Competing Magnetic Phases on a 'Kagome Staircase'

We present thermodynamic and neutron data on Ni3V2O8, a spin- 1 system on a kagome staircase. The extreme degeneracy of the kagome antiferromagnet is lifted to produce two incommensurate phases at finite T - one amplitude modulated, the other helical - plus a commensurate canted antiferromagnet for T -> 0. The H - T phase diagram is described by a model of competing first and second neighbor interactions with smaller anisotropic terms. Ni3V2O8 thus provides an elegant example of order from sub- leading interactions in a highly frustrated system.