  We utilize transverse ac susceptibility measurements to characterize magnetic
anisotropy in archetypal exchange-bias bilayers of ferromagnet Permalloy (Py)
and antiferromagnet CoO. Unidirectional anisotropy is observed for thin Py, but
becomes negligible at larger Py thicknesses, even though the directional
asymmetry of the magnetic hysteresis loop remains significant. Additional
magnetoelectronic measurements, magneto-optical imaging, as well as
micromagnetic simulations show that these surprising behaviors are likely
associated with asymmetry of spin flop distribution created in CoO during Py
magnetization reversal, which facilitates the rotation of the latter back into
its field-cooled direction. Our findings suggest new possibilities for
efficient realization of multistable nanomagnetic systems for neuromorphic
applications.
