Magnetic skyrmions are swirling magnetic textures with novel characteristics suitable for future spintronic and topological applications. Recent studies confirmed the room-temperature stabilization of skyrmions in ultrathin ferromagnets. However, such ferromagnetic skyrmions show an undesirable topological effect, the skyrmion Hall effect, which leads to their current-driven motion towards device edges, where skyrmions could easily be annihilated by topographic defects. Recent theoretical studies have predicted enhanced current-driven behavior for antiferromagnetically exchange-coupled skyrmions. Here we present the stabilization of these skyrmions and their current-driven dynamics in ferrimagnetic GdFeCo films. By utilizing element-specific X-ray imaging, we find that the skyrmions in the Gd and FeCo sublayers are antiferromagnetically exchange-coupled. We further confirm that ferrimagnetic skyrmions can move at a velocity of ~50 m s−1 with reduced skyrmion Hall angle, |θSkHE| ~ 20°. Our findings open the door to ferrimagnetic and antiferromagnetic skyrmionics while providing key experimental evidences of recent theoretical studies.

Spintronic devices based on magnetic skyrmions are a promising candidate for nextgeneration memory applications due to their nanometre-size, topologically-protected stability and efficient current-driven dynamics. Since the recent discovery of roomtemperature magnetic skyrmions, there have been reports of current-driven skyrmion displacement on magnetic tracks and demonstrations of current pulse-driven skyrmion generation. However, the controlled annihilation of a single skyrmion at room temperature has remained elusive. Here we demonstrate the deterministic writing and deleting of single isolated skyrmions at room temperature in ferrimagnetic GdFeCo films with a device-compatible stripline geometry. The process is driven by the application of current pulses, which induce spin-orbit torques, and is directly observed using a time resolved nanoscale X-ray imaging technique. We provide a current-pulse profile for the efficient and deterministic writing and deleting process. Using micromagnetic simulations, we also reveal the microscopic mechanism of the topological fluctuations that occur during this process.Nanoscale memory devices that employ magnetic materials and offer non-volatility and efficient electrical controllability have the potential to outperform and eventually replace conventional silicon-based memory technologies such as DRAM or NAND-Flash 1-3 . Among the many different types of spintronic memory devices available, those based on magnetic skyrmions -topologically non-trivial spin nanostructures -are of particular interest. 4-10 Key advantages of skyrmion-based memory device include their stability 9 , high-density arrangement 4,5 and low-power operation using electrical excitations 6-8 . Recently the room-temperature stabilization of magnetic skyrmions and their current pulse-induced displacement on nanotracks has been reported in magnetic heterostructures such as Ta/CoFeB/MgO 11,12 , Pt/Co/Ta 13 , Pt/CoFeB/MgO 13-15 , Pt/Co/Ir 16 and Pt/GdFeCo/MgO 17 where the strong interfacial Dzyaloshinskii-Moriya interaction (DMI)leads to the stabilization of the skyrmion structures 18,19 . While such current-controlled skyrmion motion is applicable to an actual device scheme, the deterministic writing and deleting of a single isolated magnetic skyrmion at room temperature is required for fully functional skyrmionic devices 10,20 .Theoretical studies have suggested that skyrmions can be created by applying localized vertical spin-polarized current to a confined geometry 21 or well-defined notches 22 .Moreover, there are suggestions that a single skyrmion can be formed by the conversion of a pair of domain walls 23,24 . However, the controlled creation of a single skyrmion, and the subsequent annihilation of the same skyrmion, has only been experimentally achieved at low temperatures with spin-polarized scanning tunneling microscopy (SP-STM) 8,25 . This approach requires the in situ deposition of material at cryogenic conditions, which may be hard to incorporate into actual commercial devices. Recently, several s...

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Magnetic skyrmions are topologically protected spin textures with attractive properties suitable for high-density and low-power spintronic device applications. Much effort has been dedicated to understanding the dynamical behaviours of the magnetic skyrmions. However, experimental observation of the ultrafast dynamics of this chiral magnetic texture in real space, which is the hallmark of its quasiparticle nature, has so far remained elusive. Here, we report nanosecond-dynamics of a 100nm-diameter magnetic skyrmion during a current pulse application, using a time-resolved pump-probe soft X-ray imaging technique. We demonstrate that distinct dynamic excitation states of magnetic skyrmions, triggered by current-induced spin–orbit torques, can be reliably tuned by changing the magnitude of spin–orbit torques. Our findings show that the dynamics of magnetic skyrmions can be controlled by the spin–orbit torque on the nanosecond time scale, which points to exciting opportunities for ultrafast and novel skyrmionic applications in the future.