Impact of Co3O4 phase on the magnetocaloric effect and magnetoresistance in La0.7Sr0.3MnO3/Co3O4 and La0.7Ca0.3MnO3/Co3O4 ceramic composites

We report the magnetic transition, magnetocaloric effect and magnetoresistance in Co3O4 modified La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 perovskites manganite. The composite, samples with nominal composition of (La0.7Ca0.3MnO3 or La0.7Sr0.3MnO3)0.9/(Co3O4)0.1 were prepared using the conventional solid-state reaction method. The phase purity and structure were confirmed by using X-ray diffraction. The scanning electron micrographs show that Co3O4 is mainly distributed at the grain boundaries and surface of the pervoskite matrix. Temperature dependent magnetization measurements and Arrott analysis reveal second order of phase transition (ferromagnetic to paramagnetic) in composite samples. A large magnetic entropy change (~3.04 J/kg K at 1 T) has been observed in La0.7Ca0.3MnO3 sample, and is suppressed due to the impact of Co3O4 phase in composite sample. On the other hand, the addition of Co3O4 as secondary phase in La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 samples enhances their relative cooling power (RCP). The RCP values of ~128 and 160 J/kg were obtained for La0.7Sr0.3MnO3/Co3O4 and La0.7Ca0.3MnO3/Co3O4 composite samples, respectively at magnetic field of 3 T. The resistivity of the composite sample was measured at the applied magnetic fields of 0.0 T and 0.5 T. The MR of 24.6% was observed for La0.7Ca0.3MnO3/Co3O4 composite at 200 K which is 12.1% higher than that of La0.7Ca0.3MnO3 pure sample. The enhanced RCP and MR of these composites make them attractive for potential applications.