Neutron-scattering observations of extreme critical slowing down in a d=3 random-field system.

Abstract

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 ${\mathrm{Fe}}_{0.46}$${\mathrm{Zn}}_{0.54}$${\mathrm{F}}_{2}$. This is manifest in the logarithmic time dependence of I(q) in the 30--${10}^{4}$-sec time domain at, and near, ${\mathrm{T}}_{\mathrm{c}}$(H) in zero-field--cooled measurements. Contrary to a report by others, ${\mathrm{T}}_{\mathrm{eq}(\mathrm{H})>{\mathrm{T}}_{\mathrm{c}}(\mathrm{H}}$) and no evidence for a first-order phase transition is found in this virtually gradient-free crystal.