Influence of rare-earth ion doping on magnetotransport behavior of potassium doped manganites

The effect of A-site cationic radius A> on structural, electronic and magnetic properties of the perovskite manganites Ln_0.67K_0.33MnO₃ (Ln = La, Pr and Nd) have been investigated. The X-ray diffraction studies show a structural transformation from rhombohedral to orthorhombic with decreasing A>. The ferro to paramagnetic transition decreases from 280 to 110 K and the temperature dependent resistivity shows a metal to insulating transition at room temperature for La_0.67K_0.33MnO₃ while insulating behavior was observed in the case of Pr and Nd substituted samples. Further, La_0.67K_0.33MnO₃ sample exhibits room temperature magnetoresistance, and may be exploited for device applications. The sign of the thermopower is negative at 300 K and its magnitude increases with decreasing A>. The lanthanum based sample shows an upturn in the resistivity data at 30 K and the observed behavior may be attributed to the combined effect of weak localization, electron–electron and electron–phonon scattering. The paramagnetic insulating part of resistivity and thermopower data was analyzed using small polaron hopping mechanism. - Highlights: • The magnetotransport properties of Ln_0.67K_0.33MnO₃ manganites were investigated. • The lanthanum doped sample exhibit an appreciable MR% at room temperature. • The magnitude of thermopower increases with decrease of average cationic radii. • The small polaron hopping mechanism explains high temperature conductivity behavior