| 1. |
- Bainsla, Lakhan, 1985, et al.
(författare)
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Large out-of-plane spin-orbit torque in topological Weyl semimetal TaIrTe 4
- 2024
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Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1, s. 4649-
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Tidskriftsartikel (refereegranskat)abstract
- The unique electronic properties of topological quantum materials, such as protected surface states and exotic quasiparticles, can provide an out-of-plane spin-polarized current needed for external field-free magnetization switching of magnets with perpendicular magnetic anisotropy. Conventional spin-orbit torque (SOT) materials provide only an in-plane spin-polarized current, and recently explored materials with lower crystal symmetries provide very low out-of-plane spin-polarized current components, which are not suitable for energy-efficient SOT applications. Here, we demonstrate a large out-of-plane damping-like SOT at room temperature using the topological Weyl semimetal candidate TaIrTe4 with a lower crystal symmetry. We performed spin-torque ferromagnetic resonance (STFMR) and second harmonic Hall measurements on devices based on TaIrTe4/Ni80Fe20 heterostructures and observed a large out-of-plane damping-like SOT efficiency. The out-of-plane spin Hall conductivity is estimated to be (4.05 ± 0.23)×104 (ℏ ⁄ 2e) (Ωm)-1, which is an order of magnitude higher than the reported values in other materials.
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| 2. |
- Bainsla, Lakhan, et al.
(författare)
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Spin-orbit torques in Co2MnGa magnetic Weyl semimetal thin films
- 2023
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Ingår i: 2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings. - 9798350338362
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Konferensbidrag (refereegranskat)abstract
- Due to the nontrivial topology in their electronic band structure, topological quantum materials are known to exhibit unconventional surface states and anomalous transport properties. In the present study, the ferromagnetic Heusler alloy Co2MnGa, which breaks time-reversal symmetry, is studied to estimate its spin-orbit torque efficiency. Epitaxial thin films with high structural ordering are obtained, which show very high values of anomalous Hall conductivity. A spin-orbit torque efficiency of 0.13±0.01 is obtained in a 20 nm Co2MnGa film. The present results open the possibility to use these exotic materials in spintronic devices and beyond.
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| 3. |
- Bainsla, Lakhan, et al.
(författare)
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Ultrathin Ferrimagnetic GdFeCo Films with Low Damping
- 2022
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 32:23, s. 2111693-
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Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic materials dominate as the magnetically active element in spintronic devices, but come with drawbacks such as large stray fields and low operational frequencies. Compensated ferrimagnets provide an alternative as they combine the ultrafast magnetization dynamics of antiferromagnets with a ferromagnet-like spin-orbit-torque behavior. However, to use ferrimagnets in spintronic devices their advantageous properties must be retained also in ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1−x thin films in the thickness range t = 2–20 nm are grown on high resistance Si(100) substrates and studied using broadband ferromagnetic resonance measurements at room temperature. By tuning their stoichiometry, a nearly compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1−x ultrathin films for the first time, with an effective magnetization of (Formula presented.) = 0.02 T and a low effective Gilbert damping constant of α = 0.0078, comparable to the lowest values reported so far in 30 nm films. These results show great promise for the development of ultrafast and energy efficient ferrimagnetic spintronic devices.
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| 4. |
- Behera, Nilamani, et al.
(författare)
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Energy-Efficient W100-xTax/ Co-Fe-B/MgO Spin Hall Nano-Oscillators
- 2022
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Ingår i: Physical Review Applied. - 2331-7019. ; 18:2
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Tidskriftsartikel (refereegranskat)abstract
- We investigate a W-Ta alloying route to reduce the auto-oscillation threshold current densities and the power consumption of nanoconstriction based spin Hall nano-oscillators. Using spin-torque ferromagnetic resonance measurements on microbars of W100-xTax(5 nm)/Co-Fe-B(t)/MgO stacks with t=1.4, 1.8, and 2.0 nm, we measure a substantial improvement in both the spin-orbit torque efficiency and the spin Hall conductivity. We demonstrate a 34% reduction in auto-oscillation threshold current density, which translates into a 64% reduction in power consumption as compared with pure W-based spin Hall nano-oscillators. Our work demonstrates the promising aspects of W-Ta alloying for the energy-efficient operation of emerging spintronic devices.
