Three-dimensional aggregation dynamics of magnetic Janus colloids with radially shifted dipoles.

Magnetic Janus colloids whose permanent dipole moments are radially shifted from the particle center exhibit broken interaction symmetry that alters self-assembly in fully three-dimensional suspensions. Using Brownian dynamics simulations of dilute, field-free systems, we examine how the radial dipolar shift s and the dipolar coupling strength λ affect nucleation, growth kinetics, orientational ordering, and cluster morphology. Across the simulated parameter range, aggregation follows a two-stage nucleation-growth scenario: an initial delayed nucleation stage is followed by sustained growth, after which the weighted mean cluster size obeys a long-time power law, 〈N_{c}〉∼t^{z}, where the exponent z depends on both s and λ. For small shifts, head-to-tail alignment dominates, producing extended chainlike and looped aggregates. Increasing s frustrates collinear bonding, broadens the bonded-pair orientational distribution, and promotes closure, branching, and compactification. At the largest simulated shifts, the cluster-size distribution shifts toward small, compact aggregates with partially compensated dipole orientations, and the growth exponent decreases systematically, indicating hindered coarsening. Comparison with previously reported quasi-two-dimensional aggregation shows that s and λ remain the governing control parameters, while fully three-dimensional motion enables out-of-plane rearrangements, higher local coordination, and three-dimensional cluster-closure pathways. These results show that, within the simulated dilute and field-free regime, radial dipole displacement provides a geometric control parameter for tuning aggregation pathways and morphology selection in three-dimensional magnetic Janus suspensions.