  Yttrium iron garnet (YIG) magnonics has sparked extensive research interests
toward harnessing magnons (quasiparticles of collective spin excitation) for
signal processing. In particular, YIG magnonics-based hybrid systems exhibit
great potentials for quantum information science because of their wide
frequency tunability and excellent compatibility with other platforms. However,
the broad application and scalability of thin-film YIG devices in the quantum
regime has been severely limited due to the substantial microwave loss in the
host substrate for YIG, gadolinium gallium garnet (GGG), at cryogenic
temperatures. In this study, we demonstrate that substrate-free YIG thin films
can be obtained by introducing the controlled spalling and layer transfer
technology to YIG/GGG samples. Our approach is validated by measuring a hybrid
device consisting of a superconducting resonator and a spalled YIG film, which
gives a strong coupling feature indicating the good coherence of our system.
This advancement paves the way for enhanced on-chip integration and the
scalability of YIG-based quantum devices.
