TY - JOUR
T1 - High-field ESR and magnetization of the triangular lattice antiferromagnet NiGa2S4
AU - Yamaguchi, Hironori
AU - Kimura, Shojiro
AU - Hagiwara, Masayuki
AU - Nambu, Yusuke
AU - Nakatsuji, Satoru
AU - Maeno, Yoshiteru
AU - Matsuo, Akira
AU - Kindo, Koichi
PY - 2010/5/1
Y1 - 2010/5/1
N2 - We report the experimental and analytical results of electron spin resonance (ESR) and magnetization at high magnetic fields of up to about 68 T of the quasi two-dimensional triangular lattice antiferromagnet NiGa 2S4. From the temperature evolution of the ESR absorption linewidth, we find a distinct disturbance of the development of the spin correlation by Z2-vortices between 23 and 8.5 K. Below Tv = 8.5 K, spin-wave calculations based on a 57° spiral spin order well explain 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 a T2 dependence by the same spin-wave calculation, but the magnitude of specific heat is much less than the observed one. The single ion anisotropy constant D/kB = 0.8K is the same order of TV(ξ/a)-2 = 0.3-0.4K where ξ and a are the correlation length and the lattice constant of the triangular plane in NiGa2S4, respectively. The relation D/kB ≤ TV(ξ/a)-2 recently derived by Kawamura et al. [H. Kawamura et al.: J. Phys. Soc. Jpn. 79 (2010) 023701] is a necessary condition for the realization of a Z2-vortex- induced topological transition, which would be destroyed by an extremely small D ≠ 0 in a classical nearest-neighbor spin model owing to the large ξ. Accordingly, these results suggest the occurrence of a Z2-vortex- induced topological transition at Tv and indicate quantum effects beyond the descriptions based on the above classical spin models, for example, those due to quadrupolar correlations.
AB - We report the experimental and analytical results of electron spin resonance (ESR) and magnetization at high magnetic fields of up to about 68 T of the quasi two-dimensional triangular lattice antiferromagnet NiGa 2S4. From the temperature evolution of the ESR absorption linewidth, we find a distinct disturbance of the development of the spin correlation by Z2-vortices between 23 and 8.5 K. Below Tv = 8.5 K, spin-wave calculations based on a 57° spiral spin order well explain 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 a T2 dependence by the same spin-wave calculation, but the magnitude of specific heat is much less than the observed one. The single ion anisotropy constant D/kB = 0.8K is the same order of TV(ξ/a)-2 = 0.3-0.4K where ξ and a are the correlation length and the lattice constant of the triangular plane in NiGa2S4, respectively. The relation D/kB ≤ TV(ξ/a)-2 recently derived by Kawamura et al. [H. Kawamura et al.: J. Phys. Soc. Jpn. 79 (2010) 023701] is a necessary condition for the realization of a Z2-vortex- induced topological transition, which would be destroyed by an extremely small D ≠ 0 in a classical nearest-neighbor spin model owing to the large ξ. Accordingly, these results suggest the occurrence of a Z2-vortex- induced topological transition at Tv and indicate quantum effects beyond the descriptions based on the above classical spin models, for example, those due to quadrupolar correlations.
KW - Frustrate magnetism
KW - High field magnetization
KW - High-field ESR
KW - NiGaS
KW - Triangular lattice
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U2 - 10.1143/JPSJ.79.054710
DO - 10.1143/JPSJ.79.054710
M3 - Article
AN - SCOPUS:77953040643
VL - 79
JO - Journal of the Physical Society of Japan
JF - Journal of the Physical Society of Japan
SN - 0031-9015
IS - 5
M1 - 054710
ER -