title: Stochastic thermodynamics of macrospins with fluctuating amplitude and direction.
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 a 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 the 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.
authors.affiliation: TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500075, Telengana, India.
authors.forename: Swarnali
authors.initials: S
authors.lastname: Bandopadhyay
authors.affiliation: Indian Institute of Technology Hyderabad, Yeddumailaram 502205, Telengana, India.
authors.forename: Debasish
authors.initials: D
authors.lastname: Chaudhuri
authors.affiliation: Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005, India.
authors.forename: A M
authors.initials: AM
authors.lastname: Jayannavar