Non-equilibrium susceptibility of superparamagnetic particles

Abstract
The linear response of an assembly of non-interacting superparamagnetic particles to a small oscillatory magnetic field is studied. An appropriate Fokker-Planck equation for the orientational distribution function of the particles is written down, and is solved approximately under the condition that the barrier height between the easy orientations is much larger than the thermal energy. The susceptibility response in then calculated from the approximate form of the distribution function.