Halide doping of ferromagnetic europium chalcogenides

The europium chalcogenides EuO, EuS, and EuSe are insulating ferromagnets at low temperatures. Rather large increases in their Curie temperature can be effected by doping to increase their electrical resistivity. Previously the doping species have been cation substitutions of “trivalent” rare earth ions or Eu-metal. It is shown here that the monovalent halide ions, particularly Cl⁻, are very effective in increasing the conductivity and Curie temperature of EuS and EuSe.