Spin-transfer torque can nucleate static and dynamic solitons [1-2]. Static solitons can be achieved in out-of-plane devices (bubbles, skyrmions, domain walls) and they can behave like quasi-particles, vortices and skyrmions[3]. In literature, a few works have been devoted to the identification of topological limit cycles [4]. We show that the mode transition from non-topological (NTD) to topological droplet (TD) or dynamical skyrmion is achieved through an intermediate region of the Dzyaloshinskii–Moriya Interaction (DMI). The terms “non-topological” and “topological” are used to identify a limit cycle with a skyrmion number 0 and 1, respectively. The time-domain traces of the mode transition exhibit non-stationary jumps from NTD to TD and viceversa. We call this new mode “instanton droplet”, characterized by continuous topological transitions. We studied a spin-valve composed of Pt(5)/Co(0.6)/Cu(4)/CoPt(4) (nm) with square cross section and circular contact to inject the current. Fig. 1(a) shows the topological density for NTD, TD, and NTD-TD states. The NTD mode is excited for D≤0.5 mJ/m2, its dynamics concerns a 360o in-plane rotation of domain wall spins and the topological density exhibits a complex behavior. The TD is excited for 1.6<D≤3.0 mJ/m2 and exhibits a core breathing dynamics synchronized with a 360o in-phase rotation and constant skyrmion number S=-1. For 0.5<D≤1.6 mJ/m2, time domain changes in the limit cycle topology are observed and configuration linkable to NTD or TD can be recognized. A continual change in the droplet topology generates incoherent emission of spin waves, being the topological transition non-stationary. References: [1] S. M. Mohseni et al., Science 339, 1295 (2013). [2] G. Finocchio et al., J. Appl. Phys. 114, 163908 (2013); V. Puliafito et al., J. Appl. Phys. 115, 17D139 (2014). [3] S. Petit-Watelot et al., Nat. Phys. 8, 682–687 (2012); S. Zhang et al., New J. of Physics 17

Instanton droplet driven by spin-transfer torque in perpendicular materials with Dzyaloshinskii–Moriya Interaction. - Presentazione orale - Conferenza internazionale

ZIVIERI, Roberto;
2016

Abstract

Spin-transfer torque can nucleate static and dynamic solitons [1-2]. Static solitons can be achieved in out-of-plane devices (bubbles, skyrmions, domain walls) and they can behave like quasi-particles, vortices and skyrmions[3]. In literature, a few works have been devoted to the identification of topological limit cycles [4]. We show that the mode transition from non-topological (NTD) to topological droplet (TD) or dynamical skyrmion is achieved through an intermediate region of the Dzyaloshinskii–Moriya Interaction (DMI). The terms “non-topological” and “topological” are used to identify a limit cycle with a skyrmion number 0 and 1, respectively. The time-domain traces of the mode transition exhibit non-stationary jumps from NTD to TD and viceversa. We call this new mode “instanton droplet”, characterized by continuous topological transitions. We studied a spin-valve composed of Pt(5)/Co(0.6)/Cu(4)/CoPt(4) (nm) with square cross section and circular contact to inject the current. Fig. 1(a) shows the topological density for NTD, TD, and NTD-TD states. The NTD mode is excited for D≤0.5 mJ/m2, its dynamics concerns a 360o in-plane rotation of domain wall spins and the topological density exhibits a complex behavior. The TD is excited for 1.6
2016
Instanton, topological droplet, non-topological droplet
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2340918
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