  Confining magnons in cavities can introduce new functionalities to magnonic
devices, enabling future magnonic structures to emulate established photonic
and electronic components. As a proof-of-concept, we report magnon confinement
in a lithographically defined all-on-chip YIG cavity created between two
YIG/Permalloy bilayers. We take advantage of the modified magnetic properties
of covered/uncovered YIG film to define on-chip distinct regions with
boundaries capable of confining magnons. We confirm this by measuring multiple
spin pumping voltage peaks in a 400 nm wide platinum strip placed along the
center of the cavity. These peaks coincide with multiple spin-wave resonance
modes calculated for a YIG slab with the corresponding geometry. The
fabrication of micrometer-sized YIG cavities following this technique
represents a new approach to control coherent magnons, while the spin pumping
voltage in a nanometer-sized Pt strip demonstrates to be a non-invasive local
detector of the magnon resonance intensity.
