Enhanced Exchange Anisotropy by Ultra-Thin Co $_{x}$ Fe $_{100 - x}(x> 80)$ Layer Insertion at the

We have investigated the exchange anisotropy in L1₂-ordered Mn ₃Ir/Co ₆₅Fe ₃₅ bilayers with inserting ultra-thin CoxFe_{100 -} x(x > 65) layer at the interface between L1₂-Mn₃ Ir and Co₆₅ Fe₃₅ layer. The unidirectional anisotropy constant, JK, was enhanced from 0.93 erg/cm² to 1.2erg/cm² at the range from 85 to 98 at.% of Co composition in CoxFe_{100 -} x insertion layer. The crystal structure of the ultra-thin Co₉₀ Fe₁₀ insertion layer was transformed to bcc structure following the bcc structured Co₆₅ Fe₃₅ layer during thermal annealing. These results suggest that the enhancement of exchange anisotropy with ultra-thin Co xFe _{100 -} x(x > 80) insertion layer is attributed to the Co-rich bcc phase formation in the insertion layer.