June Lau, National Institute of Standards and Technology
Daniel C. Ralph, Cornell University
Yimei Zhu, Brookhaven National Laboratory
Symposium Support Aldrich Materials Science
Monday PM, December 02, 2013
Hynes, Level 2, Room 206
2:30 AM - U2.01
Nanostructured Elastic Magneto-Dielectrics for Radio Frequency Applications
Mert Vural 1 Benjamin Crowgey 2 Leo Kempel 2 Peter Kofinas 3
1University of Maryland College Park USA2Michigan State University East Lansing USA3University of Maryland College Park USAShow Abstract
Functional composite materials with mechanical elasticity that possess substantial dielectric permittivity (ε), magnetic permeability (mu;), low dielectric and magnetic loss are needed for the fabrication and miniaturization of flexible electronic devices including radio-frequency (RF) antennas, sensors and electronic identification chips. We report on the fabrication of flexible magneto-dielectric composites with low magnetic and dielectric loss, achieved by dispersion of high saturation magnetization, low coercivity air-stable iron (Fe) nanoparticles and iron/silver (Fe/Ag) core-shell nanoparticles in polydimethylsiloxane (PDMS) matrices. The magneto-dielectric composites made of air-stable Fe nanoparticles are adapted for RF communication devices with broad operation frequency, since they possess high mu; (4.4) and low ε (16.4), while maintaining low magnetic (0.28) and dielectric (0.053) loss values. Additionally, the Fe nanoparticle composites allow tensile elongation of 15% before breaking, which demonstrates the flexible nature of the material. The magneto-dielectric composites fabricated using Fe/Ag core-shell nanoparticles can combine high mu; (3.68) and ε (26) with low magnetic (0.28) and dielectric (0.1) loss, which makes them suitable for the RF communication device miniaturization. The Fe/Ag core-shell nanoparticle composites can also deform plastically under tensile elongation as high as 70%.
2:45 AM - U2.02
Magnetic Hybrid Materials Based on Spinel-Metal-Oxide Nanoparticles Assembling into Carboxymethyl-Cellulose/Cetiltrimethyl-Ammonium-Bromide Templates: On the Control Its Morphological Features
Nubia Esther Torres-Mtz. 1 2 Marco Antonio Garza-Navarro 1 2 Raul Lucio-Porto 3 Domingo Ixcoatl Garcia-Gutierrez 1 2
1UANL San Nicolamp;#225;s de los Garza Mexico2UANL Apodaca Mexico3Universitamp;#233; de Nantes Nantes Cedex FranceShow Abstract
Optimization of one-pot synthetic procedure for the control of the morphological features of magnetic hybrid materials (HNM) based on spinel-metal-oxide nanoparticles (SMON) and carboxymethyl-cellulose (CMC)/cetiltrimethyl-ammonium-bromide (CTAB) coordination complexes, is reported. The influence of their synthesis parameters (precursor ratio, stirring rate, temperature and synthesis time) on the particle size distribution and the size and morphology of CMC/CTAB templates was investigated. The synthesized HNM were characterized by transmission electron microscopy and their related techniques, such as bright field and high angular annular dark field (HAADF-STEM) imaging, as well as selected area electron diffraction (SAED), using a FEI Titan G2 80-300 microscope. The interactions among SMON, CMC and CTAB were investigated by Fourier transform infrared spectroscopy (FTIR) in a Thermo Scientific Nicolet spectrometer. Magnetic response of the synthesized HNM was evaluated in a Quantum Design MPMS3. The experimental evidence suggests that, the formation of these HNM occurs due to the competition between CTAB molecules and SMON to occupy CMC intermolecular sites nearby to its carboxylate functional groups. Thus, the morphology and size of CMC/CTAB templates can be tuned varying the CTAB:SMON ratio. Moreover, it was found that the magnetic response of the HNM depends on the confinement degree of the SMON into the CMC/CTAB template. Hence, its magnetic characteristics can be adjusted controlling the size of the template, the quantity and distribution of the SMO nanoparticles within the template and its sizes.
3:00 AM - *U2.03
Electron Holography Study of Magnetic Nanostructures in Functional Materials
Daisuke Shindo 1 2 Yasukazu Murakami 1 2 Hyun Park 2 Hidekazu Tanaka 3
1Tohoku University Sendai Japan2RIKEN Wako Japan3Osaka University Ibaraki JapanShow Abstract
Electron holography is a unique electron microscopy technique to visualize electromagnetic fields on the nanometer scale. We developed the electron holography system on the basis of a JEM-3000F electron microscope by installing a Lorentz lens and a magnetizing stage for detailed study of magnetic nanostructures of various functional materials . Recently we have also utilized an HF-3300X electron microscope by which “split-illumination electron holography” can be carried out . In the split-illumination method, additional biprisms are inserted into a condenser lens system. This method is especially effective for electron holography study of specimens with strong stray fields around them. This is because a reference wave can be obtained from a region far from the specimen, being free from the stray fields. Thus, electron holography analysis with high precision can be carried out, and this system is expected to widen the application of electron holography extensively.
One of the applications of electron holography study of functional materials is magnetic nanostructure analysis of Zn-doped Fe3O4 (FZO). It was reported that shape/size-controlled nanowires obtained from solid solutions based on Fe3O4, which was prepared by atomic force microscope lithography and pulsed laser deposition, show good functionalities, e.g., nonlinear I-V character and large magnetoresistance . Dark field microscope images of FZO obtained by an energy-filtered electron microscope revealed the microstructure consisting of fine antiphase domains (APDs) whose size is less than 100nm. On the other hand, electron holography study combined with Lorentz microscopy clarified small magnetic domains whose size corresponds to that of APDs. The complex magnetic domain structure was interpreted by the change in the local spin order being induced by the modulation of Fe-O-Fe bonding in the antiphase boundary region. Eventually the good functionalities are discussed in terms of the small magnetic domains clarified by electron holography.
 D. Shindo and Y. Murakami, J. Phys. D 41, 183002 (2008).
 T. Tanigaki, Y. Inada, S. Aizawa, T. Suzuki, H. S. Park, T. Matsuda, A. Taniyama,
D. Shindo, A. Tonomura, Appl. Phys. Lett., 101, 043101 (2012).
 K. Goto, T. Kanki, T. Kawai, and H. Tanaka, Nano Lett., 10, 2772 (2010).
3:30 AM - U2.04
Energy-Loss Magnetic Circular Dichroism Measurements of Ferromagnetic Ordering in LaSrCoO3
Ahmet Gulec 1 Robert F Klie 1
1University of Illinois at Chicago Chicago USAShow Abstract
Tuning the ferromagnetism of LaCoO3 by doping bulk samples with smaller Sr atoms or straining thin film sample have been previously shown experimentally. In this work, we will use atomic-resolution Z-contrast imaging, annular bright field (ABF) imaging and electron energy-loss spectroscopy (EELS) in the aberration-corrected JEOL JEM-ARM200CF in combination with in-situ cooling experiments to examine the magnetic and spin-state transitions in La(1-x)SrxCoO3 (x=0-0.3) at liquid nitrogen and room temperature. Using energy-loss magnetic circular dichroism method, we confirm the magnetic ordering transition at room temperature with increasing doping concentrations. A magnetic transition is observed in 5% doped sample at liquid temperature. EELS mapping is, also utilized to determine the presence of nanoscale islands of different spin states using both the Co L3/L2 ratio and Oxygen prepeak intensities. Additionally, with increasing doping concentration, a change in crystal structure is measured using ABF imaging, more specifically areas with different distortions of the CoO6 octahedral within the same doping concentrations and change in distortion in different Sr doping concentrations.
The authors acknowledge funding from the National Science Foundation [DMR-0846784] and DMR-0959470 for the acquisition of the UIC JEOL JEM-ARM200CF.
3:45 AM - U2.05
Imaging Magnetization Reversal in Co/Pd-Based Pseudo-Spin-Valves with In-Field Magnetic Force Microscopy
Jun-Yang Chen 1 Tim Ashworth 2 John Michael David Coey 1
1Trinity College Dublin Ireland2NanoScan AG Duebendorf SwitzerlandShow Abstract
The use of magnetoresistive thin films based on layers with perpendicular magnetic anisotropy (PMA) is very interesting for many applications such as high density magnetic recording media, MRAM and magnetic logic. Such films can exhibit good thermal stability in nanoscale dimensions and it is easier to define an easy axis than the case for thin films with in-plane anisotropy. Basic magnetic characterization for these thin films includes measuring hysteresis loops by using magnetometry such as vibrating sample magnetometry (VSM) and superconductor quantum interference device (SQUID), or using extraordinary Hall Effect (EHE). However, these techniques can only measure average magnetization behavior. It is hard to image the magnetic domain reversal directly. Magneto-optical Kerr effect (MOKE) microscopy and magnetic force microscopy (MFM) are the two most used tools to image the magnetic domains of these thin films. The lateral resolution for MOKE is limited to micron-size, too low to image magnetic domains on the nanoscale. MFM has high resolution, and can easily image nanoscale magnetic domains. However, most MFM images are taken in zero magnetic field and cannot image magnetic domain structure during magnetization reversal.
In this work, we present non-contact MFM images taken in magnetic fields on Co/Pd-based pseudo spin valves. The multilayer sample has the following composition: Ta 5/Pd 5/(Co 0.2/Pd 1)8/Co 0.4/Cu 2.9/Co 0.4/(Pd 1/Co 0.4)3/Pd 5 (nm). All layers were grown on thermally oxidized Si wafers at 300 K by DC-magnetron sputtering in a shamrock sputtering tool. The initial magnetization curve and hysteresis loop with applied magnetic field perpendicular to the films was first measured by SQUID at 300 K. It clearly shows two step sharp switching, which indicate good PMA of our multilayers. The multilayers with thicker Co layers (0.4 nm) which lie above the Cu spacer layer have smaller coercivity. The non-contact MFM images were taken on a NanoScan hr-MFM in a constant average height mode. The height was regulated using the electrostatic force due to a DC tip-sample bias. The MFM images were taken in increasing magnetic fields, in order to elucidate the domain structure during the magnetization reversal. Starting at 0 mT, MFM images of the as-grown state reveal domains of ~1000 nm in size. These domains shrink with applied field following the initial curve until the top layer is saturated at a field of 42 mT. Taking magnetization ratios from each image, the series of MFM images matches the hysteresis loop as measured by SQUID with an offset of 10 mT which can be accounted for the additional field applied by the tip itself (the images were taken without removing the magnetic field). Once on the hysteresis loop, the domain structure was imaged at the reversal points and nicely matches the SQUID measurements. The ability to image domain reversals at such high resolution demonstrates a complementary tool for pseudo spin-valve optimization.
4:15 AM - U2.06
Direct Imaging of Magnetic Domains in Perpendicular Magnetic Recording Media Using Cs-Corrected Lorentz Transmission Electron Microscopy
Taeho Roy Kim 1 Ai Leen Koh 1 Kumar Srinivasan 2 Gerardo Bertero 2 Robert Sinclair 1
1Stanford University Stanford USA2Western Digital Corporation San Jose USAShow Abstract
Perpendicular magnetic recording (PMR) media is a technology to record data on hard disk drives with large data storage density. PMR media can store any analog information, for example, text, image or sound by converting it to digital data which is composed of either 0 or 1 as a unit of bit. Each bit is then recorded on PMR media by changing its magnetization direction either out of or into the magnetic film. Thus far, the data storage density of PMR media has been improved by decreasing the size of a bit. However, the bit size has now reached its limit and cannot be further scaled down due to superparamagnetism in which bits are no longer stable and stored data is lost. This is due to the thermal energy which can randomly flip magnetization direction of a nanometer scale bit. In order to overcome this superparamagnetism issue, a thorough understanding of the relationship between magnetic and structural properties is required. However, magnetic imaging techniques such as magnetic force microscopy, resonant x-ray holography, or neutron scattering can only image the magnetic information of the material. Herein, we present a novel technique using transmission electron microscopy (TEM) to simultaneously obtain the magnetic information as well as the structural information of the PMR media in nanometer scale.
In this study, we use Cs-corrected Lorentz TEM to directly image the magnetic domains and magnetic grains concurrently. Fresnel Lorentz TEM (FLTEM) and electron holography are both used to observe the magnetic profile of the PMR media recorded with repeating bits less than 100nm in width. In conventional FLTEM, electrons from the gun are deflected by the Lorentz force of the magnetic field perpendicular to the electron path. In defocus, this deflection forms bright and dark contrasts at the location of magnetic domain walls. Interestingly, when magnetization direction of PMR media is parallel to that of electrons from the gun whole domain appears in the image with either bright or dark contrast in large defocus. With electron holography, PMR media is viewed from the side to reveal the magnetic profile extending outside the top surface of the magnetic layer. This technique also utilizes the deflection of the electron beam due to the magnetic field of the specimen which is imaged as interference fringes. This allows the extraction of a phase image. In addition to magnetic domain images of FLTEM and electron holography, the granular structure of the PMR media is imaged in Lorentz TEM in which the objective lens is off. This allows a magnetic-field-free environment for the magnetized specimen inside the TEM while imaging. Hence, correlation between magnetic domains and granular structures is revealed by comparing FLTEM and electron holography with Lorentz TEM images. This direct imaging method of PMR media allows better understanding of the bits in nanometer scale can be widely applied to study magnetic structural relationships in nanometer scale.
4:30 AM - U2.07
Topological Nature of Magnetic Vortices in Patterned Mesoscopic Disks
Javier F Pulecio 1 Dario Arena 2 Shawn Pollard 1 Yimiei Zhu 1
1Brookhaven National Laboratory Upton USA2Brookhaven National Laboratory Upton USAShow Abstract
Functional magnetic materials have garnered interest due to the potential applications in the emerging field of spintronics. More specifically magnetic vortices have been widely studied due to the quasi-particle/topological nature and are described as having two degrees of freedom, polarity and chirality. While there has been several studies exploring the fascinating behavior of vortices under perturbations using electrical measurements, scanning probe microscopy, and synchrotron based x-ray techniques, transmission electron microscopy provides unparalleled high resolution magnetic and structural information. This allows for a detailed analysis on how the local structure of different materials affects the translation motion of a vortex core under perturbation. Here, we present a direct imaging study of magnetically soft and hard mesoscopic discs of Permalloy and Cobalt under external field perturbations from equilibrium through annihilation and nucleation. The high resolution magnetic imaging of sub 6nm in Lorentz mode affords detail below critical domain wall features of less than 20nm where the soliton-regime breaks down into transverse Bloch walls far from equilibrium. By holding the ferromagnetic system in an external field we can capture the magnetic configuration far from equilibrium states near annihilation and during the nucleation process. Integrating these experiment with micromagnetic simulations we will describe how differently magnetic vortices can behave under perturbations, which is important when attempting to use them in applications such as logic, memories, and antennas.
Work supported by the DOE-BES-MSE,under Contract number DE-AC02-98CH10886 .
4:45 AM - *U2.08
Dipolar Ordering in Self-Assembled Nanoparticle Magnets Revealed by Electron Holography
Marco Beleggia 1 M. Varon 2 T. Kasama 1 V. Puntes 2 R. E. Dunin-Borkowski 3 R. J. Harrison 4 C. Frandsen 1
1Technical University of Denmark Kgs.Lyngby Denmark2Institut Catala' de Nanotecnologia Barcelona Spain3Forschungzentrum Juelich Juelich Germany4University of Cambridge Cambridge United KingdomShow Abstract
Nanoparticle magnets are a novel class of materials, in which a lattice of magnetic ions is replaced by a meta-lattice of magnetic nanoparticles. Inter-particle exchange interactions are absent, while dipolar interactions dominate. As a result, nanoparticle magnets behave differently from conventional magnets and their properties may be controlled and tuned by selecting the spacing and compositions of the constituent nanoparticles. We have studied dipolar interactions in self-assembled Cobalt nanoparticle magnets using off-axis electron holography in the transmission electron microscope. The technique enables the orientation and magnitude of the magnetic moment of each nanoparticle in an array to be determined and correlated with the structural properties of the meta-lattice, including the degree of order of the particles and their size distribution. Our study reveals that dipolar interactions are sufficiently strong to support long-range ferromagnetic order, even when the lattice of nanoparticles is highly disordered. This observation supports the possibility of creating amorphous dipolar magnets, in contrast to the expectation that a disordered dipolar system necessarily implies spin-glass behavior.
Chain-like assemblies of 15 nm ε-Co particles were prepared with an oleic acid coating on a carbon substrate (with no external magnetic field applied). For chains that are wider than 1 particle across, the particles are typically assembled into triangular (close-packed) lattices, although square lattice arrangements are also occasionally seen. We used off-axis electron holography to map the projected magnetic fields of several elongated nanoparticle assemblies non-invasively with a nominal spatial resolution of 6.3 nm. The data set was acquired at remanence after applying an off-plane field of 2 T to the specimen, and reveals the magnetic moment topography of each chain directly.
