Anisotropic and Controllable Nonlocal Damping in Exchange Bias Bilayers

The physics at antiferromagnetic (AFM)/ferromagnetic (FM) interfaces, including exchange bias (EB) and spin current, are of key interest in spintronics. However, the relationship between the EB effect and spin current is still controversial. Here, we have observed anisotropic and controllable nonlocal damping in a typical EB system, i.e., Co/CoO bilayers. Oblique deposition of Co film with an in situ oxidized CoO top layer generates a controllable uniaxial magnetic anisotropy (UMA), and leads to reconfigurable orientations of the average interfacial uncompensated AFM spins. The Gilbert damping constant is larger in the hard axis than in the easy axis of UMA, which can be further enhanced by the training effect because of the reorientation of the average uncompensated AFM spins. Our work provides insight into the effect of EB on nonlocal damping and paves a new way to control the spin current in AFM spintronic devices.