Research
summary figure
Magnetite is a magnetic material known since more than two thousand years ago. It presents a phase transition known as the Verwey transition (at ~ 120K), in which the crystal structure changes from cubic to monoclinic, and at the same time the conductivity is reduced by two orders of magnitude. This transition strongly promoted research on metal-insulator transitions. For the first time, a team of researchers from the IQFR, Berkeley National Laboratory and the Vienna Technical University have observed this transition with surface-sensitive microscopies for the (100) orientation of magnetite. It has been found that the surface "rumbles" forming a roof-like surface at a micrometer scale, whereas the actual surface reconstruction has the same structure through the transition. This indicates that although the surface reconstruction is conceptually similar to the bulk structure below the transition, they are two distinct phenomena.
 
J. de la Figuera, Z. Novotny, M. Setvin, T. Liu, Z. Mao, G. Chen, A. T. N'Diaye, M. Schmid, U. Diebold, A. K. Schmid, G. S. Parkinson,  "Real Space Imaging of the Verwey Transition at the (100) Surface of Magnetite", Phys. Rev. B 88 (2013) 161410(R), DOI:10.1103/PhysRevB.88.161410,  arxiv 1310.1373
 
The figure shows at the top, low-energy electron microscope images (8.6 um wide) above (left) and below (right) the Verwey transition. In the middle, scanning tunneling microscopy images with atomic resolution are shown also above and below the transition. At the bottom, a profile showns the "roof" surface below the transition.