We report the low-temperature dynamics of a diluted Ising antiferromagnet (${\mathrm{Fe}}_{0.46}$${\mathrm{Zn}}_{0.54}$${\mathrm{F}}_2$) over a wide range of magnetic fields. By measuring the magnetization through a number of cooling protocols, we deduce the density of antiferromagnetic domain walls, which can be compared with predictions of the random-field Ising model (RFIM). In both magnetization-relaxation and field-cycling experiments, we find a region of the (H,T) phase diagram in which the dynamic behavior is consistent with the RFIM, as well as a theoretically unexpected region of frozen dynamics.

• Received 28 May 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.2086