Hyperfine field of positive muons in Ni

We have calculated the contact hyperfine field of positive muons in Ni using a self-consistent spin-polarized density-functional formalism. Because we find more than an order-of-magnitude enhancement of the ambient hyperfine field at the muon position, it is impossible, within the confines of a free-electron model, to achieve agreement between neutron scattering results for the interstitial-polarization and muon-precession experiments. We propose a model in which the screening of the muon charge is done by free electrons of an essentially unpolarized $4s$ band, while the hyperfine field is due mainly to the relatively unperturbed $3d$ spin density arising from the different radial character of the majority and minority spin $3d$ wave functions. This model can satisfactorily reconcile neutron scattering and muon-precession experiments and existing Ni band-structure calculations.