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 Co2P tm fcc (111) (m=1,4,7)) as well as in bcc Fe and fee (hcp, bcc) Co. Th e first-principles spin-polarized, relativistic linear muffin-tin orbi tal method is used. Therefore, both the orbital and magnetic dipole co ntributions as well as the conventional Fermi contact term are calcula ted. Calculations have been performed for both in-plane and perpendicu lar magnetizations. The calculated hyperfine field and its variation w ith crystalline structure and magnetization direction in both Fe and C o are in reasonable agreement (within 10%) with experiments. The hyper fine field of Fe (Go) in the interface monolayers in the magnetic mult ilayers is found to be substantially reduced compared with that in the corresponding bulk metal, in strong contrast to the highly enhanced m agnetic moments in the same monolayers. It is argued that the magnetic dipole and orbital contributions to the hyperfine field are approxima tely proportional to the so-called magnetic dipole moment and the orbi tal 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 predicte d to be comparable to the orbital moment and as a result, the magnetic dipole contribution to the hyperfine field is large. The anisotropy i n the hyperfine field is found to be very pronounced and to be strongl y connected with the large anisotropy in the orbital moment and magnet ic dipole moment. The induced magnetic moments and hyperfine fields in the nonmagnetic spacer layers are also calculated. The results for th e multilayers are compared with available experiments and previous non relativistic calculations.