Effect of a NiO sputtering condition on the exchange coupling of a NiFe/ NiO bilayer

An exchange-biased bilayer of NiFe (10 nm)/NiO (60 nm) for spin-valve giant magnetoresistance applications was sputter-deposited on a Si wafer. The Ar pressure for NiO deposition was varied from 0.5 to 6 mTorr, and the resultant changes in the microstructure and the chemical composition in the NiO layer were investigated. From Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy, we found that Ni ₂O ₃ was formed in the NiO layer and that its content increased as the Ar pressure was increased. This nonmagnetic second phase is thought to destroy the antiferromagnetism of the NiO layer and to weaken the exchange coupling of the NiFe/NiO bilayer.