Neutron-scattering observations of extreme critical slowing down in ad=3 random-field system

Extreme critical slowing down of the order-parameter fluctuations in a d=3 random-field Ising model system is observed in quasielastic-neutron-scattering studies of Fe0.46{Zn}0.54F₂. This is manifest in the logarithmic time dependence of I(q) in the 30--10⁴-sec time domain at, and near, Tc(H) in zero-field--cooled measurements. Contrary to a report by others, T_eq(H)>Tc(H) and no evidence for a first-order phase transition is found in this virtually gradient-free crystal.