Dynamic properties of ferromagnetic cobalt/transition metal alloy weakly substituted by magnetic rare earths

Using radio-frequency (r-f) sputtering, we hae prepared in presence of a static magnetic field, ferromagnetic thin films of composition (Co9oZr7)100-yREy (RE= Nd, Pr, Dy, Tb.. a magnetic rare earth element). The study was performed for small amounts of RE substitution (010 kG). A low in-plane uniaxial anisotropy Hk forms, whose magnitude depends upon the composition and the preparation parameters. Substitution by RE atoms affects essentially the μ frequency-response. Depending on the nature, the concentration of RE atoms and on the value of Hk, a high relative rotational permeability μ (μ' ∝ 500-3000 at frequencies up to 500 MHz) was obtained. Also depending on RE and on y, high μ'' (μ'' ∝ 400-3000 at v ∝ 1 GHz) distributed over a very broad frequency range (Δv ∝ 500-2500 MHz) was measured. Using the Landau-Lifshitz equations for high frequency permeability and the values of the magnetic parameters measured by FMR, experimental spectra could be well approximated. (orig.)