Self-assembly of nanocubes directed by surface and magnetic interactions

We study the stabilization of clusters and lattices of cuboidal particles with long-ranged magnetic dipolar and short-ranged surface interactions. Two realistic systems were considered: one with magnetization along the crystallographic direction [001] and another with magnetization along the crystallographic direction [111]. To explain the structural genesis of low energy configurations, we first studied magnetic nanocube clusters at 0 K and then analyzed their behavior at a finite temperature. Our results demonstrate that dipolar coupling can stabilize nanoparticle assemblies with cubic, planar, and linear arrangements seen previously in experiments. While attractive surface energy supports super cube formation, repulsion results in elongated structures in the form of rods and chains. We observe the stabilization of the ferromagnetic planar arrangements of the cubes standing on their corners and in contact with the edges. We illustrate that minimal energy structures depend only on the size of the assembly and the balance of surface repulsion and magnetic dipolar coupling. The presented results are scalable to different particle sizes and material parameters.