Freezing of spin and charge in La/sub 2-//sub x/Sr/sub x/CuO/sub 4/

Zero- and longitudinal-field muon spin relaxation (..mu../sup +/SR) measurements have been performed on La/sub 2-//sub x/Sr/sub x/CuO/sub 4/ alloys in both single-crystal and sintered powder forms above and below their magnetic transition temperatures, T/sub f/. The ..mu../sup +/ precession frequency ..nu.. depends only weakly on x and T/sub f/, an observation which together with resistivity data implies classical freezing of magnetic moments in the regime where the carriers are localized. For x = 0.05, critical dynamics are observed near T/sub f/. The ..mu../sup +/SR technique is shown to be very sensitive to ferromagnetically aligned pairs of Cu/sup 2+/ moments; the population of such pairs increases greatly with x. .AE