Fluctuation Theorem for a Small Engine and Magnetization Switching by Spin Torque

TL;DR

This paper applies the fluctuation theorem to a nano-magnet system, analyzing how spin-torque fluctuations induce magnetization switching and identifying a voltage threshold for probabilistic switching events.

Contribution

It introduces a novel application of the fluctuation theorem to spin-torque-induced magnetization reversal, incorporating full-counting statistics and backaction effects.

Findings

Identifies a voltage threshold for probabilistic switching.

Predicts spin-torque shot noise induces switching above the threshold.

Provides a joint probability distribution consistent with the fluctuation theorem.

Abstract

We consider a reversal of the magnetic moment of a nano-magnet by the fluctuating spin-torque induced by a non-equilibrium current of electron spins. This is an example of the problem of the escape of a particle from a metastable state subjected to a fluctuating non-conservative force. The spin-torque is the non-conservative force and its fluctuations are beyond the description of the fluctuation-dissipation theorem. We estimate the joint probability distribution of work done by the spin torque and the Joule heat generated by the current, which satisfies the fluctuation theorem for a small engine. We predict a threshold voltage above which the spin-torque shot noise induces probabilistic switching events and below which such events are blocked. We adopt the theory of the full-counting statistics under the adiabatic pumping of spin angular momentum. This enables us to account for the backaction effect, which is crucial to maintain consistency with the fluctuation theorem.