Angular Dependence of Spin Pinning in Thin Ferromagnetic Films

Abstract

A discussion of the origin of surface spin pinning in thin ferromagnetic films due to a surface layer possessing slightly different magnetic properties is presented. This model predicts that at a critical angle, measured between the normal to the film and the direction of the external magnetic field, the uniform precession condition will be the same in all regions of the film and the magnetization can be excited as a unit in the uniform precession mode. Spin-wave spectra were obtained at 9.6 and 14.6 kMc from thin films composed of Permalloy (80 Ni−20 Fe) and cobalt. The critical angle depends on the value of ω/4πγ M which varied from 0.167 to 0.667 and gave critical angles that varied from 2° to 15°. These results agree to within ±1° of the predicted values. A critical angle has occurred in every film independent of the substrate material, the cleaning procedure, or the substrate temperature during deposition. The angle dependence of the strength of the spin-pinning condition as predicted by this model at angles other than the critical angle is also compared with the experimental results.