Magnetization switching through giant spin–orbit torque in a magnetically doped topological insulator heterostructure

Fan, Yabin; Upadhyaya, Pramey; Kou, Xufeng; Lang, Murong; Takei, So; Wang, Zhenxing; Tang, Jianshi; He, Liang; Chang, Li‐Te; Montazeri, Mohammad; Yu, Guoqiang; Jiang, Wanjun; Nie, Tianxiao; Schwartz, Robert N.; Tserkovnyak, Yaroslav; Wang, Kang L.

doi:10.1038/nmat3973

Cited by 860 publications

(778 citation statements)

References 37 publications

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“…Since the as-cleaved data showed no enhancement of T C at the surface, the apparent differing values given by TEY and FY likely arise from the short ranged exchange interaction with the ferromagnetic Co overlayer. This finding can be useful for the development of new physical models of Cr-doped Bi 2 Se 3 and their use in, e.g., spintronic devices [6].…”

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confidence: 78%

“…Magnetically doped TIs are host to a wide variety of exotic physical effects, perhaps most notably the recently confirmed quantum anomalous Hall effect (QAHE) [4], which requires the breaking of the TRS through the opening of a gap around the Dirac point [5]. Furthermore, such magnetically doped TIs offer extremely high spin-orbit torques, indicating great potential for spintronic devices [6].…”

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confidence: 99%

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Magnetic proximity-enhanced Curie temperature of Cr-dopedBi2Se3thin films

et al. 2015

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We report a study on the transition temperature T C of Cr-doped topological insulator thin films, where an increase in the ferromagnetic onset can provide a pathway towards low-power spintronics in the future. Arrott plots, measured by surface-sensitive x-ray magnetic circular dichroism at the Cr L 2,3 edge as a function of field at various low temperatures, give a T C ≈ 7 K for the pristine surface. This is comparable to the bulk value of the film, which means that there is no indication that the spontaneous magnetization is different near the surface. Evaporation of a thin layer of Co onto the pristine surface of the in-situ cleaved sample increases the ordering temperature near the surface to ∼19 K, while in the bulk it rises to ∼10 K. X-ray absorption spectroscopy shows that Cr enters the Bi 2 Se 3 host matrix in a divalent state, and is unchanged by the Co deposition. These results demonstrate a straightforward procedure to increase the transition temperature of doped topological insulators.

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confidence: 78%

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Magnetic proximity-enhanced Curie temperature of Cr-dopedBi2Se3thin films

et al. 2015

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“…Popular approaches include passing a spin current through the soft layer to generate a spin transfer torque [2][3][4][5][6][7] or spin orbit torque [8][9][10][11] or domain wall motion [12][13] . Other approaches involve using voltage controlled magnetic anisotropy 14 , magnetoelectric effects [15][16][17] , magnetoionic effects 18 and magnetoelastic effects [19][20][21][22][23][24][25] .…”

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Experimental Demonstration of Complete 180° Reversal of Magnetization in Isolated Co Nanomagnets on a PMN–PT Substrate with Voltage Generated Strain

et al. 2017

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Rotating the magnetization of a shape anisotropic magnetostrictive nanomagnet with voltagegenerated stress/strain dissipates much less energy than most other magnetization rotation schemes, but its application to writing bits in non-volatile magnetic memory has been hindered by the fundamental inability of stress/strain to rotate magnetization by full 180 o . Normally, stress/strain can rotate the magnetization of a shape anisotropic elliptical nanomagnet by only up to 90 o , resulting in incomplete magnetization reversal. Recently, we predicted that applying uniaxial stress sequentially along two different axes that are not collinear with the major or minor axis of the elliptical nanomagnet will rotate the magnetization by full 180 o [1]. Here, we demonstrate this complete 180 o rotation in elliptical Co-nanomagnets (fabricated on a piezoelectric substrate) at room temperature. The two stresses are generated by sequentially applying voltages to two pairs of shorted electrodes placed on the substrate such that the line joining the centers of the electrodes in one pair intersects the major axis of a nanomagnet at ~+30 o and the line joining the centers of the electrodes in the other pair intersects at ~ -30 o . A finite element analysis has been performed to determine the stress distribution underneath the nanomagnets when one or both pairs of electrodes are activated, and this has been approximately incorporated into a micromagnetic simulation of magnetization dynamics to confirm that the generated stress can produce the observed magnetization rotations. This result portends an extremely energy-efficient non-volatile "straintronic" memory technology predicated on writing bits in nanomagnets with electrically generated stress.Nanomagnets are the bedrock of non-volatile memory. A magnetic random access memory (MRAM) cell is implemented with a magneto-tunneling junction (MTJ) consisting of two nanomagnetic layers, one hard and one soft, separated by a spacer (tunneling) layer. The soft layer is often shaped like an elliptical disc which, if sufficiently thick, has two in-plane stable magnetization directions pointing in opposite directions along the major axis of the ellipse. They encode and store the binary bits 0 and 1. The stored bit * Corresponding author. E-mail: sbandy@vcu.edu is "read" by measuring the resistance of the MTJ which has two discrete values depending on the two magnetization orientations of the soft layer, i.e., for the two bits 0 and 1. "Writing" of bits is accomplished by switching the magnetization of the soft layer between the two anti-parallel directions of stable magnetization (180 0 rotation of the magnetization) with an external agent.There are many strategies to rotate the magnetization of the soft layer. Popular approaches include passing a spin current through the soft layer to generate a spin transfer torque 2-7 or spin orbit torque [8][9][10][11] or domain wall motion [12][13] . Other approaches involve using voltage controlled magnetic anisotropy 14 , magnetoelectric effects 15-17 ...

