Effect of Low-Temperature Annealing on Magnetic Characteristics and Their Uniformity in Cobalt-Based Amorphous Alloy

The effect of heat treatment in air at 200–250°C on the magnetic properties and their uniformity in ribbon samples of the cobalt-based amorphous soft magnetic alloy AMAG-172 (Co–Ni–Fe–Cr–Mn–Si–B) was studied. In the quenched state, the nonuniformity of the magnetic properties of the ribbons is related to the manufacturing process, namely, the presence of cooling rate gradients. Heat treatment in air within the studied temperature range, with various durations of isothermal holding, was found not to improve the magnetic properties of the ribbon or enhance their uniformity. The formation of bimodal and trimodal field dependences of magnetic permeability indicates that the ribbon becomes stratified across its thickness during annealing. The decrease in maximum magnetic permeability is attributed to the reorientation of magnetization perpendicular to both the ribbon plane and the ribbon axis within its plane. The results are explained by the influence of anisotropic stresses induced by oxidation, hydrogenation of the ribbon surface, and its surface crystallization.