Magnetite, ${\mathrm{Fe}}_3{\mathrm{O}}_4$, was the first magnetic material discovered and utilized by man in Ancient Greece. Yet, some of its physical behavior continues to challenge scientists. Upon cooling to the temperature of 124 K, its electrical resistivity jumps by 2 orders of magnitude and its structure changes from a simple cubic lattice to a more complex monoclinic one. Although seven decades ago Verwey, after whom this transition is named, proposed charge ordering as the primary mechanism for the transition, its nature has not been unambiguously resolved. Rather, a complex picture involving interactions between electrons, the characteristics of their orbitals in the Fe atoms, and lattice vibrations has emerged. In this combined experimental and theoretical paper, we identify a few major pieces in this puzzle that link the two apparently different material states across the Verwey transition.

The remarkable 2012 publication of Senn, Wright, and Attfield provides an important clue into the low-temperature state. It suggests that electron localization, responsible for the dramatically increased resistivity, appears in basic three-Fe-site units, called “trimerons.” Our measurements, based on state-of-the-art x-ray diffuse scattering, clearly show that behind the remarkable apparent sharpness of the Verwey transition is the electronic correlation seen in the low-temperature state persisting in the high-temperature state above the transition. Indeed, even at room temperature, which is considerably higher than the 124-K transition temperature, electrons appear to be correlated over length scales larger than the trimeron size. Moreover, by combining ab initio electronic-structure calculations with our experimental diffuse-scattering data, we could associate some characteristic experimental features with the topology of the Fermi surface of magnetite. While the structure of the low-temperature phase was frequently considered as a key to the understanding of the Verwey transition, our work indicates that the diffuse scattering pattern above the transition actually encodes some (if not all) key information.

Observing the building blocks of the displacement pattern of the low-temperature phase at temperatures more than twice the transition is remarkable in a highly correlated electron material. This observation warrants the extension of the search for such persistent structural fingerprints to other materials.

Subject Areas

• Condensed Matter Physics
• Materials Science
• Strongly Correlated Materials