Giant perpendicular exchange bias in a sub-nanometer inverted (Co/ Pt)n/Co/IrMn structure

The phenomenon of exchange coupling has become major research area since its discovery and was extensively studied in various ferrromagnet (FM) - antiferromagnet (AFM) systems in the presence of spintronics, which usually occurs in a FM/AFM bilayer. A large exchange bias field (H
_ex
) at room temperature is preferred, but perpendicular magnetic anisotropy is found to be more desirable due to a high thermal stability for various spintronic devices. In our work, we report a giant perpendicular exchange bias H
_ex
^per
exhibited in the R-H curves of an inverted (Co/Pt)
_n
/Co/IrMn multi layer and an inverted (Co/Pt)
_n
/Co/Cu/(Co/Pt)
₄
/Co/IrMn spin valve structure, in which the Pt layers are only 114 nm in thickness and less than Co layers. H
_ex
^per
has an unusual linear scaling with the repetition n+1 of the (Co/Pt)
_n
/Co free layer, with its maximum value near the order of 1000 Oe for n+1 = 9. The in-plane exchange bias H
_ex
in is almost constant. The origin of exchange bias in inverted spin valve structure is due to Co/IrMn interfacial magnetic coupling in inverted (Co/Pt)
₄
/Co/IrMn reference layer, which is magnified by the exchange coupling between the interface Co layer and the multilayer (Co/Pt)
_n
(n = 4 for the spin valve structures) in the reference stack. As shown Figure 1, giant conventional and pseudo H
_ex
^per
in the perpendicular inverted (Co/Pt)
_n
/Co spin valves enhances their roles in perpendicular spintronic devices.