Magnetocaloric effect in La1-xCaxMnO3 for x=0.3, 0.35, and 0.4

摘要

We present systematic studies of the magnetocaloric properties of the polycrystalline La1-x Ca (x) MnO3 system for x = 0.3, 0.35, and 0.4 near a second-order phase transition from a ferromagnetic to a paramagnetic state. The crystal structure of the studied manganites was shown to be in good agreement with previous reports. The value of the magnetocaloric effect has been determined from the measurement of magnetization as a function of temperature and external magnetic field. The maximum entropy change detected in La0.7Ca0.3MnO3 at a field of 2 T reaches 8 J/kg K which exceeds that of gadolinium. In all studied samples, the paramagnetic-ferromagnetic transition is very narrow but no hysteresis is observed and the transitions are identified as second-order ones. The phase transition in La0.7Ca0.3MnO3 appears to be almost of first-order.