Large perpendicular exchange bias in IrMn/CoFe/[Pt/Co] multilayers grown on a Ta/Pt buffer layer

Abstract

Bottom pinned IrMn/[Co/Pt] multilayer films with relatively thin Pt layers (∼10 Å) grown on a Ta/Pt buffer have been found to exhibit favourable perpendicular exchange bias (PEB) and well-defined perpendicular anisotropy at room temperature. However, even the optimum film suffers from the same problem as those reported previously, i.e. the exchange bias field is just slightly larger than the coercivity. By replacing the Co layer in contact with IrMn by a 6–8 Å Co60Fe40 layer, the exchange bias is drastically enhanced while the large perpendicular anisotropy is sustained and the coercivity changes little. The exchange bias field for the IrMn/CoFe/[Pt/Co] films with sufficient high perpendicular anisotropy can reach a value as high as 950 Oe, which is almost three times the coercivity, and the corresponding unidirectional anisotropy, 0.22 erg cm−2, considerably exceeds the best result at room temperature for various PEB systems ever reported. The present result suggests that PEB strongly depends on the composition of the ferromagnetic layer across the interface, which opens an effective avenue to boost PEB.