ABSTRACT
This chapter provides an overview of muon spin relaxation functions with examples of experimental data and some remarks on historical developments. It begins with the static random local field, and examines the cases of well-defined unique local field(s), Gaussian and Lorentzian random fields, as well as a field distribution expected for incommensurate spin density wave and perturbed spin-gap systems. The chapter presents the relaxation functions in fluctuating dynamic random local fields, with examples of muon spin research (μSR) studies in MnSi and dilute-alloy spin glass systems. It considers the origin of powered exponential relaxation functions observed in spin glass and manganate systems. The μSR measurements provided the first direct evidence for the spatially inhomogeneous ordered moment size in a perturbed spin gap system. The chapter also considers a crossover from a localised moment magnet to an itinerant ferromagnet to a weak-itinerant ferromagnet (MnSi) to a non-magnetic metal.
