Abstract
The magnetization reversal induced by spin orbit torques in the presence of Dzyaloshinskii-Moriya interaction (DMI) in perpendicularly magnetized Ta/CoFeB/MgO structures were investigated by using a combination of Anomalous Hall effect measurement and Kerr effect microscopy techniques. By analyzing the in-plane field dependent spin torque efficiency measurements, an effective field value for the DMI of ~300 Oe was obtained, which plays a key role to stabilize Néel walls in the film stack. Kerr imaging reveals that the current-induced reversal under small and medium in-plane field was mediated by domain nucleation at the edge of the Hall bar, followed by asymmetric domain wall (DW) propagation. However, as the in-plane field strength increases, an isotropic DW expansion was observed before reaching complete reversal. Micromagnetic simulations of the DW structure in the CoFeB layer suggest that the DW configuration under the combined effect of the DMI and the external field is responsible for the various DW propagation behaviors.
Highlights
Current-induced highly-efficient magnetization reversal[1,2,3] and fast domain wall (DW) motion[4,5,6] by utilizing spin orbit torques (SOT)[7] have drawn much attention for their potential application in magnetic memory[8,9,10] and logic devices[11]
The current-induced magnetization switching was characterized from anomalous Hall effect (AHE) measurements and magneto-optical Kerr effect (MOKE) microscope images taken at room temperature
To understand the difference in the current-induced DW propagation process under the various Hx, we performed a micromagnetic simulation on the DW structure of the device
Summary
Current-induced highly-efficient magnetization reversal[1,2,3] and fast domain wall (DW) motion[4,5,6] by utilizing spin orbit torques (SOT)[7] have drawn much attention for their potential application in magnetic memory[8,9,10] and logic devices[11]. In the HM/FM/I structures with perpendicular magnetic anisotropy (PMA), theoretical and experimental work have verified that an external in-plane magnetic field is required for deterministic switching to break the symmetry along the current direction[3,14]. The current-induced DW depinning model proposed by Lee et al.[14] gave a better understanding of the magnetization reversal process and the role of the in-plane field in SOT-induced magnetization switching They suggested that the function of the field was to orient the magnetic moments within the DW to align a significant component parallel to the current flow, thereby allowing the torque from the SHE to produce a perpendicular equivalent field that can expand a reversed domain in all lateral directions. By micromagnetic simulations of the DW structure with the inclusion of DMI effects, we identified the origin of the current-induced asymmetric DW propagation and the role of the in-plane field in SOT-induced magnetization reversal
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