Rotation sense of the magnetization in the Co/CoO exchange-bias system probed with anisotropic magnetoresistance measurements

The possibility of tracking the average rotation sense of the magnetization vector of a ferromagnetic layer upon magnetization reversal by means of magnetotransport measurements is explored. It is demonstrated that the rotation sense of the ferromagnetic magnetization vector during a hysteresis loop can be determined for the polycrystalline Co/CoO exchange bias system by measuring the anisotropic magnetoresistance (AMR) with a specific choice of the measurement geometry. The AMR measurements reveal that the rotation direction of the magnetization vector can be reversed by performing an in-plane hysteresis loop with a magnetic field perpendicular to the cooling field. This reversal can be directly linked to the experimental fact that after training, i.e., after performing hysteresis loops with a field along the cooling field direction, the average orientation of the uncompensated magnetization of the granular CoO antiferromagnet can be largely rotated back to the initial orientation after field cooling by applying a perpendicular field with the appropriate amplitude and orientation.