Vertical-current-induced domain-wall motion in MgO-based magnetic tunnel junctions with low current densities

Shifting electrically a magnetic domain wall (DW) by the spin transfer mechanism(1-4) is one of the ways foreseen for the switching of future spintronic memories or registers(5,6). But the classical geometries where the current is injected in the plane of the magnetic layers suffer from poor efficiencies of the intrinsic torques(7,8) acting on the DWs. A way to circumvent this problem is to use vertical-current injection(9-11). For that case, theoretical calculations(12) attribute the microscopic origin of DW displacements to the out-of-plane ('field-like') spin-transfer torque(13,14). Here we report experiments in which we controllably displace a DW in the planar electrode of a magnetic tunnel junction by vertical-current injection. Our measurements confirm the major role of the out-of-plane spin torque for DW motion, and allow quantifying this term precisely. The involved current densities are about 100 times smaller than the one commonly observed with in-plane currents(15). Step-by-step resistance switching of the magnetic tunnel junction should provide a new approach to spintronic memristive devices(16-18).