Effect of Annealing on Magnetostrictive Properties of Fe–Co Alloy Thin Films

Abstract

The effect of the annealing temperature on the magnetostrictive properties of Fe–Co alloy thin films on quartz glass was systematically investigated. The saturation magnetostriction was 56 ppm for the Fe₃₂Co₆₈-sputtered thin film quenched from 673 K, and it increased to 159 ppm with increasing annealing temperature up to 1073 K. The magnetostriction above 1093 K significantly decreased with the emerging fcc phase in the Fe–Co alloy. SEM images showed that the crystal grains present in the fcc phase aggregated to form a discontinuous surface, which resulted in a decrease in the effective magnetostriction. Measurements of the magnetic properties by vibrating sample magnetometer and magnetic force microscopy revealed the enhancement of the magnetization at the crystal grain boundaries of Fe–Co alloy thin films with large magnetostriction. Thus, the heterogeneity of the magnetization can play a key role in inducing the large magnetostrictive effect.