Magnetic field-induced entropy change in phase-separated manganites

摘要

Magnetic field-induced entropy change has been experimentally studied for phase-separated manganites Eu_(0.55)Sr_(0.45)MnO_3 and La_(0.27)Nd_(0.40)Ca_(0.33)MnO_3. The entropy derived from the measured heat capacity exhibits a significant decrease under applied field in a broad temperature range below Curie temperature, and the maximum change is ～8 J/kg K for Eu_(0.55)Sr_(0.45)MnO_3 and is ～4.2 J/kg K for La_(0.27)Nd_(0.40)Ca_(0.33)MnO_3 for a field change of 0-5 T. In comparison with the calorimetric technique, Maxwell relation fails to give a proper description for the entropy change. It underestimates the entropy reduction in the low temperature range and even anticipates an entropy increase for Eu_(0.55)Sr_(0.45)MnO_3. Failures of the Maxwell relation could be ascribed to the coexistence of two phases in the compound and to the variation of the proportion of each phase with applied field.