Structural, magnetic, and electronic properties of doped Yb₂NiMnO₆ double perovskites

The multifunctional nature of doped double perovskites arises from the strong coupling between their magnetic and electronic properties. In this work, Yb₂₋ₓCaₓNiMnO₆ (x = 0.0, 0.1, 0.3) double perovskites were synthesized via a conventional solid-state reaction route, and their structural, electronic, dielectric, and magnetic characteristics were systematically investigated. X-ray diffraction confirmed monoclinic symmetry with a P2₁/n space group, supported by Rietveld refinement. Scanning electron microscopy revealed a progressive reduction in grain size with increasing Ca concentration. Dielectric studies demonstrated that the dielectric constant increases with both temperature and Ca substitution, reflecting enhanced polarisation and charge-carrier dynamics. Spectroscopic analysis indicated that Ni and Mn ions predominantly stabilize in mixed oxidation states, which govern electronic structure, facilitate polaronic hopping, and modulate magnetic exchange interactions. Ca substitution systematically lowers the Curie temperature by introducing charge imbalance and structural disorder, which weaken ferromagnetic exchange pathways. These changes promote magnetic irreversibility and glass-like behaviour, with potential implications for magnetoresistance and spintronic applications. Overall, the findings establish a clear correlation between Ca substitution, mixed-valence states, and the coupled dielectric–magnetic behavior, offering valuable insights for tailoring functional oxide materials.