Glassy relaxation without freezing in a random dipolar-coupled Ising magnet

We have measured the magnetic susceptibility, χ’+iχ’ ’, of the dilute dipolar-coupled Ising magnet ${\mathrm{LiHo}}_{0.045}$ ${\mathrm{Y}}_{0.955}$ ${\mathrm{F}}_4$ over six decades of frequency from 0.02 Hz to 20 kHz. The system behaves as an ideal relaxational glass with Arrhenius behavior in temperature of the peak in χ’ ’. Scaling data from T=100 mK to T=300 mK by the peak in χ’ ’ shows an enhanced low-frequency response at high temperatures, in contrast to expectations for spin-glasses and random-field magnets.