In order to quantify dipolar ferromagnetic order, we estimated the magnitude and orientation of the magnetic moment of each individual particle. The measurements were correlated with the geometrical arrangements of the particles. For each pair of particles, we measured the spatial separation r between their centers and the angular difference Δtheta; between their moments, from which magnetic and lattice order parameters were determined. Our results show that short-range magnetic order with small domains dominates the initial states, with the local magnetic order (ferromagnetic or antiferromagnetic) often depending on the particle lattice (triangular or square, respectively).
In contrast, at remanence after saturation, overall dipolar ferromagnetic order persists even in case of a non-triangular lattice.
We interpret our results as supporting the existence of amorphous dipolar ferromagnets: i.e., dipolar ferromagnetism in elongated nanoparticle assemblies even in the absence of underlying crystallinity.
5:15 AM - U2.09
Magnetically-Controlled Thermal Conductivity of a Magnetic Tunnel Junction
Brian M. Foley 1 Yishen Cui 2 Jiwei Lu 3 Stuart A. Wolf 3 Patrick E. Hopkins 1
1University of Virginia Charlottesville USA2University of Virginia Charlottesville USA3University of Virginia Charlottesville USAShow Abstract
Thermal transport driven by the quantized spins of electrons opens up a new realm of engineering possibilites centered around magnetic materials and processes. In addition, the ability to control these thermal processes via magnetic fields opens the door to controlling thermal properties on the nanoscale. To address this, we report on the magnetically-controlled thermal conductivity of a magnetic tunnel junction (MTJ). We synthesize the magnetic tunnel junction through deposition of a layered 7 nm Ru/3 nm CFA/2.3 nm MgO/5 nm CFA/15 nm InMn/30 nm Ru on a MgO substrate. This structure has shown nearly a factor of 4 change in electrical resistivity in the presence of a magnetic field. We measure the thermal conductivity of the MTJ using time domain thermoreflectance (TDTR); an optical pump-probe technique that has been well established to provide thermal conductivity measurements of thin films. We show that the thermal conductivity of the MTJ stack-structure can be controlled via the field strength and orientation using a rare-earth permanent magnet. The thermal conductivity exhibits a four-fold increase between its off and on states, which is attributed to the change in magnetoresistance of the MTJ due to spin-current channels.
5:30 AM - *U2.10
Exploring the Magnetization Reversal Behavior of Magnetic Nanostructures with Lorentz TEM and MFM
Amanda Petford-Long 1 3 Charudatta Phatak 1 Marc De Graef 2 Seungbum Hong 1 Mengchun Pan 3
1Argonne National Laboratory Lemont USA2Carnegie Mellon University Pittsburgh USA3Northwestern University Evanston USAShow Abstract
We have used a combination of aberration-corrected Lorentz TEM and magnetic force microscopy (MFM) to carry out in-situ magnetizing experiments and explore the magnetization reversal behavior of a range of magnetic nanostructures. In all cases we are interested in the way in which the magnetic nanostructures interact, either through layering different materials within a single nanostructure or via interactions between separate nanostructures in an array. Examples will be presented for artificial spin ice arrays, which are nanoscale geometrically-engineered systems that display magnetic spin frustration. Square spin-ice lattices with island size 290 × 130 nm were fabricated using electron-beam lithography from 20 nm thick Py films deposited by sputtering on electron-transparent silicon nitride membranes. For closely-spaced lattices the process proceeds by a cascade of islands that reverse one at a time along the lattice diagonal as an applied magnetic field is reduced. As reversal occurs, so the magnetic structure at the nodes at which four islands meet changes. Of particular note are the node structures at either end of the line of reversed islands: these carry a local net magnetization and can be regarded as magnetic monopole defects. Examples will also be presented for patterned NiFe disks (single layer, trilayer and exchange-biased) in which interlayer interactions control both the magnetic structure that forms and also the way in which magnetization reversal occurs.
Work carried out at Argonne National Laboratory, a US DOE Science Lab operated under contract DE-AC02-06CH11357 by UChicago Argonne, LLC. We acknowledge use of the Center for Nanoscale Materials at ANL, and MDG acknowledges DOE-BES for partial support (DE-FG02-01ER45893).
U3: Poster Session
Monday PM, December 02, 2013
Hynes, Level 1, Hall B
9:00 AM - U3.01
Sub-100 nm Magnetic Wires with Low Edge Roughness Made with a Bilayer Resist Electron Beam Lithography Process
Saima Afroz Siddiqui 1 Jean Anne Currivan 2 1 Sung-Min Ahn 3 Geoffrey Beach 3 Marc Baldo 1 Caroline Ross 3
1Massachusetts Institute of Technology Cambridge USA2Harvard University Cambridge USA3Massachusetts Institute of Technology Cambridge USAShow Abstract
There is great excitement in developing magnetic nanostructures for energy-efficient non-volatile memory and logic devices which rely on the movement of domain walls in nanostructured thin films. Patterning of thin films into 100 nm or less structures is essential for these applications to have switching energies and data densities competitive to that of field effect transistors. Additionally, low edge roughness is required for reproducibility of the magnetic switching characteristics, since edge roughness in the nanostructures can act as domain wall traps.
We report on patterning sub-100 nm ferromagnetic wires with very low edge roughness using a removable bilayer poly(methyl methacrylate) (PMMA) and hydrogen silsesquioxane (HSQ) resist mask. All patterning was done on silicon substrates with a native oxide. 20 nm-40 nm of polycrystalline Co60Fe20B20 was deposited using UHV DC magnetron sputter deposition. 2% PMMA in Anisole (a positive electron beam resist) and 2% HSQ in methyl isobutyl ketone (a negative electron beam resist) were spun on the CoFeB. The HSQ was exposed using a Raith 150 electron beam lithography tool at 10 kV electron energy and 400 mu;C/cm2 dose. After development, an O2 reactive ion etch (RIE) was used to remove the PMMA except under the HSQ, resulting in a bilayer removable mask. The RIE power and time are specified to the wire width. The CoFeB was ion milled using Ar ion etching at base pressure 2e-7 Torr with 10 mA beam current. After etching the pattern, the PMMA/HSQ mask was removed by NMP along with sonication. Patterned 30 nm, 50 nm, 75 nm and 100 nm wide lines were made using this method. SEM imaging gives a low average edge roughness, less than 4% of the wire width. The magnetic properties were measured using magnetic force microscopy to identify domain structures. This demonstrates the practicality of making sub-100 nm width wires using this method, that liftoff of the resist mask after etching is possible, and that these wire widths have low edge roughness to reduce pinning of domain walls in the magnetic structures.
9:00 AM - U3.02
Strain-Induced Topologically Insulating Phase of Sb2Te: A First-Principles Calculation
Eriko Takasaki 1 Hiroyoshi Momida 2 Tamio Oguchi 1 2
1Osaka University Osaka Japan2Osaka University Osaka JapanShow Abstract
Topological insulators have attracted great interest because of their interesting properties such as possible spin current on edge states, and been considered to be a promising candidate in future applications for spintronic devices. As three-dimensional topological insulators, Bi1-xSbx, Bi2Se3, and Sb2Te3 compounds have been well known. In this study, we theoretically investigate the electronic band structure of Sb2Te, which is known as a semimetal, aiming to search topologically insulating phases controlled by external strain. Our calculations are based on the density functional theory within the local density approximation using the all-electron FLAPW method including the spin-orbit interactions. At first we study the structural stability of layer stacking sequence in Sb2Te. Within the experimentally reported space group P-31m, that includes inversion symmetry, there are four crystallographically possible layer stackings. Calculated results show that the lowest-energy structure of Sb2Te has two Sb2 bilayers between Sb2Te3 quintuple layers, and calculated band structure is semimetallic with the band overlap of about 0.15eV. We calculate the Z2 topological invariant for Sb2Te by checking the parity at time-reversal invariant momenta. Calculated Z2 invariant (1;000) indicates that Sb2Te can be a strong topological insulator if the semimetallic band overlap is lifted. To search a topologically insulating phase for Sb2Te, we study strain effects on the band structure by controlling lattice constants. Our calculation shows that an in-plane strain expanding in the layer direction can induce a band gap, and as result a strain-induced topologically insulating phase for Sb2Te is actually realized. We generally discuss effects of strain and layer structure on the electronic structure of Sb2Te, focusing on role of the spin-orbit interaction.
9:00 AM - U3.03
The Tanglesome Ac Susceptibility and Crystlalline Configurations of Highly-Oriented Colossal Magnetocaloric Compunds Er5Si3.5Ge0.5 Scrutinized by X-Ray Diffraction
Lanlan Sgwendolyn Winifret Lin 1 2 3 Constantine Stassis 2 3 David Vaknin 2 3 Sasha Pecharsky 4 3 Vitalij K. Pecharsky 4 3 Karl A. Gschneidner 4 3 Vasile Ovidiu Garlea 5 2 3 Jerel L. Zarestky 5 2 3 Paul C. Canfield 2 3
1Institute of Physics, Chinese Academy of Science Winston-Salem USA2Iowa State University Ames USA3Ames Laboratory, US-DOE Ames USA4Iowa State University Ames USA5Oak Ridge National Laboratory Oak Ridge USAShow Abstract
The meticulous ac susceptibility measurement and high-resolution X-ray diffraction indagation commingled with isothermal magnetic entropy measurements from 1 K to 300 K are employed on intermetallic pseudo-binary enormous magnetocaloric lanthanide compounds Er5Si3.5Ge0.5 to adumbrate aboratively its hypostatic magnetic properties, crystalline configurations, phase transform silhouette, and lapidarian optimal mechanical idiosyncrasy, which applied to enamoredly crank out the innocuously environmentalistic, extirpating compressor, high efficient, and oecumenically retrenching-energy magnetic refrigerator applying at aeronautik voyage, sputnik, and industry automatics at our experiments. It is praiseworthy that the real part of ac susceptibility of specimen chi;ac' exhibits a precipitous pinnacle at 28.0 K with the hyperplasia of the temperature when we inflicted an ac magnetic field of 5 Oe and frequency of 1000 Hz onto the magnetic specimen. The depicted inverse chi;ac&’ function curve dependent on the temperature flaunts an approximatively linear modality notwithstanding that there appears a poignant abysm inflexion situating at 27.86 K and the 1/chi;ac' function curve commences to proliferate with the decrease of the temperature below this abyss point. The ace-high fitted coefficients of the linearity equation A and B corresponding to this function curve are 379.95 and 19.1765, respectively. Furthermore, the Endsville fitted magnetic moment of Er atom from our experiment is 9.02 mu;B and it is immaculatedly congruent with the theoretical value of 9.58 mu;B. By the same token, the imaginary part of ac susceptibility chi;ac&’&’ of the magnetic specimen manifests a spiculate aiguille locating at approximate 23 K, despite that its amplitude is just one-tenth of the real part of ac susceptibilitychi;ac&’. Succeedingly we plume-lined the crystalline configuration of magnetic specimen exploiting the advanced X-ray diffraction technique utilizing a Mo target, with the maximum operating voltage and current of 60 kV and 200 mA, respectively, scanning from 8 to 50 degrees at the room temperature. It is worthy to mention that the most vehement aiguille appears at 15.7 degree with the intensity of 1404. The second and third intensive pinnacles situate at 14.7 and 17.4 degrees respectively, and their intensities are 1091 and 932, respectively. Our X-ray diffraction pattern trenchantly reveals that this highly-oriented colossal magnetocaloric lanthanide crystal possesses the monoclinic structure with the Shubnikov space group P1121/a at room temperature. The exquisitely numerically fitted lattice parameters a b, c, and γ from our elaborate X-ray diffraction pattern are achieved as 7.3751#8491;, 14.415 #8491;, 7.5760 #8491;, and 92.947 degree, respectively. Legitimately, It is explicit that at 28 K the magnetic lanthanide compound undergoes the first-order magnetoelastic transition from a high-T monoclinic-paramagnetic-P1121/a to a low-T orthorhombic-ferromagnetic-Pnma configuration.
9:00 AM - U3.04
The Tenebrous Ac and Dc Susceptibility Proclivities of Highly-Oriented Tremendous Magnetocaloric Compounds Dy5Si3.1Ge0.9
Lanlan Sgwendolyn Winifret Lin 1 2 3 Constantine Stassis 2 3 David Vaknin 2 3 Sasha Pecharsky 4 3 Vitalij K. Pecharsky 4 3 Karl A. Gschneidner 4 3 Thomas A. Lograsso 3 4 Deborah Schlagel 3 4 Vasile Ovidiu Garlea 5 2 3 Jerel L. Zarestky 5 2 3 Paul C. Canfield 2 3 Zemin Lin 6
1Institute of Physics, CAS Winston-Salem USA2Iowa State University Ames USA3Ames Laboratory, US-DOE Ames USA4Iowa State University Ames USA5Oak Ridge National Laboratory, US-DOE Oak Ridge USA6No. 5 Middle School Yinchuan ChinaShow Abstract
The meticulous dc and ac susceptibility measurements from 1 K to 300 K are exploited on intermetallic pseudo-binary enormous magnetocaloric lanthanide compounds Dy5Si3.1Ge0.9 to adumbrate aboratively its hypostatic magnetic properties, crystalline configurations, phase transform silhouette, and optimal mechanical proclivity, which applied to enamoredly crank out the innocuously environmentalistic, extirpating compressor, high efficient, and oecumenically retrenching-energy magnetic refrigerator at our experiments. It is explicit that dc susceptibility chi;dc of specimen with diversified applied magnetic field amplitude H of 0.1, 1, and 10 kOe decrease vehemently with the prolification of H. Praiseworthy is that three curves exhibit one or two dramatically poignant aiguilles situating at the elysium of 1 to 120 K. The maximum piton values situate at 4 and 74, 72, and 22 K, respectively, corresponding to various dc magnetic amplitudes of 0.1, 1, and 10 kOe, respectively. Subsequently we plotted the delineation of inverse dc susceptibility 1/chi;dc dependent on the temperature. Noteworthy is that the curve flaunts an approximately linear relation with a variegate slope at T=73 and 100 K when H=0.1 KOe. The ace-high fitted coefficents of linear equation y = A+Bx are A1 = -120.32, B1 = 2.126, A2 = 1222.34, B2 = 15.137 corresponding to 73 Kle;Tle;100 K and Tge;100 K, respectively. The optimized fitted magnetic moment of Dy atom is 10.11 uB, rippingly congruous with the theoretical value of 10.65 uB. Furthermore, it is trenchant that the inverse dc susceptibility 1/chi;dc at H = 1 KOe displays three segments of linear modality with miscellaneous slopes at T = 5, 79, and 102 K, respectively. The topgallant fitted coefficents of linear equation y = A+Bx are A1= -649.03, B1= 9.233, A2 = -1036.49, B2 = 14.106 corresponding to 79 Kle;Tle;102 K and Tge;102 K, respectively. The ace-high fitted magnetic moment of Dy atom is 10.47 uB, consummately congruous with the theoretical value of 10.65 uB. At H = 1kOe, the 1/chi;dc flaunts a more saponaceous linearity behavior with disparate slopes at T = 82 K. The Endsville fitted coefficents of linear equation y = A+Bx are A1= -993.956, B1=13.905 when Tge;100 K. The best fitted magnetic moment of Dy atom is 10.54 uB, consummately congruous with the theoretical value of 10.65 uB. The exquisite measurement of real part of ac susceptibility chi;ac &’ versus to the temperature exhibits two precipitous pinnacles situating at 81 K and 102.3 K, respectively. Furthermore, the imaginary part of ac susceptibility chi;ac&’&’ versus temperature flaunts one abyss at T = 81 K and an aiguille at T = 102 K, respectively, immaculately consilient with the results of chi;ac &’ instance. Synoptically, the Dy5Si3.1Ge0.9 compound undergoes the first-order magnetoelastic transition from a high-T monoclinic-paramagnetic-P1121/a to a low-T orthorhombic-ferromagnetic-Pnma configurations at T= 102 K and a second magnetic transition occurs at approximately 82 K and 5 K, respectively.
