Interface reaction of Ta/NiO and its effect on exchange coupling

Ta/NiO/NiFe/Ta multilayers, utilizing Ta as the buffer layer, were prepared by RF reactive and DC magnetron sputtering. The exchange coupling field between NiO and NiFe reached a maximum value of 120 Oe at a NiO film thickness of 50 nm. The composition and chemical state at the interface region of Ta/NiO/Ta were studied using the X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there is an `intermixing layer’ at the Ta/NiO (and NiO/Ta) interface due to a thermodynamically favorable reaction: 2Ta+5NiO=5Ni+Ta<sub>2</sub>O<sub>5</sub>. This interface reaction has an effect on the exchange coupling. The thickness of the `intermixing layer’ as estimated by XPS depth-profiles was about 8–10 nm.