Muon level-crossing resonances as a probe for studying antiferromagnets at pulsed muon sources

We propose a set of measurements using the HiFi spectrometer in which muon level-crossing resonances are used to probe the internal field inside antiferromagnets in which the precession frequency is too large to observe at a pulsed muon source. The idea is based on an old experiment by Kiefl et al. on MnF2. Performing such an experiment at ISIS has the added benefit that information from the time-dependence of the relaxation can be obtained, shedding more light on the transverse couplings that occur at resonance when the principal interactions have been "cancelled out". By performing these experiments on single crystals of fluorides with the rutile structure we have the added benefit that the muon site is well-known through DFT+mu calculations by Moeller et al. The revival of this technique has the potential to become more widely used in the study of magnetic materials with muons.