Measurement of the Dynamics of the Magnetization Reversal in Individual Single-Domain Ferromagnetic Particles

Abstract

We have measured the spontaneous thermal switching of the magnetization of individual single-domain ellipsoidal ferromagnetic $\ensuremath{\gamma}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ particles. At room temperature, and in applied fields close to coercivity, the statistics of the reversal cannot be described by activation over a single-energy barrier as originally proposed by N\'eel. We suggest the dynamics of reversal occurs via a complex path in configuration space, and a complex theoretical approach is required to provide a correct description of thermally activated magnetization reversal even in single-domain ferromagnetic particles.