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)Cu-6 fcc (001), FeCu(Ag)(5) fcc (001), bcc Fe/fcc Ag-5 (001), bcc Fe-n/fcc AU(5) (001) (n=1,3,7), CokPd1 fee (111) [k(l)=1 (5), 2 (4), 3 (3)] and Co2Ptm fcc (111) (m=1,4,7)) as well as in bcc Fe and fee (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 (Go) 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. These linear relations are then demonstrated to hold rather well by using the calculated non-s-electron hyperfine fields, orbital and magnetic dipole moments. Unlike in the bulk metals and alloys, the magnetic dipole moment in the multilayers is predicted to be comparable to the orbital moment and as a result, the magnetic dipole contribution to the hyperfine field is large. The anisotropy in the hyperfine field is found to be very pronounced and to be strongly connected with the large anisotropy in the orbital moment and magnetic dipole moment. The induced magnetic moments and hyperfine fields in the nonmagnetic spacer layers are also calculated. The results for the multilayers are compared with available experiments and previous nonrelativistic calculations.