Ferromagnetic Interactions in EuS and EuSe Studied by Neutron Diffraction at Pressures up to 20.5 GPa

Using neutron diffraction at very high pressures (up to 20.5 GPa), we studied magnetic interactions in the model system EuX ( X0ex0ex=0ex0exS, Se, Te) in a wide range of lattice constants. Surprisingly, when interatomic distances decrease, the Curie temperatures increase very rapidly and in a different way for each compound. The results were used to test models of an indirect f-d exchange in magnetic semiconductors. The observed behavior cannot be explained by considering only the overlap between Eu²⁺ d orbitals, pointing out a strong influence of the $2p$ shells, neglected before, on the first neighbor magnetic interaction.