Glassy behavior in magnetic fine particles

A detailed study of the static and dynamic magnetic properties of nanocryst alline barium hexaferrite powder was done. Particles of about 10 nm diamete r exhibit the main features attributed to glassy behavior. Different result s make evident the presence of strong interactions in the studied system. T his glassy state is mostly attributed to the frustration induced by magneti c interactions between randomly distributed particles, although the surface spins contribution cannot be discarded. The effective energy barrier distr ibution obtained from the analysis of the time dependence of the thermorema nence in terms of the T ln (t/tau (0)) scaling shows a maximum located at e nergies higher than the mean anisotropy energy barrier. When doing the rela xation experiments after held cooling at increasing fields, the obtained ef fective energy distribution progressively resembles the anisotropy energy d istribution. Therefore, we demonstrate how the glassy state can be erased b y applying a magnetic held. (C) 2000 Elsevier Science B.V. All rights reser ved.