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Long range charge ordering in magnetite below the Verwey transition
J P Wright1, J P Attfield, P G Radaelli
1Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW United Kingdom. jpa@cam.ac.uk
Physical Review Letters
|January 22, 2002
Summary
Charge ordering in iron(II,III) oxide (Fe3O4) below the Verwey transition is refined, revealing non-uniform electron distribution. This charge ordering is driven by an electronic instability, not electrostatic repulsion, opening a gap via a charge density wave.
Area of Science:
- Solid-state physics
- Materials science
- Crystallography
Background:
- The Verwey transition in iron(II,III) oxide (Fe3O4) involves a change in electrical conductivity and crystal structure at 122 K.
- Understanding the charge ordering (CO) mechanism below this transition is crucial for explaining the material's electronic properties.
Purpose of the Study:
- To refine the crystal structure of Fe3O4 below the Verwey transition.
- To provide direct evidence for charge ordering on specific iron sites.
- To investigate the driving mechanism behind charge ordering.
Main Methods:
- High-resolution X-ray powder diffraction.
- Neutron powder diffraction.
- Crystal structure refinement.
Main Results:
- Direct evidence for charge ordering (CO) over four distinct octahedral Fe sites was obtained.
- Two Fe sites exhibit a charge of +2.4, and the other two show a charge of +2.6.
- The observed CO schemes do not satisfy the Anderson condition for minimum electrostatic repulsion.
Conclusions:
- Charge ordering in Fe3O4 below the Verwey transition is primarily driven by a [001] electronic instability.
- This instability leads to the opening of an electronic gap through a charge density wave mechanism.
- The findings challenge conventional models based solely on electrostatic repulsion.