Abstract
Sodium-substituted perovskitesLa0.9Na0.1MnO3 and La0.8Na0.2MnO3, which crystallize in pseudo-cubic symmetry, and are respectively a disordered and an orderedferromagnet, have been studied for their electrical behaviour. The two samples show large negativemagnetoresistance. The lesser sodium-containing system shows a metal–insulator transition at∼210 K, which is well below the temperature where it completely goes to the paramagnetic state.In the higher sodium-containing sample both the magnetic and electrical transitions wouldfall only above 300 K. In the conducting state in both samples, resistivity hascontributions from scattering from grain boundaries, electron–electron scattering andelectron–magnon (spin wave) scattering. However, in the insulating (semiconducting) stateeven the lesser sodium-containing system (in which the insulating state has beenobserved in the temperature range of study) follows small polaron hopping under anadiabatic approximation and the estimated activation energy values at differentfields are also identical to those reported in magnetically ordered perovskites.La0.9Na0.1MnO3 shows an upturn in resistivity with decreasing temperature at∼30 K which is attributed to spin-polarized intergranular tunnelling.
Published Version
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