9:00 AM - U3.05
Particulate Cobalt Ferrite - Barium Titanate Nanocomposite Films and Their Properties
Xiaohua Liu 1 2 3 Stephen O'Brien 1 2 3
1The Graduate Center, The City University of New York New York USA2City College of New York, The City University of New York New York USA3The City University of New York New York USAShow Abstract
Magnetic nanoparticles such as transition metal ferrites have been widely used in sensors and magnetic resonance imaging. The large magnetostriction coefficient and high Curie temperature of CoFe2O4 make it excellent candidate for creating ferromagnetic order at the nanoscale, and provide a pathway to fabricate nanocomposites. Barium titanate (BaTiO3), on the other hand, is well known for its excellent dielectric behavior and ferroelectric properties. In this work, a series of particulate, 0-3 type, nanocomposite films composed of ferromagnetic cobalt ferrite and ferroelectric barium titanate nanocrystals are prepared by various methods. The dielectric, ferroelectric and magnetic properties of such films are systematically investigated. Aiming at establishing and enhancing magnetoelectric coupling effect between the two phases, surface modification of the nanoparticles and various film fabrication methods will be performed. The structure and properties of the nanocomposite films will be characterized using XRD, TEM, STEM, SEM, MPMS and LCR meter.
9:00 AM - U3.06
Synthesis and Magnetic Properties of Exchange-Coupled SrFe12O19 - x Wt.%- La0.7Sr0.3MnO3 Nanocomposites via Autocombusiton Method
Jiba Nath Dahal 1 Sanjay Mishra 1 Mohammad Shahabuddin 1
1The University of Memphis Memphis USAShow Abstract
Ferrite materials are of enormous technological importance, as these materials are used as recording media for hard disks, magnetic storage, microwave, sensing devices etc. In order to meet the current technological demands, further improvement in the magnetic properties of ferrites is essential. Improvement in magnetic and dielectric properties has been reported when ferrites are used in two component composite system. Pure phase exchange coupled nanocomposites of hard-soft magnetic oxides, (1-x)SrFe12O19 - x. Wt.% La0.7Sr0.3MnO3 were prepared via autocombution method. The structural and morphological characterizations were performed via x-ray diffraction (XRD) and transmission electron microscopy (TEM). Magnetic properties of the nanocomposites were assessed as a function of soft-phase content in the nanocomposite. XRD analysis shows presence of pure phase components in the nanocomposites. TEM images show presence of needle shape Sr-Ferrite particles in close contact with La0.7Sr0.3MnO3 particles. Room temperature smooth hysteresis loops of the nancomposites clearly demonstrates efficacy of auto-combustion method in producing well exchange-coupled nanocomposites. Furthermore, a linear increase in Mr/Ms with the increase in the soft-phase content up to x=40% was observed. This indicates the presence of enhanced exchange coupling between hard and soft phases of the nanocomposite. The highest Mr/Ms ratio of 0.592 was obtained for nanocomposite containing 40 Wt.% of the soft-phase. Concomitantly enhancement in coercieve field (Hc) was also observed with the increase in the soft-phase content of the nanocomposite reaching to a value of 6.59 kOe which is 80% higher than that of SrFe12O19 (Hc~3.633 kOe) and 1156% higher than that of La0.7Sr0.3MnO3 (Hc ~523 Oe). Thus observed magnetic parameters, Mr/Ms and Hc, of the nanocomposites are far superior to the corresponding values of the individual components of the nanocomposite. The adopted synthesis method is low cost, rapid, and results in pure nanocomposite powder. This simple method seems a promising way to tailor and enhance the magnetic properties oxide based hard-soft magnetic nanocomposites.
9:00 AM - U3.07
Between Quantum and Classical: Evolution of Electron Magnetic Resonance with Growth of a Spin System Size
Brittany Bates 1 James Hilton 2 Natalia Noginova 1 Carl Bonner 1
1Norfolk State University Norfolk USA2Cornell University Ithaca USAShow Abstract
Systems with a single or several coupled electron spins are commonly described with the quantum approach while ferromagnetic domains with millions of coupled spins are classical systems. Large spin clusters and superparamagnetic nanoparticles contain hundreds of coupled electron spins, and are on the boundary between classical and quantum behavior. Electron magnetic resonance (EMR) observed in ultra-fine iron oxide nanoparticles (~ 5 nm size) reveals several features which are typical for paramagnetic spins and absent in macroscopic systems, including multiple quantum transitions observed at Hr/ m, where m = 2, 3, 4 and Hr is the field of the main resonance. In order to better understand the transition from quantum to classical behavior and magnetization dynamics at the nanoscale, we study the evolution of the EMR signal with increase of the particle size in suspensions of magnetite nanoparticles. We also test the effects of nanoparticle mutual arrangements and use of a different kind of magnetic material, such as mumetal and permalloy. The experimental data are compared with numerical simulations based on the quantum and classical approach.
9:00 AM - U3.08
Integration of Self-Assembled CoFe2O4-BiFeO3 Multiferroic Nanocomposite on Sr(Ti,Fe)O3/CeO2/YSZ-Buffered Si Substrate
Dong Hun Kim 1 Nicolas M Aimon 1 Caroline A Ross 1
1MIT Cambridge USAShow Abstract
In recent years, self-assembled nanocomposite thin films such as BaTiO3-CoFe2O4, BiFeO3-CoFe2O4 (BFO-CFO) and BiFeO3-NiFe2O4 in which a ferrimagnetic spinel phase grows epitaxially as pillars within an immiscible ferroelectric perovskite phase have attracted great interest as new multiferroic materials. However, to date these composites have been exclusively grown on single crystal oxide substrates which limits their utility in microelectronic devices. In this study we describe the integration of a spinel-perovskite epitaxial nanocomposite thin film on a Si substrate by using a Sr(Ti,Fe)O3 (STF)/CeO2 (Ceria)/YSZ (yttrium-stabilized zirconia) thin film as a buffer layer, and the tuning of its magnetic properties. We have found previously that thin films of STF with x = 0.1 ~ 0.5 exhibit room-temperature magnetism and a strong out-of-plane anisotropy when grown epitaxially on ceria/YSZ-buffered (001) Si substrates.[1-2]
From the x-ray diffraction, SEM analysis and by removing the BFO with HCl etching, it was observed that the CFO nano-pillars formed as epitaxial pillars within a BFO matrix on STF thin film. The magnetic hysteresis loop of the nanocomposite on STF thin film shows a sum of the STF thin film hysteresis and that of the CFO pillars. The STF was magnetic even though the BFO-CFO was fabricated in 5 mTorr of oxygen, despite prior evidence that STF films grown in oxygen had very low saturation magnetization. The nanocomposite on STF shows a strong out-of-plane anisotropy as a result of both the shape anisotropy of the pillars and the dominant magnetoelastic anisotropy of the CFO and STF films which are under out-of-plane compression as a result of epitaxy with the BFO matrix and CeO2 buffer layer respectively. Composition modulation of the CFO by layering it with other spinels will also be described. Results from modulated composites grown on STF/ceria/YSZ/Si enable both control of magnetic properties and integration on Si substrate of perovskite and spinel nanocomposites.
1. D. H. Kim, L. Bi, P. Jiang, G. F. Dionne, and C. A. Ross, Phys. Rev. B, 84, 014416 (2011).
2. D. H. Kim, L. Bi, N. M. Aimon, P. Jiang, G. F. Dionne, and C. A. Ross, ACS Combinatorial Science, 14, 179 (2012).
9:00 AM - U3.09
Chiral Selectivity of Noncollinear Spin-spiral Magnetic Wave Excitations in Iron Single-Wall Nanotubes
Takahiro Shimada 1 Takayuki Kitamura 1
1Kyoto University Kyoto JapanShow Abstract
The remarkable interplay of chirality and magnetism in
helical single-wall nanotubes of iron (FeSWNTs) is investigated using fully
unconstrained spin-density-functional calculations. Spin-spiral waves exist
and noncollinear helimagnetism appears only for the specific chirality of
(6,3) and (5,3) FeSWNTs, whereas collinear ferromagnetism persists in
other chiral FeSWNTs as unfolded monolayers, that is, chirality selectively
involves the unusual helimagnetic phase transition (chiral selectivity). The
emergence of quantum helimagnetism plays a variety of significant roles in
(i) the stabilization of the chiral FeSWNTs as a long-lived “magic”
structure in both freestanding and tip-suspended conditions, (ii)
interference with quantum ballistic conductance by interband repulsion,
and (iii) the involvement of chiral conductivity in which electric currents
pass helically through the FeSWNTs. These chiral characteristics are a
novel addition to the intriguing rich diversity of chirality-driven physics and phenomena.
9:00 AM - U3.10
Origin of Ferromagnetism and Magnetoelectric Coupling in Deficient Ferroelectric Nanostructures
Takahiro Shimada 1 Jie Wang 2 1 Takayuki Kitamura 1
1Kyoto University Kyoto Japan2Zhejiang University Hangzhou ChinaShow Abstract
The possible origin of dilute ferromagnetism and associated magnetoelectric coupling in deficient PbTiO3 are studied using first-principles calculations based on the screened hybrid Hartree-Fock density functional, which has successfully reproduced the band gap of PbTiO3 and the localized/delocalized defect electronic states that predominates vacancy-driven properties. We found oxygen vacancies are likely to form at surfaces and grain boundaries. Such oxygen vacancies clustered at surfaces or grain boundaries are revealed to induce ferromagnetism, whereas oxygen vacancies inside a PbTiO3 single crystal are just non-magnetic. We also demonstrate that magnetism of the oxygen vacancies at surfaces and grain boundaries shows remarkable polarization-dependence: The emerged ferromagnetism undergoes the intriguing rich transitions of the ferromagnetic-antiferromagnetic-nonmagnetic phases depending on the spontaneous polarization directions switched by external electric fields. This signifies that the magnetoelectric effect can exist in deficient PbTiO3, which is, in addition, expected to be a nonlinear coupling due to the rapid phase transition in conjunction with the local polarization switching. Our findings can provide fundamental insights for designing magnetoelectric multiferroic materials in conventional nonmagnetic ferroelectrics.
9:00 AM - U3.11
Studies of Magneto-Dielectric Coupling Properties of(1-x) Pb(Fe0.5Nb0.5)O3 - x Ni0.65Zn0.35Fe2O4 (x=0.2) Composite
Dhiren Kumar Pradhan 1 Satyaprakash Sahoo 1 Sujit K Barik 1 Venkata S Puli 2 Ram S Katiyar 1
1University of Puerto Rico San Juan USA2Tulane University New Orleans USAShow Abstract
Magnetoelectric Multiferroic materials showing coupled magnetic and electrical order parameters through strain have drawn increasing interests due to their unique physical properties and widespread technological applications in magnetic/ferroelectric data storage media, spin based and magnetocapacitive device, magnetic sensors, and nonvolatile memories, etc and also rich in fundamental physics. Here, we report Raman spectroscopic studies, and magneto-dielectric properties of a multiferroic composite ceramics, (1-x) Pb(Fe0.5Nb0.5)O3 - x Ni0.65Zn0.35Fe2O4 ( x =0.2). Pb(Fe0.5Nb0.5)O3 (PFN) is known to be a single phase multiferroic material having good ferroelectric properties, weak magnetic properties and shows very small magnetoelectric coupling around 151 K. Ni0.65Zn0.35Fe2O4 (NZFO) compound shows good magnetic properties around room temperature with good magnetostrictive properties. The X-ray diffraction patterns disclosed the presence of both PFN and NZFO binary phases in theses composites without any secondary phases. Detailed analysis of Raman spectroscopic studies revealed that apart from the presence of the zone centre Raman active modes of the parent compounds, some new peaks are observed in the low (around 30 to 50 cm-1) frequency region. The electric field controlled peak position of the low frequency Raman modes suggests these modes are of magnon in origin. The capacitance and tangent loss in this sample at room temperature decreases considerably with increasing magnetic field whereas the impedance and phase increase systematically with increasing magnetic field. The electric field control of magnetic properties at room temperature in the sample shows a considerable and systematic change of coercive field (Hc), remanent magnetization (Mr) and saturation magnetization (Ms).Our above mentioned results suggest that this composite shows very good magneto-dielectric coupling at room temperature which can be useful for potential multifunctional device applications.
9:00 AM - U3.12
Ferroelectric and Ferromagnetic Properties of Bi3.4La0.6Ti3O12/CoFe2O4 Multilayer Composite Structure
Maharaj Tomar 1 Amanda Charris-Hernandez 1
1University of Puerto Rico Mayaguez USAShow Abstract
Three and four alternate layers of Bi3.4La0.6Ti3O12/CoFe2O4 were synthesized by chemical solution method and deposited by spin coating on Pt (Pt/TiO2/SiO2/Si) substrate. The films were characterized by X-ray diffraction, SEM, dielectric response, leakage current, and ferroelectric and magnetic responses. X-ray diffraction revealed composite-like multilayer structure. SEM showed polycrystalline films grain sizes ~ 100 nm. Both composite structures show exponential decrease in dielectric constant with increasing frequency from 103 Hz to 106 Hz as typical in dielectrics. Low leakage currents (10-7 to 10-6 A) is observed with applied voltage from 5 to 8 V followed by the breakdown and space charge limited current. The composite films were characterized for ferroelectric and ferromagnetic responses. The ferroelectric polarization Pr = 30 µC/cm2 and magnetization Mr = 150 emu/cm3 were observed for the composite film structure. One can compare Pr = 85 µC/cm2 for individual Bi3.4La0.6Ti3O12 and Mr = 230 emu/cm3 for CoFe2O4 film on Pt substrate. Since there is no clustering in film deposition, the observed co-existence of ferromagnetic and ferroelectric coupling is the intrinsic property of the composite
9:00 AM - U3.13
Synthesis and Magnetic Characterization by Ferromagnetic Resonance in Ni/NiO Sub-Nanostructured Particles
Jorge Fernando Angeles Islas 1 Rafael Zamorano Ulloa 2 Jose Gerardo Cabanas Moreno 3 Daniel Ramirez Rosales 2
1Instituto Politamp;#233;cnico Nacional Mamp;#233;xico Mexico2Instituto Politamp;#233;cnico Nacional Mamp;#233;xico Mexico3Instituto Politamp;#233;cnico Nacional Mamp;#233;xico MexicoShow Abstract
The Ni/NiO nanoparticles studied in this work exhibit sub-nanostructured features, with crystallites with average diameters below 6 nm for Ni and 2 nm for NiO. These nanoparticles were obtained by mechanical alloying followed by Al leaching and passivation. The particles thus obtained have a core-shell structure with a Ni core and a NiO shell. This production process induces porosity in the particles. The powder samples were characterized by XRD, SEM-EDS, TEM, and ferromagnetic resonance (FMR) at 300 K. The FMR experiments provide information about the core and shell effects of magnetic nanoparticles. The Ni-NiO FMR spectrum showed that microwave absorption is associated with two atomic sites that differ structurally and magnetically: one with g core = 3.2855 at H = 2055G and one with g shell = 2.1605 at H = 3125 G. Using the values of g obtained by FMR spectroscopy, it was possible to determine the ratios between the orbital magnetic and spin moments, which were (µL/µS)core = 0.64 and (µL/µS)shell = 0.08. Additionally, the relationship between the orbital magnetic moments, µL-shell = 0.027 µL-core and µs-shell = 0.324 µs-core, were determined, as were the relaxation times (T2) for each region.
9:00 AM - U3.14
Studies of Multiferroic and Magnetoelectric Properties of (Bi0.95Nd0.05)(Fe0.97Mn0.03)O3
Shalini Kumari 1 Nora Ortega 1 Ashok Kumar 2 Ram S Katiyar 1
1University of Puerto Rico San Juan USA2CSIR Delhi IndiaShow Abstract
Single phase Multiferroic materials have attracted much attention due to their two or more ferroics order parameters (ferroelectric, ferromagnetic, ferroelastic and ferrotoroidic) and their coupling, which are the potential candidates for actuators, switches, magnetic field sensors, and new types of microelectronic memory devices based on magnetic order switching by electric field and vice versa. BiFeO3 (BFO) is a known room temperature multiferroic material which exhibits ferroelectricity and antiferromagnetic ordering at room temperature with high leakage current. To reduce the leakage current and improve electrical, magnetic, and multiferroic properties, we introduced small fraction of Nd and Mn at A and B-site of BFO. X-ray diffraction (XRD) patterns revealed the formation of perovskite (Bi0.95Nd0.05)(Fe0.95Mn0.03)O3 (BNFM) single phase with small (2%) trace of impurity, however Raman spectra suggest pure phase for local nanostructure. Temperature and frequency dependent dielectric studies confirmed the ferroelectric-paraelectric phase transition (Tc) at 630 K with dielectric constant 290 at 1 kHz and relaxor type behavior, this result was confirmed by temperature dependent Raman studies. The complex impedance spectroscopic technique was used to investigate the role of grain and grain boundary effects in the electrical response of the system. Reduced leakage current was obtained, it also showed negative temperature coefficient of resistance (NTCR) behavior with temperature. The above material shows non-saturating magnetic hysteresis till 7 T, with remnant magnetization ~ 0.03 emu/g and coercive field of 0.4 T. Zero field cool (ZFC) and field cool (FC) data at various bias magnetic fields suggest the spins are frustrated. Two competing forces , namely anti/ferromagnetism and superparamagnetism displayed two prominent magnetic phase transitions at low temperatures, the detailed observation will be discussed. High magnetoelectric ME coupling (120 mu;V/cm.Oe) was observed at zero bias magnetic field which reduces with increase in the applied dc magnetic field.
