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

## TL;DR

Researchers created a 3D magnonic crystal using 3D printing and observed coherent spin waves, which could lead to faster data processing technologies.

## Contribution

A scalable method for fabricating 3D magnonic crystals and the observation of coherent spin waves in such structures.

## Key findings

- Coherent magnons with distinct angular dependencies were observed in a 3D woodpile structure.
- Edge modes are localized within curved nanocaps and remain robust against field orientation changes.
- An unexpected phase evolution was found along the edges of the 3D 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.

A nanoprinted 3D magnonic woodpile crystal is measured by microresonator ferromagnetic resonance. Micromagnetic simulations are performed to analyze and visualize the detected coherent spin‐wave modes along the nickel‐coated tubes and caps for various field angles. The woodpile exhibits an unexpected phase evolution and robust edge modes.