Magnetic Properties of Some Divalent Europium Compounds

Abstract

The compounds of divalent europium form an attractive series for magnetic investigations because the magnetic ions are in S states and the crystal structures are generally simple. Moreover, true ferromagnetism, which is quite unusual in compounds, has been observed in EuO by Matthias, Bozorth, and Van Vleck. We have prepared samples of EuS, EuSe, EuTe, EuCO₃, EuTiO₃, EuZrO₃, EuSO₄, and EuCl₂, and studied their magnetic properties in the temperature range 4–300°K. The sulfide, selenide, and telluride all have the same NaCl crystal structure as EuO; we find that the first two also become ferromagnetic at low temperature, while EuTe is paramagnetic, or possibly antiferromagnetic, at 4.2°K. The Curie temperatures for EuS and EuSe are about 18° and 7°K, respectively. The saturation moments of EuS and EuSe extrapolated to 0°K correspond to 6.8 and 6.7 μ_B per Eu⁺⁺ ion, respectively, in good agreement with the expected value of 7 μ_B. None of the other compounds were ferromagnetic at liquid helium temperatures, and all exhibited θ values very near to 0°K. A tentative interpretation of the exchange interactions in the rocksalt compounds is made using a molecular field treatment.