Chiral spin torque at magnetic domain walls

Ryu, Kwang-Su; Thomas, Luc; Yang, See‐Hun; Parkin, Stuart S. P.

doi:10.1038/nnano.2013.102

Cited by 1,136 publications

(1,133 citation statements)

References 29 publications

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“…motion [8][9][10] in recent experiments. Typical heterostructures exhibiting SOTs consist of a ferromagnet (F) with a heavy nonmagnetic metal (NM) having strong spin-orbit coupling on one side, and an insulator (I) on the other side (referred to as NM/F/I structures, shown schematically in Fig.…”

mentioning

confidence: 89%

“…The structural asymmetry in various magnetic heterostructures has been engineered to reveal novel fundamental interactions between electric currents and magnetization, resulting in spin-orbit-torques (SOTs) on the magnetization [1][2][3][4][5][6] , which are both fundamentally important and technologically promising for device applications. Such SOTs have been used to realize current-induced magnetization switching [2][3][4]7 and domain-wall 3 motion [8][9][10] in recent experiments. Typical heterostructures exhibiting SOTs consist of a ferromagnet (F) with a heavy nonmagnetic metal (NM) having strong spin-orbit coupling on one side, and an insulator (I) on the other side (referred to as NM/F/I structures, shown schematically in Fig.…”

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confidence: 99%

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Switching of perpendicular magnetization by spin–orbit torques in the absence of external magnetic fields

et al. 2014

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Breaking of structural symmetries of nanomagnetic systems is of great interest for the development of ultralow-power spintronic devices. The structural asymmetry in various magnetic heterostructures has been engineered to reveal novel fundamental interactions between electric currents and magnetization, resulting in spin-orbit-torques (SOTs) on the magnetization [1][2][3][4][5][6] , which are both fundamentally important and technologically promising for device applications. Such SOTs have been used to realize current-induced magnetization switching [2][3][4]7 and domain-wall 3 motion [8][9][10] in recent experiments. Typical heterostructures exhibiting SOTs consist of a ferromagnet (F) with a heavy nonmagnetic metal (NM) having strong spin-orbit coupling on one side, and an insulator (I) on the other side (referred to as NM/F/I structures, shown schematically in Fig. 1a, which break mirror symmetry in the growth direction). In terms of device applications, the use of SOTs in NM/F/I structures allows for a significantly lower write current compared to regular spin-transfer-torque (STT) devices 4 . It can greatly improve energy efficiency and scalability [1][2][3][4][5]11 for new SOT-based devices such as magnetic random access memory (SOT-MRAM), going beyond state-of-the-art STT-MRAM.For practical applications, a critical requirement to achieve high-density SOT memory is the ability to perform SOT-induced switching without the use of external magnetic fields, in particular for perpendicularly-magnetized ferromagnets, which show better scalability and thermal stability as compared to the in-plane case 12 .However, there are currently no practical solutions that meet this requirement. In NM/F/I heterostructures studied so far, the form of the resultant current-induced SOT alone does not allow for deterministic switching of a perpendicular ferromagnet, requiring application of an additional external in-plane magnetic field to switch the perpendicular magnetization [2][3][4] . (This is a very general feature of SOT devices, which can be explained by symmetry-based arguments, as discussed below). In such experiments, the external field allows for each current direction to favor a particular orientation for the out-of-plane component of magnetization, thereby resulting in deterministic perpendicular switching. However, this external field is undesirable 4 from a practical point of view. For device applications, it also reduces the thermal stability of the perpendicular magnet by lowering the zero-current energy barrier between the stable perpendicular states, resulting in a shorter retention time if used for memory.This work provides a solution to eliminate the use of external magnetic fields, bringing SOT-based spintronic devices such as SOT-MRAM closer to practical application. We present a new NM/F/I structure, which provides a novel spin-orbit torque, resulting in zero-field current-induced switching of perpendicular magnetization. Our device consists of a stack of Ta/Co 20 Fe 60 B 20 /TaO x layers, but also has a...

