Magnetization orientation controls equilibrium structures and aggregation kinetics of charged cubic hematite particles in a quasi-two-dimensional system: Monte Carlo and Brownian dynamics simulations

Magnetic particle dispersions exhibit field-responsive aggregation and structural transitions that depend sensitively on the particle shape, magnetic configuration, and near-surface confinement, with cubic particles showing diverse contact modes. In this study, the influence of the magnetization angle of a rigidly fixed magnetic moment at the centre of charged cubic hematite particles on equilibrium structures and aggregation kinetics in a quasi-two-dimensional system is examined. Three representative orientations, namely face-normal, edge, and body-diagonal, are considered, and the magnetization direction is varied continuously to quantify the angular sensitivity. Monte Carlo simulations characterise equilibrium aggregates, while Brownian dynamics simulations track aggregation from dispersed states. Particle centres are confined to a plane, whereas rotations remain three-dimensional. Equilibrium structures depend strongly on the magnetization orientation, with face-normal alignment favouring chain-like aggregates and edge and body-diagonal orientations producing compact clusters with frequent face-to-face contact. Aggregation kinetics are controlled by the stability of small cluster units, as stable early-stage units accelerate aggregation while unstable units slow growth. A pronounced shift in the dominant aggregation mode occurs within a narrow angular range near the body-diagonal direction, between 15° and 20°, suggesting that small angular deviations can markedly alter both aggregate structures and formation pathways. Under an applied electric field, particles accumulate near the positively charged wall for all orientations, with model-dependent differences in the near-wall microstructure evident at low field strengths and reduced at higher field strengths. These findings provide a concise reference map of aggregation behaviour as a function of magnetization angle. • Charged cubic hematite particles are studied in quasi-2D via MC and BD simulations. • MC simulations show that magnetisation angle produces diverse aggregate structures. • BD simulations show that magnetisation angle controls aggregation kinetics. • A small tilt near the body-diagonal direction switches the aggregation mode. • Under an electric field, near-wall layering depends on the magnetisation model.