9:00 AM - U3.15
Atomic Scale Design of Y-Type Hexaferrite Thin Films from BaFe4O7, CoFe2O4 and Fe2O3 Targets
Marjan Mohebbi 1 Khabat Ebnabbasi 1 Hessamoddin Izadkhah 1 Carmine Vittoria 1
1Northeastern University Boston USAShow Abstract
To downsize and integrate magnetic and microwave components it is needed to make thin films of complicated stoichiometries magnetic materials. Here, we report the epitaxial growth of high quality Ba2Co2Fe12O22 thin films at the atomic scale by using alternating target laser ablation method, in which three targets of BaFe4O7, CoFe2O4 and Fe2O3 were used for sequential deposition to localize the ions in the proper crystal structure. Hexagonal Ba2Co2Fe12O22 thin film was grown on sapphire (0001). A KrF excimer laser with a wavelength of 248nm, energy of 400mJ/pulse and repetition rate of 10Hz was used and the distance between the target and the substrate was 5cm. The substrate was heated to 910°C in an oxygen pressure of 300mTorr. The four step deposition routine consisted of 12 laser pulse shots on the Fe2O3, 16 shots on the CoFe2O4, 12 shots on the Fe2O3 and finally 8 shots on BaFe4O7 targets. The growth under the above conditions was approximately 43.8 #8491;/cycle. A post annealing process at 1050C for 30min in air reinforced single phase of the film and improved the magnetic properties. The composition and structure of these films were determined by X-ray diffractometer (XRD) and scanning electron microscope (SEM) which show that the c- axis alignment falls within 0.625° of the normal to the film plane and the films are reasonably well ordered. The magnetic properties were determined by vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR). The saturation magnetization was measured to be 2520G, the magnetic uniaxial anisotropy field was estimated to be 13.2kOe and g=1.52. The magnetic and structural properties are in agreement with bulk parameters.
9:00 AM - U3.16
Multilayer Deposition of Conductive Oxide and Magnetoelectric Ferrite for Microwave Applications
Marjan Mohebbi 1 Khabat Ebnabbasi 1 Carmine Vittoria 1
1Northeastern University Boston USAShow Abstract
Magnetoelectric effect at room temperature can open up new opportunities in miniaturizing microwave devices. Here, we report an M-type magnetoelectric (ME) thin film which is grown on the oxide conductive layer of ITO by pulsed laser deposition. A single target of magnetoelectric material SrCo2Ti2Fe8O19 is prepared by conventional solid state method. The ITO/ SrCo2Ti2Fe8O19 multilayer structure is deposited on a sapphire (0001) substrate using a KrF eximer laser with a wavelength of 248 nm, energy of 400 mJ/pulse and 10 Hz repetition rate. During ITO deposition the substrate was heated up to 400°C in an oxygen atmosphere with pressure of 10mTorr for 10 min, which resulted in 400 nm thickness of ITO layer and immediately after that the substrate temperature raised to 600°C in 200 mTorr of oxygen pressure and the laser was set to impinge on SrCo2Ti2Fe8O19 target for 50 min which resulted in an amorphous film structure. After deposition, the films were annealed in oxygen atmosphere in a tube furnace at 1050°C for 40 min. The ferrite film thickness was measured to be 0.7 µm. These thin films were characterized by vibrating sample magnetometer (VSM), ferromagnetic resonance (FMR), X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS). The g-factor was calculated to be 2.66, the saturation magnetization (4πMs) was measured to be 1250 G and the FMR linewidth was 1000 Oe. The magnetoelectric measurements were performed by measuring the changes in magnetization with the application of a DC voltage which shows that the required voltage in order to observe the effect was substantially smaller than the voltage required for bulk materials with same composition. The deduced ME coupling coefficient, α, for SrCo2Ti2Fe8O19 thin film was 6.07×10-9 sm-1.
9:00 AM - U3.17
Cobalt Ferrite Nanocubes for Magnetic Data Storage Application
Liheng Wu 1 Shouheng Sun 1
1Brown University Providence USAShow Abstract
Synthesis and self-assembly of ferromagnetic/ferrimagnetic nanoparticles are important for magnetic data storage application in hard disk drive and magnetic tape. In order to get high density data storage, uniform size and shape of the nano-building blocks are needed. As an important ferrimagnetic material, cobalt ferrite (CoFe2O4) shows very high magnetic anisotropy and coercivity, which is a desirable system for this application. Here I will discuss the solution-based synthesis of uniform cobalt ferrite nanocubes. The magnetic properties can be easily tuned by controlling the size of the cube and composition of Co in cobalt ferrite. Using the self-assembly process, thin film from the uniform nanocubes is fabricated as the magnetic recording medium for the data storage demonstration.
9:00 AM - U3.18
A New Green Chemical Synthesis Method for Direct Synthesis of L10 FePt Nanoparticles from Layered Precursor Fe(H2O)6PtC16
Xiaocao Hu 1 Aldo Capobianchi 2 George C. Hadjipanayis 3
1University of Delaware Newark USA2Istituto di Struttura della Materia. CNR Rome Italy3University of Delaware Newark USAShow Abstract
Magnetically hard FePt nanoparticles have been attractive in the past few years because of their potential application in high density storage media and permanent magnets. In this work, a new green chemical strategy for the direct synthesis of L10 FePt alloy nanoparticles is reported. The starting material is a polycrystalline molecular complex (Fe(H2O)6PtC16), in which Fe and Pt atoms are arranged on alternating planes, like in the L10 structure. The starting compound was milled with crystalline NaCl to form nanocrystals. Then the mixture was annealed under reduction atmosphere (5 % H2 and 95% Ar) at 400°C for 2h with a heating rate of 5°C/min. After the reduction, the mixture was washed with water to remove the NaCl and L10 FePt nanoparticles were obtained without using organic solvents or metal additives. Transmission electron microscopy (TEM) images revealed that this method is able to produce L10 nanoparticles with different average size varying from 13.9 nm to 5.4 nm depending on the (Fe(H2O)6PtC16)/NaCl ratio. The X-Ray Diffraction (XRD) pattern showed the presence of the characteristic peaks of the fct phase. The hysteresis loop, measured both at room temperature and 50 K, shows a high coercivity of 7.6 kOe and 11.2 kOe, respectively as expected for the high anisotropy L10 phase. This method has the following advantages with respect to other wet chemical synthesis methods of L10 FePt nanoparticles; it works at temperatures much lower than those reported in the literature and without metal additives, it does not use organic solvents and it leads to a highly ordered L10 phase.
9:00 AM - U3.19
A Gradiometer Structure Based Rare Earth-Fex (RFex) Magnetoelectric Sensor
Lei Mei 1 Sebastian Rupprecht 2 Qiming Zhang 1 Qing Yang 2
1the Penn State University University Park USA2the Penn State University Hershey USAShow Abstract
It was widely recognized that the rare earth metals are critical components for many new technologies because of their extraordinary magnetic properties; for example, heavy rare earth elements of lanthanide series, such as Terbium (Tb) and Dysprosium (Dy), exhibit huge magnetic moments of 9.05 mu;B (Bohr magnetrons) and 10mu;B; compared with the conventional values of 0.6 for Ni and 2.2 for Fe. Meanwhile, the curie temperatures of rare earth-iron compounds increase with increasing rare earth concentration: the Curie temperature of amorphous TbFe2 is 388K while Terbium&’s Curie point is about 220K. Below the Curie temperature, the crystal lattice is elongated or compressed in the direction of magnetization if an external magnetic field is applied; asymmetrical lattice spacing is generated subsequently and this strain is determined by the orientation of the magnetic domains. The strain generated will get to its maximum value once all the magnetic moments become aligned with the applied field, thus the saturation magnetostriction has been reached and little strain change will be provided even more. TbFe2 could have a saturation field as high as 23KOe with a magnetostriction of 2520ppm while Tb0.3Dy0.7Fe1.92 has a saturaton field of 3.1KOe with a magnetostriction of 1800ppm (with load), both of these Rare earth-Fex components have been studied by our group and coupled with Piezo ceramic layer to form magnetoelectric sensor which is sensitive with tiny magnetic field while also has a large saturation field compared with commercialized magnetic sensors.
The Rare earth-Fex (TbFe2 or Tb0.3Dy0.7Fe1.92) layer will generate AC modulated strain if an AC magnetic field is applied, the strain will be coupled to the laminated Piezo ceramic layer (Pb(Zr, Ti)O3) and thus an AC electric charge signal will be generated because of the piezoelectricity of Pb(Zr, Ti)O3. A custom made charge amplifier is adopted for signal collection and both magnetoelectric coefficient and sensitivity were studied; the Tb0.3Dy0.7Fe1.92/ Pb(Zr, Ti)O3 sensor system presents an output as high as 84.7 mV under a charge amplifier gain of 2000pC/V while the TbFe2/ Pb(Zr, Ti)O3 sensor system has a high saturation field of 4.3KOe, this is the highest saturation point ever reported for Rare earth-Fex/Piezo coupling sensors.
A gradiometer structure is then formed with two Rare earth-Fex/Piezo coupling sensors with a baseline of 5.30 cm and used for tiny magnetic field gradient measurement. A differential output of 4.83mV is observed under a 0.0135Oe magnetic field gradient with a common mode magnetic AC signal of 1.233Oe: The common mode signal was cancelled while the gradient signal still could be measured. A noise density of 1.9*10-9 Tesla/ rt Hz at 10 Hz is also observed which proves that the gradiometer structure based Rare earth-Fex (RFex) magnetoelectric sensor system could be used for nano Tesla magnetic field gradient measurement within high common mode noise environment.
9:00 AM - U3.21
Relationship between Magnetization Dynamics and Spin, Lattice and Electrons on the Base of RE-TM Alloys
Kazimierz J. Plucinski 1
1Military University of Technology Warsaw PolandShow Abstract
RE-TM alloys, like GdFe100Co alloys are example of the multi-sublattice magnets, where an important role is played by the exchange of angular momentum between non-equivalent sublattices. GdFeCo alloys are ferrimagnets, where the Fe and Gd sublattices are coupled antiferromagnetically, while the Co magnetic moments are parallel to those of iron.
In such systems, the time scale of the magnetization dynamics becomes dependent on the exchange interaction and the balance of the angular momentum between the sublattices 
The inequivalency of the magnetic sublattices, on the one hand, and a fine balance of their angular momenta on the other, lead to a very interesting dynamic behavior. This becomes especially obvious at short time scales, when even the exchange coupling could be overmastered by an efficient energy and angular-momentum exchange with the electronic system, leading to a transient ferromagnet-like state at time scales below a few picoseconds. This state is followed by an inter-sublattice relaxation of the angular momentum, leading to a very deterministic switching of the magnetization driven solely by ultrafast laser-induced heating .
Because there are certain controversies about interpretation of the experimental results [e.g. 2,3], the following results of the theoretical analysis will be presented:
10 - analysis of the magnetization dynamic based on the three thermodynamic subsystem: the spin system, the electronic system and the lattice. Analysis of the thermodynamic approximation, taking into account short time scale, will be presented; 20 - relaxation rates between these reservoirs, associated with the characteristic energies of the interactions that mediate the coupling between these reservoirs will be analyzed; 30 - influence of the helicity-dependent absorption in the RE-TM magnetic layer, caused by the circular magnetic dichroism on magnetization dynamics, especially laser induced femtomagnetism.
 C.D.Stanciu et al., Phys. Rev. B, 73, 220402(R);  A. Kirilyuk et al., Rep. Prog. Phys., 76, 026501;  D.Popova et al., Phys. Rev., B 84, 214421.
9:00 AM - U3.22
Morphological Dependence of the Intrinsic Magnetism of dsDNA
Chang Hoon Lee 1 Young Wan Kwon 2
1Chosun University Gwangju Republic of Korea2Korea University Seoul Republic of KoreaShow Abstract
Recently, we reported the intrinsic DNA magnetism induced by a helical charge transport along the helical π-ways of dsDNAs. In the context, we used electron magnetic resonance (EMR) and superconducting quantum interference device (SQUID) magnetometer in order to detect the magnetic phenomena. In the EMR spectroscopy, we observed the extremely broad EMR peak of g>10 together with the relatively narrow one of g~2. The g>10 and g~2 were assigned as a cyclotron resonance (CR) and Zeeman magnetic transition, respectively. Here, the CR was suggested to be guided by the helical π-way of single dsDNA, which reminiscent of molecular solenoid. If such dsDNA solenoids were coherently interfered through an inductive coupling, and thus extended in the perpendicular direction to be a bundle of dsDNA solenoids in the well ordered regions of fibril structure of A-dsDNAs, a circular loop current might be formed in normal plane of the helical axis, resulting in the s-shaped magnetization (M)-magnetic field (H) curves at the magnetic field ranges of ±5000 G in SQUID measurements.
The scenario mentioned above is only possible when the helical π-ways are preserved well from molecular conformational to morphological levels. This implies that there is no CR peak in an A-dsDNAs with an amorphous phase alone. Therefore, whether the CR is or not is strongly depend on the presence or absence of the well ordered regions.
Here, we prepared various salmon DNAs under different concentrations of Na+ cation. And then, EMR (electron magntic resonance) and SQUID (superconducting quantum interference device) magnetizaton measurements were performed for them at room temperature. Especially, TEM (tunnelling electron microscope) analysis was imployed to characterize DNA's morphology. Interestingly, the DNA's magnetism has one-to-one correspondence to morphological variations.
9:00 AM - U3.23
Ferromagnetism in Compounds Consisting of Spin Icosahedra
Ryuji Tamura 1
1Tokyo University of Science Tokyo JapanShow Abstract
There exist a number of compounds which consist of spin clusters with the icosahedral symmetry such as spin dodecahedra and spin icosahedra. However, spin-glass behaviours had been commonly observed in these compounds without an exception, and only recently antiferromagnetic long-range orders were found in Cd-based binary systems . In this presentation, we report the first ferromagnetism at low temperatures in solids consisting of spin icosahedra, i.e., Au-based ternary compounds, which are described as bcc packing of rare-earth icosahedra. We will discuss the characteristic features of the ferromagnetism observed in the unique compounds. An attempt to increase the Curie temperature will be also addressed.
 Tamura et al., Phys. Rev. B 82, (2010) 220201(R).
9:00 AM - U3.24
Design Rules for Rare-Earth Replacement Magnetic Materials: MnBi and MnSb Families
Soo Kyung Kim 1 2 Hamid Garmestani 1 Kim Ferris 2 Dongsheng Li 2
1Georgia Institute of Technology Atlanta USA2Pacific Northwest National Laboratory Richland USAShow Abstract
MnBi considered as a replacement rare earth magnetic material due to its strong magnetization and coercive powers, but also its ability to retain its magnetization at elevated temperatures while related compositions suffer large diminishment. Extensive experimental studies on MnBi have shown that it is a strong ferromagnetic compound with a 2.0 T coercive force and an 4.6 MGOe energy product at 400K for the NiAs hexagonal phase[1, 2]. The magnetic anisotropies of MnBi and MnSb are similar in terms of spin-alignment, but the difference in the transition temperatures for spin alignment is large. As MnBi has a positive temperature coefficient for coercivity, a valuable trait for applications where magnetic power needs to be maintained at elevated temperatures. To investigate the origin of this temperature dependence, we have performed a series of first principles electronic structure calculation on the thermo magnetic properties of MnBi and MnSb within the local density approximation and plane wave basis using the ABINIT program system. The total magnetization and local magnetic moment in easy direction (c-axis) of these two compounds have been calculated as a function of electronic temperature from 30K to 315K. Finite temperature effects on the electronic structure were examined by cold smearing and Fermi-Dirac population methods. To discern potential structural roles, three crystal forms common to the MnX series were investigated for compositions, MnBi and MnSb, the room temperature hexagonal NiAs structure, an elevated temperature orthorhombic MnP structure, and tetragonal zincblende structure. All three forms have been observed for MnAs by earlier investigators. Our first principles calculation has shown good agreement with experimental structural and thermomagnetic results for MnBi and MnSb. Comparing results from the NiAs, MnP and zincblende-type structures, our results clearly show a structural role in the thermomagnetic behavior of these compounds, with marked temperature sensitivity for MnSb. Using thermal expansion effects derived from experimental measurement [5, 6], total magnetization of MnBi shows a small increase with larger cell volumes. Our results imply the possibility that the positive thermomagnetic property of MnBi is due to structural role and remnant even with easy-axis aligned spin moment where the magneto anisotropic spin reorientation does not occur.
