${\mathrm{BaNi}}_2{\mathrm{V}}_2{\mathrm{O}}_8:$ A two-dimensional honeycomb antiferromagnet

The magnetic properties of ${\mathrm{BaNi}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ are reported. The magnetic Ni ions are arranged in a two-dimensional (2D) honeycomb net. Susceptibility, specific heat, and neutron diffraction measurements reveal the onset of antiferromagnetic long-range ordering (LRO) close to 50 K. Diffuse scattering that is characteristic of strong 2D magnetic correlations are observed up to 100 K. $\chi \mathrm{}\left(T\right)\mathrm{}$ of $\mathrm{Ba}({\mathrm{Ni}}_{1-x}{\mathrm{Mg}}_x{)}_2{\mathrm{V}}_2{\mathrm{O}}_8$ $(0\mathrm{}<~x<~0.2)$ shows the gradual disappearance of LRO with doping.