Figure 1

Skyrmionium-based racetrack storage device. (a) Schematic presentation of the proposed device including the four constituents: writing, deleting, moving and reading. A skyrmionium, the circular object in the Co layer (gray), is written or deleted by a photosensitive switch built from gold (Au) and a semi-conductor (SC). A radial current (white) is triggered upon illuminating the antenna with a fs-laser pulse due to the applied bias voltage. The current mainly flows in the Pt layer (transparent) where the SHE injects spins (cyan) into the Co layer that are oriented perpendicularly to the plane normal and current directions. Depending on the polarity of the gate voltage, the sign of the optically activated current pulse and the orientation of the polarization are determined, so that a skyrmionium can be written or deleted. To move the skyrmionium a uniform current density j is applied along the track, again generating spins s that exert a SOT onto the skyrmionium. When a skyrmionium is located near the two leads on the right, a Hall voltage U_R can be measured, allowing for a distinct detection of a skyrmionium bit. (b) (top) Magnetic texture of a skyrmionium, and (bottom) topological charge density n_Sk with opposite signs for the inner skyrmion and the outer ring.