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

Yttrium scandium gallium aluminum garnet (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. It is shown that the pseudo-binary Y 3 Sc 2 Ga 3 O 12 -Y 3 Sc 2 Al 3 O 12 and Y 3 Sc 2 Ga 3 O 12 -Y 3 Al 5 O 12 systems are suitable for obtaining YSGAG crystals with tailored lattice parameters in the range from 12.3621 to 12.4262 Å, which are close to the lattice parameters of the most well-known representatives of the iron garnet microwave ferrite family, such as Y 3 Fe 5 O 12 (YIG). Rocking curve measurements on the completely diamagnetic YSGAG substrate crystals revealed typical FWHM values of about 22 arcsec, which is indicative of relatively high structural quality for a solid-solution crystal. Single crystalline YIG films with thicknesses between 100 nm and 2.9 μm were successfully grown on nearly lattice matched, epi-polished YSGAG substrates using liquid phase epitaxy (LPE). Magnetic and microwave measurements at room temperature reveal that the films exhibit low saturation fields, very low remanence, and narrow FMR linewidths. Furthermore, initial studies confirm that even the very first films on non-optimized diamagnetic YSGAG substrates at temperatures below 10 K outperform conventional YIG films on paramagnetic Gd 3 Ga 5 O 12 (GGG) substrates, since the linewidth of the ferromagnetic resonance (FMR) at cryogenic temperatures is not affected by interactions with the substrate material. 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. This opens the way for the development of miniaturized microwave components for application in quantum magnonics, such as hybrid-integrated quantum systems based on ultralow-damping YIG films that can operate efficiently at temperatures in the millikelvin range.