We report the experimental and the analytical results of electron spin resonance (ESR) and magnetization in high magnetic fields up to about 68 T of the quasi two-dimensional triangular lattice antiferromagnet NiGa2S4. From the temperature evolution of the ESR absorption linewidth, we find a distinct disturbing of the development of the spin correlation by Z2-vortices between 23 K and 8.5 K. Below Tv=8.5 K, spin-wave calculations based on a 57∘ spiral spin order well explains the frequency dependence of the ESR resonance fields and high field magnetization processes for H∥c and H⊥c, although the magnetization for H⊥c at high fields is different from the calculated one. Furthermore, we explain the field independent specific heat with T2-dependence by the same spin-wave calculation, but the magnitude of the specific heat is much less than the observed one. Accordingly, these results suggest the occurrence of a Z2 vortex-induced topological transition at Tv and may indicate quantum effects beyond the descriptions based on the above classical spin models.
@article{arxiv.1002.3068,
title = {High Field ESR and Magnetization of the Triangular Lattice Antiferromagnet NiGa2S4},
author = {Hironori Yamaguchi and Shojiro Kimura and Masayuki Hagiwara and Yusuke Nambu and Satoru Nakatsuji and Yoshiteru Maeno and Akira Matsuo and Koichi Kindo},
journal= {arXiv preprint arXiv:1002.3068},
year = {2015}
}