Perpendicular Exchange Anisotropy in Mn-Ir/Fe-Co/[Pt/Co] $_{4}$ Multilayers

The perpendicular unidirectional anisotropy constant, J_K^perp, of Mn-Ir/Fe-Co/[Pt/Co] ₄ multilayers was investigated by systematically changing the Fe-Co layer composition, and was compared with the in-plane unidirectional anisotropy constant, J_Kⁱⁿ, of Mn-Ir/Fe-Co bilayers. Observed trends were similar for the variation of J_K^perp and J_Kⁱⁿ against the compositional change. This result indicates that the perpendicular exchange anisotropy and in-plane exchange anisotropy are induced by similar mechanisms. On the other hand, an apparent discrepancy was pointed out between the absolute values of J_K^perp and J_Kⁱⁿ in particular for the compositional region where Fe-Co forms body-centered-cubic (bcc) structure. This significant discrepancy in the bcc-Fe-Co region was explained by the magnetic anisotropy of the Fe-Co layer, and it is expected that J_K^perp could be increased as large as J_Kⁱⁿ when strong perpendicular magnetic anisotropy is induced in the Fe-Co layer.