Verwey transition in a magnetite ultrathin film by resonant x-ray scattering

Abstract

We report a detailed study of the Verwey transition in a magnetite ultrathin film (UTF) grown on Ag(001) using resonant x-ray scattering (RXS). RXS was measured at the Fe K-edge on the crystal truncation rod of the substrate, increasing the sensitivity to the film thanks to the cross-interference, thereby obtaining an x-ray phase-shift reference and a polarization analyzer. The spectra were interpreted with ad hoc calculations based on density functional theory within a surface-scattering formalism. We observed that the UTF has a relatively sharp transition temperature ${T}_{V}=120$ K and is remarkably close to the bulk temperature for such thickness. We determined the specific Fe stacking at the interface with the substrate below ${T}_{V}$, and detected a spectroscopic signal evolving with temperature from ${T}_{V}$ up to at least ${T}_{V}+80$ K, hinting that the RT crystallographic structure does not set at ${T}_{V}$ in the UTF.