SwePub - sökning: WFRF:(Dash Saroj Prasad 1975)

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1.	Ghai, Viney, 1989, et al. (författare) Achieving Long-Range Arbitrary Uniform Alignment of Nanostructures in Magnetic Fields 2024 Ingår i: Advanced Functional Materials. - 1616-3028 .- 1616-301X. ; In Press Tidskriftsartikel (refereegranskat)abstract For magnetic field orientation of nonstructures to become a viable method to create high performance multifunctional nanocomposites, it is of paramount importance to develop a method that is easy to implement and that can induce long-range uniform nanostructural alignment. To overcome this challenge, inspired by low field nuclear magnetic resonance (NMR) technology, a highly uniform, high field strength, and compact magnetic-field nanostructure orientation methodology is presented for polymeric nanocomposites using a Halbach array, for the first time. Potential new advances are showcased for applications of graphene polymer composites by considering their electro-thermal and antibacterial properties in highly oriented orthogonal morphologies. The high level of anisotropy induced in the graphene nanocomposites studied stands out through: 1) up to four decades higher electrical conductivities recorded in comparison to their randomly oriented counterparts, at concentrations where the latter show minimal improvements compared to the unfilled polymer; 2) over 1200% improvement in thermal conductivity, 3) antibacterial surfaces at field benchmark levels with lower filler content and with the added versatility of arbitrary orientation of the nanofillers. Overall, the new method and variations thereof can open up new horizons for tailoring nanostructure and performance for virtually all major nanocomposite applications based on graphene and other types of fillers.
2.	Ngaloy, Roselle, 1994, et al. (författare) 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 Ingår i: ACS Nano. - 1936-086X .- 1936-0851. ; In Press 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.
3.	Zhao, Bing, 1990, et al. (författare) A Room-Temperature Spin-Valve with van der Waals Ferromagnet Fe 5 GeTe 2 /Graphene Heterostructure 2023 Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:16 Tidskriftsartikel (refereegranskat)abstract The discovery of van der Waals (vdW) magnets opened a new paradigm for condensed matter physics and spintronic technologies. However, the operations of active spintronic devices with vdW ferromagnets are limited to cryogenic temperatures, inhibiting their broader practical applications. Here, the robust room-temperature operation of lateral spin-valve devices using the vdW itinerant ferromagnet Fe5GeTe2 in heterostructures with graphene is demonstrated. The room-temperature spintronic properties of Fe5GeTe2 are measured at the interface with graphene with a negative spin polarization. Lateral spin-valve and spin-precession measurements provide unique insights by probing the Fe5GeTe2/graphene interface spintronic properties via spin-dynamics measurements, revealing multidirectional spin polarization. Density functional theory calculations in conjunction with Monte Carlo simulations reveal significantly canted Fe magnetic moments in Fe5GeTe2 along with the presence of negative spin polarization at the Fe5GeTe2/graphene interface. These findings open opportunities for vdW interface design and applications of vdW-magnet-based spintronic devices at ambient temperatures.
4.	Bainsla, Lakhan, 1985, et al. (författare) Large out-of-plane spin-orbit torque in topological Weyl semimetal TaIrTe 4 2024 Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1, s. 4649- 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.
5.	Bainsla, Lakhan, et al. (författare) Spin-orbit torques in Co2MnGa magnetic Weyl semimetal thin films 2023 Ingår i: 2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings. - 9798350338362 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.
6.	Bhardwaj, Vishal, et al. (författare) Observation of surface dominated topological transport in strained semimetallic ErPdBi thin films 2020 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 117:13 Tidskriftsartikel (refereegranskat)abstract In this Letter, we present experimental observation of surface-dominated transport properties in [110]-oriented strained (∼1.6%) ErPdBi thin films. The resistivity data show typical semi-metallic behavior in the temperature range of 3 K ≤ T ≤ 350 K with a transition from semiconductor- to metal-like behavior below 3 K. The metallic behavior at low temperature disappears entirely in the presence of an external magnetic field >1 T. The weak-antilocalization (WAL) effect is observed in magneto-conductance data in the low magnetic field region and follows the Hikami-Larkin-Nagaoka (HLN) model. HLN fitting estimated single coherent channel, i.e., α ∼-0.51 at 1.9 K, and the phase coherence length (Lφ) shows the Lφ ∼T-0.52 power law dependence on temperature in the range of 1.9 K-10 K, indicating the observation of 2D WAL. Shubnikov-de Haas (SdH) oscillations are observed in magneto-resistance data below 10 K and are fitted to standard Lifhsitz Kosevich theory. Fitting reveals the effective mass of charge carriers ∼0.15 me and a finite Berry phase of 0.86π± 0.16. The sheet carrier concentration and mobility of carriers estimated using SdH data are ns ∼1.35 × 1012 cm-2 and μs = 1210 cm2 V-1 s-1, respectively, and match well with the data measured using the Hall measurement at 1.9 K to be n ∼1.22 × 1012 cm-2, μ = 1035 cm2 V-1 s-1. These findings indicate the non-trivial nature and surface-dominated transport properties of strained (110) ErPdBi thin films at low temperatures.
7.	Bing, Zhao, 1990, et al. (författare) Unconventional Charge–Spin Conversion in Weyl-Semimetal WTe2 2020 Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 32:38 Tidskriftsartikel (refereegranskat)abstract An outstanding feature of topological quantum materials is their novel spin topology in the electronic band structures with an expected large charge-to-spin conversion efficiency. Here, a charge-current-induced spin polarization in the type-II Weyl semimetal candidate WTe2 and efficient spin injection and detection in a graphene channel up to room temperature are reported. Contrary to the conventional spin Hall and Rashba–Edelstein effects, the measurements indicate an unconventional charge-to-spin conversion in WTe2, which is primarily forbidden by the crystal symmetry of the system. Such a large spin polarization can be possible in WTe2 due to a reduced crystal symmetry combined with its large spin Berry curvature, spin–orbit interaction with a novel spin-texture of the Fermi states. A robust and practical method is demonstrated for electrical creation and detection of such a spin polarization using both charge-to-spin conversion and its inverse phenomenon and utilized it for efficient spin injection and detection in the graphene channel up to room temperature. These findings open opportunities for utilizing topological Weyl materials as nonmagnetic spin sources in all-electrical van der Waals spintronic circuits and for low-power and high-performance nonvolatile spintronic technologies.
