Current-driven dynamics of chiral ferromagnetic domain walls

In most ferromagnets the magnetization rotates from one domain to the next with no preferred handedness. However, broken inversion symmetry can lift the chiral degeneracy, leading to topologically rich spin textures such as spin spirals(1,2) and skyrmions(3-5) through the Dzyaloshinskii-Moriya interaction(6) (DMI). Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy metal and an oxide, the DMI stabilizes chiral domain walls(2,7) (DWs) whose spin texture enables extremely efficient current-driven motion(8-11). We show that spin torque from the spin Hall effect(12-15) drives DWs in opposite directions in Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a Neel configuration(7,16) with left-handed chirality. We directly confirm the DW chirality and rigidity by examining current-driven DW dynamics with magnetic fields applied perpendicular and parallel to the spin spiral. This work resolves the origin of controversial experimental results(10,17,18) and highlights a new path towards interfacial design of spintronic devices.