Reversible conversions between skyrmions and skyrmioniums

Abstract Skyrmions and skyrmioniums are both topological non-trivial spin textures in chiral magnetic systems. The dynamics of these particle-like excitations can be distinguished according to their spin structures, and the controlled conversion between them is the key to the diversified functionalities of spintronic devices. In this study, the dynamics and evolution of chiral spin textures are investigated in [Pt/Co]3/Ru/[Co/Pt]3 multilayers with ferromagnetic interlayer exchange coupling. Reversible conversions between skyrmions and skyrmioniums can be realized by precisely controlling the domain wall through an applied magnetic field or electric current. Mediated by a multi-Q (winding number or topological number) cluster, skyrmions can be converted to skyrmioniums through two basic mechanisms. One way is to expand skyrmions by using sinusoidal pulses to form net domains, then to delete the stripe domains of the net domain to create the skyrmionium (reduce Q to zero). The second way is to drive multi-Q clusters to move and collapse into skyrmioniums with square pulses. The skyrmion Hall effect of skyrmioniums has been suppressed to zero, which supports that the winding number of skyrmioniums indeed is reduced to zero. We have also directly observed the topological conversion of a skyrmionium into skyrmion, characterized by the abrupt emergence of the skyrmion Hall effect. The establishment of reversible conversions between different magnetic topological spin textures is an important development, which should speed the advent of the next generation of spintronic device.