We study the planar spin exchange couplings in LiNiO2 using a perturbative approach. We show that the inclusion of the trigonal crystal field splitting at the Oxygen sites leads to the appearance of antiferromagnetic exchange integrals in deviation from the Goodenough-Kanamori-Anderson rules for this 90 degree bond. That gives a microscopic foundation for the recently observed coexistence of ferromagnetic and antiferromagnetic couplings in the orbitally-frustrated state of LiNiO2. (F. Reynaud et al, Phys. Rev. Lett. 86, 3638 (2001))
@article{arxiv.cond-mat/0207104,
title = {Planar spin exchange in LiNiO_2},
author = {A. -M Daré and R. Hayn},
journal= {arXiv preprint arXiv:cond-mat/0207104},
year = {2015}
}