Journal of the Physical Society of Japan, 83, 064710 (2014), DOI: 10.7566/JPSJ.83.064710
We investigate theoretically the effective magnetic field acting on a ferromagnetic (FM) layer with a spatially varying magnetization, which is deposited on the surface of a three-dimensional topological insulator (3D-TI). When current is applied through the topological surface state of the 3D-TI, the exchange interaction between the conduction electrons and the spin texture of the FM film in the presence of the Rashba-like spin-momentum coupling of the TI, a topological gauge field (electromagnetic vector potential) is induced in the adiabatic limit, which modifies the momentum of the electron on the surface of the TI. This gives rise to an electromagnetic interaction energy from which we derive the corresponding effective field acting on the magnetic moments in the FM layer. By assuming a nanoskyrmion spin texture in the FM layer of dimension of 1 nm, as experimentally observed in recent experiments, and a current density of 108 A/cm2, we obtain an estimated effective field which is comparable to the switching fields of typical FM materials.