Ultralow-loss domain wall motion driven by a magnetocrystalline anisotropy gradient in an antiferromagnetic nanowire

Searching for a new scheme to control the antiferromagnetic (AFM) domain wall is one of the most important issues for AFM spintronic devices. In this work, we study theoretically the domain wall motion of an AFM nanowire, driven by the axial anisotropy gradient generated by an external electric field and an electrocontrol of AFM domain wall motion in the merit of ultralow energy loss is demonstrated. The domain wall velocity depending on the anisotropy gradient magnitude and intrinsic material properties is simulated based on the Landau-Lifshitz-Gilbert equation and also deduced using the energy dissipation theorem. It is shown that the domain wall moves at a nearly constant speed for the small anisotropy gradient, and this motion is accelerated for the large gradient due to the enlarged domain wall width. While the domain wall mobility is independent of the lattice dimension and types of the domain wall, it can be enhanced by the Dzyaloshinskii-Moriya interaction. In addition, the physical mechanism for much faster AFM wall dynamics than ferromagnetic wall dynamics is qualitatively explained. This work unveils a promising strategy for controlling the AFM domain walls, benefiting the future of AFM spintronic applications.

Figure 1

Illustration of an AFM domain wall in a nanowire under an anisotropy gradient, where low $K$ and high $K$ refer to the anisotropy magnitude.

Figure 2

(a) Spatial profile of the domain wall at different times, and (b) the domain wall position and energy as functions of time for $\mathrm{\Delta }K=6\times {10}^{-6}J/a$ and $K_0=0.01J$. (c) A schematic depiction of torques acting on domain wall spins under the anisotropy gradient, and (d) the position of domain wall vs time for various $\mathrm{\Delta }K$ at $K_0=0.01J$.

Figure 3

(a) The position of the domain wall as a function of time for various $K_0$ at $\mathrm{\Delta }K=4\times {10}^{-6}J/a$. The simulated (empty points) and calculated (solid lines) velocities as functions of (b) $\mathrm{\Delta }K$ for various $K_0$ and $\alpha =0.002$, and (c) α for various $\mathrm{\Delta }K$ at $K_0=0.01J$. (d) The simulated domain wall position and velocity as functions of time for large $\mathrm{\Delta }K=0.0003J/a$.

Figure 4

(a) The simulated domain wall velocity as a function of $\mathrm{\Delta }K$ for various lattice sizes, and (b) the simulated (empty points) and calculated (solid lines) velocities as functions of $D$ for various $\mathrm{\Delta }K$.

Figure 5

(a) The displacements of the domain walls of the AFM and FM systems as functions of time. (b) The local $m_y$ (top) of the FM system and $n_y$ (bottom) of the AFM system, the inserts are the schematic depictions of the precession torques. (c) The evolution of $m_y$ at various positions, the domain wall center is located at $z=350a$. (d) The simulated FM wall velocity as a function of $K_y$.