Phase Diagram of Lattice-Spin System RbCoBr$_3$

TL;DR

This paper investigates the phase diagram of the lattice-spin model of RbCoBr$_3$ using mean field approximation, revealing complex phase boundaries, intermediate phases, and the emergence of a three-sublattice ferrimagnetic state due to lattice distortion.

Contribution

It provides the first detailed phase diagram of the RbCoBr$_3$ lattice-spin system, highlighting the effects of lattice distortion on phase transitions and magnetic states.

Findings

Continuous phase boundary across the entire region

Appearance of intermediate and partial disordered phases

Existence of a three-sublattice ferrimagnetic state

Abstract

We study the lattice-spin model of RbCoBr$_3$ which is proposed by Shirahata and Nakamura, by mean field approximation. This model is an Ising spin system on a distorted triangular lattice. There are two kinds of frustrated variables, that is, the lattice and spin. We obtain a phase diagram of which phase boundary is drawn continuously in a whole region. Intermediate phases that include a partial disordered state appear. The model has the first-order phase transitions in addition to the second-order phase transitions. We find a three-sublattice ferrimagnetic state in the phase diagram. The three-sublattice ferrimagnetic state does not appear when the lattice is not distorted.