Excitation of propagating magnetization waves by microstrip antennas

NASA Astrophysics Data System (ADS)

Dmitriev, V. F.; Kalinikos, B. A.

1988-11-01

We discuss the self-consistent theory of excitation of dipole-exchange magnetization waves by microstrip antennas in a metal-dielectric-ferrite-dielectric-metal stratified structure, magnetized under an arbitrary angle to the surface. Spin-wave Green's functions are derived, describing the response of the spin-system to a spatially inhomogeneous varying magnetic field. The radiative resistance of microstrip antenna is calculated. In this case the distribution of surface current density in the antenna is found on the basis of the analytic solution of a singular integral equation. The nature of the effect of metallic screens and redistributed surface current densities in the antenna on the frequency dependence of the resistive radiation is investigated. Approximate relations are obtained, convenient for practical calculations of radiative resistance of microstrip antennas both in a free and in a screened ferromagnetic film. The theoretical calculations are verified by data of experiments carried out on monocrystalline films of iron-yttrium garnet.

Unifying Exchange Sensitivity in Transition-Metal Spin-State Ordering and Catalysis through Bond Valence Metrics.

PubMed

Gani, Terry Z H; Kulik, Heather J

2017-11-14

Accurate predictions of spin-state ordering, reaction energetics, and barrier heights are critical for the computational discovery of open-shell transition-metal (TM) catalysts. Semilocal approximations in density functional theory, such as the generalized gradient approximation (GGA), suffer from delocalization error that causes them to overstabilize strongly bonded states. Descriptions of energetics and bonding are often improved by introducing a fraction of exact exchange (e.g., erroneous low-spin GGA ground states are instead correctly predicted as high-spin with a hybrid functional). The degree of spin-splitting sensitivity to exchange can be understood based on the chemical composition of the complex, but the effect of exchange on reaction energetics within a single spin state is less well-established. Across a number of model iron complexes, we observe strong exchange sensitivities of reaction barriers and energies that are of the same magnitude as those for spin splitting energies. We rationalize trends in both reaction and spin energetics by introducing a measure of delocalization, the bond valence of the metal-ligand bonds in each complex. The bond valence thus represents a simple-to-compute property that unifies understanding of exchange sensitivity for catalytic properties and spin-state ordering in TM complexes. Close agreement of the resulting per-metal-organic-bond sensitivity estimates, together with failure of alternative descriptors demonstrates the utility of the bond valence as a robust descriptor of how differences in metal-ligand delocalization produce differing relative energetics with exchange tuning. Our unified description explains the overall effect of exact exchange tuning on the paradigmatic two-state FeO + /CH 4 reaction that combines challenges of spin-state and reactivity predictions. This new descriptor-sensitivity relationship provides a path to quantifying how predictions in transition-metal complex screening are sensitive to the method used.

Magnetic Charge Organization and Screening in Thermalized Artificial Spin Ice

NASA Astrophysics Data System (ADS)

Gilbert, Ian

2014-03-01

Artificial spin ice is a material-by-design in which interacting single-domain ferromagnetic nanoislands are used to model Ising spins in frustrated spin systems. Artificial spin ice has proved a useful system in which to directly probe the physics of geometrical frustration, allowing us to better understand materials such as spin ice. Recently, several new experimental techniques have been developed that allow effective thermalization of artificial spin ice. Given the intense interest in magnetic monopole excitations in spin ice materials and artificial spin ice's success in modeling these materials, it should not come as a surprise that interesting monopole physics emerges here as well. The first experimental investigation of thermalized artificial square spin ice determined that the system's monopole-like excitations obeyed a Boltzmann distribution and also found evidence for monopole-antimonopole interactions. Further experiments have implicated these monopole excitations in the growth of ground state domains. Our recent study of artificial kagome spin ice, whose odd-coordinated vertices always possess a net magnetic charge, has revealed a theoretically-predicted magnetic charge ordering transition which has not been previously observed experimentally. We have also investigated the details of magnetic charge interactions in lattices of mixed coordination number. This work was done in collaboration with Sheng Zhang, Cristiano Nisoli, Gia-Wei Chern, Michael Erickson, Liam O'Brien, Chris Leighton, Paul Lammert, Vincent Crespi, and Peter Schiffer. This work was primarily funded by the US Department of Energy, Office of Basic Energy Sciences, Materials Science and Engineering Division, grant no. DE-SC0005313.

Strong spin-orbit coupling and Zeeman spin splitting in angle dependent magnetoresistance of Bi{sub 2}Te{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dey, Rik, E-mail: rikdey@utexas.edu; Pramanik, Tanmoy; Roy, Anupam

We have studied angle dependent magnetoresistance of Bi{sub 2}Te{sub 3} thin film with field up to 9 T over 2–20 K temperatures. The perpendicular field magnetoresistance has been explained by the Hikami-Larkin-Nagaoka theory alone in a system with strong spin-orbit coupling, from which we have estimated the mean free path, the phase coherence length, and the spin-orbit relaxation time. We have obtained the out-of-plane spin-orbit relaxation time to be small and the in-plane spin-orbit relaxation time to be comparable to the momentum relaxation time. The estimation of these charge and spin transport parameters are useful for spintronics applications. For parallel field magnetoresistance,more » we have confirmed the presence of Zeeman effect which is otherwise suppressed in perpendicular field magnetoresistance due to strong spin-orbit coupling. The parallel field data have been explained using both the contributions from the Maekawa-Fukuyama localization theory for non-interacting electrons and Lee-Ramakrishnan theory of electron-electron interactions. The estimated Zeeman g-factor and the strength of Coulomb screening parameter agree well with the theory. Finally, the anisotropy in magnetoresistance with respect to angle has been described by the Hikami-Larkin-Nagaoka theory. This anisotropy can be used in anisotropic magnetic sensor applications.« less

Mesoscopic spin Hall effect in semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Zarbo, Liviu

The spin Hall effect (SHE) is a name given to a collection of diverse phenomena which share two principal features: (i) longitudinal electric current flowing through a paramagnetic semiconductor or metallic sample leads to transverse spin current and spin accumulation of opposite sign at opposing lateral edges; (ii) SHE does not require externally applied magnetic field or magnetic ordering in the equilibrium state of the sample, instead it relies on the presence of spin-orbit (SO) couplings within the sample. This thesis elaborates on a new type of phenomenon within the SHE family, predicted in our recent studies [Phys. Rev. B 72, 075361 (2005); Phys. Rev. Lett. 95, 046601 (2005); Phys. Rev. B 72, 075335 (2005); Phys. Rev. B 73 , 075303 (2006); and Europhys. Lett. 77, 47004 (2007)], where pure spin current flows through the transverse electrodes attached to a clean finitesize two-dimensional electron gas (2DEG) due to unpolarized charge current injected through its longitudinal leads. If transverse leads are removed, the effect manifests as nonequilibrium spin Hall accumulation at the lateral edges of 2DEG wires. The SO coupling driving this SHE effect is of the Rashba type, which arises due to structural inversion asymmetry of semiconductor heterostructure hosting the 2DEG. We term the effect "mesoscopic" because the spin Hall currents and accumulations reach optimal value in samples of the size of the spin precession length---the distance over which the spin of an electron precesses by an angle pi. In strongly SO-coupled structures this scale is of the order of ˜100 nm, and, therefore, mesoscopic in the sense of being much larger than the characteristic microscopic scales (such as the Fermi wavelength, screening length, or the mean free path in disordered systems), but still much smaller than the macroscopic ones. Although the first theoretical proposal for SHE, driven by asymmetry in SO-dependent scattering of spin-up and spin-down electrons off impurities, appeared in 1970s, it is only in the past few years that advances in optical detection of nonequilibrium magnetization in semiconductors have made possible the detection of such extrinsic SHE in groundbreaking experiments. The experimental pursuits of SHE have, in fact, been largely motivated by very recent theoretical speculations for several order of magnitude greater spin Hall currents driven by intrinsic SO mechanisms due to SO couplings existing not only around the impurity but also throughout the sample. The homogeneous intrinsic SO couplings are capable of spin-splitting the band structure and appear as momentum-dependent magnetic field within the sample which causes spin non-conservation due to precession of injected spins which are not in the eigenstates of the corresponding Zeeman term. Besides deepening our understanding of subtle relativistic effects in solids, SHE has attracted a lot of attention since it offers an all-electrical way of generating pure spin currents in semiconductors. (Abstract shortened by UMI.)

Use of the Chinese (Taiwan) version of the Social Phobia Inventory (SPIN) among early adolescents in rural areas: reliability and validity study.

PubMed

Tsai, Chia-Fen; Wang, Shuu-Jiun; Juang, Kai-Dih; Fuh, Jong-Ling

2009-08-01

To assess the screening abilities of the Chinese (Taiwan) version of the Social Phobia Inventory (SPIN) for evaluating social phobia in an adolescent community sample. A total of 3,393 students (1,669 boys, 1,724 girls), aged 13-15, completed the SPIN questionnaire. A total of 144 students were enrolled for validity. The Mini-International-Neuropsychiatric-Interview-Kid (MINI-Kid) was used to establish Diagnostic and Statistical Manual of Mental Disorders-IV diagnosis. The mean SPIN total score of all subjects was 14.2 +/- 9.4, which was higher in girls than in boys (14.7 +/- 9.4 vs. 13.7 +/- 9.1; p < 0.01). The 7th graders had the highest SPIN total scores compared with the 8th and 9th graders (15.4 +/- 9.7 vs. 13.4 +/- 9.1 and 14.0 +/- 9.4; p < 0.001). Internal consistency (Cronbach's alpha = 0.85) and test-retest reliability (r = 0.73) were both good. A cut-off score of 25 resulted in balanced sensitivity (80%) and specificity (77%). The Chinese (Taiwan) SPIN has good screening abilities. The cut-offs are different from those in other countries, and highlight the importance of culturally adapted cut-offs.

The 3D Kasteleyn transition in dipolar spin ice: a numerical study with the conserved monopoles algorithm

NASA Astrophysics Data System (ADS)

Baez, M. L.; Borzi, R. A.

2017-02-01

We study the three-dimensional Kasteleyn transition in both nearest neighbours and dipolar spin ice models using an algorithm that conserves the number of excitations. We first limit the interactions range to nearest neighbours to test the method in the presence of a field applied along ≤ft[1 0 0\\right] , and then focus on the dipolar spin ice model. The effect of dipolar interactions, which is known to be greatly self screened at zero field, is particularly strong near full polarization. It shifts the Kasteleyn transition to lower temperatures, which decreases  ≈0.4 K for the parameters corresponding to the best known spin ice materials, \\text{D}{{\\text{y}}2}\\text{T}{{\\text{i}}2}{{\\text{O}}7} and \\text{H}{{\\text{o}}2}\\text{T}{{\\text{i}}2}{{\\text{O}}7} . This shift implies effective dipolar fields as big as 0.05 T opposing the applied field, and thus favouring the creation of ‘strings’ of reversed spins. We compare the reduction in the transition temperature with results in previous experiments, and study the phenomenon quantitatively using a simple molecular field approach. Finally, we relate the presence of the effective residual field to the appearance of string-ordered phases at low fields and temperatures, and we check numerically that for fields applied along ≤ft[1 0 0\\right] there are only three different stable phases at zero temperature.

Quantum impurity models for magnetic adsorbates on superconductor surfaces

NASA Astrophysics Data System (ADS)

Žitko, Rok

2018-05-01

Magnetic atoms adsorbed on surfaces have a quenched orbital moment while their ground-state spin multiplet is partially split as a consequence of the spin-orbit coupling which, even if intrinsically weak, has a large effect due to the abrupt change of the potential at the surface. Such metal adsorbates should be modelled using quantum impurity models that include the relevant internal degrees of freedom and the interaction terms, in particular the magnetic anisotropy and the Kondo exchange coupling. When adsorbed on superconducting surfaces, these impurities have complex spectra of sub-gap excitations due to magnetic anisotropy splitting and Kondo screening. Both anisotropy splitting and Zeeman splitting due to the external magnetic field are significantly renormalized by the coupling to the substrate electrons. In this work I discuss the quantum-to-classical crossover and the applicability of classical static-local-spin picture for discussing magnetic nanostructures on superconductors.

Spin-orbit coupling calculations with the two-component normalized elimination of the small component method

NASA Astrophysics Data System (ADS)

Filatov, Michael; Zou, Wenli; Cremer, Dieter

2013-07-01

A new algorithm for the two-component Normalized Elimination of the Small Component (2cNESC) method is presented and tested in the calculation of spin-orbit (SO) splittings for a series of heavy atoms and their molecules. The 2cNESC is a Dirac-exact method that employs the exact two-component one-electron Hamiltonian and thus leads to exact Dirac SO splittings for one-electron atoms. For many-electron atoms and molecules, the effect of the two-electron SO interaction is modeled by a screened nucleus potential using effective nuclear charges as proposed by Boettger [Phys. Rev. B 62, 7809 (2000), 10.1103/PhysRevB.62.7809]. The use of the screened nucleus potential for the two-electron SO interaction leads to accurate spinor energy splittings, for which the deviations from the accurate Dirac Fock-Coulomb values are on the average far below the deviations observed for other effective one-electron SO operators. For hydrogen halides HX (X = F, Cl, Br, I, At, and Uus) and mercury dihalides HgX2 (X = F, Cl, Br, I) trends in spinor energies and SO splittings as obtained with the 2cNESC method are analyzed and discussed on the basis of coupling schemes and the electronegativity of X.

Psychometric Properties of the Mini-Social Phobia Inventory

PubMed Central

Seeley-Wait, Elizabeth; Rapee, Ronald M.

