Multiple ferromagnetic resonance in mesoscopic permalloy rings

Using a broadband microwave spectrometer we have investigated the magnetization dynamics of mesoscopic ferromagnetic disks and rings in the frequency range from 45 MHz to 20 GHz. We studied permalloy rings with an outer diameter of 2 mu m and different ring widths w. In the mesoscopic devices we find several ferromagnetic resonance (FMR) lines which shift with the in-plane magnetic field H-b. Among them, two pronounced FMR modes are identified. We attribute these modes to localized spin waves in different ring segments where the characteristic resonance frequency either decreases or increases as a function of w, depending on the orientation of the ring segment with respect to H-b. (c) 2005 American Institute of Physics.