Enhanced exchange field of NiO/NiFe biyer by dual ion beam sputtering process control

Abstract

Dual IBS (Ion Beam Sputtering) technique was used to fabricate NiO/NiFe bilayers. Various process conditions were examined to enhance the exchange field of the bilayer. Ion beam sputtering with an ion beam voltage above the threshold voltage and with the optimum ion beam current produced a fine-grained and smooth NiO film. This fine-grained surface followed by optimum etching exhibited an enhanced exchange field of 100 Oe. Growing NiO films were ion bombarded with a secondary ion-beam source having various beam voltages. The texture, surface roughness and grain size of the NiO films changed due to the ion bombardment; however, the grain size and/or surface roughness rather than texture was found to be responsible for controlling the exchange coupling. Furthermore, it was demonstrated that an optimum etching time of the NiO film prior to the depositing of NiFe for a large exchange field exists. With this optimum etching of the NiO film, surface segregated impurities could be eliminated without deteriorating the surface unnecessarily. Exchange fields and coercivities of the NiO/NiFe bilayers were measured with a MOKE (Magneto–Optic Kerr Effect) hysteresis looper and the surface properties of NiO films were examined with an AFM (Atomic Force Microscope) and an AES (Auger Electron Spectroscope).