Manifestation of the Verwey transition in the tunneling spectra of magnetite nanocrystals
School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences
Tel Aviv University - Tel Aviv 69978, Israel
2 Racah Institute of Physics and the Center for Nanoscience and Nanotechnology The Hebrew University of Jerusalem - Jerusalem 91904, Israel
Accepted: 21 July 2003
Tunneling transport measurements performed on single particles and on arrays of (magnetite) nanocrystals provide strong evidence for the existence of the Verwey metal-insulator transition at the nanoscale. The resistance measurements on nanocrystal arrays show an abrupt increase of the resistance around 100, consistent with the Verwey transition, while the current-voltage characteristics exhibit a sharp transition from an insulator gap to a peak structure around zero bias voltage. The tunneling spectra obtained on isolated particles using a scanning tunneling microscope reveal an insulator-like gap structure in the density of states below the transition temperature that gradually disappeared with increasing temperature, transforming to a small peak structure at the Fermi energy. These data provide insight into the roles played by long- and short-range charge ordering in the Verwey transition.
PACS: 71.30.+h – Metal-insulator transitions and other electronic transitions / 73.63.Bd – Nanocrystalline materials / 85.75.Mm – Spin polarized resonant tunnel junctions
© EDP Sciences, 2003