Magnetoelastic Behavior of Thin Ferromagnetic Films as a Function of Composition

Abstract

A series of films of composition varying from 72% Ni, 28% Fe to 90% Ni, 10% Fe were evaporated at a pressure of the order of 10⁻⁵ mm Hg onto a heated glass substrate (250°C) in the presence of a magnetic orienting field in the plane of the film. The composition was controlled by placing a charge of the selected composition on the filament in an amount just sufficient to make the desired 3000 A film when all of the material was evaporated. The magnetoelastic behavior of the films was studied by measuring η=ΔH_k/(Δl/l), here ΔH_k is the change in the anisotropy field upon the application of a stress sufficient to strain the film an amount Δl/l (typically 4×10⁻⁵). η was found to decrease linearly with composition to a first approximation with a slope of −26.5×10³ oe per percent nickel, with η being zero for a film composed of 81.5% Ni, 18.5% Fe. The value of η was compared with that of Λ_m for bulk material where Λ_m is the change in the magnetization divided by the applied stress in the case where the stress approaches zero and where the bulk material is biased by an applied field sufficient to yield the maximum change in Λ. Using bulk data for the saturation magnetization and Youngs modulus the value of η measured here yields a value for Λ_m which is too large by an order of magnitude.