The investigation and improved understanding of the dynamic processes in magnetic nanoparticles become more and more important as magnetic nanoparticles are promising candidates for high-speed, high-density magnetic storage (e.g. hard disks and MRAMs - magnetic random access memory devices) and sensor devices [124,125].
Recent advances in nanometer scale fabrication technology allow detailed experimental investigations on a nanometer length scale [104,105]. In high-speed storage devices magnetization reversal occurs by applying short field pulses [126]. The characteristic switching time depends on the reversal mode and is usually in the nanosecond regime. The magnetization reversal excites many spin-excitation modes (spin waves), whose understanding is important to determine the field dependent spin instability regions, where spontaneous or thermally-assisted magnetization reversal might occur [127].
The magnetization dynamics under short field pulses have been investigated in saturated NiFe disks [128] and in closure domains in Co disks [129]. However, the magnetization dynamics of the magnetic vortex state in thin Permalloy disks is markedly different from those in the uniformly magnetized state and also from the spin-waves observed in thin magnetic films.