Magnetics Society Distinguished Lecturers for 2005

Half-Metals, Spin Torque, and Nanorings
Chia-Ling Chien
The Johns Hopkins University

    The exploration of magnetic nanostructures in recent years has resulted in a string of discoveries such as interlayer coupling, giant magnetoresistance (GMR), exchange bias, and tunneling magnetoresistance. Some of these effects were utilized as read-heads in high-density magnetic recording and non-volatile magnetic storage only a few years after the original discovery. In this talk, I will describe several new topics in magnetic nanostructures from inception to realization to potential applications.
    Most magnetoelectronic properties are the results of the spin polarization of the constituent materials. The ultimate spin-polarized material with 100% spin polarization is called the half-metal. For example, magnetic tunnel junctions with half-metal electrodes would have the largest possible effect, switching between conducting and insulating states. The unique characteristics of half-metals, the experimental identifications, and the confirmation of half-metals to date will be described.
    Since electrons have spin in additional to charge, a spin-polarized current carries angular momentum. For a large current density, the angular momentum can exert a substantial torque onto a receiving magnetic entity to excite spin waves or even to switch its magnetization. The spin torque effects are accomplished in the absence of an external magnetic field. The salient aspects of the spin torque effects in different contexts, such as switching and magnetic recording without a magnetic field, will be described.
    Nanorings are small entities with special attributes. A magnetic nanoring can support vortex state despite its very small size. The two chiralities of the vortex state can be exploited for magnetic recording purposes. Multilayered nanoprings have also been proposed as vertical random access memory (VRAM) units. However, fabrication of nanorings using e-beam lithography has considerable limitations in the number of rings, ring size, and areal density. We have developed a new method with which a large number (109) of small (100 nm) rings can be fabricated with a very areal density of 45 rings per square micrometer. The magnetic and other characteristics of such arrays of nanorings will be described.


Chia-Ling Chien received the B. S. degree in Physics from Tunghai University in Taiwan in 1965, and Ph. D. degree in Physics from Carnegie-Mellon University in 1972.
    He has been a faculty member in the Department of Physics and Astronomy of Johns Hopkins University since 1976, where he is the Jacob L. Hain Professor in Arts and Sciences. He currently directs the Material Research Science and Engineering Center on Nanostructured Materials at Hopkins. His recent research focuses on magnetic nanostructures including magnetic granular solids, nanowires, multilayers, and arrays of rings and dots, and the exploration of GMR, exchange bias, half-metals, spin torque effects, Andreev reflection, and point-contact spectroscopy. He has written more than 300 journal articles and holds several patents. He is one of the ISI 1120 most cited physicists. He has served as Meeting Chair and Chair of the Advisory Committee of the Conference on Magnetism and Magnetic Materials. He has been awarded honorary professorships at Nanjing, Lanzhou, and Fudan universities in China. He has been a Fellow and the 2004 recipient of the David Adler Award of the American Physical Society.


Contact:
Prof. C. L. Chien, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218; telephone: (410) 516-8092; fax: (410) 516-7239; e-mail: clc@pha.jhu.edu

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Micro-Fabrication Techniques for Magnetic Information Storage Devices: From Bubbles to Thin-Film Recording Heads to Nanomagnetic Structures
Robert E. Fontana, Jr.
Hitachi Global Storage Technologies

    This lecture examines magnetic device structures from the perspective of thin film processing. Techniques for forming magnetic device structure minimum features will be compared with semiconductor processing. Future storage density growth in both magnetic memories and magnetic recording will be projected using semiconductor roadmaps. The “nano” characteristics (thickness and length scale) of next generation magnetic thin film heads and magnetic memory devices will be compared with solid state semiconductor designs.
    In the last 25 years, the bit cell size for storage products incorporating magnetic device structures decreased from 156 µm˛ bit cells (IBM 3390 Disk Drive) to 0.007 µm˛ (Hitachi Travelstar 5K100 Mobile Disk Drive). For the same period, the bit cell size in non-volatile memory products incorporating magnetic device structures decreased from 625 um˛ (TI 100 Kbit Bubble Memory) to 1.6 um˛ (Motorola 4 Mbit MRAM). These 103 to 105 increases in information storage densities resulted from increased understanding in the physics of magnetic phenomena, from advances in material science and engineering for magnetic thin films, from development of new magnetic modeling techniques, and from dramatic improvements in the capability to fabricate magnetic device structures with smaller minimum features.
    The manufacture of cost effective magnetic device based information storage products requires high yield processing technologies for the magnetic transducer or memory element in these products. Such processing technologies are now producing devices with 120 nm features (80 GBit/in˛ storage densities) and these same processing technologies are extendable to 30 nm features (1TBit/in˛ storage densities). The lecture will conclude with discussions on nano-scale processing challenges.


