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

We have measured the magnetic susceptibility, {χ}'+i{χ}'', of the dilute dipolar-coupled Ising magnet LiHo0.045{Y}0.955F₄ 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.