Lattice-tunable substituted iron garnets for low-temperature magnonics

Abstract

The synthesis of nm-thick epitaxial films of iron garnets by physical vapor deposition has opened up exciting opportunities for the on-chip generation and processing of microwave signals encoded in magnons. However, iron garnet thin films suffer from demanding lattice-matching and stoichiometry requirements. Here a new approach to their synthesis is developed, enabling a precise and continuous tuning of iron garnet compositions based on the co-sputtering of binary oxides. By substituting a controlled proportion of iron with additional yttrium, Y${}_3$(Y${}_x$Fe${}_{5-x}$)O${}_{12}$ films of high crystalline quality are obtained, combining a widely tunable lattice parameter and excellent magnetization dynamics. This enables iron garnet thin films suited for cryogenic applications, which have long remained impractical due to microwave losses caused by paramagnetic garnet substrates. Low-temperature ferromagnetic resonance confirms the elimination of substrate paramagnetic losses for Y${}_3$(Y${}_x$Fe${}_{5-x}$)O${}_{12}$ films lattice-matched to Y${}_3$Sc${}_2$Ga${}_3$O${}_{12}$ (YSGG), a diamagnetic substrate. The Y${}_3$(Y${}_x$Fe${}_{5-x}$)O${}_{12}$ system can be matched to other substrates such as (Gd,Y)${}_3$Sc${}_2$Ga${}_3$O${}_{12}$. Bi-substituted films of (Bi${}_{0.8}$Y${}_{2.2}$)Fe${}_5$O${}_{12}$ also have ideal lattice matching to YSGG, demonstrating the versatility of this approach. This opens unprecedented options for cation substitutions in iron garnet films, offering a promising avenue to new properties and quantum magnonic devices operating in low-temperature environments.

Main: 20 pages, 6 figures; Supplement: 24 pages, 18 figures. This is the pre-peer-reviewed version of the work submitted to Adv. Funct. Mater., where it is now published in its final form. All of the data needed to evaluate the conclusions in this work are available in main/supplementary, and have been deposited to the ETH Zurich Research Collection database under DOI 10.3929/ethz-b-000739804

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• Ultrathin bismuth-yttrium iron garnet films with tunable magnetic anisotropy
• YSGAG: The Ideal Substrate for YIG in Quantum Magnonics
• Cryogenic Magnetization Dynamics in Chemically Stabilized, Tensile-Strained Ultrathin Yttrium Iron Garnets with Tunable Magnetic Anisotropy
• Coherent Microwave Driving of Domain Wall Depinning in a Ferrimagnetic Garnet
• Disambiguating electrical detection of magnetization dynamics in magnetic insulators
• Loop-gap resonators achieving strong magnon-photon coupling in magnetic insulator thin films