Dynamics of the diluted Ising antiferromagnet Fe0.31Zn0.69F2

The diluted Ising antiferromagnet, Fe_{0.31}Zn_{0.69}F_{2}, has been investigated by dynamic susceptibility measurements in zero and and finite applied dc-fields. In zero field, there is a para- to antiferromagnetic phase transition at $T_{N} \approx {20.0 K}$, followed by a dramatic slowing down of the dynamics at low temperatures. The latter described by a pure Arrhenius law. The effect of a superposed dc-field on the antiferromagnetic phase transition and on the low-temperature dynamics is investigated, and a comprehensive static and dynamic phase diagram in the H-T plane is derived. In agreement with earlier results on the same system, $T_{N}(H)$ follows a random-exchange Ising model to random-field Ising model crossover scaling for fields $H \leq 1.5 T$. A random-field induced glassy dynamics appears for higher values of H, where the antiferromagnetic phase transition is destroyed. The low-temperature dynamics shows striking similarities with the behavior observed in reentrant antiferromagnets.