Manifestation of the Verwey transition in the tunneling spectra of magnetite nanocrystals

¹ 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

Corresponding authors: gilmar@post.tau.ac.il, milode@vms.huji.ac.il

Received: 7 March 2003
Accepted: 21 July 2003

Abstract

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.