Manipulate the magnetic anisotropy of nanoparticle assemblies in arrays

Tuning the magnetic anisotropy of nanoparticle assemblies is critical for their applications such as on-chip magnetic electronic components and electromagnetic wave absorption. In this work, we developed a facile hierarchical self-assembly method to separately control the magnetic shape and magnetocrystalline anistropy of individual nanoparticle assemblies in arrays. Since magnetic nanoparticle assemblies in the array have the same size, shape and alignment, we are able to study the magnetic properties of individual nanoparticle assembly by measuring the whole arrays. The interplay between the two magnetic anisotropies was systematically studied for disk- and bar-shaped nanoparticle assemblies. Maximum magnetic anisotropy was obtained when the easy axis of magnetic nanoparticles was aligned along the long axes of the bar-shaped nanoparticles assemblies.