Large interfacial contribution to ultrafast THz emission by inverse spin Hall effect in CoFeB/Ta heterostructure

Kumar, Sandeep; Kumar, Sunil

doi:10.1016/j.isci.2022.104718

Cited by 10 publications

(12 citation statements)

References 67 publications

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“…For the reference sample of Pt (3)/CoFe (6)/Al (3) with one FM layer, the peak THz value shows a slight decrease at low T . Considering that the spin current density j s is weakly dependent on the temperature, this reduction mainly arises from the increase of the overall film conductivity σ and the intrinsic spin Hall conductivity σ SH of Pt. , Intriguingly, the two SAF samples show remarkably different varying trends with decreasing T . In spite of the similar increasing tendency of σ SH and σ to the reference sample, the normalized THz amplitude increases considerably by 50% for the sample of t Ru = 0.9 nm governed by bilinear coupling.…”

Section: Measurement Results and Discussionmentioning

confidence: 99%

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets

Song,

Ji,

Zhang

et al. 2023

ACS Appl. Mater. Interfaces

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Spintronic terahertz (THz) emitters based on synthetic antiferromagnets (SAFs) of FM 1 /Ru/FM 2 (FM: ferromagnet) have shown great potential for achieving coherent superposition and significant THz power enhancement due to antiparallel magnetization alignment. However, key issues regarding the effects of interlayer exchange coupling and net magnetization on THz emissions remain unclear, which will inevitably hinder the performance improvement and practical application of THz devices. In this work, we have investigated the femtosecond laser-induced THz emission in Pt (3)/CoFe (3)/Ru (t Ru = 0−3.5)/CoFe (t CoFe = 1.5−10)/Pt (3) (in units of nm) films with compensated and uncompensated magnetic moments. Antiferromagnetic (AF) coupling occurs in the Ru thickness ranges of 0.2−1.1 and 1.9−2.3 nm, with the first peak (t Ru = 0.4 nm) of the AF coupling field (H ex ) significantly higher than that of the second peak (2.0 nm). Rather high THz amplitude is found for the samples with strong AF coupling. Nevertheless, despite the same remanence ratio of zero, the THz amplitude for the symmetric SAF films declines significantly as the t Ru decreases from 0.8 to 0.4 nm, which is mainly ascribed to the noncolinear magnetization vectors due to the increased biquadratic coupling term. Specifically, we demonstrate that an asymmetric SAF structure with a dominant FM layer is more favored than the completely compensated one, which could generate significantly enhanced THz electric field with well-controlled polarity and intensity. In addition, as the temperature decreases, the THz emission intensity increases for the SAF samples of t Ru = 0.9 nm with negligible biquadratic coupling, which is contrary to the decreasing trend of the t Ru = 0.4 nm sample and has been attributed to the greatly enhanced H ex .

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Section: Measurement Results and Discussionmentioning

confidence: 99%

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets

Song,

Ji,

Zhang

et al. 2023

ACS Appl. Mater. Interfaces

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“…Temperature-dependent studies 61 – 63 have been proven to be important in identifying various scattering mechanisms in the materials and subsequent determination of respective Hall conductivities. To validate the IOHE origin of the THz emission from NiFe/Nb bilayer, we have performed temperature-dependent experiments by monitoring the changes in the peak-to-peak amplitude of the THz signal as a function of the sample temperature (T) from 10 K to 300 K. The temperature sensitivity of the phonon scattering would have a significant impact on the OHE and associated phenomena because the orbital degree of angular momentum is strongly coupled with the crystal field potential 13 , 20 .…”

Section: Resultsmentioning

confidence: 99%

“…See Supplementary Section S10 for details to obtain . In the light of a temperature scaling relation 61 – 64 the spin Hall resistivity ( ) is expressed as, …”

Section: Resultsmentioning

confidence: 99%

Ultrafast THz probing of nonlocal orbital current in transverse multilayer metallic heterostructures

Kumar,

Kumar

2023

Nat Commun

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THz generation from femtosecond photoexcited spintronic heterostructures has become a versatile tool for investigating ultrafast spin-transport and transient charge-current in a non-contact and non-invasive manner. The equivalent effect from the orbital degree of freedom is still in the primitive stage. Here, we experimentally demonstrate orbital-to-charge current conversion in metallic heterostructures, consisting of a ferromagnetic layer adjacent to either a light or a heavy metal layer, through detection of the emitted THz pulses. Our temperature-dependent experiments help to disentangle the orbital and spin components that are manifested in the respective Hall-conductivities, contributing to THz emission. NiFe/Nb shows the strongest inverse orbital Hall effect with an experimentally extracted value of effective intrinsic Hall-conductivity, $${({\sigma }_{{SOH}}^{{{{{\mathrm{int}}}}}})}^{{eff}} \sim 195{\varOmega }^{-1}{{cm}}^{-1}$$ ( σ S O H int ) e f f ~ 195 Ω − 1 c m − 1 , while CoFeB/Pt shows maximum contribution from the inverse spin Hall effect. In addition, we observe a nearly ten-fold enhancement in the THz emission due to pronounced orbital-transport in W-insertion heavy metal layer in CoFeB/W/Ta heterostructure as compared to CoFeB/Ta bilayer counterpart.

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“…Time-domain THz emission spectroscopy has evolved in recent times as an alternate technique [18] which can help determine various physical properties of the carriers in condensed matter systems including the 3dTIs [3,[19][20][21] in a noncontact and non-invasive manner. It is inquisitive to determine the temperature dependent role of the ultrafast photocarriers in 3dTIs and exploit the possibility to decipher the contribution of the topological surface states in the overwhelming response from the bulk states of these systems.…”

Section: Introductionmentioning

confidence: 99%

Unveiling surface and bulk contributions in temperature dependent THz emission from Bi₂Te₃

Nivedan,

Kumar

2024

New J. Phys.

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We report evolution of the pulsed terahertz (THz) emission from Bi2Te3 topological insulator in a wide temperature range, where an interplay between the surface and bulk contributions can be addressed in a distinguishable manner. A circular photogalvanic effect-induced surface current contribution to THz generation can be clearly identified in the signal, otherwise, overwhelmed by the hot carrier decoherence in the bulk states. With the decreasing temperature, an initial sharp increase in the surface THz signal is observed before it attains a constant value below ~200 K. The bulk-to-surface scattering channels via carrier-phonon scattering are dominant only above the bulk-Debye temperature of ~180 K, and the temperature-independent behavior of it at lower temperatures is indicative of robust nature of topological surface states. THz emission due to ultrafast photon drag current in the bulk states is almost independent of temperature in the entire range, while the combined photo-Dember and band-bending effects induced photocurrent is doubled at 10 K.

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Large interfacial contribution to ultrafast THz emission by inverse spin Hall effect in CoFeB/Ta heterostructure

Cited by 10 publications

References 67 publications

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets

Ultrafast THz probing of nonlocal orbital current in transverse multilayer metallic heterostructures

Unveiling surface and bulk contributions in temperature dependent THz emission from Bi₂Te₃

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Large interfacial contribution to ultrafast THz emission by inverse spin Hall effect in CoFeB/Ta heterostructure

Cited by 10 publications

References 67 publications

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets

Ultrafast THz probing of nonlocal orbital current in transverse multilayer metallic heterostructures

Unveiling surface and bulk contributions in temperature dependent THz emission from Bi2Te3

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Unveiling surface and bulk contributions in temperature dependent THz emission from Bi₂Te₃