-Edelstein field at metal/oxide interfaces may allow for engineering spin-orbit torques without using heavy transition metals and for tuning torques by gate voltage.
[1] X. Fan et al. Nat. Commun. 4, 1799 (2013); X.Fan et al. Nat. Commun. 5, 3042 (2014)
[2] L. Liu et al. Phys. Rev. Lett. 106, 036601 (2011); T. X. Nan et al. Phys. Rev. B 91, 214416 (2015)
MD9.7: Magnetic Materials—From Fundamentals to Applications VI
Session Chairs
Nora Dempsey
Carlos Rinaldi
Thursday PM, March 31, 2016
PCC West, 100 Level, Room 105 B
2:30 PM - *MD9.7.01
Biomedical Applications of Magnetic Nanoparticles: Delivering Genes and Remote Control of Cells
Jon Dobson 1,Adam Monsalve 1
1 University of Florida Gainesville United States,
Show AbstractThe use of magnetic micro and nanoparticles for biomedical applications was first proposed in the 1920s as a way to measure the rheological properties of the cytoplasm. Since that time, particle synthesis techniques and functionality have advanced significantly. Magnetic micro and nanoparticles are now used in a variety of biomedical applications such as targeted drug delivery, MRI contrast enhancement, gene transfection, immunoassay and cell sorting. More recently, magnetic micro and nanoparticles have been used to investigate and manipulate cellular processes both in vitro and in vivo.
This talk will focus on our work developing Magnetically Activated Receptor Signaling (MARS), a magnetic nanoparticle based technique for activating cell surface receptors and controlling the activity of biomolecules such as growth factors. The basic principles involve surface functionalization of magnetic nanoparticles (MNPs) with molecules targeting specific cell surface receptors. We have investigated both antibodies targeting specific ion channels (e.g. TREK 1) and surface receptors (e.g. Platelet-derived growth factor, PDGFR) and peptides (e.g. RGD) targeting integrins. The particles bind to the receptors and, upon the application of a highgradient external magnetic field, energy is transferred to the particles. The energy delivery induces a conformation change in the receptor, activating the specific biochemical signaling pathway associated with that receptor. By targeting specific receptors, we have been able to control ion channel activity, activate bone and cartilage matrix formation, and control the differentiation of human mesenchymal stem cells both in vitro and in vivo. The technology has applications in regenerative medicine, drug screening and cell engineering. Other nanomagnetic technologies for biomedical applications will also be discussed.
3:00 PM - *MD9.7.02
Development of Micron-Scaled Magnetic Flux Sources for Biological and Medical Applications
Nora Dempsey 1
1 Institut NEEL - CNRS Grenoble France,
Show AbstractMicron-scaled magnetic flux sources have many potential applications in the fields of biology and medicine, information technology, energy transformation/management... As the size of the magnetic element is down-scaled, the strength of the magnetic field gradient it produces, and thus the force per unit volume that it can apply on another object, is up-scaled. Field gradient values as high as 106 T/m can be achieved with micron scaled structures. Hard magnetic material based structures offer the distinct advantage that they need neither an external magnetic field source nor power supply, and thus they are particularly well suited for use in autonomous, mobile devices or where space is limited. On the other hand, soft magnetic material based structures are well suited to applications requiring time varying magnetic fields. The development of high performance hard magnet based systems has been hindered to-date by the challenges faced in micro-patterning such materials while most studies related to soft magnetic structures have been limited to thin film structures or relatively low magnetization materials (e.g. FeNi, Ni).
In this presentation I will report on the preparation and patterning of high field gradient micro-flux sources based on high coercivity hard (NdFeB) and high magnetization soft (Fe, FeCo) magnetic materials. Both thick film and powder-polymer composite structures will be presented. Quantitative characterization of the stray magnetic fields produced by such structures, and the magnetic forces applied by them to test structures, will be described. Finally, I will show examples of a range of bio-related applications being developed in the framework of various collaborations.