8.	Chahal, Sumit, et al. (författare) Microwave Synthesized 2D Gold and Its 2D-2D Hybrids 2022 Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 13:28, s. 6487-6495 Tidskriftsartikel (refereegranskat)abstract Xenes, i.e., monoelemental two-dimensional atomic sheets, are promising for sensitive and ultrafast sensor applications owing to exceptional carrier mobility; however, most of them oxidize below 500 °C and therefore cannot be employed for high-temperature applications. 2D gold, an oxidation-resistant plasmonic Xene, is extremely promising. 2D gold was experimentally realized by both atomic layer deposition and chemical synthesis using sodium citrate. However, it is imperative to develop a new facile single-step method to synthesize 2D gold. Here, liquid-phase synthesis of 2D gold is demonstrated by microwave exposure to auric chloride dispersed in dimethylformamide. Microscopies (AFM and high-resolution TEM), spectroscopies (Raman, UV-vis, and X-ray photoelectron), and X-ray diffraction establish the formation of a hexagonal crystallographic phase for 2D gold. 2D-2D hybrids of 2D gold have also been synthesized and investigated for electronic/optoelectronic behaviors and SERS-based molecular sensing. DFT band structure calculation for 2D gold and its hybrids corroborates the experimental findings.
9.	Chakraborty, Suman Kumar, et al. (författare) Challenges and opportunities in 2D heterostructures for electronic and optoelectronic devices 2022 Ingår i: iScience. - : Elsevier BV. - 2589-0042. ; 25:3 Forskningsöversikt (refereegranskat)abstract Two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and their heterojunctions are prospective materials for future electronics, optoelectronics, and quantum technologies. Assembling different 2D layers offers unique ways to control optical, electrical, thermal, magnetic, and topological phenomena. Controlled fabrications of electronic grade 2D heterojunctions are of paramount importance. Here, we enlist novel and scalable strategies to fabricate 2D vertical and lateral heterojunctions, consisting of semiconductors, metals, and/or semimetals. Critical issues that need to be addressed are the device-to-device variations, reliability, stability, and performances of 2D heterostructures in electronic and optoelectronic applications. Also, stacking order-dependent formation of moiré excitons in 2D heterostructures are emerging with exotic physics and new opportunities. Furthermore, the realization of 2D heterojunction-based novel devices, including excitonic and valleytronic transistors, demands more extensive research efforts for real-world applications. We also outline emergent phenomena in 2D heterojunctions central to nanoelectronics, optoelectronics, spintronics, and energy applications.
10.	Dankert, André, 1986, et al. (författare) Efficient Spin Injection into Silicon and the Role of the Schottky Barrier 2013 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 3 Tidskriftsartikel (refereegranskat)abstract Implementing spin functionalities in Si, and understanding the fundamental processes of spin injection and detection, are the main challenges in spintronics. Here we demonstrate large spin polarizations at room temperature, 34% in n-type and 10% in p-type degenerate Si bands, using a narrow Schottky and a SiO2 tunnel barrier in a direct tunneling regime. Furthermore, by increasing the width of the Schottky barrier in non-degenerate p-type Si, we observed a systematic sign reversal of the Hanle signal in the low bias regime. This dramatic change in the spin injection and detection processes with increased Schottky barrier resistance may be due to a decoupling of the spins in the interface states from the bulk band of Si, yielding a transition from a direct to a localized state assisted tunneling. Our study provides a deeper insight into the spin transport phenomenon, which should be considered for electrical spin injection into any semiconductor.
11.	Dankert, André, 1986, et al. (författare) Electrical gate control of spin current in van der Waals heterostructures at room temperature 2017 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 8 Tidskriftsartikel (refereegranskat)abstract Two-dimensional (2D) crystals offer a unique platform due to their remarkable and contrasting spintronic properties, such as weak spin-orbit coupling (SOC) in graphene and strong SOC in molybdenum disulfide (MoS2). Here we combine graphene and MoS2 in a van der Waals heterostructure (vdWh) to demonstrate the electric gate control of the spin current and spin lifetime at room temperature. By performing non-local spin valve and Hanle measurements, we unambiguously prove the gate tunability of the spin current and spin lifetime in graphene/MoS2 vdWhs at 300 K. This unprecedented control over the spin parameters by orders of magnitude stems from the gate tuning of the Schottky barrier at the MoS2/graphene interface and MoS2 channel conductivity leading to spin dephasing in high-SOC material. Our findings demonstrate an all-electrical spintronic device at room temperature with the creation, transport and control of the spin in 2D materials heterostructures, which can be key building blocks in future device architectures.
12.	Dankert, André, 1986, et al. (författare) Hall sensors batch-fabricated on all-CVD h-BN/graphene/h-BN heterostructures 2017 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 7:1 Tidskriftsartikel (refereegranskat)abstract The two-dimensional (2D) material graphene is highly promising for Hall sensors due to its potential of having high charge carrier mobility and low carrier concentration at room temperature. Here, we report the scalable batch-fabrication of magnetic Hall sensors on graphene encapsulated in hexagonal boron nitride (h-BN) using commercially available large area CVD grown materials. The all-CVD grown h-BN/graphene/h-BN van der Waals heterostructures were prepared by layer transfer technique and Hall sensors were batch-fabricated with 1D edge metal contacts. The current-related Hall sensitivities up to 97 V/AT are measured at room temperature. The Hall sensors showed robust performance over the wafer scale with stable characteristics over six months in ambient environment. This work opens avenues for further development of growth and fabrication technologies of all-CVD 2D material heterostructures and allows further improvements in Hall sensor performance for practical applications.
