Structure transition in cluster-cluster aggregation under external fields

The structure transition in cluster-cluster aggregation (CCA) under differe nt external electric herds has been investigated by computer simulations. T he aggregates are generated from off-lattice CCA models involving the field -induced dipolar interactions and temperatures by means of a Metropolis alg orithm When the parameter K increases from 0 to infinity, the clusters grad ually change from a diffusion-limited CCA to a chainlike pattern, where K s tands for the relative strength of the field-induced dipolar interaction wi th thermal energy. The relation of fractal dimension Df to parameter K can be approximately expressed as D-f = D-E +(D-DLCA - D-E)e-(beta K) with beta = 0.64, where DE and DDLCA Stand for the fractal dimensions of the CCA whe n K-->infinity and K-->0, respectively. This structure transition is a tran sition between a prototype disorder structure and a relative order one. The transition is attributed to the variation of the dominating interaction of systems from thermal disorder to field-induced dipolar interaction with K rising.