Symposium Organizers
David P. Pappas National Institute of Standards and Technology
Vincent G. Harris Northeastern University
Michael Farle Universitaet Duisburg-Essen
Brad Engel Freescale Semiconductor, Inc.
Dexin Wang Seagate Technology
J1: Magnetic Nanoclusters and Bio-applications
Session Chairs
Tuesday PM, April 10, 2007
Room 3008 (Moscone West)
9:30 AM - **J1.1
Anisotropy and Moments in Bi-Metallic 2D Islands
Harald Brune 1
1 Institute of the Physics of Nanostructures, Ecole Polytechnique Fédérale de Lausanne, Lausanne, VD, Switzerland
Show AbstractWe establish a correlation of morphology and composition with magnetic anisotropy energies and moments in performing MOKE and XMCD measurements on island ensembles which have been characterized with STM. Strong coordination effects are evidenced with core-shell islands of Co, Fe, Pd and Pt on Pt(111). For homogeneous alloy islands we determine the concentration maximizing the blocking temperature at constant size. The role of the substrate is revealed in XMCD results on the magnetic moments and anisotropies of single atoms, such as Co, on different low-index Pd surfaces.
10:00 AM - J1.2
Tuning the Magnetic Moments and Magnetic Anisotropy of FeNi and CoRh Nanoparticles: Experiment and Theory.
Gustavo Pastor 1 , Marc Respaud 1 , J. Dorantes-Davila 1 , Bruno Chaudret 2 , Marie-Jose Casanove 3 , C. Amiens 2 , Olivier Margeat 2 , Milton Munoz-Navia 1 , David Zitoun 2 , Pierre Lecante 3
1 LNMO, INSA, CNRS, Toulouse France, 2 , LCC, Toulouse France, 3 , CEMES, Toulouse France
Show Abstract10:15 AM - J1.3
Intrinsic Damping, g-Factor and Dipolar Interaction of Monodisperse Ni and ε-Co Nanoparticle Ensembles
Igor Barsukov 1 2 , Ralf Meckenstock 2 , Juergen Lindner 2 , Zdenek Frait 1 , Michael Hilgendorff 4 , Marek Grzelczak 3 , Luis Liz-Marzan 3 , Michael Giersig 4 , Michael Farle 2
1 Institute of Physics, Department of Magnetism, Academy of Sciences of Czech Republic, Prague Czech Republic, 2 AG Farle, Fachbereich Physik, University Duisburg-Essen, Duisburg Germany, 4 , Forschungszentrum CAESAR, Bonn Germany, 3 Departamento de Química Física, University of Vigo, Vigo Spain
Show AbstractThe Ferromagnetic Resonance (FMR) is one of the best techniques to study magnetic static and dynamic properties of monodisperse nanoparticles [1] simultaneously. Multi frequency ferromagnetic resonance (MF-FMR) investigations were performed in the range of 4 to 70 GHz on monodisperse colloidal Ni (23 nm diameter) and Co (10 nm) nanoparticles. The magnetic dynamic damping factor and the spectroscopic splitting factor were determined respectively. The non-intrinsic part of the resonance linewidth as well as the line position is related to the statistically distributed anisotropy parameters and the dipolar interaction among the particles. For the full set of magnetic parameters MF-FMR investigations were performed for two external field orientations - parallel to the sample plane and perpendicularly to the plane. The planar ensembles of nanoparticles were deposited on low resistivity metallic foils from solutions by a conventional drying method.Two nano particle systems were investigated:23 nm diameter polycrystalline Ni spheres were synthesized from a NiCl2 water solution around 1 nm Pt cores. This system with the well known magnetic properties of Ni and its exact structural characterization by high resolution transmission electron microscopy allows detailed considerations of influences of anisotropy distributions in nano scaled systems and comparison with theoretical calculations. A small intrinsic damping parameter λ=2.65·108rad/s was found, it is in a very good agreement with the Ni bulk metal value λ=2.5·108rad/s. The measured g-factor (2.17±0.05) is close to the bulk value (2.21).10 nm diameter pure ε-Co spheres were synthesized. The ε phase does not exist in bulk crystals and can only be stabilized in nanostructures. The g factor (2.19±0.01) of the ε-phase is comparable to the hcp bulk value of 2.18 (gfcc=2.15) where as the intrinsic damping parameter (λε=1.4·109 rad/s) is one order of magnitude larger as the one of fcc and hcp bulk values of Co.This work was supported by the EU under grant No. MRTN-CT-2004-005567 (SyntOrbMag).[1] J. Lindner, U. Wiedwald, K. Baberschke, and M. Farle, J. Vac. Sci. Technol. A 23 (2005) 796-803[2] e.g. F. Schreiber et al., JMMM 157/158 (1996) 281-282
10:30 AM - J1.4
Particle Size Control, Structure and Magnetic Characterization of Cobalt Nanoparticles.
Abhishek Singh 1 , Gregory Young 1 , Maninder Kaur 2 , Kiumars Parvin 2 , Spencer Wong 3 , David Bruck 3 , Mehdi Varasteh 4
1 Chemical and Materials Engineering, San Jose State University, San Jose, California, United States, 2 Physics, San Jose State University, San Jose, California, United States, 3 Biology, San Jose State University, San Jose, California, United States, 4 , Alza Corporation, Mountain View, California, United States
Show AbstractCobalt nanoparticles were synthesized utilizing a hot metal reduction reaction with cobalt chloride as precursor material. The synthesis was based on worked done by Sun et al [1]. The size of the cobalt nanoparticles is controlled by the choice of the surfactant agent added to the reaction, several of which have been employed. Utilizing surfactants with larger alkane side chains results in smaller size nanoparticles. Larger alkane side chains create a steric hindrance to the formation of nanoparticles. TEM analysis of cobalt particles synthesized using a t-octyl organophosphine yielded an average particle size of 7 nm, while particles synthesized using a t-butyl organophosphine yielded an average particle size of 12 nm. X-ray diffraction measurements indicate that particles formed have a hcp structure upon synthesis. Zero-field-cooled and field-cooled magnetization measurements in the temperature range of 4.2 K to 300 K show a transition from ferromagnetism to paramagnetism with particle size dependent blocking temperature. The M-H loop measured over this temperature range shows dependence of coercive field on particle size and temperature.
Acknowledgements. This work was supported by the following grants: DARPA HR0011-05-0046 and NSF-RUI DMR-0514068.
1. Sun and C. B. Murray, “Synthesis of monodisperse cobalt nanocrystals and their assembly into magnetic superlattices,” J. Appl. Phys, 85, No. 8, 4325 (1999).
11:15 AM - **J1.5
Monodisperse Magnetic Nanoparticles: Chemical Synthesis and Potential Nanomagnetic Applications
Shouheng Sun 1
1 Department of Chemistry, Brown University, Providence, Rhode Island, United States
Show AbstractMagnetic nanoparticles are promising building blocks for fabrication of high-performance magnetic nanodevices and important labels for biomedical applications. We demonstrate that monodisperse magnetic nanoparticles of Co, Fe, CoFe, FePt, MFe2O4 (M = Fe, Co, Mn) and NM-MFe2O4 (NM = Au, Ag, Pt, Pd) with controlled size, composition, shape and structure are readily synthesized by solution phase chemical syntheses, and subsequently induced to form 2D and 3D magnetic nanoparticle superlattice arrays via self-assembly. The texture in a self-assembled array is established via the control of nanoparticle shape. Magnetic properties of these arrays are tuned from superparamagnetic to ferromagnetic with controlled magnetic moment and coercivity. Furthermore, surface modification renders the nanoparticles water soluble and accessible to various biomolecules. These well-engineered magnetic nanostructures are of great importance for understanding nanomagnetism, for fabrication of magnetic nanodevices and for biomedical applications.
11:45 AM - J1.6
HR-TEM Studies of FePt Nanoparticles by Exit Wave Reconstruction.
Daniela Sudfeld 1 , Olga Dmitrieva 1 , Nina Friedenberger 1 , Guenter Dumpich 1 , Michael Farle 1 , ChengYu Song 2 , Christian Kisielowski 2 , Markus E. Gruner 3 , Peter Entel 3
1 Experimental Physics - AG Farle, University of Duisburg-Essen, Duisburg Germany, 2 National Center for Electron Microscopy, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Physics Department, University of Duisburg-Essen, Duisburg Germany
Show Abstract12:00 PM - J1.7
Preparation of Core/shell Fe/Au for Magnetic Resonance Imaging Agent.
Shizhong Wang 1 2 , Benjamin Jarrett 2 , Angelique Louie 2 , Susan Kauzlarich 1
1 Chemistry, University of California , Davis, California, United States, 2 Biomedical Engineering, University of California, Davis, California, United States
Show Abstract12:15 PM - J1.8
Magnetic Nanocomposites with Various Morphologies.
Nicolas Pazos-Perez 1 , Michael Hilgendorff 1 , Jorge Perez-Juste 2 , Marina Spasova 3 , Luis.M. Liz-Marzán 2 , Michael Farle 3 , Michael Giersig 1
1 Nanoparticle Technology, Center of advanced european studies and research (CAESAR), Bonn Germany, 2 Physical Chemistry, University of Vigo, Vigo, Galicia, Spain, 3 Physik, Duisburg-Essen University, Duisburg Germany
Show Abstract12:30 PM - **J1.9
Spin Valve Sensors for Ultrasensitive Detection of Superparamagnetic Nanoparticles for Biological Applications.
Shan Wang 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractMagnetic nanotechnology is finding wide applications in medicine, most notably in magnetic resonance imaging and magnetic separation. However, even more exciting applications of nanotechnology in fighting cancer, heart diseases, and infectious diseases are emerging. We are developing a sensitive and quantitative molecular detection system which is based on magnetic nanotags (nanoparticles, 10-100 nm in mean diameter) and spin valve sensor arrays. The magnetic biochips can be used for rapid and portable DNA fingerprinting, pathogen detection, and proteomics. We have designed and fabricated several types of such magnetic biochips (MagArray) consisting of arrays of spin valve detectors with appropriate dimensions, surface chemistry, and microfluidics. An ASIC circuit with a footprint of 2 mm by 2 mm and including row and column addressing decoders and parallel fast readout schemes have been designed and fabricated. The MagArray chips feature redundant and high density of sensors, with a sensor density as high as 0.1 million sensors per squared cm. An advanced electronic test station has been set up as a demonstration vehicle for the integrated evaluation of our magnetic biochips with the custom magnetic nanotags and DNA-based biochemistry. The system is capable of detecting down to 1-30 nanotags.Real-time detection of biological events in the context of DNA and protein assays has been successfully performed in laboratories, suggesting that MagArray holds unparalleled capabilities as compared to existing biochip technologies. Several practical issues need to be addressed in time for MagArray to emerge as a killer application for biomedicine and biodefense in the near future.This work is supported in part by US Navy/DARPA and National Cancer Institute.
J2: Spin Transfer
Session Chairs
Tuesday PM, April 10, 2007
Room 3008 (Moscone West)
2:30 PM - **J2.1
Spin-Transfer Torques in Single-Crystalline Nanomagnets.
Daniel Buergler 1 3 , Ronald Lehndorff 1 3 , Henning Dassow 1 3 , Attila Kakay 1 3 , Riccardo Hertel 1 3 , Andre van der Hart 2 3 , Claus Schneider 1 3
1 Institut fur Festkorperforschung (IFF-9), Forschungszentrum Julich GmbH, Julich Germany, 3 CNI - Center of Nanoelectronic Systems for Informationtechnology, Forschungszentrum Julich GmbH, Julich Germany, 2 Institut fur Bio- und Nanosysteme (IBN-PT), Forschungszentrum Julich GmbH, Julich Germany
Show Abstract3:00 PM - J2.2
Intrinsic Phase Shift and Novel Dynamic Magnetization States of a Spin Torque Oscillator under ac Current Injection.
Yan Zhou 1 , Johan Persson 1 , Johan Akerman 1
1 Institute of Microelectronics and Information Technology , Royal Institute of Technology, Stockholm Sweden
Show Abstract3:15 PM - J2.3
Effects of FM/NM Interfaces on Spin Accumulation in Free Layer of Pseudo-Spin-Valve Structure
Jiuning Hu 1 , Min Ren 1 , Lei Zhang 1 , Ning Deng 1 , Hao Dong 1 , Peiyi Chen 1
1 , Institute of Microelectronics, Tsinghua Univ., Beijing China
Show Abstract3:30 PM - J2.4
Nonlinear Damping Generated by Spin Injection in a Pseudo-spin-valve Structure
Min Ren 1 , Lei Zhang 1 , Jiuning Hu 1 , Ning Deng 1 , Dong Hao 1 , Peiyi Chen 1
1 Institute of Microelectronics, Tsinghua University, Beijing China
Show AbstractThe current induced magnetic dynamics of a nanoscale pseudo-spin-valve structure was theoretically studied. The spin relaxation mechanisms and the influence of ferromagnetic/nonmagnetic interfaces on the current polarization were investigated, and a modified magnetic dynamic equation was developed. Both the free layer's local magnetic moments and itinerant electrons' spins were regarded as a macro-spin, whose movement was resulted from two items: spin relaxation due to the magnetic damping and spin accumulation due to the polarized current. The injected current not only produces a spin transfer torque, but also alters the effective magnetic field, and thus affects the damping. Therefore, the damping is nonlinear and correlative with the current. Based on the analysis of the competition between magnetic damping and current induced torque, the dynamic behaviors of magnetization switching and oscillation can be explained. Also, the expressions of critical reversal currents were obtained for different initial magnetization configurations.
4:15 PM - **J2.5
Microwave Dynamics in Spin Transfer Nanocontacts.
