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Xianqing Lin, Jun Ni
First-principles calculations have been performed to study the intrinsic spin Hall effect (SHE) and its behavior under vertical electric field in monoclinic transition metal dichalcogenide monolayers (1T$'$-MX$_2$ with M = Mo, W and X = S, Se, Te). We find that the pristine systems exhibit nonquantized intrinsic spin Hall conductivity (SHC) due to the unconserved spin around the direct band gaps though they have nontrivial band topology. The unconserved spin is attributed to the band crossings at Fermi levels for systems without SOC and the distinct composition of the band states around the crossings...
May 25, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Bivas Rana, Yasuhiro Fukuma, Katsuya Miura, Hiromasa Takahashi, YoshiChika Otani
Voltage or electric field induced magnetization dynamics promises low power spintronics devices. For successful operation of some spintronics devices such as magnetic oscillators and magnetization switching devices a clear understanding of nonlinear magnetization dynamics is required. Here, we report a detailed experimental and micromagnetic simulation study about the effect of excitation power on voltage induced local magnetization dynamics in an ultrathin CoFeB film. Experimental results show that the resonance line-width and frequency remains constant, whereas cone angle of the magnetization precession increases linearly with square-root of excitation power below threshold value, known as linear excitation regime...
May 24, 2017: Scientific Reports
Marcin Matusiak, J R Cooper, Dariusz Kaczorowski
Topological semimetals are systems in which conduction and valence bands cross each other and the crossings are protected by topological constraints. These materials provide intriguing tests for fundamental theories, while their unique physical properties promise a wide range of possible applications in low-power spintronics, optoelectronics, quantum computing and green energy harvesting. Here we report our study of the thermoelectric power of single-crystalline ZrSiS that is believed to be a topological nodal-line semimetal...
May 23, 2017: Nature Communications
Seonghoon Woo, Kyung Mee Song, Hee-Sung Han, Min-Seung Jung, Mi-Young Im, Ki-Suk Lee, Kun Soo Song, Peter Fischer, Jung-Il Hong, Jun Woo Choi, Byoung-Chul Min, Hyun Cheol Koo, Joonyeon Chang
Magnetic skyrmions are topologically protected spin textures with attractive properties suitable for high-density and low-power spintronic device applications. Much effort has been dedicated to understanding the dynamical behaviours of the magnetic skyrmions. However, experimental observation of the ultrafast dynamics of this chiral magnetic texture in real space, which is the hallmark of its quasiparticle nature, has so far remained elusive. Here, we report nanosecond-dynamics of a 100nm-diameter magnetic skyrmion during a current pulse application, using a time-resolved pump-probe soft X-ray imaging technique...
May 24, 2017: Nature Communications
H J Elmers, D Kutnyakhov, S V Chernov, K Medjanik, O Fedchenko, A Zaporozhchenko-Zymakova, M Ellguth, C Tusche, J Viefhaus, G Schönhense
Spin-momentum locking of surface states has attracted great interest in recent years due to envisioned technological applications in the field of spintronics. Normal metal surfaces like W(1 1 0) and Ir(1 1 1) show surface states with energy dispersions and spin-polarization textures, which are reminiscent of topologically non-trivial surface states. In order to understand this phenomenon the connection of bulk and surface states has to be explored. Using time-of-flight momentum microscopy with soft x-ray excitation, we present a comprehensive analysis of the bulk bands of W and Ir...
May 24, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Peng Chen, Jin-Yu Zou, Bang-Gui Liu
The electronic, magnetic, and topological properties of a CoBr2 monolayer are studied in the framework of density-functional theory (DFT) combined with tight-binding (TB) modeling in terms of the Wannier basis. Our DFT investigation and Monte Carlo simulation show that there exists intrinsic two-dimensional ferromagnetism in the CoBr2 monolayer, thanks to the large out-of-plane magnetocrystalline anisotropic energy. Our further study indicates that the spin-orbit coupling makes it become a topologically nontrivial insulator with a quantum anomalous Hall effect and topological Chern number [script C] = 4 and its edge states can be manipulated by changing the width of its nanoribbons and applying strains...
May 23, 2017: Physical Chemistry Chemical Physics: PCCP
Yunqiu Kelly Luo, Jinsong Xu, Tiancong Zhu, Guanzhong Wu, Elizabeth Joan McCormick, Wenbo Zhan, Mahesh R Neupane, Roland K Kawakami
Two dimensional (2D) materials provide a unique platform for spintronics and valleytronics due to the ability to combine vastly different functionalities into one vertically-stacked heterostructure, where the strengths of each of the constituent materials can compensate for the weaknesses of the others. Graphene has been demonstrated to be an exceptional material for spin transport at room temperature, however it lacks a coupling of the spin and optical degrees of freedom. In contrast, spin/valley polarization can be efficiently generated in monolayer transition metal dichalcogenides (TMD) such as MoS2 via absorption of circularly-polarized photons, but lateral spin or valley transport has not been realized at room temperature...
