Magnetization oscillations induced by a spin-polarized current in a point-contact geometry: Mode hopping and nonlinear damping effects

In this paper, we study magnetization excitations induced in a thin extended film by a spin-polarized dc current injected through a point contact in the current-perpendicular-to-plane geometry. Using full-scale micromagnetic simulations, we demonstrate that in addition to the oscillations of the propagating wave type, there exist also two localized oscillation modes. The first localized mode has a relatively homogeneous magnetization structure of its core and corresponds to the so-called bullet predicted analytically by Slavin and Tiberkevich [Phys. Rev. Lett. 95, 237201 (2005)]. Magnetization pattern of the second localized mode core is highly inhomogeneous, leading to a much lower power of magnetoresistance oscillations caused by this mode. We have also studied the influence of a nonlinear damping for this system and have found the following main qualitative effects: (i) the appearance of frequency jumps within the existence region of the propagating wave mode and (ii) the narrowing of the current region where the bullet mode exists, until this mode completely disappears for a sufficiently strong nonlinear damping.