William Rippard 1 , M. Pufall 1 , M. Schneider 1 , S. Russek 1 , J. Katine 2
1 , NIST, Boulder, Colorado, United States, 2 , HGST, San Jose, California, United States
Show AbstractA number of different groups have now demonstrated that polarized currents can induce both magnetic reversal and coherent microwave precession in magnetic nanostructures through the spin transfer effect. At NIST, we have largely focused on exploring and understanding the high frequency oscillations in these structures. We have shown previously that a DC current flowing through a 40 nm point contact made to a spin valve structure induces high frequency, large-angle coherent magnetic precession. The precession frequency ranges from 5-40+ GHz, and is a strong function of the field magnitude and direction, and the current. In this talk I will give an overview of our present understanding of the mechanisms determining this precession frequency and its characteristics. We have also found that the injection of an additional AC current into the device produces frequency modulation for low injected frequencies, and "injection locking" for injection frequencies near the resonant frequency. We will present an overview of the injection locking process, highlighting the similarities and differences with conventional oscillators. I will also give and overview of our investigations into the interaction of two nanocontacts made to the same magnetic mesa, which has allowed us to explore the spatial and radiative properties of the oscillators. We have found that oscillators mutually phase lock when their precession frequencies are made similar, increasing their combined output power and narrowing their linewidth, providing a mechanism for creating sources with larger output power. In addition, a giant magnetoresistance (GMR) signal is detectable at one contact due to precession at the other. We find that cutting the magnetic mesa between the contacts with a focused ion beam (see fig) modifies the contact outputs, eliminates the mutual phase locking, and strongly attenuates the GMR coupling, indicating that spin-waves rather than magnetic fields are the primary interaction mechanism. I will summarize our investigations into how the high-frequency oscillations are affected by different materials properties.
4:45 PM - J2.6
Impact of Device Variability and Circuit Phase Shift in Synchronized Spin Torque Oscillators
Johan Persson 1 , Yan Zhou 1 , Johan Akerman 1
1 Microelectronics and Applied Physics, Royal institute of technology, Kista Sweden
Show Abstract5:00 PM - J2.7
Investigation of Non Uniform Spin Excitation in Co Stripes by Locally Resolved Ferromagnetic Resonance
Ralf Meckenstock 1 , Alexei Butko 2 , Igor Barsukov 1 , Detlef Spoddig 3 , Oliver Posth 1 , Juergen Lindner 1 , Michael Farle 1
1 AG Farle, Fachbereich Physik, University of Duisburg-Essen, Duisburg Germany, 2 , Academy of Sciences, Saratov Russian Federation, 3 Experimentalphysik, University of Leipzig, Leipzig Germany
Show Abstract5:15 PM - **J2.8
The Magnetic Racetrack Memory!
Stuart Parkin 1
1 Magnetoelectronics, IBM Almaden Research Center, San Jose, California, United States
Show AbstractA proposal for a novel storage-class memory is described in which magnetic domains are used to store information in a “magnetic race-track” [1]. The magnetic race track is comprised of tall columns of magnetic material arranged perpendicularly to the surface of a silicon wafer. The columns are a few hundred nanometers in diameter and several tens of microns tall. The domains are moved up and down the race-track by nanosecond long current pulses using the phenomenon of spin momentum transfer: experiments demonstrating the current induced moment of domain walls in magnetic nano-wires will be discussed. The domain walls in the magnetic race-track are read using magnetic tunnel junction sensing devices arranged in the silicon substrate. The magnetic shift register promises a solid state memory with storage capacities and cost rivalling that of magnetic disk drives but with much improved performance and reliability. A series of experiments [2-4] which explore the current and field induced motion of domain walls (DWs) along permalloy nanowires will be discussed. The DW structure, whether vortex or transverse, and the DW chirality can be readily detected from its resistance. The current induced depinning of DWs from artificially created pinning sites - notches along the edges of the nanowires- is shown to be surprisingly insensitive to the DW structure [2]. The velocity of domain walls [3], driven by current alone in the absence of magnetic field, is shown to exceed 110 m/sec. A number of studies which show the importance of the precessional nature of the DW motion will be presented [4,5]. In particular, we find that the probability of dislodging a domain wall, confined to a pinning site oscillates with the length of the current pulse, with a period of just a few nanoseconds [4]. This behaviour is connected to a current-induced oscillatory motion of the domain wall. When the current is turned off during phases of the domain wall motion when it has sufficient momentum, the domain wall is driven out of the confining potential in the opposite direction to the flow of spin angular momentum, a sort of boomerang effect.References[1] S.S.P. Parkin, US Patent #6,834,005 (2004). [2] M. Hayashi, L. Thomas, C. Rettner, X. Jiang, R. Moriya and S.S.P. Parkin, Phys. Rev. Lett. (in press). [3] M. Hayashi, L. Thomas, Y. Bazaliy, C. Rettner, R. Moriya, X. Jiang and S.S.P. Parkin, Phys. Rev. Lett. 96, 197207 (2006). [4] L. Thomas, M. Hayashi, X. Jiang, C. Rettner and S.S.P. Parkin, Nature 443, 197 (2006). [5] M. Hayashi, L. Thomas, C. Rettner, R. Moriya and S.S.P. Parkin, Nature Physics (in press).
Symposium Organizers
David P. Pappas National Institute of Standards and Technology
Vincent G. Harris Northeastern University
Michael Farle Universitaet Duisburg-Essen
Brad Engel Freescale Semiconductor, Inc.
Dexin Wang Seagate Technology
J3: Magnetism at the Nanoscale
Session Chairs
Wednesday AM, April 11, 2007
Room 3008 (Moscone West)
9:30 AM - **J3.1
Magnetism at the Nanoscale: A Voyeur's Tale
Peter Eames 2 , E Dan Dahlberg 1
2 , NVE Corporation, Eden Prairie, Minnesota, United States, 1 School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThere has been a renaissance in magnetism in the last two decades or so. In the area of micromagnetics (although in the modern context it should be nanomagnetics), major breakthroughs have resulted from the development of new magnetic imaging techniques [1]. A powerful magnetic microscope is the magnetic force microscope (MFM), a variant of the atomic force microscope. One of the frontiers in magnetism being pushed back is to understand the domain structure and the magnetization reversal in nanometer sized particles. We have utilized the high resolution MFM (30 nm) we developed [2] to increase our fundamental understanding of magnetism on this length scale. First I will present a very elementary introduction to micromagnetics research and a description of MFM. I will then discuss the field induced magnetic reversal in stadia shaped particles on the order of hundreds of nanometers wide and about twice that in length. In general for the small aspect ratio stadia (length to width ratio) the magnetization reverses by the formation of a single vortex and its propagation down the length of a stadium (when the fields are applied perpendicular to the long axis). The surprising discovery is the importance of virtual particles (vortex-antivortex pairs) creation and annihilation in the magnetic reversal in larger aspect ratio stadia.1. E. Dan Dahlberg and Jian-Gian Zhu, Physics Today 48, 34 April 1995. 2. George D. Skidmore, Sheryl Foss, and E. Dan Dahlberg, Appl. Phys. Lett.71, 3293-3295 (1997). Supported by ONR and the University of Minnesota MRSEC.
10:00 AM - J3.2
Resistance of a Single Domain Wall in (Co/Pt)7-Multilayer-nanowires.
Christoph Hassel 1 , Mario Brands 1 , Fang-Yuh Lo 2 , Andreas Wieck 2 , Günter Dumpich 1
1 Experimental physics, University Duisburg-Essen, Duisburg Germany, 2 Angewandte Festkörperphysik, Ruhr-Universität Bochum, Bochum Germany
Show Abstract10:15 AM - **J3.3
Vortex Core Switching in Magnetic Nanostructures.
Bartel Van Waeyenberge 1 , Aleksandar Puzic 2 , Kang Wei Chou 2 , Hermann Stoll 2 , Tolek Tyliszczak 3 , Ingo Neudecker 4 , Georg Woltersdorf 4 , Christian Back 4 , Gisela Schuetz 2
1 Department of Subatomic and Radiation Physics, Ghent University, Ghent Belgium, 2 , Max-Planck-Institut für Metallforschung, Stuttgart Germany, 3 , Advanced Light Source, LBNL, Berkeley, California, United States, 4 Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Regensburg Germany
Show Abstract11:15 AM - **J3.4
Perpendicular Spin Current Driven Microwave Oscillator and Its Applications.
Jian-Gang Zhu 1 , Xiaochun Zhu 1
1 Data Storage Systems Center, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractIn this talk, we will present a novel design of spin current driven microwave oscillator with perpendicular magnetization. The oscillator consists of a perpendicularly magnetized spin polarization layer and an oscillating bi-layer that comprises a spin torque driven layer and a magnetic layer of perpendicular anisotropy with adequate interlayer exchange coupling. The perpendicularly spin polarized current can yield a sustained stable magnetization oscillation in the oscillating bi-layer around the perpendicular easy axis. The oscillating frequency can be tuned continuously with changing the injected current density from zero to tens of giga-Hz. The underlying physical mechanism of the oscillation will be discussed and a systematic micromagnetic analysis on the performance characteristics of the oscillator will be reported. One of the applications of such oscillator is to generate a local magnetic field at microwave frequencies to assist magnetic recording for hard disk drive applications.
11:45 AM - J3.5
Magnetic Ordering and Spin-glass Behaviour of Carbon Nanoclusters.
Andrei Rode 1 , Denis Arcon 2 3 , Zvonko Jaglicic 3 , Andrej Zorko 2 , Nathan Madsen 1 , Andy Christy 1 , Desmond Lau 4 , Dougal McCulloch 4 , Eugene Gamaly 1 , Barry Luther-Davies 1
1 Laser Physics Centre, RSPhysSE, The Australian National University, Canberra, Australian Capital Territory, Australia, 2 , Institute Jozef Stefan, Ljubljana Slovenia, 3 Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana Slovenia, 4 Department of Applied Physics, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia
Show Abstract12:00 PM - J3.6
Electron Spin Resonance in Ge Nanowires Doped with Transition Metals
Olga Kazakova 1 , Roman Morgunov 2 3 , Y. Tanimoto 2 , Jaideep Kulkarni 4 , Justin Holmes 4
1 , NPL, Teddington United Kingdom, 2 , Hiroshima University, Hiroshima Japan, 3 , Orenburg State University, Orenburg Russian Federation, 4 , UCC, Cork Ireland
Show AbstractThe co-existence of ferromagnetism and semiconducting properties in diluted magnetic semiconductors (DMS) has attracted great interest due to the potential importance of these materials for spintronic applications. Integration of DMS materials into electronics will require manufacturing of nanoscale components. In particular, 1D semiconductor nanostructures are proposed as building units for nanoelectronic and optoelectronic devices [1]. Recently, we have demonstrated room-temperature ferromagnetism in arrays of Ge1-xMnx aligned nanowires (NWs) with the diameter of 60 nm and length of 60 μm and studied their static magnetic properties [2]. In this report we investigate the dynamic magnetic properties of Ge NWs doped with transition metals (Mn, Cr or Co) by means of the ESR technique. The aim of this work is to investigate the influence of the transition metal type and its concentration on ESR spectra and to separate contributions from different centers to the magnetic properties of doped Ge NWs.We show that all ESR spectra contain a narrow isotropic line independently of the type of dopant ions and temperature. The line has an asymmetric Dyson lineshape and corresponds to the ESR in the subsystem of charge carriers (holes in the Ge host). It allowed us, in particular, to estimate the microwave conductivity of the NWs. In Co and Mn-doped Ge NWs, there are additionally a few wider lines related to the ferromagnetic resonance (FMR) in Co or Mn ion subsystems. An angular dependence of the FMR signal was used to determine the easy magnetisation axis and the anisotropy field in these types of NWs. Cr-doped NWs reveal a more complex anisotropic ESR spectrum corresponding to paramagnetic Cr3+ and Cr2+ ions in an octahedral environment. For all types of investigated NWs, temperature dependences of main ESR parameters are correlated in subsystems of the localized magnetic centres (Mn, Co or Cr ions) and delocalized band carriers. It implies the presence of exchange interactions between the localized Mn ions and spin-polarized carriers. This work was supported by Japanese Society for the Promotion of Science (P 05388) and RFBR (04-02-17576). [1] J. Xiang, W. Lu, Y. Hu, Y. Wu, H. Yan, and C. M. Lieber, Nature 441, 489 (2006).[2] O. Kazakova, J. S. Kulkarni, J. D. Holmes, and S .O. Demokritov, Phys. Rev. B. 72, 094415/1 (2005).
12:15 PM - J3.7
Engineering Magnetic Nanowire Heterostructures for Acoustic Sensors.
Patrick McGary 1 , Bethanie Stadler 1 , Liwen Tan 1
1 Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThe fabrication of nanowires for acoustic cilia transducers demands a composite magnetic heterostructure with a magnetostrictive transduction material, (e.g. Galfenol, Fe100–xGax), book-ended by permanent magnets (e.g. Co with [0002] texture along axes of the nanowires). These magnets bias the magnetostrictive material to a suitable operating point. Here, these heterostructures were grown by potentiostatic electrochemical deposition into anodic aluminum oxide (AAO) templates. The primary outcomes of this work were 1) controlling the Galfenol stoichiometry, 2) growing the nanowires in highly-ordered templates with small diameters, 3) controlling the segment lengths, and 4) integrating a magnetic bias within the nanowires. Magnetic properties were measured at each step of this process. First, controlling stoichiometry in the electrodeposition of metallic alloy nanowires has presented a significant challenge. For example, composition gradients along the growth length are largely unacknowledged in alloy nanowire literature. By maintaining rigid reference electrode placement, decreasing the Fe2+ and Ga3+ ion concentrations, and adding citrate as a complexing agent, the composition gradient was reduced from a variation of 20 < x < 46 atomic % Ga over 5 µm of nanowire length to 12.3 < x < 16.9 atomic % Ga over 12.5 µm of nanowire length in commercially available nanoporous templates. Second, when using highly-ordered AAO generated by a two-step anodization process with monodisperse pore diameters of 70 nm, Cu pre-wires were deposited to prevent the initial etching of the working electrode by the citrate bath. Third, a theory based on charge-capacity was developed to accurately control segment lengths during growth. Typically, the layer thicknesses in multilayered nanowires are viewed as a simple deposition time ratio, which leads to inaccuracies over the length of the wire. In order to apply this charge-based theory, the work was advanced significantly by eliminating previously uncontrolled variables such as edge deposition, uncertainties in sample area, and variations in porosity throughout commercially available templates. These were overcome by additional polymer insulation around the sample edges, digital photographic pixel integration of the deposition area window, and using highly-ordered AAO, respectively. By measuring the thickness, diameter, and center-to-center distance of the pores in each family of AAO templates with scanning electron microscopy, heterostructures of Cu/Galfenol and Co/Galfenol/Co with controlled segment lengths were fabricated in highly-ordered AAO templates. The deposition of 3 µm of Cu or Co from a sulfate bath enabled subsequent deposition of Galfenol from the citrate bath with a growth area fill factor of nearly 100%.
