Perpendicular magnetization and exchange bias in epitaxial NiO/[Ni/Pt]2 multilayers

The realization of perpendicular magnetization and perpendicular exchange bias (PEB) in magnetic multilayers is important for the spintronic applications. NiO(t)/[Ni(4 nm)/Pt(1 nm)]₂ multilayers with varying the NiO layer thickness t have been epitaxially deposited on SrTiO₃ (001) substrates. Perpendicular magnetization can be achieved when t < 25 nm. Perpendicular magnetization originates from strong perpendicular magnetic anisotropy (PMA), mainly resulting from interfacial strain induced by the lattice mismatch between the Ni and Pt layers. The PMA energy constant decreases monotonically with increasing t, due to the weakening of Ni (001) orientation and a little degradation of the Ni-Pt interface. Furthermore, significant PEB can be observed though NiO layer has spin compensated (001) crystalline plane. The PEB field increases monotonically with increasing t, which is considered to result from the thickness dependent anisotropy of the NiO layer.