Effect of CoO/Ni orthogonal exchange coupling on perpendicular anisotropy of Ni films on Pd(001)

The effect of orthogonal exchange coupling between antiferromagnetic CoO and ferromagnetic Ni/Pd(001) on the perpendicular anisotropy of Ni films is studied. The thickness range in which Ni films show a perpendicular easy magnetization axis is extended by growing CoO on top of them, however, only at temperatures below ${T}_{N}$ of CoO. The perpendicular orientation of Ni spins and the in-plane orientation of CoO spins are confirmed by the magneto-optic Kerr effect/x-ray magnetic circular dichroism and x-ray magnetic linear dichroism, respectively. Additionally, a perpendicular exchange bias shows up at low temperature.