Modification of Dzyaloshinskii-Moriya-Interaction-Stabilized Domain Wall Chirality by Driving Currents

We measure and analyze the chirality of Dzyaloshinskii-Moriya-interaction (DMI) stabilized spin textures in multilayers of $\mathrm{Ta}|{\mathrm{Co}}_{20}{\mathrm{F}}_{60}{\mathrm{B}}_{20}|\mathrm{MgO}$. The effective DMI is measured experimentally using domain wall motion measurements, both in the presence (using spin-orbit torques) and absence of driving currents (using magnetic fields). We observe that the current-induced domain wall motion yields a change in effective DMI magnitude and opposite domain wall chirality when compared to field-induced domain wall motion (without current). We explore this effect, which we refer to as current-induced DMI, by providing possible explanations for its emergence, and explore the possibility of its manifestation in the framework of recent theoretical predictions of DMI modifications due to spin currents.

Figure 1

Field-induced domain wall motion experiment. (a) DW velocity as a function of in-plane magnetic field (${\mu }_0{H}_x$), where the DW is driven by an out-of-plane magnetic field (${\mu }_0{H}_z$) of 1.5 mT. The symmetric component (black squares) is given by, $S=(v_{UD}+v_{DU})/2$, where the subscript UD refers to up-down DW and DU refers to down-up DW. (b) The antisymmetric (blue dots, $A_{UD-DU}$; red dots, $A_{DU-UD}$) component of the DW velocity, where the antisymmetric component is given by $A_{UD-DU}=2(v_{UD}-v_{DU})/(v_{UD}+v_{DU})$ (in arb. units, a.u.).

Figure 2

Current-induced domain wall motion experiment. (a) DW velocities (up-down, blue; down-up, red) are measured under the application of an in-plane magnetic field. It is measured for a current density of $+3.3\times {10}^{11}\mathrm{A}/{\mathrm{m}}^2$ (squares) and $-3.3\times {10}^{11}\mathrm{A}/{\mathrm{m}}^2$ (dots). (b) The effective DMI for different current densities. A switching of DMI chirality is observed under injection of driving current.

Figure 3

(a) A left-handed Néel-type down-up DW in the presence of an electric field pointing to the right is symmetry equivalent to a left-handed Néel-type up-down DW in the presence of an electric field pointing to the left. (b) A left-handed Néel-type down-up DW in the presence of an electric field in $z$ direction is symmetry equivalent to a left-handed Néel-type up-down DW in the presence of an electric field in $z$ direction.