Skyrmion Transport Modified by Surface Terraces in Magnetic Multilayers

Abstract

While the modification of skyrmion motion by edges and defects has been widely discussed, how the motion of skyrmions would be affected by a surface terrace remains unclear. In this work, micromagnetic simulations are performed to reveal the skyrmion transport behaviors in multilayers modified by a surface terrace. It is found that skyrmions can be partially nucleated or annihilated at the surface terrace, and the nucleation or annihilation process is related to the competition between the nucleation or annihilation barrier and the binding energy of skyrmions. Interestingly, such processes can effectively modulate the transport characteristics of the skyrmion. The skyrmion decelerates or is even blocked in the annihilation process, whereas it accelerates in the nucleation process. As a result, the skyrmion mobility can be very different between upward and downward motion, and the surface terrace can even be viewed as a surface diode for skyrmions. Meanwhile, a transverse shift of the skyrmion along the terrace occurs in the nucleation process and the shifting distance depends on the applied current. In this way, the skyrmion can be shifted to a specific trajectory by controlling the current. Based on these effects, we propose two prototypal skyrmionic devices, the skyrmion surface diode and skyrmion track selector, which are potentially useful in skyrmionics.