ON THE MAGNETIC ANISOTROPY OF THE Co AND γ-Fe₂O₃ ULTRAFINE PARTICLES

The anisotropy constants K of γ-Fe₂O₃, Co-γ-Fe₂O₃ and Co ultrafine particles precipitated in Cu-Co alloy have been measured by wing the equations for describing the relaxation of superparamagnetic particles. It is found that the anisotropy constant K of Co-γ-Fe₂O₃ fine particles is greater than that of γ-Fe₂O₃ by about 50%; the K value of Co ultrafine particles of a radius equal to 36Å is greater than that of to 48Å by about 100%. This phenomenon has been interpreted as the existence of surface anisotropy of the Co ultrafine particles.