Effect of Crystallite Size and Orientation on the Magnetization Ripple in Permalloy Films

Abstract

Permalloy films of composition 83% Ni 17% Fe ranging from polycrystalline to monocrystalline were prepared by evaporation. Conventional electron micrographs, selected area diffraction patterns, and Lorentz electron micrographs were taken to study the average magnetic ripple wavelength (λ0) as a function of the average crystallite size (a) of the film. Below a critical crystallite size, polycrystalline films showed a linear increase of the ripple wavelength with increase in crystallite size. It was found that λ0=4a in agreement with the maximum probable wavelength predicted theoretically by Rother. Films with preferred orientation showed similar behavior with λ0=10a. A plateau was reached (λ0=9000 Å, a=2000 Å, λ0=12 000 Å, a=1160 Å, respectively) after which an increase in crystallite size had no effect on the ripple wavelength. Monocrystalline films did not exhibit ripple structure and it is concluded that in these films λ0=∞.