1. Ravindran, P., et al., Physical Review B, 1999. 59(24): p. 15680-15693.
2. Yang, J.B., et al., 2002. 14(25): p. 6509-6519.
3. Payne, M.C., et al., Reviews of Modern Physics, 1992. 64(4): p. 1045-1097.
4. Suzuki, T. and H. Ido, Journal of the Physical Society of Japan, 1982. 51(10): p. 3149-3156.
5. Roberts, B.W., Physical Review, 1956. 104(3): p. 607-616.
6. Willis, B.T.M. and H.P. Rooksby, Proceedings of the Physical Society of London Section B, 1954. 67(412): p. 290-296
9:00 AM - U3.25
Core-Shell Nanostructures of Gold/Silver Functionalized MnZn Ferrite Nanoparticles in Correlation with Their Magnetic Properties
Tatiana Krentsel 1 Zakiya Skeete 1 Liqin Lin 1 Jin Luo 1 Natalya Chernova 1 Chuan-Jian Zhong 1
1State University of New York at Binghamton Binghamton USAShow Abstract
With rapid growth of nanotechnology applications in medicine the ability to guide nanoparticle targeting and control nanoparticle assembly becomes an issue of great importance. Magnetic nanoparticles coated with gold or silver featuring a unique combination of biocompatibility and magnetic properties show a great potential to use a magnetic field to guide the assembling/disassembling process with a high precision We have synthesized by a thermally-activated processing technique magnetic nanoparticles (NP) with ferrite core doped with Mn and Zn, e.g., MnZn Ferrite (MZF). The MZF NPs, upon coating with Ag or Au shell (MZF/Au and MZF/Ag nanoparticles), exhibit novel functionalities. DC magnetization and ac susceptibility tests were performed using SQUID magnetometry. The Curie-Weiss paramagnetism was observed at higher temperature for MZF/Ag nanoparticles, whereas the magnetization was larger for MZF/Au nanoparticles. This difference was probably caused by interactions between Au or Ag shell and MZF core, which had alternated the nature of the magnetic exchange within the core/shell structure. X-ray absorption measurements will be employed to examine the local chemical environment around Fe, Mn, Zn atoms inside the magnetic core, around Au and Ag atoms at the core/shell interface, as well as in the shell of magnetic nanoparticles to study the atomic-scale structures responsible for induced spin polarization at core/shell interface in magnetic nanoparticles coated with noble metals.
9:00 AM - U3.26
Structural and Magnetic Characterization of YCo5/FeNi Composite Powder Prepared by Mechanical Alloying and Subsequent Annealing
Ganesh Pokharel 1 Sanjay Mishra 1 Mohammad Shahabuddin 1
1University of Memphis Memphis USAShow Abstract
Exchange spring magnets, formed by the exchange coupled nanograins of hard and soft magnetic phases, leads to improve magnetic properties. The soft phase, rich in transition metal, enhances saturation magnetization whereas the hard phase provides the required magnetic anisotropy and stabilizes the exchange coupled soft phase from demagnetization. In order to increase the maximum energy product, (BH)max and to lower the cost due to reduction of rare earth content, YCo5 can be taken as a potential candidate for the hard phase of nanoconposite.
Magnetic hard-soft composite of YCo5-x% FeNi (x = 5, 10, 15) were prepared by high energy ball milling and subsequent vacuum annealing. Before the synthesis of these nanocomposites, the hard phase YCo5 was prepared by arc melting. The structural properties of these composite YCo5-x% FeNi (x = 5, 10, 15) were investigated by X-ray diffraction and magnetic measurements were done by Vibration sample magnetometer in the presence of 12KOe applied magnetic field. After 45m of milling, the powders were highly amorphous with specified amount of FeNi. Subsequent high vacuum annealing in the temperature range from 550°C - 750°C head to the reformation of crystalline sample with high magnetization around 104 emu/gm for 15% FeNi. Due to the annealing the sample were changed into magnetically soft phase showing low remanance and coercivity. The composite samples are seen to have low magnetocrystalline anisotropy along the basal plane. Among all the annealing temperature which is used to anneal the sample, 650°C is seen to be suitable to obtain good magnetic properties of the YCo5-x% FeNi composites.
9:00 AM - U3.27
Growth and Magnetic Interactions in Epitaxial Core-Shell Metal Oxide Nanocrystals
Yong-Lun Lanny Chen 1 Sheng-Chieh Liao 2 I-Hsuan Lin 1 Wei-Chen Kuo 3 Heng-Jui Liu 1 Jeffrey Cheung 4 Xuan Cheng 4 He-Hung Kuo 1 Ying-Jiun Chen 5 Yu-Ze Chen 2 Yu-Lun Chueh 2 Hong-Ji Lin 5 Chien-Te Chen 5 Jeng-Yih Juang 3 Chih-Huang Lai 2 Nagarajan Valanoor 4 Ying-Hao Chu 1
1National Chiao Tung University Hsinchu Taiwan2National Tsing Hua University Hsinchu Taiwan3National Chiao Tung University Hsinchu Taiwan4University of New South Wales Sydney Australia5National Synchrotron Radiation Research Center Hsinchu TaiwanShow Abstract
The interactions through the interface in nanoscale have been one of the target of primary research due to the tremendous fascinating physical properties. However, the researches on 0-dimentional transition metal oxides now are all focusing on core-shell nanoparticles/nanocrystals, which always show an irregular arrangement and are hard to control the structures well. In this study, monodispersed epitaxial core-shell oxide nanocrystals with one covering the other have been successfully created by utilizing the instable characteristics of bismuth-based complex ternary oxides. This new structure can possesses both the virtues of traditional core-shell nanostructures and the epitaxial supported nanostructures, showing the control of facet and interface of core-shell nanocrystals.
Here, we fabricated nanocrystals combined with rock-salt structure of antiferromagnetic CoO and spinel structure of ferrimagnetic Fe3O4, where we could manipulate one through the other easily. Our results show that the magnetic properties such as the magnetic anisotropy, the coercivity, and the magnetization are tunable and can be precisely controlled by the size, thickness, orientation, interface and the role of core or shell at room temperature. In addition, a large exchange bias and the direction- dependence of exchange coupling have been observed due to the strong magnetic interaction between the core and shell magnetic nanocrystals.
This approach can be expanded into all sorts of bismuth-containing oxide and then demonstrates different epitaxial core-shell metal oxide nanocomposite easily. Based on the novel structure and their possibility of convenient control of physical characteristics, this study provides us a new opportunity to understand the fundamental properties of nanoscopic metal oxides and the potential to design more desirable functional devices in the future.
Monday AM, December 02, 2013
Hynes, Level 2, Room 206
9:30 AM - U1.01
100 ps Unidirectional Magnetic Vortex Core Reversal Observed by Time-Resolved Scanning Transmission X-Ray Microscopy
Hermann Stoll 1 Matthias Noske 1 Matthias Kammerer 1 Markus Sproll 1 Georg Dieterle 1 Markus Weigand 1 Ajay Gangwar 1 2 Arne Vansteenkiste 3 Bartel Van Waeyenberge 3 Georg Woltersdorf 2 Christian H. Back 2 Gisela Schuetz 1
1Max Planck Institute for Intelligent Systems (formerly MPI for Metals Research) Stuttgart Germany2Regensburg University Regensburg Germany3Ghent University Ghent BelgiumShow Abstract
We present measurements and micromagnetic simulations demonstrating spin wave mediated magnetic vortex core reversal with excitation and reversal times of less than 100 ps.
Essential progress in the understanding of nonlinear vortex dynamics was achieved when low-field vortex core reversal was found by (sub-GHz) excitation of the vortex gyromode with 4 ns excitation time . The switching scheme involved, based on the creation and subsequent annihilation of a vortex-antivortex (VA) pair as suggested in  and investigated experimentally later , has been proven to be universal and in particular independent of the type of excitation, e.g., pulsed magnetic fields or spin transfer torque.
Vortex structures possess azimuthal spin wave modes which, compared to the gyromode, show much higher eigenfrequencies in the multi-GHz range. We demonstrated [3,4] by both, experiments and micromagnetic simulations, that unidirectional vortex core reversal also can be achieved by exciting these azimuthal spin wave modes with rotating GHz magnetic field bursts. VA pair creation and annihilation is also involved in this process [3,4].
Recently we demonstrated that spin wave mediated vortex core reversal can be realized with switching times below 100 ps. For that purpose we excited Permalloy discs in the vortex state, 0.5 mu;m in diameter and 40 nm thick, with orthogonal magnetic field pulses in x and y direction. Experimental and simulated phase diagrams will be shown. The magnetic vortex core could be successfully switched experimentally and by micromagnetic simulations with excitation times down to 70 ps. An additional delay of 20 - 30 ps for vortex core reversal will be discussed, caused by the time needed for transferring the homogeneously distributed excitation energy to the center of the vortex structure [4,5]. Even considering this phenomenon, vortex core reversal times below 100 ps have already been achieved.
Experiments have been performed by time-resolved scanning transmission X-ray microscopy at the MAXYMUS endstation at BESSY II, Berlin, which combines a time resolution of about 40 ps with a lateral resolution of about 25 nm. A sophisticated data acquisition enables operation in the standard multi-bunch mode of the synchrotron and thus allows us to take advantage of the about a magnitude higher ring current. In addition, a significant enhancement in the signal-to-noise ratio and a virtual elimination of low-frequency fluctuations and beam instabilities is obtained by a ‘lock-in&’ like technique and by performing a complete time-scan at one pixel before moving to the next one.
 B. Van Waeyenberge et al., Nature 444, 461 (2006)
 A. Vansteenkiste et al., Nature Physics 5, 332 (2009)
 M. Kammerer et al., Nature Communications 2, 279 (2011).
 M. Kammerer et al., Phys. Rev. B 86, 134426 (2012)
 M. Kammerer et al., Appl. Phys. Letters 102, 012404 (2013)
9:45 AM - U1.02
Topological Mass of Skyrmionic Spin Structures
Felix Buettner 1 2 3 C. Moutafis 4 M. Schneider 3 B. Krueger 1 C. M. Guenther 3 J. Geilhufe 5 C. von Korff Schmising 3 J. Mohanty 3 B. Pfau 3 S. Schaffert 3 M. Foerster 1 T. Schulz 1 C. A. F. Vaz 1 6 J. H. Franken 7 H. J. M. Swagten 7 M. Klaeui 1 S. Eisebitt 3 5
1University of Mainz Mainz Germany2University of Mainz Mainz Germany3Technische Universitamp;#228;t Berlin Berlin Germany4Paul Scherrer Institut Villigen PSI Switzerland5Helmholtz-Zentrum Berlin famp;#252;r Materialien und Energie GmbH Berlin Germany6Paul Scherrer Institut Villigen PSI Switzerland7Eindhoven University of Technology Eindhoven NetherlandsShow Abstract
Skyrmions are winding vector fields with a characteristic spherical topology. These configurations are found in a wide range of research areas, such as high energy physics, Bose Einstein condensates, and spin systems. Skyrmionic spin structures may arise due to various interaction energies. One example for such a winding spin structure is the magnetic bubble, which is stabilized by dipolar interactions. Recent theoretical investigations predict a GHz gyrotropic motion of such a topological configuration after excitation in a restoring potential, analogous to vortex gyration. However, in contrast to vortices, bubbles are predicted to exhibit inertial effects, manifesting in a second gyrotropic mode of reverse chirality and in additional degrees of freedom. Here we demonstrate the presence of an inertial mass in a magnetic bubble by imaging its gyrotropic trajectory using pump-probe x-ray holography. We find that the inertial mass is very large compared to other magnetic systems, which we attribute to the non-local energy reservoir of the bubble's breathing mode. The breathing mode is a unique feature of the geometrically confined skyrmionic spin structure, which is a direct consequence of its topology, and thus lends itself to describe the inertia of Skyrmions in terms of a topological mass. As such, the presence of strong inertia is also expected for other skyrmionic spin structures, including chiral Skyrmions.
10:00 AM - *U1.03
Magnetic X-Ray Microscopy - From Nanoscale Behavior to Mesoscale Phenomena
Peter Fischer 1
1CXRO/LBNL Berkeley USAShow Abstract
Over the last decade magnetism research focused on a fundamental understanding and controlling spins on a nanoscale. Recently, it has been recognized, that the next step beyond the nanoscale will be governed by mesoscale phenomena, since those are supposed to add complexity and functionality, which are essential parameters to meet future challenges in terms of speed, size and energy efficiency of spin driven devices.
Magnetic soft X-ray microscopy is a unique analytical technique combining X-ray magnetic circular dichroism (X-MCD) as element specific magnetic contrast mechanism with high spatial and temporal resolution. Utilizing the inherent time structure of current synchrotron sources fast magnetization dynamics in ferromagnetic elements can be performed with a stroboscopic pump-probe scheme with 70ps time resolution. At next generation light sources fsec spin dynamics can be addressed.
In this talk I will review recent achievements and outline future opportunities. We have found that the symmetry breaking DM interaction causes a stochastic character in the nucleation process of magnetic vortices . Time resolved studies of dipolar coupled magnetic vortices indicates the path for an efficient energy transfer mechanism, which can be used for novel magnetic logic elements . Tailoring the geometry of magnetic nanodisks allows to control the switching of circularity independently from the polarity of the vortex core . First attempts to image 3dim magnetic domain structures in rolled-up Ni nanotubes are very promising .
Future capabilities at next generation light sources, e.g. X-ray free electron lasers will allow to take snapshot images of spin structures and their ultrafast dynamics down to fundamental length and time scales.
The collaboration with Mi-Young Im, Weilun Chao, Sang-Koog Kim, Guido Meier, Vojtech Uhlir and Denis Makaro is highly appreciated. 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 under Contract No. DE-AC02-05-CH11231.
 BESAC report: From Quanta to the Continuum: Opportunities for Mesoscale Science (2012), http://science.energy.gov/~/media/bes/pdf/reports/files/OFMS_rpt.pdf
 P. Fischer, Materials Science & Engineeering R72 81-95 (2011)
 W. Chao, et al. Optics Express 20(9) 9777 (2012)
 M.-Y. Im, P. Fischer, Y. Keisuke, T. Sato, S. Kasai, Y. Nakatani, T. Ono, Nature Communications 3 983 (2012)
 H. Jung, K.-S. Lee, D.-E. Jeong, Y.-S. Choi, Y.-S. Yu, D.-S. Han, A. Vogel, L. Bocklage, G. Meier, M.-Y. Im, P. Fischer, S.-K. Kim, NPG - Scientific Reports 1 59 (2011)
 V. Uhlir, M. Urbánek, L. Hladík, J. Spousta, M.-Y. Im, P. Fischer, N. Eibagi, J. J. Kan, E. E. Fullerton and T. Scaron;ikola, Nature Nanotechnology 8 341-346 (2013)
 R. Streubel. D. Makarov, D. Karnaushenko, L. Han, O. G. Schmidt, J. Lee, S.-K. Kim, R. Schäfer, M.-Y. Im, P. Fischer (2013) submitted
10:30 AM - U1.04
Direct Correlation between Spin Structure Oscillations and Domain Wall Velocities Visualized by Dynamic Imaging
Andre Bisig 1 2 3 Martin Staerk 2 Mohammad Mawass 1 Jan Rhensius 2 Christofourous Moutafis 2 Felix Buettner 1 4 Matthias Noske 3 4 Markus Weigand 3 4 Stefan Eisebitt 4 Hermann Stoll 3 Gisela Schuetz 3 Mathias Klaeui 1 2
1University of Mainz Mainz Germany2University of Konstanz Konstanz Germany3MPI-IS Stuttgart Germany4BESSY Berlin GermanyShow Abstract
The controlled displacement of magnetic domain walls in ferromagnetic nanostructures is a key prerequisite for memory, logic and devices based on switching by domain wall motion . In domain wall logic devices driven by circular fields  the propagation of the domain wall is determined by the field strength and the frequency of the rotating field, giving an extra degree of freedom to control the domain wall motion. The effect of transverse and tangential fields on the domain wall spin structure leads to wall displacement but also to domain wall oscillations and transformations, at high domain wall velocities (Walker breakdown) as predicted numerically .
We present the first direct experimental visualization of the precessional motion of domain walls in permalloy nanorings controlled by circular fields with varying speed and strength . Employing scanning transmission x-ray microscopy (STXM) we image the propagation of a pair of domain walls in a stroboscopic measurement scheme and we determine the velocity, spin structure and phase as a function of position and excitation. We image directly dynamic domain wall transformations and find that the domain wall velocity varies strongly during the periodic transformation processes between vortex and transverse walls. The propagation and domain wall spin structures are highly reproducible, showing that we can observe the Walker breakdown, which is a deterministic process and we find good agreement with theoretical predictions.
