A comparison of ferromagnetic resonance with magnetic moment and x-ray film thickness measurements for thin Permalloy films

In an effort to resolve the ambiguity of the source of pinning of the magnetization invoked in spin-wave resonance measurements, a correlation of the ratio of magnetic moment and x-ray film thickness with the value of effective demagnetizing field 4πNM as determined from resonance, for 81% Ni-19% Fe (Permalloy) evaporated films (10−6 Torr) 40 to 400 Å thick, has been performed. The remarkable agreement of both quantities demonstrates that the thickness dependence of both quantities is related to a thickness-dependent average saturation magnetization, which is far below that of bulk material for very thin films. Furthermore, the extent of this agreement strongly suggests the absence of any significant surface anisotropy or an inhomogeneous demagnetizing field caused by surface roughness in such films. However, a series of complementary experiments shows that this large decrease of average saturation magnetization cannot be simply explained by an oxidation process.