Deterministic field-free switching of a perpendicularly magnetized ferromagnetic layer via the joint effects of the Dzyaloshinskii–Moriya interaction and damping- and field-like spin–orbit torques: an appraisal

Abstract

Field-free switching of perpendicularly magnetized ferromagnetic layer by spin orbit torque (SOT) from the spin Hall effect (SHE) is of great interest in the applications of magnetic memory devices. In this paper, we investigate the deterministic SOT switching through the joint effects of Dzyaloshinskii-Moriya Interaction (DMI) and field-like torque (FLT) by micromagnetic simulations. We confirmed that within a certain range of DMI values and charge current densities, it is possible to deterministically switch the magnetization without the assistance external magnetic field. We show that the FLT could play an adverse role in blocking and slowing down the magnetization switching under certain cases of DMI and charge current-driven field-free switching.However, in other cases, FLT can assist DMI on the deterministic field-free SOT switching. In addition, it is found that FLT can effectively expand the current density window for a deterministic field-free SOT switching in the presence of DMI.

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

“…We note that this value is very close to the absolute value of applied in-plane H ex (-20 Oe, see Fig. 3b) where magnetization switching vanishes, which is consistent with the hypothesis that the g-DMI-induced effective field is responsible for the observed field-free switching [33][34][35].…”

“…5b shows the time evolution of the average z component of the magnetization for the first sublattice (black line) together with the timing of the two current pulses. As observed in previous numerical studies [33][34][35]59], the deterministic switching starts with the nucleation of a domain at the edge of the sample because of the magnetization tilting toward an in-plane direction imposed by the DMI boundary conditions (see Fig. 5a).…”

“…domain walls and skyrmions) with broken chiral symmetry [29][30][31][32]. Therefore, DMI has recently been theoretically proposed as a symmetry-breaking mechanism which, in combination with damping-like and field-like SOTs, may enable deterministic switching in the absence of an external field [33][34][35]. However, this type of field-free combined DMI-SOT switching has not been experimentally observed to date.…”

Prospect of Spin-Orbitronic Devices and Their Applications

“…Despite the successful laboratory demonstration of the above proposals for field-free SOT-induced magnetization switching, however, the further high-demanding optimization on the their industrial applicability is required since most of these methods involve either an in-plane FM, a canted magnetization in the PMA-FM, unconventional device shapes or structures, or multiterminal (terminal number >3) devices, which may challenge the fabrication feasibility or data scalability of an external field-free SOT-MRAM. Competing spin currents from the Pt/W bilayers with opposite signs in the spin Hall angle was reported as an integration-friendly method for realizing field-free SOT induced magnetization switching in Pt/W/PMA-FM structures with proper Ta and Pt thicknesses ( Ma et al., 2018 ), but the underlying mechanism is still unclear ( Chen et al., 2020a ; Wu et al., 2020b ), which is hard to gain deeper insights into any of the above four symmetry breaking ways. Most recent data on deterministic SOT-induced magnetization switching by inserting a slightly asymmetric light-metal layer between the HM and the FM interface was also claimed as a quite scalable approach, the exact explanation of which remains elusive as well ( Razavi et al., 2020 ), since counter-intuitive uniform PMA was observed across all devices on the wafer.…”

Lack of Simple Correlation between Switching Current Density and Spin-Orbit-Torque Efficiency of Perpendicularly Magnetized Spin-Current-Generator–Ferromagnet Heterostructures

“…[2]. The physics at work might also depend on other material factors, including the Dzyaloshinskii-Moriya interaction and/or the magnetic damping [47], which requires future efforts to understand.…”