In addition, we also observe a time delay between tangential field component and the velocity evolution, due to domain wall inertia. This direct imaging technique allows us to pinpoint the origin of the domain wall inertia to the domain wall spin structure changes (see ). Beyond measuring the depinning process we see here for viscous wall motion how the Zeeman energy is not only transferred into displacement but also into exchange energy as the wall is deformed. In particular the domain wall velocity is strongly enhanced as the vortex domain wall undergoes a transformation to a transverse domain wall, which is directly linked to the energy change as the vortex core is expelled.
Finally, we systematically study the propagation of domain walls for various field strength and field rotation frequencies. We find for low domain wall velocities that the motion is dominated by pinning events, directly visualizing previous theoretical prediction of kinetic and static domain wall pinning.
 M. Hayashi, et al., Nat. Phys. 3, 21 - 25 (2007).
 D. A. Allwood et al., Science 309, 1688 (2005).
 A. Thiaville et al., in Spin Dynamics in Confined Magnetic Structures II, Springer (2006).
 A. Bisig et al., Nature Comm. (in press 2013).
 J. Rhensius et al., Phys. Rev. Lett. 104, 67201 (2010).
10:45 AM - U1.05
Magnetoelastic Coupling Behaviour from Resonant Ultrasound Spectroscopy
Michael Carpenter 1
1University of Cambridge Cambridge United KingdomShow Abstract
Strain is of fundamental importance in controlling microstructure, switching dynamics and order parameter coupling at ferroic and multiferroic phase transitions, whether the driving mechanisms are structural, ferroelectric, electronic or magnetic. Equilibrium values of spontaneous strains coupled to structural order parameters typically fall in the range ~0.1 - 5 % but the associated changes in elastic properties which they give rise to are 10&’s of %. For magnetic transitions, the strains can be sufficiently small that they may not easily be detected by conventional diffraction techniques. In this context, Resonant Ultrasound Spectroscopy (RUS) provides a particularly sensitive method of investigating the strength and dynamics of strain coupling through observations of elastic and anelastic behaviour in the frequency range ~0.1 - 2 MHz. As part of a wider study of magnetoelastic coupling phenomena in phases such as BiFeO3, KMnF3, (Pr,Ca)MnO3, (La,Ca)MnO3, FexO and PrAlO3, it has been found that the influence of elastic contributions due to other instabilities or ferroelastic twin walls can be much greater than that of the magnetic ordering. In order to investigate the limiting case of a “pure” antiferromagnetic ordering system, i.e. without other instabilities, CoF2 was selected as a model system. RUS data collected from a polycrystalline sample in the interval 10-290 K show distinct softening of the shear modulus and a peak in acoustic dissipation as T → TN (~39 K) from above and below. Softening of the shear modulus at T > TN can be fit with an expression usually used for Vogel-Fulcher freezing dynamics, perhaps implying that there is a small activation energy barrier for reorientation of spins in dynamically ordered domains within the paramagnetic phase. The softening, ΔC, scales with a tail in the strain, e, as ΔC prop; e^2. The pattern of softening at T < TN conforms closely to expectations from Landau theory for a transition with approximately tricritical character, linear/quadratic coupling between non-symmetry breaking strains and the driving order parameter, and rapid relaxation of the order parameter in response to an applied (dynamic) stress. A distinct dispersion with respect to frequency for both the softening and attenuation in the stability field of the antiferromagnetic structure has been used to determine values for relaxation times. These fall in the range 10^-8 - 10^-9 s and are believed to be due to spin-lattice coupling; they are weakly temperature dependent, increasing as temperature increases towards the Néel point. Such relaxation behaviour is not universal, however, as magnetic ordering in multiferroic YMnO3 gives rise only to elastic stiffening in proportion to the square of the magnetic order parameter. It seems likely that a second order parameter, whether ferroelectric or ferroelastic in origin, might have a profound effect on the spin-lattice relaxation dynamics.
11:30 AM - U1.06
Nickelate Thin Films: A Study Using Resonant Soft X-Ray Based-Techniques
Sara Catalano 1 Valentina Bisogni 2 Marta Gibert 1 Ronnie Sutarto 3 Feizhou He 3 Pavlo Zubko 1 Raoul Scherwitzl 1 George Sawatzky 4 3 Thorsten Schmitt 2 Jean-Marc Triscone 1
1Universitamp;#233; de Genamp;#232;ve Geneve Switzerland2Paul Scherrer Institute, Swiss Light Source Villingen Switzerland3Canadian Light Source Inc. Saskatoon Canada4University of British Columbia Vancouver CanadaShow Abstract
Perovskite nickelates (chemical formula R-NiO3, with R=Rare Earth) display a textbook example of bandwidth controlled Metal to Insulator (MI) transition and a rather unconventional AFM ground state, with the Ni spins ordered along the  direction. These compounds have recently been studied in the form of epitaxial thin films, which allows their phase diagram to be controlled using strain and thickness induced effects. Also, electric field effect and pump-probe light experiments have shown that nickelates display interesting functional properties[3,4].
Here we use synchrotron radiation to investigate the electronic configuration and the phase diagram of high quality epitaxial thin films grown by RF off-axis magnetron sputtering. We focused on the members of the family with R=Sm and R=Nd, grown on both  and  oriented substrates. We first performed Resonant Inelastic X-ray Scattering measurements. By tuning linearly polarized light at the Ni L-edge we studied the energy and temperature dependence of d-d and charge transfer excitations in the two systems. The data indicate an electronic configuration where the localized Ni d-orbitals are hybridized with the neighboring O p band. The resulting band diagram reveals the opening of a charge transfer gap as the temperature is lowered. Second, through Resonant x-ray diffraction we studied the evolution of antiferromagnetism in the two systems as a function of temperature, energy and light polarization. As a main result, a phase diagram specific for each of the films is obtained that shows how the bulk picture is modified in thin films.
 M. Medarde, J. Phys.: Condensed Matter 9, 1679-1707, (1997)
 R. Scherwitzl et al.: Phys. Rev. Lett. 106, 246403, (2011)
 R. Scherwitzl et al.: Adv. Mater. 22, 5517-5520, (2010)
 A. Caviglia et al.: Phys. Rev. Lett. 108, 136801, (2012)
11:45 AM - U1.07
Modification of Structural and Dynamic Properties of Iron Oxide Nanocrystals by Terbium-Doping
Katherine Rice 1 Stephen Russek 1 Roy Geiss 1 Yves Idzerda 2 Eric Evarts 1 Justin Shaw 1 Thomas Silva 1 Robert Usselman 1
1NIST Boulder USA2Montana State University Bozeman USAShow Abstract
Here we show that the structural and dynamical properties of iron oxide nanoparticles can be dramatically changed by incorporated rare earths in the synthesis. The particle size, crystallinity, surface spin structure, damping are all important in determining the utility of MNPs for MRI contrast and hyperthermia. We have focused on the incorporation of Tb into MNPs in an effort to increase the Gilbert damping in a manner similar to that demonstrated in metallic systems. Tb has a large orbital moment which effectively couples spin degrees of freedom to the lattice. A few percent of Tb has been shown to increase the Gilbert damping constant by a factor of 50. A surprising result in this study is that the addition of Tb to the synthesis process decreased the damping constant, rather than increased it; however there is a large unsaturable component at low temperatures.
Tb is incorporated into the synthesis in organic solution. We find that doping the particles causes a dramatic structural transformation from typical iron oxide spheres into cubes with an approximate diameter of 5 nm. X-ray diffraction (XRD) analysis shows that a change in the lattice spacing is observed by incorporating Tb in the synthesis process. XAS and XMCD show a subsitutional doping at the iron octahedral sites. Single particle energy-dispersive x-ray spectroscopy (EDS) confirms a doping concentration of approximately 4-6%. Finally, the particles are coated with SiO2 to make them compatible with biological systems.
12:00 PM - U1.08
Microwave-Assisted Synthesis and Properties of Superparamagnetic Iron Nanocomposites
Kaiyuan Luo 1 Grant Bleier 2 Erika C Vreeland 2 Yun-Ju Lee 1 Dale L Huber 2 Julia WP Hsu 1
1University of Texas at Dallas Richardson USA2Sandia National Laboratories Albuquerque USAShow Abstract
Due to the combination properties of high magnetic susceptibility and low hysteresis loss, superparamagnetic nanocomposites are promising materials in applications such as transformer cores requiring high magnetization with low loss. Fe nanoparticles with size around 20 nm have been shown to exhibit optimized superparamagnetic properties. Previous synthesis approach based on thermal decomposition of Fe(CO)5 in octadecene with oleylamine as surfactant results in Fe nanoparticles with size up to 15 nm. The superparamagnetic properties of these nanoparticles are confirmed with both AC and DC magnetic measurements. Here, we use microwave heating to synthesize Fe nanoparticles in the presence of polymers, and characterize the nanoparticle size using dynamic light scattering (DLS) and transmission electron microscope (TEM). Another approach is to synthesize the Fe nanoparticles with suitable ligands for further cross-linking between neighboring nanoparticles. The structural, chemical, and magnetic properties of these magnetic nanocomposites will be characterized by TEM, FTIR and AC magnetometry. Since inexpensive precursor Fe(CO)5, low reaction temperature (< 200°C) and short time (le; 30 min) are used in these experiments, which produce good magnetic properties, we believe that microwave-assisted synthesis of superparamagnetic Fe nanocomposite is a promising approach for high volume applications.
12:15 PM - U1.09
Multimodal Hysteretic Heating of Single Domain Magnetic Nanoparticles
Michael Gary Christiansen 1 Ritchie Chen 1 Polina Anikeeva 1
1Massachusetts Institute of Technology Cambridge USAShow Abstract
Linear response theory (LRT) is typically used to model the hysteretic heating of single domain magnetic nanoparticles (SDMNPs) by alternating magnetic fields, but recent work suggests that LRT is strictly valid only when the applied field amplitude is much less than the zero temperature coercive field. In contrast, dynamic hysteresis loop simulations of coherent reversal in SDMNPs predict saturation behavior at high fields, enhanced heating of large SDMNPs driven by fields near or above their zero temperature coercive field, and convergence with LRT at low fields. The predictive successes and failures of these two models are investigated experimentally, with precise calorimetric measurements on Fe3O4 and MnFe2O4 SDMNP samples of varying diameter over a range of field amplitudes and frequencies.
Insight gained from this comparison of theory and experiment is used to predict and demonstrate the novel technique of bimodal magnetic heating, in which subpopulations of a bimodal mixture of SDMNPs can be independently heated by applying appropriate driving conditions. Potential applications and extensions of this technique are discussed, emphasizing minimally invasive biological signaling strategies for therapy and research.
12:30 PM - U1.10
Templating of Magnetoelectric Nanocomposites by Directed Self-Assembly
Nicolas Aimon 1 Hong Kyoon Choi 1 Dong Hun Kim 1 Xueyin Sun 1 Caroline A Ross 1
1MIT Cambridge USAShow Abstract
Vertically aligned self-assembled epitaxial nanocomposites consisting of CoFe2O4 (CFO) ferrimagnetic spinel pillars embedded in a BiFeO3 (BFO) ferroelectric perovskite matrix exhibit an enhanced strain-mediated magnetoelectric coupling due to the reduced clamping constraints imposed by the substrate on the vertical CFO/BFO interfaces. This is a desirable property for transducer, sensor or memory applications, but the randomness in the location, size and shape of the nanostructures limits their applicability. In this work, a general templating method is demonstated, which enables the controlled growth of CFO, MgFe2O4 (MFO) and NiFe2O4 (NFO) pillars in predefined locations within a BFO matrix. It relies on the selective nucleation of the spinel phase in few-nanometer deep pits and trenches etched into the perovskite substrate. Because this method is process and material agnostic, it offers great flexibility in the range of achievable designs.
The presentation will first detail the fabrication method, from the creation of 1-10 nm deep topographic features in the substrates, using Focused Ion Beam nanomachining as well as self-assembled triblock terpolymer and electron beam lithographies, to the growth of 50 - 200 nm thick nanocomposites by combinatorial Pulsed Laser Deposition. Then, examples of achievable structures will be presented, including square lattices of pillars with periods between 50 nm and 100 nm, sets of parallel lines with 75 nm to 100 nm spacings, and aperiodic structures, using several different spinels (CFO, MFO and NFO). Finally, structural (electron microscopy), magnetic and electric (scanning probe microscopy) characterization results will be presented, revealing the magnetoelectric properties of the templated nanocomposites as well as the switching field distribution and magnetostatic interactions of the pillars. In the case of CFO, the switching field was around 5 kOe, on par with untemplated BFO/CFO nanocomposites.
12:45 PM - U1.11
Silica-Coated Ternary-Alloy Magnetic Nanoparticles and Their Monolithic Nanocomposites: From Fundamental Material to Device
Michael Paul Rowe 1 Amanda Whalen 1 Sean Sullivan 1 Ben Lorenzetti 1 Mindy Zhang 1
1Toyota Ann Arbor USAShow Abstract
Magnetic nanomaterials have garnered increased attention because of the promise to tailor material properties based on the engineered size and shape of the constituent components. Nanostructured magnets offer the chance for new ranges of material performance necessary for technological advancement in commercial products. Additionally, nanomaterial research is beginning to show substitutions of rare-earth element alternatives that are less-expensive and environmentally sustainable for common magnet applications. As with ‘bulk scale&’ magnets, the employment of alloys in nanoparticle magnets opens the field of possibilities for tuning material properties. The wet- synthesis and material properties are presented of ternary alloy nanoparticles (eg. Fe49%Co49%V2%) with nanometers-thick silica shells, at a scale for nanocomposite formation and device fabrication. Analyses indicate the ternary alloy is formed directly in the synthesis. This represents an advantageous flexibility for complex magnetic nanoparticles formation, and is superior to top-down methods like melt-spinning. The size and composition of such Fe49%Co49%V2%-alloy nanoparticles can be manipulated directly during their formation through simple alterations to the synthetic parameters. Nanoparticles of sizes from less-than 10nm to greater-than 140nm have been produced. Magnetic characterization, as a function of nanoparticle size, shows how the nanomaterials produced range from ferromagnetic to superparamagnetic, by size-induced changes to the blocking temperature. These adjustments in synthetic conditions to control nanoparticle size showed no evidence of impacting the ternary-alloy formation. Magnetic saturation values exceeding 100 emu/g were demonstrated here for such nanoparticles. The conjunction of high magnetic saturation and tunable coercivity (importantly without modification of the outer silica shell) lends these alloy nanomaterials to a ‘generic building block&’ motif in the formation of more complex monolithic nanocomposites for applications including alternatives to rare-earth magnets and high-efficiency power electronics components. Although individual nanoparticles (and even clusters of nanoparticles) are of scientific interest, our application of these complex nanoparticles required the formation of structurally robust nanocomposites for device application that retained their appealing/interesting nanoparticle properties. Consolidations of core/shell magnetic nanoparticles to produce complex, sintered, monolithic nanocomposites were formed. The individual feature sizes of these monolithic nanocomposites where successfully kept to the necessary nanometer scale. Monolithic nanocomposites from 8mm, up to 40mm in diameter are shown. Structural and magnetic measurements of these nanocomposites are reported. Machining these nanocomposites and use in devices as both inductor cores and the critical soft-phase in an exchange-coupled permanent magnet are shared.
June Lau, National Institute of Standards and Technology
Daniel C. Ralph, Cornell University
Yimei Zhu, Brookhaven National Laboratory
Symposium Support Aldrich Materials Science
Tuesday PM, December 03, 2013
Hynes, Level 2, Room 206
2:30 AM - U5.01
Pyroelectric Control of Rashba Spin-Split States and Spin-Relaxation Times in a GaN/InN/GaN Topological Insulator
Parijat Sengupta 1
1Purdue University West Lafayette USAShow Abstract
Topological insulators (TI) are a new state of quantum matter that possess metal-like surface states and behave as insulators in bulk. Bi2Te3, Bi2Se3 are some common examples of TIs. TI surface states are a manifestation of the strong spin-orbit coupling in these materials. Strong spin-orbit coupling which leads to band inversion in bulk is the necessary requirement for creation of TI states. Apart from spin-orbit coupling, electric field and lattice strain can also be used to invert the band structure. III-V nitrides in wurtzite phase possess a very strong internal electric field. This electric field due to intrinsic spontaneous and piezoelectric polarization (in strained nitrides) is sufficient to invert the band-ordering of a narrow-gap material such as wurtzite InN. In this work, it is demonstrated that a TI state can exist when a thin-film of InN is sandwiched between GaN layers. The combined piezoelectric and spontaneous polarization field in InN inverts the band-ordering at the Γ point.
