Angular and NiFe thickness dependence of IrMn/NiFe/IrMn thin films

The variation in exchange bias as a function of FM layer in FM/AFM/FM trilayer structure using IrMn(100 Å)/NiFe(t Å)/IrMn(100 Å) thin films is reported. Unidirectional exchange anisotropy and the uniaxial anisotropy were analysed by ferromagnetic resonance (FMR) measurements. The angular variation in resonance field, as a function of the NiFe layer thickness, manifests a unidirectional behavior for the exchange biased thin film. The variation of the unidirectional anisotropy field (H_ex) and uniaxial anisotropy field (H_k) with NiFe thickness was also determined. Results show that H_ex and H_k decreases linearly as NiFe thickness increases. When NiFe thickness reaches 800 Å, however, the trend becomes nonlinear which indicates that the uniform magnetization distribution throughout NiFe layers is preserved up to NiFe thickness of 400 Å. The H_ex of thicker NiFe layers could be from an inhomogeneous NiFe magnetization reversal due to domain formation in NiFe layer.