A zero-field μμSR study of glassy spin dynamics in γγ-MnCu

We have performed zero-field muon spin relaxation (μSR) measurements of a number of γ-MnxCu1-x alloys around the critical concentration (x=0.72) in order to investigate the dynamical properties of the system as it moves from short-range to long-range magnetic order. Above the critical concentration the muon spin relaxation is exponential in form, whilst for Mn concentrations the relaxation is stretched-exponential, with the “stretch” exponent β decreasing from unity at high temperatures (i.e. a simple monopolar Lorentzian relaxation regime) to around at the transition temperature—indicated by a divergence in the muon relaxation rate, λ. This behaviour is indicative of a concentrated spin-glass ground state. For a Mn concentration of we find a re-entrant transition, from a cluster-glass phase at to an AF phase at .