Synthesis, structure, morphology, magnetism, and magnetocaloric-effect studies of (La_1−xPr_x)_0.7Sr_0.3MnO₃ nanocrystalline perovskites

Single-Phase (La_1–xPr_x)_0.7Sr_0.3MnO₃ (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) perovskites were synthesized by the sol–gel method followed by sintering at 700 °C for 5 h. Samples with x = 0.0–0.4 are found to crystallize into rhombohedral structure (R-3c space group) while the ones with x = 0.6–1.0 crystallize into orthorhombic structure (Pbnm space group). The average particle size of the samples was in the range of 21–44 nm. All samples exhibit a ferromagnetic to paramagnetic second-order magnetic phase transition at Curie temperature, which is found to decrease linearly with increasing the Pr concentration. The magnetic coercivity was found to be small (~ 10 Oe) for all the samples, at T < T_C. The experimental effective paramagnetic moment (µ_eff) is found to increase with increasing x from 3.99 µ_B (x = 0.0) to 5.05 µ_B (x = 1.0). The magnitude of the maximum magnetic entropy change (−ΔS_M)_max. and the relative cooling power (RCP) for the samples having orthorhombic structure increases as x increases reaching a maximum value of 4.67 J/kg.K and 574 J/kg at Δµ_oH = 9 T for x = 1.0. While the ones with the rhombohedral structure have the maximum values of (−ΔS_M)_max. and RCP of 4.63 J/kg.K and 472 J/kg at Δµ_oH = 9 T are for x = 0.2. The large values of (−ΔS_M)_max. and RCP (at room temperature (RT)) and the wider temperature range of −ΔS_M for the sample with x = 0.6 suggests that this compound may be considered as magnetic refrigerant material at RT, and the other compounds can be candidates in the vicinity of RT.