Theory of time-dependent magnetic phenomena for a fine-particle ensemble

Abstract

Theory of time-dependent magnetic phenomena for an ensemble of small ferromagnetic particles with uniaxial anisotropy - Stoner-Wohlfarth (SW) particles - is presented. Magnetic viscosity of such a system is calculated using the energy barrier distribution density ϱ( E) for an SW ensemble. It is shown that, due to the nonmonotonic dependence of the energy barrier versus easy axis orientation angle, ϱ( E) has essential singularities at least for one energy value. These singularities result in nonlinear temperature behavior of the maximum magnetic viscosity S max and in complex dependence of S max versus the applied field. It is also shown that the interparticle interactions and the particle size distribution eliminate the singularities in energy barrier density, so that S max increases linearly with the temperature. The dependence of S max on the particles volume concentration, anisotropy constant and width of the particle size distribution is studied.