Effect of disorder on the magnetic and transport properties of La1-xSrxMnO3

We study a simplified model of the electronic structure of compounds of the type of La1-xSrxMnO3. The model represents each Mn4+ ion by a spin S=1/2, on which an electron can be added to produce Mn3+. We include two strong intratomic interactions in the Hamiltonian: exchange (J) and Coulomb (U). Finally, to represent the effect of Sr substitution by La in a simple way, we include a distribution of diagonal energies at the Mn sites. Then we use Green function techniques to calculate a mobility edge and the average density of states. We find that, according to the amount of disorder and to the concentration of electrons in the system, the Fermi level can cross the mobility edge to produce a metal-to-insulator transition as the magnetization decreases (increase of temperature). If the disorder is large, the system remains insulating for all concentrations. Concentrations near zero or one favor the insulating state while intermediate values of concentration favor the metallic state. Copyright (C) 1996 Elsevier Science Ltd