MUON SPIN RELAXATION STUDY OF THE (F-MU-F)- ION IN MAGNETIC FLUORIDES

A positive muon implanted in a solid fluoride insulator can form a hyd rogen-bonded (FmuF)- ion, in which the nuclear magnetic interactions c ause a distinctive zero-field (ZF) muon spin relaxation (muSR) signal. In a fluoride material in which the anions have electronic magnetic m oments, the muon's interaction with nearby F-19 nuclear moments must c ompete with its interaction with more distant but much larger anion mo ments. We report observation of this competition in ZF-muSR in MnF3 (T (N) = 43 K) and CuF2 (T(N) = 69 K). In both MnF3 and CuF2 characterist ic ZF FmuF oscillations are observed above the Neel temperature. As te mperature drops below T(N) in MnF3 the relaxation rate of the (FmuF)- signal increases dramatically. Below T(N) in CuF2 a small-amplitude hi gh-frequency coherent oscillation appears on top of the low-frequency (FmuF)- signal.