3:30 PM - MD9.7.03
Magnetically Actuated Release of Pharmacological Compounds from Magnetic Nanoparticles for Neuronal Stimulation
Michael Christiansen 1,Gabriela Romero 1,Francisco Garcia Osorio 1,Ligia Barbosa 1,Polina Anikeeva 1
1 MIT Cambridge United States,
Show AbstractRecent work has demonstrated that macroscopic heating generated by droplets of magnetic nanoparticles in an alternating magnetic field can be used to stimulate neurons via the response of temperature sensitive membrane proteins. Here, we develop an alternative, similarly noninvasive approach that, by contrast, makes use of nanoscale effects of dissipated heat to trigger the release of pharmacological compounds from nanoparticles targeted to cell membranes. In a therapeutic context, this approach would have the advantage of requiring a considerably reduced concentration of magnetic nanoparticles as well as allowing for cell-type specific modulation. The compounds released from the particles may include neurotransmitters or synaptic blockers, intended to rapidly stimulate or inhibit neural activity. As a proof of concept, we show through dye release experiments that a chemical payload conjugated to the surface of iron oxide nanoparticles via a temperature sensitive azide linker can be released at a timescale of seconds. Subsequently, we provide an in vitro demonstration of magnetically actuated excitation via the release of allyl isothiocyanate (AITC), an agonist of the ion channel TRPV1, in primary hippocampal cultures expressing the channel. Real-time fluorescence intensity changes of a genetically encoded calcium indicator, GCaMP6s, serve as a primary readout of magnetically triggered calcium ion influx into the neurons. Finally, we demonstrate and discuss possible extensions of this technique that would allow for multiple chemical signaling pathways to be independently addressed.
4:15 PM - *MD9.7.04
Lipid Base Magnetic Nanohybrids for Dual Therapy for Cancer
Dhirendra Bahadur 1
1 Department of Metallurgical Engineering and Materials Science Indian Institute of Technology-Bombay Mumbai India,
Show AbstractThe deliberate design of lipid base magnetic nanohybrids for biological applications has been enabled by new advances in synthetic procedures through different soft chemistry routes. Such nanostructures when properly functionalized can be used as effective vehicles for biological entities in vivo. We describe folate receptor targeted thermosensitive magnetic liposomes, designed to combine features of biological and magnetic drug targeting for use in magnetic hyperthermia with temperature triggered drug release.The results suggest that an integrated concept of biological and physical drug targeting and hyperthermia can be used advantageously for thermo-chemotherapy of cancers. We present another example, wherein a dual phasic system consisting of two magnetic phases with different functionalities has been investigated for dual therapy. One of the phases is used to control the temperature around the hyperthermic temperature while the other with high SAR and biocompatibility is mainly responsible for thermotherapy. Following this, we discuss some of our recent work related to pH and thermo sensitive dual drug delivery system in dual therapy mode (Hyperthermia + chemotherapy). Thin layer of lipid coated mesoporous magnetic nanoassemblies have been used for loading both hydrophilic and hydrophobic drugs. These magnetic nanohybrids provide the synergistic effects due to dual drug along with thermotherapy. Some of these aspects based on the work carried out in our laboratory will be presented. These nanostructures possess the imaging capabilities and the ability to attain hyperthermic temperature (~41–45 °C) by an external AC magnetic field. By utilizing both, the optical and magnetic properties, an in vivo bio distribution and bio-compatibility studies have been done in Nude mice. These results were further validated by measuring the iron level in different organs using ICP-AES and magnetization analyses. For efficient delivery of magnetic nano hybrids with dual drug to the diseased site, magnetic fluid based release systems will be discussed with different possibilities of thermo and pH sensitive nanoconstructs. We will particularly emphasize some of our recent in vitro as well as in vivo results on lipid based nanohybrids with multifunctional capabilities. We have further investigated the synergistic effects of dual drug and dual therapy in vivo model in nude mice. The uptake of dual drug-lipid hybrid and regression of tumors were monitored through bioluminescence imaging post dual therapy combing hyperthermia with chemotherapy.
References:
S. Chandra, K.C. Barick, D. Bahadur, “Oxide and hybrid nanaostructures for therapeutic applications”, Advanced Drug Delivery Reviews, 63, 1267-1281, 2011.
2.Lina Pradhan, R. Srivastava, D. Bahadur, “pH and thermo-sensitive thin lipid layer coated mesoporous magnetic nanoassemblies as a dual drug delivery system towards thermo-chemotherapy of cancer”, Acta Biomaterialia, 10, 2976-2987 (2014).
4:45 PM - MD9.7.05
Core-Shell Paramagnetic Gadolinium–Doped Melanin@Silica Nanoparticles for Multimodal Image–Guided Cancer Therapy
Soojeong Cho 1,Wooram Park 1,Dong-Hyun Kim 2
1 Radiology Northwestern University Chicago United States,1 Radiology Northwestern University Chicago United States,2 Robert. H. Lurie Comprehensive Cancer Center Chicago United States
Show AbstractMelanin is natural pigments that protect body from harmful rays by high efficiency of heat conversion. However, uncertainty of chemical structures and excessive redox exchange, quenching electrons on melanin surfaces limit their use in biomedical applications [1]. In this work, we designed core-shell nanostructure of gadolinium (Gd)–doped melanin@SiO2 nanoparticles for multimodal imaging of fluorescence and magnetic resonance (MR), and near infrared (NIR) laser–induced photothermal therapy.