For a certain quantum well thickness the inversion of bands happen at a threshold value of the polarization field. This suggests that tuning the internal polarization field can allow the control of band inversion. Since the creation of TI states requires inversion which in turn is polarization-dependent, this work investigates devices with varying internal fields. Internal fields are controlled by selecting a facet orientation of the quantum well layer. It is important to note that various orientations of the quantum well layer will either reduce the spontaneous or piezoelectric polarization. The choice of the facet is therefore adopted by determining the dominant polarization mechanism.
Ab-initio calculations were performed to obtain the conduction band effective mass at Γ and the direct band-gap for bulk InN. These values were inserted in to an 8-band k.p Hamiltonian including strain and the internal polarization field.
The work utilizes the spin-polarized surface states of the GaN/InN topological insulator. The surface states are degenerate at Γ. At a finite k-vector, the Rashba induced spin-splitting on the surface of this heterostructure is computed for the two spin states. The splitting under a first-order approximation is independent of k-vector and corresponds to the internal electric field&’s contribution to the Rashba coefficient α. Therefore, a pyro-electric control of spin-polarization coupled to a choice of facet orientation is accomplished.
Finally, the interplay of mechanisms that control the lifetime of spin-polarization and compute spin-relaxation times is used to design a resonant spin-lifetime transistor with InN/GaN. The lifetime of the spin-polarized states under certain conditions of growth is observed to cancel the Rashba and Dresselhaus splitting to suppress Dyakonov-Perel spin-relaxation mechanism.
2:45 AM - U5.02
Magnetotransport and Structural Properties of Thin Film Spin Gapless Semiconductors
Michelle Elizabeth Jamer 1 Badih A. Assaf 1 Trithep Devakul 1 Don Heiman 1
1Northeastern University Boston USAShow Abstract
Spin gapless semiconductors (SGS) are materials predicted to have a density of states displaying both half-metallic and zero-gap semiconducting properties. These materials are being investigated for spintronic devices due to their unique magnetic properties and high magnetic transition temperature (400-800K). Calculations predict several SGS compounds,1,2 including Mn2CoAl, Ti2CoSi, V3Al, and Ti2MnAl. Recent research has been limited to bulk SGS compounds, and the magnetic and electrical properties of SGS thin films have not been investigated.
Mn2CoAl thin films were grown by MBE on GaAs (100) substrates at 200 oC. The as-grown thin films were epitaxial with the substrate as confirmed by RHEED patterns and X-ray diffraction, which resulted in a tetragonal distortion. Annealing studies showed that the films lose their epitaxial registration and approach a cubic structure at higher annealing temperatures. At an annealing temperature of 325 oC the structure is cubic with a=c=5.80 Å. The magnetic and magnetotransport properties were investigated. The temperature-dependent resistivity shows metallic-like behavior below 200 K, but turns over into a semiconducting-like negative slope as temperature is increased above 200 K. The magnetoresistance is negative and the Hall resistivity is found to scale with ρxx2 for all temperatures and magnetic fields, expected for an intrinsic anomalous Hall effect. Furthermore, the total Hall conductivity scales with the magnetization, indicating an anonymously small Hall voltage arising from a 2-carrier system. The connection of the electrical properties with the spin-gapless properties is discussed. Synthesizing thin film SGS paves the way for future devices based on such materials.
1 S. Skaftouros, K.Ozdogan, E. Sasioglu, and I. Galanakis, App. Phys. Lett. 102, 022402 (2013).
2 Siham Ouardi, Gerhard H. Fecher, and Claudia Felser, and Jurgen Kubler, Phys. Rev. Lett. 110, 100401 (2013).
3:00 AM - *U5.03
Superconductivity, Critical Current, and Nano-Scaled Structural Defects in Iron-Based Superconductors
Qiang Li 1
1Brookhaven National Lab Upton USAShow Abstract
Although high-temperature superconducting cuprates have been discovered for more than 25 years, high-field applications are still based on low-temperature superconductors (LTS), such as Nb3Sn. Recently, we have demonstrated that the iron chalcogenide superconductors have a superior high-field performance over LTS at 4.2 K. Indeed, iron-based superconductors are of great interest for both basic science and applications, because they exhibit low critical current anisotropies with very high upper critical field slopes near Tc. In this presentation, I will discuss recent progress aimed at understanding the relationships between superconductivity, critical current, and nano-scaled structure defects in iron-based superconductors, with emphasis on superconducting films and coated conductors of iron chalcogenides. With a CeO2 buffer, critical current densities (Jc) over 106 A/cm2 were observed in FeSe0.5Te0.5 films grown on single-crystalline and flexible metal substrates. These films are capable of carrying Jc exceeding 105 A/cm2 under 30 T magnetic fields, suggesting nano-scaled defects of the size comparable to the superconducting coherence length play important roles as effective pinning centers. Furthermore, we found that these films have significantly higher Tc (>20K) as compared to bulk samples (bulk Tc ~15 K) for the entire doping regime of FeSe1-xTex. Structural analysis revealed that these films generally have significantly smaller c-axis and a-axis lattice constant than the bulk value, suggesting that the crystal structure changes have a dominating impact on the superconducting transition in iron-based superconductors.
3:30 AM - U5.04
Room Temperature Antiferromagnetism in c-FeSi
Igor Altfeder 1
1Air Force Research Laboratory Wright Patterson AFB USAShow Abstract
We will be reporting on a recent experimental discovery  of a new antiferromagnetic material, having important fundamental and practical implications for nanomagnetism and nanotechnology. Using spin-polarized scanning tunneling microscopy (SP-STM) we observed room-temperature antiferromagnetic spin ordering in thin epitaxial films of c-FeSi on Si(111). Although some earlier GMR experiments  clearly indicated such a possibility, antiferromagnetism in this material has never been directly observed or predicted in theory. Using Fe-terminated STM tip, we found unusually high (75%) spin polarization of tunneling current. We also found atomically narrow spin-domain-boundaries, indicating that c-FeSi can be used for atomic scale (~12 atoms per bit) magnetic memory storage . Our data analysis suggests that c-FeSi represents a Mott-Hubbard antiferromagnet.
 Igor Altfeder, Wei Yi, and V. Narayanamurti, “Spin Polarized Scanning Tunneling Microscopy of the Room Temperature Antiferromagnet c-FeSi”, Rapid Communication, Physical Review B 87, 020403(R) (2013)
 J. M. Pruneda, R. Robles, S. Bouarab, Ferrer, and A. Vega, “Antiferromagnetic interlayer coupling in Fe/c-SiFe/Fe sandwiches and multilayers”, Phys. Rev. B 65, 024440 (2001)
 S. Loth, S. Baumann, C. P. Lutz, D. M. Eigler, A. J. Heinrich, “Bistability in Atomic-Scale Antiferromagnets”, Science 335, 196 (2012)
3:45 AM - U5.05
Magnetotransport Measurements on Individual MnAs Nanoclusters and Nanocluster Arrangements
Martin Fischer 1 Shinya Sakita 2 Hiroaki Kato 2 Matthias T. Elm 1 Shinjiro Hara 2 Peter J. Klar 1
1Justus-Liebig-University Giessen Giessen Germany2Hokkaido University Sapporo JapanShow Abstract
The properties of ferromagnetic nanoclusters can be tuned in a wide range by adjusting their size and shape. However, many fabrication methods only yield ensembles of magnetic clusters which are oriented at random in a host material or on a substrate. Thus, most technological applications of such materials have been restricted to macroscopic devices, i.e. where the mean distance between clusters is much smaller than the characteristic device size. A macroscopic size in case of working with random cluster arrangements is essential to avoid problems due to statistical fluctuations in cluster number, size, etc and thus allows one to tune the average clusters properties only. These considerations imply for fabricating miniaturized devices based on magnetic nanoclusters, it is desirable to have means to accurately control position, orientation, size and shape of the clusters.
Selective-area metal-organic vapor-phase epitaxy (SA-MOVPE), which combines top-down structuring and epitaxial growth, enables one to fabricate sub-100 nm-structures of well-defined size and shape on specified positions on a substrate. The areas where the cluster growth shall take place are defined by a nanostructuring process which generates openings in a growth-inhibiting layer on the substrate. Amongst many different materials, the growth of ferromagnetic hexagonal MnAs nanoclusters is possible with SA-MOVPE on (111) GaAs substrates . This approach can be used to define planar magnetic sensor devices consisting of few exactly positioned MnAs clusters of well-defined shape and position .
In this contribution, the authors report on the successful SA-MOVPE growth and the electrical contacting of nanocluster arrangements consisting of single-domain MnAs nanoclusters, and present magnetoresistance measurements demonstrating the dependence of the overall resistance of these arrangements on the orientation of the magnetizations of the individual nanoclusters. In these measurements, discrete resistance changes of the single-domain MnAs nanocluster arrangements can be observed as the external magnetic field is varied. The switching behavior of the cluster magnetizations and its effect on the magnetoresistance characteristics of the MnAs nanocluster arrangements are explained by accounting for the interplay of crystalline anisotropy of hexagonal MnAs, of the form anisotropy of the clusters and of the coupling between clusters.
 Wakatsuki, T. et al.: Growth Direction Control of Ferromagnetic MnAs Grown by
Selective-Area Metal-Organic Vapor Phase Epitaxy, JJAP 48 (2009) 04C137
 Heiliger, C. et al.: Magnetic Sensor Devices Based on Ordered Planar Arrangements of
MnAs Nanocluster, IEEE Trans. Mag. 46 No. 6 (2010)
4:30 AM - *U5.06
Magnetic Nanodots Induced Novel Magnetic Phenomena
Jian Shen 1 2
1Fudan University Shanghai China2The University of Tennessee Knoxville USAShow Abstract
Study of Magnetic nanodots is at central in the field of nanomagnetism. Besides the interesting properties caused by dimensionality effect, magnetic nanodots can induce many novel phenomena when forming heterostructures with other electronic materials. In this work, I will use several examples to demonstrate their effect. These examples include 1) Collective ferromagnetic behavior of magnetic nanodot arrays on 2-dimensional electron gas, 2) Colossal magnetoresistance of organic thin films induced by inserting a layer of magnetic nanodots, and 3) Dramatic enhancement of metal-insulator transition temperature in manganites capped by a layer of magnetic nanodots. All these fascinating phenomena originate directly from the interaction between magnetic nanodots with the electronic structures of the host materials. Their underlying mechanism will also be discussed based model calculations.
5:00 AM - U5.07
Manipulation of Magnetic Shape Anisotropy in BiFeO3-CoFe2O4 Self-Assembled Thin Films
Zhiguang Wang 1 Yanxi Li 1 Jiefang Li 1 Dwight Viehland 1
1Virginia Tech Blacksburgh USAShow Abstract
We report growth of various phase architectures of self-assembled BiFeO3-CoFe2O4 (BFO-CFO) thin films on differently oriented SrTiO3 (STO) substrates. CFO forms segregated rectangular, strip and triangular nanopillars embedded in a coherent BFO matrix on (001), (110) and (111) oriented STO substrates, respectively. Nanostructures with an aspect ratio of up to 5:1 with a prominent magnetic anisotropy were obtained on both (001) and (110) STO along out-of-plane and in-plane directions, respectively. Magnetic easy axis rotation from in-plane to out-of-plane directions was realized through aspect ratio control. These studies established a detailed relationship of magnetic anisotropy with specific shape and dimensions of ordered magnetic arrays. The results suggest a way to effectively control the magnetic anisotropy in patterned ferromagnetic oxide arrays with tunable shape, aspect ratio and elastic strain conditions of the nanostructures.
5:15 AM - U5.08
Thickness-Dependent Crossover from Charge- to Strain-Mediated Magnetoelectric Coupling in Ferromagnetic/Piezoelectric Oxide Heterostructures
Steven Richard Spurgeon 1 Jennifer D. Sloppy 1 Demie Kepaptsoglou 2 Prasanna V. Balachandran 1 Siamak Nejati 3 J. Karthik 4 Anoop R. Damodaran 4 Craig L. Johnson 5 Hailemariam Ambaye 6 Richard Goyette 6 Valeria Lauter 6 Quentin M. Ramasse 2 Juan C. Idrobo 7 Kenneth K.S. Lau 3 Samuel E. Lofland 8 James M. Rondinelli 1 Lane W. Martin 4 Mitra L. Taheri 1
1Drexel University Philadelphia USA2STFC Daresbury Laboratories Warrington United Kingdom3Drexel University Philadelphia USA4University of Illinois--Urbana Champaign Urbana USA5Drexel University Philadelphia USA6Oak Ridge National Laboratory Oak Ridge USA7Oak Ridge National Laboratory Oak Ridge USA8Rowan University Glassboro USAShow Abstract
Thin film magnetoelectric oxide heterostructures are among the most promising materials for a new generation of spintronic devices, in which spin transport is used to convey information. However, prevailing theories of magnetoelectric coupling have failed to fully describe the behavior of these composites, particularly in thicker device structures. Here we present evidence for a crossover from charge- to strain-mediated interfacial coupling in heterostructures of the piezoelectric PbZrxTi1-xO3 (PZT) and the half-metal La1-xSrxMnO3 (LSMO). Using polarized neutron reflectometry we reveal the presence of a graded magnetization, which is associated with local strains and interfacial charge transfer directly measured by aberration-corrected transmission electron microscopy. We then perform density functional theory calculations to show that strain acts to suppress magnetization locally through a change in Mn-eg orbital polarization. Our results suggest a radically new model of coupling in these materials and we offer ways to tune the performance of a composite by selecting appropriate layer geometries.
This research was supported in part by Oak Ridge National Laboratory's Shared Research Equipment (ShaRE) User Program, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy. Polarized neutron reflectometry experiments were performed at the Spallation Neutron Source at Oak Ridge National Laboratory, managed by UT-Batelle, LLC for the U.S. Department of Energy. Part of this work was conducted in Drexel University&’s Centralized Research Facilities. The SuperSTEM Laboratory is supported by the U.K. Engineering and Physical Sciences Research Council.
5:30 AM - U5.09
Synthesis, Structural and Magnetic Characterization of Dy1-x RxCrO3 (R = Y, Ho, Nd)
Austin McDannald 1 Lukasz Kuna 2 Menka Jain 1 2
1University of Connecticut Storrs USA2University of Connecticut Storrs USAShow Abstract
The rare-earth orthochromites (RCrO3), such as DyCrO3, have been suggested to display both magnetic and ferroelectric order. Being multiferroic with higher Neel temperature than their manganite counterparts (RMnO3), these RCrO3 and their solid solutions (that have not been studied yet) are of great interests. However, the structural and magnetic properties of these materials remain as yet poorly understood. In this work, the solution based synthesis of phase pure DyCrO3 and several solid-solutions (including YCrO3 HoCrO3 and NdCrO3) are presented. X-ray diffraction and Raman spectroscopy were used to analyze the structure of the bulk samples. The valence states of the cations were investigated with x-ray photoelectron spectroscopy. The effect of the substituting ions was seen in the temperature dependence of the magnetic moment. Promising magnetocaloric behavior was extracted from isothermal magnetization measurements with values for the magnetocaloric effect and relative cooling power as high as 8.1 J/kg K and 196 J/kg respectively. Magnetic and ferroelectric properties of these samples will be presented in detail.
5:45 AM - U5.10
Recent Results on Quantum Materials with an X-Ray Free Electron Laser
Joshua Turner 1
1Stanford University Stanford USAShow Abstract
One of the novel tools for studying spin-electron-lattice phenomena in functional materials is the x-ray free electron laser . This is especially true in the soft x-ray range, where the L-edges exist for the transition metal oxide materials which can be studied using resonant techniques. These techniques are used to directly investigate the magnetic, charge, or orbital structure of manganites , magnetites , nickelates , and cupric oxides --the building blocks for high temperature superconductors. Most importantly is the new available information in the time domain that using an x-ray FEL offers. By using pump-probe developments with ultra-short laser and x-ray pulses, dynamics on femtosecond time scales can be observed that yield information about the time scales of the order parameters involved among the spin-electron-lattice phenomena. The coupling between the different mechanisms can be measured in these materials, and followed in real time. We review recent results in these systems and discuss the new understanding that is forming in the study of magnetic, charge, and orbital dynamics in these quantum materials.
 Nature Photonics 4, 641 - 647 (2010).
 Physical Review B 84, 241104(R) (2011); Phys. Rev. B 86 064425 (2012).
 Nature Materials 12, 882-886 (2013).
 Nature Communications 3 838 (2012); Phys. Rev. Lett. 110 127404 (2013).
 Phys. Rev. Lett. 108, 037203 (2012).