Dr. Robert E. Fontana, Jr. received the B.S., M.S., and Ph.D. degrees in electrical engineering from the M assachusetts Institute of Technology, Cambridge, in 1969, 1971, and 1975, respectively.
    He is a Research Staff Member within the recording head processing function of the San Jose Research Center, Hitachi Global Storage Technologies (GST), San Jose, CA. His technical activities have concentrated on developing and improving thin-film processing techniques for fabricating magnetic device structures, first at Texas Instruments from 1975 to 1981 with magnetic bubbles, then from 1981 to 2002 at IBM with thin-film heads, and from 2003 to the present at Hitachi GST with novel flux detecting sensors and nanostructure fabrication with e-beam lithography. During his career, he has transferred processing methodologies for magnetic bubbles, magnetoresistive thin-film heads, spin-valve giant magnetoresistive thin-film heads, and tunnel-valve thin-film heads from research concepts to manufacturing realizations. He has authored 37 papers on magnetic devices and processes and has 55 patents in thin-film magnetic structures. Dr. Fontana was named an IEEE Fellow in 1996 and he received the IEEE Cledo Brunetti Award for excellence in the art of electronic miniaturization in 2000. He was elected to the National Academy of Engineering (NAE) in 2002 for his contributions in magnetic device processing. He has served as President of the IEEE Magnetics Society (2001, 2002), as General Chair of the 1996 Magnetism and Magnetic Materials Conference, as General Chair of the 2004 Joint International Magnetics Conference and Magnetism and Magnetic Materials Conference, and is serving as an NAE member on the National Research Council’s (NRC) Board on Manufacturing and Engineering Design (2003–2005).


Contact:
Robert E. Fontana, Jr., San Jose Research Center, Hitachi GST; 650 Harry Road, San Jose, CA 95120; telephone: (408) 323 7234; fax: 408 927 2100; e-mail: robert.fontana@hitachigst.com

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Dynamics in Magnetic Micro- and Nanostructures
Burkard Hillebrands
Technische Universitdt Kaiserslautern

     For applications in sensors and in data storage, the dynamic properties of micro- and nanostructures gain increasing attendance. The fundamental excitations in these objects are con-fined spin waves, and it is useful in particular to understand their properties in view of the noise spectrum in sensor and MRAM applications.
    The lecture addresses the dynamics in homogeneously and inhomogeneously magnetized ob-jects starting with an introduction into spin waves and the effects of finite dimensions. In inhomogeneous systems the excitation spectrum is complex, and new phenomena, like local-ization and tunneling of modes are discussed. The key points are illustrated by results ob-tained by space- and time-resolved Brillouin-light-scattering technique, which allows one to follow experimentally the propagation of spin wave packets and to present the results in an animated format. To conclude the lecture, the analysis of ultra-high-frequency dynamic prop-erties (2-100 GHz) of small magnetic elements with spatial resolution in the 300 nanometer range is presented.


Burkard Hillebrands received the diploma and Ph.D. degrees in physics from the University of Cologne, Cologne, Germany, in 1982 and 1986, respectively. After a postdoctoral stay at the Optical Sciences Center, Tucson, AZ, he received the habilitation from the RWTH Aachen, Aachen, Germany, in 1993.
    He was an Asso iate Associate Professor at the University of Karlsruhe, Karlsruhe, Germany, in 1994. Since 1995, he has been a Full Professor at the University of Kaiserslautern, Kaiserslautern, Germany. He is the coordinator of the German priority program “Ultrafast Magnetization Processes,” the vice coordinator of the German research unit “New Materials with High Spin Polarization,” and he coordinates a European network on “Ultrafast Magnetization Processes in Advanced Devices.” He is currently the head of the Material Research Center for Micro- and Nanostructures (MINAS) at the University of Kaiserslautern. He is a member of the granting board for collaborative research centers (SFB) of the senate of the Deutsche Forschungsgemeinschaft and a member of the Editorial Board of the Journal of Physics D: Applied Physics . His research field is mostly in magnetoelectronics. His special interests are in spin dynamics, material properties of thin magnetic films and multilayers, exchange bias, as well as in elastic properties of layered structures. In the field of spin dynamics, he is particularly interested in dynamic magnetic excitations in confined magnetic structures, magnetic switching, and nonlinear magnetic phenomena using space- and time-resolved Brillouin light scattering spectroscopy and time-resolved Kerr effect techniques. He has published more than 170 articles, five patents and patent applications, seven book contributions, and he is co-editor of the Springer-Verlag book series on “Spin Dynamics in Confined Magnetic Structures.”


Contact:
Prof. Burkard Hillebrands, Fachbereich Physik, TU Kaiserslautern, Erwin-Schrödinger-Strasse 56, 67663 Kaiserslautern, Germany; Telefone: +49 631-205-4228; fax: +49 631-205-4095 e-mail: hilleb@physik.uni-kl.de

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