We have performed high-field magnetization and ESR measurements on Ba3CoSb2O9 single crystals, as a representative two-dimensional spin-1/2 Heisenberg antiferromagnet on a uniform triangular lattice, and have determined all the magnetic parameters. For an applied magnetic field H parallel to the ab-plane, the entire magnetization curve including the plateau at one-third of the saturation magnetization (Ms) is in excellent agreement with the results of theoretical calculations except an anomaly near (3/5)Ms, indicative of an additional field-induced transition. However, for H∥c, the magnetization curve exhibits a cusp near Ms/3. Paramagnetic resonance signals above the N\'eel temperature indicate the nearly isotropic g-factor. A detailed analysis of the collective ESR modes observed in the ordered state, combined with the magnetization process, provides evidence of the weak easy-plane anisotropy.
@article{arxiv.1303.5271,
title = {Magnetization Process and Collective Excitations in the S=1/2 Triangular-Lattice Heisenberg Antiferromagnet Ba3CoSb2O9},
author = {Takuya Susuki and Nobuyuki Kurita and Takuya Tanaka and Hiroyuki Nojiri and Akira Matsuo and Koichi Kindo and Hidekazu Tanaka},
journal= {arXiv preprint arXiv:1303.5271},
year = {2015}
}