Purely Electrical Manipulation of Magnetic Domain and Skyrmion Bubbles

In ferromagnetic materials, the exchange interaction, magnetic anisotropy, and dipolar forces dictate the domain walls (DWs), such as the Bloch- or Néel-type. An enclosed DW with a set chirality carries a topological charge of Q = ±1, in equivalence to a magnetic skyrmion. It has been long speculated that DW spin structures with greater Q could exist [1], about which, however, experimental evidences remain elusive. We demonstrate experimental evidences of a novel type of DWs which possesses a high topological charge of Q = 2. Using MOKE microscopy, we show that the chiral winding of the core magnetization of DW can be revealed by its dynamical response to the electrical current induced spin-orbit torque (SOT). The breaking of rotational symmetry as a consequence of the Q = 2 chiral DW dictates that the DW responses differently when the current flows along different directions. We demonstrate two distinctive examples. The deterministic SOT switching of a magnetic layer can be achieved by applying the current in one direction, while skyrmion bubbles are generated by applying the current to another direction. Both are realized without any magnetic field, as a benefit of the novel DW topology.

[1] Malozemoff et al., Magnetic Domain Walls in Bubble Materials, Academic Press, 1979.