Study on Magnetic Properties of Perovskite Manganite (Nd_{1-<italic>x</italic>}Pr_{<italic>x</italic>})_1.2Sr_1.8Mn₂O₇ (<italic>x</italic>=0.1, 0.2)

The isovalent substitution of Pr3+ for Nd3+ in the double-layered perovskite Nd1.2Sr1.8Mn2O7—facilitated by their comparable ionic radii and contrasting magnetic moments—enables precise control over magnetic exchange interactions and phase competition, leading to enhanced magnetocaloric performance. Polycrystalline samples (Nd1-xPrx)1.2Sr1.8Mn2O7(x=0.1, 0.2) were prepared by conventional solid state reaction method. The perovskite structure have been studied with X-ray diffraction patterns.Magnetic properties were investigated with physical property measurement system to measure the dependence of magnetization on temperature and magnetic field. XRD analysis confirms that Pr3+ doping preserves the parent tetragonal Sr3Ti2O7-type structure (space group I4/mmm) across all compositions, with no detectable secondary phases or symmetry change. Magnetization measurements reveal paramagnetic behavior above two distinct Curie temperatures—TC1=269 K and TC2=254 K—indicating phase heterogeneity. Upon cooling, each sample undergoes a paramagnetic-to-ferromagnetic transition, followed by the emergence of coexisting ferromagnetic and antiferromagnetic domains;moreover, signatures consistent with Griffiths-phase behavior are observed in all doped specimens. Under an external magnetic field of 7 T, the maximum magnetic entropy changes near the Curie temperatures are 0.384 J·kg-1·K-1 and 0.374 J·kg-1·K-1, the corresponding maximum adiabatic temperature changes are 0.119 K and 0.129 K, and the relative cooling powers (RCP) are 43.392 J/kg and 53.669 J/kg, respectively. It is further confirmed that all samples undergo a second-order magnetic phase transition near their Curie temperatures, and their critical behavior is consistent with the mean-field model. The results demonstrate that moderate Pr3+ doping induces a marginal reduction in the peak magnetic entropy change; however, it concurrently broadens the operating temperature window for magnetocaloric response, thereby enhancing the relative cooling power (RCP). Critically, all doped compositions retain second-order magnetic phase transitions, with critical behavior quantitatively consistent with mean-field theory predictions. Collectively, these findings offer experimentally grounded guidance for the rational design and performance optimization of double-layered perovskite manganites as active materials in solid-state magnetic refrigeration.