  The exchange coupling at the interfaces of magnetic superlattices consisting
of ferromagnetic $SrRuO_3$ and antiferromagnetic $SrMnO_3$ grown on (001)
oriented $SrTiO_3$ is studied with in-plane and out-of-plane orientations, with
respect to the substrate plane, of the cooling magnetic field. The
magnetization of the in-plane, field cooled hysteresis loop is lower than the
corresponding in-plane zero-field-cooled hysteresis loop. The out-of-plane
field cooled hysteresis loop is shifted, from the origin, along the graphical
magnetization axis. We attribute this irreversible rotation of the moment to
the pinning/biasing of spin in the $SrRuO_3$ layer in the vicinity of
interfaces by the antiferromagnetic $SrMnO_3$ layer.
