Synthesis, structure, morphology, magnetism, and magnetocaloric-effect studies of La_0.7Sr_0.3Mn_1−xFe_xO₃ perovskite nanoparticles

Single-phase La_0.7Sr_0.3Mn_1−xFe_xO₃ (x = 0.0, 0.04, 0.08, 0.12, 0.16, 0.20, 0.24, and 0.30) perovskites were synthesized by the sol-gel method followed by sintering at 800 °C for 5 h. The XRD showed the rhombohedral structure with the R-3c space group and there was a slight change in the lattice parameters as well as the unit cell volume of the compounds with Fe doping. The average particle size of the samples was in the range of 43–70 nm. All samples show a ferromagnetic to paramagnetic second-order magnetic phase transition at T_C and T_C decreases linearly from 370 K for x = 0 to 98 K for x = 0.3. From the XPS measurement, it was found that the oxidation state of Fe and La are + 3 and the Mn has a mixed valence state of Mn⁴⁺/Mn³⁺. The saturation magnetization and the blocking temperature were suppressed by the Fe substitution while (-ΔS_M)_max was found to decrease as Fe content increased. The sample with x = 0.08 has a Curie temperature of 297 K, the highest relative cooling power (RCP) of 153 J/kg, and (-ΔS_M)_max value of 1.46 J/kg.K at µ_oΔH = 2.8 T. The La_0.7Sr_0.3Mn_1−xFe_xO₃ iron-substituted manganites may be regarded as a prospective candidate for room-temperature magnetic refrigeration applications.