Muons in sulphur

Abstract

Longitudinal-field repolarisation measurements of positive muons in sulphur suggest the existence of two paramagnetic muon species, consistent with a molecular radical and interstitial muonium. Avoided level-crossing measurements reveal a very weak signal at low temperatures (<100 K) , ascribed to the Δ M=1 resonance of a radical with a hyperfine constant of 233±5 MHz . We report further μSR experiments in sulphur, which attempt to shed light on the dynamics of muon charge states in this material. Above 200 K, transverse-field (TF) measurements show two diamagnetic signals, one of small amplitude and low relaxation λ, the other with high λ and a T-dependent amplitude. From 200 to 300 K the amplitude of the “fast” component increases rapidly, suggesting that the species it represents is formed in a thermally activated process from a paramagnetic precursor. Its relaxation follows a similar trend, but further investigation shows that λ for this component falls above 300 K while the amplitude remains essentially constant up to the β-phase transition. The amplitude drops in the β-phase and the fast relaxation disappears in the melt, where most of the polarisation is found in a slowly relaxing signal. While no TF radical signals have been found at any temperature, very recent low-field measurements at low temperatures show features consistent with an extremely quickly relaxing prompt muonium fraction, a possible precursor for the “fast” diamagnetic component.