X-Ray Diffuse Scattering Study of Magnetite by the Valence-Difference Contrast Method

We have observed the diffuse scattering distributions associated with the charge ordering of Fe²⁺ and Fe³⁺ above the Verwey transition temperature (T _V\cong123 K) in magnetite, Fe₃O₄, by synchrotron X-rays. At a specific wavelength of λ= 1.7421 or 1.7425 Å close to the Fe K absorption edge, the anomalous scattering effect makes it possible to distinguish Fe²⁺ ions from Fe³⁺ in the X-ray diffuse intensities. X-shaped diffuse patterns appeared at 130 and 150 K on the a₁^* - a₂^* plane around the 440-type reciprocal lattice point, which were not observed at 296 K. Even for the measurement at 130 K, the X-shaped pattern disappeared when the X-rays had a lower energy resolution. Cross-shaped diffuse patterns were also observed around the 400 and 800 reciprocal lattice points. The theoretical calculations suggest that these diffuse streaks are not due to thermal diffuse scattering. Our analysis of Huang scattering revealed that the observed diffuse patterns were plausibly caused by the local displacement with Fe²⁺ and Fe³⁺ pairing among the B sites.