Nanocrystalline La0.67Sr0.33-xCaxMn1-xMxO3 (M = Ni, Co x = 0 and 0.025 (LSM, LSMN, and LSMC) perovskite manganites were synthesized via a sol–gel method. X-ray diffraction confirms a single-phase rhombohedral structure \(R\overline{3 }c\) , with slight lattice distortions induced by doping. Magnetic measurements show a clear ferromagnetic–paramagnetic transition, with Curie temperatures systematically reduced from ~ 350 K for the parent compound to ~ 320 K and ~ 315 K for the Ni- and Co-doped samples, respectively. Critical exponent analysis using Arrott plots, scaling relations, and magnetization isotherms confirms a second-order magnetic phase transition governed by long-range mean-field interactions. All samples exhibit a reversible magnetocaloric effect near the curie temperature (TC). The Ni-doped composition displays the most promising refrigeration performance, combining a broad operating temperature range with a high relative cooling power of approximately 67% of that of gadolinium under a 5 T magnetic field change. This improvement is attributed to the optimized magnetic interactions induced by co-doping. These results highlight the potential of co-doped manganites for near-room-temperature magnetic refrigeration.
