Computer simulations were used to generate two-dimensional dendrites from atoms carrying a magnetic moment parallel to the external magnetic field. The numerical model was based upon the model of diffusion-limited aggregation at multiple centers. The magnetic dipole–dipole interaction between diffusing implanted atoms and growing ferromagnetic dendrites was taken into account. It was shown that magnetically induced anisotropy of grown dendrites led to their elongation in the external field direction. In detail, the growth process of the dendrites was analyzed by measuring mean relative elongation versus number of deposited particles within the grid. The application of the multicenter diffusion-limited aggregation model to the understanding of process of dendrite growth in external fields was the main approach. For much more accurate investigations of the growth process, the evolution of dendrite systems via mean elongation against degree of lattice population was studied. The mean elongation of dendrites was estimated numerically from the ratio of the averaged size of the dendrite along the external field direction, to that perpendicular to it. The two sizes were calculated with respect to the center of mass of a given dendrite. The dependence of the elongation upon grid occupation was studied. In general, the elongation reached a maximum and then decreased to a saturation level at about 25% occupation of the grid. At the beginning of a simulation, most dendrites grew independently of each other. The distances between dendrites were large and new implanted particles did not suffer any space restriction on diffusion. The anisotropy of dendrite growth was determined, at this stage, by an anisotropy of atom diffusion due to the magnetic interaction in the vicinity of the dendrite. When the number of particles added to the dendrite system increased, collective effects had to be considered. At this stage, in addition to anisotropic dipole–dipole interactions, the growth of the dendrite was influenced by restrictions on walker-motion due to surrounding dendrites. Because all of the dendrites were elongated in the same direction, the distance between neighbours along this direction decreased more rapidly than in the perpendicular one. As a result, a so-called shadow-effect occurred. The diffusion in-flow of walkers from the perpendicular axis direction was more intensive than that from the other axis, and the dendrite anisotropy decreases.

Diffusion-Limited Aggregation at Multiple Centers: Model of Dendrite Growth at Ion Beam Synthesis of Magnetic Films in External Field. N.A.Balakirev, G.G.Gumarov, V.A.Zhikharev, V.Y.Petukhov: Computational Materials Science, 2011, 50[10], 2925-9