Indirect exchange in europium chalcogenides

The indirect exchange in heavily doped europium chalcogenides is calculated in the mean field approximation. The finite width of the conduction band and carrier statistics (splitting of spin subbands, non‐thermal degeneracy) are taken into account. The model is applied to Gd‐doped EuO and EuS for which magnetic properties are derived. The predictions agree with experimental data both in the para‐ and ferromagnetic configurations. Statistical effects lead to a renormalization of the paramagnetic Curie temperature. Its variations with electron concentration are in good agreement with experiments. Moreover, the model accounts for some particular properties, such as a Curie constant a few per cent below the theoretical one and the systematic deviation of the magnetization curve with respect to the classical Brillouin law in the ferromagnetic configuration. The stability of the ferromagnetic order is also discussed.