Melanin nanoparticles were prepared by oxidative polymerization of dopamine and then Gd were readily doped by redox site chelation in melanin nanoparticls upon adding gadolinium(III) chloride. Gd–doped melanin nanoparticles (Gd-mel) were coated with silica shell using sol-gel method. (3-aminopropyl)triethoxysilane (APTES)-fluorescein isothiocyanate (FITC) was further labeled to Gd-mel@SiO2 nanoparticles. In vitro multimodal MR/fluorescent imaging properties, biocompatibility and photothermal heating efficiency of the synthesized FITC-Gd-mel@SiO2 nanoparticles were evaluated. Finally, in vivo multimodal MR T1/fluorescent imaging and photothermal therapeutic efficacy of FITC-Gd-mel@SiO2 nanoparticles were investigated in prostate xenograft mice models.
Gd-mel@SiO2 nanoparticles of 120 nm in size were successfully synthesized. The paramagnetic property of Gd-mel@SiO2 nanoparticles was demonstrated with strong MR T1 effects in 7T MRI system. When the Gd-mel@SiO2 nanoparticles are labeled with FITC, FITC-Gd-mel@SiO2 nanoparticles exhibit strong fluorescence without innate quenching effect of melanin, which demonstrates a role of silica as passivation layers to prevent fluorescent quenching. Cells treated with Gd-mel@SiO2 nanoparticles have higher viability than those with Gd-mel nanoparticles. During in vivo study, tumors targeted with FITC-Gd-mel@SiO2 nanoparticles could be monitored in MR T1 and fluorescent imaging and FITC-Gd-mel@SiO2 nanoparticles induced the localized photothermal heating on tumors upon multimodal image-guided NIR irradiation. Finally, photothermal treatment using FITC-Gd-mel@SiO2 nanoparticles could effectively ablate tumors without any signs of recurrence; this investigation depicts the great potential of FITC-Gd-mel@SiO2 nanoparticles as a multimodal imaging and photothermal agent for cancer therapy.
[1] P. Meredith, et al. Pigment Cell Res., 2006, 19, 572
5:00 PM - MD9.7.06
Multifunctional Magnetic Nanomaterials for Biomedical Applications
Manashi Nath 1
1 Missouri Samp;T Rolla United States,
Show AbstractIn recent times multifunctional nanomaterials which refers to two or more heterogeneous compositions exhibiting diverse functionalities fused into one single nanostructure, has been at the center of attraction mainly due to the wide variety of potential applications. Of these, the optically active magnetic multifunctional nanomaterials (MMN) have gained special attention in the biomedical arena as active components of therapeutic and diagnostic agents. In the Nath laboratory, we have shifted our focus on creating Au-Fe3O4 MMNs through extensive hypothesis driven materials chemistry, with the motivation of using them as efficient hyperthermia agents for cancer treatment as well as contrast enhancing agents for biomedical imaging. The Au-Fe3O4 magnetic nanostructures are designed such that they can exhibit maximum efficiency towards heat generation under an applied magnetic field with lower dosing levels. These Au-Fe3O4 nanostructures were made by simple one-pot solution chemistry based method involving environmentally safe and benign precursors like Fe(CO)5 which was refluxed in presence of HAuCl4 and surfactants like oleic acid and oleylamine. By varying the reaction conditions we could make various kinds of MMN morphologies like core-shell, dumbbell and Janus-like nanoparticles. In a separate synthesis method, arrays of Au-Fe3O4 nanorods with uniform aspect ratio were also produced through patterned electrodeposition on lithographically created nanoelectrodes. Preliminary magnetization studies with our morphology optimized Au-Fe3O4 multi-modal nanostructures suggest that they might have better hyperthermia efficiencies than the commercially produced samples, due to optimization of the superparamagnetic property. Another notable feature was that despite the bigger size of these MMNs, coupling the Fe3O4 with Au actually led to retention of the superparamagnetic properties above the critical domain through exchange bias interactions. These Au-Fe3O4 nanoparticles were functionalized with biomolecules like cysteine and (-)EGCG (epigallocatechin gallate), which can aid in internalization of these MMNs inside the disease tissue, and also help in making them readily dispersible in water which increases the probability of cell uptake. Synthesis, characterization, detailed property studies of these Au-Fe3O4 nanoparticles along with their biofunctionalization, cell viability and toxicity evaluation will be discussed in this talk.
