Room-Temperature Spin-Orbit Torque from Topological Surface States

Wu, Hao; Zhang, Peng; Deng, Peng; Lan, Quan; Pan, Quanjun; Wang, Kang L.; Che, Xiaoyu; Li, Huang; Dai, Bingqian; Wong, Kin; Han, X. F.

doi:10.1103/physrevlett.123.207205

Cited by 156 publications

(129 citation statements)

References 45 publications

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“…Finally, we argue that these magnetization switching features are consistent with current-induced dynamics of the spin-momentumlocked TI surface state as the dominant source of the spin torques [11][12][13][14][15][16][17][18][19] . First, possibilities for the source of the spin torques other than the topological surface states may include the spin Hall effect from the bulk bands 34 and the inversion symmetry breaking of the hetero-interface, where a vertical electric field at the interface can induce Rashba spin splitting in the bulk states 35 .…”

Section: Discussionsupporting

confidence: 62%

“…Owing to the spinmomentum locking of the electrons at the TI surface state 9,10 , the flow of electrons produces nonequilibrium spin accumulation, which exerts spin torques on a FM layer adjacent to the TI surface 11,12 . The current-induced switching of the perpendicular magnetization in the FM layer in conjunction with a TI has been demonstrated in a highly efficient manner with lower critical current densities than those in FM-metal/heavy-metal heterostructures [13][14][15][16][17][18][19] . Moreover, the spin accumulation may also enable the electrical manipulation of the TI surface ferromagnetism that originates from the FM proximity coupling at the FM-layer/TI interface.…”

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confidence: 99%

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Current-induced switching of proximity-induced ferromagnetic surface states in a topological insulator

et al. 2021

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Electrical manipulation of magnetization could be an essential function for energy-efficient spintronics technology. A magnetic topological insulator, possessing a magnetically gapped surface state with spin-polarized electrons, not only exhibits exotic topological phases relevant to the quantum anomalous Hall state but also enables the electrical control of its magnetic state at the surface. Here, we demonstrate efficient current-induced switching of the surface ferromagnetism in hetero-bilayers consisting of the topological insulator (Bi1-xSbx)2Te3 and the ferromagnetic insulator Cr2Ge2Te6, where the proximity-induced ferromagnetic surface states play two roles: efficient charge-to-spin current conversion and emergence of large anomalous Hall effect. The sign reversal of the surface ferromagnetic states with current injection is clearly observed, accompanying the nearly full magnetization reversal in the adjacent insulating Cr2Ge2Te6 layer of an optimal thickness range. The present results may facilitate an electrical control of dissipationless topological-current circuits.

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Section: Discussionsupporting

confidence: 62%

mentioning

confidence: 99%

Current-induced switching of proximity-induced ferromagnetic surface states in a topological insulator

et al. 2021

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“…In our experiments, the SOT magnetization switching was performed by sweeping an in-plane external magnetic field H x under a constant DC current, or sweeping a DC/pulse current under a constant H x . For quantitative evaluation of the effective spin Hall angle in the BiSb layers, we employed the second harmonic Hall measurement with an AC current while sweeping H x 19 , 24 , 36 . Figure 1 d shows the Hall resistance of a 25 μm-wide Hall bar of sample A and B under a perpendicular magnetic field H z , which show clear perpendicular magnetic anisotropy of the CoTb layer.…”

Section: Resultsmentioning

confidence: 99%

Ultralow power spin–orbit torque magnetization switching induced by a non-epitaxial topological insulator on Si substrates

