  Ca3Ru2O7 with a Mott-like transition at 48 K features different in-plane
anisotropies of magnetization and magnetoresistance. Applying magnetic field
along the magnetic easy-axis precipitates a spin-polarized state via a
first-order metamagnetic transition, but does not lead to a full suppression of
the Mott state, whereas applying magnetic field along the magnetic hard axis
does, causing a resistivity reduction of three orders of magnitude. The
colossal magnetoresistivity is attributed to the collapse of the orbital
ordered and spin-polarized state. Evidence for a density wave is also
presented.
