Hierarchical structures of magnetic nanoparticles for controlling magnetic interactions on three different length scales

By combining top-down lithographic techniques with the meniscus-force deposition method, hierarchical structures consisting of defined regular elements on length scales from a few tens of nanometers to millimeters can be assembled out of magnetic nanoparticles. Varying the size and shape of the regular elements and distance between them offers the possibility to study magnetic coupling phenomena on three different length scales. As an example, we study hierarchical arrangements of magnetite nanoparticles (Fe₃O₄) with a diameter of d = 20 nm by ferromagnetic resonance measurements and demonstrate that the macroscopic properties of the structures are dominated by the assemblies of densely packed nanoparticles on the sub μm scale rather than by the interactions between these assemblies which are arranged on a grid with μm spacings or than by the macroscopic outer shape of the grid on the mm scale.