Stabilization of the collinear plateau phase by thermal fluctuations in the disordered triangular lattice antiferromagnet Rb$_{(1-x)}$K$_{x}$Fe(MoO$_4$)$_2$

TL;DR

This study demonstrates that thermal fluctuations can restore the collinear 1/3-plateau magnetic phase in a disordered triangular lattice antiferromagnet by overcoming static impurity effects, confirmed through experiments on diluted samples.

Contribution

It provides experimental evidence that thermal fluctuations can revive the plateau phase suppressed by static disorder in a frustrated magnetic system.

Findings

Thermal fluctuations re-establish the 1/3-plateau phase in diluted samples.

Static disorder suppresses the plateau phase at low temperatures.

Heating restores the plateau phase by enhancing thermal fluctuation effects.

Abstract

The triangular lattice antiferromagnet RbFe(MoO$_4$)$_2$ orders antiferromagnetically in a planar 120$^\circ$-structure below $T_\textrm{N}\approx 4$ K. A striking feature of RbFe(MoO$_4$)$_2$ magnetic phase diagram is the presence of collinear ``1/3-plateau'' magnetic phase, which is stabilized by thermal and quantum fluctuations at magnetization $M\approx \frac{1}{3} M_\textrm{sat}$. Static disorder caused by impurities is predicted to act against the effect of fluctuations and to suppress collinear plateau phase (Maryasin and Zhitomirsky, PRL 111, 247201 (2013)). Balance between ``dynamic'' thermal and quantum fluctuations and ``static'' impurity-induced disorder is temperature-sensitive, which allows thermal fluctuations to take over the effect of static disorder and leads to the revival of the fluctuation-stabilized ``1/3-plateau'' phase on heating. Here we present experimental results directly confirming this prediction and demonstrating re-establishment of the plateau-like phase in the diluted Rb$_{(1-x)}$K$_{x}$Fe(MoO$_4$)$_2$ sample at moderate dilution level $x=15$\% on heating as the effect of thermal fluctuations increases.