Highly ordered 3D nanoparticle superlattices investigated by microresonator ferromagnetic resonance

Magnetic nanoparticles and their assembly into highly correlated superstructures are of great interest for future applications, e.g. as material for magnon-spintronic. These systems are not only distinguished by the obvious miniaturization but by their novel physical properties emerging due to their limited size and ordered arrangement. These superstructures are formed from nanometer-sized building blocks ordered like atoms in a crystal, which render them a new class of materials.

Recently, single micrometer-sized three-dimensional magnetic nanoparticle assemblies (so-called mesocrystal) became available, exhibiting a high degree of structural order close to that of an atomic crystal. These systems provide a good basis for the magnetic investigation of nanoparticle superstructures.

Novel Microresonators, provide the necessary sensitivity for the investigation of static and dynamic magnetic properties of nano- and micrometer-sized objects using ferromagnetic resonance (FMR) [1,2]. Due to the much higher filling factor as compared to conventional microwave cavities, they offer several orders of magnitude increased sensitivity gain. A focused ion beam (FIB) was used to isolate an individual 3D mesocrystal from an ensemble [3] and to transfer it into the microresonator loop (see Fig. 1). The FMR study reveals the magnetic anisotropy of the single mesocrystal, which is corroborated by micromagnetic simulations. It was possible for us to functionalize the system and to switch between two anisotropy components.

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