Large Negative Magnetic Anisotropy in Epitaxially Grown Fe/Co Multilayer Films

We have investigated the relationship between the crystal structure and the magnetic anisotropy constant of epitaxially grown Fe/Co multilayers (ML). The Fe/Co ML grown on a Ag (100) underlayer at ambient temperature exhibits body centered cubic (bcc) structure with (100) orientation for the stacking period λ less than 15 nm. The saturation field along the film normal is much larger than the demagnetization field 4πMs, indicating negatively large magnetic anisotropy Ku. The negative Ku takes the peak value as large as −1×107 erg/cc at λ = 0.75 nm. This behavior of Ku against λ is very similar to that reported for Fe/Co (110) polycrystalline ML [Vas'ko et al., Appl. Phys. Lett. 89, 092592 (2006)]. Moreover, slight lattice distortion is observed, but the magnetoelastic contribution is much smaller than the negative Ku. These results lead to the conclusion that the negative Ku of Fe/Co ML is attributable to the interfacial magnetic anisotropy with weak crystal orientation dependence.