Efficient orbital torque in polycrystalline 
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 stacks: Theory and experiment

Liao, Liyang; Xue, Fenghua; Han, Lin‐Hai; Kim, Junyeon; Zhang, R. Q.; Li, Lun; Liu, Jiuming; Kou, Xufeng; Song, Cheng; Pan, Feng; Otani, Y.

doi:10.1103/physrevb.105.104434

Cited by 24 publications

(3 citation statements)

References 36 publications

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“…Another important phenomenon is the orbital Hall effect (OHE), which can also generate SOTs, as in the polycrystalline FM/Ru/Al 2 O 3 and FM/Cu/Al 2 O 3 [43,44]. Nevertheless, a relatively small signal of OHE was reported in the polycrystalline NiFe/Ru/Al 2 O 3 sample and the torque efficiency increases with increasing the thickness of the Ru layer from ∼3 to ∼9 nm.…”

Section: St-fmr Measurementmentioning

confidence: 99%

Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control

Song

Scheike

et al. 2023

Nanotechnology

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The demonstration of the spin-charge conversion, especially with enhanced spin Hall conductivity, is crucial for the development of energy-efficient spintronic devices such as spin-orbital torque (SOT) based magnetoresistive random access memories. In this work, fully epitaxial Ru/Cu heterostructures were fabricated with interface engineering and nanolayer insertions consisting of Cu (1nm)/Ru (1nm) structures with different numbers of periods. The atomically controlled interface was confirmed by the high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the epitaxial relationship persists even in the hybrid nanolayer insertion structures. The spin current generation was detected by the measurement of unidirectional spin Hall magnetoresistance, and the effective damping-like spin Hall efficiency (ξ_DL) was further quantitatively evaluated by the spin-torque ferromagnetic resonance with thickness dependence of the ferromagnetic layer. It is found that the sharp interface Ru/Cu film has a sizeable ξ_DL of −2.2% and the insertion of Cu/Ru nanolayers at the interface can increase the ξ_DL value to −3.7%. The former could be attributed to the interface spin-orbit filtering effect and the latter may be further understood by the intrinsic contribution from the local electronic structure tuning due to the lattice distortion near the interface. A large effective spin Hall conductivity is achieved to be (3~5)×10^5 ℏ/2eΩ^(−1)m^(−1) in the epitaxial Ru/Cu hybrid nanolayers, which is in the same range as that of platinum. This work indicates that the interfacial control with hybrid nanolayer structures can extend the SOT-based materials to highly conductive metals, even with weak spin-orbit interactions, toward high stability, low cost, and low energy consumption for spintronic applications.

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Section: St-fmr Measurementmentioning

confidence: 99%

Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control

Song

Scheike

et al. 2023

Nanotechnology

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“…The orbital origin of the long-range torque is further supported by the increase in with t FM observed for the Ni/Pt(10 nm) bilayer, shown in Figure . Recent theoretical and experimental studies have suggested that the orbital torque efficiency increases with t FM because orbital currents can propagate much longer distances than the spin dephasing length in FMs through degenerate orbital hot spots in the momentum space. − ,,− In the Ni/Pt bilayer, the orbital-to-spin current conversion through the SOC near the Ni/Pt interface may also give rise to the current-induced torque. , In this mechanism, the torque arises from the absorption of a spin current, converted from an orbital current, in the FM layer. This predicts that the torque efficiency due to this mechanism is independent of t FM , as in the case of the torque originating from the SHE.…”

mentioning

confidence: 99%

Observation of Long-Range Current-Induced Torque in Ni/Pt Bilayers

Moriya,

Taniguchi,

et al. 2024

Nano Lett.

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The generation of current-induced torques through the spin Hall effect in Pt has been key to the development of spintronics. In prototypical ferromagnetic-metal/Pt devices, the characteristic length of the torque generation is known to be about 1 nm due to the short spin diffusion length of Pt. Here, we report the observation of a longrange current-induced torque in Ni/Pt bilayers. We demonstrate that when Ni is used as the ferromagnetic layer, the torque efficiency increases with the Pt thickness, even when it exceeds 10 nm. The torque efficiency is also enhanced by increasing the Ni thickness, providing evidence that the observed torque cannot be attributed to the spin Hall effect in the Pt layer. These findings, coupled with our semirealistic tight-binding calculations of the current-induced torque, suggest the possibility that the observed long-range torque is dominated by the orbital Hall effect in the Pt layer.

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“…In contrast to spin currents, orbital currents do not precess rapidly and can propagate over longer distances than the spin dephasing length even in metallic ferromagnets. 15,17,[33][34][35][36] The mechanism underlying the long-distance orbital transport is that the orbital angular momentum is carried by limited regions of momentum space where the orbital states that constitute the orbital angular momentum are nearly degenerate. 33) While these electronic states form hot-spots for the orbital transport, the hotspot feature is negligible for the spin component because the exchange splitting is almost constant in momentum space.…”

mentioning

confidence: 99%

Nonlocal orbital torques in magnetic multilayers

Taniguchi¹,

Hayashi²,

Soya³

et al. 2023

Appl. Phys. Express

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We investigate current-induced torques in Ni/Ti/Fe/Ti multilayers. In the multilayers, we find that the damping-like torque acting on the Ni magnetization increases with the thickness of the bottom Ti layer, despite the negligible spin Hall conductivity of Ti and the presence of the Fe interlayer that effectively absorbs the transverse spins. The nonlocal nature of the observed torque is consistent with the orbital torque arising from the orbital Hall effect in the Ti layer and orbital transport through the Fe layer. This observation highlights the unique features of the orbital currents, offering enhanced flexibility in the design of spintronic devices.

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Efficient orbital torque in polycrystalline ferromagnetic−metal/Ru/Al2O3 stacks: Theory and experiment

Cited by 24 publications

References 36 publications

Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control

Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control

Observation of Long-Range Current-Induced Torque in Ni/Pt Bilayers

Nonlocal orbital torques in magnetic multilayers

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