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. The increases in electrical conductivity, and the sharpness of the magnetic transition temperatures, as determined by initial permeability measurements, are strongly related to the doping concentration. Between about 1 and 1.5% chloride doping in EuS, the magnetic inhomogeneity at the transition temperature is sharply lowered and the conductivity shows a marked increase. The different environments of the dopant, whether it is on the anion or cation site, and their effect on the spin cluster formation are discussed. © 1971.