5:15 PM - MD9.7.07
Quasi 1D Nanoarray of Superparamagnetic Iron Oxide Nanoparticles on Graphene Oxide Nanoribbons as a Promising MRI T2 Contrast Agent
Bibek Thapa 1,Daysi Diaz-Diestra 2,Juan Beltran-Huarac 1,Huadong Zen 4,Brad Weiner 2,Gerardo Morell 3
1 Physics University of Puerto Rico San Juan United States,2 Chemistry University of Puerto Rico San Juan United States4 University of Florida Gainesville United States3 Physics University of Puerto Rico San Juan United States
Show AbstractDiverse strategies have been investigated to artificially engineer the shape, size and composition of iron oxide nanoparticles (IONPs) in order to exploit their theranostics capabilities in nanomedicine. The enhancement of magnetic resonance relaxivity and the improvement of pharmacokinetic factors are essential for ultrasensitive bioimaging and biodetection. In the present work, we report the development and implementation of a nobel strategy that consists in coupling quasi 1D IONPs on polyetheramine-functionalized graphene oxide nanoribbons (pGONRs). The average size of nanoparticles is of ~11 nm, which are homogeneously distributed over supporting pGONRS (~150-200 nm long). The T1 relaxivity observed is ~20 mM-1s-1 at 1.4 T, whereas the T2 relaxivity is ~167 mM-1s-1 indicating that the hybrid material is promising as MRI T2 contrast agents. The high T2 relaxivity value found is attributed to the higher water-nanoparticle coordination number due to the elongated 1D array configuration. The X-ray diffraction and advanced spectroscopy reveal conspicuously the coexistence of both constituents with a high degree of crystallinity and purity. The colloidal stability of this hybrid material is confirmed through dynamic light scattering (DLS) and zeta potential. The MTS assays show that these nanostructures are completely harmless to different cancer cell lineages. These findings represent a step forward to design in vivo multifunctional nanoprobes suitable for theranostics in a wide range of human diseases.
Symposium Organizers
Elena A. Rozhkova, Argonne National Laboratory
Haifeng Ding, Nanjing University
Miguel Angel Garcia, Institute for Ceramic and Glass, CSIC
Carlos Rinaldi, University of Florida
Symposium Support
The Center for Nanoscale Materials – Argonne National Laboratory
MD9.8: Magnetic Materials—From Fundamentals to Applications VII
Session Chairs
Friday AM, April 01, 2016
PCC West, 100 Level, Room 105 B
10:00 AM - *MD9.8.01
Progress towards Developing New Permanent Magnets
Laura Lewis 1
1 Northeastern Univ Boston United States,
Show AbstractDevelopment of new types of permanent magnets is exceedingly difficult, with estimates concerning the typical time from discovery of new materials to implementation ranging from 17 to 20 years. Nonetheless, strong motivation persists to diversify the supply of rare-earth-based supermagnets in response to ever-growing demand in energy, defense, transportation and consumer product sectors. In contrast to many rare earth elements that are currently utilized in ultra-strong permanent magnets, the elements Fe and Ni are the most abundant, most readily processed and most studied magnetic elements in the Earth’s crust. Depending upon its local bonding environment, iron can donate a variety of effects that provide function to modern technology. As an example, equiatomic FeNi with the tetragonal L10 structure, known as tetrataenite, exhibits highly attractive properties for advanced permanent magnetic applications. However, enthusiasm for its development is tempered by its highly challenging synthesis pathways: tetrataenite is only found naturally and in appreciable volumes in selected meteorites subjected to extraordinarily slow cooling rates, as low as 0.3 K per million years. Results concerning recent progress towards laboratory-based synthesis of tetrataenite will be presented to foster discussion of its potential as a rare-earth-free permanent magnetic material. In particular, emphasis will be placed on detection of the required crystallographic rearrangement to develop appreciable magnetocrystalline anisotropy in FeNi alloys.
Acknowledgements: Support from Northeastern University and Rogers Corporation is gratefully acknowledged.
10:30 AM - MD9.8.02
Microstructure-Magnetic Property Correlations in Rare-Earth Free Permanent Magnet Alloy MnBiFe Synthesized Employing Melt Spinning
Nidhi Singh 1,Kritika Anand 1,Nithya Christopher 1,A.K. Srivastava 1,Ajay Dhar 1
1 CSIR-National Physical Laboratory New Delhi India,
Show AbstractCurrently there is a thrust worldwide to develop cost-effective rare-earth free permanent magnets owing to the rising costs of rare-earth elements. Recent developments in the area of permanent magnets have recognized Mn-based alloys as potential permanent magnetic materials due to their low cost, higher magnetic moment due to Mn atoms coupled with a high Curie temperature. MnBi is a rare-earth free ferromagnetic intermetallic compound and owing to its high magnetic anisotropy and Curie temperature makes it a promising material for permanent-magnet applications. The low temperature phase (LTP) of MnBi exhibits a coercivity which is nearly comparable to that of Nd2Fe14B, which has invoked its potential as a rare-earth free permanent magnet material.
