Magnetisation switching dynamics induced by combination of spin transfer torque and spin orbit torque

Abstract

We present a theoretical investigation of the magnetisation reversal process in CoFeB-based magnetic tunnel junctions (MTJs). We perform atomistic spin simulations of magnetisation dynamics induced by combination of spin orbit torque (SOT) and spin transfer torque (STT). Within the model the effect of SOT is introduced as a Slonczewski formalism, whereas the effect of STT is included via a spin accumulation model. We investigate a system of CoFeB/MgO/CoFeB coupled with a heavy metal layer where the charge current is injected into the plane of the heavy metal meanwhile the other charge current flows perpendicular into the MTJ structure. Our results reveal that SOT can assist the precessional switching induced by spin polarised current within a certain range of injected current densities yielding an efficient and fast reversal on the sub-nanosecond timescale. The combination of STT and SOT gives a promising pathway to improve high performance CoFeB-based devices with high speed and low power consumption.

Spin-orbit torque switching of magnetic tunnel junctions for memory applications

“…Importantly for device operation, the dispersion of these parameters recorded over long sequences of singleshot switching events also narrows down significantly. It remains an open question to what extent these observations will remain valid in MTJs scaled down to the limit of macrospin switching [214].…”

Spin-transfer and spin-orbit torques in the Landau-Lifshitz-Gilbert equation

“…2(a). Given the small dimensions of the system we expect coherent behaviour [15,28] and therefore we can model the system as a single macrospin, representing the FL of thickness 1.3 nm. We model the CoFeB/MgO MTJ [3] as characterised by M s ∼ 1.3 T [29], an interfacial anisotropy energy of 1.3 mJ/m 2 , spintorque efficiency η ∼ 0.6 and spin-torque asymmetry λ = η 2 .…”

“…Recently it has been proposed to combine spin-transfer torque and spin-orbit torque in a single device in order to complement the weaknesses of both [23,28,[31][32][33][34][35]. We consider the same 20 nm cylindrical CoFeB/MgO MTJ previously used to investigate the STT-induced dynamics, where the reference layer is magnetized along p = ẑ, the FL has the magnetisation initially aligned along −ẑ and the current density used to generate a spin-transfer torque is injected perpendicular to the MTJ stack.…”

“…We consider the same 20 nm cylindrical CoFeB/MgO MTJ previously used to investigate the STT-induced dynamics, where the reference layer is magnetized along p = ẑ, the FL has the magnetisation initially aligned along −ẑ and the current density used to generate a spin-transfer torque is injected perpendicular to the MTJ stack. Differently from the previous works [28,34], here we apply the STT and SOT current pulses for the same time given the simplicity of our model and the short time scale considered. We place a Pt contact on top of the FL to generate spin current via SHE and induce switching in the FL via SOT; this is obtained by injecting a current density along ŷdirection.…”

Probing spin dynamics of ultra-thin van der Waals magnets via photon-magnon coupling

“…The upper limit of the Gilbert damping in the 15 ML thick CGT flake is determined to be 0.021, which is comparable to commonly used ferromagnetic thin-films such as NiFe and CoFeB and thus making CGT attractive for similar device applications. We highlight that the damping parameter is key in precessional magnetisation switching 45,46 , auto-oscillations by dc currents 47,48 , and comprehensive spin-orbit transport in vdW magnetic systems 49 . The presented techniques are readily transferable to other vdW magnetic systems to study spin dynamics in atomically-thin crystalline materials.…”