Disorder, Random Fields and Competing Interactions in Antiferromagnets

Abstract

Neutron scattering studies of disordered antiferromagnets have proved to be a very profitable way of studying random systems. Several recent examples are selected and include a detailed study of the phase transition of a d = 3 Ising system showing a well defined transition with properties different from these of a pure d = 3 Ising system. Much of the article is then concerned with the effect of a random field on the ordering and phase transitions. It is shown that random fields do have a large effect on the critical properties and in practice destroy the long range order in the good Ising systems with d = 2 and d = 3, although not in a nearly Heisenberg-like system. These results are compared with current theories and the discrepancies discussed. Finally measurements on a system with competing interactions are discussed and shown to be strongly influenced by the random fields produced in that system.