Chemical inhomogeneity induced by coexistence of Mn polyhedra in Sm₂Mn₂O₅: Steady change and reversible magnetocaloric effect

This study investigates the magnetocaloric properties of Sm₂Mn₂O₅ (SMO), synthesized via the solid-state method. SMO crystallizes in the orthorhombic Pbam space group, with Mn³⁺ and Mn⁴⁺ occupying square pyramidal and octahedral sites. Structural analysis reveals Jahn-Teller-driven distortions influencing magnetic exchange, resulting in a stable and reversible magnetocaloric effect (MCE). Magnetic and thermodynamic measurements show a ferromagnetic (FM) transition (T_C ≈ 53.1 K) within a Griffiths phase (51.8–96.6 K) and a field-independent antiferromagnetic (AFM) transition (T_N ≈ 14.4 K). The maximum magnetic entropy change (-ΔS_m) is 8.6 J/kg·K with a refrigerant capacity (RC) of 76.5 J/kg under a 5T field. These results underline SMO's stability and efficiency as a magnetocaloric material. Structural distortions and ligand field effects are key to enhancing its performance. SMO emerges as a promising candidate for low-temperature magnetic refrigeration, with potential for optimization through doping.