Dynamics of the spin-glass freezing inCd0.6Mn0.4Te

We report on dynamic magnetic properties at low temperatures (4.2<T<30 K) of the disordered Heisenberg frustrated antiferromagnet ${\mathrm{Cd}}_{0.6}$ ${\mathrm{Mn}}_{0.4}$Te over an extended range of frequencies or of corresponding observation times ${(10\mathrm{}}^{\mathrm{-}6}$<$t_{\mathrm{obs}<3\mathrm{}\times {10}^3}$ s). At high frequencies, the real (${\chi }_{\nu }^{\mathcal{’}}$) and imaginary (${\chi }_{\nu }^{\mathcal{’}\mathcal{’}}$) parts of the susceptibility are determined from accurate Faraday-rotation experiments while the dynamics for longer characteristic times are investigated in a weak field, through superconducting quantum-interference device (SQUID) measurements of the magnetization. Starting from two different dynamic criteria, (i) the significant change of the relaxation of the in-field magnetization to step variations of the temperature and (ii) the appearance of long-time thermoremanent magnetization relaxation, we deduce a value $T_{f0}$=12.9±0.1 K for the freezing temperature.