The Interpretation of Magnetic Viscosity

The consideration of a simple model, based on the Stoner and Wohlfarth model of magnetic reversal including time-dependence, allows the measurement of the key viscosity parameter Lambda to be related to the micromagnetic changes occurring in the material. An aligned system with a log-normal distribution of volumes has been studied and the measured value of Lambda at each field related to the mean volume of the particles which are reversing at that field. It is also shown that, when the system is not aligned, there is no longer a simple relationship between Lambda and the physical processes occurring. This is because in this instance Lambda is a complex average over the ensemble.