Dynamic susceptibility of concentric permalloy rings with opposite chirality vortices.

The high frequency dynamic behaviour of concentric permalloy nanorings with vortex domain structures with a thickness of 20 nm, a width in the range of 100 nm-250 nm, and a separation in the range of 10 nm-600 nm is investigated by micromagnetic simulations. The aim is to explore the ferromagnetic resonance of the concentric ring structure as a function of geometric parameters of the system. The dynamic susceptibility spectrum and spatial localization of the ferromagnetic resonance mode are investigated for varying ring widths and separations. The frequency of oscillation is significantly impacted by the presence of the magnetostatic interaction between each ring and can be modulated by a variation in the ring width and separation. The spatial localization of the uniform mode is found to vary as a function of ring separation, which corresponds to a large variation in amplitude of the real and imaginary components of the dynamic susceptibility.