Ab initio giant magnetoresistance and current-induced torques in $\mathrm{Cr}∕\mathrm{Au}∕\mathrm{Cr}$ multilayers

We report on an ab initio study of giant magnetoresistance (GMR) and current-induced torques (CITs) in $\mathrm{Cr}∕\mathrm{Au}∕\mathrm{Cr}$ trilayers that is based on nonequilibrium Green’s functions and spin-density functional theory. We find substantial GMR due primarily to a spin-dependent resonance centered at the $\mathrm{Cr}∕\mathrm{Au}$ interface and predict that the CITs are strong enough to switch the antiferromagnetic order parameter at current densities $\sim 100$ times smaller than switching current densities in ferromagnetic metal circuits.

Figure 1

(Color online) GMR as a function of spacer thickness. There is a sizable GMR for all spacer thicknesses. The inset shows the geometry for the four-layer spacer configuration—up and down spins are colored red and blue (light and dark), respectively. The configuration above illustrates an antiparallel configuration.

Figure 2

(Color online) Layer- and spin-resolved density of states at the Fermi energy for a Cr-Au single interface system. Layers 1–12 are Cr, and 13–24 are Au. The pronounced enhancement of the density of states in layer 12 reflects the interface resonance. The spin polarization of the interface resonance is consistent with the fact that $T_{\downarrow }>T_{\uparrow }$ in the transport calculation.

Figure 3

(Color online) Number of propagating states in the [001] direction at the Fermi energy for bulk antiferromagnetic Cr.

Figure 4

(Color online) Transverse-momentum-resolved Fermi-energy density of states 8, 10, 12, and 16 of the single interface Cr-Au system. Layer 12 is the Cr layer closest to the interface. Layer 8 shows bulk Cr characteristics (compare to Fig. 3), while layer 16 shows bulk Au characteristics.

Figure 5

(Color online) Density of states for layers 10–14 of the single interface Cr-Au system. The DOS relaxes to its bulk shape a couple of layers away from the interface. Layer 12 is the interface Cr layer, and the Fermi energy is 0.

Figure 6

(Color online) Layer-resolved current-induced torque per current. The $(X,Y,Z)$ directions in the legend refer to the directions of the induced torques. The solid arrows in the figure refer to the orientation of the Cr interface spin. The torque is localized in the first layer of the Cr.