Spatially anisotropic Heisenberg kagome antiferromagnet

Abstract

In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite has recently been the subject of experimentalstudies (Hiroi et al 2001 J. Phys. Soc. Japan 70 3377; Fukaya et al 2003 Phys. Rev. Lett. 91 207603;Bert et al 2004 J. Phys.: Condens. Matter 16 S829; Bert et al 2005 Phys. Rev. Lett. 95 087203). Ithas been suggested that the magnetic properties of this material are described by aspin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic exchange couplings. Wereport on investigations of the symmetric generalization of this model in the large limit. We obtain a detailed description of the dependence ofpossible ground states on the anisotropy and on the spin lengthS. A fairly rich phase diagram with a ferrimagnetic phase, incommensurate phases with andwithout long-range order and a decoupled chain phase emerges.