Charge order in Fe₂OBO₃

Ivan Leonov

Center for Electronic Correlations and Magnetism, Institute for Physics, University of Augsburg,
Universitätsstr. 1, 86159 Augsburg, Germany

Charge ordering in the low-temperature monoclinic structure of iron oxoborate (Fe2OBO3) is investigated using the local spin density approximation (LSDA)+U method. While the difference between t2g minority occupancies of Fe2+ and Fe3+ cations is large and gives direct evidence for charge ordering, the static ``screening'' is so effective that the total 3d charge separation is rather small. The occupied Fe2+ and Fe3+ cations are ordered alternately within the chain which is infinite along the α- direction. The charge order obtained by LSDA+U is consistent with observed enlargement of the β angle. An analysis of the exchange interaction parameters demonstrates the predominance of the interribbon exchange interactions which determine the whole L-type ferrimagnetic spin structure.