Effect of Ba2+ Substitution at A-site on Structural, Electrical, and Magnetic Properties of Sm0.5Ca0.5MnO3 Perovskite Manganite

Mixed-valence perovskite manganites have attracted considerable attention due to their intriguing properties, such as colossal magnetoresistance and charge ordering (CO). In this study, Sm0.5Ca0.5-xBaxMnO3 (x = 0, 0.10, 0.20, 0.30, and 0.40) manganites were synthesized via the conventional solid-state reaction method to investigate the effect of Ba2+ substitution on their structural, magnetic, and electrical properties. X-ray diffraction patterns confirmed that all samples were single-phase and crystallized in an orthorhombic structure with a Pnma space group. Rietveld refinement indicated an increase in unit cell volume with increasing Ba2+ concentration, suggesting the successful substitution of Ba2+ at the Ca2+ site. Four-point probe resistivity measurements performed over the temperature range of 30–300 K under 0 T and 0.8 T revealed that all Ba-substituted samples remained insulating. Nevertheless, the application of an external magnetic field led to noticeable reduction in resistivity, signifying the presence of magnetoresistance. The increasing Ba2+ concentration further reduced resistivity values, indicating the weakening of the CO phase. This effect was attributed to an increase in the average A-site ionic radius, which enhanced the electron bandwidth. Despite the Ba2+ substitution, the A-site mismatch cation had a more dominant impact than the increasing bandwidth, resulting in insulating behavior. Magnetic susceptibility measurements showed that Sm0.5Ca0.5MnO3 exhibited paramagnetic behavior with a charge-ordering temperature, TCO ≈ 270 K. Ba2+ substitution (x = 0.10–0.40) led to a weakening in charge ordered state and a reduction in the Néel temperature, TN.