Nanosecond Skyrmion Dynamics driven by Spin-orbit Torques observed by Time-resolved X-ray Transmission Microscopy

Abstract

Magnetic skyrmions are swirling spin texture exhibiting large potential as information unit in spin-electronic devices due to their unique topological properties. Recent studies demonstrated that, at room temperature, a train of magnetic skyrmions can be displaced by electric pulse currents[1-3], by taking static images before and after the current pulses. However, for the development of ultrafast skyrmionic devices, it is important to understand their dynamic behaviors such as skyrmion breathing[4], gyration[4,5], or skyrmion Hall effect[4,6,7]. Such observation of ultrafast dynamics of chiral skyrmions in real spaces is still challenging due to the experimental limitations that simultaneously achieve nanosecond time resolution and <100 nm spatial resolution. In this talk, we will demonstrate the nanosecond-dynamics of chiral skyrmions driven by current-induced spin-orbit torques in Pt/CoFeB/ MgO multilayers, directly observed by time-resolved X-ray microscopy[8]. Unlike earlier studies, we first show that, in the absence of magnetic field, skyrmion state can be generated by applying electrical bipolar pulses which causes thermal excitations. More importantly, using time-resolved microscopy, we reveal that two distinctive skyrmion excitation states, breathing-like and translational excitation states, can be achieved and readily manipulated by tuning the amplitude of spin-orbit torques. Micromagnetic simulations were performed to understand the physical origin, and the results reveal the massless particle-like nature of magnetic skyrmions at room temperature. In sum, we believe that our findings provide important physical understanding of room temperature magnetic skyrmions and also offer unique electrical manipulation methods that could realize the development of ultrafast skyrmionic applications in the future.