Site Specific Valence Above and Below the Verwey Transition in Magnetite
EMSL Project ID
17805
Abstract
ABSTRACT: The Verwey transition has historically been described as an electron-ordering transition in a mixed-valent system that results in ordering of the formal valence states in the low-temperature phase. The exact nature of the Verwey transition in Fe3O4 (magnetite) is a long standing and controversial problem. A recent explaination (Pasternak, 2003), based on Mossbauer spectroscopy at high pressure, is that magnetite undergoes a coordination crossover in which charge density is shifted from octahedral to tetrahedral sites, and the spinel structure changes from inverse to normal. A crucial experimental test of this proposed explaination is to directly determine the site specific Fe valence through the transition. This can be accomplished using Diffraction Anomalous Fine Structure (DAFS) with crystalline magnetite. Previous DAFS measurements on bulk single crystals were complicated by strong self absorption. To avoid this complication, we propose to measure the Fe DAFS on epitaxially grown magnetite films with thicknesses under 2500A, well below the absorption length for Fe K-alpha radiation. The magnetite films will be grown at the EMSL facility. The DAFS measurements and analysis will be performed at the Advanced Photon Source, Sector 20.Pasternak MP, Xu WM, Rozenberg GK, et al.
Pressure-induced coordination crossover in magnetite; the breakdown of the Verwey-Mott localization hypothesis
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 265 (2): L107-L112 SEP 2003
Project Details
Project type
Exploratory Research
Start Date
2006-01-25
End Date
2007-02-28
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members