May 23, 2017: Nano Letters
Noah E Horwitz, Brian T Phelan, Jordan N Nelson, Catherine M Mauck, Matthew D Krzyaniak, Michael R Wasielewski
Photoexcitation of electron donor-acceptor molecules frequently produces radical ion pairs with well-defined initial spin-polarized states that have attracted significant interest for spintronics. Transfer of this initial spin polarization to a stable radical is predicted to depend on the rates of the radical ion pair recombination reactions, but this prediction has not been tested experimentally. In this study, a stable radical/electron donor/chromophore/electron acceptor molecule, BDPA(•)-mPD-ANI-NDI, where BDPA(•) is α,γ-bisdiphenylene-β-phenylallyl, mPD is m-phenylenediamine, ANI is 4-aminonaphthalene-1,8-dicarboximide, and NDI is naphthalene-1,4:5,8-bis(dicarboximide), was synthesized...
May 22, 2017: Journal of Physical Chemistry. A
Ying-Hao Chu, Tahta Amrillah, Yugandhar Bitla, Kwangwoo Shin, Tiannan Yang, Ying-Hui Hsieh, Yu-You Chiou, Heng-Jui Liu, Thi Hien Do, Dong Su, Yi-Chun Chen, Shien-Uang Jen, Long-Qing Chen, Kee Hoon Kim, Jenh-Yih Juang
Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on the spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains as a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating self-assembled ferroelectric-ferrimagnetic bulk heterojunction on flexible muscovite via the van der Waals epitaxy is adopted...
May 22, 2017: ACS Nano
Aniekan Ukpong
This paper presents the results of ab initio studies of the electronic spin manipulation, inversion, filtering and transport using a ferromagnetic multilayer heterostructure. Spin-polarized electronic structure calculations are performed based on van der Waals density functional theory to give unique insights to the generation, manipulation and transport of coherent spin conductance. By using an exact theory of the self-consistent ground state of the Fe-hBN/graphene multilayer as a model of the magnetic tunnel junction, this paper unravels the hidden asymmetries in the spin-resolved charge densities...
May 22, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Xue Zeng, Junwei Zhang, Shimeng Zhu, Xia Deng, Hongbin Ma, Junli Zhang, Qiang Zhang, Peng Li, Desheng Xue, Nigel J Mellors, Xixiang Zhang, Yong Peng
Low-dimensional spinel ferrites have recently attracted increasing attention because their tunable magnetic properties make them attractive candidates as spin-filtering tunnel barriers in spintronic devices and as magnetic components in artificial multiferroic heterostructures. Although we know that the distribution of cations (Fe(3+) and Co(2+)) in a spinel structure governs its magnetic properties, their distribution in the so-called ideal inverse spinel structure of a ferrite, CoFe2O4, has not yet been imaged with sub-ångstrom resolution...
May 22, 2017: Nanoscale
H Khani, M Esmaeilzadeh, F Kanjouri
Generation of large currents, versatile functionality, and simple structures are of fundamental importance in the development of adiabatic quantum pump devices with nanoscale dimensions. In the present study, we propose an adiabatic quantum pump with a simple structure based on molybdenum disulfide, MoS2, to generate large spin and valley resolved currents. We show that pure and fully polarized spin and valley currents can be easily generated by employing two potential gates and using an exchange magnetic field...
May 22, 2017: Physical Chemistry Chemical Physics: PCCP
Iriya Muneta, Toshiki Kanaki, Shinobu Ohya, Masaaki Tanaka
A major issue in the development of spintronic memory devices is the reduction of the power consumption for the magnetization reversal. For this purpose, the artificial control of the magnetic anisotropy of ferromagnetic materials is of great importance. Here, we demonstrate the control of the carrier-energy dependence of the magnetic anisotropy of the density of states (DOS) using the quantum size effect in a single-crystal ferromagnetic material, GaMnAs. We show that the mainly twofold symmetry of the magnetic anisotropy of DOS, which is attributed to the impurity band, is changed to a fourfold symmetry by enhancing the quantum size effect in the valence band of the GaMnAs quantum wells...
