Doping-induced spin Hall ratio enhancement in A15-phase, Ta-doped Beta-W thin films
Mohsin Z. Minhas, Avanindra K. Pandeya, Bharat Grover, Alessandro Fumarola, Ilya Kostanovskiy, Wolfgang Hoppe, Georg Woltersdorf, Amilcar Bedoya-Pinto, Stuart S… 展开作者
Mohsin Z. Minhas, Avanindra K. Pandeya, Bharat Grover, Alessandro Fumarola, Ilya Kostanovskiy, Wolfgang Hoppe, Georg Woltersdorf, Amilcar Bedoya-Pinto, Stuart S. P. Parkin, Mazhar N. Ali
As spintronic devices become more and more prevalent, the desire to find Pt free materials with large spin Hall effects is increasing. Previously it was shown that Beta W, the metastable A15 structured variant of pure W, has charge-spin conversion efficiencies on par with Pt, and it was predicted that Beta W(Ta) alloys should be even more efficient. Here we demonstrate the enhancement of the spin Hall ratio (SHR) in A15-phase Beta W films doped with Ta (W(4-x)Tax where x is between 0.28 and 0.4, deposited at room temperature using DC magnetron co-sputtering. In close agreement with theoretical predictions, we find that the SHR of the doped films was approx. 9 percent larger than pure Beta W films. We also found that the SHRs in devices with Co2Fe6B2 were nearly twice as large as the SHRs in devices with Co4Fe4B2. This work shows that by optimizing deposition parameters and substrates, the fabrication of the optimum W3Ta alloy should be feasible, opening the door to commercially viable, Pt free, spintronic devices.
We report on Cr doping effect in Mn3Sn polycrystalline films with both uniform and modulation doping. It is found that Cr doping with low concentration does not cause notable changes to the structural and magnetic properties of Mn3Sn, but it significantly enhances the anomalous Hall conductivity, particularly for modulation-doped samples at low temperature. A Hall conductivity as high as 184.8 Ω-1 cm-1 is obtained for modulation-doped samples at 50 K, in a sharp contrast to vanishingly small values for undoped samples at the same temperature. We attribute the enhancement to the change of Fermi…
Tuning of the electronic properties of pre-synthesized colloidal semiconductor nanocrystals (NCs) by doping plays a key role in the prospect of implementing them in printed electronics devices such as transistors, and photodetectors. While such impurity doping reactions have already been introduced, the understanding of the doping process, the nature of interaction between the impurity and host atoms, and the conditions affecting the solubility limit of impurities in nanocrystals are still unclear. Here, we used a post-synthesis diffusion based doping reaction to introduce Ag impurities into I…
Sulfur and nitrogen dual doped graphene have been extensively investigated in the field of oxygen reduction reaction, supercapacitors and batteries, but their magnetic and absorption performance have not been explored. Besides, the effects of doping sequence of sulfur and nitrogen atoms on the morphology, structural property and the corresponding microwave absorption performance of the dual doped graphene remain unexplored. In this work, nitrogen and sulfur dual doped graphene with different doping sequence were successfully prepared using a controllable two steps facile thermal treatment meth…
The band gap of two-dimensional (2D) semiconductors can be efficiently tuned by gate electric field, which is so called the Stark effect. We report that doping, which is essential in realistic devices, will substantially change the Stark effect of few-layer transition metal dichalcogenides in unexpected ways. Particularly in bilayer structures, because of the competition between strong quantum confinement and intrinsic screening length, electron and hole dopings exhibit surprisingly different Stark effects: doped electrons actively screen the external field and result in a nonlinear Stark effe…
Doping is an effective way to modify the electronic property of two-dimensional (2D) materials and endow them with new functionalities. However, wide-range control of the substitutional doping concentration with large scale uniformity remains challenging in 2D materials. Here we report in-situ chemical vapor deposition growth of vanadium (V) doped monolayer molybdenum disulfide (MoS2) with widely tunable doping concentrations ranging from 0.3 to 13.1 at%. The key to regulate the doping concentration lies in the use of appropriate V precursors with different doping abilities, which also generat…
We report the growth of electrically-resistive vanadium-doped beta-Ga2O3 single crystals via the optical floating zone technique. By carefully controlling the growth parameters V-doped crystals with very high electrical resistivity compared to the usual n-type V-doped beta-Ga2O3 (ne~10^(18)/cm^3) can be synthesized. The optical properties of such high resistive V-doped b-Ga2O3 are significantly different compared to the undoped and n-doped crystals. We study the polarization-dependent Raman spectra, polarization-dependent transmission, temperature-dependent photoluminescence in the optical wav…