2009-01-01

Objective: Although a potentially useful measure, to date, there has been only one published test of the psychometric properties of the Mini-Social Phobia Inventory (Mini-SPIN). Therefore, the psychometric properties of the Mini-SPIN, a brief 3-item screen for social anxiety disorder, were examined. Method: Participants were 186 patients diagnosed with social anxiety disorder (DSM-IV criteria) attending a specialized anxiety disorders clinic for treatment, and 56 nonclinical participants were recruited to serve as comparisons. Participants were diagnosed using the Anxiety Disorders Interview Schedule for DSM-IV, and they also completed the Mini-SPIN, the Social Interaction Anxiety Scale (SIAS), and the Social Phobia Scale (SPS). Construct validity for the Mini-SPIN was assessed by its correlations with the SIAS and the SPS. Reliability, internal consistency, discriminant validity, and sensitivity to change were also examined, and receiver operating characteristic curve analysis was conducted to determine guidelines regarding cutoff scores for the Mini-SPIN. The study was conducted between April 1999 and December 2001. Results: Supporting findings from a previous study, strong support was found for the Mini-SPIN's ability to discriminate individuals with social anxiety disorder from those without the disorder. Receiver operating characteristic analysis revealed that using a cutoff score of 6 or greater (P < .001), the Mini-SPIN demonstrates excellent sensitivity, specificity, and positive and negative predictive values. Conclusions: Findings suggest that the Mini-SPIN is a reliable and valid instrument for screening social anxiety disorder in adults. Importantly, the use of the Mini-SPIN in primary care may be one way to address the underrecognition of social anxiety disorder in such settings. Due to the ease and brevity of the measure, it also shows potential for use in epidemiology. Given that this study has revealed the ability of the Mini-SPIN to reflect treatment change, the Mini-SPIN may also be considered for use in treatment outcome studies that specifically require minimal assessment. PMID:19956461

Kondo effect with tunable spin-orbit interaction in LaTiO3/CeTiO3/SrTiO3 heterostructure.

PubMed

Ghising, Pramod; Das, Debarchan; Das, Shubhankar; Hossain, Z

2018-07-18

We have fabricated epitaxial films of CeTiO 3 (CTO) on (0 0 1) oriented SrTiO 3 (STO) substrates, which exhibit highly insulating and diamagnetic properties. X-ray photoelectron spectroscopy was used to establish the 3+  valence state of the Ce and Ti ions. Furthermore, we have also fabricated δ (CTO) doped LaTiO 3 (LTO)/SrTiO 3 thin films which exhibit variety of interesting properties including Kondo effect and spin-orbit interaction (SOI) at low temperatures. The SOI shows a non-monotonic behaviour as the thickness of the CTO layer is increased and is reflected in the value of characteristic SOI field ([Formula: see text]) obtained from weak anti-localization fitting. The maximum value of [Formula: see text] is 1.00 T for δ layer thickness of 6 u.c. This non-monotonic behaviour of SOI is attributed to the strong screening of the confining potential at the interface. The screening effect is enhanced by the CTO layer thickness and the dielectric constant of STO which increases at low temperatures. Due to the strong screening, electrons confined at the interface are spread deeper into the STO bulk where it starts to populate the Ti [Formula: see text] subbands; consequently the Fermi level crosses over from [Formula: see text] to the [Formula: see text] subbands. At the crossover region of [Formula: see text] where there is orbital mixing, SOI goes through a maximum.

Pulsar Polar Cap Heating and Surface Thermal X-ray Emission. 1; Curvature Radiation Pair Fronts

NASA Technical Reports Server (NTRS)

Harding, Alice K.; Muslimov, Alexander G.; White, Nicholas E. (Technical Monitor)

2002-01-01

We investigate the effect of pulsar polar cap (PC) heating produced by positrons returning from the upper pair formation front. Our calculations are based on a self-consistent treatment of the pair dynamics and the effect of electric field screening by the returning positrons. We calculate the resultant X-ray luminosities and discuss the dependence of the PC heating efficiencies on pulsar parameters, such as characteristic spin-down age, spin period, and surface magnetic field strength. In this study we concentrate on the regime where the pairs are produced in a magnetic field by curvature photons emitted by accelerating electrons. Our theoretical results are not in conflict with the available observational x-ray data and suggest that the effect of PC heating should significantly contribute to the thermal x-ray fluxes from middle-aged and old pulsars. The implications for current and future x-ray observations of pulsars are briefly outlined.

Comparative economic evaluation of data from the ACRIN National CT Colonography Trial with three cancer intervention and surveillance modeling network microsimulations.

PubMed

Vanness, David J; Knudsen, Amy B; Lansdorp-Vogelaar, Iris; Rutter, Carolyn M; Gareen, Ilana F; Herman, Benjamin A; Kuntz, Karen M; Zauber, Ann G; van Ballegooijen, Marjolein; Feuer, Eric J; Chen, Mei-Hsiu; Johnson, C Daniel

2011-11-01

To estimate the cost-effectiveness of computed tomographic (CT) colonography for colorectal cancer (CRC) screening in average-risk asymptomatic subjects in the United States aged 50 years. Enrollees in the American College of Radiology Imaging Network National CT Colonography Trial provided informed consent, and approval was obtained from the institutional review board at each site. CT colonography performance estimates from the trial were incorporated into three Cancer Intervention and Surveillance Modeling Network CRC microsimulations. Simulated survival and lifetime costs for screening 50-year-old subjects in the United States with CT colonography every 5 or 10 years were compared with those for guideline-concordant screening with colonoscopy, flexible sigmoidoscopy plus either sensitive unrehydrated fecal occult blood testing (FOBT) or fecal immunochemical testing (FIT), and no screening. Perfect and reduced screening adherence scenarios were considered. Incremental cost-effectiveness and net health benefits were estimated from the U.S. health care sector perspective, assuming a 3% discount rate. CT colonography at 5- and 10-year screening intervals was more costly and less effective than FOBT plus flexible sigmoidoscopy in all three models in both 100% and 50% adherence scenarios. Colonoscopy also was more costly and less effective than FOBT plus flexible sigmoidoscopy, except in the CRC-SPIN model assuming 100% adherence (incremental cost-effectiveness ratio: $26,300 per life-year gained). CT colonography at 5- and 10-year screening intervals and colonoscopy were net beneficial compared with no screening in all model scenarios. The 5-year screening interval was net beneficial over the 10-year interval except in the MISCAN model when assuming 100% adherence and willingness to pay $50,000 per life-year gained. All three models predict CT colonography to be more costly and less effective than non-CT colonographic screening but net beneficial compared with no screening given model assumptions. RSNA, 2011

Effect of Spin-Orbit Coupling on the Actinide Dioxides AnO2 (An=Th, Pa, U, Np, Pu, and Am): A Screened Hybrid Density Functional Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wen, Xiaodong; Martin, Richard L.; Roy, Lindsay E.

2012-10-21

We present a systematic comparison of the lattice structures, electronic density of states, and band gaps of actinide dioxides, AnO₂ (An=Th, Pa, U, Np, Pu, and Am) predicted by the Heyd-Scuseria-Ernzerhof screened hybrid density functional (HSE) with the self-consistent inclusion of spin-orbit coupling(SOC). The computed HSE lattice constants and band gaps of AnO₂ are in consistently good agreement with the available experimental data across the series, and differ little from earlier HSE results without SOC. ThO₂ is a simple band insulator (f⁰), while PaO₂, UO₂, and NpO₂ are predicted to be Mott insulators. The remainders (PuO₂ and AmO₂) show considerablemore » O2p/An5f mixing and are classified as charge-transfer insulators. We also compare our results for UO₂, NpO₂, and PuO₂with the PBE+U, self interaction correction (SIC), and dynamic mean-field theory (DMFT) many-body approximations.« less

Negativity as the entanglement measure to probe the Kondo regime in the spin-chain Kondo model

NASA Astrophysics Data System (ADS)

Bayat, Abolfazl; Sodano, Pasquale; Bose, Sougato

2010-02-01

We study the entanglement of an impurity at one end of a spin chain with a block of spins using negativity as a true measure of entanglement to characterize the unique features of the gapless Kondo regime in the spin-chain Kondo model. For this spin chain in the Kondo regime we determine—with a true entanglement measure—the spatial extent of the Kondo screening cloud, we propose an ansatz for its ground state and demonstrate that the impurity spin is indeed maximally entangled with the cloud. To better evidence the peculiarities of the Kondo regime, we carry a parallel analysis of the entanglement properties of the Kondo spin-chain model in the gapped dimerized regime. Our study shows how a genuine entanglement measure stemming from quantum information theory can fully characterize also nonperturbative regimes accessible to certain condensed matter systems.

Size Effects in the Resistivity of Kondo and Spin-Glass Wires

NASA Astrophysics Data System (ADS)

van Haesendonck, Chris

1998-03-01

Recently, several experiments have focused on possible size effects for the Kondo scattering in thin-film structures of very dilute magnetic alloys (concentration ~ 100 ppm) (For an overview, see M.A. Blachly and N. Giordano, Phys. Rev. B 51), 12537 (1995).. Intuitively, one expects size effects to occur as soon as the sample dimensions become smaller than the size of the Kondo screening cloud which induces a compensation of the local magnetic moments below the Kondo temperature. Since the size of the Kondo cloud is predicted to be of the order of 1 μ m, one should be able to observe pronounced size effects in thin-film Kondo alloys which have been patterned by standard electron beam lithography. Experiments performed by other groups have indeed revealed an important reduction of the slope of the Kondo resistivity for samples with micrometer dimensions. These experiments also show that the size effects are affected by disorder. On the other hand, our experiments on AuFe wires, which have been prepared by flash evaporation as well as by ion implantation, indicate the absence of size effects for the Kondo scattering down to a width of 38 nm. Therefore, the existence of the Kondo cloud remains a controversial issue. The size effects have also been investigated for more concentrated spin-glass alloys (concentration ~ 1 at.%). The resistivity measurements of thin-film spin glasses indicate that intrinsic size effects may be present for length scales below 100 nm (K.R. Lane et al., Phys. Rev. B 51), 945 (1995); G. Neuttiens et al., Europhys. Lett. 34, 617 (1996).. Due to the damping of the RKKY interaction by elastic defect scattering, size effects in the spin-glass regime can be strongly affected by disorder.

The f ( R ) halo mass function in the cosmic web

DOE Office of Scientific and Technical Information (OSTI.GOV)

Braun-Bates, F. von; Winther, H.A.; Alonso, D.

An important indicator of modified gravity is the effect of the local environment on halo properties. This paper examines the influence of the local tidal structure on the halo mass function, the halo orientation, spin and the concentration-mass relation. We use the excursion set formalism to produce a halo mass function conditional on large-scale structure. Our simple model agrees well with simulations on large scales at which the density field is linear or weakly non-linear. Beyond this, our principal result is that f ( R ) does affect halo abundances, the halo spin parameter and the concentration-mass relationship in anmore » environment-independent way, whereas we find no appreciable deviation from \\text(ΛCDM) for the mass function with fixed environment density, nor the alignment of the orientation and spin vectors of the halo to the eigenvectors of the local cosmic web. There is a general trend for greater deviation from \\text(ΛCDM) in underdense environments and for high-mass haloes, as expected from chameleon screening.« less

SPIN1, negatively regulated by miR-148/152, enhances Adriamycin resistance via upregulating drug metabolizing enzymes and transporter in breast cancer.

PubMed

Chen, Xu; Wang, Ya-Wen; Gao, Peng

2018-05-09

Spindlin1 (SPIN1), a protein highly expressed in several human cancers, has been correlated with tumorigenesis and development. Alterations of drug metabolizing enzymes and drug transporters are major determinants of chemoresistance in tumor cells. However, whether the metabolizing enzymes and transporters are under the control of SPIN1 in breast cancer chemoresistance has not yet been defined. SPIN1 expression in breast cancer cells and tissues was detected by quantitative real-time PCR (qRT-PCR) and immunohistochemistry. Chemosensitivity assays in vitro and in vivo were performed to determine the effect of SPIN1 on Adriamycin resistance. Downstream effectors of SPIN1 were screened by microarray and confirmed by qRT-PCR and Western blot. Luciferase assay and Western blot were used to identify miRNAs regulating SPIN1. We showed that SPIN1 was significantly elevated in drug-resistant breast cancer cell lines and tissues, compared with the chemosensitive ones. SPIN1 enhanced Adriamycin resistance of breast cancer cells in vitro, and downregulation of SPIN1 by miRNA could decrease Adriamycin resistance in vivo. Mechanistically, drug metabolizing enzymes and transporter CYP2C8, UGT2B4, UGT2B17 and ABCB4 were proven to be downstream effectors of SPIN1. Notably, SPIN1 was identified as a direct target of the miR-148/152 family (miR-148a-3p, miR-148b-3p and miR-152-3p). As expected, miR-148a-3p, miR-148b-3p or miR-152-3p could increase Adriamycin sensitivity in breast cancer cells in vitro. Moreover, high expression of SPIN1 or low expression of the miR-148/152 family predicted poorer survival in breast cancer patients. Our results establish that SPIN1, negatively regulated by the miR-148/152 family, enhances Adriamycin resistance in breast cancer via upregulating the expression of drug metabolizing enzymes and drug transporter.

Extensive screening for herbal extracts with potent antioxidant properties

PubMed Central

Niwano, Yoshimi; Saito, Keita; Yoshizaki, Fumihiko; Kohno, Masahiro; Ozawa, Toshihiko

2011-01-01

This paper summarizes our research for herbal extracts with potent antioxidant activity obtained from a large scale screening based on superoxide radical (O2•−) scavenging activity followed by characterization of antioxidant properties. Firstly, scavenging activity against O2•− was extensively screened from ethanol extracts of approximately 1000 kinds of herbs by applying an electron spin resonance (ESR)-spin trapping method, and we chose four edible herbal extracts with prominently potent ability to scavenge O2•−. They are the extracts from Punica granatum (Peel), Syzygium aromaticum (Bud), Mangifera indica (Kernel), and Phyllanthus emblica (Fruit). These extracts were further examined to determine if they also scavenge hydroxyl radical (•OH), by applying the ESR spin-trapping method, and if they have heat resistance as a desirable characteristic feature. Experiments with the Fenton reaction and photolysis of H2O2 induced by UV irradiation demonstrated that all four extracts have potent ability to directly scavenge •OH. Furthermore, the scavenging activities against O2•− and •OH of the extracts of P. granatum (peel), M. indica (kernel) and P. emblica (fruit) proved to be heat-resistant. The results of the review might give useful information when choosing a potent antioxidant as a foodstuff. For instance, the four herbal extracts chosen from extensive screening possess desirable antioxidant properties. In particular, the extracts of the aforementioned three herbs are expected to be suitable for food processing in which thermal devices are used, because of their heat resistance. PMID:21297917

High-efficiency optical pumping of nuclear polarization in a GaAs quantum well

NASA Astrophysics Data System (ADS)

Mocek, R. W.; Korenev, V. L.; Bayer, M.; Kotur, M.; Dzhioev, R. I.; Tolmachev, D. O.; Cascio, G.; Kavokin, K. V.; Suter, D.

