Charge and Orbital Correlations at and above the Verwey Phase Transition in Magnetite

Abstract

The subtle interplay among electronic degrees of freedom (charge and orbital orderings), spin and lattice distortion that conspire at the Verwey transition in magnetite (Fe3O4) is still a matter of controversy. Here, we provide compelling evidence that these electronic orderings are manifested as a continuous phase transition at the temperature where a spin reorientation takes place at around 130 K, i.e., well above TV approximately 121 K. The Verwey transition seems to leave the orbital ordering unaffected whereas the charge ordering development appears to be quenched at this temperature and the temperature dependence below TV is controlled by the lattice distortions. Finally, we show that the orbital ordering does not reach true long range (disorder), and the correlation length along the c-direction is limited to 100 angstroms.

Speed limit of the insulator–metal transition in magnetite

“…This means that on the timescale of the ultrafast intensity quench, the low-temperature monoclinic lattice tilt angle and the trimeron lattice coherence length remain unchanged with respect to the static case. We note that the observed static coherence length of λ coh = 385 ± 10 nm is in good agreement with literature values [3].…”

“…Fluctuations to this trimeron order have been observed up to 80 K above T V in neutron scattering studies [11,12]. 3 In many oxide materials [13,14] the insulator-metal transition has been discussed in terms of freezing in fluctuating lattice and electronic (charge, spin and orbital) order, sometimes in combination with the occurrence of phase separation [15,16]. However, due to the many competing degrees of freedom, the close energetic proximity of the different phases often obscures the exact nature of these phase transitions as they are probed in thermal equilibrium [17].…”

“…As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown [1], magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible [2][3][4][5][6][7][8]. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase [9].…”

Electronic orders in the Verwey structure of magnetite

“…5 However, the ground state of magnetite has remained a contentious issue for over 70 years, as microtwinning of Cc domains below the Verwey transition hampers diffraction studies of the low-temperature structure. Partial structure refinements from powder diffraction data [6][7][8] and resonant x-ray studies [9][10][11][12][13] have led to a variety of proposed charge-ordered and bond-dimerized ground state models in recent years. [14][15][16][17][18][19][20] An x-ray refinement of the full low-temperature Cc superstructure of magnetite was recently reported.…”

Comparative Study of the Electronic Structures of Fe3O4and Fe2SiO4

“…One of them is the insulating gap that does not close completely at high temperatures [29]. Recently, the resonant X-ray scattering studies revealed that charge-orbital ordering starts to develop about 10 K above T V [30]. The charge-orbital fluctuations couple to phonons producing the critical diffuse scattering.…”