Morphology-Dependent Self-Assembly of Au−Fe3O4 Dumbbell Nanoparticles in Applied Magnetic Field: Implications for Magnetic Hyperthermia

The solution of magnetic dumbbell nanoparticles containing gold and iron oxide assembles into much more complicated patterns than the single-phase nanoparticles, when a magnetic field is applied. Controlled manipulations of these patterns in the solution are possible due to the improved functionality of the dumbbell nanoparticles as individual building blocks. The anisotropic shape of the dumbbell nanoparticles offers an additional parameter for controlling self-assembly, which is not present for their spherical counterparts. We found two geometric parameters of the dumbbell nanoparticles associated with their overall size and shape, which we varied by synthesizing four dumbbell nanoparticles of different dimensions. Using a combination of small-angle neutron and X-ray scattering techniques, we were able to demonstrate distinctly different self-assembled patterns for all four samples, ranging from 1D to 2D chains with head-to-tail and/or side-by-side configurations. The self-assembly studies were complemented by additional transmission electron microscopy, DC magnetization, and X-ray diffraction measurements to establish a relation between shape-induced anisotropy and competing magnetic dipolar interactions for dumbbell nanoparticles. The results of this work provide a guideline for design and optimization strategies for the use of dumbbell nanoparticles in magnetic hyperthermia applications.