Muon-spin-rotation experiments in orthoferrites

A systematic study of the behavior of positive muons in orthoferrites $R{\mathrm{FeO}}_3$ has been performed. Measurements as a function of temperature and applied magnetic field have been made for $R$ = Sm, Eu, Dy, Ho, Y, and Er. Typically several different sites are occupied by the muons at low temperatures, and transitions occur to one stable site with temperature-dependent rate constants. By comparing the measured internal magnetic fields with calculated dipolar fields of the iron ions, the position of the stable muon site was found to be on the mirror plane $m$ about 1 Å from the nearest oxygen ion, implying the formation of the hydroxyl analog ${\left(\mathrm{O}\mu \right)}^{-}$. Muon diffusion was observed for $R=\mathrm{Sm}$ with about 10 $\frac{\mathrm{jumps}}{\mu \mathrm{s}}$ at 296 K.