Ion-irradiated Skyrmion Racetracks for current induced Skyrmion guiding at Room Temperature

Abstract

Magnetic skyrmions are localized chiral whirling of magnetization that hold great promise as nanoscale information carrier. Skyrmion racetrack memory and logic devices have recently been proposed where trains of skyrmions in tracks are manipulated by electrical current [1]. These devices require the controlled nucleation and current driven motion of skyrmions in narrow tracks. In particular, the skyrmion Hall effect (i.e. the skyrmion motion towards the track edge), is a critical issue as it can lead to the skyrmion annilation [2–5].Here, we report on the controlled nucleation and current induced guiding of magnetic skyrmions along tracks defined by local He+ ion irradiation on an ultrathin sputtered magnetic film at room temperature. A He+ focused ion beam was used to define 150 nm wide tracks (red areas, Fig.1a) within a sputtered ultrathin Pt/Co/MgO film patterned into 3-µm-wide tracks [5,6].Magnetometry and Brillouin Light Scattering measurements show that the He+ ion irradiation results in a decrease of the perpendicular magnetic anisotropy as well as the Dzyaloshinskii-Moriya interaction. Under a small perpendicular magnetic field, this leads to the nucleation of skyrmion racetrack (Fig.1b), whose size and density can be tuned by the field amplitude. Experiments of current induced skyrmion motion, show that the skyrmions move along the He+ ion defined tracks (Fig.2 a-f) for two different angles of the current injection. The track acts as a local potential well that guides the skyrmion trajectory, which allows to suppress the skyrmion Hall effect and also it helps in gaining the velocity along the track line. These results are in line with micromagnetic simulations using experimentally derived magnetic and transport parameters (Fig.2 g-h). A deeper insight into the dynamics of the moving skyrmions using micromagnetic simulations show that the steady-state velocity of the skyrmions can be enhanced by tuning the magnetic damping parameter and the height of the ion-defined potential well. These results open a new path to nucleate and guide skyrmions in racetrack memory and logic devices. **