We consider superparamagnetic particles with cubic anisotropy where the anisotropy constant is negative. It is found that in the limit of a high barrier for a magnetization reversal, three (and only three) time constants are needed in order to describe the relaxation rate of an ensemble of such particles. It is further shown that their ratios tend towards 1:2:3. Asymptotic expressions for this limit are obtained theoretically that depend exponentially on the barrier height. Numerical computations in a limited region of barrier height give reasonably close results for all practical purposes. But the asymptotic conditions of a high barrier are not as yet realized in the region where the computations are carried. Still, the 1:2:3 ratios between the time constants seem to be confirmed by the numerical results.

• Received 16 June 1976

DOI:https://doi.org/10.1103/PhysRevB.16.1285