  We report local probe investigations of the magnetic interaction between
BiFeO3 films and a ferromagnetic Co0.9Fe0.1 layer. Within the constraints of
intralayer exchange coupling in the Co0.9Fe0.1, the multiferroic imprint in the
ferromagnet results in a collinear arrangement of the local magnetization and
the in-plane BiFeO3 ferroelectric polarization. The magnetic anisotropy is
uniaxial, and an in-plane effective coupling field of order 10 mT is derived.
Measurements as a function of multiferroic layer thickness show that the
influence of the multiferroic layer on the magnetic layer becomes negligible
for 3 nm thick BiFeO3 films. We ascribe this breakdown in the exchange coupling
to a weakening of the antiferromagnetic order in the ultrathin BiFeO3 film
based on our X-ray linear dichroism measurements. These observations are
consistent with an interfacial exchange coupling between the CoFe moments and a
canted antiferromagnetic moment in the BiFeO3.
