A case study of bilayered spin-$1/2$ square lattice compound [VO(HCOO)${}_2\cdot$(H${}_2$O)]

Abstract

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 $J_1/k_{\mathrm{B}}\simeq 11.7$~K and next-nearest-neighbour interaction $J_2/k_{\mathrm{B}}\simeq 0.02$~K. It undergoes a Néel antiferromagnetic ordering at $T_{\mathrm{N}}\simeq 1.1$~K. The ratio ${\theta }_{\mathrm{CW}}/T_{\mathrm{N}}\simeq 10.9$ reflects excellent two-dimensionality of the spin-lattice in the compound. A strong in-plane anisotropy is inferred from the linear increase of $T_{\mathrm{N}}$ with magnetic field, consistent with the structural data.

9 pages, 7 figures, 1 table