Ab initio description of spin relaxation at finite temperatures
Dr. Yi Liu (University of Twente)

Temperature dependent spin relaxation in magnetic materials, which is described in terms of a Gilbert damping parameter and a spin-flip diffusion length, is of general interest in both research and application. Using a first-principles implementation of relativistic scattering theory[1], we calculate these properties in real materials without including tunable parameters. We modeled the temperature effect on the lattice and spin degrees of freedom by introducing “frozen thermal lattice/spin disorder” schemes[2]. These frozen thermal disorder yielded results with good qualitative and reasonable quantitative agreement with experiment. We improve the description of the temperature effect by using phonons and magnons that are calculated from first-principles and populated to generate “snapshots” of lattice vibrations and spin fluctuations. We apply this method to non-magnetic metals Cu, Pd, and Pt, and magnetic Fe. The calculated temperature dependent electrical resistivities agree with experiment very well, justifying our procedure. The spin-flip diffusion length we obtain scales linearly with the corresponding conductivity for Pd and Pt, in agreement with the Elliott-Yafet relation. We also explore an alternative way of describing temperature dependent spin disorder, where we improve the frozen thermal spin disorder by using the measured temperature dependent magnetization. A better agreement with experiment for the calculated resistivity of Fe is obtained using this method. We also calculate the Gilbert damping and compare it with the measurements, where we find that combining lattice and spin disorder only decreases the low-temperature damping but does not increase the high-temperture damping.
[1] A. A. Starikov, P. J. Kelly, A. Brataas, Y. Tserkovnyak, and G. E. W. Bauer, Phys. Rev. Lett. 105, 236601 (2010).
[2] Y. Liu, A. A. Starikov, Z. Yuan, and P. J. Kelly, Phys. Rev. B 84, 014412 (2011).