We have studied the spin excitations of ferromagnetic rings and observed a distinct series of quantized modes in the vortex state. We attribute them to spin waves that circulate around the ring and interfere constructively. They form azimuthal eigenmodes of a magnetic ring resonator which we resolve up to the fourth order. The eigenfrequencies are calculated semianalytically and classified as a function of magnetic field by a quantization rule which takes into account a periodic boundary condition. Strikingly each mode exists only below a characteristic field.
We perform broadband spin-wave spectroscopy on thin submicrometer-wide Ni 80 Fe 20 magnetic wires. Intentionally, we apply the in-plane magnetic field under an angle that is a few degrees off with respect to the in-plane hard-axis direction. In an intermediate field regime we find dipole-exchange modes that, as substantiated by micromagnetic simulations, reflect spin waves in intrinsically formed nanometer-wide channels along the wire. Interestingly, this phenomenon is not ruled by the outer boundary conditions at the geometrical edges but by a deterministic zig-zag shaped magnetization configuration that varies on the nanometer scale in the inner part of the wire. In our case the individual channel width is only 65 nm, about a factor of five smaller than the geometrical width of 300 nm. Internal spin-wave guiding becomes possible, resembling the gradedindex approach for optical wave guiding in fibers. This opens new perspectives for spin-wave propagation in magnonic waveguides.
The spin dynamics in narrow ferromagnetic rings is studied in the frequency range from 45MHzto20GHz at room temperature. Our broadband spectrometer allows us to monitor the ferromagnetic resonance of characteristic spin configurations as a function of an external field μ0H. We observe hysteresis and irreversible jumps of the resonance frequencies which we attribute to onion-to-vortex and vortex-to-reversed-onion transitions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.