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| 5. |
- Behera, Nilamani, et al.
(författare)
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Ultra-Low Current 10 nm Spin Hall Nano-Oscillators
- 2024
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Ingår i: Advanced Materials. - 0935-9648 .- 1521-4095. ; 36:5
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Tidskriftsartikel (refereegranskat)abstract
- Nano-constriction based spin Hall nano-oscillators (SHNOs) are at the forefront of spintronics research for emerging technological applications, such as oscillator-based neuromorphic computing and Ising Machines. However, their miniaturization to the sub-50 nm width regime results in poor scaling of the threshold current. Here, it shows that current shunting through the Si substrate is the origin of this problem and studies how different seed layers can mitigate it. It finds that an ultra-thin Al2O3 seed layer and SiN (200 nm) coated p-Si substrates provide the best improvement, enabling us to scale down the SHNO width to a truly nanoscopic dimension of 10 nm, operating at threshold currents below 30 (Formula presented.) A. In addition, the combination of electrical insulation and high thermal conductivity of the Al2O3 seed will offer the best conditions for large SHNO arrays, avoiding any significant temperature gradients within the array. The state-of-the-art ultra-low operational current SHNOs hence pave an energy-efficient route to scale oscillator-based computing to large dynamical neural networks of linear chains or 2Darrays.
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| 6. |
- Behera, Nilamani, et al.
(författare)
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Ultra-low-current Spin Hall Nano-oscillators
- 2023
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Ingår i: 2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings. - 9798350338362
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Konferensbidrag (refereegranskat)abstract
- We report on the magnetodynamic properties and the magnetization auto-oscillations of ultra-low current 20 nm width nano-constriction spin Hall nano-oscillators (SHNOs) fabricated on different substrates and seed layers. Combining an optimized W88Ta12 alloy, low damping CoFeB, and a moderate perpendicular magnetic anisotropy, we push the threshold current down to 35 μA in the best devices. The best overall magnetodynamic properties and lowest threshold currents are obtained when using a 3 nm thick AlOx seed layer in between the high-resistance Si substrate and the W88Ta12 layer.
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| 7. |
- Ngaloy, Roselle, 1994, et al.
(författare)
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Strong In-Plane Magnetization and Spin Polarization in (Co 0.15 Fe 0.85 ) 5 GeTe 2 /Graphene van der Waals Heterostructure Spin-Valve at Room Temperature
- 2023
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Ingår i: ACS Nano. - 1936-086X .- 1936-0851. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Van der Waals (vdW) magnets are promising, because of their tunable magnetic properties with doping or alloy composition, where the strength of magnetic interactions, their symmetry, and magnetic anisotropy can be tuned according to the desired application. However, so far, most of the vdW magnet-based spintronic devices have been limited to cryogenic temperatures with magnetic anisotropies favoring out-of-plane or canted orientation of the magnetization. Here, we report beyond room-temperature lateral spin-valve devices with strong in-plane magnetization and spin polarization of the vdW ferromagnet (Co0.15Fe0.85)5GeTe2 (CFGT) in heterostructures with graphene. Density functional theory (DFT) calculations show that the magnitude of the anisotropy depends on the Co concentration and is caused by the substitution of Co in the outermost Fe layer. Magnetization measurements reveal the above room-temperature ferromagnetism in CFGT and clear remanence at room temperature. Heterostructures consisting of CFGT nanolayers and graphene were used to experimentally realize basic building blocks for spin valve devices, such as efficient spin injection and detection. Further analysis of spin transport and Hanle spin precession measurements reveals a strong in-plane magnetization with negative spin polarization at the interface with graphene, which is supported by the calculated spin-polarized density of states of CFGT. The in-plane magnetization of CFGT at room temperature proves its usefulness in graphene lateral spin-valve devices, thus revealing its potential application in spintronic technologies.