In this paper, we have analysed the electronic and mechanical properties of Nitrogen(N) doped (6,1) SWCNTs based on first-principles and Molecular dynamic (MD) simulation. A schematic N-doping on SWCNT was performed along zigzag(zz) and armchair(ac) direction. Armchair doping is considered parallel to the tube axis while the zigzag is along the cross-section perpendicular to the tube axis. In doping pattern (both zz and ac) we have observed the variation in electronic properties for even number of N-doping and odd number of N-doping. To study the mechanical properties we have adopted ab-initio…
The crystal structure of MoS$_2$ with strong covalent bonds in plane and weak Van der Waals interactions out of plane gives rise to interesting properties for applications such as solid lubrication, optoelectronics, and catalysis, which can be enhanced by transition-metal doping. However, the mechanisms for improvement and even the structure of the doped material can be unclear, which we address with theoretical calculations. Building on our previous work on Ni-doping of the bulk 2H phase, now we compare to polytypes (1H monolayer and 3R bulk), to determine favorable sites for Ni and the dopin…
A comprehensive current-voltage (I-V) characterization is performed for three different Schottky contacts; Pt, Ni and Ti, to unintentionally doped (UID) \{beta}-(Al0.19Ga0.81)2O3 grown by molecular beam epitaxy (MBE) on \{beta}-Ga2O3 for temperatures ranging between 25C -300C. Reciprocal space mapping shows the (Al0.19Ga0.81)2O3 films are strained and lattice matched to the substrate. Schottky Barrier Height (SBH), ideality factor (n), and series resistance (Rs) are extracted from the I-V characteristics for the three types of metals and temperatures. Room temperature capacitance-voltage (C-V)…
Metal-ion doping can effectively regulate the metal-insulator transition temperature in $\mathrm{VO}_2$. Experiments found that the pentavalent and hexavalent ion doping dramatically reduces the transition temperature while the trivalent ion doping increases the transition temperature and induces intermediate phases. Based on the phase-field model of the metal-insulator transition in $\mathrm{VO}_2$ we developed previously, we formulate a Landau potential of the metal-ion-doped $\mathrm{VO}_2$ taking account of the effects of doping on the electron correlation and lattice structure. The effect…
Currently, Fe doping in the ~10^18 cm-3 range is the most widely-available method for producing semi-insulating single crystalline beta-Ga2O3 substrates. Red luminescence features have been reported from multiple types of Ga2O3 samples including Fe-doped -Ga2O3, and attributed to Fe or N at O. Herein, however, we demonstrate that the high-intensity red luminescence from Fe-doped beta-Ga2O3 commercial substrates consisting of two sharp peaks at 689 nm and 697 nm superimposed on a broader peak centered at 710 nm originates from Cr impurities present at a concentration near 2 ppm. The red emissio…
Two-dimensional (2D) materials with robust magnetism have drawn immense attention for their promising applications in spintronics. Recently, intrinsic ferromagnetic vanadium triiodide (VI3) has been synthesized experimentally. To enhance its spintronic property, we modified VI3 by interstitial doping with 3d transition metals (TM) and used first-principles calculations to investigate the geometric structure, formation energy, electronic property, and magnetism of pristine VI3 and 3d TM-doped VI3 monolayer. Among eight transition metal (Sc-, Ti-, V-, Cr-, Mn-, Fe-, Co-, and Ni-) doped VI3 mater…
Using Density functional theory (DFT) in conjunction with a solvation model we have investigated the phenomenon of eletrode-electrolyte interaction at the electrode surface and its consequences on the electrochemical properties like the charge storage and total capacitance of doped and substituted oxygen functionalised Ti$_{3}$C$_{2}$ supercapcitor electrode. We have studied nitrogen doped, nitrogen substituted and molybdenum substituted Mxenes in acidic electrolyte H$_{2}$SO$_{4}$ solution. By considering nitrogen doping at different sites, we found that the greatest capacitance is obtained f…
Stoner factors of doped 122 Fe-based superconductors: First principles results
本文研究了不同掺杂122铁基超导体（BaFe $_2$ As $_2$，SrFe $_2$ As $_2$）的Stoner因子随掺杂浓度的变化规律。我们的第一性原理电子结构计算表明，对于Co/Ru（电子或等电子）掺杂在Fe位或P掺杂在As位的结果在减少的Stoner因子随着掺杂浓度的增加。相反，在Na/K（空穴）掺杂的情况下，在Ba位点处，Stoner因子对于更高的掺杂浓度增强。这可以被认为是在这些系统中的“磁波动”的高度的指标。我们发现，Stoner因子唯一地跟随着磷族元素高度z $_{As}$ /Fe-As键长随各种掺杂的变化。我们计算的费米面解释了不同掺杂122系统的Stoner因子行为的差异;费米面嵌套程度越大，Stoner因子值越大，反之亦然。
