The magnetothermal behavior of mixed-valence Eu3O4

The mixed-valence compound Eu3O4 was prepared by heating an equimolar mixture of EuO and Eu2O3 at 1800 degrees 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 similar to 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 (-Delta S-mag) calculated from heat capacity data of Eu3O4 is approximately 12.7 J/kg K at 6.5 K for a magnetic field change (Delta B) of 5 T. The adiabatic temperature change (Delta T-ad) in Eu3O4 at 7 K is about 7.0 K for a Delta B of 5 T. Also, the magnetic entropy change (-Delta S-mag) calculated from magnetization data in Eu3O4 is approximately 13.6 J/kg K at 6.3 K for a magnetic field change (Delta B) 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. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3204662]