Versatile Motion Control of a Magnetic Skyrmion Pair with Spin Transfer Torques

We studied the motion of a skyrmion pair under the action of independently controllable spin transfer torques. A skyrmion pair made of two coupled skyrmions with opposite skyrmion numbers moves along the direction of the current flow when the currents flowing in the two skyrmions, are identical while it moves perpendicular to the direction of current flow where the currents flow in opposite directions. Manipulating all the degrees of freedom for the strengths of both currents enables the directional motion of the skyrmion pair. We used the Thiele equation to investigate how the strengths of the currents are related with the motion of the skyrmion, and we obtained a tensor that provided the relation between the currents and the force that binds the two skyrmions, and we were able to realize a designed motion. We performed a dynamic simulation of the motion of the skyrmion pair and compared the results with those calculated using the Thiele equation.