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Randall H Victora

Graduate Faculty (Electrical Engineering)

victo004 @ umn.edu

Victora, Randall H.jpeg

President-Elect, IEEE Magnetics Society, 2007-2008, Treasurer, IEEE Magnetics Society, 2005-2006, General Chairman, 50th Annual Conference on Magnetism and Magnetic Materials, 2005, Program Co-Chairman, Joint MMM-INTERMAG Conference, 2001, Program, Co-Chairman, INTERMAG 1995, Publications Co-Chairman of MMM Conference and Guest Editor of Journal of Applied Physics, 1992-1993, Member, IEEE Magnetics Society ADCOM 2001-2004, Co-organizer, Division of Materials Physics Focused Session on Magnetic Nanostructures, Ultrathin Films, and Surfaces, 1996, University Adviser, National Storage Industry Consortium Executive Board, 2001-2003, Member Program Committee, Conference on Magnetism and Magnetic Materials, 1992, 1993, 1995, and 1999, Member, Program Committee, Joint MMM/INTERMAG Conference, 1991, 1994, Member, Program Committee, INTERMAG 2002, Member, Advisory Committee, Conference on Magnetism and Magnetic Materials, 1994-2009 (Chairman 2006), Member, Program Committee, Magnetic Interfaces and Nanostructures Technical Group of the American Vacuum Society, 1997-1999

Summary of Interests
The theoretical study of magnetism and magnetics, particularly for application to magnetic recording and other magnetic devices. This work includes micromagnetic simulation, calculation of electronic structure, and analytic theory. [Research Web Page]

About My Work

In 1986, Victora was the first individual to demonstrate accurate prediction of hysteretic phenomena for a material of moderate coercivity using only microstructural input. Several of the techniques that were introduced are now widely used today. Two years later, he derived on the basis of thermal fluctuations, a scaling relationship between switching fields and measurement times. The predicted power dependence differed from the widely assumed, but unjustified, value. Although originally controversial, its accuracy was subsequently demonstrated experimentally. It is now widely accepted and used for accurate predictions within basic science and the magnetic recording industry. More recently, Professor Victora with his student, Alex Dobin, demonstrated that 4 magnon relaxation in thin films can dominate the switching process for large rotations of the magnetization. Counter intuitively, they found that a large rotation will actually reach equilibrium more swiftly than a small rotation owing to its nonlinear nature. Furthermore, they derived a scaling law for relaxation owing to surface roughness. Both of these predictions have been observed in recent experiments. In a more applied vein, Victora and another student (Xiao Shen) discovered a magnetic recording media that consists of a magnetically hard part exchange coupled to a magnetically soft part within the same grain. This “Exchange Coupled Composite Media (ECC)” media can more than double the recording density. This work is widely recognized as the likely development path for recording media and early versions have appeared in products.

Selected Publications

X. Chen and R.H. Victora,, “Effect of Pinholes in Magnetic Tunnel Junctions”, Appl. Phys. Lett. 91, 212104 (2007)

J. Saha and R.H. Victora, “Spontaneous Exchange Bias: Uniaxial Anisotropy in an Otherwise Isotropic System”, Phys. Rev. B 76, 100405(R), (2007)

J. Saha, J.S. Parker, B.T. Bolon, A. Abin-Fuentes, C. Leighton, and R.H. Victora, “Comparison between Micromagnetic Simulation and Experiment for the Co/γ-FeMn Exchange-Biased System”, J. Appl. Phys. 102, 073901

M. Kapoor and R.H. Victora, “Comparisons of Recording Head Designs for Perpendicular and Exchange Coupled Composite Media”, IEEE Trans. Magn. 43, 2289

S. Hernandez, M. Kapoor, and R.H. Victora, “Antiferromagnet for Hard Layer of Exchange Coupled Composite Media”, Appl. Phys. Lett. 90, 132505 [abstract]

A. Yu. Dobin and R.H. Victora, “Surface Roughness Induced Extrinsic Damping in Thin Magnetic Films”, Phys. Rev. Lett. 92, 257204, 2004.

Education

B.S. (physics and mathematics) Massachusetts Institute of Technology 1980
Ph.D. (physics) University of California, Berkeley, 1985