双层自旋$1/2$正方晶格化合物[ VO（HCOO）$_2\cdot$（H $_2$ O）]的研究
A case study of bilayered spin-$1/2$ square lattice compound [VO(HCOO)$_2\cdot$(H$_2$O)]
摘要：
本文报道了[VO（HCOO）$_2\cdot$（H $_2$ O）]多晶的合成，并通过X射线衍射、磁化率、高场磁化强度、热容和电子自旋共振测量等手段详细研究了其结构和磁性。它以正交晶系结构结晶，空间群为$Pcca$。它的特征是扭曲的VO $_6$八面体通过HCOO连接体（甲酸根阴离子）连接，形成具有双层结构的二维正方形晶格网络。根据受抑正方晶格模型对磁化率、高场磁化强度和热容数据的分析明确地建立了具有最近邻相互作用$J_1/k_{\rm B} \simeq 11.7$ ~K和次最近邻相互作用$J_2/k_{\rm B} \simeq 0.02$ ~K的化合物的准二维性质。它在$T_{\rm N} \simeq 1.1$ ~K处经历Néel反铁磁有序。比率$θ_{\rm CW}/T_{\rm N} \simeq 10.9$反映了化合物中自旋晶格的优异二维性。从$T_{\rm N}$随磁场的线性增加推断出强的面内各向异性，与结构数据一致。
英文摘要：
We present the synthesis and a detail investigation of structural and magnetic properties of polycrystalline [VO(HCOO)$_2\cdot$(H$_2$O)] by means of x-ray diffraction, magnetic susceptibility, high-field magnetization, heat capacity, and electron spin resonance measurements. It crystallizes in a orthorhombic structure with space group $Pcca$. It features distorted VO$_6$ octahedra connected via HCOO linker (formate anions) forming a two-dimensional square lattice network with a bilayered structure. Analysis of magnetic susceptibility, high field magnetization, and heat capacity data in terms of the frustrated square lattice model unambiguously establish quasi-two-dimensional nature of the compound with nearest neighbour interaction $J_1/k_{\rm B} \simeq 11.7$~K and next-nearest-neighbour interaction $J_2/k_{\rm B} \simeq 0.02$~K. It undergoes a Néel antiferromagnetic ordering at $T_{\rm N} \simeq 1.1$~K. The ratio $θ_{\rm CW}/T_{\rm N} \simeq 10.9$ reflects excellent two-dimensionality of the spin-lattice in the compound. A strong in-plane anisotropy is inferred from the linear increase of $T_{\rm N}$ with magnetic field, consistent with the structural data.
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