  We have carried out detailed experimental studies of the exchange bias effect
of a series of CoO/Co(111) textured bilayers with different Co layer thickness,
using the magneto-optical Kerr effect, SQUID magnetometry, polarized neutron
reflectivity, x-ray diffraction, and atomic force microscopy. All samples
exhibit a pronounced asymmetry of the magnetic hysteresis at the first
magnetization reversal as compared to the second reversal. Polarized neutron
reflectivity measurements show that the first reversal occurs via nucleation
and domain wall motion, while the second reversal is characterized by
magnetization rotation. Off-specular diffuse spin-flip scattering indicates the
existence of interfacial magnetic domains. All samples feature a small positive
exchange bias just below the blocking temperature, followed by a dominating
negative exchange bias field with decreasing temperature. For very thin
Co-films the coexistence of ferromagnetic domains with parallel and
perpendicular magnetization directions leads to a peculiar shape of the
hysteresis with an extended plateau like region of almost zero magnetization.
