Studies of Curie-point increases in EuO

Abstract

The ferromagnetic transition temperature (TC) of EuO has been increased from 69°to 135°K by selectively doping to increase the electrical conductivity. Three different chemical systems have been studied: the EuO-Eu, the EuO-Eu-RE2O3, and the EuO-RES systems (RE is a rare earth other than europium). Compositions in the latter system were multiphase because the solubility of the rare-earth sulfides in EuO is very small and it was necessary to add about 10% to cause significant Curie-temperature increase. Single crystals have been grown from ternary compositions in the EuO-Eu-RE2O3 system with magnetizations at 77°K as high as 170 G cm3/g and ferromagnetic Curie temperatures (TC) close to the paramagnetic θ values, a condition not observed in the other doped europium chalcogenides. The effect of the Eu metal on the formation of these crystals and its role in "forcing" the trivalent rare-earth oxide into the rock-salt lattice is discussed. From Kerr measurements and the optical absorption data it is shown that the magnitude of the rotation of the doped material at 80°K is equal to that of pure EuO at 18°K. This makes this material attractive for use in magneto-optical devices operating at nitrogen temperature. © 1968 The American Institute of Physics.