Monocrystalline free standing 3D yttrium iron garnet magnon nano resonators

TL;DR

This paper reports the successful fabrication of free-standing 3D monocrystalline yttrium iron garnet nanoresonators with excellent magnetic properties, enabling advanced magnonic and nanomechanical applications.

Contribution

It introduces a novel fabrication process for free-standing 3D YIG nanoresonators with high-quality magnetic properties, advancing magnonics and nanostructure manufacturing.

Findings

Fabrication of free-standing monocrystalline YIG 3D nanoresonators.

Observation of low-damping spin wave excitations.

High-quality magnetic properties comparable to epitaxial films.

Abstract

Nano resonators in which mechanical vibrations and spin waves can be coupled are an intriguing concept that can be used in quantum information processing to transfer information between different states of excitation. Until now, the fabrication of free standing magnetic nanostructures which host long lived spin wave excitatons and may be suitable as mechanical resonators seemed elusive. We demonstrate the fabrication of free standing monocrystalline yttrium iron garnet (YIG) 3D nanoresonators with nearly ideal magnetic properties. The freestanding 3D structures are obtained using a complex lithography process including room temperature deposition and lift-off of amorphous YIG and subsequent crystallization by annealing. The crystallization nucleates from the substrate and propagates across the structure even around bends over distances of several micrometers to form e.g. monocrystalline resonators as shown by transmission electron microscopy. Spin wave excitations in individual nanostructures are imaged by time resolved scanning Kerr microscopy. The narrow linewidth of the magnetic excitations indicates a Gilbert damping constant of only $\alpha = 2.6 \times 10^{-4}$ rivalling the best values obtained for epitaxial YIG thin film material. The new fabrication process represents a leap forward in magnonics and magnon mechanics as it provides 3D YIG structures of unprecedented quality. At the same time it demonstrates a completely new route towards the fabrication of free standing crystalline nano structures which may be applicable also to other material systems.