Thermal stability of anisotropic and isotropic Co alloy thin-film media is investigated. The orientation ratio of CoCrTa(Pt)/Cr media was controlled by the mechanical texture of the NiP/Al substrates. Bulk magnetic properties, delta M curves and time decay of magnetization in the circumferential and radial directions were measured. The maximum magnetic viscosity coefficient calculated from the time decay of magnetization in the circumferential direction was higher than that in the radial direction for a mechanically textured sample, while it was similar in both directions for a non-textured sample. The magnetic viscosity coefficient in the circumferential direction is smaller than that in the radial direction when the reverse field is in the range of the demagnetization field for thin-film recording media. This implies that an anisotropic sample (namely, a sample with a high orientation ratio) will be more thermally stable when it is not exposed to a large external magnetic field.

In this paper, we will present a study of the time-dependence effect in alumite perpendicular media at different thicknesses. Important parameters of the time-dependence effect such as magnetic viscosity and activation volume are investigated. Viscosity as a function of applied field (viscosity curve) exhibits a short plateau at a low field and then decreases monotonously with increasing field. After correcting for the demagnetizing field, the shape of the intrinsic viscosity curves changes to the well-known shape of the viscosity curve of in-plane media, i. e. , they have a peak near Hc. The intrinsic viscosity curves obtained from the experiments were fitted to an analytical model by Chantrell et al., from which, we found that the effective switching volumes obtained by fitting are much smaller than the column volumes, indicating that the reversal mechanism is incoherent.