2017-11-01

The dynamic polarization of nuclear spins by photoexcited electrons is studied in a high quality GaAs/AlGaAs quantum well. We find a surprisingly high efficiency of the spin transfer from the electrons to the nuclei as reflected by a maximum nuclear field of 0.9 T in a tilted external magnetic field of 1 T strength only. This high efficiency is due to a low leakage of spin out of the polarized nuclear system, because mechanisms of spin relaxation other than the hyperfine interaction are strongly suppressed, leading to a long nuclear relaxation time of up to 1000 s. A key ingredient to that end is the low impurity concentration inside the heterostructure, while the electrostatic potential from charged impurities in the surrounding barriers becomes screened through illumination by which the spin relaxation time is increased compared to keeping the system in the dark. This finding indicates a strategy for obtaining high nuclear spin polarization as required for long-lasting carrier spin coherence.

The Coulomb based magneto-electric coupling in multiferroic tunnel junctions and granular multiferroics

NASA Astrophysics Data System (ADS)

Udalov, O. G.; Beloborodov, I. S.

2018-05-01

We study magneto-electric effect in two systems: i) multiferroic tunnel junction (MFTJ) - magnetic tunnel junction with ferroelectric barrier and ii) granular multiferroic (GMF) in which ferromagnetic (FM) metallic grains embedded into ferroelectric matrix. We show that the Coulomb interaction influences the magnetic state of the system in several ways: i) through the spin-dependent part of the Coulomb interaction; ii) due to the Coulomb blockade effect suppressing electron hopping and therefore reducing magnetic coupling; and iii) through image forces and polarization screening that modify the barrier for electrons in MFTJ and GMF. We show that in the absence of spin-orbit or strain-mediated coupling magneto-electric effect appears in GMF and MFTJ. The Coulomb interaction depends on the dielectric properties of the system. For GMF it depends on the dielectric constant of FE matrix and for MFTJ on the dielectric constant of the FE barrier. Applying external electric field one can tune the dielectric constant and the Coulomb interaction. Thus, one can control magnetic state with electric field.

Interacting potential between spinons in the compact QED3 description of the Heisenberg model

NASA Astrophysics Data System (ADS)

Dillenschneider, R.; Richert, J.

2008-02-01

We implement a Chern-Simons (CS) contribution into the compact QED3 description of the antiferromagnetic Heisenberg model in two dimensions at zero temperature. The CS term allows for the conservation of the SU(2) symmetry of the quantum spin system and fixes the flux through a plaquette to be a multiple of π as was shown by Marston. We work out the string tension of the confining potential which acts between the spinons and show that the CS term induces a screening effect on the magnetic field only. The confining potential between spinons is not affected by the CS flux. The strict site-occupation by a single spin 1/2 is enforced by the introduction of an imaginary chemical potential constraint.

DFT Analysis of Spin Crossover in Mn(III) Complexes: Is a Two-Electron S = 2 to S = 0 Spin Transition Feasible?

PubMed

Amabilino, Silvia; Deeth, Robert J

2017-03-06

Six-coordinate, rigorously octahedral d 4 Mn(III) spin crossover (SCO) complexes are limited by symmetry to an S = 1 (intermediate spin, IS) to S = 2 (high spin, HS) transition. In order to realize the potential S = 0 to S = 2 transition, a lower symmetry and/or change in coordination number is needed, which we explore here computationally. First, a number of complexes are analyzed to develop a reliable and relatively fast DFT protocol for reproducing known Mn(III) spin state energetics. The hybrid meta-GGA functional TPSSh with a modest split valence plus polarization basis set and an empirical dispersion correction is found to predict correctly the ground spin state of Mn(III) complexes, including true low-spin (LS) S = 0 systems, with a range of donor sets including the hexadentate [N 4 O 2 ] Schiff base ligands. The electronic structure design criteria necessary for realizing a ΔS = 2 SCO transition are described, and a number of model complexes are screened for potential SCO behavior. Five-coordinate trigonal-bipyramidal symmetry fails to yield any suitable systems. Seven-coordinate, approximately pentagonal bipyramidal symmetry is more favorable, and when a known pentadentate macrocyclic donor is combined with π-acceptor axial ligands, a novel Mn(III) complex, [Mn(PABODP)(PF 3 ) 2 ] 3+ (PABODP = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene), is predicted to have the right spin state energetics for an S = 0 to S = 2 transition. Successful synthesis of such a complex could provide the first example of a ΔS = 2 SCO transition for d 4 Mn(III). However, the combination of a rigid macrocycle and a high coordination number dilutes the stereochemical activity of the d electrons, leading to relatively small structural changes between HS and LS systems. It may therefore remain a challenge to realize strong cooperative effects in Mn(III) systems.

Non-equilibrium Transport in Carbon based Adsorbate Systems

NASA Astrophysics Data System (ADS)

Fürst, Joachim; Brandbyge, Mads; Stokbro, Kurt; Jauho, Antti-Pekka

2007-03-01

We have used the Atomistix Tool Kit(ATK) and TranSIESTA[1] packages to investigate adsorption of iron atoms on a graphene sheet. The technique of both codes is based on density functional theory using local basis sets[2], and non-equilibrium Green's functions (NEGF) to calculate the charge distribution under external bias. Spin dependent electronic structure calculations are performed for different iron coverages. These reveal adsorption site dependent charge transfer from iron to graphene leading to screening effects. Transport calculations show spin dependent scattering of the transmission which is analysed obtaining the transmission eigenchannels for each spin type. The phenomena of electromigration of iron in these systems at finite bias will be discussed, estimating the so-called wind force from the reflection[3]. [1] M. Brandbyge, J.-L. Mozos, P. Ordejon, J. Taylor, and K. Stokbro. Physical Review B (Condensed Matter and Materials Physics), 65(16):165401/11-7, 2002. [2] Jose M. Soler, Emilio Artacho, Julian D. Gale, Alberto Garcia, Javier Junquera, Pablo Ordejon, and Daniel Sanchez-Portal. Journal of Physics Condensed Matter, 14(11):2745-2779, 2002. [3] Sorbello. Theory of electromigration. Solid State Physics, 1997.

Spinomotive force induced by a transverse displacement current in a thin metal or doped-semiconductor sheet: Classical and quantum views.

NASA Astrophysics Data System (ADS)

Hu, Chia-Ren

2004-03-01

We present classical macroscopic, microscopic, and quantum mechanical arguments to show that in a metallic or electron/hole-doped semiconducting sheet thinner than the screening length, a displacement current applied normal to it can induce a spinomotive force along it. The magnitude is weak but clearly detectable. The classical arguments are purely electromagnetic. The quantum argument, based on the Dirac equation, shows that the predicted effect originates from the spin-orbit interaction, but not of the usual kind. That is, it relies on an external electric field, whereas the usual S-O interaction involves the electric field generated by the ions. Because the Dirac equation incorporatesThomas precession, which is due to relativistic kinematics, the quantum prediction is a factor of two smaller than the classical prediction. Replacing the displacement current by a charge current, and one obtains a new source for the spin-Hall effect. Classical macroscopic argument also predicts its existence, but the other two views are controversial.

Mott-metal transition in layered perovskite iridate thin films via field-effect doping

NASA Astrophysics Data System (ADS)

Cheema, Suraj; Turcaud, Jeremy; Nelson, Chris; Salahuddin, Sayeef; Ramesh, Ramamoorthy

We report on electrostatic gating of spin-orbit coupled Mott insulator Sr2IrO4 (Sr214) via ferroelectric field effect doping. Field effect doping has been used to modulate electronic phenomena in emerging 2D systems and strongly correlated oxides, but 5 d systems with large spin-orbit coupling have yet to be explored. Upon switching the polarization field of ferroelectric Pb(Zr20Ti80)O3 (PZT) to the down-poled (electron-accumulation) state, temperature-dependent resistivity measurements indicate extremely metallic behavior in the ultrathin Sr214 channel. This work successfully closes the Mott gap in Sr214 in a ''clean'' doping environment free of chemical disorder, thereby strengthening the link to the isostrucutral high-Tc cuprates, as Sr214 has been predicted to host d-wave superconductivity upon electron doping the parent antiferromagnetic insulating phase. Furthermore, the metallic behavior in Sr214 persists for thickness beyond the expected screening length, suggestive of a collective carrier delocalization mechanism. Electrostatically doped carriers prove to be a useful method for tuning the competition between spin-orbit and Coulomb interactions in order to trigger novel phase transitions, such as the Mott-metal crossover. This work was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231.

Manipulations of the features of standard video lottery terminal (VLT) games: effects in pathological and non-pathological gamblers.

PubMed

Loba, P; Stewart, S H; Klein, R M; Blackburn, J R

2001-01-01

The present study was conducted to identify game parameters that would reduce the risk of abuse of video lottery terminals (VLTs) by pathological gamblers, while exerting minimal effects on the behavior of non-pathological gamblers. Three manipulations of standard VLT game features were explored. Participants were exposed to: a counter which displayed a running total of money spent; a VLT spinning reels game where participants could no longer "stop" the reels by touching the screen; and sensory feature manipulations. In control conditions, participants were exposed to standard settings for either a spinning reels or a video poker game. Dependent variables were self-ratings of reactions to each set of parameters. A set of 2(3) x 2 x 2 (game manipulation [experimental condition(s) vs. control condition] x game [spinning reels vs. video poker] x gambler status [pathological vs. non-pathological]) repeated measures ANOVAs were conducted on all dependent variables. The findings suggest that the sensory manipulations (i.e., fast speed/sound or slow speed/no sound manipulations) produced the most robust reaction differences. Before advocating harm reduction policies such as lowering sensory features of VLT games to reduce potential harm to pathological gamblers, it is important to replicate findings in a more naturalistic setting, such as a real bar.

A fast screening protocol for carotid plaques imaging using 3D multi-contrast MRI without contrast agent.

PubMed

Zhang, Na; Zhang, Lei; Yang, Qi; Pei, Anqi; Tong, Xiaoxin; Chung, Yiu-Cho; Liu, Xin

2017-06-01

To implement a fast (~15min) MRI protocol for carotid plaque screening using 3D multi-contrast MRI sequences without contrast agent on a 3Tesla MRI scanner. 7 healthy volunteers and 25 patients with clinically confirmed transient ischemic attack or suspected cerebrovascular ischemia were included in this study. The proposed protocol, including 3D T1-weighted and T2-weighted SPACE (variable-flip-angle 3D turbo spin echo), and T1-weighted magnetization prepared rapid acquisition gradient echo (MPRAGE) was performed first and was followed by 2D T1-weighted and T2-weighted turbo spin echo, and post-contrast T1-weighted SPACE sequences. Image quality, number of plaques, and vessel wall thicknesses measured at the intersection of the plaques were evaluated and compared between sequences. Average examination time of the proposed protocol was 14.6min. The average image quality scores of 3D T1-weighted, T2-weighted SPACE, and T1-weighted magnetization prepared rapid acquisition gradient echo were 3.69, 3.75, and 3.48, respectively. There was no significant difference in detecting the number of plaques and vulnerable plaques using pre-contrast 3D images with or without post-contrast T1-weighted SPACE. The 3D SPACE and 2D turbo spin echo sequences had excellent agreement (R=0.96 for T1-weighted and 0.98 for T2-weighted, p<0.001) regarding vessel wall thickness measurements. The proposed protocol demonstrated the feasibility of attaining carotid plaque screening within a 15-minute scan, which provided sufficient anatomical coverage and critical diagnostic information. This protocol offers the potential for rapid and reliable screening for carotid plaques without contrast agent. Copyright © 2016. Published by Elsevier Inc.

A Non-Perturbative Treatment of Quantum Impurity Problems in Real Lattices

NASA Astrophysics Data System (ADS)

Allerdt, Andrew C.

Historically, the RKKY or indirect exchange, interaction has been accepted as being able to be described by second order perturbation theory. A typical universal expression is usually given in this context. This approach, however, fails to incorporate many body effects, quantum fluctuations, and other important details. In Chapter 2, a novel numerical approach is developed to tackle these problems in a quasi-exact, non-perturbative manner. Behind the method lies the main concept of being able to exactly map an n-dimensional lattice problem onto a 1-dimensional chain. The density matrix renormalization group algorithm is then employed to solve the newly cast Hamiltonian. In the following chapters, it is demonstrated that conventional RKKY theory does not capture the crucial physics. It is found that the Kondo effect, i.e. the screening of an impurity spin, tends to dominate over a ferromagnetic interaction between impurity spins. Furthermore, it is found that the indirect exchange interaction does not decay algebraically. Instead, there is a crossover upon increasing JK, where impurities favor forming their own independent Kondo states after just a few lattice spacings. This is not a trivial result, as one may naively expect impurities to interact when their conventional Kondo clouds overlap. The spin structure around impurities coupled to the edge of a 2D topological insulator is investigated in Chapter 7. Modeled after materials such as silicine, germanene, and stanene, it is shown with spatial resolution of the lattice that the specific impurity placement plays a key role. Effects of spin-orbit interactions are also discussed. Finally, in the last chapter, transition metal complexes are studied. This really shows the power and versatility of the method developed throughout the work. The spin states of an iron atom in the molecule FeN4C 10 are calculated and compared to DFT, showing the importance of inter-orbital coulomb interactions. Using dynamical DMRG, the density of states for the 3d-orbitals can also be obtained.

Spin dependence of ferroelectric polarization in the double exchange model for manganites

NASA Astrophysics Data System (ADS)

Solovyev, I. V.; Nikolaev, S. A.

