High-Field ESR and Magnetization of the Triangular Lattice Antiferromagnet NiGa₂S₄

Abstract

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 2 S 4 . From the temperature evolution of the ESR absorption linewidth, we find a distinct disturbance of the development of the spin correlation by Z 2 -vortices between 23 and 8.5 K. Below T v ¼ 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 k 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 T 2 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 (2010) 023701] is a necessary condition for the realization of a Z 2 -vortex-induced topological transition, which would be destroyed by an extremely small D 6 ¼ 0 in a classical nearest-neighbor spin model owing to the large . Accordingly, these results suggest the occurrence of a Z 2 -vortex-induced topological transition at T v and indicate quantum effects beyond the descriptions based on the above classical spin models, for example, those due to quadrupolar correlations.

Magnetic properties of the quasi-two-dimensional antiferromagnet Ni0.7Al2S3.7Higo1, Ishii2, Menard3 et al. 2011Phys. Rev. BSelf Cite4280View full textAdd to dashboardCite

“…36,37 As we will discuss, the ESR measurement has clarified D/k B < ∼ 0.1 K, which is consistent with the above estimate within the error bar. Figure 3(a) indicates the temperature dependence of the specific heat C P .…”

“…We compare the resonance mode of this compound with that of NiGa 2 S 4 , which is well fitted to one of the ESR resonance modes calculated based on the 57 • spiral spin structure with easy-plane anisotropy. 37 The spin Hamiltonian in this case is written as…”

Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4and NiGa2SZhao1, Réotier2, Yaouanc3 et al. 2012Phys. Rev. B175261View full textAdd to dashboardCite

“…The ESR linewidth in NiGa 2 S 4 above T * has been analyzed in terms of lifetime broadening by critical spin fluctuations. 21,22 The linewidth depends much less on temperature than the muon relaxation rate, and exhibits an anomaly at 23 K ∼ 3 T * that was interpreted as a crossover between critical regimes. It should be noted that the ESR experiments were carried out in a field of 20 T, corresponding to a Zeeman energy ∼ 2 k B T * ; such a large field is expected to perturb the spin fluctuation spectrum in theoretical scenarios for the 2D THAFM.…”

“…Third-nearest-neighbor antiferromagnetic exchange is dominant, with a weak nearest-neighbor ferromagnetic interaction 17,21 as suggested by calculated superexchange pathways. 42 A phase transition, possibly influenced by impurity effects, is indicated by a cusp and weak bifurcation between field-cooled (FC) and zerofield-cooled (ZFC) dc magnetic susceptibilities χ dc (T ) at T * = 8.5-9 K. 18 A drastic slowing of Ni 2+ spin fluctuations as T * is approached from above is observed in NMR, 20 ESR, 21,22 and muon spin relaxation (µSR) 23,[25][26][27][28] experiments, with a frozen or nearly-frozen Ni 2+ spin state below T * characterized by an order-parameter-like temperature dependence of the (nearly) frozen moment and strong spin fluctuations down to 25 mK. The frequency-dependent ac magnetic susceptibility χ ac (T ) suggests a spin-glasslike transition at a lower temperature T f = 2.2-2.7 K. 29 Based on these results, a viscous "spin-gel" or extended thermodynamic critical regime has been proposed between ∼T f and T * .…”

Universal Berezinskii-Kosterlitz-Thouless dynamic scaling in the intermediate time range in frustrated Heisenberg antiferromagnets on a triangular lattice

“…Experimental studies of magnetic materials with triangular lattice, in particular NaCrO 2 [11][12][13][14], NiGa 2 S 4 [15][16][17][18][19][20][21], κ − (BEDT − TTF) 2 Cu 2 (CN) 3 [22][23][24] EtMe 3 Sb[Pd(dmit) 2 ] 2 [25,26], reveal distinct anomaly behavior at non-zero temperatures, typical of phase transitions and non-trivial dynamic properties above and below the observed phase transition [11,14,17,19,20].…”