12:30 PM - J3.8
Magnetic Field Driven Nanowire Rotation in Suspension
K. Keshoju 1 , H. Xing 1 , Li Sun 1
1 Mechanical Engineering, University of Houston, Houston, Texas, United States
Show AbstractThe capability of manipulating nanoscale entities in suspensions will not only help the control of distribution and alignment of nano-fillers during polymer composite synthesis but also can lead to the development of novel micro-nano fluidic components and biomedical sensors/devices. Using template assisted electrodeposition, metallic and semiconducting nanowires with controlled size (diameter and length) and composition modulation have been effectively synthesized. Incorporation of magnetic segments onto these nanowires during electrodeposition allows us to use external magnetic field to manipulate their motion in suspensions. This offers a practical, cost-effective and non-contact approach to control the motion of nano-materials. Based on proper demagnetizing and magnetizing procedures, we are able to control the remnant magnetization of individual nanowire and thus the nanowire-field interactions. Nanowire responses in fluids with different viscosities have been investigated by using distilled water, ethylene glycol, mixed solutions of hexadecane/octadecane, and polydimethylsiloxane (PDMS). A quantitative model based on the analysis of competing magnetic torque and resisting fluid drag force has been developed to describe the nanowire rotational motion under the influence of uniform external field. Unlike the classical fluid dynamic analysis where either a cylinder translational motion or a rotation motion around cylinder axis is considered, the varying linear velocity along the wire axis need to be taken into account when a wire is rotating around its midpoint.
12:45 PM - J3.9
Existence of Ferromagnetism in Ion Irradiated Fullerene.
Amit Kumar 1 , D. Avasthi 1 , J. Pivin 2 , A. Tripathi 1
1 Materials Science Group, Inter-University Accelarator Centre, New Delhi, New Delhi, India, 2 CSNSM, Orsay Campus, Orsay France
Show AbstractJ4: Spin Polarized Materials
Session Chairs
Wednesday PM, April 11, 2007
Room 3008 (Moscone West)
2:30 PM - **J4.1
EuO1-x - A Highly Versatile Ferromagnetic Semiconductor for Use in Silicon-Based Spintronics.
Andreas Schmehl 1 2 , Venu Vaithyanathan 1 , Darrell Schlom 1 , Stefan Thiel 2 , Alexander Herrnberger 2 , Jochen Mannhart 2 , Lena Fitting 3 , David Muller 3 , Tassilo Heeg 4 , Jürgen Schubert 4 , Marco Liberati 5 , Yves Idzerda 5 , Yuri Barash 6
1 Department of Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 2 Center for Electronic Correlations and Magnetism, University of Augsburg, Augsburg Germany, 3 Department of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 4 Institute of Bio- and Nanosystems (IBN1-IT), Research Centre Jülich, Jülich Germany, 5 Department of Physics, Montana State University, Bozeman, Montana, United States, 6 Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka Russian Federation
Show Abstract3:00 PM - J4.2
Exchange Bias with a Magnetoelectric, Multiferroic Antiferromagnet
Lane Martin 1 2 , Ying-Hao Chu 1 2 , Kilho Lee 1 2 , Mikel Barry 1 2 , Pu Yu 1 2 , Padraic Shafer 1 2 , Qian Zhan 1 2 , R. Ramesh 1 2
1 Materials Science and Engineering and Physics, University of California, Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractMagnetoelectric multiferroics, or materials that simultaneously show some magnetic and ferroelectric order, like BiMnO3 and BiFeO3, have piqued the interest of researchers worldwide with the promise of coupling between magnetic and electric order parameters. Over the last few years, much has been learned about the underlying interactions in these intrinsic multiferroics and how the properties of these materials can be controlled. An excellent example of this is BiFeO3 (BFO), a material system in which recent evidence points to direct and controllable coupling between antiferromangetism and ferroelectricity. At the same, great advances in exchange anisotropy have occurred since the first discovery of this phenomenon in 1956. Exchange anisotropy (bias) describes the phenomena associated with the exchange anisotropy created at the interface between and antiferromagnet (AFM) and a ferromagnet (FM). Exchange bias (EB) has been used in a wide variety of applications including permanent magnets, recording media, and domain stabilizers in recording heads based on anisotropic magnetoresistance. To this point, however, no one has yet demonstrated an EB system that has an electrically tunable EB nor has anyone created an EB system that does not have significant training–the systematic reduction of EB field with repeated hysteretic switching of the magnetization of the system, outside of single crystal AFM EB systems. To address these issues, we report the growth of thin film heterostructures of the ferromagnet Co0.9Fe0.1 (CoFe) and the magnetoelectric, antiferromagnet BFO grown on SrRuO3 bottom electrodes on vicinally cut single crystal SrTiO3 substrates of various orientations using pulsed laser deposition. Structural analysis using X-ray diffraction and transmission electron microscopy reveals high quality films with the pristine interfaces required for exchange anisotropy interactions. Additional studies of the CoFe films with electron energy loss spectroscopy reveal no apparent oxidation of the FM layer. Magnetic measurements of the heterostructures performed using a superconducting quantum interference device (SQUID) magnetometer, a vibrating sample magnetometer, and a loop tracer show EB fields as large as ~80 Oe and enhancement of the coercive field of CoFe up to at least 380K. Samples demonstrate no training effect in that they have been subjected to over 14,000 hysteresis loops and show no change in the EB field. Simple device structures, including spin valves made from CoFe/Cu/CoFe/BFO heterostructures, have also been produced and show in-plane magnetoresistance of about 2.25% in initial studies. Finally, the ultimate goal of this work is to exploit the magnetoelectric coupling of the BFO layer to control EB with an applied electric field. Work towards this goal will be presented and the implications of such a discovery examined.
3:15 PM - J4.3
Magnetoresistance in the Multilayer-Coated Films of Hole Doped Lanthanum Manganites Grown by Polymer Assisted Deposition
Menka Jain 1 , P. Shukla 1 , Y. Li 1 , M. Hundley 1 , T. McCleskey 1 , A. Burrell 1 , R. DePaula 1 , Q. Jia 1
1 Materials Physics and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractThe effect of colossal magnetoresistance (CMR) in hole-doped lanthanum manganites (La1-xMxMnO3, where M=Sr, Ca, and Ba) has attracted significant interest in the past decade due to their potential applications in magnetic sensors and other magnetic devices. The figure of merit of these CMR materials for many applications is the magnetoresistance {MR = (ρH-ρ0)/ρ0, where ρH and ρ0 are the resistivities with and without a magnetic field, respectively}. Multilayer coated films of La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) were grown on single crystalline LaAlO3 substrates by polymer assisted deposition developed recently at the Los Alamos National Laboratory. This multilayer approach was used to effectively utilize the properties of both LSMO and LCMO with an aim to achieve higher MR values near room temperature. Maximum MR as high as -66% at μ0H=5 T has been obtained at 295K for the multilayer-coated films with LSMO/LCMO volume ratio of 60/40. For comparison, film of a single-phase La0.67Sr0.198Ca0.132MnO3, which is a uniformly-mixed phase of the LSMO/LCMO at a volume ratio of multilayers, shows a maximum MR of -58% at 280K. These results clearly indicate that transition temperature or MR can be manipulated through multilayer-coating of two manganite materials, which cannot be achieved by simply changing the composition in these manganites.
3:30 PM - J4.4
Large Low Field Magnetoresistance in Nanocrystalline La0.7Sr0.3MnO3 Manganite
Anurag Gaur 1 , Ghanshyam Varma 1
1 Physics, Indian Institute of Technology Roorkee, Roorkee, Uttaranchal, India
Show Abstract4:15 PM - J4.5
Magnetic and transport properties of Sr2Fe1-xAlxMoO6.
Erwan Hemery 1 2 , Grant Williams 1 2 , Joe Trodahl 1
1 , MacDiarmid Institute, Wellington New Zealand, 2 , Industrial Research Ltd, Wellington New Zealand
Show Abstract4:30 PM - J4.6
Magnetic Anisotropy Studies of La0.67Sr0.33MnO3 Thin Films and Nano Wires.
Guus Rijnders 1 , Evert Houwman 1 , Mercy Mathews 1 , J. Cock Lodder 1 , Ronnie Jansen 1 , Dave H.A. Blank 1
1 MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show Abstract4:45 PM - J4.7
Highly Spin-Polarized Complex Chalcogenide Thin Films of CuCr2Se4 for Spintronic Applications
Joanna Bettinger 1 , Rajesh Chopdekar 1 2 , Marco Liberati 3 4 , Janell Neulinger 5 , Mairbek Chshiev 6 , Yayoi Takamura 1 , Lisa Alldredge 1 2 , Elke Arenholz 4 , Yves Idzerda 3 , Angelica Stacy 5 , William Butler 6 7 , Yuri Suzuki 1
1 Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 2 Applied Physics, Cornell University, Ithaca, New York, United States, 3 Physics, Montana State University, Bozeman, Montana, United States, 4 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 Chemistry, UC Berkeley, Berkeley, California, United States, 6 MINT Center, University of Alabama, Tuscaloosa, Alabama, United States, 7 Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractThough a number of complex magnetic oxides have been studied for use in spin-based electronic devices, the family of complex magnetic chalcogenides has been largely overlooked. In this work, we report the successful growth of highly spin-polarized chalcogenide thin films of CuCr2Se4, which are promising candidates for spin-based electronic applications due to the relatively high magnetization and Curie temperature above room temperature. We also present electronic structure calculations for CuCr2Se4 that, together with magnetic and transport data, imply that the stoichiometric compound is a metallic ferromagnetic with relatively low density of hole-like carriers at the Fermi energy. In this nearly half-metallic material, the magnetic moment is primarily due to the high spin-polarized Cr density of states balanced by small contributions from the Cu and Se sites with opposite magnetization. These calculations also predict that a deficiency of Se will deplete the minority density of states at the Fermi energy perhaps leading to a half-metal. We have successfully grown thin films of CuCr2Se4 by pulsed laser deposition on isostructural MgAl2Se4 (100) at 600-650 °C in a vacuum background of 10-6 Torr. Quartz tube annealing then occurs anneal in a Se-rich environment at 475 °C for 48 hours. X-ray diffraction confirms the structure of CuCr2Se4 on MgAl2Se4 substrates as well as a secondary phase of Cr2Se3. X-ray absorption spectroscopy indicates that the chemical structure at the surface of the films is similar to that of bulk CuCr2Se4 single crystals. Magnetization measurements using a SQUID magnetometer indicate that these films saturate with a magnetic moment close to 5 μB per formula unit and a Tc above of approximately 405-410 K. These values are similar to those found for bulk samples of CuCr2Se4.[1] X-ray magnetic circular dichroism shows that the magnetism persists to the surface of the film, as is essential for use of these films as the electrode material in a magnetic tunnel junction. Resistivity and Hall effect measurements are consistent with a p-type ferromagnetic metallic behavior and with the electronic structure calculations.[1] F.K. Lotgering. Solid State Commun. 2 (1964) 55.
5:00 PM - J4.8
The Study of Component, Structure of (MgNiMnZn)1+xFe2-xO4 and their Effect on Impedance Spectra.
Huibin Qin 1 , Jijun Zhou 1 , Junming Xu 1 , Liang Zheng 1 , Ji Hu 1
1 college of electronic information , Hangzhou Dianzi University, Hangzhou, Zhejiang province, China
Show AbstractJ5: Poster Session: Magnetic Nanostructures and Devices
Session Chairs
Thursday AM, April 12, 2007
Salon Level (Marriott)
9:00 PM - J5.1
Abnormal Antiferromagnetic-like Nickel Interface Magnetism on Magneto-optical Properties of Cobalt-platinum Films.
Chiung Wu Su 1 , Ching Song Shern 2
1 Department of Applied Physics, National Chiayi University, Chiayi Taiwan, 2 Department of Physics, National Taiwan Normal University, Taipei Taiwan
Show Abstract9:00 PM - J5.10
Thermomagnetic Monitoring of Fe-Pt Alloy Nanoparticles.
Hyun Gil Cha 1 , Young Hwan Kim 1 , Chang Woo Kim 1 , Young Soo Kang 1
1 Chemistry, Pukyong National Univ., Pusan Korea (the Republic of)
Show AbstractHigh temperature solution phase decomposition of Fe(CO)5 and reduction of Pt(acac)2 in the presence of stabilizers oleic acid and oleyl amine are employed to produce Fe-Pt alloy nanoparticles. The Fe and Pt composition of the nanoparticle materials can be tuned by adjusting the molar ratio of Fe(CO)5 to Pt(acac)2, and the compositions ranging from Fe30Pt70 to Fe80Pt20 are obtained. As synthesized Fe-Pt alloy nanoparticles possess disordered fcc structure and show superparamagnetic behavior. The magnetic phase structural change during thermal annealing was monitored by thermomagnetic analysis (TMA).
