Frequency-dependent complex permeability in rare earth-substituted cobalt/nonmagnetic transition metal soft ferromagnetic amorphous thin films

Using radio frequency (rf) sputtering, we have prepared in presence of a static magnetic field, ferromagnetic thin films of composition (Co93Zr7)100−yREy(RE=Nd,Pr,Dy,Tb... a magnetic rare earth element). This study was performed for small amounts of RE substitution (0<y<3). These films exhibit attractive soft magnetic properties similar to CoZr alloys: low coercivity (Hc∼1 Oe), and a high saturation induction (4πMs≳10 kG). A low in-plane uniaxial anisotropy Hk was induced, 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 ν∼1 GHz) distributed over a very broad frequency range (Δν∼500–2500 MHz) could be measured.