Speaker
Description
Three-dimensional (3D) magnonics is emerging as a promising direction for extending wave-based information processing beyond planar device concepts. 3D magnetic architectures open opportunities for tailoring high-frequency dynamics and guiding microwave signals in all three spatial directions on a chip. Yet, achieving coherent excitation and reliable readout in fully connected 3D nanomagnetic systems remains a central challenge.
Here I present recent progress based on a scalable nanofabrication route combining two-photon lithography and atomic layer deposition. Using this approach, we realized fully connected 3D ferromagnetic Ni woodpile nanonetworks and observed rich spin-wave spectra with distinct bulk and surface modes up to 25 GHz. To coherently access these modes, we developed two complementary device platforms. In a narrowband approach, entire 3D crystals were embedded in a planar microwave microresonator and studied by ferromagnetic resonance at discrete frequencies. In a broadband approach, the crystals were integrated onto a coplanar waveguide, while micro-focused Brillouin light scattering enabled spatially resolved detection on selected structural levels. Together, these approaches establish pathways for coherent spectroscopy of 3D magnonic crystals. I will also discuss the next step toward 3D magnon transport and reconfigurable functionality, where spin-wave transmission is expected to depend sensitively on magnetic states. Realizing such functionality requires fabrication approaches with enhanced geometrical control and material flexibility. In this context, I will outline ongoing work at TU Wien based on focused electron beam induced deposition of 3D ferromagnetic nanostructures, which offers high-resolution direct-write fabrication, smaller feature sizes, and access to Fe-based architectures. First fabricated structures and initial magnetic characterization pave the way toward future studies of state-dependent magnon transport in 3D magnetic conduits. This work was supported by the SNSF (No. 197360) and the European Community under the Horizon 2020 Program, Contract No. 101001290 (3DNANOMAG).