Influence of Ni content on structural, magnetocaloric and electrical properties in manganite La0.6Ba0.2Sr0.2Mn1-xNixO3 (0 ≤ x ≤ 0.1) type perovskites

We present a detailed study on the physical properties of La0.6Ba0.2Sr0.2Mn1-xNixO3 samples (x = 0.00, 0.05 and 0.1). The ceramics were fabricated using the sol-gel route. Structural refinement, employing the Rietveld method, disclosed a rhombohedral R3c phase. The magnetization vs. temperature plots show a paramagnetic-ferromagnetic (PM-FM) transition phase at the T-C (Curie temperature), which decreases from 354 K to 301 K. From the Arrott diagrams M(2)vs. mu H-0/M, we can conclude the phase transition is of the second order. Based on measurements of the isothermal magnetization around T-C, the magnetocaloric effects (MCEs) have been calculated. The entropy maximum change (-Delta S-M) values are 7.40 J kg(-1) K-1, 5.6 J kg(-1) K-1 and 4.48 J kg(-1) K-1, whereas the relative cooling power (RCP) values are 232 J kg(-1), 230 J kg(-1) and 156 J kg(-1) for x = 0.00, 0.05 and 0.10, respectively, under an external field (mu H-0) of 5 T. Through these results, the La0.6Ba0.2Sr0.2Mn1-xNixO3 (0 <= x <= 0.1) samples can be suggested for use in magnetic refrigeration technology above room temperature. The electrical resistivity (rho) vs. temperature plots exhibit a transition from metallic behavior to semiconductor behavior in the vicinity of TM-SC. The adiabatic small polaron hopping (ASPH) model is applied in the PM-semiconducting part (T > T-MS). Throughout the temperature range, rho is adjusted by the percolation model. This model is based on the phase segregation of FM-metal clusters and PM-insulating regions.