We have studied the properties of clusters of colloidal magnetic particles generated from a 2D aggregation model with dipolar interparticle interactions. Particles diffuse off-lattice, experiencing dipolar 1 with the already attached particles until either they stick to the cluster or wander far away and are removed. Our results are interpreted in terms of a fractal dimension that is a monotonically decreasing function of the temperature, varying between a definite value close to 1 at T=0, and the limit T → ∞, corresponding to free diffusion-limited aggregation. By analyzing orientational correlation functions, an ordered state is found at low temperatures; this state is destroyed by the fractal disorder generated at high T. Our study could be relevant in understanding aggregation of dipolar colloids and phase transitions in Langmuir monolayers.
Magnetic particles ferrofluids cluster aggregation dipolar interactions
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