13.	Dankert, André, 1986, et al. (författare) High Performance Molybdenum Disulfide Field Effect Transistors with Spin Tunnel Contacts 2014 Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 8:1, s. 476-482 Tidskriftsartikel (refereegranskat)abstract Molybdenum disulfide has recently emerged as a promising two-dimensional semiconducting material for nanoelectronic, optoelectronic, and spintronic applications. Here, we investigate the field-effect transistor behavior of MoS2 with ferromagnetic contacts to explore its potential for spintronics. In such devices, we elucidate that the presence of a large Schottky barrier resistance at the MoS2/ferromagnet interface is a major obstacle for the electrical spin injection and detection. We circumvent this problem by a reduction in the Schottky barrier height with the introduction of a thin TiO2 tunnel barrier between the ferromagnet and MoS 2. This results in an enhancement of the transistor on-state current by 2 orders of magnitude and an increment in the field-effect mobility by a factor of 6. Our magnetoresistance calculation reveals that such integration of ferromagnetic tunnel contacts opens up the possibilities for MoS 2-based spintronic devices.
14.	Dankert, André, 1986, et al. (författare) Origin and evolution of surface spin current in topological insulators 2018 Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 97:12 Tidskriftsartikel (refereegranskat)abstract The Dirac surface states of topological insulators offer a unique possibility for creating spin polarized charge currents due to the spin-momentum locking. Here we demonstrate that the control over the bulk and surface contribution is crucial to maximize the charge-to-spin conversion efficiency. We observe an enhancement of the spin signal due to surface-dominated spin polarization while freezin g out the bulk conductivity in semiconducting Bi1.5Sb0.5Te1.7Se1.3 below 100K. Detailed measurements up to room temperature exhibit a strong reduction of the magnetoresistance signal between 2and100K, which we attribute to the thermal excitation of bulk carriers and to the electron-phonon coupling in the surface states. The presence and dominance of this effect up to room temperature is promising for spintronic science and technology.
15.	Dankert, André, 1986, et al. (författare) Room Temperature Electrical Detection of Spin Polarized Currents in Topological Insulators 2015 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:12, s. 7976-7981 Tidskriftsartikel (refereegranskat)abstract Topological insulators (TIs) are a new class of quantum materials that exhibit a current-induced spin polarization due to spin-momentum locking of massless Dirac Fermions in their surface states. This helical spin polarization in three-dimensional (3D) TIs has been observed using photoemission spectroscopy up to room temperatures. Recently, spin polarized surface currents in 3D TIs were detected electrically by potentiometric measurements using ferromagnetic detector contacts. However, these electric measurements are so far limited to cryogenic temperatures. Here we report the room temperature electrical detection of the spin polarization on the surface of Bi2Se3 by employing spin sensitive ferromagnetic tunnel contacts. The current-induced spin polarization on the Bi2Se3 surface is probed by measuring the magnetoresistance while switching the magnetization direction of the ferromagnetic detector. A spin resistance of up to 70 mΩ is measured at room temperature, which increases linearly with current bias, reverses sign with current direction, and decreases with higher TI thickness. The magnitude of the spin signal, its sign, and control experiments, using different measurement geometries and interface conditions, rule out other known physical effects. These findings provide further information about the electrical detection of current-induced spin polarizations in 3D TIs at ambient temperatures and could lead to innovative spin-based technologies.
16.	Dankert, André, 1986, et al. (författare) Spin-Polarized Tunneling through Chemical Vapor Deposited Multilayer Molybdenum Disulfide 2017 Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 11:6, s. 6389-6395 Tidskriftsartikel (refereegranskat)abstract The two-dimensional (2D) semiconductor molybdenum disulfide (MoS2) has attracted widespread attention for its extraordinary electrical-, optical-, spin-, and valley-related properties. Here, we report on spin-polarized tunneling through chemical vapor deposited multilayer MoS2 (∼7 nm) at room temperature in a vertically fabricated spin-valve device. A tunnel magnetoresistance (TMR) of 0.5–2% has been observed, corresponding to spin polarization of 5–10% in the measured temperature range of 300–75 K. First-principles calculations for ideal junctions result in a TMR up to 8% and a spin polarization of 26%. The detailed measurements at different temperature, bias voltages, and density functional theory calculations provide information about spin transport mechanisms in vertical multilayer MoS2 spin-valve devices. These findings form a platform for exploring spin functionalities in 2D semiconductors and understanding the basic phenomena that control their performance.
17.	Dankert, André, 1986, et al. (författare) Spin transport and precession in graphene measured by nonlocal and three-terminal methods 2014 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:19, s. 192403 - Tidskriftsartikel (refereegranskat)abstract We investigate the spin transport and precession in graphene by using the Hanle effect in nonlocal and three-terminal measurement geometries. Identical spin lifetimes, spin diffusion lengths, and spin polarizations are observed in graphene devices for both techniques over a wide range of temperatures. The magnitude of the spin signals is well explained by spin transport models. These observations rules out any signal enhancements or additional scattering mechanisms at the interfaces for both geometries. This validates the applicability of both the measurement methods for graphene based spintronics devices and their reliable extractions of spin parameters.