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Switching of perpendicular magnetization by spin–orbit torques in the absence of external magnetic fields

et al. 2014

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Section: Arxiv:170406402v1 [Cond-matmtrl-sci] 21 Apr 2017mentioning

confidence: 99%

“…However, these experiments only measured the switching probability as a function of pulse amplitude and duration, while the mechanism and the timescale of magnetization reversal remain unknown. Microscopy studies performed using the magneto-optic Kerr effect have extensively probed SOT-induced DW displacements [14][15][16][17][18][19]28 , revealing the role played by the Dzyaloshinskii-Moriya interaction (DMI) in stabilizing chiral DW structures that have very high mobility 17,18,[29][30][31][32][33] . Such investigations have a spatial resolution of the order of 1 µm, but only probed the static magnetization after current injection, similar to the pulsed switching experiments 1,26,27 .…”

Section: Arxiv:170406402v1 [Cond-matmtrl-sci] 21 Apr 2017mentioning

confidence: 99%

“…Such a delay is a major issue for STT devices, since thermal fluctuations result in a switching time distribution that is several ns wide 22,23 . Furthermore, the SOT-induced magnetization dynamics is governed by strong damping in the monodomain regime 24,25 and fast domain wall motion in the multidomain regime [16][17][18] , both favoring rapid reversal of the magnetization.Recent investigations of SOTs in ferromagnet/heavy metal layers showed that reliable switching can be achieved by the injection of current pulses as short as 200 ps in Pt/Co and Ta/CoFeB structures 1,26,27 . However, these experiments only measured the switching probability as a function of pulse amplitude and duration, while the mechanism and the timescale of magnetization reversal remain unknown.…”

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Spatially and time-resolved magnetization dynamics driven by spin–orbit torques

et al. 2017

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Current-induced spin-orbit torques (SOTs) represent one of the most effective ways to manipulate the magnetization in spintronic devices. The orthogonal torquemagnetization geometry, the strong damping, and the large domain wall velocities inherent to materials with strong spin-orbit coupling make SOTs especially appealing for fast switching applications in nonvolatile memory and logic units. So far, however, the timescale and evolution of the magnetization during the switching process have remained undetected. Here, we report the direct observation of SOTdriven magnetization dynamics in Pt/Co/AlO x dots during current pulse injection.Time-resolved x-ray images with 25 nm spatial and 100 ps temporal resolution reveal that switching is achieved within the duration of a sub-ns current pulse by the fast nucleation of an inverted domain at the edge of the dot and propagation of a tilted domain wall across the dot. The nucleation point is deterministic and alternates between the four dot quadrants depending on the sign of the magnetization, current, and external field. Our measurements reveal how the magnetic symmetry is broken by the concerted action of both damping-like and field-like SOT and show that reproducible switching events can be obtained for over 10 12 reversal cycles. arXiv:1704.06402v1 [cond-mat.mtrl-sci] 21 Apr 2017Controlling the magnetic state of ultrathin heterostructures using electric currents is key to developing nonvolatile memory devices with minimal static and dynamic power consumption 1 . A promising approach for magnetic switching is based on injecting an in-plane current into a ferromagnet/heavy metal bilayer, where the spin-orbit torques (SOTs) 2,3 resulting from the spin Hall effect and interface charge-spin conversion 4-8 provide an efficient mechanism to reverse the magnetization 1,9,10,12-15 and manipulate domain walls (DWs) [16][17][18][19] .SOT switching schemes can be easily integrated into three-terminal magnetic tunnel junctions having either in-plane 10 or out-of-plane 20 magnetization. Although the threeterminal geometry is more demanding in terms of size, it offers desirable features compared to the two-terminal spin-transfer torque (STT) approach presently used in magnetic random access memories (MRAM) 21 . One such feature is the separation of the read and write current paths in the tunnel junction, which avoids electrical stress of the oxide barrier during writing and allows for independent optimization of the tunneling magnetoresistance during reading. The other crucial feature is the switching speed, which is expected to be extremely fast because the spin accumulation inducing the SOTs is orthogonal to the quiescent magnetization, leading to a negligible incubation delay. Such a delay is a major issue for STT devices, since thermal fluctuations result in a switching time distribution that is several ns wide 22,23 . Furthermore, the SOT-induced magnetization dynamics is governed by strong damping in the monodomain regime 24,25 and fast domain wall motion in the m...

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