DIFFUSION OF POSITIVE MUONS IN ZONE-REFINED IRON BELOW ROOM-TEMPERATURE

The relaxation rate λ of μ+ spin in α-iron polycrystals and single crystal of 99.995% purity has been measured from 299 down to 50 K. At room temperature it is 0.14 μsec-1, much smaller than ever observed. Above 120 K its temperature dependence obeys an Arrhenius law (activation energy 44 ± 3 meV) for the μ+ diffusion. Previous values in less pure samples are discussed in terms of internal field inhomogeneity and of μ+ trapping by chemical or non-chemical defects. The deduced diffusion rate is proportional to T2 in the whole temperature region studied. © 1979.