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Physics & Astronomy Colloquium – Fall 2020 – Mewes
October 7, 2020 @ 3:30 pm - 5:00 pm
Speaker: Tim Mewes (University of Alabama)
Title: Magnetization Dynamics and Damping
The dynamics and the damping of magnetization are of paramount importance to understand and predict the properties of magnetic materials used in a variety of applications. For example, spin-transfer torque magnetic random-access memory cells (STT-MRAM) are expected to switch fast, reliably, and with low power consumption, which requires low damping materials. The Landau-Lifshitz-Gilbert equation of motion  and extensions thereof have been extremely successful in enabling predictions of the magnetization dynamics of materials both analytically and using micromagnetic simulations. Experimentally, magnetization dynamics can be elegantly probed in the frequency domain using ferromagnetic resonance (FMR). Recent progress in broadband ferromagnetic resonance techniques have provided valuable new insights in the magnetization dynamics and the damping mechanisms of magnetic materials.
In this lecture, I will introduce the fundamentals of magnetization dynamics and damping. I will discuss their importance for many applications, including hard disk drive read heads, spin-transfer torque magnetic random-access memories and new skyrmions based devices. I will talk about various mechanisms that can contribute to the damping of the magnetization in thin films including spin-orbit relaxation, spin pumping, and two-magnon scattering. The presentation will show how recent developments in broadband ferromagnetic resonance enable precise measurements of the dynamics and damping in thin magnetic films and multilayers especially when combined with angle and temperature dependent measurements . This will include a discussion of the recently discovered anisotropic damping in exchange biased films [3, 4].
 T. L. Gilbert, “A Lagrangian formulation of the gyromagnetic equation of the magnetization fields (abstract only),” Phys. Rev., vol. 100, p. 1243, 1955.
 B. Khodadadi, A. Rai, A. Sapkota et al., “Conductivity-Like Gilbert Damping due to Intraband Scattering in Epitaxial Iron,” arXiv preprint arXiv:1906.10326, 2019.
 T. Mewes, R. L. Stamps, H. Lee et al., “Unidirectional Magnetization Relaxation in Exchange-Biased Films,” Magnetics Letters, IEEE, vol. 1, pp. 3500204-3500204, 2010.
 J. Beik Mohammadi, J. M. Jones, S. Paul et al., “Broadband ferromagnetic resonance characterization of anisotropies and relaxation in exchange-biased IrMn/CoFe bilayers,” Physical Review B, vol. 95, no. 6, p. 064414, 02/15/ 2017.
Speaker Biography: Tim Mewes received the bachelor’s and Ph.D. degrees in physics from the University of Kaiserslautern, Kaiserslautern, Germany, in 1999 and 2002, respectively. He was subsequently a Post-Doctoral Researcher with The Ohio State University, Columbus, OH, USA. He joined The University of Alabama, Tuscaloosa, AL, USA, in 2005, where he is currently a Professor with the Department of Physics and Astronomy. In 2011, he became a Visiting Fellow with the Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD, USA. He has published over 70 articles in peer reviewed journals on epitaxial growth, magnetic resonance force microscopy, magnetization dynamics, damping, and micromagnetics.
Dr. Mewes is a member of the American Physical Society. In 2010, he was a recipient of the National Science Foundation CAREER Award for the investigation of the magnetization dynamics and damping in magnetic nanostructures, and in 2014, he was a recipient of the IBM Faculty Award. He was the Chair of the 2016 IEEE International Conference of Microwave Magnetics in Tuscaloosa. He is currently the Chair of the Alabama Chapter of the IEEE Magnetics Society. He was active in the program committees of several other international magnetism conferences. During his undergraduate and graduate studies, he was a Scholar of the German Academic Scholarship Foundation.