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

The triangular lattice antiferromagnet RbFe(MoO${}_4$)${}_2$ orders antiferromagnetically in a planar 120${}^{\circ }$-structure below $T_{\text{N}}\approx 4$ 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.