Critical line for irreversibility in spin glasses

Abstract

An experimental study of irreversible phenomena in amorphous FeMn is reported. Irreversibility is characterized by the existence of both non-equilibrium susceptibility and magnetic viscosity. Both disappear above a critical line Tc(H) which is identified as the de Almeida-Thouless line for spin glasses. Tc(H) is, within experimental resolution, independent of time-scale in the range 30–700 s and has the form τ∝h^φ, where τ and h are the reduced temperature and the reduced field respectively, φ = 0·75 ± 0·15 and the field prefactor is ∼15. These results are discussed within the framework of recent mean-field models for spin glasses.