Features of the interaction of a magnon Bose–Einstein condensate with acoustic modes in yttrium iron garnet films

The interaction of a magnon Bose–Einstein condensate (mBEC) in a perpendicularly magnetized yttrium iron garnet film with high-order acoustic modes appearing at the sizes of an yttrium iron garnet substrate has been studied experimentally. Narrow energy absorption lines of the mBEC have been observed at the coincidence of frequencies. The minimum relaxation of the mBEC has been detected under acoustic antiresonance conditions when the precession frequency is exactly in the middle between acoustic resonance modes. This discovery will allow the optimization of coherence times when fabricating quantum magnonic devices.