Multiferroicity in the generic easy-plane triangular lattice antiferromagnet RbFe(MoO4)2

TL;DR

This paper investigates the multiferroic properties of RbFe(MoO4)2, a quasi-2D triangular lattice antiferromagnet, revealing how its magnetic interactions and field-induced phases relate to its multiferroicity.

Contribution

It provides a quantitative spin Hamiltonian for RbFe(MoO4)2 and links its multiferroic behavior to the physics of the 2D XY triangular lattice antiferromagnet.

Findings

Easy-plane anisotropy is about one-third of the dominant exchange.

Magnetic fields induce fluctuations stabilizing finite-field phases.

Dzyaloshinskii-Moriya interactions generate ferroelectricity only at zero field.

Abstract

RbFe(MoO4)2 is a quasi-two-dimensional (quasi-2D) triangular lattice antiferromagnet (TLA) that displays a zero-field magnetically-driven multiferroic phase with a chiral spin structure. By inelastic neutron scattering, we determine quantitatively the spin Hamiltonian. We show that the easy-plane anisotropy is nearly 1/3 of the dominant spin exchange, making RbFe(MoO4)2 an excellent system for studying the physics of the model 2D easy-plane TLA. Our measurements demonstrate magnetic-field induced fluctuations in this material to stabilize the generic finite-field phases of the 2D XY TLA. We further explain how Dzyaloshinskii-Moriya interactions can generate ferroelectricity only in the zero field phase. Our conclusion is that multiferroicity in RbFe(MoO4)2, and its absence at high fields, results from the generic properties of the 2D XY TLA.