Relation of conduction changes and magnetic properties inNd1−xPbxMnO3 (0.10 ≤ x ≤ 0.25)

Abstract

Measurements of bulk conductivity and dielectric relaxation processes by ac methodsincluding complex-plane impedance analyses have been carried out on insulating, together with measurements of four-probe dc conductivity and magnetic susceptibility, so asto investigate the correlation between bulk conduction and short-range ferromagnetism due todouble-exchange (DE) interactions working even above ferromagnetic ordering temperature(Tc). In bulk conduction, there are three temperature regimes where different processesdominate the electronic conduction: (i) the paramagnetic regime above thetemperature at the onset of deviation of inverse magnetic susceptibility from theCurie–Weiss law, (ii) the intermediate regime and (iii) the temperature region belowTc. Though the polaronic conduction occurs in both high-temperature andintermediate regions, the hopping energy and the energy required to createa free hopping polaron differ considerably in these regimes. An anomalyemerges in both bulk conduction and dielectric relaxation processes aroundTc atx = 0.20 and this anomalybecomes more clear at x = 0.25. By taking account of electron–phonon interactions, these results are discussed mainlyin terms of the DE mechanism that brings about short-range ferromagnetism.