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The magnetic hyperfine interaction of the 119 Sn probe nucleus on the R site of the ferro-and ferrimagnetic RFe 2 (R = Sm-Tm, Lu, Zr, Hf and U) and RCo 2 (R = Gd-Er) compounds has been investigated by Mössbauer 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 RFe 2 compounds, the ratio B hf /µ 3d remains essentially constant across the series at a value of 30 T/µ 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 RCo 2 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 (ErCo 2 ) to about 0.7 (GdCo 2 ). 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.

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