Macrospin Models of Spin Transfer Dynamics

TL;DR

This paper models spin transfer dynamics in spin valves using macrospin approximation, comparing simulations with experiments and identifying key discrepancies in frequency dependence and magnetic phases.

Contribution

It introduces a macrospin model incorporating various physical effects to quantitatively compare with experimental data on spin transfer dynamics.

Findings

Simulations reproduce many experimental features.

Discrepancies in current dependence of precession frequency.

Differences in predicted microwave quiet magnetic phase.

Abstract

The current-induced magnetization dynamics of a spin valve are studied using a macrospin (single domain) approximation and numerical solutions of a generalized Landau-Lifshitz-Gilbert equation. For the purpose of quantitative comparison with experiment [Kiselev {\it et al.} Nature {\bf 425}, 380 (2003)], we calculate the resistance and microwave power as a function of current and external field including the effects of anisotropies, damping, spin-transfer torque, thermal fluctuations, spin-pumping, and incomplete absorption of transverse spin current. While many features of experiment appear in the simulations, there are two significant discrepancies: the current dependence of the precession frequency and the presence/absence of a microwave quiet magnetic phase with a distinct magnetoresistance signature. Comparison is made with micromagnetic simulations designed to model the same experiment.