18.	Dankert, André, 1986, et al. (författare) Thermal creation of electron spin polarization in n-type silicon 2013 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:24, s. article nr. 242405- Tidskriftsartikel (refereegranskat)abstract Conversion of heat into a spin-current in electron doped silicon can offer a promising path for spin-caloritronics. Here, we create an electron spin polarization in the conduction band of n-type silicon by producing a temperature gradient across a ferromagnetic tunnel contact. The substrate heating experiments induce a large spin signal of 95 μV, corresponding to 0.54 meV spin-splitting in the conduction band of n-type silicon by Seebeck spin tunneling mechanism. The thermal origin of the spin injection has been confirmed by the quadratic scaling of the spin signal with the Joule heating current and linear dependence with the heating power.
19.	Dankert, André, 1986, et al. (författare) Tunnel Magnetoresistance with Atomically Thin Two‐Dimensional Hexagonal Boron Nitride Barriers 2015 Ingår i: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 8:4, s. 1357-1364 Tidskriftsartikel (refereegranskat)abstract The two-dimensional atomically thin insulator hexagonal boron nitride (h-BN) constitutes a new paradigm in tunnel based devices. A large band gap, along with its atomically flat nature without dangling bonds or interface trap states, makes it an ideal candidate for tunnel spin transport in spintronic devices. Here, we demonstrate the tunneling of spin-polarized electrons through large area monolayer h-BN prepared by chemical vapor deposition in magnetic tunnel junctions. In ferromagnet/h-BN/ferromagnet heterostructures fabricated on a chip scale, we show tunnel magnetoresistance at room temperature. Measurements at different bias voltages and on multiple devices with different ferromagnetic electrodes establish the spin polarized tunneling using h-BN barriers. These results open the way for integration of 2D monolayer insulating barriers in active spintronic devices and circuits operating at ambient temperature, and for further exploration of their properties and prospects.
20.	Dash, Saroj Prasad, 1975, et al. (författare) 23. Near-surface compositional oscillations of Co diffused into Si (100) at-60° C: a study by high-resolution Rutherford backscattering 2009 Ingår i: Applied Physics A: Materials Science and Processing. - 1432-0630 .- 0947-8396. ; 97:3, s. 651- Tidskriftsartikel (refereegranskat)
21.	Dash, Saroj Prasad, 1975, et al. (författare) 24. Initial stages of growth of iron on silicon for spin injection through Schottky barrier 2011 Ingår i: Physica Status Solidi (B): Basic Research. - 1521-3951 .- 0370-1972. ; 248, s. 2300- Tidskriftsartikel (refereegranskat)
22.	Dash, Saroj Prasad, 1975, et al. (författare) 26. Subsurface enrichment of Co in Si (100) at initial stages of growth at room temperature 2007 Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 90, s. 132109- Tidskriftsartikel (refereegranskat)
23.	Dash, Saroj Prasad, 1975 (författare) A transfer technique for high mobility graphene devices on commercially available hexagonal boron nitride 2011 Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. Tidskriftsartikel (refereegranskat)
24.	Dash, Saroj Prasad, 1975, et al. (författare) Electric field effects on spin accumulation in Nb-doped SrTiO3 using tunable spin injection contacts at room temperature 2014 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:21 Tidskriftsartikel (refereegranskat)abstract We report on features in charge transport and spin injection in an oxide semiconductor, Nb-doped SrTiO3. This is demonstrated using electrically tunable spin injection contacts which exploit the large electric field at the interface and its interplay with the relative permittivity of the semiconductor. We realize spin accumulation in Nb-doped SrTiO3 which displays a unique dependence of the spin lifetime with bias polarity. These findings suggest a strong influence of the interface electric field on the charge transport as well as on spin accumulation unlike in conventional semiconductors and opens up promising avenues in oxide spintronics.
25.	Dash, Saroj Prasad, 1975 (författare) Electrical creation of spin polarization in silicon at room temperature 2009 Ingår i: Nature. - 0028-0836 .- 1476-4687. Tidskriftsartikel (refereegranskat)
26.	Dash, Saroj Prasad, 1975, et al. (författare) Initial stages of growth of iron on silicon for spin injection through Schottky barrier 2011 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 248:10, s. 2300-2304 Tidskriftsartikel (refereegranskat)abstract The characterization of ferromagnet-semiconductor interfaces with monolayer (ML) depth resolution is an important issue in the development of spin injection devices. In this article, highly resolved depth distributions of Fe have been measured during the initial stages of growth of Fe on Si (100) at room temperature by in situ high-resolution Rutherford backscattering spectrometry. Extensive in-diffusion of Fe has been observed even for the coverage of 0.0325 ML of Fe. At this coverage the Si crystal structure is apparently still conserved. Every second Si layer is depleted of Fe, thus giving rise to compositional oscillations of Fe. At higher coverages strong interdiffusion occurs resulting in the formation of silicides at the interface. Even at 9.2 ML of Fe coverage, no pure Fe layers were observed.
27.	Dash, Saroj Prasad, 1975 (författare) Oscillatory spin-polarized tunnelling from silicon quantum wells controlled by electric field 2010 Ingår i: Nature Materials. - 1476-4660 .- 1476-1122. Tidskriftsartikel (refereegranskat)
28.	Dash, Saroj Prasad, 1975, et al. (författare) Silicon spintronics at room temperature 2010 Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - 0277-786X. ; 7760:77600J Tidskriftsartikel (refereegranskat)
29.	Dash, Saroj Prasad, 1975 (författare) Spin Logic and Emergent Spin Phenomena in 2D Materials Heterostructures 2023 Ingår i: 2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings. Konferensbidrag (refereegranskat)abstract Two-dimensional (2D) materials and their van der Waals heterostructures represent a new platform to realize novel spin-based phenomena and device applications. We demonstrated robust spin interconnect, spin multiplexing, and multifunctional spin logic operation using large-area CVD graphene based spintronic devices. In order to control the spin polarization in graphene, we engineered 2D material heterostructures by combining the best of different materials in one ultimate unit and realized strong proximity induced spin-orbit coupling and magnetism. We showed that the graphene-based heterostructures are also useful for the detection of current-induced spin-polarization in topological materials and proximity interactions. Finally, room temperature spin-valve devices could be realized using van der Waals ferromagnet in heterostructures with graphene. These findings open a new platform for electrical creation and gate-control of spin polarization and provide new opportunities for all-2D heterostructure spintronic devices and integrated spin circuits.
