High-field magnetic structure of the triangular antiferromagnet RbFe(MoO4)2

TL;DR

This study investigates the high-field magnetic phases of the quasi-two-dimensional triangular antiferromagnet RbFe(MoO4)2 using NMR and neutron diffraction, revealing detailed magnetic structures and phase transition characteristics.

Contribution

It provides the first detailed determination of magnetic moment arrangements in various high-field phases of RbFe(MoO4)2, including the nature of phase transitions.

Findings

Identification of Y, UUD, V, and fan magnetic phases.

First-order transition from V to fan phase.

Continuous transition from fan to paramagnetic phase.

Abstract

The magnetic H - T phase diagram of a quasi-two-dimensional antiferromagnet RbFe(MoO4)2 with an equilateral triangular lattice structure is studied with 87Rb NMR and neutron diffraction techniques. This combination of experimental techniques allows us to determine the ordered components of the magnetic moments on the Fe3+ ions within various high-field phases - the Y, UUD, V, and fan structures, stabilized in the compound by the in-plane magnetic field. It is also established that the transition from the V to the fan phase is of first-order, whereas the transition from the fan phase to the polarized paramagnetic phase is continuous. An analysis of the NMR spectra shows that the high-field fan phase of RbFe(MoO4)2 can be successfully described by a periodic commensurate oscillation of the magnetic moments around the field direction in each Fe layer combined with an incommensurate modulation of the magnetic structure perpendicular to the layers.