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https://www.readbyqxmd.com/read/28811470/bias-induced-up-to-100-spin-injection-and-detection-polarizations-in-ferromagnet-bilayer-hbn-graphene-hbn-heterostructures
#1
M Gurram, S Omar, B J van Wees
We study spin transport in a fully hBN encapsulated monolayer-graphene van der Waals heterostructure at room temperature. A top-layer of bilayer-hBN is used as a tunnel barrier for spin-injection and detection in graphene with ferromagnetic cobalt electrodes. We report surprisingly large and bias-induced (differential) spin-injection (detection) polarizations up to 50% (135%) at a positive voltage bias of + 0.6 V, as well as sign inverted polarizations up to -70% (-60%) at a reverse bias of -0.4 V. This demonstrates the potential of bilayer-hBN tunnel barriers for practical graphene spintronics applications...
August 15, 2017: Nature Communications
https://www.readbyqxmd.com/read/28799738/structural-dependent-optical-properties-of-self-organized-bi2se3-nanostructures-from-nanocrystals-to-nanoflakes
#2
Shang-Dong Yang, Liao Yang, Yuxiang Zheng, Wen-Jie Zhou, Meng-Yu Gao, Songyou Wang, Rong-Jun Zhang, Liangyao Chen
Bismuth selenide (Bi2Se3), with a wide bulk band gap and single massless Dirac cone at the surface, is a promising three-dimensional topological insulator. Bi2Se3 possesses gapless surface states and an insulator-like bulk band gap as a new type of quantum matter. Different Bi2Se3 nanostructures were prepared using electron beam evaporation (EBE) with high production efficiency. The structural investigations by energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM), and X-ray diffraction (XRD) revealed the sample stoichiometries and the structural transition mechanism from nanocrystals to nanoflakes...
August 11, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28798346/the-edge-stresses-and-phase-transitions-for-magnetic-bn-zigzag-nanoribbons
#3
Junkai Deng, Yuefeng Yin, Huanhuan Niu, Xiangdong Ding, Jun Sun, Nikhil V Medhekar
The edge states are of particular importance to understand fundamental properties of finite two-dimensional (2D) crystals. Based on first-principles calculations, we investigated on the bare zigzag boron nitride nanoribbons (zzBNNRs) with different spin-polarized states well localized at and extended along their edges. Our calculations examined the edge stress, which is sensitively dependent on the magnetic edge states, for either B-terminated edge or N-terminated edge. Moreover, we revealed that different magnetic configurations lead to a rich spectrum of electronic behaviors at edges...
August 10, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28795576/proximity-band-structure-and-spin-textures-on-both-sides-of-topological-insulator-ferromagnetic-metal-interface-and-their-charge-transport-probes
#4
Juan Manuel Marmolejo-Tejada, Kapildeb Dolui, Predrag Lazić, Po-Hao Chang, Søren Smidstrup, Daniele Stradi, Kurt Stokbro, Branislav K Nikolić
The control of recently observed spintronic effects in topological-insulator/ferromagnetic-metal (TI/FM) heterostructures is thwarted by the lack of understanding of band structure and spin textures around their interfaces. Here we combine density functional theory with Green's function techniques to obtain the spectral function at any plane passing through atoms of Bi2Se3 and Co or Cu layers comprising the interface. Instead of naively assumed Dirac cone gapped by the proximity exchange field spectral function, we find that the Rashba ferromagnetic model describes the spectral function on the surface of Bi2Se3 in contact with Co near the Fermi level EF(0), where circular and snowflake-like constant energy contours coexist around which spin locks to momentum...
August 16, 2017: Nano Letters
https://www.readbyqxmd.com/read/28794430/metallic-ferromagnetic-films-with-magnetic-damping-under-1-4%C3%A2-%C3%A3-%C3%A2-10-3
#5
Aidan J Lee, Jack T Brangham, Yang Cheng, Shane P White, William T Ruane, Bryan D Esser, David W McComb, P Chris Hammel, Fengyuan Yang
Low-damping magnetic materials have been widely used in microwave and spintronic applications because of their low energy loss and high sensitivity. While the Gilbert damping constant can reach 10(-4) to 10(-5) in some insulating ferromagnets, metallic ferromagnets generally have larger damping due to magnon scattering by conduction electrons. Meanwhile, low-damping metallic ferromagnets are desired for charge-based spintronic devices. Here, we report the growth of Co25Fe75 epitaxial films with excellent crystalline quality evident by the clear Laue oscillations and exceptionally narrow rocking curve in the X-ray diffraction scans as well as from scanning transmission electron microscopy...