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“…6−9 Recent studies have shown a giant spin−orbit torque in TI originating from the strong spin− orbit interaction, 10,11 which enabled the current-induced magnetization switching through spin-transfer torque with a low current density. The unique feature of 3D TI, for instance, is that it has both insulating bulk and gapless Dirac surface states.…”

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Electrical Detection of Spin-Polarized Surface States Conduction in (Bi_0.53Sb_0.47)₂Te₃ Topological Insulator

et al. 2014

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Strong spin−orbit interaction and time-reversal symmetry in topological insulators enable the spin-momentum locking for the helical surface states. To date, however, there has been little report of direct electrical spin injection/ detection in topological insulator. In this Letter, we report the electrical detection of spin-polarized surface states conduction using a Co/Al 2 O 3 ferromagnetic tunneling contact in which the compound topological insulator (Bi 0.53 Sb 0.47 ) 2 Te 3 was used to achieve low bulk carrier density. Resistance (voltage) hysteresis with the amplitude up to about 10 Ω was observed when sweeping the magnetic field to change the relative orientation between the Co electrode magnetization and the spin polarization of surface states. The two resistance states were reversible by changing the electric current direction, affirming the spin-momentum locking in the topological surface states. Angle-dependent measurement was also performed to further confirm that the abrupt change in the voltage (resistance) was associated with the magnetization switching of the Co electrode. The spin voltage amplitude was quantitatively analyzed to yield an effective spin polarization of 1.02% for the surface states conduction in (Bi 0.53 Sb 0.47 ) 2 Te 3 . Our results show a direct evidence of spin polarization in the topological surface states conduction. It might open up great opportunities to explore energy-efficient spintronic devices based on topological insulators. KEYWORDS: Topological insulator, spin polarization, surface states, spin-momentum locking, spin detection S ince the discovery of two-dimensional (2D) and threedimensional (3D) topological insulators (TIs), 1−5 they have attracted extensive research interest for their exotic physical properties that could lead to dissipationless transport in the quantum spin Hall state. 6−9 Recent studies have shown a giant spin−orbit torque in TI originating from the strong spin− orbit interaction, 10,11 which enabled the current-induced magnetization switching through spin-transfer torque with a low current density. The unique feature of 3D TI, for instance, is that it has both insulating bulk and gapless Dirac surface states. 8,9 Ternary TI compounds, such as (Bi x Sb 1−x ) 2 Te 3 , have been widely investigated for their tunability to achieve low bulk carrier density and manifest topological surface states conduction. 12,13 The presence of surface states is supported by extensive angle-resolved photoemission spectroscopy (ARPES) measurements and transport studies, 14−20 such as Shubnikov-de Haas (SdH) and Aharonov Bohm (AB) quantum oscillations. Because of the strong spin−orbital interaction in TI, direct back scatterings from nonmagnetic impurities are prohibited by the time-reversal symmetry. 8,9 More importantly, the spin-momentum locking naturally leads to a currentinduced spin polarization in surface states; 21 the surface states conduction is spin-polarized once an electric current is passed through a TI film, and this spin polarization can be...

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Magnetization switching through giant spin–orbit torque in a magnetically doped topological insulator heterostructure

Cited by 860 publications

References 37 publications

Magnetic proximity-enhanced Curie temperature of Cr-dopedBi2Se3thin films

Magnetic proximity-enhanced Curie temperature of Cr-dopedBi2Se3thin films

Experimental Demonstration of Complete 180° Reversal of Magnetization in Isolated Co Nanomagnets on a PMN–PT Substrate with Voltage Generated Strain

Electrical Detection of Spin-Polarized Surface States Conduction in (Bi_0.53Sb_0.47)₂Te₃ Topological Insulator

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Magnetization switching through giant spin–orbit torque in a magnetically doped topological insulator heterostructure

Cited by 860 publications

References 37 publications

Magnetic proximity-enhanced Curie temperature of Cr-dopedBi2Se3thin films

Magnetic proximity-enhanced Curie temperature of Cr-dopedBi2Se3thin films

Experimental Demonstration of Complete 180° Reversal of Magnetization in Isolated Co Nanomagnets on a PMN–PT Substrate with Voltage Generated Strain

Electrical Detection of Spin-Polarized Surface States Conduction in (Bi0.53Sb0.47)2Te3 Topological Insulator

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Electrical Detection of Spin-Polarized Surface States Conduction in (Bi_0.53Sb_0.47)₂Te₃ Topological Insulator