30.	Dash, Saroj Prasad, 1975, et al. (författare) Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface 2011 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 84:5 Tidskriftsartikel (refereegranskat)abstract Although the creation of spin polarization in various nonmagnetic media via electrical spin injection from a ferromagnetic tunnel contact has been demonstrated, much of the basic behavior is heavily debated. It is reported here that, for semiconductor/Al(2)O(3)/ferromagnet tunnel structures based on Si or GaAs, local magnetostatic fields arising from interface roughness dramatically alter and even dominate the accumulation and dynamics of spins in the semiconductor. Spin precession in inhomogeneous magnetic fields is shown to reduce the spin accumulation up to tenfold, and causes it to be inhomogeneous and noncollinear with the injector magnetization. The inverted Hanle effect serves as the experimental signature. This interaction needs to be taken into account in the analysis of experimental data, particularly in extracting the spin lifetime tau(s) and its variation with different parameters (temperature, doping concentration). It produces a broadening of the standard Hanle curve and thereby an apparent reduction of tau(s). For heavily doped n-type Si at room temperature it is shown that tau(s) is larger than previously determined, and a new lower bound of 0.29 ns is obtained. The results are expected to be general and to occur for spins near a magnetic interface not only in semiconductors but also in metals and organic and carbon-based materials including graphene, and in various spintronic device structures.
31.	Dash, Saroj Prasad, 1975 (författare) Spin transport in two-dimensional materials and van der Waals heterostructures 2016 Ingår i: 2016 Ieee 16th International Conference on Nanotechnology (Ieee-Nano). - 9781509014934 ; , s. 986-986 Konferensbidrag (refereegranskat)
32.	Dash, Saroj Prasad, 1975, et al. (författare) Spintronics with Graphene and van der Waals Heterostructures 2017 Ingår i: World Scientific. - : WORLD SCIENTIFIC. - 9789813149823 ; , s. 241-258 Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract The outstanding spin transport properties of graphene make it an ideal candidate for chip scale spin communication devices. Motivated by this prospect, over the past decade, remarkable progress has been made in enhancing the spin transport parameters in graphene. Apart from simple graphene devices, van der Waals heterostructures of graphene have been fabricated by laminating other two-dimensional crystals with graphene. Such heterostructures of graphene with insulating hexagonal boron nitride (h-BN) as a substrate and gate dielectric or as spin tunnel barrier have been used to achieve efficient spin injection, large spin coherence time and diffusion length in graphene. In this chapter, we present two important advancements in the field of graphene spintronics: First, the recent achievement of long distance spin communication in large scale chemical vapor deposited graphene, and second, the demonstration of enhanced spin injection and spin filtering effects in ferromagnet/h-BN-graphene van der Waals heterostructures. We discuss how these results feature in the present state-of-the art and open new avenues for future developments.
33.	Dash, Saroj Prasad, 1975, et al. (författare) Tunnel Contacts for Spin Injection into Silicon: The Si-Co Interface with and without a MgO Tunnel Barrier - A Study by High-Resolution Rutherford Backscattering 2012 Ingår i: Advances in Materials Science and Engineering. - : Hindawi Limited. - 1687-8442 .- 1687-8434. ; 2012, s. Art. no. 902649- Forskningsöversikt (refereegranskat)abstract In order to obtain high spin injection efficiency, a ferromagnet-semiconducor Schottky contact must be of high crystalline quality. This is particularly important in the case of ferromagnet-silicon interfaces, since these elements tend to mix and form silicides. In this study Co-Si (100) interfaces were prepared in three different ways: by evaporation at room temperature, low temperature (-60°C), and with Sb as surfactant, and their interface structures were analyzed by high-resolution RBS (HRBS). In all cases more or less strong in-diffusion of Co with subsequent silicide formation was observed. In order to prevent the mixing of Co and Si, ultra thin MgO tunnel barriers were introduced in-between them. In situ HRBS characterization confirms that the MgO films were very uniform and prevented the mixing of the Si substrate with deposited Co and Fe films effectively, even at 450°C.
34.	Datta, Sawani, et al. (författare) Anomalies in the Dirac bands in the proximity of correlated electrons 2024 Ingår i: Nanoscale. - 2040-3372 .- 2040-3364. ; 16:29, s. 13861-13866 Tidskriftsartikel (refereegranskat)abstract Dirac fermions, particles with zero rest mass, are observed in topological materials and are believed to play a key role in the exotic phenomena in fundamental science and the advancement of quantum technology. Most of the topological systems studied so far are weakly correlated systems and the study of their properties in the presence of electron correlation is an interesting emerging area of research, where the electron correlation is expected to enhance the effective mass of the particles. Here, we studied the properties of Dirac bands in a non-symmorphic layered Kondo lattice system, CeAgSb2, employing high-resolution angle-resolved photoemission spectroscopy and first-principles calculations. In addition to the Dirac cones due to non-symmorphic symmetry, this material hosts Dirac fermions in the squarenet layer in the proximity of a strongly correlated Ce layer exhibiting Kondo behavior. Experimental results reveal crossings of the highly dispersive linear bands at the Brillouin zone boundary due to non-symmorphic symmetry. In addition, there are anisotropic Dirac cones constituted by the squarenet Sb 5p states forming a diamond-shaped nodal line. These Dirac bands are linear in a wide energy range with an unusually high slope. Interestingly, near the local Ce 4f bands, these bands exhibit a change in the slope akin to the formation of a ‘kink’ observed in other materials due to electron-phonon coupling. The emergence of such exotic properties in proximity to strongly correlated electronic states has significant implications in the study of complex quantum materials including unconventional superconductors.
