Narrow autoresonant magnetization structures in finite-length ferromagnetic nanoparticles.

The autoresonant approach to excitation and control of large-amplitude uniformly precessing magnetization structures in finite-length easy axis ferromagnetic nanoparticles is suggested and analyzed within the Landau-Lifshitz-Gilbert model. These structures are excited by using a spatially uniform, oscillating, chirped frequency magnetic field, while the localization is imposed via boundary conditions. The excitation requires the amplitude of the driving oscillations to exceed a threshold. The dissipation effect on the threshold is also discussed. The autoresonant driving effectively compensates the effect of dissipation but lowers the maximum amplitude of the excited structures. Fully nonlinear localized autoresonant solutions are illustrated in simulations and described via an analog of a quasiparticle in an effective potential. The precession frequency of these solutions is continuously locked to that of the drive, while the spatial magnetization profile approaches the soliton limit when the length of the nanoparticle and the amplitude of the excited solution increase.