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 °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 (-ΔS_mag) 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 (ΔT_ad) in Eu₃O₄ at 7 K is about 7.0 K for a ΔB of 5 T. Also, the magnetic entropy change (-ΔS_mag) 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. [ABSTRACT FROM AUTHOR]