Paramagnetic fluctuations in MnO

A shift in the muon spin-relaxation rate in MnO is observed around 540 K, i.e. about 4.5 times T-N. This result confirms earlier observations using spin-polarized electron diffraction of a significant change in the paramagnetic spin system taking place at this temperature. This change might be caused by the transition from a state with correlated magnetic clusters to independently fluctuating spins. Furthermore, we have confirmed previous findings that at low temperature, the implanted muons are situated at sites close to manganese ions and that, as the temperature is increased, they diffuse and are trapped at manganese vacancies. In addition, we have observed that the muons are detrapped and start to diffuse again at temperatures above 800 K.