Topological and non-topological magnetic solitons can exist either as static (vortices, bubbles, skyrmions, etc.) or dynamical (droplets, vortex-antivortex pair, etc.) states (limit cycles) in both conservative and dissipative magnetic systems. In this work it is shown the effect of the interfacial Dzyaloshinskii–Moriya Interaction (i-DMI) on the topology of droplets excited by a localized perpendicular spin-polarized current. According to micromagnetic simulations it is shown that the phase diagram i-DMI as a function of the polarized current at zero magnetic field exhibits a complex scenario with regions characterized by static and dynamic states. In the dynamical part, it is possible to identify topological stable and unstable regions. The topological stable regions are linked to the excitation of droplets with skyrmion number either equal to one (topological) or zero (non-topological). The zero skyrmion number droplets are characterized by the non-stationary time domain excitation of both topological and non-topological droplets modes. The transition between these two modes is coupled to an emission of incoherent spin-waves. It is also developed an analytical model demonstrating that the topological droplet can be seen as a linear radial mode of a static skyrmion state stabilized by a perpendicular spin-polarized current. The analytical frequency of the topological droplet mode is expressed as the solution of an algebraic equation written in terms of the magnetic parameters. The results obtained by means of the analytical model confirm the red-shift behaviour of the topological mode frequencies as a function of the current density predicted by micromagnetic simulations. The interplay between topology and dynamics is discussed by introducing the notion of topological degeneracy according to which two topological droplet textures (hedgehog-like and vortex-like, respectively) having different ground-state energies are characterized by the same topological charge. The analysis of the symmetry properties of the linearized equations of motion demonstrates the non-reciprocal role of the spin polarized current on the topological mode dynamics. This work was supported by the project PRIN2010ECA8P3 from Italian MIUR. [1] T. Moriya, Phys. Rev. Lett. 4, 228 (1960). [2] R. Zivieri et al., “Topological skyrmion dynamics driven by spin-transfer torque”, submitted to Phys. Rev. X.
Topological skyrmion dynamics in perpendicular magnetic materials excited by a spin-polarized current - Presentazione orale by R. Zivieri
ZIVIERI, Roberto;
2015
Abstract
Topological and non-topological magnetic solitons can exist either as static (vortices, bubbles, skyrmions, etc.) or dynamical (droplets, vortex-antivortex pair, etc.) states (limit cycles) in both conservative and dissipative magnetic systems. In this work it is shown the effect of the interfacial Dzyaloshinskii–Moriya Interaction (i-DMI) on the topology of droplets excited by a localized perpendicular spin-polarized current. According to micromagnetic simulations it is shown that the phase diagram i-DMI as a function of the polarized current at zero magnetic field exhibits a complex scenario with regions characterized by static and dynamic states. In the dynamical part, it is possible to identify topological stable and unstable regions. The topological stable regions are linked to the excitation of droplets with skyrmion number either equal to one (topological) or zero (non-topological). The zero skyrmion number droplets are characterized by the non-stationary time domain excitation of both topological and non-topological droplets modes. The transition between these two modes is coupled to an emission of incoherent spin-waves. It is also developed an analytical model demonstrating that the topological droplet can be seen as a linear radial mode of a static skyrmion state stabilized by a perpendicular spin-polarized current. The analytical frequency of the topological droplet mode is expressed as the solution of an algebraic equation written in terms of the magnetic parameters. The results obtained by means of the analytical model confirm the red-shift behaviour of the topological mode frequencies as a function of the current density predicted by micromagnetic simulations. The interplay between topology and dynamics is discussed by introducing the notion of topological degeneracy according to which two topological droplet textures (hedgehog-like and vortex-like, respectively) having different ground-state energies are characterized by the same topological charge. The analysis of the symmetry properties of the linearized equations of motion demonstrates the non-reciprocal role of the spin polarized current on the topological mode dynamics. This work was supported by the project PRIN2010ECA8P3 from Italian MIUR. [1] T. Moriya, Phys. Rev. Lett. 4, 228 (1960). [2] R. Zivieri et al., “Topological skyrmion dynamics driven by spin-transfer torque”, submitted to Phys. Rev. X.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
