Matching domain-wall configuration and spin-orbit torques for efficient domain-wall motion

In our numerical study, we identify the best conditions for efficient domain-wall motion by spin-orbit torques originating from the spin Hall effect or Rashba effect. We demonstrate that the effect depends critically on the domain-wall configuration, the current injection scheme, and the symmetry of the spin-orbit torque. The best identified configuration corresponds to a Néel wall driven by the spin Hall effect in a narrow strip with perpendicular magnetic anisotropy. In this case, the domain-wall velocity can be a factor of 10 larger than that for the conventional current-in-plane spin-transfer torque.

Figure 1

(a) Schematic view of the three different DW types that have been considered, i.e., head-to-head DW in an in-plane magnetized strip, Bloch or Néel DW in an out-of-plane magnetized strip. (b) Parallel geometry in which the ferromagnetic layer (F) is parallel to the spin-orbit (SO) layer on the whole length of the strip. (c) Perpendicular geometry for which the SO strip is perpendicular to the F strip.

Figure 2

DW shift as a function of time under different possible SO torques in the parallel geometry. A steady motion is found for the case of a Néel wall excited by SHE (red curve) whereas for Néel wall with RE, the DW is only shifted (blue curve). Inset: Néel DW velocity induced by SHE vs current density in parallel geometry.

Figure 3

DW velocity as a function of DW position inside the F strip. Zero corresponds to the center of the intersection with the SO strip that is 200 nm wide. A steady motion is found for Bloch DW excited by SHE and for HTH DW excited by RE. Two regimes are identified, i.e., (I) the DW is inside the intersection area and a steady motion is obtained, and (II) the DW is outside the intersection and an inertial motion with decreasing velocity is found.