Quantitative Study of the Magnetization Ripple in Ferromagnetic Ni–Fe Alloy Films

Abstract

Magnetization ripple in Ni–Fe thin films has been investigated by several workers, but no systematic study of the ripple structure over a significant range of alloy composition, substrate deposition temperature, and measurement temperature has been published. The present report describes the results of such a study. Room-temperature measurements of the ripple amplitude θ0 and wavelength λ have been measured as a function of alloy composition from 50% Ni to 90% Ni for films deposited at room temperature. In addition, θ0 and λ have been measured from 25° to 450°C for 76% Ni films evaporated at temperatures from −180° to 400°C. For all data, θ0 and λ are in order of magnitude agreement with Hoffmann's calculations (10−2 rad and 1 μ, respectively). As a function of alloy composition, the ripple amplitude exhibits a minimum in the vicinity of 73% Ni. The wavelength is independent of alloy composition. For 76% Ni films deposited at −180°C, the ripple wavelength is independent of measuring temperature. The amplitude θ0 decreases to zero at about 330°C and does not reappear at higher temperatures, contrary to the reappearance reported by others. For higher deposition temperatures, the scatter in the data is much higher than for −180°C and ripple could be observed as high as 450°C. The ripple amplitude increases with substrate deposition temperature, as expected from the increase in grain size. Two points concerning the present data should be emphasized. (1) The results are in reasonable agreement with Hoffmann's theory. (2) The data constitute a systematic description of magnetization ripple in Ni–Fe films.