Temperature of the Formation of a Protective Polymer Coating and the Magnetic Properties of Cobalt-Based Amorphous Alloys

The influence of the polymer coating used in the manufacture of magnetic shields and of the conditions of its formation on the distribution of the magnetization and on the magnetic properties of shields has been studied. Samples of a ribbon of the Co-based soft-magnetic amorphous alloy AMAG-172 (Co–Ni–Fe–Cr–Mn–Si–B) with a saturation magnetostriction close to zero were used in the study. The coating was deposited in the temperature range of 90–130°C on the ribbon subjected to heat treatments in air that form a state with a negative saturation magnetostriction. The change of magnetic characteristics was investigated over a two year period. It has been shown that there is a temperature range in which a change in the sign of the saturation magnetostriction occurs upon the formation of the coating. This change is due to a change in the structural-phase state of the ribbon because of the diffusion processes that occur upon heating. The formation of the coating leads to a reduction in the maximum magnetic permeability; nevertheless, over a two year period, no decrease in μ_max is observed in the ribbon with a coating formed in the 110–130°C temperature range.