Dynamic Neutron Depolarization and Small-Angle Scattering Studies of the Superparamagnetic System Cu-L%Co

Abstract

The magnetic properties of small single-domain ferromagnetic particles dispersed in a nonmagnetic matrix are mainly governed by their magnetic anisotropy energies which in turn depend essentially on the particle size. In particular the anisotropy energy barrier is responsible for the transition from superparamagnetic to magnetically stable behaviour. After a sudden removal of an external saturizing magnetic field thermal agitation causes the spontaneous magnetization directions of the particles to reach thermal equilibrium, i.e. to redistribute themselves by homogeneous rotation with equal probability into all equivalent easy directions. The macroscopic magnetization of the ensemble thus vanishes with time