Dynamic Exchange Coupling between Magnets Mediated by Attenuating Elastic Waves

Coupling between spatially separated magnets can be mediated by excitations such as photons and phonons, which can be characterized as coherent coupling and dissipative coupling with real and imaginary coupling rate. We theoretically predict the existence of dynamic exchange coupling in a closed magneto-elastic system mediated by attenuating elastic waves and whose coupling rate is complex in general, leading to alternating repulsive or attractive spectrum depending on thickness of the elastic media. The presence of dynamic exchange coupling and its competition with coherent coupling are numerically verified according to the generalized Hooke's law in magneto-elastic systems. The predicted mechanism provides a new strategy to synchronize precessing magnets as well as other excitations over long distance and pave the way for non-Hermitian engineering of collective modes in hybrid magnonics, phononics and photonics.Comment: 12 pages, 6 figures (including supplemental materials

Circulating cavity magnon polaritons

We predict magnon-polariton states circulating unidirectionally in a microwave cavity when loaded by a number of magnets on special lines. Realistic finite-element numerical simulations, including dielectric, time-dependent, and nonlinear effects, confirm the validity of the approximations of a fully analytical input-output model. We find that a phased antenna array can focus all power into a coherent microwave beam with controlled direction and an intensity that scales with the number of magnets.</p