Magnetoelastic Sensitivity and Composition of Permalloy Films

Abstract

The compositional dependence of the magnetoelastic sensitivity of Permalloy films has been studied by a number of investigators, but their results are in disagreement regarding the compositions required for zero magnetostriction, the agreement with bulk values, and the anisotropy of the magnetoelastic coefficients. This paper reports measurements on cylindrical films of torsional strain sensitivity (H _l/γ) and absolute compositional analyses by refined x‐ray fluorescence techniques to a precision not attained before. Although the average zero magnetostriction point (ZMP) is found at 80.3% Ni, the data suggest that there are probably structural variations from film to film which cause real variations of ±0.5% in the ZMP. Torsional strain sensitivity is correlated with measurements of tensile strain sensitivity (η). The shear coefficient B_γ is found to be 1.21 times the tensile coefficient B_β. The slope of η versus composition for these electroplated films is in reasonable agreement with the other data on evaporated films. The inferred slope of magnetostriction λ versus composition is significantly below that for bulk Permalloy.