2007/03/31 by R. A. Duine, Álvaro S. Núñez, A. S. Nunez +2 · 8 citations
Physics and Astronomy · #Magnetic properties of thin films #Quantum and electron transport phenomena #Theoretical and Computational Physics #cond-mat.mes-hall
paper · pdf · doi:10.1103/physrevb.75.214420
published as Phys. Rev. B 75, 214420 (2007) · 14 pages, 3 figures
openalex publication_date 2007/06/18 · arxiv created 2007/07/18 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
We present a microscopic treatment of current-induced torques and thermal fluctuations in itinerant ferromagnets based on a functional formulation of the Keldysh formalism. We find that the nonequilibrium magnetization dynamics is governed by a stochastic Landau-Lifschitz-Gilbert equation with spin-transfer torques. We calculate the Gilbert damping parameter \ensuremathα and the nonadiabatic spin transfer torque parameter \ensuremathβ for a model ferromagnet. We find that \ensuremathβ\ensuremath≠\ensuremathα, in agreement with the results obtained using imaginary-time methods of Kohno et al. [J. Phys. Soc. Jpn. 75, 113706 (2006)]. We comment on the relationship between s\text\ensuremath-d and isotropic-Stoner toy models of ferromagnetism and more realistic density-functional-theory models, and on the implications of these relationships for predictions of the \ensuremathβ∕\ensuremathα ratio which plays a central role in domain-wall motion. Only for a single-parabolic-band isotropic-Stoner model with an exchange splitting that is small compared to the Fermi energy does \ensuremathβ∕\ensuremathα approach 1. In addition, our microscopic formalism naturally incorporates the fluctuations needed in a nonzero-temperature description of the magnetization. We find that to first order in the applied electric field, the usual form of thermal fluctuations via a phenomenological stochastic magnetic field holds.