Theory of spin polarization around an interstitial positive muon in ferromagnetic materials

A simple theory of the hyperfine field seen by a positive muon at an interstitial site in a ferromagnetic material is presented. The d-electrons are assumed to be localised on the ion-site and responsible for the magnetic moment. The s-electrons are then allowed to form a free-electron band and participate in the screening of the muon charge. The theoretical results are compared with recent measurements of the hyperfine field at μ+ sites in Fe, Co and Ni. (author)