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

Abstract

In the past few years, there have been a number of proposals for fabricating magnetic memories based on the current-induced motion of magnetic domain walls. A device that uses a novel geometry for injecting electrical currents into the sample is shown to work with current densities that are two orders of magnitude lower than in previous approaches. Shifting electrically a magnetic domain wall (DW) by the spin transfer mechanism1,2,3,4 is one of the ways foreseen for the switching of future spintronic memories or registers5,6. But the classical geometries where the current is injected in the plane of the magnetic layers suffer from poor efficiencies of the intrinsic torques7,8 acting on the DWs. A way to circumvent this problem is to use vertical-current injection9,10,11. For that case, theoretical calculations12 attribute the microscopic origin of DW displacements to the out-of-plane (‘field-like’) spin-transfer torque13,14. 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 currents15. Step-by-step resistance switching of the magnetic tunnel junction should provide a new approach to spintronic memristive devices16,17,18.