August 10, 2017: Nature Communications
https://www.readbyqxmd.com/read/28782141/elucidation-of-dual-magnetic-relaxation-processes-in-dinuclear-dysprosium-iii-phthalocyaninato-triple-decker-single-molecule-magnets-depending-on-the-octacoordination-geometry
#6
Keiichi Katoh, Yu Aizawa, Takaumi Morita, Brian K Breedlove, Masahiro Yamashita
When applying single-molecule magnets (SMMs) to spintronic devices, control of the quantum tunneling of the magnetization (QTM) as well as a spin-lattice interactions are important. Attempts have been made to use not only coordination geometry but also magnetic interactions between SMMs as an exchange bias. In this manuscript, we report that dinuclear dysprosium(III) (DyIII) SMMs with the same octacoordination geometry undergo dual magnetic relaxation processes at low temperature. In the dinuclear DyIII phthalocyaninato (Pc2-) triple-decker type complex [(Pc)Dy(ooPc)Dy(Pc)] (1) (ooPc2- = 2,3,9,10,16,17,23,24-octakis(octyloxy)-19H,31H-phthalocyaninato) with a square-antiprismatic (SAP) geometry, the ground state is divided by the Zeeman effect, and level intersection occurs when a magnetic field is applied...
August 7, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28782030/giant-rashba-splitting-in-2d-organic-inorganic-halide-perovskites-measured-by-transient-spectroscopies
#7
Yaxin Zhai, Sangita Baniya, Chuang Zhang, Junwen Li, Paul Haney, Chuan-Xiang Sheng, Eitan Ehrenfreund, Zeev Valy Vardeny
Two-dimensional (2D) layered hybrid organic-inorganic halide perovskite semiconductors form natural "multiple quantum wells" that have strong spin-orbit coupling due to the heavy elements in their building blocks. This may lead to "Rashba splitting" close to the extrema in the electron bands. We have used a plethora of ultrafast transient, nonlinear optical spectroscopies and theoretical calculations to study the primary (excitons) and long-lived (free carriers) photoexcitations in thin films of 2D perovskite, namely, (C6H5C2H4NH3)2PbI4...
July 2017: Science Advances
https://www.readbyqxmd.com/read/28782025/observation-of-ultralong-valley-lifetime-in-wse2-mos2-heterostructures
#8
Jonghwan Kim, Chenhao Jin, Bin Chen, Hui Cai, Tao Zhao, Puiyee Lee, Salman Kahn, Kenji Watanabe, Takashi Taniguchi, Sefaattin Tongay, Michael F Crommie, Feng Wang
The valley degree of freedom in two-dimensional (2D) crystals recently emerged as a novel information carrier in addition to spin and charge. The intrinsic valley lifetime in 2D transition metal dichalcogenides (TMD) is expected to be markedly long due to the unique spin-valley locking behavior, where the intervalley scattering of the electron simultaneously requires a large momentum transfer to the opposite valley and a flip of the electron spin. However, the experimentally observed valley lifetime in 2D TMDs has been limited to tens of nanoseconds thus far...
July 2017: Science Advances
https://www.readbyqxmd.com/read/28780869/on-surface-synthesis-of-heptacene-organometallic-complexes
#9
José I Urgel, Hironobu Hayashi, Marco Di Giovannantonio, Carlo A Pignedoli, Shantanu Mishra, Okan Deniz, Masataka Yamashita, Thomas Dienel, Pascal Ruffieux, Hiroko Yamada, Roman Fasel
We report the on-surface formation of Au-directed heptacene organometallic complexes on a Au(111) template in an ultrahigh vacuum environment. Successive thermal annealing steps investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy, temperature-programmed desorption and density functional theory reveal the formation of heptacene organometallic complexes via a selective two-step activation of an α-diketone-protected heptacene precursor. Furthermore, we demonstrate the efficiency of tip-induced deprotection experiments as a complementary strategy in the complex formation...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28777633/antiferroelectric-topological-insulators-in-orthorhombic-amgbi-compounds-a-li-na-k
#10
Bartomeu Monserrat, Joseph W Bennett, Karin M Rabe, David Vanderbilt
We introduce antiferroelectric topological insulators as a new class of functional materials in which an electric field can be used to control topological order and induce topological phase transitions. Using first principles methods, we predict that several alkali-MgBi orthorhombic members of an ABC family of compounds are antiferroelectric topological insulators. We also show that epitaxial strain and hydrostatic pressure can be used to tune the topological order and the band gap of these ABC compounds. Antiferroelectric topological insulators could enable precise control of topology using electric fields, enhancing the applicability of topological materials in electronics and spintronics...
