The temperature dependence of the longitudinal relaxation time of positive-muon spin in paramagnetic MnO has been determined by measuring the ${\mu }^{+}-e^{+}$ forward/backward asymmetry. The relaxation time, $T_1=2.00\mathrm{}$ μsec at 124 K can be accounted for in terms of exchange-fluctuating ${\mathrm{Mn}}^{++}$ atomic dipolar fields; the increase of $T_1$ with temperature shows that the relaxation is further slowed by fast diffusional motion of the ${\mu }^{+}$.

• Received 25 May 1978

DOI:https://doi.org/10.1103/PhysRevLett.41.421