Single-shot dynamics of spin–orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions

Abstract

Current-induced spin-transfer torques (STT) and spin-orbit torques (SOT) enable the electrical switching of magnetic tunnel junctions (MTJs) in nonvolatile magnetic random access memories. In order to develop faster memory devices, an improvement of the timescales underlying the currentdriven magnetization dynamics is required. Here we report all-electrical time-resolved measurements of magnetization reversal driven by SOT in a three-terminal MTJ device. Single-shot measurements of the MTJ resistance during current injection reveal that SOT switching involves a stochastic two-step process consisting of a domain nucleation time and propagation time, which have different genesis, timescales, and statistical distributions compared to STT switching. We further show that the combination of SOT, STT, and voltage control of magnetic anisotropy (VCMA) leads to reproducible sub-ns switching with a spread of the cumulative switching time smaller than 0.2 ns. Our measurements unravel the combined impact of SOT, STT, and VCMA in determining the switching speed and efficiency of MTJ devices. Switching nanomagnets by current injection offers unparalleled scalability, as well as low power and high speed operation compared to control via external magnetic fields 1-3. Spin-transfer torques (STT) 1,4 are presently employed in memory and spin logic applications 5,6 to control the state of magnetic tunnel junctions (MTJ) via an electric current passing through the reference and free magnetic layers, which allows also for efficient readout of the MTJ through the tunnel magnetoresistance (TMR). Time-resolved studies of magnetization reversal in spin valve 7,8 and MTJ devices 9-12 have shown that STT enables switching on a timescale of 100 to 1 ns, depending on the driving current 13 and external field 14. However, STT switching is characterized by nonreproducible dynamic paths and incubation times up to several tens of ns long, which limit the reliability and speed of the reversal process to about 10-20 ns, even when mitigation strategies based on large driving currents or noncollinear spin injection are employed 13,15,16. These limitations may be overcome by magnetization reversal driven by spin-orbit torques (SOT) 3,17-19 , which has been recently demonstrated in three-terminal MTJs with in-plane 20,21 as well as out-of-plane magnetization 22-25. SOT switching combines an in-plane current injection geometry with charge-to-spin conversion due to the spin Hall effect and interfacial spin scattering 3. Such a geometry decouples the write and read current paths, improving the MTJ endurance and operation speed by minimizing electrical stress of the tunnel barrier and allowing for tuning the barrier thickness for high TMR, fast read-out, and minimal read disturbances. Moreover, in devices with perpendicular magnetization, the injected spin current is orthogonal to the quiescent magnetization of the free layer, thus providing an "instant on" torque that is expected to minimize the switching incubation time 25-27 .

Prospect of Spin-Orbitronic Devices and Their Applications

“…In a broad sense, spintronic probabilistic devices are not limited to the fluctuated LBNMs. The stochastic behaviors can also be found in non-deterministic current-induced magnetization switching processes ( Grimaldi et al., 2020 ), enabling to be exploited for probabilistic computing. Particularly, since thermal activation plays an important role in the STT-induced switching dynamics, the magnetization is not amenable to be switched at a low current regime and the switching probability increases with growing current density and pulse duration.…”

“…One basic idea is to adjust the interlayer coupling field direction by magnetically or electrically pre-magnetizing the in-plane FM pinning layer within the “T-type” magnetically coupled HM/PMA-FM free layer/spacer layer/in-plane FM pinning layer stacks ( Sheng et al., 2018a ; Wan et al., 2017 ; Wang et al., 2018b ), as shown in Figure 5 A. Typically, the voltage-controlled magnetic anisotropy (VCMA) in the FM ( Lee et al., 2016 ; Baek et al., 2018b ; Wang, 2018 ; Grimaldi et al., 2020 ) (i.e., Figure 5 B), as well as the gate-voltage tunable spin-orbit current from either a metal oxide ( Mishra et al., 2019 ) as illustrated in Figure 5 C, semiconductor ( Chen et al., 2018b ), a van der Waals crystal ( Benitez et al., 2020 ), or a topological insulator ( Fan et al., 2016 ), provides a class of powerful electrical manipulation methods for programmable spin-orbit logics. Besides, introducing other multiferroic behaviors beyond the ferromagnetism, such as the ferroelectric/HM/FM heterostructure ( Cai et al., 2017 ; Belopolski et al., 2019 ; Filianina et al., 2020 ; Noël et al., 2020 ; Fang et al., 2020 ) (see Figure 5 D) and the novel proposal of magnetoelectric spin-orbit logics (MESO, see Figure 5 E), can also bring additional nonvolatile freedoms for realizing all electrically programmable functionalities ( Manipatruni et al., 2019 ).…”

Route Towards Efficient Magnetization Reversal Driven by Voltage Control of Magnetic Anisotropy

“…Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG-SPINTEC, 38000 Grenoble, France. 3 Technical University of Cluj-Napoca, Cluj-Napoca, Romania. * Corresponding authors: coriolan.tiusan@phys.utcluj.ro, liliana.buda@cea.fr…”

“…In an era dominated by an increasing demand of information processing speed and efficient information storage, spintronics can offer novel solutions to circumvent some of the limitations presently reached by conventional microelectronics technologies [1] [2] [3]. In the last decade, magnetization manipulation by electric fields entered the race for energy efficient methods for information storage when the very first mentions of electric field manipulation of magnetization in ferromagnetic semiconductors and 3d metals opened this research direction [4] [5].…”

Optoelectronic domain-wall motion for logic computing

“…ΔT from laser shining. 21 The reduction of some magnetic parameters upon increasing temperature, 22 which will contribute to a larger domain-wall depinning probability and motion velocity, is not included in our simulations. But we note that overall functionalities that we demonstrated in this work remain valid though the required laser fluence or SOT current density could be lower.…”