Understanding the Mössbauer spectrum of magnetite below the Verwey transition: Ab initio calculations, simulation, and experiment

Magnetite is often the subject of M\"ossbauer spectroscopy experiments either as a part of fundamental research of this compound or during various geological studies. However, the complicated structure of the low-temperature phase of magnetite exhibits 24 crystallographic iron sites, which presents a considerable obstruction for spectrum interpretation. In this work, we carried out ab initio calculations to obtain a complete set of hyperfine parameters of all the sites, and we used these parameters to simulate the corresponding M\"ossbauer spectrum. Simulation analysis suggested an approximation of the spectrum by four sextets. Parameters of these four sextets were calculated, and the approximation was shown to be appropriate. Further, the M\"ossbauer spectrum of a high-quality synthetic single crystal of magnetite was measured at 4 K, allowing for a comparison of the theoretical results with the experimental data. Finally, the four-sextet approximation was successfully applied to fit the measured spectrum.