Skyrmionium creation and annihilation: Experimental and micromagnetic simulation demonstration

Topological spin structures have recently received tremendous attention in condensed matter physics and information science. In addition to the frequently studied skyrmion, skyrmioniums that exhibit a zero topological charge are also promising for spintronics memory carriers. Here, through integrating an interfacial asymmetric Ta/CoFeB/MgO multilayer device with an on-chip conducting wire that induces Oersted fields and Joule heating, we show experimentally the creation and annihilation of magnetic Néel-type skyrmioniums at room temperature, without applying external magnetic fields. In particular, we observe two distinct annihilation dynamics of the skyrmionium by a polar magneto-optical Kerr microscope. Under the direction of Oersted fields that are parallel to the core direction of the skyrmionium, the skyrmionium shrinks inward to form a skyrmion. Under the antiparallel configuration, skyrmionium expands outward to form a stripe domain. By performing micromagnetic simulations, we reveal the Néel-type skyrmionium formation and annihilation dynamics as well as the corresponding energy changes among different magnetic states. Our findings could be important for understanding the formation and annihilation dynamics of skyrmioniums, which also provide an on-chip non-electrical-contact manipulating method of skyrmioniums.