A first-principles calculation of the magnetic moments and hyperfine parameters in amorphous Fe-B alloys

The electronic structure of ferromagnetic amorphous alloys Fe 1-x B x (0.14<or=x<or=0.23) is calculated from first principles using the tight-binding linear muffin-tin orbital method in the atomic spheres approximation for realistic structural models. The concentration dependences of magnetization and average hyperfine parameters at iron nuclei (hyperfine magnetic fields and isomer shifts) are discussed with respect to the main mechanisms of their origin and to the structural characteristics of the atomic models used. The concentration behaviour of the magnetization is explained by means of the charge transfer from boron to iron which amounts to 0.75 electrons per boron atom and which is accompanied by a change in the shape of the density-of-states curves. It is shown that the composition dependence of the isomer shift is controlled by the interatomic charge transfer together with the intra-atomic s-d electron conversion. The behaviour of the hyperfine field can be explained by a core polarization proportional to the local magnetic moment of iron atom and by a valence contribution due to the s-d hybridization. The calculated values agree fairly well with existing experimental data.