Biskyrmion fractionalization in frustrated ferromagnetic nanotracks

Abstract

A stable fusion of two skyrmions is called biskyrmion, which has a topological charge equal to 2. Here, we investigate this object with two cores in frustrated ferromagnetic racetracks. Biskyrmion dynamics induced by a spin-polarized current is analyzed, and the biskyrmion Hall effect is compared with the usual skyrmion Hall effect. We also study the chance of biskyrmion fractionalization in a single skyrmion, a phenomenon that reduces the topological charge of the system by one-half. From the topological perspective, a change in the topological sector is a drastic phenomenon allowed only in discrete lattices. In general, such a change leads to the total annihilation of the topological structure. Here, we show that the biskyrmion splits into a skyrmion and a burst of spin waves (emerging from the destroyed skyrmion). Such dissociation is possible by impelling the biskyrmion against a peculiar hole-defect, which must be able to destroy only one skyrmion, also impeding that the generated spin waves strike the other skyrmion. Our results suggest practical ways to manipulate the shape and chirality of spin textures via lattice defects, which can be intentionally inserted in magnetic thin films.