Averaged equation for energy diffusion on a graph reveals bifurcation diagram and thermally assisted reversal times in spin-torque driven nanomagnets

TL;DR

This paper introduces an averaged energy diffusion equation on a graph to analyze spin-torque nanomagnet dynamics, revealing bifurcation points, critical currents, and thermally assisted reversal times, aligning with experimental data.

Contribution

It develops a novel averaged equation for energy diffusion on a graph that captures low-damping nanomagnet dynamics and predicts bifurcations and reversal times.

Findings

Identifies critical currents for stable precessional states.

Derives a Nél-Brown-type formula for reversal times.

Matches theoretical predictions with experimental results.

Abstract

Driving nanomagnets by spin-polarized currents offers exciting prospects in magnetoelectronics, but the response of the magnets to such currents remains poorly understood. We show that an averaged equation describing the diffusion of energy on a graph captures the low-damping dynamics of these systems. From this equation we obtain the bifurcation diagram of the magnets, including the critical currents to induce stable precessional states and magnetization switching, as well as the mean times of thermally assisted magnetization reversal in situations where the standard reaction rate theory of Kramers is no longer valid. These results match experimental observations and give a theoretical basis for a N\'eel-Brown-type formula with an effective energy barrier for the reversal times.