Spin-transfer torque generated by a topological insulator

Mellnik, Alex; Lee, Joon Sue; Richardella, Anthony; Grab, Jennifer; Mintun, Peter J.; Fischer, Mark H.; Vaezi, Abolhassan; Manchon, Aurélien; Kim, Eunah; Samarth, N.; Ralph, Daniel

doi:10.1038/nature13534

Cited by 1,252 publications

(1,328 citation statements)

References 42 publications

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“…15,16,18,19 Moreover, the performance of spin current generation in the STO/LAO heterostructure is similar or even better than the emerging topological insulator Bi2Se3 with SOT efficiency of ~0.43-3.5. 22,25,26 Our observation further confirms the previous report, which shows a strong current induced Rashba effective field HR with the value of ~1.76 T for a charge current density of JC = 10 5 A/cm 2 . 8 In our STO/LAO/CFB device, there is a ~3.1-nm thin LAO insulting layer separating the STO/LAO spin source and CFB magnetic layer, which is different from previous cases with a direct contact of the heavy metal (or topological insulator) with a ferromagnetic layer.…”

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confidence: 92%

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO₃–LaAlO₃ Oxide Interface

et al. 2017

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Two-dimensional electron gas (2DEG) formed at the interface between SrTiO3 (STO) and LaAlO3 (LAO) insulating layer is supposed to possess strong Rashba spin-orbit coupling. To date, the inverse Edelstein effect (i.e. spin-to-charge conversion) in the 2DEG layer is reported. However, the direct effect of charge-to-spin conversion, an essential ingredient for spintronic devices in a current induced spin-orbit torque scheme, has not been demonstrated yet.Here we show, for the first time, a highly efficient spin generation with the efficiency of ~6.3 in the STO/LAO/CoFeB structure at room temperature by using spin torque ferromagnetic resonance.In addition, we suggest that the spin transmission through the LAO layer at high temperature range is attributed to the inelastic tunneling via localized states in the LAO band gap. Our findings may lead to potential applications in the oxide insulator based spintronic devices.

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confidence: 92%

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO₃–LaAlO₃ Oxide Interface

et al. 2017

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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] .…”

mentioning

confidence: 99%

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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confidence: 99%

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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Spin-transfer torque generated by a topological insulator

Cited by 1,252 publications

References 42 publications

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO₃–LaAlO₃ Oxide Interface

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO₃–LaAlO₃ Oxide Interface

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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Spin-transfer torque generated by a topological insulator

Cited by 1,252 publications

References 42 publications

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO3–LaAlO3 Oxide Interface

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO3–LaAlO3 Oxide Interface

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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Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO₃–LaAlO₃ Oxide Interface

Room-Temperature Giant Charge-to-Spin Conversion at the SrTiO₃–LaAlO₃ Oxide Interface

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