Quantitative characterization of the spin-orbit torque using harmonic Hall voltage measurements

Hayashi, Masamitsu; Kim, Junyeon; Yamanouchi, Michihiko; Ohno, Hideo

doi:10.1103/physrevb.89.144425

Cited by 468 publications

(438 citation statements)

References 51 publications

(72 reference statements)

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“…Figs. 4(a) Since the measured Hall voltages simultaneously include the contributions from the planar Hall effect (PHE) and AHE, the R Hall can be expressed by [33], 2 11 cos sin sin 2 22…”

Section: Resultsmentioning

confidence: 99%

Current-induced magnetization switching in Pt/Co/Ta with interfacial decoration by insertion of Cr to enhance perpendicular magnetic anisotropy and spin–orbit torques

Cui¹,

Chen²,

Liu³

et al. 2017

Appl. Phys. Express

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“…Figs. 4(a) Since the measured Hall voltages simultaneously include the contributions from the planar Hall effect (PHE) and AHE, the R Hall can be expressed by [33], 2 11 cos sin sin 2 22…”

Section: Resultsmentioning

confidence: 99%

Current-induced magnetization switching in Pt/Co/Ta with interfacial decoration by insertion of Cr to enhance perpendicular magnetic anisotropy and spin–orbit torques

Cui¹,

Chen²,

Liu³

et al. 2017

Appl. Phys. Express

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“…In this case, the spin Hall effect at the top and bottom interfaces are expected to work in concert to enhance the total Slonczewski-like torque. We perform harmonic measurements of the current-induced effective fields 21,[28][29][30][31] and characterize current-induced switching in a series of Pt/Co/Ta stacks with PMA. We find that the effective fields and switching efficiency increase significantly with increasing Ta overlayer thickness, yielding an effective spin Hall angle of up to 0.34, which is the largest value observed to date in a metallic system.…”

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Enhanced spin-orbit torques in Pt/Co/Ta heterostructures

Woo

Mann

Tan

et al. 2014

Applied Physics Letters

222

194

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Spin-orbit torques (SOTs) are studied in perpendicularly magnetized ultrathin Co films sandwiched between two heavy metals, Pt and Ta. A significant enhancement of the Slonczewski-like torque is achieved by placing dissimilar metals with opposite spin Hall angles on opposite sides of the ferromagnet. SOTs were characterized through harmonic measurements and the contribution by the Ta overlayer was isolated by systematically varying its thickness. An effective spin Hall angle of up to 34% is observed, along with a sizable field-like torque that increases with increasing Ta layer thickness. Current-induced switching measurements reveal a corresponding increase in switching efficiency, suggesting that by engineering both interfaces in trilayer structures, the SOTs can be significantly improved. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4902529] Current-induced torques in ultrathin ferromagnets sandwiched by a heavy metal and an oxide have been of significant recent interest for highly efficient magnetization switching [1][2][3][4][5][6][7][8] and domain wall motion.9-14 In these systems, strong spinorbit torques (SOTs) can arise through the spin Hall effect (SHE) [2][3][4]13,[15][16][17][18][19] and the Rashba effect 11,[20][21][22][23] at the heavymetal/ferromagnet interface, which can be exploited for lowpower operation of spintronic memory and logic devices. These effects produce both a Slonczewski-like torque [24][25][26] that drives magnetization switching, and a field-like torque 27 whose effective field lies parallel to the interface and orthogonal to the current flow direction. The Slonczewski-like torque is similar to the spin-transfer torque in conventional currentperpendicular-to-plane geometries, and is conveniently parameterized by an effective spin Hall angle h SH , which refers to the ratio of out-of-plane spin current to in-plane charge current. Since the efficiency of SOT switching relates directly to the magnitude of h SH , much effort is currently directed at identifying materials and interfaces for which h SH is large.Pt and Ta have been the most widely examined spin Hall metals due to their relatively high spin Hall angles, $þ0.07 for Pt (Refs. 2, 13, and 17) and $À0.12 to À0.15 for b-Ta (Ref.3) and their simultaneous utility as underlayers that promote perpendicular magnetic anisotropy (PMA) in thin Co and CoFe(B) films. Recent work has aimed to increase the SHE efficiency by seeking other heavy metals and alloys with larger h SH , with a record of þ0.3 having been reported for beta phase W. 4 To date, most work has focused on heavy-metal/ferromagnet/oxide trilayer structures, where the oxide layer plays the role of breaking inversion symmetry, without actively contributing to the SOTs. One could therefore anticipate that by engineering SOTs at both interfaces, the efficiency of current-induced torques could be further increased using already-known spin Hall materials.Here, we examine SOTs in ultrathin Co films sandwiched between two heavy metals, Pt and Ta, whose spin Hall ang...

