Motion-induced inertial effects and topological phase transitions in skyrmion transport.

When the skyrmion dynamics beyond the particle-like description is considered, this topological structure can deform due to a self-induced field. In this work, we perform Monte Carlo simulations to characterize the skyrmion deformation during its steady movement. In the low-velocity regime, the deformation in the skyrmion shape is quantified by an effective inertial mass, which is related to the dissipative force. When skyrmions move faster, the large self-induced deformation triggers topological transitions. These transitions are characterized by the proliferation of skyrmions and a different total topological charge, which is obtained as a function of the skyrmion velocity. Our findings provide an alternative way to describe the dynamics of a skyrmion that accounts for the deformations of its structure. Furthermore, such motion-induced topological phase transitions make it possible to control the number of ferromagnetic skyrmions through velocity effects.

Scattering modes of skyrmions in a bilayer system with ferromagnetic coupling.

Magnetic skyrmions are quasiparticle-like textures that are topologically different from a single domain magnetization state. Their topological protection, combined with the low current density needed to move them, make these objects relevant to be used as information storage structures. In such a context, the analysis of the interactions between skyrmions is interesting and relevant for future applications. In this work, through micromagnetic simulations and numerical calculations, we studied the interaction between two skyrmions living on different parallel ferromagnetic racetracks connected by an exchange-like interaction. The upper and lower racetracks are separated by a height offset and the interaction between the upper and the lower skyrmion is analyzed in terms of the magnetic and geometrical parameters. Three states are predicted, as a function of these parameters: scattered or free skyrmions, bound skymions, and annihilated skyrmions. Our results, presented in a phase diagram, demonstrate that even in the case here called free skyrmions, there is a small and brief interaction when both are close enough, but the skyrmion in the top layer does not drag the skyrmion in the bottom layer. For bound skyrmions, both keep linked during larger times. In the latter case, there are strong changes in the velocity of the skyrmions induced by the effect of a higher effective mass when both are coupled.

Ultrafast domain wall propagation due to the interfacial Dzyaloshinskii-Moriya interaction.

It is shown that the interplay between curvature and interfacial Dzyalonshinsky-Moriya interaction (DMI) is a pathway to ultrafast domain wall (DW) dynamics in ferromagnetic nanotubes. In this work, we theoretically study the effect that interfacial DMI has on the average velocity of a vortex DW in thin ferromagnetic nanotubes grown around a core composed of heavy atoms. Our main result shows that by delaying the Walker breakdown instability, the DW average velocity is of the order of 103 m s-1, which is greater than usual values for these systems. The remarkable velocities achieved through this configuration could greatly benefit the development of spintronic devices.

Domain wall manipulation in magnetic nanotubes induced by electric current pulses.

We propose that the injection of electric currents can be used to independently manipulate the position and chirality of vortex-like domain walls in metallic ferromagnetic nanotubes. We support this proposal upon theoretical and numerical assessment of the magnetization dynamics driven by such currents. We show that proper interplay between the tube geometry, magnitude of the electric current and the duration of a current pulse, can be used to manipulate the position, velocity and chirality of a vortex domain wall. Our calculations suggest that domain wall velocities greater than 1 km s(-1) can be achieved for tube diameters of the order of 30 nm and increasing with it. We also find that the transition from steady to precessional domain wall motion occurs for very high electric current densities, of the order of 10(13) A m(-2). Furthermore, the great stability displayed by such chiral magnetic configurations, and the reduced Ohmic loses provided by the current pulses, lead to highly reproducible and efficient domain wall reversal mechanisms.