However, MnBi exists in several phases, which are stiochiometrically very close, rendering the synthesis of its LTP rather difficult. There have been extensive research efforts in MnBi alloys towards increasing their resistance to degradation, improving their magnetic properties and to form a stable phase that exhibits a high Curie temperature. To address these problems, we present the results of our experimental investigations on the effect of elemental Fe additions in MnBi on the resulting structural and magnetic properties. Fe, a ferromagnetic transition metal, was chosen in the present work since it has a high saturation magnetization and does not produce any significant change in the lattice symmetry although it leads to noticeable changes in their lattice parameters. Elemental Mn, Bi and Fe powders were repeatedly arc-melted in a stiochiometric proportion to yield ingots with a composition of Mn50Bi45Fe5. These arc-melted ingots were then melt-spun at optimized process parameters, which yielded continuous nanocrystalline ribbons with a uniform thickness of < 40 µm. It was observed that the addition of Fe in MnBi although increases the coercivity but at the expense of magnetization. The melt-spun Mn50Bi45Fe5 alloy ribbons, annealed at optimized conditions, exhibited a Ms ~ 40 emu/g, Mr ~ 20 emu/g and Hc ~ 2.2 kOe with (BH)max ≥ 2 MGOe at room temperature. The morphology of the melt-spun alloys was investigated employing FESEM and their structure was characterized using XRD and HRTEM and was then correlated with their resulting magnetic properties to establish structure-property correlation in these alloys. Work is presently underway to enhance the magnetic properties of these alloys by varying the Fe content in MnBi and further optimizing the melt spinning and annealing parameters.
*Corresponding author: singhnidhi@nplindia.org
10:45 AM - MD9.8.03
Melt Spun Nanostructured α″-Fe16N2 Foils for RE-free- Permanent Magnets
Md Mehedi 1,Yanfeng Jiang 2,Jian-Ping Wang 1
1 Chemical Engineering and Materials Science University of Minnesota Minneapolis United States,2 Electrical and Computer Engineering University of Minnesota Minneapolis United States2 Electrical and Computer Engineering University of Minnesota Minneapolis United States,1 Chemical Engineering and Materials Science University of Minnesota Minneapolis United States
Show AbstractRare-earths are expensive with an unstable market, and the extraction process is energy intensive and hazardous to the environment and the human health. Thus, rare-earth-free permanent magnet is regarded as the one of the biggest challenges of this decade for a clean and sustainable energy solution. We have been exploring to synthesize permanent magnets based on two abundant and cheap elements in the crust and nature, iron and nitrogen, which obviates the necessity of rare-earths. The α″-Fe16N2 has a high saturation magnetization of 2.6 T [1,2] or more and a high magnetocrystalline anisotropy of 2107 erg/cc.[2,3] However, it is very challenging to produce Fe16N2 phase in bulk format due to its metastability and low thermal stability, and metastability of nitrogen in iron lattice during diffusion and quenching process. We are reporting an approach to prepare bulk foils of α″-Fe16N2 which can be directly obtained from a melt spinning process. We also prove that further thermal and mechanical processing can produce a α″-Fe16N2 permanent magnet. The α″-Fe16N2 phase purity is approximately 50% wt. We also tuned the microstructure of α″-Fe16N2 by doping different elements, and obtained a 30-50 nm grain size which is equal to the single domain size of α″-Fe16N2 magnet. In this conference, we will present about the novel processing technique of α″-Fe16N2 foils with reasonable phase purity and finely tuned microstructure.
References:
[1] H. Takahashi, K. Mitsuoka, M. Komuro, Y. Sugita, J. Appl. Phys. 1993, 73, 6060.
[2] T. K. Kim, M. Takahashi, Appl. Phys. Lett. n.d., 20, 492.
[3] N. Ji, M. S. Osofsky, V. Lauter, L. F. Allard, X. Li, K. L. Jensen, H. Ambaye, E. Lara-Curzio, J. P. Wang, Phys. Rev. B - Condens. Matter Mater. Phys. 2011, 84, DOI 10.1103/PhysRevB.84.245310.
