Origin of the long-wavelength magnetic modulation in Ca3Co2O6

The origin of the long-wavelength incommensurate magnetic structure of Ca3Co2O6 is discussed considering possible interchains super-superexchange paths. The experimental value of the propagation vector k=(0,0,Delta) with Delta>1 can be reproduced only if one considers the next-nearest super-superexchange interaction. A spin-dimer analysis using the extended Huckel tight-binding method confirms that, despite longer interatomic Co-Co distances, the latter interaction is indeed much stronger. The stability of the observed structure with respect to certain commensurate states is discussed.