Magnetic properties and x-ray photoelectron spectroscopy study of NiO/NiFefilms prepared by magnetron sputtering

Ta/NiOx/N81Fe19/Ta multilayers were prepared by rf reactive and dc magnetro n sputtering. The exchange-coupling field (H-ex) and the coercivity (H-c) o f NiOx/Ni81Fe19 as a function of the ratio of Ar to O-2 during the depositi on process were studied. The composition and chemical states at the interfa ce region of NiOx/NiFe were also investigated using the x-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that the ratio of Ar to O-2 has a great effect on the nickel chemical states in NiOx film. When the ratio of Ar to O-2 is equal to 7 and the argon sputter ing pressure is 0.57 Pa, the x value is approximately 1 and the valence of nickel is +2. At this point, NiOx is antiferromagnetic NiO and the correspo nding H-ex is the largest. As the ratio of Ar/O-2 deviates from 7, the exch ange-coupling field (H-ex) will decrease due to the presence of magnetic de fects such as Ni+3 or metallic Ni at the interface region of NiOx/NiFe, whi le the coercivity (H-c) will increase due to the metallic Ni. XPS studies a lso show that there are two thermodynamically favorable reactions at the Ni O/NiFe interface: NiO+Fe=Ni+FeO and 3NiO+2Fe=3Ni+Fe2O3. These interface rea ction products are magnetic defects at the interface region of NiO/NiFe, it is believed that these magnetic defects would have an effect on the exchan ge-coupling field (H-ex) and the coercivity (H-c) of NiO/NiFe. (C) 2001 Ame rican Institute Of Physics.