May 22, 2017: Nature Communications
Y Q Huang, Y X Song, S M Wang, I A Buyanova, W M Chen
A three-dimensional (3D) topological insulator (TI) is a unique quantum phase of matter with exotic physical properties and promising spintronic applications. However, surface spin current in a common 3D TI remains difficult to control and the out-of-plane spin texture is largely unexplored. Here, by means of surface spin photocurrent in Bi2Te3 TI devices driven by circular polarized light, we identify the subtle effect of the spin texture of the topological surface state including the hexagonal warping term on the surface current...
May 22, 2017: Nature Communications
Dawei Kang, Bowen Wang, Caijuan Xia, Haisheng Li
Zigzag graphene nanoribbons (ZGNRs) are expected to serve as the promising component in the all-carbon spintronic device. It remains challenging to fabricate a device based on ZGNRs with high spin-filter efficiency and low experimental complexity. Using density functional theory combined with nonequilibrium Green's function technique, we studied the spin-dependent transport properties of the tailored zigzag graphene nanoribbon. A perfect spin-filtering effect is found in the tailored structure of ZGNR. The nearly 100% spin-polarized current and high magneto-resistance ratio can be obtained by applying a homogeneous magnetic field across the device...
December 2017: Nanoscale Research Letters
Gong Chen, Sang Pyo Kang, Colin Ophus, Alpha T N'Diaye, Hee Young Kwon, Ryan T Qiu, Changyeon Won, Kai Liu, Yizheng Wu, Andreas K Schmid
Chiral spin textures in ultrathin films, such as skyrmions or chiral domain walls, are believed to offer large performance advantages in the development of novel spintronics technologies. While in-plane magnetized films have been studied extensively as media for current- and field-driven domain wall dynamics with applications in memory or logic devices, the stabilization of chiral spin textures in in-plane magnetized films has remained rare. Here we report a phase of spin structures in an in-plane magnetized ultrathin film system where out-of-plane spin orientations within domain walls are stable...
May 19, 2017: Nature Communications
Simranjeet Singh, Jyoti Katoch, Tiancong Zhu, Keng-Yuan Meng, Tianyu Liu, Jack T Brangham, Fengyuan Yang, Michael E Flatté, Roland K Kawakami
Two-dimensional materials provide a unique platform to explore the full potential of magnetic proximity-driven phenomena, which can be further used for applications in next-generation spintronic devices. Of particular interest is to understand and control spin currents in graphene by the magnetic exchange field of a nearby ferromagnetic material in graphene-ferromagnetic-insulator (FMI) heterostructures. Here, we present the experimental study showing the strong modulation of spin currents in graphene layers by controlling the direction of the exchange field due to FMI magnetization...
May 5, 2017: Physical Review Letters
Qunhong Weng, Dmitry G Kvashnin, Xi Wang, Ovidiu Cretu, Yijun Yang, Min Zhou, Chao Zhang, Dai-Ming Tang, Pavel B Sorokin, Yoshio Bando, Dmitri Golberg
Engineering of the optical, electronic, and magnetic properties of hexagonal boron nitride (h-BN) nanomaterials via oxygen doping and functionalization has been envisaged in theory. However, it is still unclear as to what extent these properties can be altered using such methodology because of the lack of significant experimental progress and systematic theoretical investigations. Therefore, here, comprehensive theoretical predictions verified by solid experimental confirmations are provided, which unambiguously answer this long-standing question...
May 19, 2017: Advanced Materials
Yanping Liu, Xiang Liu, Yanjing Zhang, Qinglin Xia, Jun He
We report on the observation of an unexpected sudden increase of resistance in bilayer graphene nanomesh (GNM) in the temperature range 270 ∼ 300 K that is strongly dependent on the magnetic field strength. We conjecture that the sharp increase in resistance originates from ripple scattering as induced by substrate roughness. The observed result is evidence of extrinsic corrugation in bilayer GNM as an additional scattering source that contributes to significant resistance. The observed weak localization in the GNM indicates intervalley scattering induced by lattice defects acts as resonant scatterers attribute to the high D peak...
June 9, 2017: Nanotechnology
Anmin Zheng, Guoying Gao, Hai Huang, Jinhua Gao, Kailun Yao
Using density-functional theory, we investigate the electronic and magnetic properties of an adatom (Na, Cu and Fe) on ABA- and ABC-stacked (Bernal and rhombohedral) trilayer graphenes. In particular, we study the influence of an applied gate voltage on magnetism, as it modifies the electronic states of the trilayer graphene (TLG) as well as changes the adatom spin states. Our study performed for a choice of three different adatoms (Na, Cu, and Fe) shows that the nature of adatom-graphene bonding evolves from ionic to covalent in moving from an alkali metal (Na) to a transition metal (Cu or Fe)...
May 17, 2017: Physical Chemistry Chemical Physics: PCCP
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