Theoretical considerations on the transport property of La1-xCaxMnO3 in the paramagnetic regime

The transport properties of La1-xCaxMnO3 single crystal in the paramagnetic state is investigated from both the theoretical and the experimental point of view. The temperature dependence of the resistivity calculated by using the Monte Carlo technique within the framework of the double-exchange mode l shows a sharp peak structure and a large magnetoresistance under the appl ication of the magnetic field in the vicinity of the metal-insulator transi tion temperature, T-MI. The experimental result for the resistivity can be fitted well with both a variable-range hopping (VRH) and a small-polaron ho pping (SPH) conduction in the paramagnetic state, whereas the Monte Carlo s imulation works well with a VRH model but displays some deviations close to T-MI With a SPH model, This is largely due to poor knowledge of the lattic e effect in the double-exchange model. On the basis of our analysis on the transport property above T-MI we propose that both the spin-disorder scatte ring and the lattice distortion should be considered to explain the nature of the localization in the paramagnetic regime. (C) 2000 Elsevier Science L td. All rights reserved.