Effect of Ca2+ Doping on the Structural, Magnetic and Magneto-Transport Properties of La1-xCaxMnO3 Manganites: Insights from XPS and 55Mn IFNMR Studies.

In this study, La1-xCaxMnO3 (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.