Large Perpendicular Exchange Bias in CoFeB/MgO Systems Pinned by a Bottom IrMn Layer via an Interfacial CoFe/Ta Composite Layer

CoFeB/MgO films with perpendicular magnetization pinned by an antiferromagnetic IrMn layer have been explored. CoFeB/MgO films directly grown on an antiferromagnetic IrMn layer exhibit insufficient perpendicular magnetic anisotropy (PMA) to overcome shape anisotropy. With a Ta dusting layer inserted into the CoFeB layer, perpendicular magnetization and perpendicular exchange bias (PEB) are simultaneously acquired in IrMn/CoFeB/MgO films. More significantly, when the CoFeB sublayer between IrMn and Ta is replaced by a thin CoFe layer, the PEB is drastically enhanced with large PMA sustained. Through optimizing the thicknesses of CoFe and Ta, a PEB field of about 540 Oe is achieved in the CoFeB films with an effective perpendicular anisotropy field of about 2.5 kOe. The present results suggest that the interfacial CoFe/Ta composite layer insertion paves the way to establish large PEB in the IrMn/CoFeB/MgO system.