Current-driven dynamics of chiral ferromagnetic domain walls

Controlling the direction of propagation of domain walls in magnetic nanowires is essential for their use in proposed device applications. It is now shown that Dzyaloshinskii–Moriya interactions determine the chirality of domain walls in metallic ferromagnets placed between a heavy metal and an oxide, which in turn means the direction of propagation can be determined by choosing suitable material properties. 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 spirals1,2 and skyrmions3,4,5 through the Dzyaloshinskii–Moriya interaction6 (DMI). Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy metal and an oxide, the DMI stabilizes chiral domain walls2,7 (DWs) whose spin texture enables extremely efficient current-driven motion8,9,10,11. We show that spin torque from the spin Hall effect12,13,14,15 drives DWs in opposite directions in Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a Néel configuration7,16 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 results10,17,18 and highlights a new path towards interfacial design of spintronic devices.