μSR in UAs

UAs has the NaCl structure and undergoes a first order transition into a type I (single k) antiferromagnetic state at 123 K, followed by a second first order transition at 62 K into a type IA (double k) antiferromagnetic structure. μSR spectra of a powder sample were taken in zero and transverse fields up to 0.3 T. They cover the paramagnetic and the two antiferromagnetic states. The most significant features of our data are: i) a first increase of relaxation rate below T=180 K; ii) a sudden jump in both, relaxation rate and frequency shift at T=123 K, together with a small decrease in initial asymmetry (≈15%); iii) no μ⁺ spin rotation in zero field in the type I state; iv) an overlay, of 3 spectra in the type IA state. Two of these spectra show spin rotation in zero field. Their frequencies are clearly temperature dependent. In a transverse field of 5 and 10 mT the external field adds nearly fully to the internal field. Work supported in part by the Bundesministerium fur Forschung und Technologie, Federal Republic Germany.