  We report a polarized neutron diffraction study conducted to reveal the
nature of the weak ferromagnetic moment in the superconducting ferromagnet
UCoGe. We find that the ordered moment in the normal phase in low magnetic
fields (B // c) is predominantly located at the U atom and has a magnitude of
about 0.1 muB at 3 T, in agreement with bulk magnetization data. By increasing
the magnetic field the U moment grows to about 0.3 muB in 12 T and most
remarkably, induces a substantial moment (about 0.2 muB) on the Co atom
directed antiparallel to the U moment. The anomalous polarizability of the Co
3d orbitals is unique among uranium intermetallics and might reflect the
proximity to a magnetic quantum critical point of UCoGe in zero field.
