Mechanisms limiting the coherence time of spontaneous magnetic oscillations driven by DC spin-polarized currents

TL;DR

This paper investigates the factors limiting the coherence time of magnetic oscillations driven by DC spin-polarized currents, highlighting thermal effects and mode transitions as key influences.

Contribution

It identifies thermal deflections and mode transitions as mechanisms limiting coherence time, and shows coherence can exceed macrospin simulation predictions.

Findings

Coherence time is limited by thermal deflections at low temperature.

Thermally-activated mode transitions limit coherence at high temperature.

Observed coherence times can surpass macrospin simulation predictions.

Abstract

The spin-transfer torque from a DC spin-polarized current can generate highly-coherent magnetic precession in nanoscale magnetic-multilayer devices. By measuring linewidths of spectra from the resulting resistance oscillations, we argue that the coherence time can be limited at low temperature by thermal deflections about the equilibrium magnetic trajectory, and at high temperature by thermally-activated transitions between dynamical modes. Surprisingly, the coherence time can be longer than predicted by simple macrospin simulations.