Damping dependence of spin-torque effects in thermally assisted magnetization reversal

TL;DR

This paper investigates how damping influences spin-torque-induced magnetization reversal times in nanomagnets, using a generalized Landau-Lifshitz-Gilbert framework that incorporates thermal noise and spin-transfer torque effects.

Contribution

It introduces a method to evaluate reversal times across a wide damping range by extending the Kramers turnover problem to magnetic systems, bridging low and intermediate damping regimes.

Findings

Reversal time depends on damping strength.

The model accounts for thermal fluctuations and spin-transfer torque.

Results applicable to nanomagnets with specific anisotropies.

Abstract

Thermal fluctuations of nanomagnets driven by spin-polarized currents are treated via the Landau-Lifshitz-Gilbert equation as generalized to include both the random thermal noise field and Slonczewski spin-transfer torque terms. The magnetization reversal time of such a nanomagnet is then evaluated for wide ranges of damping by using a method which generalizes the solution of the so-called Kramers turnover problem for mechanical Brownian particles, thereby bridging the very low damping and intermediate damping Kramers escape rates, to the analogous magnetic turnover problem. The reversal time is then evaluated for a nanomagnet with the free energy density given in the standard form of superimposed easy-plane and in-plane easy-axis anisotropies with the dc bias field along the easy axis.