11:30 AM - MD9.8.04
The Influence of Severe Plastic Deformation on Magnetic Properties of Ferromagnetic 4-f Elements: Tb and Dy
Sergey Taskaev 2,Konstantin Skokov 2,Vladimir Khovaylo 1,Dmitriy Karpenkov 1,Maxim Ulyanov 1,Dmitriy Bataev 1,Anatoliy Pellenen 3
1 Chelyabinsk State University Chelyabinsk Russian Federation,2 MISiS Moscow Russian Federation,2 MISiS Moscow Russian Federation,1 Chelyabinsk State University Chelyabinsk Russian Federation1 Chelyabinsk State University Chelyabinsk Russian Federation3 South Ural State University Chelyabinsk Russian Federation
Show AbstractIn this work we continue our previous investigations of the severe plastic deformation (SPD) on the magnetic properties of 4-f elements, with special accent on magnetic anisotropy and magnetic transformations. As it shown in [1], severe plastic deformation has a great effect on magnetic properties of 4-f elements. For instance, in Gd a significant increase of the magnetocrystalline anisotropy (up to 2 orders of magnitude) has been observed. The aim of this work is to investigate other important for permanent magnets industry ferromagnetic elements Tb and Dy for a change in physical properties.
The interest in this matter is far from being purely academic. Severe plastic deformation procedures are very interesting for designing novel functional materials. Depending on the degree of deformation, magnetic, structural or thermodynamic properties could be varied in severely deformed materials, especially in thin ribbons of SPD-treated materials.
As it shown in [1] a significant depression of magnetic and thermodynamic properties occurs in severely deformed samples of Gd. The reason of such behavior is in a giant magnetic anisotropy induced by SPD. This unexpected phenomena drives to a new thermodynamic and magnetic properties of severely deformed Gd ribbons [1] which are inapplicable after the SPD-treatment for magnetocaloric applications without additional heat treatment procedure. The heat treatment regimes are directly connected with the degree of plastic deformation [2].
In the talk we report the magnetic properties of thin Tb and Dy ribbons obtained with the help of SPD technique. The deformation of the materials achieved the values about 70 times and this greatly affect on magnetic properties of deformed materials. In the case of Tb the enhancement the coercive force during SPD (it is two times larger in compare to raw material). This feature is helpful for designing novel magnetic materials (especially hard magnetic materials). Special accent is made for magnetocaloric properties of the SPD treated Tb and Dy metals.
Authors appreciate Russian Science Foundation grant 15-12-10008 for financing this work.
References
[1] S. V. Taskaev, M. D. Kuz`min, K. P. Skokov, D. Yu. Karpenkov, A. P. Pellenen, V. D. Buchelnikov and O. Gutfleisch, JMMM 331, 33 (2013).
[2] S. V. Taskaev, V. D. Buchelnikov, A. P. Pellenen, M. D. Kuz’min, K. P. Skokov, D. Yu. Karpenkov, D. S. Bataev and O. Gutfleisch, J. Appl. Phys. 113, 17A933 (2013).
11:45 AM - MD9.8.05
Metglas/Polyvinylidene Fluoride Laminates for Magnetoelectric Energy Harvesting from Power Cords
Myung-Eun Song 1,Yongke Yan 1,Shashank Priya 1
1 Center for Energy Harvesting Materials and Systems Blacksburg United States,
Show AbstractMagnetic fields surround any electrical device including power lines, house wiring and appliances due to the currents they produce. Magnetic fields are not easily weakened by most materials but strength decreases with distance. We can harvest electric power from magnetic fields that occur naturally, such as a byproduct of technology. In this study, magnetoelectric energy harvesting from power cords using flexible energy harvesters was performed. The flexible magnetoelectric laminates were attached to power cords to integrate into the cord’s rubber layer. For the flexible magnetoelectric laminates, Metglas and polyvinylidene fluoride (PVDF) are mainly utilized as magnetostrictive and piezoelectric layer, respectively. The energy is obtained by magnetoelectric energy harvesters on outer and inner layer of power cords. The method covering inner layer of power cord provides ~30mV higher output voltage than that of outer layer of power cord. A considerable magnitude of output voltage with value of 242mV was obtained by a long flexible energy harvester on inner layer of power cord. The flexible energy harvester is the key to recycling technological byproduct produced around the home.