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“…We defined the longitudinal direction as the direction of the applied current and transverse direction as the directions transverse to the current, as shown in Figure 1(a). The effective field along longitudinal and transverse directions (H L and H T , respectively) can therefore be quantitatively evaluated from the measured V  and V 2 based on the formula derived by Hayashi et al 18 We first evaluated the SOT in the [Co (0.9 nm)/Pt (2 nm)] 8 MLs by adopting the respectively, showing a comparable  L(T) and K eff to the cases with single FM layer, 11,19 but with largely enhanced M S *t, that is, improved thermal stability. 15 Besides, because the  L is 2.6 times larger than the  T , the damping-like torque arisen by the spin current from the giant spin Hall effect of Pt layers should be the main source of the SOT in the Co/Pt MLs.…”

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“…14,15 Although a high SOT has been reported on the Co/Pd MLs recently, 13 no systematic works have been done for explaining the presence of SOT in the multilayers, where the spin currents from heavy metal may counteract each other and no Rashba interaction can be seen without structure inversion asymmetry. By conducting the lock-in technique, [16][17][18] the dependence of SOT efficiencies of the Co/Pt MLs on different repeating layer number (N) is investigated. Besides, Cu and Ta are inserted into the Co/Pt MLs for modifying the interfacial conditions to clarify the origin of SOT in multilayers system and to tune the strength of SOT efficiency.…”

mentioning

confidence: 99%

“…On all of the Hall-bars, we further fabricated the Ta(10 nm)/Pt(100 nm) electrodes by photolithography, DC magnetron sputtering, and lift-off process sequentially to conduct the following measurements. To study the SOT quantitatively, the lock-in measurements with planar Hall effect correction 18 were conducted on the Hall-bar structure for acquiring the in-phase first harmonic (V  ) and the out-of-phase second harmonic (V 2 ) Hall voltages. We defined the longitudinal direction as the direction of the applied current and transverse direction as the directions transverse to the current, as shown in Figure 1(a).…”

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confidence: 99%

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Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy

Huang

Wang

Lin

et al. 2015

Applied Physics Letters

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To address thermal stability issues for spintronic devices with a reduced size, we investigate spin-orbit torque in Co/Pt multilayers with strong perpendicular magnetic anisotropy. Note that the spin-orbit torque arises from the global imbalance of the spin currents from the top and bottom interfaces for each Co layer.By inserting Ta or Cu layers to strengthen the top-down asymmetry, the spin-orbit torque efficiency can be greatly modified without compromised perpendicular magnetic anisotropy. Above all, the efficiency builds up as the number of layers increases, realizing robust thermal stability and high spin-orbit-torque efficiency simultaneously in the multilayers structure.

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Quantitative characterization of the spin-orbit torque using harmonic Hall voltage measurements

Cited by 468 publications

References 51 publications

Current-induced magnetization switching in Pt/Co/Ta with interfacial decoration by insertion of Cr to enhance perpendicular magnetic anisotropy and spin–orbit torques

Current-induced magnetization switching in Pt/Co/Ta with interfacial decoration by insertion of Cr to enhance perpendicular magnetic anisotropy and spin–orbit torques

Enhanced spin-orbit torques in Pt/Co/Ta heterostructures

Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy

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