Tuesday AM, December 03, 2013
Hynes, Level 2, Room 206
9:00 AM - *U4.01
Novel Materials with High Spin-Polarization
William H Butler 1 Kamaram Munira 1 Jonathon Romero 1
1University of Alabama Tuscaloosa USAShow Abstract
We have recently completed a survey of L21 structure Heusler alloys which have composition A2BC where A and B are transition metals but C is not. The L21 structure can be understood by considering the cases, (i) A=B=C for which the L21 structure is equivalent to bcc and (ii) B=Cne;A for which the L21 structure is equivalent to B2 or CsCl. Finally, if every other B atom in the B2 structure is replaced by a C, atom one obtains L21. Our survey of the L21 structure Heusler alloys included all alloys for which A=(Cr, Mn, Fe, Co, Ru, or Rh), B=(Ti, V, Cr, Mn, or Fe) and C=(Al, Ga, In, Si, Ge, Sn, P, As, or Sb). We find that there is an almost universal tendency among these alloys to form in a state which has an electronic structure such that either the “up” or “down” spin channel has exactly three occupied states per atom. This has the effect of causing the spin-moment per formula unit to be given by M=Z-24, where Z is the number of valence electrons per formula unit. Often there will be a gap in the density of states for the spin channel with precisely 12 filled electronic states per formula unit (3 per atom). This gap adds an additional stability to the phase. Evidence for this can be seen when one plots the energy versus magnetic moment for a given lattice constant. There is typically a minimum near M=Z-24 and for the systems with a gap at the Fermi energy, there is a discontinuity in the slope of the E vs. M curve leading to a characteristic “v” shape. This tendency for the transition metal atoms to shuffle electrons between spin channels to satisfy the Slater-Pauling condition of 3 electrons per atom in one of the spin channels often leads to multiple solutions of the DFT equations, some of which may be physically accessible via changes in magnetic field or in lattice volume. Another intersting feature is the existence of with 100% polarization of the density of states at the Fermi energy and zero magnetic moment. Such materials would be expected to have extremely large domains, no shape anisotropy and extremely fast magnetization dynamics. These materials offer the potential for materials design since they allow one to adjust the lattice through isovalent variation of the C element, to adjust the magnetization, and to adjust the anisotropy through layering of different half-metallic alloys along the (001) direction.
This work was supported in part by NSF DMREF Grant number 1235396 and by C-SPIN, one of the six SRC STARnet Centers, sponsored by MARCO and DARPA
9:30 AM - U4.02
Kondo-Suppressed Spin Accumulation in Nanoscopic Non-Local Spin Transport Devices
Liam O'Brien 1 2 Dima Spivak 3 Michael J Erickson 3 Haile. Ambaye 4 Richard J Goyette 4 Valeria Lauter 4 Paul A Crowell 3 Chris Leighton 1
1University of Minnesota Minneapolis USA2University of Cambridge Cambridge United Kingdom3University of Minnesota Minneapolis USA4Oak Ridge National Laboratory Oak Ridge USAShow Abstract
By separating spin- from electrical-currents, nanoscopic lateral non-local spin valves (NLSVs)  provide a direct probe of spin transport in metals. In addition to their potential to further our fundamental understanding of spin transport in metals, NLSVs are also relevant to future spintronic devices such as CPP GMR sensors and have even been proposed as a disruptive technology for HDD read heads .
In our recent work  we have performed an extensive investigation of nanoscopic NLSVs, employing transparent interface limit devices fabricated via e-beam lithography, in situ multi-angle deposition, and UHV e-beam evaporation. Multiple ferromagnet/normal metal (F/N) combinations—using Co, Ni, NiFe, Fe, Cu and Al—have been explored, providing a wide picture of NLSV spin transport, including the importance of impurity scattering, and a critical assessment of the general adherence to Elliot-Yafet spin relaxation. One issue in particular that has eluded explanation is the non-monotonic T dependence of the NLSV spin accumulation signal, ΔR_NL(T), e.g. in Ni80Fe20/Cu devices. In this work we elucidate its origin and demonstrate a simple means to mitigate this suppression. Remarkably, our experimental results clearly show that this non-monotonicity cannot be attributed to the properties of a single F or N material. In fact, we find that the downturn in ΔR_NL occurs only for materials combinations where the F is known to form a local moment as a dilute impurity in N. We show detailed analysis of the data provides strong evidence of the importance of Kondo physics in these systems, a factor that is not typically considered. Significantly, careful studies using techniques such as polarized neutron reflectometry rule out alternative possibilities related to ordering/freezing of interfacial magnetic phases.
Systematic fitting of ΔR_NL(T) as a function of F separation, and direct quantitative comparison with Hanle effect measurements, reveal that the downturn in ΔR_NL is in fact predominantly due to suppression of the injected current polarization, α, which we argue to be a direct manifestation of the Kondo effect in a spin transport device. Good agreement is found between the onset of depolarization and the Kondo temperature, T_K, and a logarithmic decrease in ΔRNL is found around T_K, as might be anticipated if Kondo physics is important. Moreover, using a judiciously chosen thin (5 nm) interlayer we demonstrate that by preventing formation of local moment impurities at the F/N interface this effect can be mitigated and the low-T α almost completely restored.
This work thus highlights the dramatic effect interfacial-moment-forming impurities have on spin injection and relaxation in metallic systems, and presents an important new challenge for the theoretical description of these spin transport devices.
 Jedema, et al., Nature 410, 345-8 (2001).
 Hitachi GST, US Patent 0296202 (2010)
 O&’Brien, Crowell, Leighton et al., in preparation (2013).
9:45 AM - U4.03
Determination of the Origin of the Spin Seebeck Effect - Bulk vs. Interface Effects
Andreas Kehlberger 1 Rene Roeser 1 Gerhard Jakob 1 Ulrike Ritzmann 2 Denise Hinzke 2 Ulrich Nowak 2 Mehmet C. Onbasli 3 Dong Hun Kim 3 Caroline A. Ross 3 Matthias B. Jungfleisch 4 Burkard Hillebrands 4 Mathias Klaeui 1
1Johannes Gutenberg-University Mainz Mainz Germany2University of Konstanz Konstanz Germany3Massachusetts Institute of Technology Cambridge USA4Technische Universitamp;#228;t Kaiserslautern Kaiserslautern GermanyShow Abstract
In the research field of spin caloric transport one of most the prominent and still not understood effects is the spin-Seebeck effect (SSE) in magnetic insulators . Different mechanisms have been put forward to explain the SSE including parasitic surface effects. Due to this gap of knowledge the underlying mechanism has to be proved.
We present a systematic study of the SSE in Yttrium Iron Garnet (YIG) films of different thicknesses . From the thickness dependence of the measured inverse spin Hall Voltage we can unambiguously identify the origin of the measured longitudinal SSE signals. A comparison with the thickness dependence of the recently discovered spin Hall magneto resistance (SMR)  allows us to estimate the influence of the interface on the SSE signal and to identify the genuine origin of the SSE in the bulk of the YIG. Corresponding simulations on atomistic length scales allow us to explain the thickness dependence of the inverse spin Hall Voltage from a finite propagation length of the thermally excited magnons, that are identified as the source of the SSE. Eventually these could be used to manipulate domain walls very efficiently .
 K. Uchida et al., Nature Mater. 9, 894 (2010)
 A. Kehlberger et al., arXiv:1306.0784 (2013)
 H. Nakayama et al., Phys. Rev. Lett. 110, 206601 (2013)
 P. Möhrke et al., Solid State Commun.,150, pp. 489-491 (2010)
10:00 AM - *U4.04
Observation of a Berry Phase Anti-Damping Spin-Orbit Torque
Andrew Ferguson 1 Hidekazu Kurebayashi 1 Jairo Sinova 3 4 Dong Fang 1 Andy Irvine 1 Joerg Wunderlich 5 4 Vit Novak 4 Richard Campion 2 Bryan Gallagher 2 Erin Vehstedt 3 4 Liviu Zarbo 4 Karel Vyborny 4 Tomas Jungwirth 4 2
1University of Cambridge Cambridge United Kingdom2University of Nottingham Nottingham United Kingdom3Texas Aamp;M College Station USA4Institute of Physics ASCR Prague Czech Republic5Hitachi Cambridge Laboratory Cambridge United KingdomShow Abstract
Our experiments focus on spin-orbit torque (SOT) in the ferromagnetic semiconductor (Ga,Mn)As. Due to the bulk inversion asymmetry, SOT effects are possible in a uniform ferromagnetic system, removing any spin transfer torque effects that may come from the spin-hall effect. An electrical current in this spin-orbit coupled ferromagnet leads to a spin polarization of the charge carriers and consequently a torque is applied to the magnetization. This torque can lead to reversible switching of the magnetization [1,2], but in our experiments we apply a microwave frequency alternating current to resonantly drive the magnetization . In such a spin-orbit ferromagnetic resonance technique we are able to simply determine the symmetry and magnitude of the SOT.
The first experiments in (Ga,Mn)As measured a field like torque, the current leading to in-plane components of the carrier spin-polarization (Sx, Sy), which are approximately independent of the magnetization orientation within the sample . More recently we observe an anti-damping torque, with similar magnitude to the in-plane torque, characterized by magnetization-dependent spin polarization, Sz(M). This anti-damping torque is due to the Berry phase acquired by charge carriers accelerating in the spin-orbit coupled bandstructure.
We expect the Berry phase anti-damping SOT to also be present in ferromagnet/paramagnet bilayers with broken structural inversion symmetry (e.g. ). Therefore, two scattering-independent relativistic mechanisms (the spin hall effect and SOT) can contribute to the current-induced magnetization switching in those technologically important magnetic structures.
 A. Chernyshov et al. Nat. Phys. 5, 656 (2009).
 M. Endo, F. Matsukura, and H. Ohno, Appl. Phys. Lett. 97, 222501 (2010).
 D. Fang et al. Nat. Nano. 6, 413 (2011).
 I. Garate and A. H. MacDonald Phys. Rev. B 80, 134403 (2009).
 I. M. Miron et al. Nature 476, 189 (2011).
10:30 AM - *U4.05
Giant Topological Hall Effect in Strained Fe0.7Co0.3Si Epilayers
Nicholas Porter 1 Priyasmita Sinha 1 Michael Ward 2 Alexey Dobrynin 3 Timothy Charlton 4 Christy Kinane 4 Sean Langridge 4 Christopher Marrows 1
1University of Leeds Leeds United Kingdom2University of Leeds Leeds United Kingdom3Diamond Light Source Didcot United Kingdom4STFC Rutherford Appleton Laboratory Didcot United KingdomShow Abstract
The coupling of electron spin to real-space magnetic textures leads to a variety of interesting magnetotransport effects. The skyrmion spin textures often found in chiral B20-lattice magnets give rise, via real-space Berry phases, to the topological Hall effect, but it is typically rather small. Here we show that B20-ordered Fe0.7Co0.3Si epilayers grown on Si (111) substrates display a giant topological Hall effect due to the combination of three favourable properties: they have a high spin-polarisation, a large ordinary Hall coefficient, and small skyrmions. Moreover they show enhanced ordering temperatures due to the presence of epitaxial strain. The topological Hall resistivity is as large as ~750 nOmega;cm at helium temperatures. Furthermore, we observed a drop in the longitudinal resistivity of ~100 nOmega;cm at low temperatures in the same field range, suggesting it is of topological origin. That such strong effects can be found in material grown in thin film form on commercial silicon wafer bodes well for skyrmion-based spintronics.
We would like to acknowledge funding from EPSRC and the FP7 ITN Q-NET.
11:30 AM - *U4.06
Spin-Orbit Torques in Ferromagnetic Thin Films
Ioan Mihai Miron 1 K. Garello 2 E. Jue 1 G. Gaudin 1 P. J. Zermatten 1 M. V. Costache 2 S. Auffret 1 S. Bandiera 1 B. Rodmacq 1 J. Vogel 5 S. Pizzini 5 A. Schuhl 5 P. Gambardella 2 3 4
1SPINTEC Grenoble France2Universitat Autonoma de Barcelona (UAB) Barcelona Spain3Catalan Institute of Nanotechnology (ICN-CIN2) Barcelona Spain4Instituciamp;#243; Catalana de Recerca i Estudis Avanamp;#231;ats (ICREA) Barcelona Spain5Namp;#233;el Institute CNRS Grenoble FranceShow Abstract
Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay data storage media, thanks to their ability to retain a stable magnetization state over long periods of time and their compliance with increasing miniaturization steps. A major concern is that the same anisotropy properties that make a material attractive for storage also make it hard to write. We address this issue by investigating novel spin torque mechanisms based on spin-orbit effects. It is well known that spin-orbit coupling is ultimately responsible for magnetocrystalline anisotropy and damping. Under certain conditions, however, spin-orbit effects might either induce [1,2,3] or enhance [4,5] specific spin torque mechanisms.
We show that in materials lacking inversion symmetry, the spin accumulation induced by the current creates torques on the magnetization. We analyze the expected symmetry of these torques in uniformly magnetized layers as well as magnetic domain walls, and evidence experimentally their existence in agreement with symmetry arguments. We discuss our results in terms of known Spin Orbit mechanisms such as Rashba or Spin Hall Effect, and show that the complexity of the experimental observations goes beyond the predictions of simple models. 1. A. Manchon and S. Zhang, PRB 78 212405 (2008); 2. I.M. Miron et al. Nature Materials 9, 230-234 (2010); 3. I.M. Miron et al. Nature 476, 189-193 (2011); 4. I.M. Miron et al. PRL 102, 137202 (2009); 5. I.M. Miron et al. Nature Materials 10, 419 (2011).
12:00 PM - *U4.07
Giant Spin Hall Effect Induced by Doping Copper with Small Amount of Strong Spin Orbit Coupling Impurities
YoshiChika Otani 1 2
1University of Tokyo Kashiwa Japan2RIKEN Wako JapanShow Abstract
The spin Hall effect (SHE) is a key ingredient for future spintronic devices since it is the only method to convert charge currents into spin currents or vice-versa with using neither ferromagnets nor magnetic fields. Platinum is one of the most common SHE materials exhibiting reasonably large spin Hall (SH) angle of a few percent. However it is a costly metal, being unsuitable for the practical application. In this work, we demonstrate large extrinsic SHEs can be induced in Cu-based alloys by adding small amount of strong spin-orbit coupling impurity such as Ir and Bi. Our analyses based on the 3 dimensional Valet-Fert model yielded the spin Hall angle of 0.02 for CuIr alloys , almost the same as that for Pt, and that of -0.24 for CuBi alloys .
 Y. Niimi, M. Morota, D. H. Wei, C. Deranlot, M. Basletic, A. Hamzic, A. Fert, and Y. Otani, Phys. Rev. Lett. 106, 126601-1~4 (2011).
 Y. Niimi,Y. Kawanishi,D. H. Wei, C. Deranlot, H. X. Yang, M. Chshiev, T. Valet, A. Fert, and Y. Otani, Phys. Rev. Lett. 109, 156602-1~5 (2012).
12:30 PM - *U4.08
The Giant Spin Hall Effect and Spin Torque Phenomena in Multilayer Ferromagnetic/Normal Metal Nanostructures
Robert Buhrman 1
1Cornell University Ithaca USAShow Abstract
The recently discovery that a charge current flowing through certain high atomic number (e.g. Pt, Ta, or W) thin film micro- or nano-strips can exert a quite substantial spin torque on an adjacent thin film magnetic material has great potential for spintronics applications. For example the anti-damping spin transfer torque that results from the transverse spin current that can be efficiently generated via the giant spin Hall effect (SHE) in these high Z materials by a longitudinal electrical current has been demonstrated to reversibly switch the magnetization direction of in-plane magnetized nano-magnets, to induce persistent microwave magnetic oscillations in such nano-magnets, and to facilitate the high speed manipulation of domain walls in magnetic nano-strips. The deterministic switching of the magnetization direction of ultra-thin magnetic layers with perpendicular magnetic anisotropy has also been achieved, and attributed by various groups to either the spin torque arising from the spin Hall effect, or to the field-like torque arising from a different, interfacial, spin-orbit interaction, or to a combination of both. Here I will report recent results from our studies of this giant SHE and related spin torque phenomena, including investigations into the characteristics and quantitative strength of the SHE in the aforementioned and other high Z thin film materials, and into the fundamental role that the interfacial spin-mixing conductance plays in determining the effectiveness of the SHE for exerting strong anti-damping spin torques on the adjacent ferromagnet. I will also summarize results from an investigation of the spin-orbit torques found in a variety of NM/FM/Oxide device configurations as determined using three different techniques that have recently been utilized to quantitatively measure the magnitude and the sign of these torques: DC bias measurements, second-harmonic AC signal measurements, and spin-torque ferromagnetic resonance (ST-FMR). I will discuss the variation in the apparent character of the spin-orbit torques as indicated by these different types of measurements, and as found in different materials configurations and as affected by the modification of the electrical and magnetic properties of the multilayer structures.