Abstract
The magnetite Fe3O4, being anciently known magnetic material to human kind and remaining in leading positions for development of advanced technologies presently, demonstrates a number of puzzling physical phenomena, being at focus of extensive research for more than century. Recently the pressure-induced anomalous behavior of physical properties of magnetite in vicinity of the structural phase transition, occurring at P ~ 25–30 GPa, has attracted particular attention, and its nature remains unclear. Here we study the magnetic and electronic properties of magnetite across high pressure anomaly and in the pressure-induced phase by means of 57Fe synchrotron Moessbauer spectroscopy and neutron diffraction. The hyperfine interaction parameters behavior was systematically analysed over pressure 0–40 GPa and temperature 10–290 K ranges. In the high pressure phase the ferrimagnetic order formation below TNP ~ 420 K was observed and spin arrangement symmetry was deduced. The structural, magnetic and electronic phase diagram of magnetite in the discussed pressure range is established.
Highlights
Magnetite is the most oldest known magnetic mineral, playing important role in natural life and development of technological applications
The spectra measured at P = 8 GPa in the temperature range 290–100 K can be well fitted with the two sextet components, one corresponding to the Fe3+ ions in high spin (HS) state (S = 5/2) located in the tetrahedral (A) sites and second one to the mixed Fe3+ and Fe2+ (S = 2) ions in HS state located in the octahedral (B) sites with relative abundance 1:2, respectively
For the temperature (10–290 K) and pressure (8–28 GPa) ranges the HhfA value exceeds the HhfB one and their relative difference is weakly affected by variation of thermodynamic parameters (Fig. 3, Supplementary Table 1)
Summary
Magnetite is the most oldest known magnetic mineral, playing important role in natural life and development of technological applications. The temperature and pressure mediated charge redistribution over the sites with tetrahedral and octahedral oxygen coordination via the inverse-to-normal transition in the spinel structure, [Fe3+]A[Fe2+Fe3+]BO4 → [Fe2+]A[Fe3+Fe3+]BO4, was proposed, based on the Moessbauer spectroscopy and powder X-ray diffraction data[17,18]. A realization of the high spin (HS) to intermediate spin (IS) transition of Fe2+ ions at P ~ 12–16 GPa was assumed in the X-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy study[15]. Another mechanism of the enhanced electron delocalization was suggested in the later Moessbauer spectroscopy, single crystal X-ray diffraction and XMCD experiments[16,19]. A high spin to low spin (LS) state crossover of Fe3+ ions at pressures around 40 GPa was evidenced[20,21]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