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| 8. |
- Ngaloy, Roselle, et al.
(författare)
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Strong In-Plane Magnetization and Spin Polarization in (Co0.15Fe0.85)5GeTe2/Graphen e van der Waals Heterostructure Spin-Valve at Room Temperature
- 2024
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 18:7, s. 5240-5248
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Tidskriftsartikel (refereegranskat)abstract
- Van der Waals (vdW) magnets are promising, because of their tunable magnetic properties with doping or alloy composition, where the strength of magnetic interactions, their symmetry, and magnetic anisotropy can be tuned according to the desired application. However, so far, most of the vdW magnet-based spintronic devices have been limited to cryogenic temperatures with magnetic anisotropies favoring out-of-plane or canted orientation of the magnetization. Here, we report beyond room-temperature lateral spin-valve devices with strong in-plane magnetization and spin polarization of the vdW ferromagnet (Co0.15Fe0.85)5GeTe2 (CFGT) in heterostructures with graphene. Density functional theory (DFT) calculations show that the magnitude of the anisotropy depends on the Co concentration and is caused by the substitution of Co in the outermost Fe layer. Magnetization measurements reveal the above room-temperature ferromagnetism in CFGT and clear remanence at room temperature. Heterostructures consisting of CFGT nanolayers and graphene were used to experimentally realize basic building blocks for spin valve devices, such as efficient spin injection and detection. Further analysis of spin transport and Hanle spin precession measurements reveals a strong in-plane magnetization with negative spin polarization at the interface with graphene, which is supported by the calculated spin-polarized density of states of CFGT. The in-plane magnetization of CFGT at room temperature proves its usefulness in graphene lateral spin-valve devices, thus revealing its potential application in spintronic technologies.
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| 9. |
- Rani, D., et al.
(författare)
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Spin-gapless semiconductors: Fundamental and applied aspects
- 2020
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 128:22
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Tidskriftsartikel (refereegranskat)abstract
- Spin-gapless semiconductors (SGSs) are new states of quantum matter, which are characterized by a unique spin-polarized band structure. Unlike conventional semiconductors or half-metallic ferromagnets, they carry a finite bandgap for one spin channel and a close (zero) gap for the other and thus are useful for tunable spin transport applications. It is one of the latest classes of materials considered for spintronic devices. A few of the several advantages of SGS include (i) a high Curie temperature, (ii) a minimal amount of energy required to excite electrons from the valence to conduction band due to zero gap, and (iii) the availability of both charge carriers, i.e., electrons as well as holes, which can be 100% spin-polarized simultaneously. In this perspective article, the theoretical foundation of SGS is first reviewed followed by experimental advancements on various realistic materials. The first band structure of SGS was reported in bulk Co-doped PbPdO 2, using first-principles calculations. This was followed by a large number of ab initio simulation reports predicting SGS nature in different Heusler alloy systems. The first experimental realization of SGS was made in 2013 in a bulk inverse Heusler alloy, Mn 2CoAl. In terms of material properties, SGS shows a few unique features such as nearly temperature-independent conductivity ( sigma) and carrier concentration, a very low temperature coefficient of resistivity, a vanishingly small Seebeck coefficient, quantum linear magnetoresistance in a low temperature range, etc. Later, several other systems, including 2-dimensional materials, were reported to show the signature of SGS. There are some variants of SGSs that can show a quantum anomalous Hall effect. These SGSs are classic examples of topological (Chern) insulators. In the later part of this article, we have touched upon some of these aspects of SGS or the so-called Dirac SGS systems as well. In general, SGSs can be categorized into four different types depending on how various bands corresponding to two different spin channels touch the Fermi level. The hunt for these different types of SGS materials is growing very fast. Some of the recent progress along this direction is also discussed.
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