The magnetothermal behavior of mixed-valence Eu3O4

Abstract

The mixed-valence compound Eu3O4 was prepared by heating an equimolar mixture of EuO and Eu2O3 at 1800 °C for 30 h in a sealed tungsten crucible. Room temperature x-ray powder diffraction measurements showed that Eu3O4 is single phase. Magnetic measurements on polycrystalline Eu3O4 are in good agreement with the results reported previously. The heat capacity of Eu3O4 from ∼2 to 300 K was not reported in the past. The magnetocaloric effect in Eu3O4 was measured for different applied magnetic fields. The magnetic entropy change (−ΔSmag) calculated from heat capacity data of Eu3O4 is approximately 12.7 J/kg K at 6.5 K for a magnetic field change (ΔB) of 5 T. The adiabatic temperature change (ΔTad) in Eu3O4 at 7 K is about 7.0 K for a ΔB of 5 T. Also, the magnetic entropy change (−ΔSmag) calculated from magnetization data in Eu3O4 is approximately 13.6 J/kg K at 6.3 K for a magnetic field change (ΔB) of 5 T, which is slightly higher than that from the heat capacity data, but is within experimental error. A metamagnetic transition was observed between 0.3 and 0.5 T, however, some antiferromagnetic correlations appear to exist in the magnetically induced ferromagnetic phase at B>3 T.