Phase diagram for Ca1-xYxMnO3 type crystals

We present a simple model to study the electron doped manganese perovskites . The model considers the competition between double exchange mechanism for itinerant electrons and antiferromagnetic superexchange interaction for lo calized electrons. It represents each Mn4+ ion by a spin 1/2, on which an e lectron can be added to produce Mn3+ we include a hopping energy t, a stron g intratomic ferromagnetic interaction exchange J (in the limit J/t --> inf inity), and an interatomic antiferromagnetic interaction K between the loca l spins. Using the Renormalized Perturbation Expansion and a Mean Field App roximation on the hopping terms and on the superexchange interaction, we ca lculate the free energy. From it, the stability of the antiferromagnetic, c anted, ferromagnetic, and novel spin glass phases can be determined as func tions of the parameters characterizing the system. The model results can be expressed in terms of t and K for each value of the doping x in phase diag rams. The magnetization m and canting angle theta can also be calculated as functions of temperature for fixed values of doping and model parameters. (C) 1999 Elsevier Science Ltd. All rights reserved.