Electronic and magnetic structure of ultrathin cobalt-chromium superlattices

In order to study exchange coupling and spin distributions at atomically abrupt ferromagnetic/antiferromagnetic interfaces, we construct lattice-matched Co/Cr superlattice models. We consider in some detail strained-layer superlattices composed of alternating regions of ferromagnetic bcc Co and antiferromagnetic bcc Cr with repeat periods ranging from 4 to 8 atomic layers. For computational simplicity, Cr is represented by a theoretically stabilized commensurate antiferromagnetic spin arrangement. The superlattice spin distributions are determined by carrying out first-principles self-consistent spin-polarized linearized muffin-tin-orbital electronic-structure calculations. We find that the magnetic properties of the Co/Cr superlattices are dominated by the ferromagnetic Co layers, though the antiferromagnetic character of bcc Cr is still evident. For superlattices containing 1 Co layer and 3 to 7 Cr layers per repeat period, there is only one stable spin arrangement corresponding to ferromagnetic coupling across the Co/Cr interfaces. For superlattices containing thicker Co regions, e.g., 3 Co layers and 5 Cr layers, there are two distinct spin arrangements corresponding to ferromagnetic as well as antiferromagnetic coupling across the Co/Cr interfaces. We also discuss lattice-matched 10-layer hcp-Co/bcc-Cr superlattices, as well as the implications of our results for other complicated Co/Cr superlattices.