MAGNETIC-PROPERTIES OF RARE EARTH-COBALT AMORPHOUS FILMS

Magnetic properties, especially the subnetwork moments of rare earth (RE) and Co in RE-Co amorphous alloy films with RE=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm are investigated based on mean field analysis of the temperature dependence of saturation magnetization. The dependence of the magnetic moment mu(Co) of a Co atom on the RE content is found to be almost independent of RE species except for RE=Ce and Gd. The mu(Co), for RE=Ce, decreases with increasing RE content more quickly than the other cases; this can be attributed to the fact that Ce becomes a 4+ ion in Ce-Co alloy. The mu(Co), for Gd, on the other hand, is found to decrease at a slower rate with increasing RE content. The apparent magnetic moments for various RE atoms are smaller than the theoretical values for RE(3+) except Gd, but the moments are almost independent of the RE content. More precisely, the apparent moments for Ce and Sm are estimated to be zero. The former can be explained by the assumption that Ce becomes a 4+ ion, and the latter by the antiferromagnetic alignment of Sm ions. For other RE species, the decrease of the apparent moment is explained by conical distribution of the RE moment, namely, sperimagnetism. The values of exchange integral J(CoCo) between Co-Co atoms are about 2.2 X 10(-21) J, almost independent of the RE species, but those of J(CoR) between Co and various RE atoms are found to decrease almost linearly from 4.5 X 10(-22) J for RE=Pr to 2 X 10(-22) J for RE=Tm with increasing atomic number. The integral J(RR) between RE-RE is too small to be determined.