Measurement of thermal switching of the magnetization of single domain particles (invited)

We present an experimental study of the thermally activated switching of the magnetization of individual isolated γ-Fe2O3 particles. These particles are prolate ellipsoids ∼3000 Å long and 650 Å wide. The measured angular dependence of the switching field, Hs(θ), is consistent at large angles with a uniform rotation, but as θ approaches zero, other modes of reversal appear possible, and most likely the mode of reversal is curling. By measuring the probability of reversal of the moment as a function of time and applied magnetic field at T∼300 K, we found that the switching was thermally assisted, but couldn’t be described by hopping over a single energy barrier. Our results indicate that the dynamics of switching are described by a complex path in the energy landscape.