OBSERVATION OF CONTINUOUS AND DISCONTINUOUS ORDERING IN A RANDOM-FIELD ISING-MODEL SYSTEM

The effects of random fields on the Ising model structural phase trans ition in Tb(AsxV1-x)O-4 have been examined by optical diffraction and birefringence. The mixed compounds show discontinuous ordering feature s on cooling which are attributed to the formation of a domain state f ollowed by a transition to long-range order. On warming, the transitio n is nearly continuous, with an apparent order-parameter critical expo nent unchanged from pure TbVO4. (C) 1998 Elsevier Science B.V. All rig hts reserved.