12:00 PM - MD9.8.06
The Origin of Magnetic Ordering in Sr3YCo4O10+x
Matthew Chisholm 1,Takayoshi Kishida 2,Myron Kapetanakis 1,Jiaqiang Yan 1,Brian C. Sales 1,Sokrates Pantelides 1,Stephen Pennycook 4
1 Oak Ridge National Laboratory Oak Ridge United States,2 Asahi Kasei Corporation Shizuoka Japan3 Vanderbilt University Nashville United States,1 Oak Ridge National Laboratory Oak Ridge United States4 National University of Singapore Singapore Singapore
Show AbstractTransition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt’s ability to adopt various oxidation and spin state configurations. The oxygen-deficient perovskite Sr3YCo4O10+x (SYCO) exhibits the highest ferromagnetic ordering temperature of any of the perovskite cobaltates with Tc = 335K. There have been several contending structural models for SYCO, extracted from X-ray and neutron diffraction, but there is no consensus on the precise atomic structure of this material. The undisputed facts are that SYCO exhibits antiferromagnetic ordering with asymmetric spin-up and spin-down magnetic moments, characteristic of ferrimagnetism. The different structural models correspond to different origins for the observed ferrimagnetism, with no apparent resolution. Here we report a combined investigation of SYCO using aberration-corrected scanning transmission electron microscopy and density functional theory calculations. In order to take into account the correlation effects of the 3d electrons of Co ions we employ the GGA+U approximation with a typical value of the effective Hubbard parameter of U=3eV using the Dudarev approach and an energy cut-off of 600eV for the plane wave basis set. Based on these results, we propose a new model for SYCO that has antiferromagnetic Co3+ ions in the high spin state in the oxygen-deficient tetrahedral CoO4.25 layers. However, our images and model show that the observed ferromagnetism in SYCO arises from the fully oxygenated CoO6 octahedral layers. The Co3+ ions in these layers are antiferromagnetically aligned with alternating high spin and intermediate spin resulting in ferrimagnetism. The new model reproduces all the experimental ABF-STEM image feature shapes, intensities, distortions and angles. The calculated magnetic properties of the new structure are also in excellent agreement with the experimental data. The work was partially supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division and by DOE Grant No. DE-FG02-09ER46554. Numerical calculations were performed at the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
MD9.9: Magnetic Materials—From Fundamentals to Applications VIII
Session Chairs
Friday PM, April 01, 2016
PCC West, 100 Level, Room 105 B
2:30 PM - *MD9.9.01
Improved Performance in Interface-Engineered Ferroelectric and Multiferroic Tunnel Junctions for Memory Applications
Di Wu 2
1 College of Engineering and Applied Sciences Nanjing University Nanjing China,2 National Lab. of Solid State Microstructures, Nanjing University Nanjing China,
Show AbstractFerroelectric tunnel junctions (FTJs) are composed of two metal electrodes separated by an ultrathin ferroelectric barrier. The reversal of polarization direction in the ferroelectric barrier makes the barrier height flip in two non-volatile states. This produces a high and a low tunneling resistance state that can be used to represent ’0‘ and ’1‘ for memory applications. If ferromagnetic metal electrodes are used to construct multiferroic tunnel junctions (MFTJs), the tunneling resistance can be controlled separately by an electrical pulse or a magnetic field to produce four non-volatile states in a single memory cell. Although these non-destructive read-out ferroelectric memories are attractive, low on/off ratio obtained in FTJs and MFTJs is among major obstacles to their applications. We introduce interface engineering to enhance the asymmetry in the metal/ferroelectric/metal junctions to achieve improved on/off ratios. A heavily doped semiconductor electrode is proposed to replace one of the metal electrodes in a FTJ. The polarization reversal switches the semiconductor surface from accumulation to depletion via the ferroelectric field effect, leading to the simultaneous control on the barrier height and barrier width. The on/off ratio is enhanced by 2 orders since electrons have to tunnel through an extra depletion barrier in the off state. In all-oxide MFTJs, a dielectric layer is inserted into the electrode/ferroelectric interface. The device can also be regarded as a dielectric/ferroelectric composite barrier sandwiched in two ferromagnetic electrodes. The dielectric insertion effectively increases the screening length of one electrode and enhances the on/off ratio. Clear four-state memory functions can thus be observed.
3:00 PM - MD9.9.03
Structural Order and Magnetism of Epitaxial La2MnNiO6 Thin Films
Timothy Droubay 1,Steven Spurgeon 1,Yingge Du 2,David Keavney 3,Arun Devaraj 2,Steve Heald 3,Peter Sushko 1,Torgny Gustafsson 4,Scott Chambers 1
1 Physical and Computational Sciences Directorate Pacific Northwest National Laboratory Richland United States,2 Environmental and Molecular Sciences Laboratory Pacific Northwest National Laboratory Richland United States3 Advanced Photon Source Argonne National Laboratory Argonne United States4 Department of Physics and Astronomy Rutgers Piscataway United States
Show AbstractA fascinating class of oxides with potential for technological applications due to the near room-temperature ferromagnetism are the double perovskites (A2BB'O6). We have investigated La2NiMnO6/SrTiO3(001) grown using molecular beam epitaxy and have found transition temperatures and saturation magnetization values considerably less than expected (290K, 5 μB/f.u.) despite the fact that Mn(IV) and Ni(II) are ferromagnetically coupled in the as-deposited films as determined using x-ray absorption spectroscopy and x-ray magnetic circular dichroism. Aberration-corrected transmission electron microscopy and atom probe tomography (APT) reveals that the B-site sublattice is disorderded in the as-grown film despite excellent volume-averaged stoichiometry. Post-growth air annealing results in significant increases in the following; (i) structural ordering, (ii) saturation magnetization, (iii) ferromagnetic transition temperature, and (iv) resistivity. While the magnetic moment increases, the value remains below the maximum predicted value due to the nucleation during growth and persistence of NiO inclusions with needle-like shapes. First principles modeling suggests the presence of O vacancies facilitates structural disorder even though the double perovskite remains the most stable phase.
