High magnetoresistance in La0.5Nd0.15Ca0.25A0.1MnO3 (A = Ca, Li, Na, K) CMR manganites: Correlation between their magnetic and electrical properties

The influence of A-site cation disorder of monovalent alkali ions on structural and magneto-transport properties of colossal magnetoresistive (CMR) materials has been reported. All the compounds crystallize in Pbnm space group with orthorhombic symmetry. At low temperature, the samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition and a semiconductor to metallic one. The variation in both Curie temperature (T-c) and metal-semiconductor transition temperature (T-MS) can be explained by the change in Mn4+ content and average A-site cation radius. A decrease in resistivity in the vicinity of T-MS has been observed with an increase in the applied magnetic field. The values of T-c are dose to T-MS, signifying strong correlations between the magnetic and electrical properties. The electrical resistivity data in paramagnetic-semiconducting region (T > T-MS) may be described by the adiabatic small polaron hopping (ASPH) model. Maximum magnetoresistance (MR%) has been observed in the vicinity of T-MS.