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We present overdamped micromagnetic simulations of the time evolution of magnetic droplet solitons which are formed in a thin film with perpendicular magnetic anisotropy by injecting a spin polarized current through a circular nanocontact. The overdamped dynamics help explore the effective energy landscape of these structures and permit identification of stationary states that are either energy extrema or saddle configurations. Our micromagnetic simulations start with configurations that are numerical solutions of a one-dimensional model where the magnetization depends only on the radial distance to the center of the nanocontact. We verify that these solutions correspond either to energy minima or saddle states, and use them to estimate thermal activation barriers for various current strengths. From the two-dimensional micromagnetic simulations, we identify a new persistent state which does not appear in the one-dimensional model. [ABSTRACT FROM AUTHOR]

We calculate the most probable reaction paths for thermally induced magnetization reversal of a nanomagnet under the influence of spin transfer torque. The presence of the spin transfer torque implies that the standard reaction rate theory of Kramers cannot be used since the dynamics no longer shows detailed balance and so the magnetization reversals are nonequilibrium transitions. Thin film nanomagnets with a biaxial anisotropy, a shape anisotropy that leads to in-plane magnetization with a preferred axis in the plane, are considered. The reaction pathways and rates are computed using geometrical Minimum Action Method. Our results indicate that the transition state has an out-of-plane magnetization component, in contrast to the case without an applied spin transfer torque. [ABSTRACT FROM AUTHOR]

We study the magnetization dynamics of thin-film magnetic elements with in-plane magnetization subject to a spin current flowing perpendicular to the film plane. We derive a reduced partial differential equation for the in-plane magnetization angle in a weakly damped regime. We then apply this model to study the experimentally relevant problem of switching of an elliptical element when the spin polarization has a component perpendicular to the film plane, restricting the reduced model to a macrospin approximation. The macrospin ordinary differential equation is treated analytically as a weakly damped Hamiltonian system, and an orbit-averaging method is used to understand transitions in solution behaviors in terms of a discrete dynamical system. The predictions of our reduced model are compared to those of the full Landau-Lifshitz-Gilbert-Slonczewski equation for a macrospin. [ABSTRACT FROM AUTHOR]