9:00 PM - J5.11
Nanostructural Characterization of L10-FePt Nanoparticles and Polycrystalline TiN Underlayers.
Yoshiko Tsuji 1 , Suguru Noda 1 , Yukio Yamaguchi 1
1 Chemical System Engineering, The University of Tokyo, Tokyo Japan
Show Abstract9:00 PM - J5.12
Effects of Ta on the Microstructure and Magnetic Properties of FePt Thin Films.
Sangho Jin 1 , Soonju Kwon 1
1 Material science and engineering, POSTECH, Pohang Korea (the Republic of)
Show Abstract9:00 PM - J5.13
Magnetic Phase Transitions in Fe50Pt50-xRhx Thin Films.
Dieter Lott 1 , Jochen Fenske 1 , Frank Klose 2 , Gary Mankey 3 , Prakash Mani 3 , Wolfgang Schmidt 4 , Andreas Schreyer 1
1 , GKSS research center, Geesthacht Germany, 2 Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 MINT Center, University of Alabama, Tuscaloosa, Alabama, United States, 4 , Research Center Juelich, Juelich Germany
Show Abstract9:00 PM - J5.14
Exchange Coupled Double Layer Films for Blue Laser CAD-MSR Magneto-optical Storage.
Xianying Wang 1 , Junhe Yang 1 , Fuxi Gan 2
1 , Shanghai Institute of Technology, Shanghai China, 2 , Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai China
Show Abstract9:00 PM - J5.15
Polarized Neutron Reflectivity Studies on Lattice-matched FePt3/CoPt3 Antiferromagnetic /ferromagnetic Films.
Dieter Lott 1 , Hailemariam Ambaye 2 , Frank Klose 2 , Gary Mankey 4 , Max Wolff 3 , Prakash Mani 4 , Andreas Schreyer 1
1 , GKSS research center, Geesthacht Germany, 2 Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 MINT Center, University of Alabama, Tuscaloosa, Alabama, United States, 3 Department of Physics, Ruhr-University Bochum, Bochum Germany
Show Abstract9:00 PM - J5.17
Spin Accumulation in Ferromagnetic/nonmagnetic Devices.
Oliver Posth 1 , Mario Brands 1 , Guenther Dumpich 1
1 Experimental physics, University of Duisburg-Essen, Duisburg Germany
Show Abstract9:00 PM - J5.18
Magnetic Properties of Superlattice CoSi Nanowires.
Kwanyong Seo 1 , Sidhartha Varadwadj 1 , Paritosh Mohanty 1 , Myung-Hwa Jung 2 , Younghun Jo 2 , Bongsoo Kim 1
1 Chemistry, KAIST, Daejeon Korea (the Republic of), 2 , Korea Basic Science Institute, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - J5.19
Size and Thickness Dependencies of Static and Dynamic Magnetic Properties in Nanoscale Square Antidot Arrays.
Minghui Yu 1 , Leszek Malkinski 1 , Leonard Spinu 1 , Weilie Zhou 1 , Scott Whittenburg 1
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show Abstract9:00 PM - J5.2
Magnetic Anisotropy and Magnetization of Fe Monolayers on InP(001)
Khalil Zakeri-Lori 1 , Thomas Kebe 1 , Jürgen Lindner 1 , Michael Farle 1
1 Fachbereich Physik, Experimentalphysik-AG Farle, Universität Duisburg-Essen, Duisburg Germany
Show Abstract9:00 PM - J5.20
Effect of Magnetostatic Interactions on Microwave Absorption of Patterned Arrays of Magnetic Nanostripes.
Leszek Malkinski 1 , Minghui Yu 1 , Donald Scherer II 1 , Leonard Spinu 1 , Scott Whittenburg 1 , Zachary Davis 1
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show Abstract9:00 PM - J5.21
Analysis of Electrodeposited NiFe Thin Films for the Development of Planar Fluxgate Magnetic Sensors.
Thais dos Santos 1 , Marcelo Mulato 1
1 Physics and Mathematics, University of São Paulo, Ribeirao Preto-SP, SP, Brazil
Show Abstract9:00 PM - J5.22
Characterization of Nanostructured Yttrium Iron Garnet Ferrites
Joong-Hee Nam 1 , Young-Ho Lee 1 , Hyo Tae Kim 1
1 , Korea Institute of Ceramic Engineering and Technology, Seoul Korea (the Republic of)
Show Abstract9:00 PM - J5.23
Fabrication of Nanoscale Magnets on Cantilevers for Magnetic Resonance Force Microscopy
Steven Hickman 1 , Sean Garner 2 , Lee Harrell 3 , Boyan Penkov 4 , Seppe Kuehn 1 , John Marohn 1
1 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 2 Physics, Cornell University, Ithaca, New York, United States, 3 Physics, United States Military Academy, West Point, New York, United States, 4 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractMagnetic resonance force microscopy(MRFM) is an emerging technique for acquiring magnetic resonance images of a single molecule; to date we have demonstrated a sensitivity of ~105 proton spins. In MRFM the force exerted on the cantilever, per spin, is proportional to the field gradient from the cantilever’s magnetic tip. To increase the force requires reducing the magnet size. Achieving the attonewton force sensitivity necessary to image single spins requires mitigating surface induced dissipation. We choose to meet both of these conditions by creating nanoscale tip magnets the leading edge of silicon cantilevers. As proof of concept, we will present a 50-nm wide overhanging cobalt magnet fabricated by a process involving electron beam lithography and anisotropic KOH etching, as well as cantilevers with 50-600 nm wide, non-overhanging magnets. Our current goal is to integrate these fabrication processes. With our designed cantilever, we expect a sensitivity of better than 103 protons.
9:00 PM - J5.3
Comparative Study in Magnetic Properties of Ni/Co/Pt(111) and Co/Ni/Pt(111).
Ching-Song Shern 1 , Huei-Ying Ho 1
1 Physics, National Taiwan Normal University, Taipei Taiwan
Show Abstract9:00 PM - J5.4
On the Physics of Magnetic Anisotropy in Co/Pd Multilayer Thin Films.
Darren Smith 1 , Chunsheng Ee 1 , Shishan Zhang 2 , T. Lee 3 , Sakhrat Khizroev 4 , Dmitri Litvinov 1 2
1 Center for Nanomagnetic Systems, University of Houston, Houston, Texas, United States, 2 Chemical and Biomolecular Engineering, University of Houston, Houston, Texas, United States, 3 Chemistry, University of Houston, Houston, Texas, United States, 4 Physics, University of Houston, Houston, Texas, United States
Show Abstract[Co/Pd]N multilayer films where thicknesses of cobalt and palladium layers are in a few monolayer range exhibit high magnetic anisotropy perpendicular to the film surface where variations of Co and Pd layer thicknesses in a bilayer stack have strong effect on multilayer magnetic properties. Such magnetic multilayers have been extensively explored as recording medium candidates for high density magnetic recording applications. The origin of the perpendicular anisotropy is believed to be due to the hybridization of the d-shell electrons at the interfaces between Co and Pd layers. High anisotropy exchange coupled (Co/Pd)N multilayers designed for bit-patterned medium applications were deposited using room temperature magnetron sputtering. Magnetic properties as functions of Co and Pd layer thicknesses were correlated with XPS data, which is commonly used to probe the binding energies and valence band positions. Although the typical probing depth of XPS to limited to about 2-3nm, it is sufficient for the evaluation of the 1-2 topmost bilayers in a multilayer stack and, thus, infer the relevant details of the bandstructure of the entire film. Confirming theoretical predictions, it is demonstrated, for the first time, that d-shells of Pd atoms are modified where the strongest hybridization occurs at the Co/Pd interfaces and rapidly vanishes away from the Co/Pd interfaces. The highest hybridization of Pd atoms is observed for about one monolayer thick Co layers in the bilayer stack. Variation of deposition conditions such as deposition pressure have not shown measurable influence on the hybridization indicating that magnetic properties in these films are dominated by the film microstructure. The rapid growth of magnetic moment in Co/Pd films as the thickness of Co is increased can be explained by the additional magnetic moment contributed by the Pd atoms when their d-shells hybridize.
9:00 PM - J5.5
Magnetization Reversal in a Submicron GaMnAs Devices.
Uzma Rana 1 2 3
1 , University of Cambridge, Cambridge United Kingdom, 2 , Hitachi Cambridge Laboratory, Cambridge, CB3 0HE, United Kingdom, 3 , Microelectronices Research Center, Cambridge, CB3 0HE, United Kingdom
Show Abstract9:00 PM - J5.6
Fabrication of Crystalline CrO2 Micro-Pallets on MgO by Pulsed Laser Deposition.
Helia Jalili 1 , Nina Heinig 2 , Tong Leung 1
1 Physics and Chemistry , University of Waterloo, Waterloo, Ontario, Canada, 2 Chemistry, University of Waterloo, Waterloo, Ontario, Canada
Show AbstractChromium dioxide may be ideally suited for spintronic applications, because it is a completely spin-polarized ferromagnet at room temperature. However, CrO2 is metastable at room temperature and normal pressure, making it difficult to fabricate in a form suitable for building devices. We have grown CrO2 thin films on MgO(001) substrates using Pulsed Laser Deposition(PLD). The effects of changing the laser power, growth temperature and O2 pressure were studied. Epitaxial CrO2 was obtained in an optimized set of growth conditions. High resolution x-ray diffraction further suggested that the epitaxial growth consisted of the CrO2(110) on the MgO(001) surface. SEM and AFM studies showed that the morphology of the surface consists of predominantly micro-pallets with needle nanostructure present near the sample edge.
9:00 PM - J5.8
Magnetic and Structural Properties of FINEMET Nano Powder Fabricated by Mechanical Milling Method.
Seongmin Hong 1 2 , CheolGi Kim 1 2 , Chong-Oh Kim 1 2
1 Material Science and Engineering, Chungnam National University, Deajeon Korea (the Republic of), 2 , Research Center for Advanced Magnetic Materials, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - J5.9
Carbon Combustion Synthesis and Magnetic Properties of Cobalt Ferrite Nanoparticles
Long Chang 1 2 , Karen Martirosyan 3 2 , Dmitri Litvinov 1 2 , James Rantschler 1 2 , Sakhrat Khizroev 4 2 , Dan Luss 3 2
1 Electrical and Computer Engineering, University of Houston, Houston, Texas, United States, 2 Center for Nanomagnetic System, University of Houston, Houston, Texas, United States, 3 Deparment of Chemical Engineering, University of Houston, Houston, Texas, United States, 4 Electrical Engineering, University of Houston, Riverside, California, United States
Show AbstractThis paper presents a study of magnetic properties of cobalt ferrite, CoFe2O4, nano-particles produced by Carbon Combustion Synthesis of Oxides (CCSO). In CCSO the exothermic oxidation of carbon generates a thermal reaction wave that propagates at a velocity of 0.1-3 mm/s through the solid reactant mixture converting it to the desired complex oxide without any external power consumption and using rather inexpensive raw materials. Synthesis of cobalt ferrite was conducted by loading a loose reactant mixture (CoO, Fe2O3 and graphite) into a ceramic boat that was placed inside a cylindrical stainless steel vessel fed with oxygen. After local ignition a high temperature front (up to 1200 °C) propagates through the sample transforming the reactants to cobalt ferrite. Quick reaction time (order of seconds) inhibits grain growth and the release of carbon dioxide generates highly porous powder (up to 55 % porosity). Graphite concentration, oxygen flow rate, and the packing density of the sample strongly affect the magnetic properties, microstructures, and crystallographic order of the products. Submicron clusters (60-200 nm) of CoFe2O4 were synthesized in three experiments where the maximum combustion temperature (Tmax) of the propagating front was either 850 °C, 1050 °C or 1200 °C. The variation of Tmax did not result in significant changes (~5%) of the coercivity (Hc=700 Oe) or specific magnetization (σs ~ 47 emu/g) of the product. The quenching front method, combined with XRD, SEM and VSM characterization, was used to determine the evolution of composition, microstructure, coercivity and specific magnetization within the reaction zone. While the specific magnetization increases monotonically (up to 47 emu/g) with increasing distance from the quenching front (up to 20 mm), the maximum coercivity of ~940 Oe was observed in powders formed at about 5 mm from the quenching front.
Symposium Organizers
David P. Pappas National Institute of Standards and Technology
Vincent G. Harris Northeastern University
Michael Farle Universitaet Duisburg-Essen
Brad Engel Freescale Semiconductor, Inc.
Dexin Wang Seagate Technology
J6: NanoMagnetic Devices
Session Chairs
Thursday AM, April 12, 2007
Room 3008 (Moscone West)
10:00 AM - **J6.1
Ferroelectric and Multiferroic Tunnel Junctions.
Evgeny Tsymbal 1
1 Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractSo far almost all the existing tunnel junctions were based on non-polar dielectrics. An interesting possibility to extend the functionality of tunnel junctions is to use a ferroelectric insulator as a barrier to make a ferroelectric tunnel junction (FTJ) [1]. Recent experimental and theoretical findings demonstrate that ferroelectricity persists down to vanishingly small sizes which make ferroelectric tunnel junctions feasible. FTJs offer exciting prospects for device applications. In particular, the electric-field-induced polarization reversal in a ferroelectric barrier may have a profound effect on the conductance of a FTJ. One of the mechanisms is the incomplete screening of polarization charges which makes the depolarization field and hence the potential profile seen by transport electrons different for the opposite polarization orientations [2]. In addition, the polarization switching changes positions of ions near the interfaces. This affects the atomic orbital hybridizations at the interface and electronic properties of the barrier and hence alters the transmission probability. Functional properties of a FTJ can be extended by replacing normal metal electrodes by ferromagnets which makes the junction multiferroic. In such a multiferroic tunnel junction (MFTJ), where a thin ferroelectric film is used as a barrier, spin-dependent tunneling may be controlled by reversing the electric polarization of the ferroelectric[3]. In other words, by changing the electric polarization of the barrier one can influence the spin polarization of the tunneling current and the tunneling magnetoresistance. Thus, such a MFTJ which combines ferromagnetic electrodes and a ferroelectric barrier may provide a new degree of freedom in magnetoelectronic devices. This talk will address the physics of FTJs and MFTJs based on our recent model and first-principles calculations. [1] E. Y. Tsymbal and H. Kohlstedt, Tunneling across a ferroelectric, Science 313, 181 (2006).[2] M. Y. Zhuravlev, R. F. Sabirianov, S. S. Jaswal, and E. Y. Tsymbal, Giant electroresistance in ferroelectric tunnel junctions, Phys. Rev. Lett. 94, 246802 (2005).[3] M. Y. Zhuravlev, S. S. Jaswal, E. Y. Tsymbal, and R. F. Sabirianov, Ferroelectric switch for spin injection, Appl. Phys. Lett. 87, 222114 (2005).
