DYNAMIC PROPERTIES OF FERROMAGNETIC COBALT TRANSITION METAL-ALLOYS WITH WEAK SUBSTITUTION BY MAGNETIC RARE-EARTHS/

Using radio-frequency (r-f) sputtering, we have prepared in presence o f a static magnetic field, ferromagnetic thin films of composition (Co 93Zr7)100-yREy (RE = Nd, Pr, Dy, Tb... a magnetic rare earth element). The study was performed for small amounts of RE substitution (0 < y < 3). These films exhibit attractive soft magnetic properties similar t o CoZr alloys: low coercivity (H(c) approximately 1 Oe), and a high sa turation induction (B(s) > 10 kG). A low in-plane uniaxial anisotropy H(k) forms, whose magnitude depends upon the composition and the prepa ration parameters. Substitution by RE atoms affects essentially the mu frequency-response. Depending on the nature, the concentration of RE atoms and on the value of H(k), a high relative rotational permeabilit y mu (mu' approximately 500-3000 at frequencies up to 500 MHz) was obt ained. Also depending on RE and on y, high mu'' (mu'' approximately 40 0-3000 at v approximately 1 GHz) distributed over a very broad frequen cy range (DELTAv approximately 500-2500 MHz) was measured. Using the L andau-Lifshitz equations for high frequency permeability and the value s of the magnetic parameters measured by FMR, experimental spectra cou ld be well approximated.