Magnetic hyperfine fields at 119Sn probe nuclei on the R sites of the cubic rare-earth Laves-phase compounds RFe2 and RCo2

The magnetic hyperfine interaction of the Sn-119 probe nucleus on the R site of the ferro- and ferrimagnetic RFe2 (R = Sm-Tm, Lu, Zr, Hf and U) and RCo2 ( R = Gd-Er) compounds has been investigated by Mossbauer spectroscopy technique. It was found that the magnetic hyperfine fields (B-hf) exhibit quite different behaviours in the two series of the compounds. For the RFe2 compounds, the ratio B-hf/mu(3d) remains essentially constant across the series at a value of 30 T/mu(B) (within +/- 4%), also for nonmagnetic R = Zr, Lu and Hf. This means that a contribution to B-hf from the 4f magnetic moments of the R sublattice is absent. In RCo2 compounds, the total hyperfine field is the sum of two contributions: one is the 4f contribution (B-4f) and the other is 3d contribution (B-3d). The 3d and 4f contributions have the same relative sign; both contributions are positive with respect to the 3d moments direction. The B-4f contribution is relatively large: the ratio B-4f/B-3d varies from about 0.4 (ErCo2) to about 0.7 (GdCo2). The results demonstrate that the transfer of the electron polarization from the R atoms to the hybrid bonds is extremely sensitive to the features of the 3d electrons of the transition-metal subsystem.