Theory of spin torques and giant magnetoresistance in antiferromagnetic metals

Spintronics in ferromagnetic metals is built on a complementary set of phenomena in which magnetic configurations influence transport coefficients and transport currents alter magnetic configurations. Here, we propose that corresponding effects occur in circuits containing antiferromagnetic metals. The critical current for order parameter orientation switching can be smaller in the antiferromagnetic case because of the absence of shape anisotropy and because spin torques can act through the entire volume of an antiferromagnet. We discuss possible applications of antiferromagnetic metal spintronics.

Figure 1

(Color online) The model heterostructure for which we perform our calculations.

Figure 2

Landauer-Buttiker conductance as a function of the angle $\theta$ between the magnetization orientations ${\widehat{\mathbf{\Omega }}}_i$ on opposite sides of the paramagnetic spacer layer. There is a sizable giant magnetoresistance effect, with larger conductance at smaller $\theta$ and weak dependence on layer thicknesses. These results were obtained for $\mathbf{\Delta }∕t=1$ and ${ϵ}_i=0$.

Figure 3

Local spin-transfer torques in the downstream antiferromagnet. The in-plane spin transfer is staggered and therefore effective in driving coherent order parameter dynamics. The out-of-plane spin-transfer component is ineffective because it is not staggered. These results were obtained for $\mathbf{\Delta }∕t=1$, ${ϵ}_i=0$, $\theta =\pi ∕2$, $N=50$, and $M=50$.

Figure 4

Total spin transfer torque action on the downstream antiferromagnet, as a function of $\theta$. We used the parameters $\mathbf{\Delta }∕t=1$ and ${ϵ}_i=0$.

Figure 5

Derivative of the total spin transfer torque per unit current, $Mg(\theta =\pi )$, acting on the downstream antiferromagnet with respect to the angle $\theta$ at $\theta =\pi$ as a function of $M$. We used the parameters $\mathbf{\Delta }∕t=1$ and ${ϵ}_i=0$.