  The phase diagram of Sr3Ru2O7 contains a metamagnetic transition that
bifurcates to enclose an anomalous phase with intriguing properties - a large
resistivity with anisotropy that breaks the crystal-lattice symmetry. We
propose that this is a magnetic analogue of the spatially inhomogeneous
superconducting Fulde-Ferrel-Larkin-Ovchinnikov state. We show - through a
Ginzburg-Landau expansion where the magnetisation transverse to the applied
field can become spatially inhomogeneous - that a Stoner model with electronic
band dispersion can reproduce this phase diagram and transport behaviour.
