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J. Gooth, T. Böhnert, J. Gluschke, B. Hamdou, S. Barth, D. Goerlitz, R. Zierold, K. Nielsch:
"Trimeron Lattice Relaxation in Magnetite Nanowires - Crossing the Verwey Transition from above TV";
Talk: 2014 MRS Spring Meeting & Exhibit, San Francisco, California, USA; 2014-04-21 - 2014-04-25; in: "2014 MRS Spring Meeting - Abstract & Program Book", (2014), #1.

Understanding metal-insulator transitions in strongly correlated oxides requires full knowledge about the crystal and charge structure above and below the transition point, a specific temperature, pressure or electric field. One of the oldest and best-known correlated oxides is magnetite (Fe3O4). More than 60 years ago Verwey discovered that bulk magnetite undergoes a phase transition at 122 K marked by a sharp change in electronic, magnetic, thermal, and structural properties. Ever since then Fe3O4 and in particular the so-called Verwey transition has been an object of extensive research and great controversy. At present the crystal and charge structure above and below the Verwey temperature as well as the melting of the trimeron lattice into the charge-fluctuating state, equivalent to crossing the Verwey transition from below TV, has been disentangled. However, the freezing dynamics of the fluctuating charges into the trimeron lattice has not been analyzed to date.
We report on the relaxation of the electric field excited state in single crystalline magnetite nanowires below the Verwey temperature determined by current driven ac resistance measurements. Fe3O4 nanowires were grown in a cold-wall low pressure chemical vapor deposition (CVD). We attribute the relaxation process to trimeron lattice formation via hopping transport after excitation to the charge-fluctuating state. Our results reveal the dynamic of the Verwey transition, crossing TV from above. Trimeron lattice formation occurs on the millisecond time scale around TV, continuously slowing down its dynamics as temperature is decreased. We show, that the charge ordering process in magnetite needs to be activated by 0.13 eV. This work shows how nanostructures can help to understand fundamental material properties, inaccessible in bulk material.