Evidence for differentiation in the iron-helicoidal-chain in GdFe${}_3$(BO${}_3$)${}_4$

Abstract

We report on a single-crystal X-ray structure study of $GdF{e}_3(B{O}_3{)}_4$ at room temperature and at T=90 K. At room temperature $GdF{e}_3(B{O}_3{)}_4$ crystallizes in a trigonal space group R32 (No. 155), the same as found for other members of iron-borate family $RF{e}_3(B{O}_3{)}_4$. At 90 K the structure of $GdF{e}_3(B{O}_3{)}_4$ has transformed to the space group $P{3}_1{2}_1$ (No. 152). The low-temperature structure determination gives new insight into the weakly first-order structural phase transition at 156 K and into the related Raman phonon anomalies. The discovery of two inequivalent iron chains in the low temperature structure provide new point of view on the low-temperature magnetic properties.

Subm. to Acta Cryst. B