The magnetic excitations in $\mathrm{CoP}{\mathrm{S}}_3$, a two-dimensional van der Waals (vdW) antiferromagnet with ${\mathrm{Co}}^{2+}$ ion on a honeycomb lattice, have been measured using powder inelastic neutron scattering. The absence of spin-orbit exciton around 30 meV indicates that ${\mathrm{Co}}^{2+}$ ions in $\mathrm{CoP}{\mathrm{S}}_3$ have an $S=3/2$ state rather than a spin-orbital entangled $J_{\mathrm{eff}}=1/2$ ground state. And, clear dispersive spin waves are observed with a large spin gap of ∼13 meV. The magnon spectra were fitted using an XXZ-type $J_1\text{−}{J}_2\text{−}{J}_3$ Heisenberg Hamiltonian with single-ion anisotropy assuming no magnetic exchange interaction between the honeycomb layers. The best-fit parameters show ferromagnetic exchange interactions $J_1=-2.08\mathrm{meV}$ and $J_2=-0.26\mathrm{meV}$ for the nearest- and second-nearest neighbors and a sizable antiferromagnetic exchange interaction $J_3=4.21\mathrm{meV}$ for the third-nearest neighbor with the strong easy-axis anisotropy $K=-2.06\mathrm{meV}$. The anisotropic XXZ-type Hamiltonian could only achieve a suitable fitting. The exchange interaction for the out-of-plane spin component is smaller than that for the in-plane one by a ratio $\alpha =J_z/J_x=0.6$. Our result directly shows that $\mathrm{CoP}{\mathrm{S}}_3$ is an experimental realization of the XXZ model with a honeycomb lattice in two-dimensional vdW magnets.

中文翻译：

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二维蜂窝格子XXZ型范德华反铁磁CoPS3中的自旋波

内的磁激发 $\mathrm{警察}{\mathrm{小号}}_3$，二维范德华（vdW）反铁磁体 ${\mathrm{有限公司}}^{2+}$使用粉末非弹性中子散射测量了蜂窝状晶格上的离子。30 meV附近没有自旋轨道激子表明${\mathrm{有限公司}}^{2+}$ 离子在 $\mathrm{警察}{\mathrm{小号}}_3$ 有一个 $\mathrm{小号}=3/2$ 状态而不是自旋轨道纠缠 ${Ĵ}_{效}=\mathrm{1个}/2$基态。而且，观察到清晰的色散自旋波，自旋间隙约为13 meV。磁振子光谱使用XXZ型拟合${Ĵ}_{\mathrm{1个}}\text{-}{Ĵ}_2\text{-}{Ĵ}_3$假设蜂窝层之间没有磁交换相互作用的具有单离子各向异性的海森堡哈密顿量。最佳拟合参数显示铁磁交换相互作用${Ĵ}_{\mathrm{1个}}=-2.08\mathrm{病毒}$ 和 ${Ĵ}_2=-0.26\mathrm{病毒}$ 最近邻和第二近邻以及相当大的反铁磁交换相互作用 ${Ĵ}_3=4.21\mathrm{病毒}$ 易轴各向异性强的第三近邻 $ķ=-2.06\mathrm{病毒}$。各向异性的XXZ型哈密顿量只能实现合适的拟合。平面外自旋分量的交换相互作用比平面内自旋分量的交换相互作用小$\alpha ={Ĵ}_{ž}/{Ĵ}_X=0.6$。我们的结果直接表明$\mathrm{警察}{\mathrm{小号}}_3$ 是二维vdW磁铁中带有蜂窝格的XXZ模型的实验实现。