Controlling Skyrmion Hall Angle by engineering mixed skyrmions with stray fields*

Skyrmions, topologically protected quasi particles in magnetic materials, are widely explored as candidate excitations to store and transmit information. The dynamics of an isolated skyrmion on a racetrack is limited by the Magnus force for a Neel skyrmion and damping force for a Bloch skyrmion. For identical parameters, Neel and Bloch skyrmions tend to move perpendicular to each other. This orthogonality can be understood by the fact that Neel and Bloch skyrmions can be continuously deformed into each other by a 90 degree rotation in parameter space, which can also be seen as a 90 degree rotation of a frame of reference fixed on a point on the boundary of the skyrmion. Accordingly for a mixed skyrmion it is possible to achieve a movement parallel to the drive current with zero spin Hall angle, which is ideal for controlled skyrmion motion in racetrack applications. The mixed skyrmion can be engineered by a combination of the interfacial DMI, which favors the Neel skyrmion, and the stray field which favors the Bloch skyrmion, without the use of synthetic antiferromagnetic multilayer structures.