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.
