First-principles studies of modulated Co/Cu superlattices with strongly and weakly exchange-biased Co-monolayers

Abstract First-principles calculations have been performed in order to determine effective exchange integrals between strongly and weakly exchange-coupled Co monolayers in certain novel periodic CoCu 2 /CoCu n -superlattices and related systems with three or more non-equivalent Co planes. For 3 ≤ n ≤ 6 we find that there are two non-equivalent exchange integrals j and J , which have opposite signs, i.e. the strong coupling J is antiferromagnetic and the weak coupling j ferromagnetic, and differ for n ≠ 4 from each other by one order of magnitude. It is shown that the results depend on the system as a whole and cannot be obtained from separate parts. From our results we suggest that ‘spin valve’ systems with similar modulated structures should be considered when trying to obtain good magneto-resistance together with low switching-fields.