Quantum magnonics leverages the quantum properties of magnons to advance nanoscale quantum information technologies. Ferrimagnetic yttrium iron garnet (YIG), known for exceptionally long magnon lifetimes, is a cornerstone material typically grown as thin films on gadolinium gallium garnet (GGG) for lattice matching. However, paramagnetic GGG introduces detrimental damping at low temperatures due to substrate magnetization, undermining quantum applications. Here, we study magnetic damping in a 150nm-thick YIG film on a yttrium scandium gallium aluminum garnet (YSGAG) substrate, a newly developed diamagnetic alternative to GGG. Using ferromagnetic resonance spectroscopy down to 30mK, we compare YIG/YSGAG with a conventional YIG/GGG reference system. We demonstrate that the YIG/YSGAG system maintains low damping from 300K to 30mK, with α=4.29×10−5 at room temperature, comparable to the best YIG/GGG films and bulk YIG, with no low-temperature upturn. The diamagnetic substrate eliminates the dissipation mechanisms that dominate on magnetized GGG, preserving low magnetic damping across the full temperature range. Consequently, YSGAG serves as an ideal substrate for YIG films in quantum magnonics and is paving the way for the development of spin-wave-based quantum technologies.
@article{arxiv.2508.19044,
title = {YSGAG: The Ideal Substrate for YIG in Quantum Magnonics},
author = {Rostyslav O. Serha and Carsten Dubs and Christo Guguschev and Bernd Aichner and David Schmoll and Julien Schäfer and Jaganandha Panda and Matthias Weiler and Philipp Pirro and Michal Urbánek and Andrii V. Chumak},
journal= {arXiv preprint arXiv:2508.19044},
year = {2026}
}