High-Frequency Permeability of Isotropic Co-Based Amorphous Films

The dependence of soft magnetic properties on the annealing conditions of Co-based amorphous films of different thicknesses was investigated in detail, in order to obtain films with a high isotropic initial permeability at high frequencies. It was found that the microscopic anisotropy of films annealed in a rotating field was increased isotropically by field-free annealing below the Curie temperature (Tc). Thinner films with a larger microscopic anisotropy exhibited a higher isotropic permeability at high frequencies. This occurred because the natural resonance frequency is increased by increases in the microscopic anisotropy, and the influence of the eddy current on the initial permeability becomes a dominant factor at high frequencies.