Competing Magnetic Phases on a Kagomé Staircase

We present thermodynamic and neutron data on ${\mathrm{N}\mathrm{i}}_3{\mathrm{V}}_2{\mathrm{O}}_8$, a spin-1 system on a kagomé staircase. The extreme degeneracy of the kagomé antiferromagnet is lifted to produce two incommensurate phases at finite $T$—one amplitude modulated, the other helical—plus a commensurate canted antiferromagnet for $T\to 0$. The $H\mathrm{\text{−}}T$ phase diagram is described by a model of competing first and second neighbor interactions with smaller anisotropic terms. $\mathrm{N}{\mathrm{i}}_3{\mathrm{V}}_2{\mathrm{O}}_8$ thus provides an elegant example of order from subleading interactions in a highly frustrated system.