Decomposition of the relativistic hyperfine interaction operator: Application to the ferromagnetic alloy systems fcc ${\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x},$ fcc ${\mathrm{Fe}}_x{\mathrm{Pd}}_{1-x},$ and fcc ${\mathrm{Co}}_x{\mathrm{Pt}}_{1-x}$

A scheme developed by Pyper to decompose within relativistic Hartree-Fock theory the hyperfine interaction operator into the conventional Fermi contact, spin dipolar and orbital contributions is modified to split the hyperfine field of magnetic solids calculated in a fully relativistic way on the basis of spin-density-functional theory in an analogous way. The resulting expressions are used to examine the hyperfine fields for the disordered alloy systems fcc ${\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x},$ fcc ${\mathrm{Fe}}_x{\mathrm{Pd}}_{1-x},$ and fcc ${\mathrm{Co}}_x{\mathrm{Pt}}_{1-x}$ making use of the spin-polarized relativistic Korringa-Kohn-Rostoker coherent-potential approximation method of band-structure calculation. In particular the contribution of non-$s$ electrons to the hyperfine fields are discussed in detail. Special emphasize is laid on their relationship to the corresponding contributions to the spin and spin-orbit-induced orbital magnetic moments.