Effects of Ni2+ and Cr3+ Substitution at Mn-Site on Structural and Electrical Resistivity of Charge Ordered Divalent-Doped Sm0.5Ca0.5MnO3 Manganite

Abstract

Perovskite manganites (R1-xAxMnO3) are widely studied for their unique magneto-transport properties, especially the metal-insulator transitions. Sm0.5Ca0.5MnO3 is a prototypical half-doped manganite known for its strong charge-ordering (CO) behaviour and high CO temperature (TCO ≈ 270 K), which limits its practical applications due to persistent insulating characteristics. Throughout this study, the effect of partial Mn-site substitution with Ni2+and Cr3+ions in relation to the structural and electrical transport properties of Sm0.5Ca0.5Mn1-xAxO3 (A = Ni, Cr; x = 0.07) is investigated to explore potential suppression of the CO state and the promotion of ferromagnetic metallic (FMM) behaviour. Polycrystalline of the samples were synthesized via solid-state reaction. X-ray diffraction tied with Rietveld refinement confirmed single-phase orthorhombic pnma structure across all samples. Substitution with Ni2+resulted in an increase in unit cell volume while Cr3+ substitution slightly reduced it and attributed to differences in ionic radii. Both substitutions reduced the Jahn–Teller distortion; however, Cr³⁺ was more effective due to its stronger coupling with the Mn–O–Mn network and enhanced double-exchange interactions. The Ni²⁺-substituted sample remains insulating, although its resistivity is reduced due to lattice disorder.In contrast, Cr3+ substitution induced a clear metallic-insulating transition at TMI = 55 K (0 T) and 75 K (0.8 T), evidencing effective CO suppression and enhancement of double exchange driven FMM interactions. These findings demonstrate that Mn-site Cr3+substitution is a promising approach for destabilizing the CO state and inducing metallic behavior in strongly CO manganites with implications for future magnetoresistive and spintronic device applications.