Broadband spin dynamics of Permalloy rings in the circulation state

The spin dynamics of the remanent state of circulating magnetization in micrometer-scale Permalloy rings is studied by broadband ferromagnetic resonance. A number of resonance modes are observed, depending upon the geometries of coupling the transient excitation to the ring and of magneto-optically monitoring the response. The two dominant modes involve precession with uniform phase around the ring, or in a circularly antisymmetric standing wave pattern with two nodes. Other magnetic normal modes are also excited but with much smaller amplitude.