Intermediate-valence–driven magnetic complexity in Sm2MnCeO6+δ (SMCO) double perovskite: Coupled structural stability, Griffiths phase dynamics, and multifunctional potential

Understanding how mixed-valence rare-earth ions mediate magnetic complexity in oxide perovskites is critical for advancing multifunctional materials for energy and spin-based technologies. Here, we report a comprehensive structural, electronic, and magnetic investigation of the oxygen-rich double perovskite Sm2MnCeO6+δ (SMCO), synthesized via a high-temperature solid-state route. Rietveld-refined X-ray diffraction (XRD) confirms a single-phase cubic structure (Ia3d), while X-ray Photoemission spectroscopy (XPS) reveals pronounced intermediate valence behaviour of Ce (Ce3+/Ce4+), accompanied by mixed Mn2+/Mn3+/Mn4+ and Sm2+/Sm3+ states. These coupled redox configurations generate a rich magnetic landscape characterized by long-range antiferromagnetic (AFM) ordering below a Néel temperature (TN) of 13.8 K, emergent ferromagnetic (FM) correlations with a Curie temperature (TC) of 43.7 K, and an extended Griffiths phase (GP) spanning 46.2–139.1 K. The coexistence of short-range FM clusters within a paramagnetic (PM) matrix highlights the critical role of oxygen non-stoichiometry and Ce-driven electron hybridization in governing magnetic exchange pathways. This work establishes SMCO as a model system for exploiting intermediate valence effects to engineer tuneable magnetic responses, offering promising avenues for catalytic, solid oxide fuel cell, and spintronic applications operating under demanding thermal environments.