AGGREGATION AND INTERMEDIATE PHASES IN DILUTE SPIN SYSTEMS

We study a variety of dilute annealed lattice spin systems. For site d iluted problems with many internal spin states, we uncover a new phase characterized by the occupation and vacancy of staggered sublattices. In cases where the uniform system has a low temperature phase, the st aggered states represent an intermediate phase. Furthermore, in many o f these cases, we show that (at least part of) the phase boundary sepa rating the low-temperature and staggered phases is a line of phase coe xistence - i.e. the transition is first order. We also study the pheno menon of aggregation (phase separation) in bond diluted models. Such t ransitions are known, trivially, to occur in the large-q Potts models. However, it turns out that phase separation is typical in bond dilute d spin systems with many internal states. (In particular, a bond aggre gation transition is not tied to a discontinuous transition in the uni form system.) Along the portions of the phase boundary where any of th ese phenomena occur, the prospects for a Fisher renormalization effect are deemed to be highly unlikely or are ruled out altogether.