MAGNETIC-PROPERTIES OF ISOLATED RH AND RU IMPURITIES IN PD AND PD-FE - A THEORETICAL-STUDY

We perform self-consistent electronic-structure calculations to invest igate the possible existence and formation mechanism of local magnetis m in isolated late-4d transition-metal impurities in Pd and dilute Pd- Fe alloys, using the local-spin-density approximation and the cluster model for simulating the bulk. We find that Ru in Pd exhibits a giant moment of 4mu(B), but reduced in magnitude compared to its 3d counterp art Fe in Pd. Tc and Rh in Pd turn out to be nonmagnetic, the latter i n disagreement with time-differential perturbed-angular-correlation (T DPAC) experiments, which suggest a reduced giant moment per Rh atom al so. The self-consistent small d-band splittings in the primary ferroma gnetic impurity-host d-d hybridization allow for an electronic exchang e conversion mechanism, varying in extent across the 4d series, with c onsequent reduction in the impurity-site local moment and in the host- d spin polarization. The effective suppression of the spin fluctuation s from the impurity-host d-sp interaction is thereby also undermined, resulting in high spin-fluctuation temperatures T(K). In very dilute P d-Fe alloys, a local moment of approximately 1mu(B) is seen to stabili ze at the Rh or Ru site when in the polarization cloud surrounding an Fe atom. The enhancement in the exchange splitting and in the host-d p olarization, producing an extensive polarization cloud with a giant mo ment, suggests a decrease in T(K). At higher Fe concentrations, decora tion of the probe with Fe atoms results in polarization clouds with ul tralarge stabilized local moments, also observed via TDPAC, which incr ease in jumps of at least the approximately 3.4mu(B) d moment on each Fe atom.