Charge order in Fe₂OBO₃: An LSDA+U study

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 t2_g 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 a 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.