Temperature dependence of ferromagnetic resonance in granular Cu-Co alloy

Ferromagnetic resonance (FMR) spectra (derivatives of microwave power absor ption) were measured in a granular, ribbon-shaped melt-spun Cu90Co10 alloy in a wide range of temperatures from 10 K up to room temperature. Prior to measurements the sample was annealed at 773 K for 1 h in order to create a well-developed granular structure. The results are interpreted using the Ki ttel FMR equations originally introduced for thin ferromagnetic films, as w ell as by using an Arrhenius-type exponential function for superparamagneti c relaxations. These results are also compared with the experimental data o btained from low-field susceptibility measurements in both, zero-field-cool ing and field-cooling modes. It is shown that FMR spectroscopy is a useful tool for studying magnetic properties of granular magnets consisting of nan ometer-scale single-domain particles, in particular, if the resonance spect ra are measured in a wide range of temperatures, thus allowing for identifi cation of the magnetic phases of the particles. The derived value of 10(-13 ) s for the characteristic time of superparamagnetic relaxations is four or ders of magnitude smaller than that commonly used while analyzing data yiel ded by just one measuring technique. The obtained results allowed us to est imate the first order constant of the magnetocrystalline anisotropy for fcc Co particles in the copper matrix K-1=-4.2x10(6) erg/cm(3). (C) 2000 Ameri can Institute of Physics. [S0021-8979(00)07213-3].