mu SR evidence of low frequency spin fluctuations in the AF phase of hole-doped NiO

mu SR measurements in the antiferromagnetic (AF) phase of Ni1-xLixO for 0 l ess than or equal to x less than or equal to 0.10 are reported. While in pu re NiO the muon longitudinal depolarization rate lambda(mu) is found almost temperature independent, in the Li-doped compounds broad maxima around 130 K are observed. These maxima are associated with the progressive freezing of the spin fluctuations of S = 1/2 defects induced by the localization of the extra-holes. From the temperature dependence of lambda(mu) and the stre tched exponential form of the depolarization, insights on the distribution of correlation times for the fluctuating field at the muon site are derived .