Critical reexamination of resonant soft x-ray Bragg forbidden reflections in magnetite

Abstract

Magnetite, ${\text{Fe}}_{3}{\text{O}}_{4}$, displays a highly complex low-temperature crystal structure that may be charge and orbitally ordered. Many of the recent experimental claims of such ordering rely on resonant soft x-ray diffraction at the oxygen $K$ and iron $L$ edges. We have reexamined this system and undertaken soft x-ray diffraction experiments on a high-quality single crystal. Contrary to previous claims in the literature, we show that the intensity observed at the Bragg forbidden ${(00\frac{1}{2})}_{c}$ reflection can be explained purely in terms of the low-temperature structural displacements around the resonant atoms. This does not necessarily mean that magnetite is not charge or orbitally ordered but rather that the present sensitivity of resonant soft x-ray experiments does not allow conclusive demonstration of such ordering.