Muon spin relaxation studies in frustrated and/or low-dimensional spin systems

An overview is given on muon spin relaxation (μSR) measurements in frustrated and/or low dimensional spin systems. In the frustrated Kagomé lattice system SrCr8Ga4O19, we observed dynamic spin fluctuations of ∼ 30 GHz, without any static frozen component even atT=0.1 K, much below the susceptibility-cusp temperatureTg=3.5 K. This is in clear contrast with the case in dilute-alloy spin glassesCuMn andAuFe, where static order develops belowTg. We also present the dimensionality dependence of the sub-lattice magnetization curves in 2-d Heisenberg systems, the remarkable suppression of the ordering temperature in a 1-d system Sr2CuO3, the observation of activation type spin dynamics in a 1-d Ising ferromagnet (DMeFc)(TCNE) aboveTc, slow spin fluctuations (∼ 60 MHz) in Haldane-gap systems at low temperatures, and some results from organic 1-d and 2-d magnetic systems.