10:30 AM - J6.2
Spin-dependent Tunneling in a Semi-metal Inserted Magnetic Tunnel Junction.
Kyoung-il Lee 1 , Kiyoung Lee 1 , Joonyeon Chang 2 , Suk-hee Han 2 , Kyung-Ho Shin 2 , Mark Johnson 3 , Wooyoung Lee 1
1 Department of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of), 2 Nano Device Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 3 , Naval Research Center, Washington, District of Columbia, United States
Show Abstract10:45 AM - J6.3
Ballistic Anisotropic Magnetoresistance Measurements of Electrodeposited Co Nanocontacts.
Chunjuan Zhang 1 2 , Andrei Sokolov 2 3 , Evgeny Tsymbal 2 3 , Jody Redepenning 1 2 , Bernard Doudin 4
1 Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 3 Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 4 Institut de Physique et de Chimie des Matériaux de Strasbourg (IPCMS), Université Louis Pasteur, Strasbourg France
Show AbstractAs the dimension of a metallic conductor is reduced to the scale of electron mean free pass so that conduction electrons pass without scattering, electric transport becomes ballistic. This behaviour ultimately leads to conductance quantization, revealing a quantum-mechanical nature of electrons. In ballistic ferromagnetic metal conductors, properties of electrons such as their wavelength depend on their spin angular momentum, which results in spin-dependent conductance quantization and leads to unusual magnetoresistive phenomena. One of them is ballistic anisotropic magnetoresistance (BAMR), a quantized change in the ballistic conductance according to the direction of magnetization. Here we report the first observation of BAMR in Co electrodeposited nanocontacts by in-situ investigation of their spin-dependent transport properties. By measuring the conductance as a function of the applied magnetic field direction at saturation, we find the step-wise variation of the ballistic conductance, signature of the BAMR effect. Our results show that BAMR can be positive and negative, and exhibits symmetric and asymmetric angular dependences, consistent with our theoretical predictions. The observed magnetoresistance phenomenon may be appealing for the future generation of electronic devices, such as quantum switches and logic circuits, adding the possibility to control the quantized conductance by applied magnetic fields.
11:30 AM - J6.4
First Principles Modelling of the Electrical Properties of Emerging Nanoscale Devices.
Kurt Stokbro 1
1 , Atomistix, Palo Alto, California, United States
Show AbstractWhen the minimum feature size of electronic devices are approaching the atomic scale it is necessary to take into account the quantum nature of electrons. This means that the local chemistry of the device plays an important role for determining the device properties. In this talk I will describe quantum mechanical calculations of nanoscale devices, based on Density Functional Theory (DFT) coupled with the Non Equilibrium Green’s Function (NEGF) method as implemented in the Atomistix Tool Kit (ATK) from Atomistix. The background of the theory will be presented as well as the limitations and future extensions.The insight that can be gained by quantum modelling of nanoscale devices will be illustrated through results for the spin-dependent transport in 1-D graphene sheets, and across interfaces between different magnetic materials.
11:45 AM - J6.5
Spin Wave Based Logic Circuits
Alexander Khitun 1 , Mingqiang Bao 1 , Joo-Young Lee 1 , Kang Wang 1 , Dok Won Lee 2 , Shan Wang 2
1 Electrical Engineering, UCLA, Los Angeles, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show Abstract We investigate spin wave propagation and interference in conducting ferromagnetic nanostructures for potential application in spin wave based logic circuits. The novelty of this approach is that information transmission is accomplished without charge transfer. A bit of information is encoded into the phase of spin wave propagating in a nanometer thick ferromagnetic film. A set of “AND”, “NOR”, and “NOT” logic gates can be realized in one device structure by utilizing the effect of spin wave superposition. We present experimental data on spin wave transport in 100nm CoFe films at room temperature obtained by the propagation spin wave spectroscopy technique. Spin wave transport has been studied in the frequency range from 0.5 GHz to 6.0 GHz under different configurations of the external magnetic field. Both phase and amplitude of the spin wave signal are sensitive to the external magnetic field showing 4dB/20G and 60Deg/10G modulation rates, respectively. The performance of logic circuits is illustrated by numerical modeling based on the obtained experimental data. Potentially, spin wave based logic circuits may compete with traditional electron-based ones in terms of logic functionality and power consumption. The shortcomings of the spin wave based circuits are discussed.
12:00 PM - J6.6
Permanent-Magnet Free Biasing of MR Sensors with Tunable Sensitiviyy
Sean Halloran 1 , Fabio daSilva 1 2 , David Pappas 1
1 Magnetic Sensors, National Institute of Standards and Technonogy, Boulder, Colorado, United States, 2 Physics, University of Colorado at Denver and Health Sciences Center, Denver, Colorado, United States
Show Abstract Exchange coupling between ferromagnetic (FM) and antiferromagnetic (AF) films has been observed across Ru spacer layers. The coupling strength was found to be a function of the thickness of the buffer layer.2,3,4 In this work, we have exploited this coupling to stabilize the magnetization and tailor the magnetic gain of the sensor for a wide range of applications. Because the structure is deposited as a single stack, it significantly reduces the number of patterning steps relative to a permanent magnet biased scheme. Ruthenium (Ru) is used as the coupling layer and is self aligned with the FM and IrMn AF pinning layer. The Ru thickness is varied to change the slope of the transfer curve, i.e. the sensitivity. Sensor devices are fabricated using DC magnetron sputtering and a lift-off photoresist. The sensors have a bipolar output, a medium to high (tunable) field sensitivity, and a wide dynamic range. The results show that this biasing scheme is well suited for barber pole and soft adjacent layer (SAL) based sensors. We demonstrate an application of these sensors in a 256 channel read head used for forensic imaging of magnetic tape media.2. W.H. Meiklejohn and C.P. Bean, Phys. Rev. 102, 1413 1956; 105, 904, 1957.3. L. Thomas, A.J. Kellock and S.S.P. Parkin, J. Appl. Phys. 87 (9), 5061, 1 May 2000.4. D. Wang, J. Daughton, C. Nordman, P. Eames and J. Fink, J. Appl. Phys. 99, 2006.
12:15 PM - J6.7
Focused Ion Beam Structured Co/Pt Multilayers for Field-coupled Magnetic Somputing.
Markus Becherer 1 , Gyorgy Csaba 2 , Rainer Emling 1 , Lili Ji 3 , Wolfgang Porod 3 , Paolo Lugli 2 , Doris Schmitt-Landsiedel 1
1 Institute for Technical Electronics, Technical University Munich, Munich Germany, 2 Institute for Nanoelectronics, Technical University Munich, Munich Germany, 3 Department of Electrical Engineering, Center for Nanoscience and Technology, University of Notre Dame, South Bend, Indiana, United States
Show Abstract12:30 PM - J6.8
Integrating Inductors with Magnetic Materials
Don Gardner 1 , Gerhard Schrom 2 , Peter Hazucha 2 , Fabrice Paillet 2 , Tanay Karnik 2 , Shekhar Borkar 2
1 CRL, Intel Labs, Intel Corp., Santa Clara, California, United States, 2 CRL, Intel Labs, Intel Corp., Hillsboro, Oregon, United States
Show Abstract The integration of on-chip inductors with magnetic materials into silicon process technology has been a major challenge in the move towards monolithic solutions for wireless microelectronics, power delivery, and EMI noise reduction. Although software simulation of inductors using two layers of magnetic material have been suggesting that very large increases in inductance are possible, it has proven to be difficult to achieve. On-chip inductors with 2 levels of amorphous CoZrTa were integrated into an advanced 130 nm CMOS process to obtain over an order of magnitude (19×) increase in inductance and Q-factor, significantly greater than prior values of ≤2.3× for on-chip inductors. The magnetic material operates at frequencies up to and beyond 6.4 GHz for 1 nH inductors. The spirals are elongated to take advantage of the uniaxial magnetic anisotropy of the film. Magnetic vias are incorporated into the design to complete the path for the magnetic flux. With such improvements, the effects of eddy currents, skin effect, and proximity effect become clearly visible at high frequencies. Many materials science challenges had to be overcome to integrate magnetic materials into a microelectronics process. High-temperature stability (>250 °C) was one challenge to make the magnetic material compatible with Si technology. It was examined using X-ray diffraction, TEM, and measurement of the magnetic moment as a function of temperature and time. The coercivity and saturation magnetization of the magnetic material are also important because they will determine the hysteretic losses and maximum current. B-H magnetic hysteresis loops and the permeability versus applied magnetic field were measured to study the saturation magnetization and hysteretic losses. The CoZrTa alloy exhibits an extremely small coercivity of 0.015 Oe thereby minimizing hysteretic losses, a relatively high saturation magnetization of 15 kG, and a high resistivity of 100 μΩ-cm that will reduce eddy current dampening. The small-signal permeability as a function of frequency up to 3 GHz was also modeled and measured as a function of film thickness. The analytical model demonstrates that skin effect and eddy current dampening become significant for films thicker than 0.1 μm thick and that laminations are necessary. Analytical modeling demonstrated that laminations can be used to increase the maximum quality factor and high-frequency inductance. Laminations were fabricated by alternately depositing layers of CoZrTa followed by exposure to an oxidizing ambient to form Co oxide that can be easily etched. In measurements of inductors using a 0.5 μm thick magnetic film composed of five 0.1 μm laminations, the rolloff frequency was increased from 300 MHz to 800 MHz. Depending on the application and the frequency of operation, laminations, patterned slots in the magnetic films, and high resistivity may be needed to control eddy current dampening and skin effect.
12:45 PM - J6.9
Thermally Activated Martensitic Transformation in Ferromagnetic Shape-Memory Alloy Ni-Mn-Ga Thin Films
Michael Hagler 1 , Markus Chmielus 1 , Volodymyr Chernenko 2 , Makoto Ohtsuka 3 , Peter Mullner 1
1 Materials Science and Engineering, Boise State University, Boise, Idaho, United States, 2 , Institute of Magnetism, Kiev Ukraine, 3 IMRAM, Tohoku University, Sendai Japan
Show AbstractNi-Mn-Ga ferromagnetic shape memory alloys (FSMA) tend to undergo a deformation upon the application of a magnetic field. The strain is attributed to twin boundary motion in the martensitic phases of Ni2MnGa and to the martensitic transformation itself. In an effort to harness the shape memory effect for use in sensors, actuators, and micro-devices, the behavior of Ni-Mn-Ga thin films is attracting attention. Substrate curvature measurements which yield the in-plane film stress were done with Ni-Mn-Ga films on Silicon substrates in the temperature range between room temperature and 60°C. The film thickness was varied between 0.1 μm and 3 μm. During the wafer bow curvature measurements, stress levels of 1.2 GPa were attained. A temperature dependence of the martensitic phase transformation was observed, which is attributed to the constraints imposed on the film by the substrate. The transformation rate follows an Arrhenius law with the activation energy of 0.8eV.
J7/I9: Joint Session: MRAM Materials and Devices
Session Chairs
Thursday PM, April 12, 2007
Room 3006 (Moscone West)
2:30 PM - **J7.1/I9.1
Advancements In Writing Technology For Dense MRAM
Hiroaki Yoda 1
1 R&D center, Toshiba, Kawasaki Japan
Show AbstractA room temperature TMR discovery made reading signal quite large. MgO barrier made scalability regarding reading easy. However, write selectivity and large write current have been the two major issues. In this paper, write technologies are reviewed and MRAM scalability is discussed.Designs to open the window,called a disturb-robust design have been a main topic.A first disturb-robust design called “toggle switching” was demonstrated in 4Mbit MRAM. In this design, a synthetic storage layer made of anti-ferromagnetic coupled magnets was used and a write sequence was properly set.The window was quite large and solved the first issue. To lower the current while keeping the window open, a synthetic layer made of four magnets and interlayers was proposed. The film growth is the point and is under development.Another disturb robust design using unique MTJ shape was proposed. At a selected state, the magnetization rotates coherently. At a half-selected state, the two curving magnetization configuration is formed in storage layer which resists switching. Then,the window was enlarged. The shape was optimized to have fabrication friendliness. The resultant shape is called “propeller shape". Chip yield of diagnostic arrays with one million MTJs was over 50% and the design was proved. This design led to another success of 16Mbit MRAM demonstration with 1.8V voltage supply and 42.3% array efficiency. The design also lowered the current to 4mA. Another disturb robust design was proposed in which both synthetic storage layer with unbalanced magnets and unique shape were used. This design has borderless write window along word line current. Optimization of the parameter is under development.Another important technology for writing is an electromagnet wire. To enhance the field, soft magnet covers a metal wire on its three sides except the side facing MTJs. An advanced proces technology was developed to make the magnet protrude to right beside the MTJs. At 90 nm node, 4mA write current can generates magnetic field of about 60-100 Oe or larger. Even toough the switching fields are increased to assure the non-volatility of small MTJs, the increase in available field compensates. These write technologies are believed to push MRAM to scale to 256Mbit.Recently, new write principle called spin momentum transfer was demonstrated. The spin polarized current flips the storage magnet. This new principle realizes the potential cell size of 6F^2 if the threshold current density is reduced to 5-10 x10-5 A/cm^2. Summary:There were great advancements in write technology just in three years. These advancements realized 4Mbit and 16Mbit MRAM chip demonstrations and are thought to extend MRAM scalability to 256Mbit. Write efficiency improvements extend the scalability further.ACKNOWLEDGMENT:The authors would like to acknowledge NEDO and NEC for supports and discussions.
