Bulk and surface resonance properties of amorphous Gd-Co films

The magnetic properties of Gd1-xCoxamorphous films (0.81 < x < 0.95) were studied systematically using ferromagnetic resonance and in-plane hysteresis measurements. The various magnetic characteristics such as the magnetization and its temperature dependence, the induced anisotropy, and the ferromagnetic relaxation mechanism were studied in detail. The ferromagnetic resonance (FMR) spectra were interpreted using a model of two exchange-coupled layers: a thick one corresponding to the bulk of the film and a thin one of about 300 Å which forms at the free surface of the films by a preferential oxidation of the rare earth. The location of the surface layer at the film-air interface was demonstrated directly by a chemical etching experiment. The magnetic properties of the two layers and the changes of these layers as functions of various annealing treatments were reported. It was shown particularly that annealing in argon develops a well-defined spin-wave (SW) spectrum in the surface layer. The contribution to the line width of the surface layer arises from an impurity-type relaxation mechanism probably due to the presence of a small percentage of Co in the ionic state. It was suggested that annealing in Ar leads to an atomic reconstruction of this surface layer.