Field-Free Spin–Orbit Torque Switching of Perpendicular Magnetization by the Rashba Interface

Abstract

Current-induced spin–orbit torques (SOTs) enable efficient electrical manipulation of the magnetization in heterostructures with a perpendicular magnetic anisotropy through the Rashba effect or spin-Hall effect. However, in conventional SOT-based heterostructures, an in-plane bias magnetic field along the current direction is required for the deterministic switching. Here, we report that the field-free SOT switching can be achieved by introducing a wedged oxide interface between a heavy metal and a ferromagnet. The results demonstrate that the field-free SOT switching is determined by a current-induced perpendicular effective field (H z eff) originating from the interfacial Rashba effect due to the lateral structural symmetry-breaking introduced by the wedged oxide layer. Furthermore, we show that the sign and magnitude of H z eff exhibit a significant dependence on the interfacial oxygen content, which can be controlled by the inserted oxide thickness. Our findings provide a deeper insight into the field-free SOT switching by the interfacial Rashba effect.

Tailoring Multilevel‐Stable Remanence States in Exchange‐Biased System through Spin‐Orbit Torque

“…Accordingly, the output signal that represents the multilevel states in MTJs will move from the anomalous Hall resistance to an immediate response in the possible larger TMR variation. Regarding to the elimination of the assistance field in SOT‐tailored magnetic states, there are many methods that could be used to realize the field‐free SOT switching in perpendicularly magnetized materials, such as by introducing a lateral structural asymmetry, [ 45,46 ] engineering a tilted anisotropy, [ 47 ] using interlayer exchange coupling, [ 36,48 ] and even using a magnetic hard mask in the fabrication of SOT‐based MRAM. [ 49 ] Furthermore, although the multilevel remanence states driven by SOT is achieved in a micron‐sized device in this work, the conclusion may be extended to the nanometer‐sized devices based on the previous reports about the double‐biased loops observed in the nanometer scale.…”

Field-free spin-orbit torque-induced switching of perpendicular magnetization in a ferrimagnetic layer with a vertical composition gradient

“…Typically, for memory applications where information is encoded in the direction of the magnetization in magnets with perpendicular magnetic anisotropy (PMA), SOT switching is realized in a non-magnet/ferromagnet (NM/FM) or NM/FIM heterostructure with the assistance of an external in-plane magnetic field H ex along the current direction 1 , 2 , 10 – 12 . SOTs originating from the spin Hall effect (SHE) in the NM (e.g., heavy metals 2 , 10 or topological insulators 11 , 12 ) or from the Rashba effect 1 , 13 at the NM/FM interface can drive the adjacent magnetization to switch, while H ex breaks the in-plane inversion symmetry and leads to a deterministic switching direction for a particular direction of the in-plane current.…”

High‐Efficiency Spin–Orbit Torque Switching Using a Single Heavy‐Metal Alloy with Opposite Spin Hall Angles

“…Moreover, it is known that for perpendicular magnetic anisotropy (PMA) SOT device, an in‐plane magnetic field collinear with the current is often required to break the symmetry between up and down magnetization directions, which cannot meet the need of the practical application. [ 2,24,25 ] Metallic antiferromagnets such as Ir–Mn and Pt–Mn have been shown to serve as the spin current source and as the pinning layer to create exchange bias, [ 10,26–29 ] yet the field‐annealing approach is needed to produce the in‐plane effective field, which will significantly hinder them for practical applications.…”