Micromagnetic simulations of the magnetization precession induced by a spin-polarized current in a point-contact geometry (Invited)

Abstract

This paper is devoted to numerical simulations of the magnetization dynamics driven by a spinpolarized current in extended ferromagnetic multilayers when a point-contact setup is used. We present (i) detailed analysis of methodological problems arising by such simulations and (ii) physical results obtained on a system similar to that studied in Rippard et al., Phys. Rev. Lett., 92, 027201 (2004). We demonstrate that the usage of a standard Slonczewski formalism for the phenomenological treatment of a spin-induced torque leads to a qualitative disagreement between simulation results and experimental observations and discuss possible reasons for this discrepancy.

Spin-torque driven magnetization dynamics: Micromagnetic modeling

“…Already in [62] another non-linear localized mode was detected. In contrast to the solution found in [67], this additional mode had a kernel with a highly complicated magnetization structure consisting of two vortex-antivortex pairs (see Fig.…”

“…Before we start with the discussion of experiments and simulations obtained in the point contact geometry, we would like to point out that simulations of this geometry encounter several complicated methodological problems [61,62,48], which make this kind of simulations much more challenging than modelling of the nanopillar devices.…”

“…The spatial profile of this dissipation increase and the maximum dissipation value at the area border should be chosen carefully: if the profile is too steep, wave reflection can still occur due to too rapid a change of the medium properties. The rigorous theory how to choose such a profile is also not available (although numerical criteria whether the profile is chosen correctly, do exist [62,63]), so the corresponding operation is still more art than science.…”

“…However, this derivation has not been done yet and it is not clear whether it can be done at all. For this reason we have proposed a numerical trick basing on the introduction of a space-dependent dissipation [61,62]. Namely, dissipation constant at and near the point contact area is set to real physical dissipation value, so that oscillations of the point contact area and the emitted wave are not affected.…”

Numerical Simulations of Nano-Scale Magnetization Dynamics

“…The evolution of the individual particle is governed by the Landau-Lifshitz-Gilbert (LLG) equation -a semi-classical approximation allowing to represent the time evolution of the magnetization vector M depending on applied magnetic fields and spin-polarized currents passing through the particle. Micromagnetics is a rapidly-developing field allowing tackling many serious problems (Fidler & Schrefl, 2000;Berkov & Gorn, 2006). It is far simpler to implement in comparison with first principles calculations, so that modern computers can be efficiently used even for 3D micromagnetic simulations of large systems (Scholz et al, 2003;Vukadinovic & Boust, 2007).…”