2014-11-01

The double exchange (DE) model is systematically applied for studying the coupling between ferroelectric (FE) and magnetic orders in several prototypical types of multiferroic manganites. The model itself was constructed for the magnetically active Mn 3 d bands in the basis of Wannier functions and includes the effect of screened onsite Coulomb interactions in the Hartree-Fock approximation. All model parameters were derived from the first-principles electronic-structure calculations. The essence of our approach for the FE polarization is to use the Berry-phase theory, formulated in terms of occupied Wannier functions, and to evaluate the asymmetric spin-dependent change of these functions in the framework of the DE model. This enables us to quantify the effect of the magnetic symmetry breaking and derive several useful expressions for the electronic polarization P , depending on the relative directions of spins. The spin dependence of P in the DE model is given by the isotropic correlation functions ei.ej between directions of neighboring spins. Despite formal similarity with the magnetostriction mechanism, the magnetoelectric coupling in the proposed DE theory is not related to the magnetically driven FE atomic displacements and can exist even in compounds with the centrosymmetric crystal structure, if the spatial distribution of ei.ej does not respect the inversion symmetry. The proposed theory is applied to the solution of three major problems: (i) the magnetic-state dependence of P in hexagonal manganites, using YMnO3 as an example; (ii) the microscopic relationship between canted ferromagnetism and P in monoclinic BiMnO3; (iii) the origin of FE activity in orthorhombic manganites. Particularly, we will show that for an arbitrary noncollinear magnetic structure, propagating along the orthorhombic b axis and antiferromagnetically coupled along the c axis, the polarization is induced by an inhomogeneous distribution of spins and can be obtained by scaling the one of the E-type antiferromagnetic (AFM) phase with the prefactor depending only on the relative directions of spins and being the measure of this spin inhomogeneity. This picture works equally well for the twofold (HoMnO3) and fourfold (TbMnO3) periodic manganites. The basic difference is that, even despite some spin canting of the relativistic origin and deviation from the collinear E-type AFM alignment, the twofold periodic magnetic structure remains strongly inhomogeneous, which leads to large P . On the contrary, the fourfold periodic magnetic structure can be viewed as a moderately distorted homogeneous spin spiral, which corresponds to much weaker P .

Experiments on Quantum Hall Topological Phases in Ultra Low Temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Rui-Rui

2015-02-14

This project is to cool electrons in semiconductors to extremely low temperatures and to study new states of matter formed by low-dimensional electrons (or holes). At such low temperatures (and with an intense magnetic field), electronic behavior differs completely from ordinary ones observed at room temperatures or regular low temperature. Studies of electrons at such low temperatures would open the door for fundamental discoveries in condensed matter physics. Present studies have been focused on topological phases in the fractional quantum Hall effect in GaAs/AlGaAs semiconductor heterostructures, and the newly discovered (by this group) quantum spin Hall effect in InAs/GaSb materials.more » This project consists of the following components: 1) Development of efficient sample cooling techniques and electron thermometry: Our goal is to reach 1 mK electron temperature and reasonable determination of electron temperature; 2) Experiments at ultra-low temperatures: Our goal is to understand the energy scale of competing quantum phases, by measuring the temperature-dependence of transport features. Focus will be placed on such issues as the energy gap of the 5/2 state, and those of 12/5 (and possible 13/5); resistive signature of instability near 1/2 at ultra-low temperatures; 3) Measurement of the 5/2 gaps in the limit of small or large Zeeman energies: Our goal is to gain physics insight of 5/2 state at limiting experimental parameters, especially those properties concerning the spin polarization; 4) Experiments on tuning the electron-electron interaction in a screened quantum Hall system: Our goal is to gain understanding of the formation of paired fractional quantum Hall state as the interaction pseudo-potential is being modified by a nearby screening electron layer; 5) Experiments on the quantized helical edge states under a strong magnetic field and ultralow temperatures: our goal is to investigate both the bulk and edge states in a quantum spin Hall insulator under time-reversal symmetry-broken conditions.« less

The Vainshtein mechanism in the cosmic web

DOE Office of Scientific and Technical Information (OSTI.GOV)

Falck, Bridget; Koyama, Kazuya; Zhao, Gong-bo

We investigate the dependence of the Vainshtein screening mechanism on the cosmic web morphology of both dark matter particles and halos as determined by ORIGAMI. Unlike chameleon and symmetron screening, which come into effect in regions of high density, Vainshtein screening instead depends on the dimensionality of the system, and screened bodies can still feel external fields. ORIGAMI is well-suited to this problem because it defines morphologies according to the dimensionality of the collapsing structure and does not depend on a smoothing scale or density threshold parameter. We find that halo particles are screened while filament, wall, and void particlesmore » are unscreened, and this is independent of the particle density. However, after separating halos according to their large scale cosmic web environment, we find no difference in the screening properties of halos in filaments versus halos in clusters. We find that the fifth force enhancement of dark matter particles in halos is greatest well outside the virial radius. We confirm the theoretical expectation that even if the internal field is suppressed by the Vainshtein mechanism, the object still feels the fifth force generated by the external fields, by measuring peculiar velocities and velocity dispersions of halos. Finally, we investigate the morphology and gravity model dependence of halo spins, concentrations, and shapes.« less

A 360-degree floating 3D display based on light field regeneration.

PubMed

Xia, Xinxing; Liu, Xu; Li, Haifeng; Zheng, Zhenrong; Wang, Han; Peng, Yifan; Shen, Weidong

2013-05-06

Using light field reconstruction technique, we can display a floating 3D scene in the air, which is 360-degree surrounding viewable with correct occlusion effect. A high-frame-rate color projector and flat light field scanning screen are used in the system to create the light field of real 3D scene in the air above the spinning screen. The principle and display performance of this approach are investigated in this paper. The image synthesis method for all the surrounding viewpoints is analyzed, and the 3D spatial resolution and angular resolution of the common display zone are employed to evaluate display performance. The prototype is achieved and the real 3D color animation image has been presented vividly. The experimental results verified the representability of this method.

Validation and Diagnostic Efficiency of the Mini-SPIN in Spanish-Speaking Adolescents

PubMed Central

Garcia-Lopez, LuisJoaquín; Moore, Harry T. A.

2015-01-01

Objectives Social Anxiety Disorder (SAD) is one of the most common mental disorders in adolescence. Many validated psychometric tools are available to diagnose individuals with SAD efficaciously. However, there is a demand for shortened self-report instruments that identify adolescents at risk of developing SAD. We validate the Mini-SPIN and its diagnostic efficiency in overcoming this problem in Spanish-speaking adolescents in Spain. Methods The psychometric properties of the 3-item Mini-SPIN scale for adolescents were assessed in a community (study 1) and clinical sample (study 2). Results Study 1 consisted of 573 adolescents, and found the Mini-SPIN to have appropriate internal consistency and high construct validity. Study 2 consisted of 354 adolescents (147 participants diagnosed with SAD and 207 healthy controls). Data revealed that the Mini-SPIN has good internal consistency, high construct validity and adequate diagnostic efficiency. Conclusions Our findings suggest that the Mini-SPIN has good psychometric properties on clinical and healthy control adolescents and general population, which indicates that it can be used as a screening tool in Spanish-speaking adolescents. Cut-off scores are provided. PMID:26317695

Validation and Diagnostic Efficiency of the Mini-SPIN in Spanish-Speaking Adolescents.

PubMed

Garcia-Lopez, LuisJoaquín; Moore, Harry T A

2015-01-01

Social Anxiety Disorder (SAD) is one of the most common mental disorders in adolescence. Many validated psychometric tools are available to diagnose individuals with SAD efficaciously. However, there is a demand for shortened self-report instruments that identify adolescents at risk of developing SAD. We validate the Mini-SPIN and its diagnostic efficiency in overcoming this problem in Spanish-speaking adolescents in Spain. The psychometric properties of the 3-item Mini-SPIN scale for adolescents were assessed in a community (study 1) and clinical sample (study 2). Study 1 consisted of 573 adolescents, and found the Mini-SPIN to have appropriate internal consistency and high construct validity. Study 2 consisted of 354 adolescents (147 participants diagnosed with SAD and 207 healthy controls). Data revealed that the Mini-SPIN has good internal consistency, high construct validity and adequate diagnostic efficiency. Our findings suggest that the Mini-SPIN has good psychometric properties on clinical and healthy control adolescents and general population, which indicates that it can be used as a screening tool in Spanish-speaking adolescents. Cut-off scores are provided.

Electric Dipolar Kondo Effect Emerging from a Vibrating Magnetic Ion

NASA Astrophysics Data System (ADS)

Hotta, Takashi; Ueda, Kazuo

2012-06-01

When a magnetic ion vibrates in a metal, it inevitably introduces a new channel of hybridization with conduction electrons, and in general, the vibrating ion induces an electric dipole moment. In such a situation, we find that magnetic and nonmagnetic Kondo effects alternatively occur due to the screening of the spin moment and electric dipole moment of the vibrating ion. In particular, the electric dipolar two-channel Kondo effect is found to occur for a weak Coulomb interaction. We also show that a magnetically robust heavy-electron state appears near the fixed point of the electric dipolar two-channel Kondo effect. We believe that the vibrating magnetic ion opens a new door in Kondo physics.

Coplanar back contacts for thin silicon solar cells

NASA Technical Reports Server (NTRS)

Thornhill, J. W.; Sipperly, W. E.

1980-01-01

A process for fabricating 2 to 3 mil wraparound solar cells was formulated. Sample thin wraparound cells were fabricated using this process. The process used a reinforced perimeter construction to reduce the breakage that occurs during handling of the wafers. A retracting piston post was designed and fabricated to help minimize the breakage that occurs during the screen printing process. Two alternative methods of applying the aluminum back surface field were investigated. In addition to the standard screen printed back surface field, both spin-on and evaporated aluminum techniques were researched. Neither spin-on nor evaporated aluminum made any noticeable improvement over the screen printing technique. A fine screen mesh was chosen for the application of the aluminum paste back surface field. The optimum time and temperature for firing the aluminum turned out to be thirty seconds at 850 C. The development work on the dielectric included looking at three dielectrics for the wraparound application. Transene 1000, Thick Film Systems 1126RCB and an in house formulation 61-2-2A were all tested. Cells with pre-dielectric thickness of 3.0-0-3.5 mils using Transene 1000 as the wraparound dielectric and the procedure outlined above showed an average efficiency of 10.7 percent. Thinner cells were fabricated, but had an unacceptable yield and efficiency.

Synchronization of spin-transfer torque oscillators by spin pumping, inverse spin Hall, and spin Hall effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg

2015-02-14

We have proposed a method to synchronize multiple spin-transfer torque oscillators based on spin pumping, inverse spin Hall, and spin Hall effects. The proposed oscillator system consists of a series of nano-magnets in junction with a normal metal with high spin-orbit coupling, and an accumulative feedback loop. We conduct simulations to demonstrate the effect of modulated charge currents in the normal metal due to spin pumping from each nano-magnet. We show that the interplay between the spin Hall effect and inverse spin Hall effect results in synchronization of the nano-magnets.

Spin Seebeck effect and thermal spin galvanic effect in Ni80Fe20/p-Si bilayers

NASA Astrophysics Data System (ADS)

Bhardwaj, Ravindra G.; Lou, Paul C.; Kumar, Sandeep

2018-01-01

The development of spintronics and spin-caloritronics devices needs efficient generation, detection, and manipulation of spin current. The thermal spin current from the spin-Seebeck effect has been reported to be more energy efficient than the electrical spin injection methods. However, spin detection has been the one of the bottlenecks since metals with large spin-orbit coupling is an essential requirement. In this work, we report an efficient thermal generation and interfacial detection of spin current. We measured a spin-Seebeck effect in Ni80Fe20 (25 nm)/p-Si (50 nm) (polycrystalline) bilayers without a heavy metal spin detector. p-Si, having a centrosymmetric crystal structure, has insignificant intrinsic spin-orbit coupling, leading to negligible spin-charge conversion. We report a giant inverse spin-Hall effect, essential for the detection of spin-Seebeck effects, in the Ni80Fe20/p-Si bilayer structure, which originates from Rashba spin orbit coupling due to structure inversion asymmetry at the interface. In addition, the thermal spin pumping in p-Si leads to spin current from p-Si to the Ni80Fe20 layer due to the thermal spin galvanic effect and the spin-Hall effect, causing spin-orbit torques. The thermal spin-orbit torques lead to collapse of magnetic hysteresis of the 25 nm thick Ni80Fe20 layer. The thermal spin-orbit torques can be used for efficient magnetic switching for memory applications. These scientific breakthroughs may give impetus to the silicon spintronics and spin-caloritronics devices.

Gambling goals predict chasing behavior during slot machine play.

PubMed

Lister, Jamey J; Nower, Lia; Wohl, Michael J A

2016-11-01

The purpose of this study was to test the effect of gambling goals (i.e., gambling achievement-orientation) on chasing behavior (i.e., decision to chase, chasing spins) over and above known antecedents (e.g., problem gambling severity, winning money motivations, approach/avoidance motivation). Young adult gamblers (N=121) were provided $20 and invited to use those funds on a slot machine situated in an immersive virtual reality casino. Unbeknownst to participants, outcomes were manipulated such that a nominal amount of money was either won or lost (depending on experimental condition) after 30 spins. Before the 31st spin, participants were asked if they wished to continue play. If they agreed, all successive spin outcomes were a loss. This permitted an assessment of what factors influence a player's: (1) decision to chase and (2) the number of chasing spins played in the face of loss. Almost all participants (n=95, 78.5%) screened positive for problem gambling symptoms. The majority of gamblers decided to chase (n=67, 55.4%). In bivariate analyses, higher gambling goal and problem gambling severity scores (but not approach/avoidance nor 'loss/win' condition) were positively related to both forms of chasing. Gamblers 'motivated to win money' were more likely to decide to chase. In multivariate analyses, higher gambling goals best accounted for both forms of chasing independent of known antecedents. This study provides the first evidence that gambling goals can influence chasing. Implications for shaping responsible gambling approaches to be more consistent with motivations for play are discussed. Copyright © 2016 Elsevier Ltd. All rights reserved.

On the origin of the peculiar cataclysmic variable AE Aquarii

NASA Astrophysics Data System (ADS)

Beskrovnaya, N. G.; Ikhsanov, N. R.

