Time dependent magnetization of a system of fine cobalt particles

Measurements are presented which show that the magnetisation of a system of fine cobalt particles at 77°K is time dependent. The system examined in this work is of fine cobalt particles with median diameter D
v
= 70 Å dispersed in toluene. The particles have been found to be in the fcc phase. The time decay of magnetisation has been found to be logarithmic. The time dependence coefficient
A = -d\bar{I}/dLnt
varies with the applied field H and is a maximum for H = H
c
the coercive force. These observations are in good agreement with the theory presented in this paper.