Stochastic Thermodynamics of Micromagnetics with Spin Torque

TL;DR

This paper extends stochastic thermodynamics to micromagnetics with spin torque, revealing entropy pumping effects and the possibility of heat-to-work conversion, supported by theoretical derivations and numerical verification.

Contribution

It introduces a stochastic Landau-Lifshitz model with spin torque, establishes thermodynamic relations, and uncovers entropy pumping leading to novel heat engine behavior.

Findings

Entropy pumping due to spin torque influences system dynamics.

The system can operate as a heat engine converting heat into magnetic work.

Fluctuation theorem for entropy and work verified numerically.

Abstract

In this work, we study the stochastic dynamics of micro-magnetics interacting with a spin-current torque. We extend the previously constructed stochastic Landau-Lifshitz equation to the case with spin-current torque, and verify the conditions of detailed balance. Then we construct various thermodynamics quantities such as work and heat, and prove the second law of thermodynamics. Due to the existence of spin-torque and the asymmetry of the kinetic matrix, a novel effect of entropy pumping shows up. As a consequence, the system may behave as a heat engine which constantly transforms heat into magnetic work. Finally, we derive a fluctuation theorem for the joint probability density function of the pumped entropy and the total work, and verify it using numerical simulations.