Figure 2: Current-induced motion of skyrmions in the top and bottom FM layers of an AFM-coupled bilayer nanotrack.
From: Magnetic bilayer-skyrmions without skyrmion Hall effect
Top views of the motion of skyrmions at selected interlayer exchange coupling constants and times driven by spin currents with (a) the current-perpendicular-to-plane (CPP) injection geometry and (b) the current-in-plane (CIP) injection geometry. The size of the AFM-coupled bilayer nanotrack is 500 × 50 × 3 nm3, where D=3.5 mJ m−2. The skyrmions are initially created by the MTJ skyrmion injector placed on the top FM layer at x=100 nm. For the CPP case, the spin current in the bottom FM layer is applied along +z but polarized along +y. The skyrmion in the bottom FM layer moves along the nanotrack driven by the spin current, whereas the skyrmion in the top FM layer moves accordingly due to the interlayer AFM exchange coupling. For the CIP case, the skyrmions in both the top and bottom FM layers are driven by in-plane spin-polarized currents. The skyrmions velocities in the top (open symbols) and bottom (solid symbols) FM layers as functions of the current density j for (c) the large interlayer AFM exchange stiffness Ainter=−6 pJ m−1 and (d) the small interlayer AFM exchange stiffness Ainter=−0.06 pJ m−1. For the CIP case, the square, triangle and star symbols indicate different values of the non-adiabatic torque constant β of 0.15, 0.3 and 0.6, respectively. The cross symbol denotes the decoupling as well as the destruction of skyrmions in the top and bottom FM layers because of a large driving current density and a small interlayer AFM exchange coupling, where the velocities are calculated just before the destruction of skyrmions.
