Fluctuation theorem of a mesoscopic engine and spin switching

Based on the fluctuation theorem of a small engine, we present a description of the stochastic dynamics of a mesoscopic system. We apply it to the problem of the escape of a particle from a metastable state subjected to a fluctuating nonconservative force, which is beyond the description of the fluctuation‐dissipation theorem. As an example, we consider a reversal of a small magnetic moment by fluctuating spin‐torque. The joint probability distribution of input heat and output work is derived from the full‐counting statistics under adiabatic pumping. We predict a threshold voltage above which the spin‐torque shot noise induces probabilistic switching events, and below which such events are blocked.