Antiferromagnetic ordering in Cu₂OCl₂ studied by the muon spin rotation/relaxation technique

We report on muon spin rotation/relaxation (νSR) studies of the cuprate mineral melanothallite, Cu₂OCl₂, over a temperature range between 4.1 and 300K. This compound has a pyrochlore-like corner-shared OCu ₄ tetrahedral network with an S ≤ 1/2 system. The magnetic susceptibility shows a broad maximum around 140K and drops at 70K. In the νSR measurement, we observed clear muon spin precession spectra below 70K that is evidence for a long-range magnetic ordered state. However, the time spectra also exhibit exponential damping even in the ordered state, suggesting a possible influence of geometrical frustration in this compound. This renders the need for careful examination of the magnetic structure of the ordered state.