Random Field Ising Model

This paper gives an introduction to the Random Field Ising Model (RFIM). Since its rst discussion in the paper by Imry and Ma 1] there has been great interest in this model, since Ising or Ising-like systems in random elds are a good representation of a large number of impure materials. These show features that can not be understood by studying ideal systems (i.e. Ising model). There are a lot of interesting topics related to the RFIM e.g. the stability of the ferromagnetic phase and lower critical dimension d l , interface properties, order of the phase transition, scaling laws, renormalisation group treatment and crossover phenomena. We will then more speciically discuss the 3d RFIM that is currently under strong investigation, in particular the problem of characterizing the phase transition. Since diluted antiferromagnets are a convenient probe for studying random elds in an experimentally controlable way (and have been shown to belong to the same static critical behaviour universality class) they will be discussed in some detail. Experimental data will be presented to compare with the theoretical predictions made.