Large perpendicular exchange bias in CoFeB/MgO systems pinned by a bottom IrMn layer through an interfacial CoFe/Ta composite layer

Exchange bias (EB) refers to the magnetic hysteresis loop shifting away from zero field due to the exchange interaction between a ferromagnet (FM) and an antiferromagnet (AF) across their common interface [1]. Nowadays the FM/AF EB structure with in-plane anisotropy has been widely adopted in hard disk drives and magnetic random access memories based on spin valves and magnetic tunnel junctions (MTJs). Compared with in-plane anisotropy, perpendicular magnetic anisotropy (PMA) is more desirable for spintronic devices owing to the better downsizing scalability and higher thermal stability for the encoded information. The recent discovery of appreciable interfacial PMA in the CoFeB/MgO films and further demonstration of high performance perpendicular MTJs represent significant steps towards next-generation spintronic devices [2]. However, there is no study on the perpendicular exchange bias (PEB) effect of the perpendicular CoFeB/MgO films generated by AF pinning materials, and all perpendicular CoFeB/MgO based MTJs are pseudo spin valve type. In this work, we have explored the exchange bias of the CoFeB/MgO films pinned by an antiferromagnetic IrMn layer along the perpendicular direction.