2015-02-01

The nova-like variable AE Aquarii is a close binary system containing a red dwarf and a magnetized white dwarf rotating with the period of 33 s. A short spin period of the white dwarf is caused by an intensive mass exchange between the system components during a previous epoch. We show that a high rate of disk accretion onto the white dwarf surface resulted in temporary screening of its magnetic field and spin-up of the white dwarf to its present spin period. Transition of the white dwarf to the ejector state occurred at a final stage of the spin-up epoch after its magnetic field had emerged from the accreted plasma due to diffusion. In the frame of this scenario AE Aqr represents a missing link in the chain of Polars evolution and the white dwarf resembles a recycled pulsar.

Radiation reaction for spinning bodies in effective field theory. II. Spin-spin effects

NASA Astrophysics Data System (ADS)

Maia, Natália T.; Galley, Chad R.; Leibovich, Adam K.; Porto, Rafael A.

2017-10-01

We compute the leading post-Newtonian (PN) contributions at quadratic order in the spins to the radiation-reaction acceleration and spin evolution for binary systems, entering at four-and-a-half PN order. Our calculation includes the backreaction from finite-size spin effects, which is presented for the first time. The computation is carried out, from first principles, using the effective field theory framework for spinning extended objects. At this order, nonconservative effects in the spin-spin sector are independent of the spin supplementary conditions. A nontrivial consistency check is performed by showing that the energy loss induced by the resulting radiation-reaction force is equivalent to the total emitted power in the far zone. We find that, in contrast to the spin-orbit contributions (reported in a companion paper), the radiation reaction affects the evolution of the spin vectors once spin-spin effects are incorporated.

Extended Area Exit Pupil Viewer.

DTIC Science & Technology

1985-08-01

viewing to normal Zoom-500 stereomicroscope viewing. Previous EAEP viewers typically have incorporated a spinning lenticular screen and associated...is uncorrected spherical aberration and astigmatism that limit image resolution. The complex optical path in the microscope also makes it inefficient

Multi-electron double quantum dot spin qubits

NASA Astrophysics Data System (ADS)

Nielsen, Erik; Kestner, Jason; Barnes, Edwin; Das Sarma, Sankar

2013-03-01

Double quantum dot (DQD) spin quits in a solid state environment typically consist of two electron spins confined to a DQD potential. We analyze the viability and potential advantages of DQD qubits which use greater then two electrons, and present results for six-electron qubits using full configuration interaction methods. The principal results of this work are that such six electron DQDs can retain an isolated low-energy qubit space that is more robust to charge noise due to screening. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Pbte Nanostructures for Spin Filtering and Detecting

NASA Astrophysics Data System (ADS)

Grabecki, G.

2005-08-01

An uniqueness of lead telluride PbTe relies on combination of excellent semiconducting properties, like high electron mobility and tunable carrier concentration, with paraelectric behavior leading to huge dielectric constant at low temperatures. The present article is a review of our experimental works performed on PbTe nanostructures. The main result is observation of one-dimensional quantization of the electron motion at much impure conditions than in any other system studied so far. We explain this in terms of dielectric screening of Coulomb potentials produced by charged defects. Furthermore, in an external magnetic field, the conductance quantization steps show very pronounced spin splitting, already visible at several kilogauss. This indicates that PbTe nanostructures have a potential as local spin filtering devices.

Effect of hyperfine-induced spin mixing on the defect-enabled spin blockade and spin filtering in GaNAs

NASA Astrophysics Data System (ADS)

Puttisong, Y.; Wang, X. J.; Buyanova, I. A.; Chen, W. M.

2013-03-01

The effect of hyperfine interaction (HFI) on the recently discovered room-temperature defect-enabled spin-filtering effect in GaNAs alloys is investigated both experimentally and theoretically based on a spin Hamiltonian analysis. We provide direct experimental evidence that the HFI between the electron and nuclear spin of the central Ga atom of the spin-filtering defect, namely, the Gai interstitials, causes strong mixing of the electron spin states of the defect, thereby degrading the efficiency of the spin-filtering effect. We also show that the HFI-induced spin mixing can be suppressed by an application of a longitudinal magnetic field such that the electronic Zeeman interaction overcomes the HFI, leading to well-defined electron spin states beneficial to the spin-filtering effect. The results provide a guideline for further optimization of the defect-engineered spin-filtering effect.

[The use of the T2-weighted turbo-spin-echo sequence in studying the neurocranium. A comparison with the conventional T2-weighted spin-echo sequence].

PubMed

Siewert, C; Hosten, N; Felix, R

1994-07-01

T2-weighted spin-echo imaging is the standard screening procedure in MR imaging of the neurocranium. We evaluated fast spin-echo T2-weighted imaging (TT2) of the neurocranium in comparison to conventional spin-echo T2-weighted imaging (T2). Signal-to-noise and contrast-to-noise ratio of normal brain tissues (basal ganglia, grey and white matter, CSF fluid) and different pathologies were calculated. Signal-to-noise ratio and contrast-to-noise ratio were significantly higher in TT2 than in T2 (with the exception of gray-to-white matter contrast). Tissues with increased content of water protons (mobile protons) showed the highest contrast to surrounding tissues. The increased signal intensity of fat must be given due attention in fatty lesions. Because the contrast-to-noise ratio between white matter and basal ganglia is less in TT2, Parkinson patients have to be examined by conventional T2. If these limitations are taken into account, fast spin-echo T2-weighted imaging is well appropriate for MR imaging of the neurocranium, resulting in heavy T2-weighting achieved in a short acquisition time.

Spin Current Noise of the Spin Seebeck Effect and Spin Pumping

NASA Astrophysics Data System (ADS)

Matsuo, M.; Ohnuma, Y.; Kato, T.; Maekawa, S.

2018-01-01

We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck effect and spin pumping in a normal-metal-(NM-)ferromagnet(FM) bilayer system. Starting with a simple ferromagnet-insulator-(FI-)NM interface model with both spin-conserving and non-spin-conserving processes, we derive general expressions of the spin current and the spin-current noise at the interface within second-order perturbation of the FI-NM coupling strength, and estimate them for a yttrium-iron-garnet-platinum interface. We show that the spin-current noise can be used to determine the effective spin carried by a magnon modified by the non-spin-conserving process at the interface. In addition, we show that it provides information on the effective spin of a magnon, heating at the interface under spin pumping, and spin Hall angle of the NM.

Analytical energy gradient for the two-component normalized elimination of the small component method

NASA Astrophysics Data System (ADS)

Zou, Wenli; Filatov, Michael; Cremer, Dieter

2015-06-01

The analytical gradient for the two-component Normalized Elimination of the Small Component (2c-NESC) method is presented. The 2c-NESC is a Dirac-exact method that employs the exact two-component one-electron Hamiltonian and thus leads to exact Dirac spin-orbit (SO) splittings for one-electron atoms. For many-electron atoms and molecules, the effect of the two-electron SO interaction is modeled by a screened nucleus potential using effective nuclear charges as proposed by Boettger [Phys. Rev. B 62, 7809 (2000)]. The effect of spin-orbit coupling (SOC) on molecular geometries is analyzed utilizing the properties of the frontier orbitals and calculated SO couplings. It is shown that bond lengths can either be lengthened or shortened under the impact of SOC where in the first case the influence of low lying excited states with occupied antibonding orbitals plays a role and in the second case the jj-coupling between occupied antibonding and unoccupied bonding orbitals dominates. In general, the effect of SOC on bond lengths is relatively small (≤5% of the scalar relativistic changes in the bond length). However, large effects are found for van der Waals complexes Hg2 and Cn2, which are due to the admixture of more bonding character to the highest occupied spinors.

Observation of the Spin Nernst Effect in Platinum

NASA Astrophysics Data System (ADS)

Goennenwein, Sebastian

Thermoelectric effects - arising from the interplay between thermal and charge transport phenomena - have been extensively studied and are considered well established. Upon taking into account the spin degree of freedom, however, qualitatively new phenomena arise. A prototype example for these so-called magneto-thermoelectric or spin-caloritronic effects is the spin Seebeck effect, in which a thermal gradient drives a pure spin current. In contrast to their thermoelectric counterparts, not all the spin-caloritronic effects predicted from theory have yet been observed in experiment. One of these `missing' phenomena is the spin Nernst effect, in which a thermal gradient gives rise to a transverse pure spin current. We have observed the spin Nernst effect in yttrium iron garnet/platinum (YIG/Pt) thin film bilayers. Upon applying a thermal gradient within the YIG/Pt bilayer plane, a pure spin current flows in the direction orthogonal to the thermal drive. We detect this spin current as a thermopower voltage, generated via magnetization-orientation dependent spin transfer into the adjacent YIG layer. Our data shows that the spin Nernst and the spin Hall effect in in Pt have different sign, but comparable magnitude, in agreement with first-principles calculations. Financial support via Deutsche Forschungsgemeinschaft Priority Programme SPP 1538 Spin-Caloric Transport is gratefully acknowledged.

Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures

NASA Astrophysics Data System (ADS)

Savero Torres, W.; Sierra, J. F.; Benítez, L. A.; Bonell, F.; Costache, M. V.; Valenzuela, S. O.

2017-12-01

Spin Hall effects have surged as promising phenomena for spin logics operations without ferromagnets. However, the magnitude of the detected electric signals at room temperature in metallic systems has been so far underwhelming. Here, we demonstrate a two-order of magnitude enhancement of the signal in monolayer graphene/Pt devices when compared to their fully metallic counterparts. The enhancement stems in part from efficient spin injection and the large spin resistance of graphene but we also observe 100% spin absorption in Pt and find an unusually large effective spin Hall angle of up to 0.15. The large spin-to-charge conversion allows us to characterise spin precession in graphene under the presence of a magnetic field. Furthermore, by developing an analytical model based on the 1D diffusive spin-transport, we demonstrate that the effective spin-relaxation time in graphene can be accurately determined using the (inverse) spin Hall effect as a means of detection. This is a necessary step to gather full understanding of the consequences of spin absorption in spin Hall devices, which is known to suppress effective spin lifetimes in both metallic and graphene systems.

Spin pumping and inverse spin Hall effects—Insights for future spin-orbitronics (invited)

DOE PAGES

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

2015-03-13

Quantification of spin-charge interconversion has become increasingly important in the fast-developing field of spin-orbitronics. Pure spin current generated by spin pumping acts a sensitive probe for many bulk and interface spin-orbit effects, which has been indispensable for the discovery of many promising new spin-orbit materials. Here, we apply spin pumping and inverse spin Hall effect experiments, as a useful metrology, and study spin-orbit effects in a variety of metals and metal interfaces. We also quantify the spin Hall effects in Ir and W using the conventional bilayer structures, and discuss the self-induced voltage in a single layer of ferromagnetic permalloy.more » Finally, we extend our discussions to multilayer structures and quantitatively reveal the spin current flow in two consecutive normal metal layers.« less

Effects of symmetry and spin configuration on spin-dependent transport properties of iron-phthalocyanine-based devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, Li-Ling; School of Science, Hunan University of Technology, Zhuzhou 412007; Yang, Bing-Chu, E-mail: bingchuyang@csu.edu.cn

2014-07-21

Spin-dependent transport properties of nanodevices constructed by iron-phthalocyanine (FePc) molecule sandwiched between two zigzag graphene nanoribbon electrodes are studied using first-principles quantum transport calculations. The effects of the symmetry and spin configuration of electrodes have been taken into account. It is found that large magnetoresistance, large spin polarization, dual spin-filtering, and negative differential resistance (NDR) can coexist in these devices. Our results show that 5Z-FePc system presents well conductive ability in both parallel (P) and anti-parallel (AP) configurations. For 6Z-FePc-P system, spin filtering effect and large spin polarization can be found. A dual spin filtering and NDR can also bemore » shown in 6Z-FePc-AP. Our studies indicate that the dual spin filtering effect depends on the orbitals symmetry of the energy bands and spin mismatching of the electrodes. And all the effects would open up possibilities for their applications in spin-valve, spin-filter as well as effective spin diode devices.« less

How to realize a spin-dependent Seebeck diode effect in metallic zigzag γ-graphyne nanoribbons?

PubMed

Wu, Dan-Dan; Liu, Qing-Bo; Fu, Hua-Hua; Wu, Ruqian

2017-11-30

The spin-dependent Seebeck effect (SDSE) is one of the core topics of spin caloritronics. In the traditional device designs of spin-dependent Seebeck rectifiers and diodes, finite spin-dependent band gaps of materials are required to realize the on-off characteristic in thermal spin currents, and nearly zero charge current should be achieved to reduce energy dissipation. Here, we propose that two ferromagnetic zigzag γ-graphyne nanoribbons (ZγGNRs) without any spin-dependent band gaps around the Fermi level can not only exhibit the SDSE, but also display rectifier and diode effects in thermal spin currents characterized by threshold temperatures, which originates from the compensation effect occurring in spin-dependent transmissions but not from the spin-splitting band gaps in materials. The metallic characteristics of ZγGNRs bring about an advantage that the gate voltage is an effective route to adjust the symmetry of spin-splitting bands to obtain pure thermal spin currents. The results provide a new mechanism to realize spin-Seebeck rectifier and diode effects in 2D materials and expand material candidates towards spin-Seebeck device applications.

Hyperpolarization of “Neat” Liquids by NMR Signal Amplification by Reversible Exchange

PubMed Central

2016-01-01

We report NMR Signal Amplification by Reversible Exchange (SABRE) hyperpolarization of the rare isotopes in “neat” liquids, each composed only of an otherwise pure target compound with isotopic natural abundance (n.a.) and millimolar concentrations of dissolved catalyst. Pyridine (Py) or Py derivatives are studied at 0.4% isotopic natural abundance 15N, deuterated, 15N enriched, and in various combinations using the SABRE-SHEATH variant (microTesla magnetic fields to permit direct 15N polarization from parahydrogen via reversible binding and exchange with an Ir catalyst). We find that the dilute n.a. 15N spin bath in Py still channels spin order from parahydrogen to dilute 15N spins, without polarization losses due to the presence of 14N or 2H. We demonstrate P15N ≈ 1% (a gain of 2900 fold relative to thermal polarization at 9.4 T) at high substrate concentrations. This fundamental finding has a significant practical benefit for screening potentially hyperpolarizable contrast agents without labeling. The capability of screening at n.a. level of 15N is demonstrated on examples of mono- and dimethyl-substituted Py (picolines and lutidines previously identified as promising pH sensors), showing that the presence of a methyl group in the ortho position significantly decreases SABRE hyperpolarization. PMID:26029349

Spin wave amplification using the spin Hall effect in permalloy/platinum bilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gladii, O.; Henry, Y.; Bailleul, M.

