Hysteresis loops of Co-Pt perpendicular magnetic multilayers

We develop a phenomenological model to study magnetic hysteresis in two samples designed as possible perpendicular recording media. A stochastic cellular automaton model captures cooperative behaviour in the nucleation of magnetic domains. We show how this simple model turns broad hysteresis loops into loops with sharp drops like those observed in these samples, and explains their unusual features. We also present, and experimentally verify, predictions of this model, such as the temperature dependence of the hysteresis loop shape, and the existence and time dependence of drops in first-order reversal curves. We suggest how insights from this model may apply more generally.