Chemical states of the atoms in magnetic multilayers Ta/NiO x /Ni81Fe19/Ta and Co/AlO x /Co

Ta/NiO x /Ni81Fe19/Ta and Co/AlO x /Co multilayers were prepared by rf reactive and dc magnetron sputtering. The exchange coupling field (H ex) and the coercivity (H c) of NiO x /Ni81Fe19 as a function of the ratio of Ar to O2 during the deposition process were studied. The composition and chemical states at the interface region of NiO x /NiFe were also investigated using the X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that when the ratio of Ar to O2 is equal to 7 and the argon sputtering pressure is 0.57 Pa, the x value is approximately 1 and the valence of nickel is +2. At this point, NiO x is antiferromagnetic NiO and the corresponding Hex is the largest. As the ratio of Ar/O2 deviates from 7, the H ex will decrease due to the presence of magnetic impurities such as Ni+3 or metallic Ni at the interface region of NiO x /NiFe, while the H c will increase due to the metallic Ni. Al layers in Co/AlO x /Co multilayers were also studied by angle-resolved XPS. Our finding is that the bottom Co could be completely covered by depositing an Al layer about 1.8 nm. The thickness of AlO x was 1.2 nm.