Effect of Metal-Oxide Phase on the Magnetic and Magnetocaloric Properties of La 0.7 Ca 0.3 MnO 3 -MO (MO=CuO, CoO, and NiO) Composite.

The study reports the synthesis and characterization of the magnetic and magnetocaloric effects of metal-oxide (MO) modified La_0.7Ca_0.3MnO₃ perovskites manganite. The powder composite samples, with a nominal composition of (1 − x)La_0.7Ca_0.3MnO₃-xMO (Wt.% x = 0.0, 2.5, 5.0), were prepared using the facile autocombustion method, followed by an annealing process. The phase purity and structure were confirmed by X-ray diffraction. Temperature and field-dependent magnetization measurements and Arrott analysis revealed mixed first- and second-order phase transition (ferromagnetic to paramagnetic) in composite samples. The phase transition temperature shifted to lower temperatures with the addition of MO in the composite. A large magnetic entropy change (4.75 JKg⁻¹K⁻¹ at 1T and 8.77 JKg⁻¹K⁻¹ at 5T) was observed in the La_0.7Ca_0.3MnO₃ (LCMO) sample and was suppressed, due to the presence of the MO phase in the composite samples. On the other hand, the addition of MO as a secondary phase in the LCMO samples enhanced their relative cooling power (RCP). The RCP of all composite samples increased with respect to the pristine LCMO, except for LCMO–5%NiO. The highest RCP value of 267 JKg⁻¹ was observed in LCMO–5%CuO samples, which was 23.4% higher than the 213 JKg⁻¹ observed for the pure LCMO at a magnetic field of 5T. The enhanced RCP of these composites makes them attractive for potential refrigeration applications. [ABSTRACT FROM AUTHOR]