Relation of conduction changes and magnetic properties in Nd_1 <i>x</i>Pb_<i>x</i>MnO₃(0.10  <i>x</i>  0.25)

Abstract

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