35.	Fang, Hanlin, 1992, et al. (författare) Localization and interaction of interlayer excitons in MoSe 2 /WSe 2 heterobilayers 2023 Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 14:1 Tidskriftsartikel (refereegranskat)abstract Transition metal dichalcogenide (TMD) heterobilayers provide a versatile platform to explore unique excitonic physics via the properties of the constituent TMDs and external stimuli. Interlayer excitons (IXs) can form in TMD heterobilayers as delocalized or localized states. However, the localization of IX in different types of potential traps, the emergence of biexcitons in the high-excitation regime, and the impact of potential traps on biexciton formation have remained elusive. In our work, we observe two types of potential traps in a MoSe2/WSe2 heterobilayer, which result in significantly different emission behavior of IXs at different temperatures. We identify the origin of these traps as localized defect states and the moiré potential of the TMD heterobilayer. Furthermore, with strong excitation intensity, a superlinear emission behavior indicates the emergence of interlayer biexcitons, whose formation peaks at a specific temperature. Our work elucidates the different excitation and temperature regimes required for the formation of both localized and delocalized IX and biexcitons and, thus, contributes to a better understanding and application of the rich exciton physics in TMD heterostructures.
36.	Gaur, A.P.S., et al. (författare) Cold cathode emission studies on topographically modified few layer and single layer MoS2 films 2016 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 108:4 Tidskriftsartikel (refereegranskat)abstract Nanostructured materials, such as carbon nanotubes, are excellent cold cathode emitters. Here, we report comparative field emission (FE) studies on topographically tailored few layer MoS2films consisting of ⟨0001⟩ plane perpendicular (⊥) to c-axis (i.e., edge terminated vertically aligned) along with planar few layer and monolayer (1L) MoS2films. FE measurements exhibited lower turn-on field Eto (defined as required applied electric field to emit current density of 10 μA/cm2) ∼4.5 V/μm and higher current density ∼1 mA/cm2, for edge terminated vertically aligned (ETVA) MoS2films. However, Eto magnitude for planar few layer and 1L MoS2films increased further to 5.7 and 11 V/μm, respectively, with one order decrease in emission current density. The observed differences in emission behavior, particularly for ETVA MoS2 is attributed to the high value of geometrical field enhancement factor (β), found to be ∼1064, resulting from the large confinement of localized electric field at edge exposed nanograins. Emission behavior of planar few layers and 1L MoS2films are explained under a two step emission mechanism. Our studies suggest that with further tailoring the microstructure of ultra thin ETVA MoS2films would result in elegant FE properties.
37.	Gaur, A.P.S., et al. (författare) Manipulation of exciton and trion quasiparticles in monolayer WS2 via charge transfer 2019 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 115:17 Tidskriftsartikel (refereegranskat)abstract Charge doping in transition metal dichalcogenide is currently a subject of high importance for future electronic and optoelectronic applications. Here, we demonstrate chemical doping in the CVD-grown monolayer (1L) of WS2 by a few commonly used laboratory solvents by investigating the room temperature photoluminescence (PL). The appearance of distinct trionic emission in the PL spectra and quenched PL intensities suggests n-type doping in WS2. The temperature-dependent PL spectra of the doped 1L-WS2 reveal a significant enhancement of trions emission intensity over the excitonic emission at low temperature, indicating the stability of trion at low temperature. The temperature-dependent exciton-trion population dynamic has been modeled using the law of mass action of trion formation. These results shed light on the solution-based chemical doping in 1L-WS2 and its profound effect on the photoluminescence which is essential for the control of optical and electrical properties for optoelectronic applications.
38.	Gaur, A.P.S., et al. (författare) Surface Energy Engineering for Tunable Wettability through Controlled Synthesis of MoS2 2014 Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:8, s. 4314-4321 Tidskriftsartikel (refereegranskat)abstract MoS2 is an important member of the transition metal dichalcogenides that is emerging as a potential 2D atomically thin layered material for low power electronic and optoelectronic applications. However, for MoS2 a critical fundamental question of significant importance is how the surface energy and hence the wettability is altered at the nanoscale in particular, the role of crystallinity and orientation. This work reports on the synthesis of large area MoS2 thin films on insulating substrates (SiO2/Si and Al2O3) with different surface morphology via vapor phase deposition by varying the growth temperatures. The samples were examined using transmission electron microscopy and Raman spectroscopy. From contact angle measurements, it is possible to correlate the wettability with crystallinity at the nanoscale. The specific surface energy for few layers MoS2 is estimated to be about 46.5 mJ/m2. Moreover a layer thickness-dependent wettability study suggests that the lower the thickness is, the higher the contact angle will be. Our results shed light on the MoS2–water interaction that is important for the development of devices based on MoS2 coated surfaces for microfluidic applications.
39.	Guimarães, Marcos, et al. (författare) Disorder is not always bad for charge-to-spin conversion in WTe 2 2021 Ingår i: Matter. - : Elsevier BV. - 2590-2393 .- 2590-2385. ; 4:5, s. 1440-1441 Tidskriftsartikel (refereegranskat)abstract The Wang group at Stanford University demonstrates disordered WTe films for efficient charge-to-spin conversion phenomena. The deposition of these films by sputtering and the charge-to-spin conversion resilience against disorder make them attractive for applications in new magnetic memory devices.