3:00 PM - **J7.2/I9.2
Materials and Device Technology of Toggle Magnetic Random Access Memory.
Jason Janesky 1 , N. Rizzo 1 , M. Deherrera 1 , K. Smith 1 , K. Nagel 1 , M. Martin 1 , J. Craigo 1 , J. Sun 1 , J. Slaughter 1 , B. Engel 1 , G. Grynkewich 1 , M. Durlam 1
1 Technology Solutions Organization, Freescale Semiconductor, Chandler, Arizona, United States
Show Abstract3:30 PM - J7.3/I9.3
Thermally Stable and Scalable Magnetic Structure for High Density Magnetic Random Access Memory
Hao Meng 1 , Jian-Ping Wang 1
1 Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States
Show Abstract3:45 PM - J7.4/I9.4
Electrical Study of Ferromagnet Metal Gate MOS Diode: Towards a Magnetic Memory Cell Integrated on Silicon.
Mehdi Kanoun 1 , Rabia Benabderrahmane 1 , Christophe Duluard 1 , Bsiesy Ahmad 1 2 , Claire Baraduc 1 , Nicolas Bruyant 1 , Herve Achard 3 , Antoine Filipe 4
1 SPINTEC, CEA, Grenoble France, 2 , Université Joseph fourrier, Grenoble France, 3 , CEA/LETI, Grenoble France, 4 , Spintron, Marseille France
Show Abstract4:30 PM - **J7.5/I9.5
Manipulating Nanomagnets Using Spin-Transfer Torques.
Dan Ralph 1
1 Physics Department, Cornell University, Ithaca, New York, United States
Show AbstractWhen a spin-polarized current interacts with a magnet, it can transfer spin angular momentum to the magnet and thereby apply a torque. This spin-transfer effect can be used to manipulate the magnetic-moment direction of small magnets much more efficiently than using magnetic fields, so that the mechanism is under investigation to see whether it might provide improved performance for the writing process in magnetic random access memories (MRAM). To enable this application of spin transfer, it will be important both to minimize the current levels needed to produce magnetic switching and and also to understand how the nanomagnet responds to a spin transfer torque so as to make the switching process reproducible.I will describe development of experimental techniques that have allowed us to probe the detailed magnetic dynamics that result from spin-transfer torques in magnetic tunnel junctions and spin-valve devices. We find that spin transfer from a DC current can be used either to produce magnetic reversal between static states or to excite steady-state precessional modes. Time-domain measurements using current pulses show that the switching time as a function of current amplitude follows the form expected from the conservation of angular momentum, and switching times less than 1 ns can be achieved. In the regime of steady-state precession driven by a DC current, we have achieved linewidths comparable to 1 part in 2000 of the precession frequency for nanopillar-shaped devices. We have also used spin-transfer from an AC current, and from combinations of AC and DC currents, to perform ferromagnetic resonance (FMR) measurements of single nanomagnets in magnetic tunnel junctions and spin valves. This enables a detailed characterization of both the fundamental normal mode for precession and higher-order more spatially-nonuniform modes in individual magnetic devices. An analysis of spin-transfer FMR lineshapes provides information about the mechanism behind the spin-transfer torque, and a direct measurement of the damping in a single nanomagnet. I will close by summarizing progress at Cornell in developing spin-transfer devices suitable for non-volatile MRAM elements and also for frequency-tunable nanoscale microwave oscillators.
5:00 PM - J7.6/I9.6
Low-RA MgO Tunnel Junctions for SMT- MRAM
Renu Dave 1 , P. Mather 1 , F. Mancoff 1 , N. Rizzo 1 , B. Butcher 1 , J. Slaughter 1
1 , Freescale Semiconductor, Inc, Chandler, Arizona, United States
Show AbstractSpin momentum transfer (SMT) switching is a candidate programming method that may enable higher density and lower power operation for future magnetic random access memory (MRAM). SMT switching employs a current passing directly through the magnetic tunnel junction (MTJ) bits with a current density high enough for the torque from the spin-polarized tunneling current to switch the free layer. SMT-MRAM requires MTJ material with higher magnetoresistance ratio (MR) and lower resistance than used in the field-switched MRAM currently in production. Here, we report several key properties of high-quality MTJ material and devices with low-RA MgO tunnel barriers. Different oxidation processes were evaluated to fabricate the tunnel junctions with RA in the range of 2-50 Ω-μm2 , including: plasma oxidation, radical oxidation, and natural oxidation of thin Mg layers. A comparison of MTJ material attributes will be given for different oxidation processes, including: MR, RA range, breakdown voltages (Vbd), and the fitted electrical barrier height and width. We also measured the physical barrier width using a novel x-ray reflectivity (XRR) technique and compare it to the electrical barrier width parameter for MgO barriers made with different processes. Surprisingly, the XRR results show an expansion of the layer upon oxidation of metallic Mg, rather than contraction as predicted by bulk density calculations. Expansion factors in the range of 1.06 to 1.17 were measured for different MgO processes. MTJ devices were fabricated on 200 mm Si wafers using optical lithography to form bits with sizes as small as 100 nm X 200 nm. Low-bias MR values upto 120% were obtained in patterned bits with CoFeB free layers with RA~7 Ω-μm2. Quasistatic critical currents of 0.8 mA (5x106 A/cm2) were obtained with thermally-stable bits having a thermal energy barrier of 45kT, corresponding to a zero-temperature critical current density of 1x107 A/cm2.
5:15 PM - J7.7/I9.7
Interfacial Oxide and Barrier Engineering in MgO Based Magnetic Tunnel Junctions.
John Read 1 , Phillip Mather 2 , Robert Buhrman 1
1 , Cornell University, Ithaca, New York, United States, 2 , Freescale Semiconductor, Inc., Chandler, Arizona, United States
Show Abstract5:30 PM - J7.8/I9.8
Defect-Mediated Properties of Magnetic Tunnel Junctions.
Julian Velev 1 , Kirill Belashchenko 1 , Sitaram Jaswal 1 , Evgeny Tsymbal 1
1 Department of Physics, University of Nebraska, Lincoln, Nebraska, United States
Show AbstractMagnetic tunnel junctions (MTJs) have recently attracted considerable interest due to their potential applications in magnetic field sensors and non-volatile magnetic random access memories. Defects play an important role in the properties of metal oxides which are currently used as barrier layers in MTJs. However, so far first-principles models of MTJs have mostly been limited to ideal MTJs. In this work we study the effect of O vacancies on the interlayer exchange coupling (IEC) and tunneling magnetoresistance (TMR) in Fe/MgO/Fe tunnel junctions. First-principles calculations based on density functional theory show that the presence of neutral O vacancies (F centers) affect significantly the IEC. We find that resonant tunneling through the F centers makes the IEC antiferromagnetic for thin barriers but with increasing MgO thickness the resonance contribution to IEC is reduced resulting in the ferromagnetic coupling typical for perfect MgO barriers. This behavior is consistent with the available experimental data. Also we demonstrate that O vacancies have a profound effect on TMR. F centers produce occupied localized s states and unoccupied resonant p states in the gap of MgO. We demonstrate that F centers affect the conductance by either resonant transmission or non-resonant scattering of tunneling electrons both causing a substantial reduction of TMR as compared to the ideal MTJs. These results are important for the understanding of the physical mechanisms responsible for IEC and TMR in industrially-important MTJs. Supported by NSF-MRSEC.
5:45 PM - J7.9/I9.9
Magnetic Junctions Exhibiting Spin Filter and Magnetic Tunnel Junction Behavior as a Function of Temperature.
Brittany Nelson-Cheeseman 1 , Rajesh Chopdekar 2 1 , Joanna Bettinger 1 , Yayoi Takamura 1 , Elke Arenholz 3 , Yuri Suzuki 1
1 Materials Science and Engineering, University of California - Berkeley, Berkeley, California, United States, 2 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 3 , Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractJ8: Poster Session: Magnetic Nanostructures and Devices II
Session Chairs
Friday AM, April 13, 2007
Salon Level (Marriott)
9:00 PM - J8.1
Photodynamic Effect of 5-aminolevulinic Acid-adsorbed Superparamagnetic Nanoparticles with PEG and Lecithin Interlayer.
Sang-Im Park 1 3 , Jong-Hwan Lim 2 , Jong-Hee Kim 3 , Cheol-Gi Kim 1 3 , Chong-Oh Kim 1 3
1 Materials Science and Eng., Chungnam National University, Daejeon Korea (the Republic of), 3 Research Center for Advanced Magnetic Materials, Chungnam National University, Daejeon Korea (the Republic of), 2 Division of veterinary pharmacology and toxicology, Chungnam National University, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - J8.10
Synthesis and Characterization of Nd-Fe-B Based Alloy by Reduction Diffusion
Chang Woo Kim 1 , Young Hwan Kim 1 , Hyun Gil Cha 1 , Young Soo Kang 1
1 Chemistry, Pukyong National Univ., Pusan Korea (the Republic of)
Show Abstract9:00 PM - J8.11
Effects of Additives on Hydrogen Absorption and Desorption Characteristics of Nd(Fe,Mo)12 Alloys.
Jingzhi Han 1 , Shunquan Liu 1 , Changsheng Wang 1 , Honglin Du 1 , Haiying Chen 1 , Yingchang Yang 1
1 School of Physics, Peking University, Beijing China
Show Abstract9:00 PM - J8.12
Synthesis and Investigation of SmCo5 Magnetic Nanoparticles
Yan Li 1 , Xiao Li Zhang 1 , Ru Qiao 1 , Ri Qiu 1 , Young Soo Kang 1
1 Chemistry, Pukyong National Univ., Pusan Korea (the Republic of)
Show Abstract9:00 PM - J8.14
Magnetorheological Fluids and Applilcations.
Tianbao Xie 1
1 Physics, Linfield College, McMinnville, Oregon, United States
Show Abstract9:00 PM - J8.15
Properties of Carbon Nanotube Polymer Composites in a Magnetic Field.
Erin Camponeschi 1 , Richard Vance 2 , Hamid Garmestani 1 , Rina Tannenbaum 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Engineering, Washington State University, Pulman, Washington, United States
Show Abstract9:00 PM - J8.16
Diamagnetic Levitation for Passive Tilt Sensors.
Martin Winistoerfer 1 , Lihong (Heidi) Jiao 1
1 School of Engineering, Grand Valley State University, Grand Rapids, Michigan, United States
Show Abstract9:00 PM - J8.17
Analysis Interaction Field Strength and Spectrum from Microhysteresis Loops.
Lin-Xiu Ye 1 , Jia-Mou Lee 1 2 , Juhng-Perng Su 1 2 , Te-ho Wu 1 2
1 Taiwan SPIN Research Center, Nat'l Yunlin Univ. of Science and Technology, Douliou Taiwan, 2 Graduate school of Engineering Science and Technology, Nat'l Yunlin Univ. of Science and Technology, Douliou Taiwan
Show Abstract9:00 PM - J8.2
Characteristics of Lecithin-adsorbed Magnetic Nanoparticle and Biocompatibility of its Fluid.
Sang-Im Park 1 3 , Jong-Hwan Lim 2 , Jong-Hee Kim 3 , CheolGi Kim 1 3 , Chong-Oh Kim 1 3
1 Materials Science and Eng., Chungnam National University, Daejeon Korea (the Republic of), 3 Research Center for Advanced Magnetic Materials, Chungnam National University, Daejeon Korea (the Republic of), 2 Div. of Veterinary Pharmacology and Toxicology, Chungnam National University, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - J8.3
Effect of Doxorubicin-conjugate Magnetite Nanoparticle for Biomedicine: Cytotoxicity Studies.
