Novel diamagnetic garnet-type substrate single crystals for ultralow-damping yttrium iron garnet Y3Fe5O12 films at cryogenic temperatures

TL;DR

This paper reports the growth of high-quality diamagnetic garnet-type substrates suitable for epitaxial YIG films, demonstrating their advantages at cryogenic temperatures for low-damping microwave applications in quantum systems.

Contribution

It introduces novel diamagnetic garnet-type single crystals as substrates for ultralow-damping YIG films, showing improved low-temperature magnetic properties over conventional substrates.

Findings

High structural quality of grown crystals (FWHM ~22 arcsec)

Successful epitaxial growth of YIG films on these substrates

YIG/YSGAG system exhibits superior low-temperature FMR linewidth stability

Abstract

Y3Sc2Ga3O12-Y3Sc2Al3O12 and Y3Sc2Ga3O12-Y3Al5O12 (YSGAG) solid solution single crystals with diameters up to 30 mm and total lengths up to about 100 mm were grown by the conventional Czochralski technique. Rocking curve measurements on polished sections revealed typical FWHM values of about 22 arcsec, which is indicative of relatively high structural quality for a solid-solution crystal. The grown substrate crystals are nearly lattice-matched with Y3Fe5O12 (YIG) to allow epitaxial growth of high-quality thin films. Single crystalline YIG films with thicknesses between 100 nanometer and 2.9 micrometer were successfully grown on epi-polished YSGAG substrates using liquid phase epitaxy (LPE). Selected magnetic and microwave properties of the epitaxial films, which still exhibit small lattice misfits to the substrates, were then studied at room temperature. In addition, initial low-temperature investigations confirm that the YIG/YSGAG system is superior to the conventional YIG/GGG (Gd3Ga5O12) system at temperatures below 10 K, as the ferromagnetic resonance (FMR) linewidth does not increase with decreasing temperature. Therefore, the novel diamagnetic substrates are better suited for microwave applications at low temperature, as excessive damping losses induced by paramagnetic substrates can be avoided. It therefore seems to be a suitable pathway to achieve scalable microwave components for hybrid-integrated quantum systems based on ultralow-damping YIG films that can operate efficiently at millikelvin temperatures.