40.	Hoque, Anamul Md, 1988, et al. (författare) All-electrical creation and control of spin-galvanic signal in graphene and molybdenum ditelluride heterostructures at room temperature 2021 Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 4:1 Tidskriftsartikel (refereegranskat)abstract The ability to engineer new states of matter and control their spintronic properties by electric fields is at the heart of future information technology. Here, we report a gate-tunable spin-galvanic effect in van der Waals heterostructures of graphene with a semimetal of molybdenum ditelluride at room temperature due to an efficient spin-charge conversion process. Measurements in different device geometries with control over the spin orientations exhibit spin-switch and Hanle spin precession behavior, confirming the spin origin of the signal. The control experiments with the pristine graphene channels do not show any such signals. We explain the experimental spin-galvanic signals by theoretical calculations considering the spin-orbit induced spin-splitting in the bands of the graphene in the heterostructure. The calculations also reveal an unusual spin texture in graphene heterostructure with an anisotropic out-of-plane and in-plane spin polarization. These findings open opportunities to utilize graphene-based heterostructures for gate-controlled spintronic devices.
41.	Hoque, Anamul Md, 1988, et al. (författare) Charge-spin conversion in layered semimetal TaTe2 and spin injection in van der Waals heterostructures 2020 Ingår i: Physical Review Research. - 2643-1564. ; 2:3 Tidskriftsartikel (refereegranskat)abstract A spin-polarized current source using nonmagnetic layered materials is promising for next-generation all-electrical spintronic science and technology. Here we electrically created spin polarization in a layered semimetal TaTe2 via the charge-spin conversion process. Using a hybrid device of TaTe2 in a van der Waals heterostructure with graphene, the spin polarization in TaTe2 is efficiently injected and detected by nonlocal spin-switch, Hanle spin precession, and inverse spin Hall effect measurements. Systematic experiments at different bias currents and gate voltages in a vertical geometry prove the TaTe2 as a nonmagnetic spin source at room temperature. These findings demonstrate the possibility of making an all-electrical spintronic device in a two-dimensional van der Waals heterostructure, which can be essential building blocks in energy-efficient spin-orbit technology.
42.	Iordanidou, Konstantina, 1989, et al. (författare) Electric Field and Strain Tuning of 2D Semiconductor van der Waals Heterostructures for Tunnel Field-Effect Transistors 2023 Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 15:1, s. 1762-1771 Tidskriftsartikel (refereegranskat)abstract Heterostacks consisting of low-dimensional materials are attractive candidates for future electronic nanodevices in the post-silicon era. In this paper, using first-principles calculations based on density functional theory (DFT), we explore the structural and electronic properties of MoTe2/ZrS2 heterostructures with various stacking patterns and thicknesses. Our simulations show that the valence band (VB) edge of MoTe2 is almost aligned with the conduction band (CB) edge of ZrS2, and (MoTe2)m/(ZrS2)m (m = 1, 2) heterostructures exhibit the long-sought broken gap band alignment, which is pivotal for realizing tunneling transistors. Electrons are found to spontaneously flow from MoTe2 to ZrS2, and the system resembles an ultrascaled parallel plate capacitor with an intrinsic electric field pointed from MoTe2 to ZrS2. The effects of strain and external electric fields on the electronic properties are also investigated. For vertical compressive strains, the charge transfer increases due to the decreased coupling between the layers, whereas tensile strains lead to the opposite behavior. For negative electric fields a transition from the type-III to the type-II band alignment is induced. In contrast, by increasing the positive electric fields, a larger overlap between the valence and conduction bands is observed, leading to a larger band-to-band tunneling (BTBT) current. Low-strained heterostructures with various rotation angles between the constituent layers are also considered. We find only small variations in the energies of the VB and CB edges with respect to the Fermi level, for different rotation angles up to 30°. Overall, our simulations offer insights into the fundamental properties of low-dimensional heterostructures and pave the way for their future application in energy-efficient electronic nanodevices.
43.	Irfan, Bushra, et al. (författare) Surface dominated magnetotransport in Bi 2 Te 2.15 Se 0.85 topological insulator 2018 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 124:21 Tidskriftsartikel (refereegranskat)abstract Topological insulators (TIs) represent a new state of matter possessing an attractive surface spin texture with possible applications in quantum computation and spintronics. The growth of prototypical TIs such as Bi 2Te 3 and Bi 2Se 3 still remains a major challenge, because of vacancies and defects leading to an unintentional doping of the crystals creating a parallel conduction channel in the bulk. Here, we synthesized the Bi 2Te 2.15Se 0.85 (BTS) TI using a modified Bridgeman technique. Magnetotransport studies at different angles and temperatures of the device made on thin (BTS) flakes reveal the 2D nature of the weak antilocalization signal and surface dominated transport properties at low temperatures.
44.	Jansen, R., et al. (författare) 19. Electrical spin injection into moderately doped silicon enabled by tailored interfaces 2010 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 82:24, s. 241305- Tidskriftsartikel (refereegranskat)
45.	Jansen, R., et al. (författare) Silicon spintronics with ferromagnetic tunnel devices 2012 Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 27:8 Forskningsöversikt (refereegranskat)abstract In silicon spintronics, the unique qualities of ferromagnetic materials are combined with those of silicon, aiming at creating an alternative, energy-efficient information technology in which digital data are represented by the orientation of the electron spin. Here we review the cornerstones of silicon spintronics, namely the creation, detection and manipulation of spin polarization in silicon. Ferromagnetic tunnel contacts are the key elements and provide a robust and viable approach to induce and probe spins in silicon, at room temperature. We describe the basic physics of spin tunneling into silicon, the spin-transport devices, the materials aspects and engineering of the magnetic tunnel contacts, and discuss important quantities such as the magnitude of the spin accumulation and the spin lifetime in the silicon. We highlight key experimental achievements and recent progress in the development of a spin-based information technology.
