Phase transitions and metastable states in the presence of random fields

The application of a uniform magnetic field to a diluted Ising antiferromagnet produces a random staggered field and so can be used to study the random field Ising model. In this paper we describe neutron scattering measurements on MnxZn1−xF2. They show that at low temperatures there are many metastable states which are all stable for experimentally accessible times. There is a sharp boundary in the H/T plane which separates metastability from ergodicity. The critical phenomena close to this metastability boundary is discussed.