doi:10.1002/adfm.202503644engLegrand, WilliamKemna, YanaSchären, StefanWang, HanchenPetrosyan, DavitHolder, LuiseSchlitz, RichardAguirre, Myriam H.Lammel, MichaelaGambardella, PietroLattice-Tunable Substituted Iron Garnets for Low-Temperature MagnonicsART-2025-144467The 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, Y3(YxFe5−x)O12 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 Y3(YxFe5−x)O12 films lattice-matched to Y3Sc2Ga3O12 (YSGG), a diamagnetic substrate. The Y3(YxFe5−x)O12 system can be matched to other substrates such as (Gd, Y)3Sc2Ga3O12. Bi-substituted films of (Bi0.8Y2.2)Fe5O12 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.2025http://zaguan.unizar.es/record/16177810.1002/adfm.202503644http://zaguan.unizar.es/record/161778oai:zaguan.unizar.es:161778info:eu-repo/grantAgreement/EC/H2020/101007825/EU/ULtra ThIn MAgneto Thermal sEnsor-Ing/ULTIMATE-IThis project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No H2020 101007825-ULTIMATE-Iinfo:eu-repo/grantAgreement/EC/H2020/872631 /EU/Memristive and multiferroic materials for emergent logic units in nanoelectronics/MELONThis project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No H2020 872631 -MELONAdvanced Functional Materials (2025), 2503644 [16 pp.]All rights reservedhttp://www.europeana.eu/rights/rr-f/info:eu-repo/semantics/closedAccess