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

Abstract We report the magnetic transition, magnetocaloric effect and magnetoresistance in Co 3 O 4 modified La 0.7 Ca 0.3 MnO 3 and La 0.7 Sr 0.3 MnO 3 perovskites manganite. The composite, samples with nominal composition of (La 0.7 Ca 0.3 MnO 3 or La 0.7 Sr 0.3 MnO 3 ) 0.9 /(Co 3 O 4 ) 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 Co 3 O 4 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 La 0.7 Ca 0.3 MnO 3 sample, and is suppressed due to the impact of Co 3 O 4 phase in composite sample. On the other hand, the addition of Co 3 O 4 as secondary phase in La 0.7 Ca 0.3 MnO 3 and La 0.7 Sr 0.3 MnO 3 samples enhances their relative cooling power (RCP). The RCP values of ~128 and 160 J/kg were obtained for La 0.7 Sr 0.3 MnO 3 /Co 3 O 4 and La 0.7 Ca 0.3 MnO 3 /Co 3 O 4 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 La 0.7 Ca 0.3 MnO 3 /Co 3 O 4 composite at 200 K which is 12.1% higher than that of La 0.7 Ca 0.3 MnO 3 pure sample. The enhanced RCP and MR of these composites make them attractive for potential applications.