μ+ diffusion in cubic f-electron compounds observed by high transverse field μ+ SR

Abstract

Positive muon (μ+) diffusion was observed in cubic f-electron compounds PrPb3 and SmAg2In by means of the μ+ spin rotation (μ+SR) method in high transverse field applied along the [001] direction. The applied field splits one crystallographic site into two magnetically inequivalent sites. The μ+ diffusion between these magnetically different sites drastically influences the μ+SR frequencies, so that two lines are gradually merged into one line at increasing temperature due to the motional narrowing effect. The μ+ hopping rate Ω derived from the μ+SR line shape follows the Arrhenius law, namely, Ω = Ω0 exp(−U/kBT) in both cases. The preexponential factor Ω0 suggests that the dominant mechanism of μ+ diffusion is classical over-the-barrier hopping in PrPb3 for 140<T<200 K and phonon-assisted quantum tunneling in SmAg2In for 40<T<70 K.