Multiple Magnetic Domain Wall Injector Driven by Spin-Orbit Torque in a Two-Terminal Device

We performed micromagnetic simulations on a multiple magnetic domain wall injector in a two-terminal device where a magnetic gradient is implanted at one end. In the magnetic gradient region, successive up-down magnetization is generated by the spin-orbit torque and, in turn, injected into the magnetic wire with a strong perpendicular magnetic anisotropy, resulting in multiple domain propagation. We found that the threshold current for the multiple domain injection is minimized when an effective magnetic anisotropy at the end becomes nearly zero. As the effective anisotropy becomes more negative, the threshold current increases with a magnetic anisotropy gradient because the gradient acts as a barrier to the domain injection. Our result provides design rules for the optimized magnetic anisotropy gradient for the multiple domain generation and injection.