Magnetic hyperfine fields for Sn atoms in rare-earth intermetallides: huge deviation from proportionality between Bhf and Sz

The magnetic hyperfine fields for 119Sn impurity atoms, localized in Ga sites of ferromagnetic intermetallic compounds RGa (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm), were measured by the Mössbauer spectroscopy technique. At T=5 K, the hyperfine field value (Bhf) varies from 3.3 T in TmGa to 28.0 T in GdGa. Huge deviation from the proportionality between Bhf and the projection of the R3+ ion spin (Sz=(g−1)J) was found. As the atomic number of the R element increases, the Bhf/Sz ratio drastically decreases from 12.6 T for PrGa to 3.3 T for TmGa. This unexpected result can be explained by the strong dependency of Bhf value on the relationship between the Sn–R atomic separation (Rnn) and the radius of the magnetic 4f shell (R4f). In the framework of this concept, the available experimental data for Sn atom in the rare-earth compounds with non-magnetic sp elements were considered. The data may be described by the universal dependency on the single parameter, λ=Rnn/R4f.