Viscous magnetization of chromium-dioxide particles: effect of increased magnetocrystalline anisotropy

Samples of chromium dioxide particles with a range of remanent coercivities H_r, but with identical particle size distributions were prepared in order to study the effect of changes in the magnetocrystalline anisotropy on the time-dependent magnetization. Comparisons have been made with three cobalt modified gamma-Fe₂ O₃ samples. The field-dependent fluctuation field H _f, derived from measurements of magnetic viscosity as a function of applied field H, has been used to characterize the time-dependent magnetic switching of the particles. Plots of H _f/H_r against H/H_r are unaffected by anisotropy variations in either pigment type. The interpretation is that the details of the magnetics and the reversal mode are not primarily responsible for the more pronounced time-dependent magnetization effects observed in CrO₂ and that the more likely explanation is the high state of magnetic excitation associated with the low Curie temperature