Determination of activation volumes in thin film media

The activation volume of reversal νact is a critical parameter in the characterization of thin film media since it determines the smallest unit of a magnetic material that can be reversed in a single step and hence defines the minimum bit size. In the recent past, there have been reports in the literature of a number of methods to determine the activation volume and it has become apparent that these methods provide inconsistent results. In this work, we describe both a theoretical and experimental comparison between the two principle methods used to determine the fluctuation field and hence the activation volume in thin film media. We have examined a thin film medium and find that inconsistencies between the methods do occur. These can be attributed to the reversible component of magnetization. We show that measurements of the fluctuation field, which is the fundamental quantity, determined from measurements of the ratio of the magnetic viscosity to the irreversible susceptibility are consistent with meas...