FREE-CARRIER CONCENTRATION-DEPENDENCE OF GD-GD EXCHANGE CONSTANT IN SNTE-GD

In some samples of SnTe:Gd the measured paramagnetic Curie temperature strongly depends on the Fermi level position. The semi-quantitative t heory which explains this effect is presented. The theory is based on Kasuya's model of exchange interaction between two 4f spins of rare ea rth ions. In this model the interaction between 4f electrons and the v alence band goes via Gd atomic 5d orbitals which, contrary to the 4f o rbitals are much more extended in space. The exchange integral and the paramagnetic Curie temperature dependence on the Fermi level position are calculated.