While doping is widely used for tuning physical properties of perovskites in experiments, it remains a challenge to exactly know how doping achieves the desired effects. Here, we propose an empirical and computationally tractable model to understand the effects of doping with Fe-doped BaTiO$_{3}$ as an example. This model assumes that the lattice sites occupied by Fe ion and its nearest six neighbors lose their ability to polarize, giving rise to a small cluster of defective dipoles. Employing this model in Monte-Carlo simulations, many important features like reduced polarization and the conv…
In this paper, the effect of B and N doping on the phonon induced thermal conductivity of graphene has been investigated. This study is important when one has to evaluate the usefulness of electronic properties of B and N doped graphene. We have performed the calculations by employing density functional perturbation theory(DFPT) to calculate the inter-atomic forces=force constants of pristine/doped graphene. Thermal conductivity calculations have been carried out by making use of linearized Boltzmann transport equations (LBTE) under single-mode relaxation time approximation (RTA). The thermal …
We investigated the influence of doping antiferromagnetic MnN in polycrystalline MnN/CoFe exchange bias systems, showing high exchange bias of up to 1800 Oe at room temperature. The thermal stability of those systems is limited by nitrogen diffusion that occurs during annealing processes. In order to improve the thermal stability, defect energies of elements throughout the periodic table substituting Mn were calculated via density functional theory. Elements calculated to have negative defect energies bind nitrogen stronger to the lattice and could be able to prevent diffusion. We prepared exc…
Performing deep level transient spectroscopy (DLTS) on Schottky diodes, we investigated defect levels below the conduction band minima (Ec) in Czochralski (CZ) grown unintentionally-doped (UID) and vertical gradient freeze (VGF)-grown Zr-doped beta-Ga2O3 crystals. In UID crystals with an electron concentration of 10^17 cm-3, we observe levels at 0.18 eV and 0.46 eV in addition to the previously reported 0.86 (E2) and 1.03 eV (E3) levels. For 10^18 cm-3 Zr-doped Ga2O3, signatures at 0.30 eV (E15) and 0.71 eV (E16) are present. For the highest Zr doping of 5*10^18 cm-3, we observe only one signa…
Optimal doping and entropic origin of giant thermopower in doped Mott insulators
这篇论文已被作者撤回，因为结果是不正确的，由于使用的杂质求解器，在大的相互作用强度和以上的半填充失败。这首先导致了新的杂质求解器的开发（arXiv：1202.5814或Phys.Rev. B 86，085133（2012）），其次导致了具有不同结论的热电势结果的完全修订。因此，提交了一篇关于热电的新论文（arXiv：1209.4349），并撤回了目前的论文。
Toxic-free metal halide perovskites have become forefront for commercialization of the perovskite solar cells and optoelectronic devices. In the present study, for the first time we show that particular metal doping in CsGeCl3 halide can considerably enhance the absorbance both in the visible and ultraviolet light energy range. By using DFT based first principles method Mn and Ni is doped at the Ge-site of CsGeCl3 halide. We investigate the detailed structural, optical, electronic and mechanical properties of all the doped compositions theoretically. The study of optical properties exhibits th…
We report the electronic properties of single crystals of candidate nodal-line semimetal CaAgP. The transport properties of CaAgP are understood within the framework of a hole-doped nodal-line semimetal. In contrast, Pd-doped CaAgP shows a drastic increase of magnetoresistance at low magnetic fields and a strong decrease of electrical resistivity at low temperatures probably due to weak antilocalization. Hall conductivity data indicated that the Pd-doped CaAgP has not only hole carriers induced by the Pd doping, but also high-mobility electron carriers in proximity of the Dirac point. Electric…
Stability, Electronic and Magnetic properties of magnetically doped topological insulators Bi2Se3, Bi2Te3 and Sb2Te3
在拓扑绝缘体（TI）中，磁与无带隙表面态的相互作用被预言会引起一些奇异的量子现象。然而，TI的有效磁性掺杂在实验上仍然具有挑战性。采用第一性原理计算方法，研究了Bi $_{2}$ Se $_{3}$，Bi $_{2}$ Te $_{3}$和Sb $_{2}$ Te $_{3}$中V，Cr，Mn和Fe的磁掺杂特性.我们发现，对于所有三个TI的阳离子位点的替代掺杂是最积极有利的阴离子丰富的环境作为最佳的生长条件。进一步我们的研究结果表明，在4%的标称掺杂浓度下，Cr和Fe掺杂的Bi $_{2}$ Se $_{3}$、Bi $_{2}$ Te $_{3}$和Cr掺杂的Sb $_{2}$ Te $_{3}$保持为绝缘体，而V、Mn和Fe掺杂的Sb $_{2}$ Te $_{3}$的所有TI变为金属。我们还发现，Cr掺杂Bi $_{2}$ Se $_{3}$的磁相互作用倾向于铁磁，而Fe掺杂Bi $_{2}$ Se $_{3}$的磁相互作用倾向于反铁磁.最后，我们利用蒙特卡罗模拟估算了有希望的铁磁绝缘体（Cr掺杂Bi $_{2}$ Se $_{3}$）的磁耦合和居里温度。这些发现可能为磁感应铁磁的实验研究提供重要的指导。
In this work, the thermal transport properties of thorium dioxide (ThO$_2$, thoria) with low levels of substitutional uranium (U) doping are explored. We observe strong indications of resonant phonon scattering, an interaction between phonons and electronic degrees of freedom, induced by this doping in addition to common ``impurity'' scattering due to mass and interatomic force constant differences. Uranium doping levels of 6\%, 9\%, and 16\% were studied in a single hydrothermally synthesized U-doped thoria crystal with spatially-varying U doping levels. Within this crystal, isoconcentration …