Khang

Nakano

Shirokura

et al. 2020

Sci Rep

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The large spin Hall effect in topological insulators (TIs) is very attractive for ultralow-power spintronic devices. However, evaluation of the spin Hall angle and spin-orbit torque (SOT) of TIs is usually performed on high-quality single-crystalline TI thin films grown on dedicated III-V semiconductor substrates. Here, we report on room-temperature ultralow power SOT magnetization switching of a ferrimagnetic layer by non-epitaxial BiSb TI thin films deposited on Si/SiO 2 substrates. We show that non-epitaxial BiSb thin films outperform heavy metals and other epitaxial TI thin films in terms of the effective spin Hall angle and switching current density by one to nearly two orders of magnitude. The critical SOT switching current density in BiSb is as low as 7 × 10 4 A/cm 2 at room temperature. The robustness of BiSb against crystal defects demonstrate its potential applications to SOT-based spintronic devices. Charge-to-spin conversion utilizing the strong spin-orbit coupling (SOC) in non-magnetic materials has become a very attractive concept with possible applications to various spintronic devices, such as spin-orbit torque (SOT) magnetoresistive random access memories (MRAM) 1 , racetrack memories 2 , and spin torque nano-oscillators 3,4. These SOT-based spintronic devices are superior to their spin-transfer torque (STT)-based counterparts in terms of driving current, speed, and long-term durability 5,6. In SOT-based devices, a perpendicular pure spin current density J s is generated by an in-plane charge current density J e in the non-magnetic layer through the spin Hall effect (SHE) 7-9 , whose charge-to-spin conversion efficiency is characterized by the spin Hall angle θ SH = (2e/ℏ) J s /J e. Thus, finding spin Hall materials with large θ SH and high electrical conductivity is crucial for SOT applications, and there have been huge efforts so far to achieve that goal. In the well-studied heavy metals (HMs) such as Pt 10-13 , Ta 14 , and W 15-17 , θ SH is of the order of ~ 0.1, and the typical critical switching current density J c in bilayers of heavy metals/ferromagnet with perpendicular magnetic anisotropy is typically of the order of 10 7 A/cm 2 for continuous direct currents (DC) and 10 8 A/cm 2 for nano-second (ns) pulse currents. The large switching current density requires large driving transistors, whose size limits the bit density of SOT-MRAM. Meanwhile, large θ SH (> 1) have been observed in topological insulators (TIs) 18,19 thanks to their strong SOC and Dirac-point-driven singularity of the Berry phase on their topologically protected surface states 20. Thus, significant reduction of the driving current density from 10 7-10 8 A/cm 2 to 10 5-10 6 A/cm 2 can be expected for SOT-based devices 21-25 , particularly in SOT-MRAM whose their large writing current density is the major obstacle for reducing the writing power consumption and increasing the bit density. However, evaluation of θ SH and SOT switching by TIs is usually performed on single-crystalline TI thin films deposited on dedicated III-V...

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“…However, the magnetic anisotropy of the commonly used high-T C materials (e.g., CoFeB and Py) strongly relies on the interfacial conditions, and it usually favors an in-plane orientation when the FM thin film is directly grown on the TI layer [89]. To address the challenge, one can insert a light metal spacer (i.e., ~2 nm Mo or Ti) to form the TI/Ti(Mo)/CoFeB/ MgO multilayer structures so that interfacial PMA can be established while keeping the spin current in the TI layer (Figure 10a) [90,91]. Alternatively, by depositing bulk PMA material (e.g., ferrimagnetic alloy Co x Tb 1-x with optimized Co-to-Tb ratio), room-temperature SOT switching has also been observed in the Bi 2 Se 3 /CoTb/SiN x stacks [92].…”

Section: Ti-based Magnetic Heterostructures For Spintronics Applicationsmentioning

confidence: 99%

Topological insulators-based magnetic heterostructures

Yao

Chen

et al. 2021

Advances in Physics: X

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The combination of magnetism and topology in magnetic topological insulators (MTIs) has led to unprecedented advancements of time reversal symmetry-breaking topological quantum physics in the past decade. Compared with the uniform films, the MTI heterostructures provide a better framework to manipulate the spin-orbit coupling and magnetic/spin properties. In this review, we summarize the fundamental mechanisms related to the physical orders host in (Bi,Sb) 2 (Te,Se) 3 -based hybrid systems. Besides, we provide an assessment on the general strategies to enhance the magnetic coupling and spin-orbit torque strength through different structural engineering approaches and effective interfacial interactions. Finally, we offer an outlook of MTI heterostructures-based spintronics applications, particularly in view of their feasibility to achieve room-temperature operation.

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Room-Temperature Spin-Orbit Torque from Topological Surface States

Cited by 156 publications

References 45 publications

Current-induced switching of proximity-induced ferromagnetic surface states in a topological insulator

Current-induced switching of proximity-induced ferromagnetic surface states in a topological insulator

Ultralow power spin–orbit torque magnetization switching induced by a non-epitaxial topological insulator on Si substrates

Topological insulators-based magnetic heterostructures

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