Current-induced torques in continuous antiferromagnetic textures

We study the influence of an electric current on a continuous noncollinear antiferromagnetic texture. Despite the lack of a net magnetic moment, we find that the exchange interaction between conduction electrons and local magnetization generally results in current-induced torques that are nonzero and similar in phenomenology to spin-transfer torques in ferromagnets. We present the generalization of the nonlinear sigma model equation of motion for the Néel vector that includes these current-induced torques, and briefly discuss the resulting current-induced antiferromagnetic domain wall motion and spin-wave Doppler shift. We give an interpretation of our results using a unifying picture of current-induced torques in ferromagnets and antiferromagnets, in which they are viewed as being due to the current-induced spin polarization resulting from an effective spin-orbit coupling.

Figure 1

Illustration of a smooth antiferromagnetic magnetization texture.

Figure 2

Transmission probability as a function of Fermi energy ${\epsilon }_F/t$ for $\Delta /t=0.1$ (solid lines) and $\Delta /t=0.2$ (dashed lines) for both the antiferromagnetic (thin lines) and ferromagnetic (thick line, only the $\Delta =0.2$ is shown and the $\Delta =0.1$ is similar) cases. We considered a lattice with $82$ sites.

Figure 3

Plot of the current-induced out-of-plane spin density vs the antiferromagnetic texture wavelength $\lambda$. The solid line corresponds to $\Delta /t=0.1$ and the dashed line to $\Delta /t=0.2$. The Fermi energy ${\epsilon }_F/t=0.79$.

Figure 4

Plot of the current-induced out-of-plane spin density vs the texture wavelength $\lambda$ for a ferromagnet. The solid line corresponds to $\Delta /t=0.1$ and the dashed line to $\Delta /t=0.2$. The Fermi energy ${\epsilon }_F/t=0.79$.

Figure 5

Plot of the velocity $\mathit{v}$ that parametrizes current-induced torques in bulk antiferromagnets vs ${\epsilon }_F/t$. The solid line corresponds to $\Delta /t=0.1$ and the dashed line to $\Delta /t=0.2$. The number of lattice sites is equal to $82$.

Figure 6

Plot of the velocity ${\mathit{v}}_s$ that parametrizes current-induced torques in bulk ferromagnets vs ${\epsilon }_F/t$. The solid line corresponds to $\Delta /t=0.1$ and the dashed line to $\Delta /t=0.2$. The number of lattice sites is taken to be $82$.