Fully-frustrated octahedral antiferromagnets: emergent complexity in external field

TL;DR

This paper investigates the complex magnetic phases of fully frustrated octahedral antiferromagnets under external magnetic fields, revealing a rich phase diagram with fractional magnetization plateaus and stable states due to order by disorder.

Contribution

It provides the first detailed Monte Carlo simulation-based phase diagram for the fully frustrated octahedral antiferromagnet, identifying multiple stable field-induced magnetic states.

Findings

Discovery of fractional magnetization plateaus at 1/3 and 2/3

Identification of eight stable field-induced states

Revelation of order by disorder stabilizing complex phases

Abstract

Octahedral antiferromagnets are distinguished by crystal lattices composed of octahedra of magnetic ions. In the fully frustrated case, the Heisenberg Hamiltonian can be represented as a sum of squares of total spins for each octahedral block. We study the fully frustrated spin model for a lattice of edge-shared octahedra, which corresponds to the J1-J2 fcc antiferromagnet with J2/J1 = 1/2. The magnetization process at this strongly frustrated point features a remarkably rich sequence of different magnetic phases that include fractional plateaus at m = 1/3 and 2/3 values of the total magnetization. By performing extensive Monte Carlo simulations we construct the H-T phase diagram of the classical model with eight field-induced states, which acquire stability via the order by disorder mechanism. These antiferromagnetic states have distinct spin configurations of their octahedral blocks. The same spin configurations are also relevant for the fully frustrated corner-shared model bringing an apparent similarity to their field-induced states.