Sang-Im Park 1 3 , Jong-Hwan Lim 2 , Jong-Hee Kim 3 , CheolGi Kim 1 3 , Chong-Oh Kim 1 3
1 Materials Science and Eng., Chungnam National University, Daejeon Korea (the Republic of), 3 , Research Center for Advanced Magnetic Materials, Daejeon Korea (the Republic of), 2 Div. of Veterinary Pharmacology and Toxicology, Chungnam National University, Daejeon Korea (the Republic of)
Show Abstract9:00 PM - J8.4
Proliferation and Alignment of Osteoblasts (MC3T3) on Oriented Magnetic Nano-Composites
Hilana Lewkowitz-Shpuntoff 1 2 , Nicole Brenner 1 , Mary Wen 1 , Nadine Pernodet 1 , Miriam Rafailovich 1
1 , Stony Brook University, Stonybrook, New York, United States, 2 , Princeton University, Princeton, New Jersey, United States
Show Abstract9:00 PM - J8.5
Preparation of Magnetite Nanoparticles by Thermal Decomposition of Hematite Powder in the Presence of Organic Solvent
Chun-Rong Lin 1 , Ray-Kuang Chiang 2 , Chih-Jung Chen 3 , Hsin-Yi Lai 3 , Igor S. Lyubutin 4 , Egor A. Alkaev 4
1 Department of Mechanical Engineering, Southern Taiwan University of Technology, Tainan Taiwan, 2 Department of Electronic Materials, Far East University, Tainan Taiwan, 3 Department of Mechanical Engineering, National Cheng Kung University, Tainan Taiwan, 4 Institute of Crystallography, Russian Academy of Sciences, Moscow Russian Federation
Show AbstractMagnetite (Fe3O4) is the focus of a great deal of recent research because of its numerous potential applications in various areas such as magnetic recording media, GMR sensors, sealing, photonic crystals and biotechnology [1, 2]. Synthesis of magnetite powders using pure hematite (α-Fe2O3) has been studied for a long time and was found to be induced by either reduction of hematite by CO/CO2 or H2 [3] or magnetomechanical activation [4]. In this paper, magnetite nanoparticles were successfully prepared using thermal decomposition of hematite (α-Fe2O3) powder in the presence of high boiling point solvent. The 6 mmol of α-Fe2O3 fine powder (~150nm) and 36 mL of 1-octadecene solvent were added into a three-necked bottle, and purged with N2 for inhibiting the effect of oxygen. The mixture was then heated under stirring to reaction temperature 320 °C and kept at this temperature for the desired time (~2 to 28 hrs). The influence of the reaction time on transformation process was analyzed with X-ray diffraction (XRD), Mössbauer spectroscopy (MS), and magnetic measurements. XRD patterns show that the phase of intermediate was composed of spinel and corundum phase (α-Fe2O3). The 57Fe Mössbauer spectra were recorded at temperatures 80 - 300 K. The room temperature spectrum of magnetite (spinel phase) shows that the ratio SB/SA areas for octahedral B and tetrahedral A sites is close to 2 which indicates the stoichiometric composition (Fe3+)tet[Fe2+Fe3+]octO4 of the magnetite particles. The structure transformation proportion of Fe3O4 to α-Fe2O3 strongly depends on reaction times. After reflux for 28 hrs the hematite-magnetite transformation was complete. The mean crystallite size of pure phase of Fe3O4 particles is about 40 nm. The saturation magnetization increases with the reaction time, which corresponds to an increase of Fe3O4 in the samples. For pure phase of Fe3O4, the temperature dependence of the coercivity, remanence, as well as the magnetization all shows an abrupt change near 125 K, and the Verwey transition temperature was found at 125 K. The hyperfine parameters of Mössbauer spectrum measured at low temperature also indicate that the Verwey phase transition occurs. In other words, the Verwey transition is an indication that the magnetite particles exactly grew up in the synthesized compounds. However, the Verwey transition is significantly broadened and occurs at a lower temperature as the concentration of α-Fe2O3 increased. This thermal decomposition process provided a method to prepare pure Fe3O4 as well as Fe3O4/α-Fe2O3 nanocomposites useful for various magnetic applications.References[1] X. Batlle and A. Labarta, J. Phys. D: Appl. Phys. 35, R15 (2002).[2] Q. A. Pankhurst, J. Connolly, S. K. Jones, J. Dobson, J. Phys. D: Appl. Phys. 36, R167 (2003).[3] A. Pineau, N. Kanari, I. Gaballah, Thermochim. Acta 447, 89 (2006).[4] W. A. Kaczmarek, B. W. Ninham, IEEE Trans. Magn. 30, 732 (1994).
9:00 PM - J8.6
Preparation and Magnetic Properties of Monodisperse Nanocomposite Hollow Spheres
Chun-Rong Lin 1 , Cheng-Chien Wang 2 , I-Han Chen 2
1 Department of Mechanical Engineering, Southern Taiwan University of Technology, Tainan Taiwan, 2 Department of Chemical Engineering and Material Engineering, Southern Taiwan University of Technology, Tainan Taiwan
Show AbstractHollow spheres, especially for nanometer to micrometer dimensions, represent the special physical and chemical properties which have attracted great attention due to their potential applications [1]. In this article, we present a simple process to prepare the hollow ceramic (CoFe2O4/SiO2) composite nanospheres and hollow alloy (Co33Fe67/SiO2) composite nanospheres.Hollow CoFe2O4/SiO2 composite nanospheres were prepared by calcining polymer/CoFe2O4/SiO2 core/shell composite spheres which were synthesized by the sol-gel method following the chemical co-precipitation. In a typical process, the monodisperse polymer poly(MMA-co-MAA) latex (450 nm) was used as a core template. To create hollow CoFe2O4/SiO2 spherical structures with various sizes of CoFe2O4 nanoparticles, the hybrid PMMA/CoFe2O4/SiO2 core-shell spheres were subsequently calcined in the temperature range from 450 to 900 °C for 4h. On the other hand, the hollow Co33Fe67/SiO2 composite nanospheres were formed by reduction of hollow CoFe2O4/SiO2 nanospheres in a stream of H2/Ar mixed gas at 900 °C for 8 hrs.X-ray diffraction (XRD) pattern shows that the coated phase of the hollow CoFe2O4/SiO2 composite nanospheres has a cubic spinel ferrite structure. The average crystallite sizes of the coated CoFe2O4 nanoparticles, depending on the calcined temperature, are in the range from 2.2 to 10.1 nm. Based on the thermogravimetric analysis (TGA), we found that the content of CoFe2O4 is 73 wt% in the hollow CoFe2O4/SiO2 composite shell. The scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs show that the hollow spheres are uniform. According to the line scanning EDX analysis of the cross section of hollow spheres, the SiO2 is not only coated on the surface of sphere but also distributed over the shell of hollow sphere. The thickness of shell of hollow spheres is about 40 nm. Room temperature magnetic measurement shows that the hollow nanospheres can go from superparamagnetic to ferromagnetic behavior depending on the sizes of CoFe2O4 nanoparticles. The saturation magnetization is clearly decreases as the particle size decreased. In comparison to the bulk value of CoFe2O4 (80 emu /g), the saturation magnetization of the nanoparticles in the shell is about 1.3 to 15 times less.This phenomenon can be interpreted as the effect of surface spin canting when the particle size is reduced.As for the hollow alloy (Co33Fe67/SiO2) composite nanospheres, the magnetic phase has a body-centered cubic structure and an average crystallite size of 28.7 nm. This alloy nanospheres exhibit a ferromagnetic behavior with saturation magnetization of 170 emu/g, coercivity of 250 Oe, and Curie temperature of 968 °C. Due to metallic and ferromagnetic behavior of Co33Fe67 nanoparticles, these hollow spheres can be used as a lightweight electromagnetic wave absorbers [2].References[1] F. Caruso, Adv. Mater. 13 (2001) 11.[2] S. S. Kim et al, J. Magn. Magn. Mater. 271 (2004) 39.
9:00 PM - J8.7
Magneto-transport Properties in La0.75Sr0.25MnO3/CoFe2O4 Multilayer
Lung Jie Hung 1 , Jeng-Hwa Liao 1 , Tai Bor Wu 1
1 Materials Science and Engineering, National Tsing-Hua University, Hsinchu Taiwan
Show Abstract9:00 PM - J8.8
Magnetotransport properties in La0.67Sr0.33MnO3/Pb (Zr0.5Ti0.5)O3/La0.67Sr0.33MnO3 heterostructures
Jeng-Hwa Liao 1
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Taiwan
Show AbstractOver the past few years, doped manganites with the perovskitelike structure RxA1-xMnO3 ( R = rare earth elements and A = alkaline earth elements ) have been extensively investigated due to their colossal magnetoresistance ( CMR ) properties. Several studies of this material are in the form of thin films including multilayer structures, made in a combination among ferromagnetic, antiferromagnetic, and paramagnetic, whose properties are much different from their single layer structures. Recently, materials in which combined ferromagnetism with ferroelectricity were know as multiferroic. These structures offer an opportunity in designing the various novel devices which are uncompleted alone by either ferroelectric or magnetic materials. Here, we have fabricated a triilayers composed of a ferroelectric, namely Pb(Zr0.5Ti0.5)O3 (PZT); and a ferromagnetic, namely La0.75Sr0.25MnO3 (LSMO). The transport properties of LSMO/PZT/LSMO triilayers were characterized with and without applying voltage in order to observe the magneto-electric exchange coupling between the PZT and the LSMO layer.Strained La0.75Sr0.25MnO3/PbZr0.5Ti0.5O3/La0.75Sr0.25MnO3 trilayers were grown on Nb-doped STO (001) single crystal substrates using rf sputtering. Theθ-2θx-ray diffraction (XRD) analyses reveal the growth of c-axis-oriented PZT. The phi scans confirm the epitaxy between the LSMO and PZT layer. The PZT layer was polarized by applying a voltage of 10V. The magnetization measurements were performed with a superconducting quantum interference device (SQUID) magnetometer in zero-field-cooled (ZFC) and field-cooled (FC). The hysteresis loops of all the samples were measured at T =10 K in FC and ZFC. A relationship between the polarization of PZT layer and the interlayer magnetic coupling is discussed.
9:00 PM - J8.9
Magneto-optical Spectroscopy of La(2/3)Sr1/3MnO3 Films Grown by Pulsed Laser Deposition onto (100) and (110) SrTiO3 Substrates.
Martin Veis 1 , Jan Mistrik 2 , Tomuo Yamaguchi 3 , Eva Liskova 1 , Stefan Vsinovsky 1 , Anne-Marie Haghiri-Gosnet 4 , Philippe Lecoeur 4 , Jean-Pierre Renard 4 , Wilfrid Prellier 5 , Bernard Mercey 5
1 , Charles University, Prague Czech Republic, 2 , University Pardubice, Pardubice Czech Republic, 3 , Shizuoka University, Hamamatsu Japan, 4 , Universite Paris XI, Paris France, 5 , CRISMAT-ISMRA, Caen France
Show Abstract
Symposium Organizers
David P. Pappas National Institute of Standards and Technology
Vincent G. Harris Northeastern University
Michael Farle Universitaet Duisburg-Essen
Brad Engel Freescale Semiconductor, Inc.
Dexin Wang Seagate Technology
J9: Surfaces & Spectroscopy
Session Chairs
Friday AM, April 13, 2007
Room 3008 (Moscone West)
9:30 AM - **J9.1
Magnetic Imaging with X-rays and Femtosecond Laser Pulses.
Thomas Eimueller 1
1 Experimental Physics IV, Ruhr-University of Bochum, Bochum Germany
Show AbstractMagnetic storage and memory technology, guided by “smaller and faster”, demands for element selective imaging methods that enable studying magnetization reversal processes on a nanometer length and a picoseconds time scale in a quantitative way. Despite only 13 years old, the field of x-ray magnetic imaging is able to meet these needs. This talk presents synchrotron based imaging techniques that use x-ray magnetic circular dichroism (XMCD), as a large, element-specific magnetic contrast.
Magnetic Transmission X-ray Microscopy (MTXM) allows imaging magnetic domains and magnetization reversal processes in externally applied magnetic fields with a < 20 nm lateral resolution in a quantitative and element-selective way [1] as will be presented at selected samples. Focus will be given on a new class of magnetic material: magnetically coated, self-organized nanospheres, which are promising for building large-scale patterned media. The geometrical film thickness variation can be used to induce a spin-reorientation transition (SRT) at the surface of the spheres.
A different, heat induced SRT demonstrates both the technique of Photoemission Electron Microscopy (X-PEEM) and time resolved magnetic imaging using optical excitation with femtosecond laser pulses. Interestingly, a slow recovery of the original anisotropy has been found in an Fe/Gd multilayer, possibly connected with the small anisotropy of this system. The time resolution of these synchrotron experiments is limited by the pulse width and the jitter of the X-ray pulses to about 100 ps.
[1] T. Eimüller, P. Fischer P., M. Köhler, M. Scholz, P. Guttmann, G. Denbeaux, S. Glück, G. Bayreuther, G. Schmahl, D. Attwood, G. Schütz, Appl. Phys. A 73, 697-701 (2001)
10:00 AM - J9.2
Anisotropic X-ray Magnetic Linear Dichroism at the Fe L2,3 Edges in Fe3O4 Thin Films and Other Systems.
Elke Arenholz 1 , Gerrit van der Laan 2
1 ALS, LBNL, Berkeley, California, United States, 2 Magnetic Spectroscopy Group, Daresbury Laboratory, Warrington WA4 4AD United Kingdom
Show Abstract10:15 AM - J9.3
Consecutive Spin-Reorientation Transitions Induced by Noble-Metal Capping of Ultrathin Magnetic Films
Farid El Gabaly 1 , Kevin McCarty 2 , Andreas Schmid 3 , Juan de la Figuera 1
1 Dpt. de Fisica de la Materia Condensada and Centro de Microanálisis de Materiales, Universidad Autonoma de Madrid, Madrid, Madrid, Spain, 2 , Sandia National Laboratories, Livermore, California, United States, 3 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe magnetic anisotropy can be significantly modified at surfaces and interfaces of ultrathin metallic films. These effects lead to a rich variety of new phenomena that are currently applied in the design of magnetic nanodevices. To properly understand these effects, it is desirable to grow layers that are essentially perfect on the atomic scale, and to characterize them on a local scale. Spin polarized electron microscopy is a technique that allows for real-time, real-space determination of the magnetization on the nanometer scale, even during growth experiments.In bare cobalt on Ru(0001) films, we have previously observed thickness-dependent spin reorientation transitions where the magnetization direction in remanence turns from lying within the film plane to an out-of-plane orientation and back into the plane. The transitions occur in consecutive thickness of one, two and three atomic layers. Bare Co/Ru(0001) films with 3 ML or greater thickness are always magnetized in-plane.Noble metal capping layers on magnetic films are also known to modify the properties of the underlying magnetic films. For example, it has been observed that magnetic anisotropy can change as a function of overlayer thickness. We present in this work in-situ, microscopic observations of the anisotropy changes induced by noble-metal (Cu, Ag, and Au) capping layers. Even 1 or 2 atomic layers of the noble metal have a dramatic effect on the magnetization -- for example, in in-plane magnetized Co films with thickness of 3 ML or more, the magnetization can be rotated to the out-of-plane direction and back into the in-plane direction by depositing noble-metal capping layers which differ in thickness in one atomic layer.
