Evidence for differentiation in the iron-helicoidal chain in GdFe3(BO3)4

Abstract

A single-crystal X-ray structure study of gadolinium triiron tetraborate, GdFe_3(BO_3)_4, at room temperature and at 90 K is reported. At room temperature GdFe_3(BO_3)_4 crystallizes in a trigonal space group, R32 (No. 155), the same as found for other members of the iron borate family RFe_3(BO_3)_4. At 90 K the structure of GdFe_3(BO_3)_4 transforms to the space group P3_{1}21 (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 presence of two inequivalent iron chains in the low-temperature structure provides a new perspective on the interpretation of the low-temperature magnetic properties.