Magnetic skyrmions are particle-like magnetization configurations which can be found in materials with broken inversion symmetry. Their topological nature allows them to circumvent around random pinning sites or impurities as they move within the magnetic layer, which makes them interesting as information carriers in memory devices. However, when the skyrmion is driven by a current, a Magnus force is generated which leads to the skyrmion moving away from the direction of the conduction electron flow. The deflection poses a serious problem to the realization of skyrmion-based devices, as it leads to skyrmion annihilation at the film edges. Here, we show that it is possible to guide the movement of the skyrmion and prevent it from annihilating by surrounding and compressing the skyrmion with strong local potential barriers. The compressed skyrmion receives higher contribution from the spin transfer torque, which results in the significant increase of the skyrmion speed.

Current-driven skyrmions drift from the intended direction of motion in a thin magnetic film due to the presence of the Magnus force and are annihilated upon reaching the film edge. This paper proposes two methods to engineer a 1D potential well to confine the skyrmion motion in the center region of nanowires and thus preventing annihilation. By patterning the magnetic anisotropy of the film or by adding a layer of magnetic material at the edges, the barrier height and width of the potential well can be controlled. Magnetic skyrmions in such nanowires can then be guided to traverse only along the axis of the nanowire, even in nanowires with steep bends. In addition, we also report a compression mechanism where the skyrmion size and separation distance can be reduced by modifying the potential well, thus increasing the skyrmion packing density in a nanowire. The guided motion and high skyrmion density made possible by our proposed methods will allow for the realization of high density skyrmion based memory.Index Terms-Magnetic skyrmions, micromagnetic simulations, perpendicular magnetic anisotropy, spin structures.

In two closely spaced nanowires system, where domain walls exist in both of the nanowires, applying spin-polarized current to any of the nanowire will induce domain wall motions in the adjacent nanowire. The zero-current domain wall motion is accommodated by magnetostatic interaction between the domain walls. As the current density is increased, chirality flipping is observed in the adjacent nanowire where no current is applied. When current is applied to both nanowires, the coupled domain wall undergoes oscillatory motion. Coupling breaking is observed at a critical current density which varies in a non-linear manner with respect to the interwire spacing.

The operating performance of a domain wall-based magnetic device relies on the controlled motion of the domain walls within the ferromagnetic nanowires. Here, we report on the dynamics of coupled Néel domain wall in perpendicular magnetic anisotropy (PMA) nanowires via micromagnetic simulations. The coupled Néel domain wall is obtained in a sandwich structure, where two PMA nanowires that are separated by an insulating layer are stacked vertically. Under the application of high current density, we found that the Walker breakdown phenomenon is suppressed in the sandwich structure. Consequently, the coupled Néel domain wall of the sandwich structure is able to move faster as compared to individual domain walls in a single PMA nanowire.

2014). Multi-vortex states in magnetic nanoparticles. Applied physics letters, 105(15).