10:30 AM - J9.4
HRTEM and EELS Studies of Py/Al and Co/Al Multilayers.
Jiaming Zhang 1 , M. Crimp 1 , N. Theodoropoulou 2 , A. Sharma 2 , T. Haillard 2 , R. Loloee 2 , W. Pratt 2 , J. Bass 2
1 Department of Chemical Engineering and Materials Science, Michigan State University, East lansing, Michigan, United States, 2 Department of Physics and Astronomy, Michigan State University, East lansing, Michigan, United States
Show AbstractFerromagnetic/Non-magnetic (F/N) metallic multilayers measured in the current-perpendicular-to-plane (CPP) geometry show giant magnetoresistance (MR) and are promising candidates for use in future high density storage devices. F/Al interfaces were recently shown to have large interface specific resistances, which can enhance the CPP-resistance. But the CPP resistances and MRs showed some instability over time at room temperature and upon annealing to 450K. To help understand the sources of both the large interface specific resistances and their apparent instabilities, we have undertaken cross-sectional high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) studies of both as-sputtered and annealed Py/Al and Co/Al multilayers. We find well-layered, but rough structures, with interfaces within columnar grains being tilted up to ~15°from the normal to the growth direction. HRTEM images appear to show diffused interfaces, but a through-focus series of images suggests considerable grain overlap in the electron beam direction, thereby complicating interpretation. A combination of HRTEM imaging and EELS analysis suggests that any interfacial mixing is limited in scale, and shows no evidence of intermetallic compound formation.
11:15 AM - **J9.5
Interaction of Electrons, Magnons, and Phonons in the Femtosecond Regime: Pump-Probe Experiments on the Gd(0001) Surface.
Uwe Bovensiepen 1
1 Physics Department, Freie Universität Berlin, Berlin Germany
Show AbstractThe dynamics of collective excitations of electrons, phonons, and spins are of fundamental interest to develop a microscopic understanding of interactions among elementary excitations and of the respective relaxation mechanisms. Potentially, such an insight facilitates new applications in data processing and storage technology. The present work employs pump-probe investigations on the femto- and picosecond timescale to study the ultrafast dynamics of electrons, spin-waves, and phonons after intense optical excitation. The Gd(0001) surface which serves as a model system for a low dimensional ferromagnet is investigated by complementary time-resolved techniques, photoelectron spectroscopy and linear / non-linear optical spectroscopy. The energy relaxation of hot electrons is analyzed by transient changes of the binding energy and the line width of the occupied component of the 5dz2 surface state and by changes of the electron distribution function around the Fermi level. In combination with a simplified description by the two-temperature model this analysis characterizes the optically excited state quantitatively. We analyze the mechanism that leads to a drop in spin polarization upon optical excitation, which is observed in non-linear magnetooptics. Since the exchange splitting of the surface state, analyzed by time-resolved photoemission, is not affected under these non-equilibrium conditions, we propose spin-flip scattering of hot electrons to be responsible. In addition, the Gd(0001) surface presents a previously unknown coupled phonon-magnon mode, which can be excited by femtosecond laser pulses. Time-resolved detection of the optical second harmonic yield separates spin dynamics from electron and lattice contributions by the symmetry with respect to magnetization reversal. A coherent phonon-magnon mode at 3 THz which is driven by electronic excitations of surface and bulk states has been observed. Time-resolved photoemission provides information on the interaction mechanism. We find that the binding energy of the surface state oscillates at the same frequency which suggests a phonon-magnon coupling due to modulation of the exchange splitting or due to spin-flip scattering, contrary to the conventional type mediated by spin-orbit interaction. Calculations of the surface state binding energy upon lattice contraction by density functional theory show that the exchange splitting is not affected by the lattice contraction. This favors spin-flip scattering over a dynamical change of exchange splitting to mediate the coupled coherent excitation of the phonon and magnon subsystems.Collaboration with G. Bihlmayer and S. Blügel from the research center in Jülich, Germany and funding by the Deutsche Forschungsgemeinschaft through SPP 1133 is gratefully acknowledged.
11:45 AM - J9.6
Thermal Stability of Fe Monolayers on GaAs(001): Morphology and Magnetism
Khalil Zakeri-Lori 1 , Christian Urban 2 , Ulrich Koehler 2 , Thomas Kebe 1 , Juergen Lindner 1 , Michael Farle 1
1 Fachbereich Physik, Experimentalphysik-AG Farle, Universität Duisburg-Essen, Duisburg Germany, 2 Institut für Experimentalphysik IV / AG Oberflächen, Ruhr Universität Bochum, Bochum Germany
Show Abstract12:00 PM - J9.7
Magnetic and Optical Properties of Composite Noble-metal-ferromagnetic Metal Thin Films.
R. Alejandra Lukaszew 1 , Jonathan Skuza 1 , Michelle Sestak 1
1 Physics and Astronomy, University of Toledo, Toledo, Ohio, United States
Show Abstract12:15 PM - J9.8
Magnetic Properties of NiO Clusters.
Yuan Ping Feng 1 , Guowen Peng 1 , Rongqin Wu 1 , Jun Ding 2 , Yoshiyuki Kawazoe 3
1 Department of Physics, National University of Singapore, Singapore Singapore, 2 Department of Materials Science and Engineering, National University of Singapore, Singapore Singapore, 3 Institute of Materials Research, Tohoku University, Sendai Japan
Show AbstractEven though NiO is anti-ferromagnetic, recent experimental studies indicated that nanocrystalline NiO could be ferromagnetic. We carried out first-principles electronic structure calculations based on density functional theory and the LDA+U method to investigate structures and magnetic properties of NiO clusters. Our preliminary results indicate that a small NiO cluster prefers anti-ferromagnetic state if the magnetic moments can be compensated. However, this compensation is not always possible, for example at the surfaces and edges of a nanocrystal, which leads to the ferromagnetism observed in experiment.
12:30 PM - J9.9
Synthesis and Characterization of Gd-doped ZnO Nanocrystals.
Rahul Singhal 1 , Adrian Parra 1 , Oscar Perez 2 , Maharaj Tomar 1 , Sandra Dussan 1
1 Physics, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 2 2.Department of General Engineering, Materials Science and Engineering, , University of Puerto Rico, Mayaguez, Puerto Rico, United States
Show AbstractJ10: Nanoengineered Magnetic Media and HDD Storage
Session Chairs
Friday PM, April 13, 2007
Room 2005 (Moscone West)
2:30 PM - **J10.1
Nano-Scale Design of Perpendicular Recording Media
Andreas Berger 1
1 San Jose Research Center, Hitachi Global Storage Technologies, San Jose, California, United States
Show AbstractThe hard disk drive (HDD) industry is presently undergoing a major technical change by implementing what is known as perpendicular recording technology. In this technology, the information is stored as bits into ferromagnetic material that is magnetized perpendicular to the disk plane, in contrast to the previously used longitudinal recording, for which the magnetization is oriented in-plane. This fundamental change has significant advantages, leading to much higher information recording densities and capacities, but also requires a complete overhaul of the HDD component technology, such as recording heads and recording media. In particular, recording media are fundamentally altered due to their changed role in perpendicular recording. They not only serve as the information storage unit as previously in longitudinal recording, but also have an active role in the magnetic recording process itself. Thus, perpendicular media had to be completely redesigned and now contain three key functional layer stacks: the soft-magnetic underlayer that aids the write process by mirror-imaging the actual write head, the exchange break layer that forms a non-magnetic template for the recording layer, and the now perpendicular recording layer itself. To accomplish the successful product implementation of this advanced media structure, many new inventions had to be incorporated into the nano-scale design, and many more are needed and are presently pursued to leverage the full potential of this new HDD recording technology.
3:00 PM - J10.2
Low-Temperature Polyol Synthesis of Nanocrystalline Co and CoPt Alloys.
Rahul Singhal 1 , Erick Pajares 2 , Javier Perez 2 , E. Rodriguez 3 , Oscar Perez 4 , Maharaj Tomar 1
1 Physics, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 2 Department of Mechanical Engineering, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 3 Department of Chemical Engineering, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 4 Department of General Engineering-Materials Science and Engineering, University of Puerto Rico, Mayaguez, Puerto Rico, United States
Show Abstract3:15 PM - J10.3
Study of Magnetic FePt Nanostructures Integrated with Silicon.
Gopinath Trichy 1 , Jagdish Narayan 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show Abstract3:30 PM - J10.4
Evaluation of Boron Atomic Sites in Longitudinal CoPtCrB HDD Media by Ultrasoft Pseudoptentials Calculation and HR-TEM Analysis.
Kaoru Shoda 1 , Seiji Takeda 1
1 Department of Physics, Graduate School of Science, Osaka University, 1-16 Machikane-yama, Toyonaka, Osaka, Japan
Show Abstract4:15 PM - **J10.5
Exchange Coupled Composite Magnetic Recording Media.
Randall Victora 1 , Stephanie Hernandez 1 , Manish Kapoor 1 , Xiao Shen 1
1 ECE, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractConventional perpendicular media with switching field Hs, saturation magnetization Ms, and grain volume V has a ratio ζ=2ΔE/(Hs×Ms×V)=1.0. This low thermal stability ΔE to switching field ratio limits the use of conventional perpendicular media in ultra high density recording. We have proposed [1] an exchange coupled composite (ECC) media that consists of two regions with magnetic hard and soft materials that are coupled to each other by quantum mechanical exchange. The ratio ζ of ECC media can be higher than 2.0. Ideally, the recording areal density would therefore increase by a factor greater than two. We have calculated hysteresis loops as a function of exchange coupling within each grain and between neighboring grains and for various applied field angles. Results show that, for optimized materials, the smallest switching field occurs when the easy axis and the applied field are aligned, which is the case for perpendicular recording near the track center. Thus, the same perpendicular writer writes narrower tracks on ECC media than on conventional perpendicular media. A single grain of ECC media was simulated by sub-dividing it into small cubes and introducing appropriate exchange within different regions of the grain. Field sweep time analysis revealed that ECC media was capable of following a rapidly changing field more closely than regular perpendicular media. In addition, a micromagnetic approach using Langevin dynamics was adopted to study the response of ECC grains to thermal fluctuations. We found an attempt frequency f0 of thermally assisted reversal for a 15 nm long, 5 nm diameter ECC grain to be ~ 1000 GHz. In comparison to typical perpendicular recording media (f0 ~ 1 GHz), this suggests that anisotropy can be increased with a corresponding decrease in volume to result in a further 25% improvement in areal density owing to thermal fluctuation assisted recording. Optimal media designs have employed a low magnetization hard layer. A more easily achievable design may consist of replacing the hard layer with a synthetic antiferromagnet consisting of two ferromagnetic hard layers coupled by an antiferromagnetic exchange interaction. This new design is shown to decrease the switching field and increase the thermal stability ratio when compared to regular ECC media.[1] R. H. Victora and X. Shen, "Composite media for perpendicular magnetic recording", IEEE Trans. Magn. 41, pp. 537-542,(2005)
4:45 PM - J10.6
Control of Magnetic Properties of Co/Pd Multilayers by use of Dopants
Divya Namuduri 1 , James Rantschler 1 , Dmitri Litvinov 1
1 , University of Houston, Houston, Texas, United States
Show AbstractThe magnetic properties of the Co/Pd multilayers depend mainly on their microstructure. By addition of dopants to the multilayers, their microstructure can be varied, which implies that their magnetic properties can be controlled. In the current study the effect of doping Co/Pd multilayers has been studied. Co/Pd multilayers exhibit large magnetic anisotropy with easy axis perpendicular to the plane. This makes them potential candidates for high density perpendicular magnetic recording media. In the recent past, extensive research has been done on doping the Co layer, to enhance its magnetic properties like coercivity, saturation magnetization and intergranular exchange energy. In this work, the Palladium layer has been doped rather than the Cobalt, which keeps the magnetic layer pure. It is expected that changing the lattice structure or lattice properties of Pd layer, will have a pronounced effect on the magnetic properties of the multilayer stack. Aluminum and Copper were used as dopants. Samples with 3Å Co and 8Å (Pd-X) on a 5nm Ta underlayer were prepared by magnetron sputtering (X = Al, Cu). Relative percentages of Pd-X were varied from 0-100% of X (by varying sputter rates). Vibrating Sample Magnetrometry measurements were made to measure the hysteresis loops. X-Ray Photon Spectroscopy was used to accurately determine the Pd-X relative composition. X-Ray Diffraction technique was used to determine the crystal structure of the sputtered multilayers. AFM/MFM measurements were made to measure the grain size and distribution. In the case of Al doped multilayers, it was observed that by doping the Pd layer even with a small amount of Al (~13%), the easy axis was no longer perpendicular to the plane. In case of Copper this was observed at around 7%. The saturation magnetization decreased from 360 emu/cc to 20 emu/cc as Al percentage increased from 0-100%.
5:00 PM - J10.7
DualAC MFM Imaging of High Density Perpendicular Recording Media.
Jason Li 1 , Jason Cleveland 1 , Roger Proksch 1
1 , Asylum Research, Santa Barbara, California, United States
Show Abstract5:15 PM - **J10.8
Trends in Nano-Scaled Magnetic Reader Transducer.
Song Xue 1
1 , Seagate, Bloomington, Minnesota, United States
Show AbstractFor the past 50 years or so, the area density in magnetic recording has increased by almost 8 orders of magnitude. Today, the advanced magnetic reader typically has a reader width less than 100 nm. As the reader width continues to shrink, trade-off among performance, magnetic stability, and reliability poses serious challenges for further increasing area density.We will review process technologies to fabricate nano-scale magnetic reader sensor. We will also discuss a few reader device options available to us; there are Current-In-Plane Spin Valve (CIP SV), Tunnel Magetoresistive Valve (TMR), and Current Perpendicular to Plane Spin Valve (CPP SV).Scaling limits in those reader transducers will also be discussed.