Spin-orbit-torque-induced magnetic domain wall motion in Ta/CoFe nanowires with sloped perpendicular magnetic anisotropy

Abstract

In materials with the gradient of magnetic anisotropy, spin-orbit-torque-induced magnetization behaviour has attracted attention because of its intriguing scientific principle and potential application. Most of the magnetization behaviours microscopically originate from magnetic domain wall motion, which can be precisely depicted using the standard cooperative coordinate method (CCM). However, the domain wall motion in materials with the gradient of magnetic anisotropy using the CCM remains lack of investigation. In this paper, by adopting CCM, we established a set of equations to quantitatively depict the spin-orbit-torque-induced motion of domain walls in a Ta/CoFe nanotrack with weak Dzyaloshinskii–Moriya interaction and magnetic anisotropy gradient. The equations were solved numerically, and the solutions are similar to those of a micromagnetic simulation. The results indicate that the enhanced anisotropy along the track acts as a barrier to inhibit the motion of the domain wall. In contrast, the domain wall can be pushed to move in a direction with reduced anisotropy, with the velocity being accelerated by more than twice compared with that for the constant anisotropy case. This substantial velocity manipulation by anisotropy engineering is important in designing novel magnetic information devices with high reading speeds.

Current-Induced Spin-Orbit Torque and Field-Free Switching in Mo -Based Magnetic Heterostructures

“…It has been shown that current-induced Oersted field has a non-negligible zcomponent at the edges of Hall-bar sample [56], which will further create a longitudinal domain wall in some cases [57]. It has also been shown by simulations that an effective out-of-plane field will be created by the magnetic anisotropy gradient, which can be utilized to drive domain wall motion [58,59]. Therefore, we postulate that the current that we applied will first create a longitudinal domain wall in the sample, and then the magnetization switching will be achieved by lateral domain wall motion, which is driven by the transverse magnetic anisotropy gradient.…”

Readable High-Speed Racetrack Memory Based on an Antiferromagnetically Coupled Soft/Hard Magnetic Bilayer

“…H→eff includes the effective fields contributed from exchange coupling in every FM layer, the interlayer RKKY exchange coupling, the magnetic anisotropy energy, the demagnetization energy, and the DMI. H SO is the effective field of the SOT, and it is expressed as [15]:HSO=μBθSHJ/γ0normaleMSLz…”

“…All the parameters used in our simulation are in an experimentally achievable range. Without loss of generality, we applied a positive DMI constant and a positive spin-Hall angle that ensures the motion of a right-handed DW against the direction of the current (along the direction of electron flow) [15]. The change of the sign of DMI or the spin Hall angle only reverses the motion direction of the DW but does not influence the conclusion of this paper.…”

“…In the early stage, the racetrack memory was made of a ferromagnetic (FM) nanowire, and the current-induced motion of DWs is attributed to the exchange of angular momentum between the spin of the moving electron and the magnetic moment in the DW (the so-called spin-transfer torque (STT) effect) [3,4,5,6,7,8]. In recent years, a new type of racetrack memory consisting of heavy metal (HM)/FM bilayer nanowires was proposed [9,10,11,12,13,14,15,16,17]. In the HM/FM bilayer track, the FM layer exhibits a perpendicular magnetic anisotropy (PMA), and the DW structure in the FM layer shows chirality due to the Dzyaloshinskii–Moriya interaction (DMI) at the HM/FM interface.…”

Voltage control of domain walls in magnetic nanowires for energy-efficient neuromorphic devices

“…The heavy metal layer leads to a perpendicular magnetic anisotropy (PMA) in the CoFeB layer, and a Dzyaloshinskii-Moriya interaction (DMI) which stabilizes chiral domain walls. In order to achieve controlled positioning of the DW we propose current clocked DW motion in conjunction with a gradient in the PMA [24,25]. Notches are placed at regular intervals to arrest the DW at different locations of the racetrack.…”