Incommensurate spin density wave in metallic ${\mathrm{V}}_{2\mathrm{-}\mathit{y}}$${\mathrm{O}}_3$

We show by neutron diffraction that metallic ${\mathrm{V}}_{2\mathrm{-}7}$${\mathrm{O}}_3$ develops a spin density wave below ${\mathit{T}}_{\mathit{N}}$≊9 K with incommensurate wave vector q≊1.7${\mathit{c}}^{\mathrm{*}}$ and an ordered moment of 0.15${\mathrm{\mu }}_{\mathit{B}}$. The weak ordering phenomenon is accompanied by strong, nonresonant spin fluctuations with a velocity c=67(4) meV Å. The spin correlations of the metal are very different from those of the insulator and place ${\mathrm{V}}_{2\mathrm{-}\mathit{y}}$${\mathrm{O}}_3$ in a distinct class of Motte-Hubbard systems where the wave vector for magnetic order in the metal is far from a high symmetry commensurate reciprocal lattice point.