Ferromagnetic resonance evidence for a surface ferromagnetic layer in Co-Cr thin films

Abstract

We studied the ferromagnetic resonance spectra, at 9.8 and 35.2 GHz microwave frequencies, of electron-beam-evaporated Co-Cr magnetic thin films with multiple resonances and found evidence for a surface ferromagnetic layer by chemically etching the samples. The temperature dependence of the line widths of samples with a bulk and surface resonance suggests that the relaxation mechanism in the surface layer is of the impurity type and probably involves the presence of some Co in an oxidized state. The line width of the surface layer is nearly frequency independent, whereas the bulk resonance line widths are frequency dependent with one resonance whose properties suggest incomplete saturation at 9.8 GHz.