Basic considerations for magnetization dynamics in the combined presence of spin-transfer torques and thermal fluctuations

Abstract

This article reviews basic theoretical features of Gilbert magnetization dynamics of a single domain magnetic film in the presence of Slonczewski spin-transfer torques, with and without thermal fluctuations taken into account. Rather than showing results of detailed numerical calculations, the discussion here is restricted to basic analytical results and conclusions which can mostly be derived from simply the form of the equations of motion, as well as elementary considerations based on classical stability analysis and the fluctuation-dissipation theorem. The presents work describes how interesting features of spin-transfer may be viewed as arising from non-equilibrium thermodynamics that are a direct consequence of the nonreciprocal nature of spin-transfer torques. The present article discusses fairly general results for spin-torque induced instability without thermal fluctuations, as well as the case of thermally activated magnetization reversal in uniaxial devices in the combined presence of external fields, thermal fluctuations, and spin-transfer torques. The results will be discussed and briefly compared and contrasted with that of prior work.