46.	Karpiak, Bogdan, 1992, et al. (författare) 1D ferromagnetic edge contacts to 2D graphene/h-BN heterostructures 2018 Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 5:1, s. 014001- Tidskriftsartikel (refereegranskat)abstract We report the fabrication of one-dimensional (1D) ferromagnetic edge contacts to two-dimensional (2D) graphene/h-BN heterostructures. While aiming to study spin injection/detection with 1D edge contacts, a spurious magnetoresistance signal was observed, which is found to originate from the local Hall effect in graphene due to fringe fields from ferromagnetic edge contacts and in the presence of charge current spreading in the nonlocal measurement configuration. Such behavior has been confirmed by the absence of a Hanle signal and gate-dependent magnetoresistance measurements that reveal a change in sign of the signal for the electron-and hole-doped regimes, which is in contrast to the expected behavior of the spin signal. Calculations show that the contact-induced fringe fields are typically on the order of hundreds of mT, but can be reduced below 100 mT with careful optimization of the contact geometry. There may be an additional contribution from magnetoresistance effects due to tunneling anisotropy in the contacts, which needs further investigation. These studies are useful for optimization of spin injection and detection in 2D material heterostructures through 1D edge contacts.
47.	Karpiak, Bogdan, 1992, et al. (författare) Gate-tunable Hall sensors on large area CVD graphene protected by h-BN with 1D edge contacts 2017 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 122:5 Tidskriftsartikel (refereegranskat)abstract Graphene is an excellent material for Hall sensors due to its atomically thin structure, high carrier mobility, and low carrier density. However, graphene devices need to be protected from the environment for reliable and durable performance in different environmental conditions. Here we present magnetic Hall sensors fabricated on large area commercially available chemical vapor deposited (CVD) graphene protected by exfoliated hexagonal boron nitride (h-BN). To connect the graphene active regions of Hall samples to the outputs, 1D edge contacts were utilized which show reliable and stable electrical properties. The operation of the Hall sensors shows the current-related sensitivity up to 345 V/(AT). By changing the carrier concentration and type in graphene by the application of gate voltage, we are able to tune the Hall sensitivity.
48.	Karpiak, Bogdan, 1992, et al. (författare) Magnetic proximity in a van der Waals heterostructure of magnetic insulator and graphene 2020 Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 7:1 Tidskriftsartikel (refereegranskat)abstract Engineering 2D material heterostructures by combining the best of different materials in one ultimate unit can offer a plethora of opportunities in condensed matter physics. Here, in the van der Waals heterostructures of the ferromagnetic insulator Cr2Ge2Te6 and graphene, our observations indicate an out-of-plane proximity-induced ferromagnetic exchange interaction in graphene. The perpendicular magnetic anisotropy of Cr2Ge2Te6 results in significant modification of the spin transport and precession in graphene, which can be ascribed to the proximity-induced exchange interaction. Furthermore, the observation of a larger lifetime for perpendicular spins in comparison to the in-plane counterpart suggests the creation of a proximity-induced anisotropic spin texture in graphene. Our experimental results and density functional theory calculations open up opportunities for the realization of proximity-induced magnetic interactions and spin filters in 2D material heterostructures and can form the basic building blocks for future spintronic and topological quantum devices.
49.	Khademi, Maha, et al. (författare) Large Non-Volatile Frequency Tuning of Spin Hall Nano-Oscillators using Circular Memristive Nano-Gates 2024 Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 45:2, s. 268-271 Tidskriftsartikel (refereegranskat)abstract Spin Hall nano oscillators (SHNOs) are promising candidates for neuromorphic computing due to their miniaturized dimensions, non-linearity, fast dynamics, and ability to synchronize in long chains and arrays. However, tuning the individual SHNOs in large chains/arrays, which is key to implementing synaptic control, has remained a challenge. Here, we demonstrate circular memristive nano-gates, both precisely aligned and shifted with respect to nano-constriction SHNOs of W/CoFeB/HfOx, with increased quality of the device tunability. Gating at the exact center of the nano-constriction region is found to cause irreversible degradation to the oxide layer, resulting in a permanent frequency shift of the auto-oscillating modes. As a remedy, gates shifted outside of the immediate nano-constriction region can tune the frequency dramatically (>200 MHz) without causing any permanent change to the constriction region. Circular memristive nano-gates can, therefore, be used in SHNO chains/arrays to manipulate the synchronization states precisely over large networks of oscillators.
50.	Khokhriakov, Dmitrii, 1991, et al. (författare) Gate-tunable spin-galvanic effect in graphene-topological insulator van der Waals heterostructures at room temperature 2020 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 11:1 Tidskriftsartikel (refereegranskat)abstract Unique electronic spin textures in topological states of matter are promising for emerging spin-orbit driven memory and logic technologies. However, there are several challenges related to the enhancement of their performance, electrical gate-tunability, interference from trivial bulk states, and heterostructure interfaces. We address these challenges by integrating two-dimensional graphene with a three-dimensional topological insulator (TI) in van der Waals heterostructures to take advantage of their remarkable spintronic properties and engineer proximity-induced spin-charge conversion phenomena. In these heterostructures, we experimentally demonstrate a gate-tunable spin-galvanic effect (SGE) at room temperature, allowing for efficient conversion of a non-equilibrium spin polarization into a transverse charge current. Systematic measurements of SGE in various device geometries via a spin switch, spin precession, and magnetization rotation experiments establish the robustness of spin-charge conversion in the Gr-TI heterostructures. Importantly, using a gate voltage, we reveal a strong electric field tunability of both amplitude and sign of the spin-galvanic signal. These findings provide an efficient route for realizing all-electrical and gate-tunable spin-orbit technology using TIs and graphene in heterostructures, which can enhance the performance and reduce power dissipation in spintronic circuits.

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