First-principles study of the magnetic hyperfine field in Fe and Co multilayers

We present ab initio calculations of the magnetic hyperfine field and magnetic moments in several Fe and Co multilayers (Fe(Co${)}_2$ ${\mathrm{Cu}}_6$ fcc (001), FeCu(Ag${)}_5$ fcc (001), bcc Fe/fcc ${\mathrm{Ag}}_5$ (001), bcc ${\mathrm{Fe}}_{\mathit{n}}$/fcc ${\mathrm{Au}}_5$ (001) (n=1,3,7), ${\mathrm{Co}}_{\mathit{k}}$ ${\mathrm{Pd}}_1$ fcc (111) [k(l)=1 (5), 2 (4), 3 (3)] and ${\mathrm{Co}}_2$ ${\mathrm{Pt}}_{\mathit{m}}$ fcc (111) (m=1,4,7)) as well as in bcc Fe and fcc (hcp, bcc) Co. The first-principles spin-polarized, relativistic linear muffin-tin orbital method is used. Therefore, both the orbital and magnetic dipole contributions as well as the conventional Fermi contact term are calculated. Calculations have been performed for both in-plane and perpendicular magnetizations. The calculated hyperfine field and its variation with crystalline structure and magnetization direction in both Fe and Co are in reasonable agreement (within 10%) with experiments. The hyperfine field of Fe (Co) in the interface monolayers in the magnetic multilayers is found to be substantially reduced compared with that in the corresponding bulk metal, in strong contrast to the highly enhanced magnetic moments in the same monolayers. It is argued that the magnetic dipole and orbital contributions to the hyperfine field are approximately proportional to the so-called magnetic dipole moment and the orbital moment, respectively.