  In terms of the fully relativistic screened Korringa-Kohn-Rostoker method we
investigate the effect of stacking faults on the magnetic properties of
hexagonal close-packed cobalt. In particular, we consider the formation energy
and the effect on the magnetocrystalline anisotropy energy (MAE) of four
different stacking faults in hcp cobalt -- an intrinsic growth fault, an
intrinsic deformation fault, an extrinsic fault and a twin-like fault. We find
that the intrinsic growth fault has the lowest formation energy, in good
agreement with previous first-principles calculations. With the exception of
the intrinsic deformation fault which has a positive impact on the MAE, we find
that the presence of a stacking fault generally reduces the MAE of bulk Co.
Finally, we consider a pair of intrinsic growth faults and find that their
effect on the MAE is not additive, but synergic.