July 21, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28773127/ab-initio-investigations-of-magnetic-properties-and-induced-half-metallicity-in-ga1-xmnxp-x-0-03-0-25-0-5-and-0-75-alloys
#11
Amel Laref, Abeer AlMudlej, Slimane Laref, Jun Tao Yang, Yong-Chen Xiong, Shi Jun Luo
Ab-initio calculations are performed to examine the electronic structures and magnetic properties of spin-polarized Ga1-xMnxP (x = 0.03, 0.25, 0.5, and 0.75) ternary alloys. In order to perceive viable half-metallic (HM) states and unprecedented diluted magnetic semiconductors (DMSs) such as spintronic materials, the full potential linearized augmented plane wave method is utilized within the generalized gradient approximation (GGA). In order to tackle the correlation effects on 3d states of Mn atoms, we also employ the Hubbard U (GGA + U) technique to compute the magnetic properties of an Mn-doped GaP compound...
July 7, 2017: Materials
https://www.readbyqxmd.com/read/28771925/radical-enhanced-charge-transport-in-single-molecule-phenothiazine-electrical-junctions
#12
Junyang Liu, Xiaotao Zhao, Qusiy Al-Galiby, Xiaoyan Huang, Jueting Zheng, Ruihao Li, Cancan Huang, Yang Yang, Jia Shi, David Zsolt Manrique, Colin Lambert, Martin R Bryce, Wenjing Hong
We studied the single-molecule conductance through an acid oxidant triggered phenothiazine (PTZ) based radical junction using the Mechanically Controllable Break Junction technique. The electrical conductance of the radical state was enhanced by up to 200 times compared to the neutral state, with high stability lasting for at least two months and high junction formation probability at room-temperature. Theoretical studies revealed that the conductance increase is due to a significant decrease of HOMO-LUMO gap and also the enhanced transmission close to the HOMO orbital when the radical forms...
August 3, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28770919/unconventional-magnetic-anisotropy-in-one-dimensional-rashba-system-realized-by-adsorbing-gd-atom-on-zigzag-graphene-nanoribbons
#13
Zhenzhen Qin, Guangzhao Qin, Bin Shao, Xu Zuo
The Rashba effect, a spin splitting in electronic band structures, attracts much attention for potential applications in spintronics with no requirement of an external magnetic field. Realizing a one-dimensional (1D) Rashba system is a big challenge due to the difficulties of growing high-quality heavy-metal nanowires or introducing strong spin-orbit coupling (SOC) and broken inversion symmetry in flexible materials. Here, based on first-principles calculations, we propose a pathway to realize the Rashba spin-split by adsorbing Gd atom on zigzag graphene nanoribbons (Gd-ZGNR) and further investigate the magnetic anisotropy energy (MAE)...
August 3, 2017: Nanoscale
https://www.readbyqxmd.com/read/28765592/fabrication-of-epitaxial-fe3o4-film-on-a-si-111-substrate
#14
Nozomi Takahashi, Teodor Huminiuc, Yuta Yamamoto, Takashi Yanase, Toshihiro Shimada, Atsufumi Hirohata, Taro Nagahama
The application of magnetic oxides in spintronics has recently attracted much attention. The epitaxial growth of magnetic oxide on Si could be the first step of new functional spintronics devices with semiconductors. However, epitaxial spinel ferrite films are generally grown on oxide substrates, not on semiconductors. To combine oxide spintronics and semiconductor technology, we fabricated Fe3O4 films through epitaxial growth on a Si(111) substrate by inserting a γ-Al2O3 buffer layer. Both of γ-Al2O3 and Fe3O4 layer grew epitaxially on Si and the films exhibited the magnetic and electronic properties as same as bulk...
August 1, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28762955/perpendicularly-magnetized-co-sub-20-sub-fe-sub-60-sub-b-sub-20-sub-layer-sandwiched-between-au-with-low-gilbert-damping
#15
Piotr Kuswik, Hubert Głowiński, Emerson Coy, Janusz Dubowik, Feliks Stobiecki
Nowadays, the CoFeB thin layered film is intensively studied because of its potential applications in spintronic devices, especially for devices based on spin-transfer torque phenomenon. Hitherto, it was shown that CoFeB may possess perpendicular magnetic anisotropy (PMA) when it is sandwiched between different layers (e.g. MgO, Pt, Pd, Ta, W). However, there is no experimental evidence that CoFeB, sandwiched between Au layers, has strong PMA. Moreover, in comparison with other noble metals, the Au-based film systems exhibit the smallest spin pumping effect, which provides the main contribution to the damping in thin films in contact with heavy metals...
