EFFECT OF DISORDER ON THE MAGNETIC AND TRANSPORT-PROPERTIES OF LA1-XSRXMNO3

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