Coherent Spin Waves in Curved Ferromagnetic Nanocaps of a 3D‐Printed Magnonic Crystal

Abstract Coherent magnon modes in a truly 3D magnonic crystal have yet to be investigated. This scientific gap exists despite numerous theoretical predictions of miniband formation and edge modes with topological protection. Such properties are key to advancing nanomagnonics for ultrafast data processing. In this work, a scalable nanotechnology for fabricating 3D magnonic crystals embedded in an on‐chip microresonator is presented. It is realized by two‐photon lithography of a 3D woodpile structure and atomic layer deposition of 30‐nm‐thick nickel film. Operated near 14 and 24 GHz, the microresonator output revealed numerous coherent magnons with distinct angular dependencies reflecting the underlying face‐centered cubic lattice. Micromagnetic simulations show that the edge modes are localized within curved nanocaps and remain robust against changes in field orientation. Along an edge, they exhibit an unexpected phase evolution. These findings advance the development of functional microwave circuits with 3D magnonic crystals and strengthen their visionary prospects for edge‐dominated magnon modes.