Low-temperature structure transition in hexagonal LuFeO3*

The structural change of h-LuFeO$_3$ films at low temperature has been studied using x-ray diffraction and x-ray absorption experiments. The results are analyzed using the displacements of three phonon modes that are related to the P6$_3$/mmc to P6$_3$cm structural transition. The data indicate that the in-plane motion of the Fe and apex oxygen are responsible for the observed anomaly in both x-ray absorption and diffraction experiments. This subtle structural transition may be an origin of the low temperature magnetic phase transition at $T_R$=130 K.