The study reports the influence of rare-earth ion doping on the structural, magnetic, and magnetocaloric properties of ferrimagnetic Gd_3−xRE_xFe₅O₁₂ (RE = Y, Nd, Sm, and Dy, x = 0.0, 0.25, 0.50, and 0.75) garnet compound prepared via facile autocombustion method followed by annealing in air. X-Ray diffraction (XRD) data analysis confirmed the presence of a single-phase garnet. The compound’s lattice parameters and cell volume varied according to differences in ionic radii of the doped rare-earth ions. The RE³⁺ substitution changed the site-to-site bond lengths and bond angles, affecting the magnetic interaction between site ions. Magnetization measurements for all RE³⁺-doped samples demonstrated paramagnetic behavior at room temperature and soft-ferrimagnetic behavior at 5 K. The isothermal magnetic entropy changes (−ΔS_M) were derived from the magnetic isotherm curves, M vs. T, in a field up to 3 T in the Gd_3−xRE_xFe₅O₁₂ sample. The maximum magnetic entropy change ($-∆S_M^{max}$) increased with Dy³⁺ and Sm³⁺substitution and decreased for Nd³⁺ and Y³⁺ substitution with x content. The Dy³⁺-doped Gd_2.25Dy_0.75Fe₅O₁₂ sample showed $-∆S_M^{max}$~2.03 Jkg⁻¹K⁻¹, which is ~7% higher than that of Gd₃Fe₅O₁₂ (1.91 Jkg⁻¹K⁻¹). A first-principal density function theory (DFT) technique was used to shed light on observed properties. The study shows that the magnetic moments of the doped rare-earths ions play a vital role in tuning the magnetocaloric properties of the garnet compound.

The study reports the synthesis and characterization of the magnetic and magnetocaloric effects of metal-oxide (MO) modified La_0.7Ca_0.3MnO₃ perovskites manganite. The powder composite samples, with a nominal composition of (1 − x)La_0.7Ca_0.3MnO₃-xMO (Wt.% x = 0.0, 2.5, 5.0), were prepared using the facile autocombustion method, followed by an annealing process. The phase purity and structure were confirmed by X-ray diffraction. Temperature and field-dependent magnetization measurements and Arrott analysis revealed mixed first- and second-order phase transition (ferromagnetic to paramagnetic) in composite samples. The phase transition temperature shifted to lower temperatures with the addition of MO in the composite. A large magnetic entropy change (4.75 JKg⁻¹K⁻¹ at 1T and 8.77 JKg⁻¹K⁻¹ at 5T) was observed in the La_0.7Ca_0.3MnO₃ (LCMO) sample and was suppressed, due to the presence of the MO phase in the composite samples. On the other hand, the addition of MO as a secondary phase in the LCMO samples enhanced their relative cooling power (RCP). The RCP of all composite samples increased with respect to the pristine LCMO, except for LCMO–5%NiO. The highest RCP value of 267 JKg⁻¹ was observed in LCMO–5%CuO samples, which was 23.4% higher than the 213 JKg⁻¹ observed for the pure LCMO at a magnetic field of 5T. The enhanced RCP of these composites makes them attractive for potential refrigeration applications.