Current-induced torque originating from orbital current

Tazaki, Yuya; Kageyama, Yuito; Hayashi, Hiroki; Harumoto, Takashi; Gao, Tenghua; Shi, Ji; Ando, Kotoji

doi:10.48550/arxiv.2004.09165

Cited by 11 publications

(18 citation statements)

References 25 publications

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“…Considering the negligible SOC of Cu*, a conventional SHE-induced SMR cannot lead to the novel MR in the 𝛽𝛽 scan. Also, the spin REE is believed not to be the origin of SOT in Py / Cu* heterostructures [26], and thus the Rashba-Edelstein MR cannot explain the result. From the above considerations, we argue that the OREMR is the most plausible mechanism for the observed MR in the 𝛽𝛽 scan.…”

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confidence: 96%

“…Indeed, the work of Ref. [26] indicates the emergence of the orbital current and orbital torque. The signs for the effective SOT are opposite in Py / Cu / CuOx and Fe / Cu / CuOx, which cannot be explained by the conventional spin current scenario.…”

mentioning

confidence: 99%

“…If the SOC is taken into consideration, the chiral orbital angular momentum texture couples to the spin angular momentum, leading to the coexistence of the spin REE and OREE [19]. Importantly, recent experiments indicate that the natural oxidation of Cu can lead to large SOTs [23][24][25][26], with the interpretation of the results agreeing that the physics of the OREE most likely plays a crucial role in the Cu oxide heterostructures, as the electrical generation of orbital current does not require SOC which is very weak in CuOx [25][26][27]. The surface of the naturally oxidized Cu is electrically insulating and the interface between the metallic ferromagnetic layer (FM) / CuOx is considered vital for the effect [24].…”

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confidence: 99%

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Observation of the Orbital Rashba-Edelstein Magnetoresistance

Ding

Liang

et al. 2022

Phys. Rev. Lett.

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We report the observation of magnetoresistance (MR) originating from the orbital angular momentum transport (OAM) in a Permalloy (Py) / oxidized Cu (Cu*) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The angular dependence of the MR depends on the relative angle between the induced OAM and the magnetization in a similar fashion as the spin Hall magnetoresistance (SMR). Despite the absence of elements with large spin-orbit coupling, we find a sizable MR ratio, which is in contrast to the conventional SMR which requires heavy elements. By varying the thickness of the Cu* layer, we confirm that the interface is responsible for the MR, suggesting that the orbital Rashba-Edelstein effect is responsible for the generation of the OAM. Through Py thickness-dependence studies, we find that the effective values for the spin diffusion and spin dephasing lengths of Py are significantly larger than the values measured in Py / Pt bilayers, approximately by the factor of 2 and 4, respectively. This implies that another mechanism beyond the conventional spin-based scenario is responsible for the MR observed in Py / Cu* structures -originated in a sizeable transport of OAM. Our findings not only unambiguously demonstrate current-induced torques without using any heavy elements via the OAM channel but also provide an important clue towards the microscopic understanding of the role that OAM transport can play for magnetization dynamics.

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confidence: 96%

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confidence: 99%

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confidence: 99%

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Observation of the Orbital Rashba-Edelstein Magnetoresistance

Ding

Liang

et al. 2022

Phys. Rev. Lett.

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“…The orbital current is similar to the spin current in many ways because both orbital angular momentum (OAM) and spin transform in the same way under symmetry operations. Thus, experiments so far have focused on light element systems where the spin current contribution is expected to be negligible [29][30][31][32][33][34], or systems where the orbital and spin currents compete with each other and are opposite in sign [33,35,36]. Although these experiments imply the presence of the orbital current, which can hardly be explained by the spin current picture, they are far from being "direct" confirmations of the orbital current.…”

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confidence: 99%

Long-Range Orbital Magnetoelectric Torque in Ferromagnets

Go¹,

Jo²,

Kim³

et al. 2021

Preprint

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“…[26] strongly supports that an interfacial mechanism is responsible for the SOT when the oxidized Cu is electrically insulating. One of the proposed mechanisms suggests a crucial role of the ORE in surface oxidized Cu, by which "orbital current" is generated and injected into the adjacent ferromagnet [27][28][29]. However, another mechanism based on spin-vorticity coupling has also been proposed [30].…”

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confidence: 99%

Orbital Rashba effect in surface oxidized Cu film

Go,

Jo,

Gao

et al. 2020

Preprint

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Recent experimental observation of unexpectedly large current-induced spin-orbit torque in surface oxidized Cu on top of a ferromagnet suggested a possible role of the orbital Rashba effect (ORE). With this motivation, we investigate the ORE from first principles by considering an oxygen monolayer on top of a Cu(111) film. We show that surface oxidization of Cu film leads to gigantic enhancement of the ORE for states near the Fermi surface. The resulting chiral orbital texture in the momentum space is exceptionally strong, reaching ∼ 0.5h in magnitude. We find that resonant hybridization between O p-states and Cu d-states is responsible for the emergence of the ORE. We demonstrate that application of an external electric field generates huge orbital Hall current, which is an order of magnitude larger than the spin Hall current found in heavy metals. This implies that "orbital torque" mechanism may be significant in surface oxidized Cu/ferromagnet structures. It also encourages experimental verification of the orbital texture in surface oxidized Cu through optical measurements such as angle-resolved photoemission spectroscopy.

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Current-induced torque originating from orbital current

Cited by 11 publications

References 25 publications

Observation of the Orbital Rashba-Edelstein Magnetoresistance

Observation of the Orbital Rashba-Edelstein Magnetoresistance

Long-Range Orbital Magnetoelectric Torque in Ferromagnets

Orbital Rashba effect in surface oxidized Cu film

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