2016-05-16

We investigate the effect of an electrical current on the attenuation length of a 900 nm wavelength spin-wave in a permalloy/Pt bilayer using propagating spin-wave spectroscopy. The modification of the spin-wave relaxation rate is linear in current density, reaching up to 14% for a current density of 2.3 × 10{sup 11} A/m{sup 2} in Pt. This change is attributed to the spin transfer torque induced by the spin Hall effect and corresponds to an effective spin Hall angle of 0.13, which is among the highest values reported so far. The spin Hall effect thus appears as an efficient way of amplifying/attenuating propagating spin waves.

Electric-field-induced modification of the magnon energy, exchange interaction, and curie temperature of transition-metal thin films.

PubMed

Oba, M; Nakamura, K; Akiyama, T; Ito, T; Weinert, M; Freeman, A J

2015-03-13

The electric-field-induced modification in the Curie temperature of prototypical transition-metal thin films with the perpendicular magnetic easy axis, a freestanding Fe(001) monolayer and a Co monolayer on Pt(111), is investigated by first-principles calculations of spin-spiral structures in an external electric field (E field). An applied E field is found to modify the magnon (spin-spiral formation) energy; the change arises from the E-field-induced screening charge density in the spin-spiral states due to p-d hybridizations. The Heisenberg exchange parameters obtained from the magnon energy suggest an E-field-induced modification of the Curie temperature, which is demonstrated via Monte Carlo simulations that take the magnetocrystalline anisotropy into account.

Half-metallic properties, single-spin negative differential resistance, and large single-spin Seebeck effects induced by chemical doping in zigzag-edged graphene nanoribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Xi-Feng; Zhou, Wen-Qian; Hong, Xue-Kun

2015-01-14

Ab initio calculations combining density-functional theory and nonequilibrium Green’s function are performed to investigate the effects of either single B atom or single N atom dopant in zigzag-edged graphene nanoribbons (ZGNRs) with the ferromagnetic state on the spin-dependent transport properties and thermospin performances. A spin-up (spin-down) localized state near the Fermi level can be induced by these dopants, resulting in a half-metallic property with 100% negative (positive) spin polarization at the Fermi level due to the destructive quantum interference effects. In addition, the highly spin-polarized electric current in the low bias-voltage regime and single-spin negative differential resistance in the highmore » bias-voltage regime are also observed in these doped ZGNRs. Moreover, the large spin-up (spin-down) Seebeck coefficient and the very weak spin-down (spin-up) Seebeck effect of the B(N)-doped ZGNRs near the Fermi level are simultaneously achieved, indicating that the spin Seebeck effect is comparable to the corresponding charge Seebeck effect.« less

Spin caloric effects in antiferromagnets assisted by an external spin current

NASA Astrophysics Data System (ADS)

Gomonay, O.; Yamamoto, Kei; Sinova, Jairo

2018-07-01

Searching for novel spin caloric effects in antiferromagnets, we study the properties of thermally activated magnons in the presence of an external spin current and temperature gradient. We predict the spin Peltier effect—generation of a heat flux by spin accumulation—in an antiferromagnetic insulator with cubic or uniaxial magnetic symmetry. This effect is related to the spin-current induced splitting of the relaxation times of the magnons with the opposite spin direction. We show that the Peltier effect can trigger antiferromagnetic domain wall motion with a force whose value grows with the temperature of a sample. At a temperature larger than the energy of the low-frequency magnons, this force is much larger than the force caused by direct spin transfer between the spin current and the domain wall. We also demonstrate that the external spin current can induce the magnon spin Seebeck effect. The corresponding Seebeck coefficient is controlled by the current density. These spin-current assisted caloric effects open new ways for the manipulation of the magnetic states in antiferromagnets.

Effective one body approach to the dynamics of two spinning black holes with next-to-leading order spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Damour, Thibault; Jaranowski, Piotr; Schaefer, Gerhard

2008-07-15

Using a recent, novel Hamiltonian formulation of the gravitational interaction of spinning binaries, we extend the effective one body (EOB) description of the dynamics of two spinning black holes to next-to-leading order (NLO) in the spin-orbit interaction. The spin-dependent EOB Hamiltonian is constructed from four main ingredients: (i) a transformation between the 'effective' Hamiltonian and the 'real' one; (ii) a generalized effective Hamilton-Jacobi equation involving higher powers of the momenta; (iii) a Kerr-type effective metric (with Pade-resummed coefficients) which depends on the choice of some basic 'effective spin vector' S{sub eff}, and which is deformed by comparable-mass effects; and (iv)more » an additional effective spin-orbit interaction term involving another spin vector {sigma}. As a first application of the new, NLO spin-dependent EOB Hamiltonian, we compute the binding energy of circular orbits (for parallel spins) as a function of the orbital frequency, and of the spin parameters. We also study the characteristics of the last stable circular orbit: binding energy, orbital frequency, and the corresponding dimensionless spin parameter a{sub LSO}{identical_to}cJ{sub LSO}/(G(H{sub LSO}/c{sup 2}){sup 2}). We find that the inclusion of NLO spin-orbit terms has a significant 'moderating' effect on the dynamical characteristics of the circular orbits for large and parallel spins.« less

Prediction of Spin-Polarization Effects in Quantum Wire Transport

NASA Astrophysics Data System (ADS)

Fasol, Gerhard; Sakaki, Hiroyuki

1994-01-01

We predict a new effect for transport in quantum wires: spontaneous spin polarization. Most work on transport in mesoscopic devices has assumed a model of non interacting, spin-free electrons. We introduce spin, electron pair scattering and microscopic crystal properties into the design of mesoscopic devices. The new spin polarization effect results from the fact that in a single mode quantum wire, electron and hole bands still have two spin subbands. In general, these two spin subbands are expected to be split even in zero magnetic field. At sufficiently low temperatures the electron pair scattering rates for one spin subband ( e.g., the spin-down) can be much larger than for the other spin subband. This effect can be used for an active spin polarizer device: hot electrons in one subband ( e.g., `spin up') pass with weak pair scattering, while electrons in the opposite subband ( e.g., `spin down'), have high probability of scattering into the `spin-up' subband, resulting in spin polarization of a hot electron beam.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michal, V. P., E-mail: vincent.michal@cea.fr

The formalism for analyzing the magnetic field distribution in the vortex lattice of Pauli-limit heavy-electron superconductors is applied to the evaluation of the vortex lattice static linewidth relevant to the muon spin rotation ({mu}SR) experiment. Based on the Ginzburg-Landau expansion for the superconductor free energy, we study the evolution with respect to the external field of the static linewidth both in the limit of independent vortices (low magnetic field) with a variational expression for the order parameter and in the near H{sub c2}{sup P}(T) regime with an extension of the Abrikosov analysis to Pauli-limit superconductors. We conclude that in themore » Ginzburg-Landau regime in the Pauli-limit, anomalous variations of the static linewidth with the applied field are predicted as a result of the superconductor spin response around a vortex core that dominates the usual charge-response screening supercurrents. We propose the effect as a benchmark for studying new puzzling vortex lattice properties recently observed in CeCoIn{sub 5}.« less

FAST TRACK COMMUNICATION: Eight-logic memory cell based on multiferroic junctions

NASA Astrophysics Data System (ADS)

Yang, Feng; Zhou, Y. C.; Tang, M. H.; Liu, Fen; Ma, Ying; Zheng, X. J.; Zhao, W. F.; Xu, H. Y.; Sun, Z. H.

2009-04-01

A model is proposed for a device combining a multiferroic tunnel junction with a magnetoelectric (ME) film in which the magnetic configuration is controlled by the electric field. Calculations embodying the Green's function approach show that the magnetic polarization can be switched on and off by an electric field in the ME film due to the effect of elastic coupling interaction. Using a model including the spin-filter effect and screening of polarization charges, we have produced eight logic states of tunnelling resistance in the tunnel junction and have obtained corresponding laws that control them. The results provide some insights into the realization of an eight-logic memory cell.

Extrinsic spin Hall effect in graphene

NASA Astrophysics Data System (ADS)

Rappoport, Tatiana

The intrinsic spin-orbit coupling in graphene is extremely weak, making it a promising spin conductor for spintronic devices. In addition, many applications also require the generation of spin currents in graphene. Theoretical predictions and recent experimental results suggest one can engineer the spin Hall effect in graphene by greatly enhancing the spin-orbit coupling in the vicinity of an impurity. The extrinsic spin Hall effect then results from the spin-dependent skew scattering of electrons by impurities in the presence of spin-orbit interaction. This effect can be used to efficiently convert charge currents into spin-polarized currents. I will discuss recent experimental results on spin Hall effect in graphene decorated with adatoms and metallic cluster and show that a large spin Hall effect can appear due to skew scattering. While this spin-orbit coupling is small if compared with what it is found in metals, the effect is strongly enhanced in the presence of resonant scattering, giving rise to robust spin Hall angles. I will present our single impurity scattering calculations done with exact partial-wave expansions and complement the analysis with numerical results from a novel real-space implementation of the Kubo formalism for tight-binding Hamiltonians. The author acknowledges the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.

Spin Hall and Spin Swapping Torques in Diffusive Ferromagnets

NASA Astrophysics Data System (ADS)

Pauyac, Christian Ortiz; Chshiev, Mairbek; Manchon, Aurelien; Nikolaev, Sergey A.

2018-04-01

A complete set of the generalized drift-diffusion equations for a coupled charge and spin dynamics in ferromagnets in the presence of extrinsic spin-orbit coupling is derived from the quantum kinetic approach, covering major transport phenomena, such as the spin and anomalous Hall effects, spin swapping, spin precession, and relaxation processes. We argue that the spin swapping effect in ferromagnets is enhanced due to spin polarization, while the overall spin texture induced by the interplay of spin-orbital and spin precession effects displays a complex spatial dependence that can be exploited to generate torques and nucleate or propagate domain walls in centrosymmetric geometries without the use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.

Theory of High-T{sub c} Superconducting Cuprates Based on Experimental Evidence

DOE R&D Accomplishments Database

Abrikosov, A. A.

1999-12-10

A model of superconductivity in layered high-temperature superconducting cuprates is proposed, based on the extended saddle point singularities in the electron spectrum, weak screening of the Coulomb interaction and phonon-mediated interaction between electrons plus a small short-range repulsion of Hund's, or spin-fluctuation, origin. This permits to explain the large values of T{sub c}, features of the isotope effect on oxygen and copper, the existence of two types of the order parameter, the peak in the inelastic neutron scattering, the positive curvature of the upper critical field, as function of temperature etc.

Spin Hall effects

NASA Astrophysics Data System (ADS)

Sinova, Jairo; Valenzuela, Sergio O.; Wunderlich, J.; Back, C. H.; Jungwirth, T.

2015-10-01

Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Despite being observed only a decade ago, these effects are already ubiquitous within spintronics, as standard spin-current generators and detectors. Here the theoretical and experimental results that have established this subfield of spintronics are reviewed. The focus is on the results that have converged to give us the current understanding of the phenomena, which has evolved from a qualitative to a more quantitative measurement of spin currents and their associated spin accumulation. Within the experimental framework, optical-, transport-, and magnetization-dynamics-based measurements are reviewed and linked to both phenomenological and microscopic theories of the effect. Within the theoretical framework, the basic mechanisms in both the extrinsic and intrinsic regimes are reviewed, which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. Also reviewed is the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin generation used in many measurements of the spin Hall angle. A further connection to the spin-current-generating spin Hall effect to the inverse spin galvanic effect is given, in which an electrical current induces a nonequilibrium spin polarization. This effect often accompanies the spin Hall effect since they share common microscopic origins. Both can exhibit the same symmetries when present in structures comprising ferromagnetic and nonmagnetic layers through their induced current-driven spin torques or induced voltages. Although a short chronological overview of the evolution of the spin Hall effect field and the resolution of some early controversies is given, the main body of this review is structured from a pedagogical point of view, focusing on well-established and accepted physics. In such a young field, there remains much to be understood and explored, hence some of the future challenges and opportunities of this rapidly evolving area of spintronics are outlined.

Identification of species by multiplex analysis of variable-length sequences

PubMed Central

Pereira, Filipe; Carneiro, João; Matthiesen, Rune; van Asch, Barbara; Pinto, Nádia; Gusmão, Leonor; Amorim, António

2010-01-01

The quest for a universal and efficient method of identifying species has been a longstanding challenge in biology. Here, we show that accurate identification of species in all domains of life can be accomplished by multiplex analysis of variable-length sequences containing multiple insertion/deletion variants. The new method, called SPInDel, is able to discriminate 93.3% of eukaryotic species from 18 taxonomic groups. We also demonstrate that the identification of prokaryotic and viral species with numeric profiles of fragment lengths is generally straightforward. A computational platform is presented to facilitate the planning of projects and includes a large data set with nearly 1800 numeric profiles for species in all domains of life (1556 for eukaryotes, 105 for prokaryotes and 130 for viruses). Finally, a SPInDel profiling kit for discrimination of 10 mammalian species was successfully validated on highly processed food products with species mixtures and proved to be easily adaptable to multiple screening procedures routinely used in molecular biology laboratories. These results suggest that SPInDel is a reliable and cost-effective method for broad-spectrum species identification that is appropriate for use in suboptimal samples and is amenable to different high-throughput genotyping platforms without the need for DNA sequencing. PMID:20923781

Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics

DOE PAGES

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

2016-03-07

In this paper, we investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. Finally, we also suggest that metallic antiferromagnets may be good candidates for the investigationmore » of various unidirectional effects related to novel spin-orbitronics phenomena.« less

[Validation of the portuguese version of the Mini-Social Phobia Inventory (Mini-SPIN)].

