Heterogeneous dynamics and ageing in a dense ferro-glass.

ABSTRACT

Repulsive magnetic fluids show a dynamical freezing above a volume fraction Φ(*), which depends on the physico-chemistry of the system. Φ(*) is here determined by a magneto-optical technique. The out-of-equilibrium dynamics of a glass-forming magnetic fluid (Φ = 1.2Φ(*)) is studied by x-ray photon correlation spectroscopy and analyzed in terms of intensity auto-correlation functions. The relaxation is age dependent and follows a compressed exponential law with a characteristic time scaling as the inverse of the scattering vector Q. The dynamical susceptibility χ is then deduced from a time resolved correlation analysis at an intermediate Q and for ages larger than 10(4) s.