We have investigated the exchange anisotropy in Ll 2-ordered Mn 3Ir/Co 65Fe 35 bilayers with inserting ultra-thin Co x Fe 100-x(x > 65) layer at the interface between Ll 2-Mn 3 Ir and Co 65Fe 35 layer. The unidirectional anisotropy constant, J K, was enhanced from 0.93 erg/cm 2 to 1.2erg/cm 2 at the range from 85 to 98 at.% of Co composition in Co xFe 100-x insertion layer. The crystal structure of the ultra-thin Co 90Fe 10 insertion layer was transformed to bcc structure following the bcc structured Co 65Fe 35 layer during thermal annealing. These results suggest that the enhancement of exchange anisotropy with ultra-thin Co x-Fe 100-x(x > 80) insertion layer is attributed to the Co-rich bcc phase formation in the insertion layer.
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