2022 年 65 巻 9 号 p. 405-410
Under the competition of ferromagnetic interaction and Dzyaloshinskii-Moriya interaction, magnetic vortices in real-space, skyrmions, can be induced on a topological insulator (TI), which reflects the chiral spin structure on the gapped Dirac cone in the momentum space. Here, we observe skyrmions emerge on surfaces of two self-assembled ferromagnetic TI layers, Mn(Bi1-xSbx)2Te4, separated by a spacer of non-magnetic TI layer, (Bi1-xSbx)2Te3, through topological Hall effect (THE) by tuning the Fermi level with optimizing the Bi/Sb ratio. By the spacer-thickness-dependence of the magnitude of THE, we find that the moderate coupling of surface states between the top and bottom Mn(Bi1-xSbx)2Te4 layers is essentially important for inducing and stabilizing skyrmions. Moreover, the highly-ordered Mn atoms in the Mn(Bi1-xSbx)2Te4 lead to a strong exchange interaction therein, making skyrmions “soft magnetic”. This would open an avenue toward a topologically robust easy-rewritable novel magnetic memory for spintronics.