Gavinolla Srinivas Reddy

In this study, La_1−xCa_xMnO₃ (LCMO) samples (x = 0.3, 0.4 and 0.5) were synthesized using a sol–gel method and their structural, electronic, magnetic and magneto–transport properties were investigated. Structural analysis by XRD confirmed orthorhombic perovskite structure. FTIR studies indicated the changes in bond length and bond angle of Mn–O/Mn–O–Mn bonds; FESEM/EDAX confirmed a polycrystalline nature. Magneto–transport studies revealed a decrease in ferromagnetic metal–paramagnetic semiconductor transition temperature with the increase in Ca²⁺ content. Magneto–transport studies also revealed that the resistivity in the ferromagnetic metallic region was predominantly governed by the extrinsic spin–polarized tunneling (SPT) mechanism along with double-exchange interaction, whereas charge transport in the paramagnetic semiconducting region at higher temperatures was due to variable-range hopping conduction. Magnetoresistance was at its maximum near the transition temperature, but decreased at lower temperature (77 K). XPS and ⁵⁵Mn IFNMR confirmed coexistence of Mn³⁺/Mn⁴⁺, while IFNMR results at 77 K confirmed high-frequency electron exchange among Mn³⁺ and Mn⁴⁺ ions due to double exchange interaction. VSM studies at 300 K showed that the paramagnetic nature of the samples and susceptibility decreased with the increase in Ca²⁺ content. The close agreement between the magnetoresistance behavior and the ⁵⁵Mn IFNMR results confirms the role of the intrinsic DE interaction in governing the magnetotransport properties of LCMO.