  We demonstrate a high-quality spin orbit torque nano-oscillator comprised of
spin wave modes confined by the magnetic field by the strongly inhomogeneous
dipole field of a nearby micromagnet. This approach enables variable spatial
confinement and systematic tuning of magnon spectrum and spectral separations
for studying the impact of multi-mode interactions on auto-oscillations. We
find these dipole field-localized spin wave modes exhibit good characteristic
properties as auto-oscillators--narrow linewidth and large amplitude--while
persisting up to room temperature. We find that the linewidth of the
lowest-lying localized mode is approximately proportional to temperature in
good agreement with theoretical analysis of the impact of thermal fluctuations.
This demonstration of a clean oscillator with tunable properties provides a
powerful tool for understanding the fundamental limitations and linewidth
contributions to improve future spin-Hall oscillators.
