Additive Manufacturing and Exploration of Three-Dimensional Ferromagnetic Nanonetworks for 3D Magnonics and 3D Spintronics

The growing demand for high-speed, miniaturized, and energy-efficient information technologies has intensified interest in beyond-CMOS paradigms such as magnonics and spintronics. In particular, spin waves, which are collective excitations of magnetization, offer a charge-free medium for GHz-frequency signal transmission and processing. Three-dimensional (3D) magnetic architectures offer unique opportunities to explore new physical phenomena, enable novel functionalities, and enhance integration density in spin-based devices. However, the lack of a versatile and scalable 3D nanofabrication technique hindered the process. In this thesis, I present a comprehensive investigation into the fabrication, characterization, and functional integration of 3D ferromagnetic nanonetworks. We first demonstrate a scalable additive manufacturing approach by combining two-photon lithography (TPL) and atomic layer deposition (ALD) to realize unprecedented 3D Ni nanonetworks with periodic woodpile unit cells. These structures, extending up to 17µmin height, constitute 3D magnonic crystals with repeated units in all three spatial dimensions. Brillouin light scattering (BLS) microscopy reveals rich spin-wave spectra with distinct bulk and surface magnon modes extending up to 25 GHz. Micromagnetic simulations using MuMax3 uncover spatially quantized precession patterns. We also studied the angle- and spatially-dependent modes. We systematically investigate the size-dependent effects on magnon spectra, revealing that lattice periods below 1.5µm and unit cell units of at least 4 × 4 × 5 are required to sustain ultra-high frequency surface modes. Increasing the vertical repetition (z-direction) induces a transition from isotropic to anisotropic in-plane dispersion and leads to the emergence of robust edge modes that are resilient to structural perturbations. Furthermore, we achieve functional integration onto coplanar waveguides (CPW), allowing the direct excitation and BLS detection of edge modes. We observed asymmetric excitation efficiency around the ferromagnetic resonance and the suppression of BLS signal at specific frequencies suggests magnonic bandgap formation. To get the signal and response from the whole structure, individual 3D Ni woodpile structure is transferred into planar microwave resonators for angle-dependent ferromagnetic resonance (FMR) studies, and we performed the measurement. The angular dependencies measurements at 14.26 and 23.85GHz reveal a rich set of modes, in excellent agreement with COMSOL-based micromagnetic simulations. We identify the extended bulk and localized end-cap modes, with the latter showing narrow linewidths and remarkable robustness to field orientation. We then turn to the remanent-state magnetization textures, investigated using magnetic force microscopy (MFM) and BLS mapping. By engineering the unit cell number in z-direction, we can tailor the spin textures distribution, the spatial mode profiles, edge localization, and fre