Incommensurate Phase of a Triangular Frustrated Heisenberg Model Studied via Schwinger-Boson Mean-Field Theory

Abstract

We study a triangular frustrated antiferromagnetic Heisenberg model with nearest-neighbor interaction $J_1$ and third-nearest-neighbor interactions $J_3$ by means of Schwinger-boson mean-field theory. It is shown that an incommensurate phase exists in a finite region in the parameter space for an antiferromagnetic $J_3$ while $J_1$ can be either positive or negtaive. A detailed solution is presented to disclose the main features of this incommensurate phase. A gapless dispersion of quasiparticles leads to the intrinsic $T^2$-law of specific heat. The local magnetization is significantly reduced by quantum fluctuations (for S=1 case, a local magnetization is estimated as $m=<S_i>\approx 0.6223$). The magnetic susceptibility is linear in temperature at low temperatures. We address possible relevance of these results to the low-temperature properties of NiGa${}_2$S${}_4$. From a careful analysis of the incommensurate spin wave vector, the interaction parameters for NiGa${}_2$S${}_4$ are estimated as, $J_1\approx -3.8755$K and $J_3\approx 14.0628$K, in order to account for the experimental data.

9pages, 3figures

References in corpus (1)

• First-Order Transition to Incommensurate Phase with Broken Lattice Rotation Symmetry in Frustrated Heisenberg Model