A zero-field SR study of glassy spin dynamics in -MnCu

Abstract We have performed zero-field muon spin relaxation ( μ SR) measurements of a number of γ - Mn x Cu 1 - 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 ⩽ 71 at % 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 1 3 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 73 at % we find a re-entrant transition, from a cluster-glass phase at T g ≈ 260 K to an AF phase at T N ≈ 140 K .