Engineering of intrinsic chiral torques in magnetic thin films based on the Dzyaloshinskii-Moriya interaction

Abstract

The establishment of chiral coupling in thin magnetic films with inhomogeneous anisotropy has led to the development of novel artificial systems of fundamental and technological interest. The chiral coupling itself is enabled by the Dzyaloshinskii-Moriya interaction (DMI) enforced by the patterned non-collinear magnetization [1-4]. Here, we create a domain wall track with out-of-plane (OOP) magnetization coupled to OOP stripes on each side via narrow parallel strips with in-plane magnetization as shown in Fig.1 (a). Since the chiral coupling prefers antiparallel OOP magnetization configuration over the parallel case, the regions of noncollinear magnetization in a single magnetic layer can be used to bias the domain wall velocity, as shown in series of Kerr images in Fig.1 (b). To tune the chiral torques, the design of the magnetic racetracks can be modified by varying the width of the tracks or the width of the transition region between noncollinear magnetizations, reaching effective chiral magnetic fields of up to 8 mT. Furthermore, we show how the magnitude of the chiral torques can be estimated by measuring asymmetric domain wall velocities. We also demonstrate spontaneous domain wall motion propelled by intrinsic torques even in the absence of any external driving force, which is of high importance for domain wall motion-based neuromorphic devices.  Figure 1: (a) Schematic of a DW racetrack with OOP magnetization delimited by two strips with IP anisotropy. The energy landscape of the DW racetrack is monotonous, except for local DW pinning sites. (b) Sequence of Kerr images of asymmetric DW motion in a racetrack with wOOP = 950 nm. The dashed lines correspond to the position of the IP magnetized strip while the full lines correspond to the boundary of the magnetic track. 80 current pulses are applied between each image; the pulse duration is 50 ns and the current density is 3.6×1011 A/m2.