3:15 PM - MD9.9.04
Controlling the Magnetic Anisotropy in Ultrathin Metal Films by Epitaxial Strain: Model and Experiment
Artur Braun 1
1 EMPA Duebendorf Switzerland,
Show AbstractFor magnetic data recording and storage, the orientation of the magnetization vector is a very important parameter. I will show how this parameter can be precisely controlled in ultrathin epitaxial film growth via delicate balancing of the various energetic contributions to the overall anisotropy energy. Particularly, the choice of the substrate and film material and film thickness allows to completely control this balance. It turns out that the magnetoelastic anisotropy energy can play an important role in this aspect and can be controlled via the film thickness, plus the epitaxial strain parameter and Poisson's ratio. I will present experimental data from the system Ni on Cu3Au(001) plus an analytical exact mathematical model which allows prediction of the anisotropy reorienation thickness at which the in-plane magnetization changes to out-of-plane magnetization. I will also briefly show how the situation is with thin iron ad cobalt films on the same substrate.
A Braun. Quantitative model for anisotropy and reorientation thickness of the magnetic moment in thin epitaxially strained metal films. Physica B 373, (2006) 346-354.
A Braun, B. Feldmann, M. Wuttig. Strain - induced perpendicular magnetic anisotropy in ultrathin Ni films on Cu3Au (001). Journal of Magnetism and Magnetic Materials 171, 1/2, 16 - 28 (1997).
3:30 PM - MD9.9.05
Tunneling Magnetoresistance Comparison between Top-Pinned and Top-Free Co2Fe6B2/MgO based Perpendicular Magnetic-Junctions with [Co/Pt]n-synthetic Anti-Ferromagnetic Layer
Jong Ung Baek 1,Du Yeong Lee 2,Seung Eun Lee 2,Tae Hun Shim 2,Jea-Gun Park 2
1 Nano Semiconductor Engineering Hanyang University Seoul Korea (the Republic of),2 Electron and Computer Engineering Hanyang University Seoul Korea (the Republic of)1 Nano Semiconductor Engineering Hanyang University Seoul Korea (the Republic of),2 Electron and Computer Engineering Hanyang University Seoul Korea (the Republic of)
Show AbstractPerpendicular-spin-transfer-torque magnetic-random-access-memory (p-STT MRAMs) as a terra-bit memory cell has been developed. It has many advantages such as low power consumption, fast read/write speed and nonvolatile characteristics. However, p-STT MRAMs have still challengeable issues for terra-bit memory; poor tunnel barrier quality, unstable perpendicular-magnetic-anisotropy (PMA) at a high annealing temperature and low tunneling-magnetic–resistance (TMR) ratio. In order to solve these problems, much research has been studied. We also have studied by modifying the structure of perpendicular-magnetic tunnel junction (p-MTJs). The p-MTJ consists of four main layers; free layer (Co2Fe6B2), tunnel barrier (MgO), pinned layer (Co2Fe6B2) and synthetic anti-ferromagnetic (SyAF) layer. Generally, there are two types of structures for p-MTJ, free layer / tunnel barrier / pinned layer / SyAF layer called as ‘top-pinned structure’ and SyAF layer / pinned layer / tunnel barrier / free layer called as ‘top-free structure’. We previously reported the top-pinned p-MTJ with the TMR ratio of 120 %, and other group recently reported the top-free p-MTJ with the TMR ratio of 164 %. The difference between the two structures is only the position of SyAF layer. So far, the study on the comparison between the magnetic properties of the two structures has not been reported, yet. Therefore, in our presentation, we will present in detail the effect of structural difference on CoFeB-MgO p-MTJs by CIPT, HR-TEM and VSM, et cetera. In addition, we will review the advantages and disadvantages of two structures.
Acknowledgment
This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Korea government (No. 2014R1A2A1A01006474 & No. 1004608) and Brain Korea 21 PLUS Program in 2014