Negative muon spin precession in ferromagnets and the hyperfine anomaly

A muonic atom μ-Z is a pseudonucleus with a peculiar charge and magnetization distribution. When embedded in a solid host this pseudonucleus appears to the atomic electrons very similar to an isolated impurity nucleus with charge Z-1. However, the hyperfine field Bsub(μ) at the μ- differs from the hyperfine field Bsub(n) seen by a nucleus of charge Z-1 since the muon wave function extends outside the nucleus. This difference in the hyperfine fields gives rise to the so called hyperfine anomaly. In a ferromagnet this anomaly may be measured by a combined μ-SR and NMR experiment. The authors present measurements of Bsub(μ) for μ-Ni taken at three well-defined sample temperatures. (Auth.)