Large magnetocaloric entropy change at room temperature in soft ferromagnetic manganites.

In this paper, La 0.75 Ca 0.25- x Na x MnO 3 ( x = 0.15 and 0.20) samples were prepared by the flux method. Crystallographic study revealed that the x = 0.15 sample is characterized by the coexistence of a mixture of orthorhombic and rhombohedral structures with Pbnm and R 3̄ c space groups, respectively. While, the x = 0.20 sample crystallized in the rhombohedral structure with a R 3̄ c space group. Magnetic data, under a magnetic field of 0.05 T, indicated that our samples undergo a ferromagnetic (FM)-paramagnetic (PM) phase transition, on increasing the temperature. The magnetic field dependence of the magnetocaloric properties of La 0.75 Ca 0.25- x Na x MnO 3 ( x = 0.15 and 0.20) samples, with the second phase transition, was investigated. Near room temperature, the x = 0.20 sample exhibited a large magnetic entropy change with maxima of 6.01 and 3.12 J kg -1 K -1 , respectively, under applied magnetic fields of 5 and 2 T. Also, the relative cooling power (RCP) was calculated. According to hysteresis cycles, for our studied samples, at 10 K a typical soft FM behavior with a low coercive field was observed. These results make our samples promising candidates for magnetic refrigerators, magnetic recording, and memory devices.