The activation volumes of reversal in ultrafine particles

Measurements of the activation volume of reversal and the fluctuation field of a system of ultrafine cobalt particles are reported. The measurements were performed in a range of applied fields so as to enable a comparison to be made with theoretical models which are often applied to more complex materials, such as NdFeB magnets. The values obtained for the activation volume are in broad quantitative agreement with the particle size as determined by other methods, which provides the first unambiguous verification of the activation volume model of magnetization reversal