Quasi two-dimensional antiferromagnet on a triangular lattice RbFe(MoO4)2

TL;DR

This paper investigates the magnetic properties and phase diagram of RbFe(MoO4)2, a quasi-two-dimensional triangular lattice antiferromagnet, revealing multiple magnetic phases, a magnetization plateau, and phase transitions under varying magnetic fields.

Contribution

It provides detailed experimental characterization of the magnetic phases and transitions in RbFe(MoO4)2, highlighting its layered structure and complex phase behavior.

Findings

Identification of a non-collinear triangular spin structure below T_N=3.8 K

Observation of a magnetization plateau at one-third saturation

Detection of an additional first-order phase transition at 35 kOe

Abstract

RbFe(MoO4)2 is a rare example of a nearly two-dimensional Heisenberg antiferromagnet on a triangular lattice. Magnetic resonance spectra and magnetization curves reveal that the system has a layered spin structure with six magnetic sublattices. The sublattices within a layer are arranged in a triangular manner with the magnetization vectors 120 degree apart. The H-T phase diagram, containing at least five different magnetic phases is constructed. In zero field, RbFe(MoO4)2 undergoes a phase transition at T_N=3.8 K into a non-collinear triangular spin structure with all the spins confined in the basal plane. The application of an in-plane magnetic field induces a collinear spin state between the fields H_c1=47 kOe and H_c2=71 kOe and produces a magnetization plateau at one-third of the saturation moment. Both the ESR and the magnetization measurements also clearly indicate an additional first-order phase transition in a field of 35 kOe. The exact nature of this phase transition is uncertain.