Tracking muons to their final states in model systems

We recently studied KF to investigate muon sites and diffusion pathways, owing to its simple structure and low cation nuclear moment. However, the data showed a very small asymmetry and strange relaxation that we were unable to explain. This result prompted us to consider muon behaviour more widely in the alkali halides, with previous studies suggesting a delayed diamagnetic state is formed through a prompt paramagnetic species. This early work proposed that state conversion is mediated by defect states. One of the crucial assumptions in μSR is that any defects that may be caused by the implantation of the muon are sufficiently far away that they do not affect the final muon spectra, but if the hypothesis from this early work is found to be correct then this could have profound implications for μSR. As alkali fluorides weren’t part of this early study and their measurements on the halides were carried out over a comparatively restricted temperature range, we believe that it’s opportune to take a fresh look at these materials. As well as at-resonance RF measurements to determine state conversion rates, we plan to use a combination of 90º pulsed RF methods and DFT to characterise the final states. The original study will be extended to encompass the alkali fluorides, where the F− ion so often plays a role in significantly modifying the muonic properties of these materials.