We report on the microscopic magnetic model of a spin-1/2 magnet BaV3O8. In contrast to earlier phenomenological analysis, our density-functional band-structure calculations combined with quantum Monte-Carlo simulations establish a relatively simple and non-frustrated model of weakly coupled spin chains with the intrachain coupling of J∼ 38 K and the Neel temperature of TN∼ 6 K, both in excellent agreement with the experiment. The intrachain coupling between the spin-1/2 V+4 ions takes place via two contiguous V+5O4 tetrahedra forming an extended superexchange pathway with the V+4--V+4 distance of 7.44 A. Surprisingly, this pathway is preferred over shorter V+4--V+4 connections, owing to peculiarities in the interacting orbitals of the magnetic V+4 ions and V+5 ions that are non-magnetic, but feature low-lying 3d states contributing to the superexchange process. We also note that the crystal structure of BaV3O8 supports the long-sought uniform arrangement of Dzyaloshinsky-Moriya (DM) couplings on a spin-1/2 chain. While our calculations yield only a weak DM anisotropy in BaV3O8, the crystal structure of this compound provides a suitable framework for the search of spin chains with the uniform DM anisotropy in other compounds of the vanadate family.
@article{arxiv.1308.5305,
title = {Spin-chain magnetism and uniform Dzyaloshinsky-Moriya anisotropy in BaV$_3$O$_8$},
author = {Alexander A. Tsirlin},
journal= {arXiv preprint arXiv:1308.5305},
year = {2014}
}