PubMed

D'El Rey, Gustavo José Fonseca; Matos, Cláudia Wilmor

2009-01-01

Social phobia (also known as social anxiety disorder) is a severe mental disorder that brings distress and disability. The aim of this study was validate to the Portuguese language the Mini-Social Phobia Inventory (Mini-SPIN) in a populational sample. We performed a discriminative validity study of the Mini-SPIN in a sample of 644 subjects (Mini-SPIN positive group: n = 218 and control/negative group: n = 426) of a study of anxiety disorders' prevalence in the city of Santo André-SP. The Portuguese version of the Mini-SPIN (with score of 6 points, suggested in the original English version) demonstrated a sensitivity of 95.0%, specificity of 80.3%, positive predictive value of 52.8%, negative predictive value of 98.6% and incorrect classification rate of 16.9%. With score of 7 points, was observed an increase in the specificity and positive predictive value (88.6% and 62.7%), while the sensitivity and negative predictive value (84.8% and 96.2%) remained high. The Portuguese version of the Mini-SPIN showed satisfactory psychometric qualities in terms of discriminative validity. In this study, the cut-off of 7, was considered to be the most suitable to screening of the generalized social phobia.

Direct detection of spin Nernst effect in platinum

NASA Astrophysics Data System (ADS)

Bose, A.; Bhuktare, S.; Singh, H.; Dutta, S.; Achanta, V. G.; Tulapurkar, A. A.

2018-04-01

Generation of spin current lies at the heart of spintronic research. The spin Hall effect and the spin Seebeck effect have drawn considerable attention in the last few years to create pure spin current by heavy metals and ferromagnets, respectively. In this work, we show the direct evidence of heat current to spin current conversion in non-magnetic Platinum by the spin Nernst effect (SNE) at room temperature. This is the thermal analogue of the spin Hall effect in non-magnets. We have shown that the 8 K/μm thermal gradient in Pt can lead to the generation of pure spin current density of the order of 108 A/m2 by virtue of SNE. This opens up an additional possibility to couple the relativistic spin-orbit interaction with the thermal gradient for spintronic applications.

Enhanced thermo-spin effects in iron-oxide/metal multilayers

NASA Astrophysics Data System (ADS)

Ramos, R.; Lucas, I.; Algarabel, P. A.; Morellón, L.; Uchida, K.; Saitoh, E.; Ibarra, M. R.

2018-06-01

Since the discovery of the spin Seebeck effect (SSE), much attention has been devoted to the study of the interaction between heat, spin, and charge in magnetic systems. The SSE refers to the generation of a spin current upon the application of a thermal gradient and detected by means of the inverse spin Hall effect. Conversely, the spin Peltier effect (SPE) refers to the generation of a heat current as a result of a spin current induced by the spin Hall effect. Here we report a strong enhancement of both the SSE and SPE in Fe3O4/Pt multilayered thin films at room temperature as a result of an increased thermo-spin conversion efficiency in the multilayers. These results open the possibility to design thin film heterostructures that may boost the application of thermal spin currents in spintronics.

Spontaneous Currents in Superconducting Systems with Strong Spin-Orbit Coupling

NASA Astrophysics Data System (ADS)

Mironov, S.; Buzdin, A.

2017-02-01

We show that Rashba spin-orbit coupling at the interface between a superconductor and a ferromagnet should produce a spontaneous current in the atomic thickness region near the interface. This current is counterbalanced by the superconducting screening current flowing in the region of the width of the London penetration depth near the interface. Such a current-carrying state creates a magnetic field near the superconductor surface, generates a stray magnetic field outside the sample edges, changes the slope of the temperature dependence of the critical field Hc 3 , and may generate the spontaneous Abrikosov vortices near the interface.

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1 -x Alloys

NASA Astrophysics Data System (ADS)

Ou, Yongxi; Ralph, D. C.; Buhrman, R. A.

2018-03-01

Robust spin Hall effects (SHE) have recently been observed in nonmagnetic heavy metal systems with strong spin-orbit interactions. These SHE are either attributed to an intrinsic band-structure effect or to extrinsic spin-dependent scattering from impurities, namely, side jump or skew scattering. Here we report on an extraordinarily strong spin Hall effect, attributable to spin fluctuations, in ferromagnetic FexPt1 -x alloys near their Curie point, tunable with x . This results in a dampinglike spin-orbit torque being exerted on an adjacent ferromagnetic layer that is strongly temperature dependent in this transition region, with a peak value that indicates a lower bound 0.34 ±0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced peak in the effective spin-mixing conductance of the FM /FePt interface, and determine the spin diffusion length in these FexPt1 -x alloys. These results establish new opportunities for fundamental studies of spin dynamics and transport in ferromagnetic systems with strong spin fluctuations, and a new pathway for efficiently generating strong spin currents for applications.

Gardnerella infection as distinguished from cervical dysbacteriosis: the advantageous spin-off of cervical screening.

PubMed

Klomp, Johanna M; Ouwerkerk-Noordam, Elisabeth; Boon, Mathilde E; van Haaften, Maarten; Heintz, A Peter M

2009-01-01

To evaluate cytologic diagnoses of dysbacteriosis and Gardnerella infection and to obtain insight into the diagnostic problems of Gardnerella. One hundred randomly selected samples of each of 3 diagnostic series were rescreened by 2 pathologists, resulting in 2 rescreening diagnoses and a consensus diagnosis. A smear was considered unequivocal when the original O code and the O code of the consensus diagnoses were equal and discordant when the flora diagnoses of the 2 pathologists differed. Discordance was highest in the dysbacteriotic series (20%) and lowest in the healthy group (4%). Unequivocal diagnoses were established in 65% of the dysbacteriotic smears, 80% of the Gardnerella smears and 93% of the healthy smears. Misclassification of Gardnerella occurred in the presence of clusters of bacteria mixed with spermatozoa. Blue mountain cells in Gardnerella infection can be identified unequivocally in cervical smears. Because of the clinical importance of treating Gardnerella, such advantageous spin-offs of cervical screening should be exploited.

A Theoretical Approach to Selection of a Biologically Active Substance in Ultra-Low Doses for Effective Action on a Biological System.

PubMed

Boldyreva, Liudmila Borisovna

2018-05-01

 An approach is offered to selecting a biologically active substance (BAS) in ultra-low dose for effective action on a biological system (BS). The technique is based on the assumption that BAS in ultra-low doses exerts action on BS by means of spin supercurrent emerging between the spin structure created by BAS, on the one hand, and the spin structure created by BS, on the other hand. According to modern quantum-mechanical concepts, these spin structures may be virtual particles pairs having precessing spin (that is, be essentially spin vortices in the physical vacuum) and created by the quantum entities that BAS and BS consist of. The action is effective provided there is equality of precession frequencies of spins in these spin structures.  In this work, some methods are considered for determining the precession frequencies of spins in virtual particles pairs: (1) determination of energy levels of quantum entities that BS and BAS consist of; (2) the use of spin-flip effect of the virtual particles pair spin, the effect being initiated by action of magnetic vector potential (the spin-flip effect takes place when the varied frequency of the magnetic vector potential equals the precession frequency of the spin); (3) determining the frequencies of photons effectively acting on BS.  It is shown that the effect of BAS in ultra-low doses on BS can be replaced by the effect of a beam of low-intensity photons, if the frequency of photons equals the precession frequency of spin in spin structures created by BS. Consequently, the color of bodies placed near a biological system is able to exert an effective action on the biological system: that is "color therapy" is possible. It is also supposed that the spin-flip effect may be used not only for determining the precession frequency of spin in spin structures created by BS but also for therapeutic action on biological systems. The Faculty of Homeopathy.

Analysis of Hanle-effect signals observed in Si-channel spin accumulation devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takamura, Yota, E-mail: takamura@spin.pe.titech.ac.jp; Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552; Akushichi, Taiju

2014-05-07

We reexamined curve-fitting analysis for spin-accumulation signals observed in Si-channel spin-accumulation devices, employing widely-used Lorentz functions and a new formula developed from the spin diffusion equation. A Si-channel spin-accumulation device with a high quality ferromagnetic spin injector was fabricated, and its observed spin-accumulation signals were verified. Experimentally obtained Hanle-effect signals for spin accumulation were not able to be fitted by a single Lorentz function and were reproduced by the newly developed formula. Our developed formula can represent spin-accumulation signals and thus analyze Hanle-effect signals.

Extrinsic Rashba spin-orbit coupling effect on silicene spin polarized field effect transistors

NASA Astrophysics Data System (ADS)

Pournaghavi, Nezhat; Esmaeilzadeh, Mahdi; Abrishamifar, Adib; Ahmadi, Somaieh

2017-04-01

Regarding the spin field effect transistor (spin FET) challenges such as mismatch effect in spin injection and insufficient spin life time, we propose a silicene based device which can be a promising candidate to overcome some of those problems. Using non-equilibrium Green’s function method, we investigate the spin-dependent conductance in a zigzag silicene nanoribbon connected to two magnetized leads which are supposed to be either in parallel or anti-parallel configurations. For both configurations, a controllable spin current can be obtained when the Rashba effect is present; thus, we can have a spin filter device. In addition, for anti-parallel configuration, in the absence of Rashba effect, there is an intrinsic energy gap in the system (OFF-state); while, in the presence of Rashba effect, electrons with flipped spin can pass through the channel and make the ON-state. The current voltage (I-V) characteristics which can be tuned by changing the gate voltage or Rashba strength, are studied. More importantly, reducing the mismatch conductivity as well as energy consumption make the silicene based spin FET more efficient relative to the spin FET based on two-dimensional electron gas proposed by Datta and Das. Also, we show that, at the same conditions, the current and {{I}\\text{on}}/{{I}\\text{off}} ratio of silicene based spin FET are significantly greater than that of the graphene based one.

Spin transport study in a Rashba spin-orbit coupling system

PubMed Central

Mei, Fuhong; Zhang, Shan; Tang, Ning; Duan, Junxi; Xu, Fujun; Chen, Yonghai; Ge, Weikun; Shen, Bo

2014-01-01

One of the most important topics in spintronics is spin transport. In this work, spin transport properties of two-dimensional electron gas in AlxGa1-xN/GaN heterostructure were studied by helicity-dependent photocurrent measurements at room temperature. Spin-related photocurrent was detected under normal incidence of a circularly polarized laser with a Gaussian distribution. On one hand, spin polarized electrons excited by the laser generate a diffusive spin polarization current, which leads to a vortex charge current as a result of anomalous circular photogalvanic effect. On the other hand, photo-induced spin polarized electrons driven by a longitudinal electric field give rise to a transverse current via anomalous Hall Effect. Both of these effects originated from the Rashba spin-orbit coupling. By analyzing spin-related photocurrent varied with laser position, the contributions of the two effects were differentiated and the ratio of the spin diffusion coefficient to photo-induced anomalous spin Hall mobility Ds/μs = 0.08 V was extracted at room temperature. PMID:24504193

Analytical energy gradient for the two-component normalized elimination of the small component method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zou, Wenli; Filatov, Michael; Cremer, Dieter, E-mail: dcremer@smu.edu

2015-06-07

The analytical gradient for the two-component Normalized Elimination of the Small Component (2c-NESC) method is presented. The 2c-NESC is a Dirac-exact method that employs the exact two-component one-electron Hamiltonian and thus leads to exact Dirac spin-orbit (SO) splittings for one-electron atoms. For many-electron atoms and molecules, the effect of the two-electron SO interaction is modeled by a screened nucleus potential using effective nuclear charges as proposed by Boettger [Phys. Rev. B 62, 7809 (2000)]. The effect of spin-orbit coupling (SOC) on molecular geometries is analyzed utilizing the properties of the frontier orbitals and calculated SO couplings. It is shown thatmore » bond lengths can either be lengthened or shortened under the impact of SOC where in the first case the influence of low lying excited states with occupied antibonding orbitals plays a role and in the second case the jj-coupling between occupied antibonding and unoccupied bonding orbitals dominates. In general, the effect of SOC on bond lengths is relatively small (≤5% of the scalar relativistic changes in the bond length). However, large effects are found for van der Waals complexes Hg{sub 2} and Cn{sub 2}, which are due to the admixture of more bonding character to the highest occupied spinors.« less

Broad Area Review of the Enhanced Flight Screening Program

DTIC Science & Technology

1998-03-17

Hondo, TX, and Ruidoso , NM. Because this was a combined effort without AFOTEC involvement, both ASD and the contractor were responsible for the...testing at Ruidoso , NM (elevation 6,811 MSL) to evaluate high-density altitude performance. During the test, extra emphasis was placed on spin

Classroom Analysis of Rotating Space Vehicles in 2001: A Space Odyssey.

ERIC Educational Resources Information Center

Borgwald, James M.; Schreiner, Serge

1993-01-01

This article describes the use of modern science fiction movies as a vehicle to teach scientific principles. The resulting artificial gravity from a spinning space station in movie "2001" is calculated from measurements taken off of the screen. A mathematical explanation is provided. (MVL)

Antiferromagnetic spintronics

NASA Astrophysics Data System (ADS)

Baltz, V.; Manchon, A.; Tsoi, M.; Moriyama, T.; Ono, T.; Tserkovnyak, Y.

2018-01-01

Antiferromagnetic materials could represent the future of spintronic applications thanks to the numerous interesting features they combine: they are robust against perturbation due to magnetic fields, produce no stray fields, display ultrafast dynamics, and are capable of generating large magnetotransport effects. Intense research efforts over the past decade have been invested in unraveling spin transport properties in antiferromagnetic materials. Whether spin transport can be used to drive the antiferromagnetic order and how subsequent variations can be detected are some of the thrilling challenges currently being addressed. Antiferromagnetic spintronics started out with studies on spin transfer and has undergone a definite revival in the last few years with the publication of pioneering articles on the use of spin-orbit interactions in antiferromagnets. This paradigm shift offers possibilities for radically new concepts for spin manipulation in electronics. Central to these endeavors are the need for predictive models, relevant disruptive materials, and new experimental designs. This paper reviews the most prominent spintronic effects described based on theoretical and experimental analysis of antiferromagnetic materials. It also details some of the remaining bottlenecks and suggests possible avenues for future research. This review covers both spin-transfer-related effects, such as spin-transfer torque, spin penetration length, domain-wall motion, and "magnetization" dynamics, and spin-orbit related phenomena, such as (tunnel) anisotropic magnetoresistance, spin Hall, and inverse spin galvanic effects. Effects related to spin caloritronics, such as the spin Seebeck effect, are linked to the transport of magnons in antiferromagnets. The propagation of spin waves and spin superfluids in antiferromagnets is also covered.

