Ferromagnetic resonance studies of cobalt-copper alloys - art. no. 184419

A systematic study of the ferromagnetic resonance (FMR) of the metastable C oxCu100-x granular alloy ribbons prepared by melt-spinning was made as a fu nction of magnetic field angle relative to the normal to the plane of the r ibbon, and annealing temperature. This study allowed changes in the Co grai ns to be followed. The measurements were performed at room temperature, for cobalt concentrations of x = 3. 5, 10, and 15, with samples both as-east a nd annealed for 1 h at temperatures between 400 and 800 degreesC. In order to obtain the resonance fields and linewidths. the FMR spectra were fitted as a sum of absorption and dispersion functions. We observed that the reson ance fields and linewidths vary in a systematic way with the angle of the m agnetic field. with Co concentration, and with the annealing temperature. T hese results were interpreted using the Kittel equation for ferromagnetism. as well as simulations of the resonance field with the angle derived for s pherical superparamagnetic grains. The analysis of the FMR spectra indicate s grains whose mean diameters vary between 1.4 +/- 0.1 nm and 4.1 +/- 0.1 n m. depending on the cobalt concentration and annealing temperature. In addi tion, measurements of Co5Cu95 annealed samples show a reduction in their ma gnetization at certain temperatures. This reduction is probably induced by a change in the crystal structure of the cobalt grains, or by the dissoluti on of the smaller ferromagnetic grains in the Cu matrix.