Stochastic thermodynamics of macrospins with fluctuating amplitude and direction

TL;DR

This paper investigates the stochastic thermodynamics of macrospins with fluctuating amplitude and direction, deriving entropy production and fluctuation theorems within a generalized Langevin framework.

Contribution

It introduces a comprehensive analysis of energy balance and entropy production in macrospins considering both amplitude and directional fluctuations, extending previous models.

Findings

Derived fluctuation theorems for entropy production in macrospins.

Demonstrated the importance of trajectory conjugation in fluctuation theorems.

Showed the entropy increase due to irreversible processes and heat dissipation.

Abstract

We consider stochastic energy balance and entropy production (EP) in a generalized Langevin dynamics of macrospins, allowing for both amplitude and direction fluctuations, under external magnetic field. EP is calculated using Fokker-Planck equation, distinguishing between reversible and irreversible parts of probability currents. The system entropy increases due to irreversible non-equilibrium processes, and reduces as heat dissipates to surrounding environment. Using path probability distributions of time-forward trajectories and conjugate trajectories under time reversal, we obtain fluctuation theorems (FT) for total stochastic EP. We show that the choice of conjugate trajectories is crucial in obtaining entropy like quantities that obey FTs.