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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.
Sondezi et al. (Sat,) studied this question.