August 1, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28762733/chern-insulator-and-chern-half-metal-states-in-the-two-dimensional-spin-gapless-semiconductor-mn2c6s12
#16
Aizhu Wang, Xiaoming Zhang, Yuanping Feng, Mingwen Zhao
Two-dimensional metal-organic frameworks (2D-MOFs) with exotic electronic structures are drawing increasing attention. Here, using first-principles calculations, we demonstrate a spin-gapless MOF, namely, Mn2C6S12, with the coexistence of a spin-polarized Dirac cone and parabolic degenerate points. The Curie temperature evaluated from Monte Carlo simulations implies Mn2C6S12 possessing stable ferromagnetism at room temperature. Taking the spin-orbit coupling into account, the Dirac cone is gapped and the degenerate points are lifted, giving rise to multiple topologically nontrivial states with nonzero Chern number, which imply the possibility of Mn2C6S12 to be a Chern insulator and a Chern half-metal...
August 1, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28762399/hydrogenated-carbon-nanotube-based-spin-caloritronics
#17
Hong-Li Zeng, Yan-Dong Guo, Xiao-Hong Yan, Jie Zhou
Spin caloritronics has drawn much attention as it combines thermoelectrics and spintronics together. Carbon-based structures, such as graphene, have been found to exhibit different kinds of spin caloritronic features. However, a study of spin caloritronics in carbon nanotubes (CNTs) is still lacking. Using first-principles calculations, we investigate the spin-Seebeck effect (SSE) in partially hydrogenated CNTs. It is found that linear hydrogenation could make CNTs acquire magnetism and exhibit the spin-Seebeck effect...
August 16, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28758897/skew-scattering-dominated-anomalous-hall-effect-in-co-i-sub-x-sub-i-mgo-sub-100-i-x-i-sub-granular-thin-films
#18
Qiang Zhang, Yan Wen, Yuelei Zhao, Peng Li, Xin He, Junli Zhang, Yao He, Yong Peng, Ronghai Yu, Xixiang Zhang
We investigated the mechanism(s) of the anomalous Hall effect (AHE) in magnetic granular materials by fabricating 100-nm-thick thin films of Co<i><sub>x</sub></i>(MgO)<sub>100-<i>x</i></sub> with a Co volume fraction of 34≤<i>x</i>≤100 using co-sputtering at room temperature. We measured the temperature dependence of longitudinal resistivity (<i>ρ<sub>xx</sub></i>) and anomalous Hall resistivity (<i>ρ</i><sub>AHE</sub>) from 5 K to 300 K in all samples...
July 31, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28758656/magnetization-reversal-in-circular-vortex-dots-of-small-radius
#19
M Goiriena-Goikoetxea, K Y Guslienko, M Rouco, I Orue, E Berganza, M Jaafar, A Asenjo, M L Fernández-Gubieda, L Fernández Barquín, A García-Arribas
We present a detailed study of the magnetic behavior of Permalloy (Ni80Fe20 alloy) circular nanodots with small radii (30 nm and 70 nm) and different thicknesses (30 nm or 50 nm). Despite the small size of the dots, the measured hysteresis loops manifestly display the features of classical vortex behavior with zero remanence and lobes at high magnetic fields. This is remarkable because the size of the magnetic vortex core is comparable to the dot diameter, as revealed by magnetic force microscopy and micromagnetic simulations...
July 31, 2017: Nanoscale
https://www.readbyqxmd.com/read/28756667/chern-insulator-and-chern-half-metal-states-in-the-two-dimensional-spin-gapless-semiconductor-mn2c6s12
#20
Aizhu Wang, Xiaoming Zhang, Yuan Ping Feng, Mingwen Zhao
Two-dimensional metal-organic frameworks (2D-MOFs) with exotic electronic structures are drawing increasing attention. Here, using first-principles calculations, we demonstrate a spin-gapless MOF, namely Mn2C6S12 with the coexistence of spin-polarized Dirac cone and parabolic degenerate points. The Curie temperature evaluated from Monte Carlo simulations implies Mn2C6S12 possessing stable ferromagnetism at room temperature. Taking the spin-orbit coupling into account, the Dirac cone is gaped and the degenerate points are lifted, giving rise to multiple topologically nontrivial states with nonzero Chern number, which imply the possibility of Mn2C6S12 to be a Chern insulator and a Chern half-metal...
July 30, 2017: Journal of Physical Chemistry Letters
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