Phase diagram of electron-doped Mn perovskites

We study the competition between ferromagnetic double exchange and antiferr omagnetic superexchange present in Mn perovskites. The model represents eac h Mn4+ ion by a spin 1/2, on which an electron can be added to produce Mn3. We include a hopping energy t, a strong intratomic interaction exchange J (in the limit J/t --> infinity), and an interatomic antiferromagnetic inte raction K between the local spins. Using the renormalized perturbation expa nsion and a mean-field approximation we calculate the free energy from whic h the stability of the antiferromagnetic, canted, ferromagnetic and 'pseudo -spin-glass' phases can be determined. The phase diagram can be drawn in te rms of temperature and doping x, for each value of K/t. We discuss the pres ence of new 'pseudo-spin-glass' phases. (C) 1999 Published by Elsevier Scie nce B.V. All rights reserved.