TY - JOUR
T1 - Experimental charge density of hematite in its magnetic low temperature and high temperature phases
AU - Theissmann, R.
AU - Fuess, H.
AU - Tsuda, K.
N1 - Funding Information:
R.T. thanks the Alexander von Humboldt foundation and the Japan Society for the Promotion of Science (JSPS) for funding (Feodor Lynen-fellowship). M. Tanaka is gratefully acknowledged for the kind invitation to conduct this research project at his former institute in Sendai. R. Schmechel is gratefully acknowledged for his consistent support and many fruitful discussions. K. Saitoh, H. Ehrenberg, G. Rollmann and G. Schierning are gratefully acknowledged for fruitful discussions. G. Schierning is gratefully acknowledged for carefully proofreading the manuscript. Computation time at the Center for Computational Sciences and Simulations at the University of Duisburg-Essen, Center for Scientific Computing (CSC) at University of Frankfurt and the Rubens–Cluster at the Unviersity of Siegen via the “Resourcenverbund NRW” are gratefully acknowledged. M. Weitzel, P. Erhart and R. Zinnetullin are gratefully acknowledged for their technical support using the cluster computers. M. Takata is acknowledged for his support in using the beamline BL02B2 at Spring8.
PY - 2012/9
Y1 - 2012/9
N2 - Structural parameters of hematite (α-Fe 2O 3), including the valence electron distribution, were investigated using convergent beam electron diffraction (CBED) in the canted antiferromagnetic phase at room temperature and in the collinear antiferromagnetic phase at 90K. The refined charge density maps are interpreted as a direct result of electron-electron interaction in a correlated system. A negative deformation density was observed as a consequence of closed shell interaction. Positive deformation densities are interpreted as a shift of electron density to antibinding molecular orbitals. Following this interpretation, the collinear antiferromagnetic phase shows the characteristic of a Mott-Hubbard type insulator whereas the high temperature canted antiferromagnetic phase shows the characteristic of a charge transfer insulator. The break of the threefold symmetry in the canted antiferromagnetic phase was correlated to the presence of oxygen-oxygen bonding, which is caused by a shift of spin polarized charge density from iron 3d-orbitals to the oxygen ions. We propose a triangular magnetic coupling in the oxygen planes causing a frustrated triangular spin arrangement with all spins lying in the oxygen planes. This frustrated arrangement polarizes the super-exchange between iron ions and causes the spins located at the iron ions to orient in the same plane, perpendicular to the threefold axis.
AB - Structural parameters of hematite (α-Fe 2O 3), including the valence electron distribution, were investigated using convergent beam electron diffraction (CBED) in the canted antiferromagnetic phase at room temperature and in the collinear antiferromagnetic phase at 90K. The refined charge density maps are interpreted as a direct result of electron-electron interaction in a correlated system. A negative deformation density was observed as a consequence of closed shell interaction. Positive deformation densities are interpreted as a shift of electron density to antibinding molecular orbitals. Following this interpretation, the collinear antiferromagnetic phase shows the characteristic of a Mott-Hubbard type insulator whereas the high temperature canted antiferromagnetic phase shows the characteristic of a charge transfer insulator. The break of the threefold symmetry in the canted antiferromagnetic phase was correlated to the presence of oxygen-oxygen bonding, which is caused by a shift of spin polarized charge density from iron 3d-orbitals to the oxygen ions. We propose a triangular magnetic coupling in the oxygen planes causing a frustrated triangular spin arrangement with all spins lying in the oxygen planes. This frustrated arrangement polarizes the super-exchange between iron ions and causes the spins located at the iron ions to orient in the same plane, perpendicular to the threefold axis.
KW - Convergent beam electron diffraction
KW - Hematite
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U2 - 10.1016/j.ultramic.2012.04.006
DO - 10.1016/j.ultramic.2012.04.006
M3 - Article
C2 - 22796553
AN - SCOPUS:84864029727
VL - 120
SP - 1
EP - 9
JO - Ultramicroscopy
JF - Ultramicroscopy
SN - 0304-3991
ER -