Tunable Conversion of Topological Spin Texture from Domain Wall Pair for Magnetic Memory Application in Specially Designed Magnetic Nanotracks

Topological spin textures have drawn intense attention due to interesting fundamental physics and possible application in non-volatile information carriers as well as logic gate devices. Here, in a specially designed race track that consists of three narrow nanotracks connected to a wide nanotrack, we investigate the role of geometry in domain wall (DW) pair to skyrmion conversion using micromagnetic simulation. In particular, tunable DW to skyrmion or fractional skyrmion conversion is achieved for a selected material parameter with a separation length of 10 or 30 nm (or combination of both) between the narrow nanochannels. By suitably varying the spacing between the narrow nanotracks symmetrically and asymmetrically, we control the dynamics of skyrmions and fractional skyrmions along with the trajectory. Interestingly, if the separation length between the top and middle (or middle and bottom) nanochannel is 30 nm, a fractional skyrmion is formed. The DW pair to skyrmion conversion time depends on the separation between the narrow nanochannels, e.g., for 10 nm separation, the conversion time of DW pair to skyrmion from the top nanochannel is ∼0.3 ns, and the same for the 30 nm separation is ∼2 ns. Analysis of the topological number of spin texture suggests the creation of two skyrmions in the case of 10 nm separation between the narrow nanochannels, whereas for 30 nm separation, a skyrmion and a fractional skyrmion are formed. Furthermore, the analysis of total energy and other energy terms shows a non-monotonic variation during the conversion of DW to skyrmion at the junction. Finally, the increase or decrease in the total energy value depends on the formation of skyrmions or fractional skyrmions. Thus, we infer that the enforced geometrical constraints and the interplay of various energies play a crucial role in controlling the topology and skyrmion formation. Based on these findings, we believe that a skyrmion racetrack made up of three nanochannels will help achieve efficient controllable skyrmion dynamics, which may have application potential in magnetic memory operations.