Phase diagram for Ca_{1-x}Y_xMnO_3 type crystals

TL;DR

This paper introduces a theoretical model to analyze the phase diagram of electron-doped manganese perovskites, considering competing magnetic interactions and predicting various magnetic phases as functions of doping and temperature.

Contribution

It presents a simplified model combining double exchange and superexchange interactions, providing phase diagrams and magnetic properties for Ca_{1-x}Y_xMnO_3 type crystals.

Findings

Identification of stability regions for different magnetic phases.

Prediction of phase transitions with doping and temperature.

Calculation of magnetization and canting angles.

Abstract

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 localized electrons. It represents each Mn^{4+} ion by a spin 1/2, on which an electron can be added to produce Mn^{3+}; we include a hopping energy t, a strong intratomic interaction exchange J (in the limit J/t>>1), and an interatomic antiferromagnetic interaction K between the local spins. Using the Renormalized Perturbation Expansion and a Mean Field Approximation on the hopping terms and on the superexchange interaction we calculate the free energy. From it, the stability of the antiferromagnetic, canted, ferromagnetic, and novel spin glass phases can be determined as functions 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 diagrams. The magnetization m and canting angle can also be calculated as fuctions of temperature for fixed values of doping and model parameters.