Metallization of magnetite (Fe3O4) under high pressure

Abstract

Electrical resistivity measurements have been made on a good qualified single crystalline magnetite (Fe3O4) at temperatures from 300 down to 3.0 K under pressure up to 10 GPa. A steep change in resistivity at the Verwey transition temperature has been observed at pressure below 6.5 GPa, which shows a quite distinct result reported in prior work. Moreover, the Verwey transition temperature has been found to decrease nonlinearly with increasing pressure and it disappears at around 8 GPa. Above 8 GPa magnetite exhibits metallic behavior. The residual-resistivity ratio of the metallic state is observed to be more than 350. This finding of a metallic ground state in magnetite provides insight into the understanding of the Verwey transition in magnetite.

Electrical and magnetic properties of ε-Fe3N nanoparticles synthesized by chemical vapor condensation process

“…Additionally, electrons in amorphous Fe 3 O 4 shells with a finite-size were strongly localized by decreasing the mean free path, according to Mott's localization theory for disordered systems [39]. Above the Verwey transition (T v $120 K) in Fe 3 O 4 , it was pointed out that the material was a semiconductor with a small band gap [40,41], although it behaved as a semimetal with a finite density of delocalized states at the Fermi level [42]. Highly nonstoichiometric Fe 3 O 4 nanopowders [43] showed no conductivity change, when the Verwey transition occurs, but with a magnetic susceptibility variation.…”

Aspects of the Verwey transition in magnetite

“…The observed pressure induced metallic behavior [16] can be naturally understood since the pressure should effectively increase the value of K in Eq. (3) (or K A and K B in Eqs.…”

“…Besides, the expected short range fluctuation of the CO due to the frustration in V ij [11], arising from the fact that the network connecting the Fe(B) ions forms a coupled tetrahedra system, is not found either in neutron scattering [12] or in resonant X-ray scattering measurements [13]. Furthermore, the recent NMR [14] and X-ray anomalous scattering [15] experiments for T < T V even cast doubts on the existence of CO. Todo et al [16], based on these suggestions and their finding of pressure-induced metallic ground state above 8 GPa, proposed that the low temperature phase below T V may be a kind of "Mott insulator" where the B sites are forming dimers due to orbital ordering (OO).…”

XMCD under pressure at the FeKedge on the energy-dispersive beamline of the ESRF

“…Below 860 K magnetite shows ferrimagnetic behavior with magnetic moments on site A aligned antiparallel to magnetic moments on site B (Anisimov et al, 1996). Above 6 GPa the phase transition process is still under discussion (Rozenberg et al, 1996), (Todo et al, 2001). Figure 5 shows normalized XMCD and XANES signals obtained at 10 GPa.…”