Nature Commun. 4, 2671 (2013)

The chirality, or handedness, of magnetic domain walls can affect the wall propagation direction and speed in current-induced domain wall motion. In thin magnetic films that are in contact with normal metals, the domain wall chirality is induced by the Dzyaloshinskii–Moriya interaction at the interface between the two materials. Changes in this interaction can therefore be used to control current-induced domain wall dynamics. Yizheng Wu, Andreas Schmid and colleagues at the Lawrence Berkley National Laboratory, Fudan University and Kyung Hee University have now shown that the chirality of domain walls in Co/Ni multilayers can be controlled by engineering the Dzyaloshinskii–Moriya interaction at the interface with the non-magnetic substrate, either Ir or Pt.

The researchers first image the spin structure of chiral Néel-type domain walls by spin-polarized low-energy electron microscopy, and observe the opposite chirality for multilayer stacks on Pt (right-handed) or Ir (left-handed) substrates. Then, by inserting an Ir layer between the Co/Ni stack and the Pt substrate, the researchers demonstrate that they can tune the strength of the Dzyaloshinskii–Moriya interaction by varying the thickness of the Ir layer, thus controlling the chirality of the domain walls. By increasing the thickness from 0.6 of a monolayer to 2.5 monolayers and then to 3 monolayers, the researchers observe right-handed chiral Néel walls, achiral Bloch walls and left-handed chiral Néel walls.