Crossover of polaron conductivity and the inhomogeneous state of lanthanummanganites in the magnetic phase transition region

The transport properties of lanthanum manganites over a wide range of tempe ratures below the magnetic phase transition point are discussed within the model of a two-phase composite whose phases differ in the magnetic order an d charge carrier concentration. The volume ratio of the phases depends on t he temperature and the magnetic field. The magnetoelastic polarons are char ge carriers in both phases, and the metal-dielectric transition occurs as a percolation transition accompanied by the crossover of the polaron conduct ivity. The results obtained by numerical simulation of the resistivity, mag netoresistance, and thermopower are compared with the experimental data for La0.7Mn1.3O3-delta thin films. The theoretical and experimental data are i n good agreement. (C) 2001 MAIK "Nauka/Interperiodica".