The magnetic phases of the ideal spin-1/2 triangular-lattice antiferromagnet Ba3CoSb2O9 are identified and studied using 135,137Ba nuclear magnetic resonance (NMR) spectroscopy in magnetic fields ranging to 30T, oriented parallel and near perpendicular to the crystallographic ab-plane. For both directions, the saturation field is approximately 33T. Notably, the NMR spectra provide microscopic evidence for the stabilization of an up-up-down spin configuration for in-plane fields, giving rise to an one-third magnetization plateau (Msat/3), as well as for a higher field phase transition near to ∼(3/5)Msat for both field orientations. Phase transitions are signaled by the evolution of the NMR spectra, and in some cases through spin-lattice relaxation measurements. The results are compared with expectations obtained from a semi-classical energy density modeling, in which quantum effects are incorporated by effective interactions extracted from the spin-wave analysis of the two-dimensional model. The interlayer coupling also plays a significant role in the outcome. Good agreement between the model and the experimental results is achieved, except for the case of fields approaching the saturation value applied along the c-axis.
@article{arxiv.1308.6331,
title = {Quantum phase diagram of the $S=1/2$ triangular-lattice antiferromagnet Ba$_3$CoSb$_2$O$_9$},
author = {G. Koutroulakis and T. Zhou and C. D. Batista and Y. Kamiya and J. D. Thompson and S. E. Brown and H. D. Zhou},
journal= {arXiv preprint arXiv:1308.6331},
year = {2015}
}