Magnetic phase diagram of rare-earth orthorhombic perovskite oxides

TL;DR

This paper develops a comprehensive magnetic model for rare-earth orthorhombic perovskite oxides using density functional theory and spin dynamics, revealing the microscopic origins of spin reorientations and magnetization reversals.

Contribution

It introduces a general Heisenberg model that explains the microscopic mechanisms behind spin reorientations and magnetization reversals in these compounds.

Findings

Magnetization reversal depends on superexchange and Dzyaloshinsky-Moriya interactions.

Smooth spin reorientation occurs through a coexisting region between phases.

Different rotation rates of spin sublattices cause the intermediate coexistence region.

Abstract

Spin reorientation and magnetisation reversal are two important features of the rare-earth orthorhombic provskites ($RM$O$_{3}$'s) that have attracted a lot of attention, though their exact microscopic origin has eluded researchers. Here, using density functional theory and classical atomistic spin dynamics we build a general Heisenberg magnetic model that allows to explore the whole phase diagram of the chromite and ferrite compounds and to scrutinize the microscopic mechanism responsible for spin reorientations and magnetisation reversals. We show that the occurrence of a magnetization reversal transition depends on the relative strength and sign of two interactions between rare-earth and transition-metal atoms: superexchange and Dzyaloshinsky-Moriya. We also conclude that the presence of a smooth spin reorientation transition between the so-called $\Gamma_4$ and the $\Gamma_2$ phases through a coexisting region, and the temperature range in which it occurs, depends on subtle balance of metal--metal (superexchange and Dzyaloshinsky-Moriya) and metal--rare-earth (Dzyaloshinsky-Moriya) couplings. In particular, we show that the intermediate coexistence region occurs because the spin sublattices rotate at different rates.