Reduced Spin Hall Effects from Magnetic Proximity.

DOE PAGES

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

2015-03-26

We investigate temperature-dependent spin pumping and inverse spin Hall effects in thin Pt and Pd in contact with Permalloy. Our experiments show a decrease of the spin Hall effect with decreasing temperature, which is attributed to a temperature-dependent proximity effect. The spin Hall angle decreases from 0.086 at room temperature to 0.042 at 10 K for Pt and is nearly negligible at 10 K for Pd. By first-principle calculations, we show that the spin Hall conductivity indeed reduces by increasing the proximity-induced spin magnetic moments for both Pt and Pd. This work highlights the important role of proximity-induced magnetic orderingmore » to spin Hall phenomena in Pt and Pd.« less

Inverse spin Hall and spin rectification effects in NiFe/FeMn exchange-biased thin films

NASA Astrophysics Data System (ADS)

Garcia, W. J. S.; Seeger, R. L.; da Silva, R. B.; Harres, A.

2017-11-01

Materials presenting high spin-orbit coupling are able to convert spin currents in charge currents. The phenomenon, known as inverse spin Hall effect, promises to revolutionize spintronic technology enabling the electrical detection of spin currents. It has been observed in a variety of systems, usually non-magnetic metals. We study the voltage emerging in exchange biased Ta/NiFe/FeMn/Ta thin films near the ferromagnetic resonance. Measured signals are related to both inverse spin Hall and spin rectification effects, and two distinct protocols were employed to separate their contributions.The curve shift due to the exchange bias effect may enable high frequency applications without an external applied magnetic field.

Spin filtering effect generated by the inter-subband spin-orbit coupling in the bilayer nanowire with the quantum point contact

PubMed Central

Wójcik, Paweł; Adamowski, Janusz

2017-01-01

The spin filtering effect in the bilayer nanowire with quantum point contact is investigated theoretically. We demonstrate the new mechanism of the spin filtering based on the lateral inter-subband spin-orbit coupling, which for the bilayer nanowires has been reported to be strong. The proposed spin filtering effect is explained as the joint effect of the Landau-Zener intersubband transitions caused by the hybridization of states with opposite spin (due to the lateral Rashba SO interaction) and the confinement of carriers in the quantum point contact region. PMID:28358141

Thermally Generated Spin Signals in a Nondegenerate Silicon Spin Valve

NASA Astrophysics Data System (ADS)

Yamashita, Naoto; Ando, Yuichiro; Koike, Hayato; Miwa, Shinji; Suzuki, Yoshishige; Shiraishi, Masashi

2018-05-01

Thermally generated spin signals are observed in a nondegenerate Si spin valve. The spin-dependent Seebeck effect is used for thermal spin-signal generation. A thermal gradient of about 200 mK at the interface of Fe and Si enables the generation of a spin voltage of 8 μ V at room temperature. A simple expansion of the conventional spin-drift-diffusion model that takes into account the spin-dependent Seebeck effect shows that semiconductor materials are more promising for thermal spin-signal generation comparing than metallic materials, and thus enable efficient heat recycling in semiconductor spin devices.

Observation of Spin Hall Effect in Photon Tunneling via Weak Measurements

PubMed Central

Zhou, Xinxing; Ling, Xiaohui; Zhang, Zhiyou; Luo, Hailu; Wen, Shuangchun

2014-01-01

Photonic spin Hall effect (SHE) manifesting itself as spin-dependent splitting escapes detection in previous photon tunneling experiments due to the fact that the induced beam centroid shift is restricted to a fraction of wavelength. In this work, we report on the first observation of this tiny effect in photon tunneling via weak measurements based on preselection and postselection technique on the spin states. We find that the spin-dependent splitting is even larger than the potential barrier thickness when spin-polarized photons tunneling through a potential barrier. This photonic SHE is attributed to spin-redirection Berry phase which can be described as a consequence of the spin-orbit coupling. These findings provide new insight into photon tunneling effect and thereby offer the possibility of developing spin-based nanophotonic applications. PMID:25487043

Interface-driven spin-torque ferromagnetic resonance by Rashba coupling at the interface between nonmagnetic materials

DOE PAGES

Jungfleisch, M. B.; Zhang, W.; Sklenar, J.; ...

2016-06-20

The Rashba-Edelstein effect stems from the interaction between the electron's spin and its momentum induced by spin-orbit interaction at an interface or a surface. It was shown that the inverse Rashba-Edelstein effect can be used to convert a spin current into a charge current. Here, we demonstrate the reverse process of a charge-to spin-current conversion at a Bi/Ag Rashba interface. We show that this interface-driven spin current can drive an adjacent ferromagnet to resonance. We employ a spin-torque ferromagnetic resonance excitation/detection scheme which was developed originally for a bulk spin-orbital effect, the spin Hall effect. In our experiment, the directmore » Rashba-Edelstein effect generates an oscillating spin current from an alternating charge current driving the magnetization precession in a neighboring permalloy (Py, Ni 80Fe 20) layer. As a result, electrical detection of the magnetization dynamics is achieved by a rectificationmechanism of the time dependent multilayer resistance arising from the anisotropic magnetoresistance.« less

Spin Hall Effects in Metallic Antiferromagnets

DOE PAGES

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun; ...

2014-11-04

In this paper, we investigate four CuAu-I-type metallic antiferromagnets for their potential as spin current detectors using spin pumping and inverse spin Hall effect. Nontrivial spin Hall effects were observed for FeMn, PdMn, and IrMn while a much higher effect was obtained for PtMn. Using thickness-dependent measurements, we determined the spin diffusion lengths of these materials to be short, on the order of 1 nm. The estimated spin Hall angles of the four materials follow the relationship PtMn > IrMn > PdMn > FeMn, highlighting the correlation between the spin-orbit coupling of nonmagnetic species and the magnitude of the spinmore » Hall effect in their antiferromagnetic alloys. These experiments are compared with first-principles calculations. Finally, engineering the properties of the antiferromagnets as well as their interfaces can pave the way for manipulation of the spin dependent transport properties in antiferromagnet-based spintronics.« less

Magneto-Seebeck effect in spin valves

NASA Astrophysics Data System (ADS)

Zhang, X. M.; Wan, C. H.; Wu, H.; Tang, P.; Yuan, Z. H.; Zhang, Q. T.; Zhang, X.; Tao, B. S.; Fang, C.; Han, X. F.

2017-10-01

The magneto-Seebeck (MS) effect, which is also called magneto-thermo-power, was observed in Co/Cu/Co and NiFe/Cu/Co spin valves. Their Seebeck coefficients in the parallel state were larger than those in the antiparallel state, and the MS ratio defined as (SAP -SP)/SP could reach -9% in our case. The MS effect originated not only from trivial giant magnetoresistance but also from spin current generated due to spin-polarized thermoelectric conductivity of ferromagnetic materials and subsequent modulation of the spin current by different spin configurations in spin valves. A simple Mott two-channel model reproduced a -11% MS effect for the Co/Cu/Co spin valves, qualitatively consistent with our observations. The MS effect could be applied for simultaneously sensing the temperature gradient and the magnetic field and also be possibly applied to determine spin polarization of thermoelectric conductivity and the Seebeck coefficient of ferromagnetic thin films.

Polar-Core Spin Vortex of Quasi-2D Spin-2 Condensate in a Flat-Bottomed Optical Trap

NASA Astrophysics Data System (ADS)

Zheng, Gong-Ping; Chang, Gao-Zhan; Li, Pin; Li, Ting

2017-10-01

Motivated by the recent experiments realized in a flat-bottomed optical trap [Science 347 (2015) 167; Nat. Commun. 6 (2015) 6162], we study the ground state of polar-core spin vortex of quasi-2D spin-2 condensate in a homogeneous trap plus a weak magnetic field. The exact spatial distribution of local spin is obtained and the vortex core are observed to decrease with the growth of the effective spin-spin interaction. For the larger effective spin-spin interaction, the spatial distribution of spin magnitude in spin-2 condensate we obtained agrees well with that of spin-1 condensate in a homogeneous trap, where a polar-core spin vortex was schematically demonstrated as a fully-magnetized planar spin texture with a zero-spin core. The effective spin-spin interaction is proportional to both the bare spin-spin interaction and the radius of the homogeneous trap, simultaneously. Thus the polar-core spin vortex we obtained can be easily controlled by the radius of the trap. Supported by the National Natural Science Foundation of China under Grant No. 11274095, the Key Scientific Research Project of Henan Province of China under Grant No. 16A140011, and the High Performance Computing Center of Henan Normal University

Detection of pure inverse spin-Hall effect induced by spin pumping at various excitation

NASA Astrophysics Data System (ADS)

Inoue, H. Y.; Harii, K.; Ando, K.; Sasage, K.; Saitoh, E.

2007-10-01

Electric-field generation due to the inverse spin-Hall effect (ISHE) driven by spin pumping was detected and separated experimentally from the extrinsic magnetogalvanic effects in a Ni81Fe19/Pt film. By applying a sample-cavity configuration in which the extrinsic effects are suppressed, the spin pumping using ferromagnetic resonance gives rise to a symmetric spectral shape in the electromotive force spectrum, indicating that the motive force is due entirely to ISHE. This method allows the quantitative analysis of the ISHE and the spin-pumping effect. The microwave-power dependence of the ISHE amplitude is consistent with the prediction of a direct current-spin-pumping scenario.

The Effect of Heme Environment on the Hydrogen Abstraction Reaction of Camphor in P450cam Catalysis: A QM/MM Study

PubMed Central

Altun, Ahmet; Guallar, Victor; Friesner, Richard A.; Shaik, Sason; Thiel, Walter

2010-01-01

The discrepancies between the published QM/MM studies (Schöneboom, J. C.; Cohen, S.; Lin, H.; Shaik, S.; Thiel, W. J. Am. Chem. Soc. 2004, 126, 4017 / Guallar, V.; Friesner, R. A. J. Am. Chem. Soc. 2004, 126, 8501) on H-abstraction of camphor in P450cam have largely been resolved. The crystallographic water molecule 903 situated near the oxo atom of Compound I acts as a catalyst for H-abstraction, lowering the barrier by about 4 kcal/mol. Spin density at the A-propionate side chain of heme can occur in the case of incomplete screening, but has no major effect on the computed barrier. PMID:16551096

Correlated electron-hole mechanism for molecular doping in organic semiconductors

NASA Astrophysics Data System (ADS)

Li, Jing; D'Avino, Gabriele; Pershin, Anton; Jacquemin, Denis; Duchemin, Ivan; Beljonne, David; Blase, Xavier

2017-07-01

The electronic and optical properties of the paradigmatic F4TCNQ-doped pentacene in the low-doping limit are investigated by a combination of state-of-the-art many-body ab initio methods accounting for environmental screening effects, and a carefully parametrized model Hamiltonian. We demonstrate that while the acceptor level lies very deep in the gap, the inclusion of electron-hole interactions strongly stabilizes dopant-semiconductor charge transfer states and, together with spin statistics and structural relaxation effects, rationalize the possibility for room-temperature dopant ionization. Our findings reconcile available experimental data, shedding light on the partial vs. full charge transfer scenario discussed in the literature, and question the relevance of the standard classification in shallow or deep impurity levels prevailing for inorganic semiconductors.

Spin pumping and inverse spin Hall effects in heavy metal/antiferromagnet/Permalloy trilayers

NASA Astrophysics Data System (ADS)

Saglam, Hilal; Zhang, Wei; Jungfleisch, M. Benjamin; Jiang, Wanjun; Pearson, John E.; Hoffmann, Axel

Recent work shows efficient spin transfer via spin waves in insulating antiferromagnets (AFMs), suggesting that AFMs can play a more active role in the manipulation of ferromagnets. We use spin pumping and inverse spin Hall effect experiments on heavy metal (Pt and W)/AFMs/Py (Ni80Fe20) trilayer structures, to examine the possible spin transfer phenomenon in metallic AFMs, i . e . , FeMn and PdMn. Previous work has studied electronic effects of the spin transport in these materials, yielding short spin diffusion length on the order of 1 nm. However, the work did not examine whether besides diffusive spin transport by the conduction electrons, there are additional spin transport contributions from spin wave excitations. We clearly observe spin transport from the Py spin reservoir to the heavy metal layer through the sandwiched AFMs with thicknesses well above the previously measured spin diffusion lengths, indicating that spin transport by spin waves may lead to non-negligible contributions This work was supported by US DOE, OS, Materials Sciences and Engineering Division. Lithographic patterning was carried out at the CNM, which is supported by DOE, OS under Contract No. DE-AC02-06CH11357.

Highly efficient and tunable spin-to-charge conversion through Rashba coupling at oxide interfaces

NASA Astrophysics Data System (ADS)

Lesne, E.; Fu, Yu; Oyarzun, S.; Rojas-Sánchez, J. C.; Vaz, D. C.; Naganuma, H.; Sicoli, G.; Attané, J.-P.; Jamet, M.; Jacquet, E.; George, J.-M.; Barthélémy, A.; Jaffrès, H.; Fert, A.; Bibes, M.; Vila, L.

2016-12-01

The spin-orbit interaction couples the electrons’ motion to their spin. As a result, a charge current running through a material with strong spin-orbit coupling generates a transverse spin current (spin Hall effect, SHE) and vice versa (inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronic functionalities and devices, some of which do not require any ferromagnetic material. However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronic hetero- and mesostructures. Here, we make use of an interface-driven spin-orbit coupling mechanism--the Rashba effect--in the oxide two-dimensional electron system (2DES) LaAlO3/SrTiO3 to achieve spin-to-charge conversion with unprecedented efficiency. Through spin pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES and highlight the importance of a long scattering time to achieve efficient spin-to-charge interconversion.

Thermal imaging of spin Peltier effect

NASA Astrophysics Data System (ADS)

Daimon, Shunsuke; Iguchi, Ryo; Hioki, Tomosato; Saitoh, Eiji; Uchida, Ken-Ichi

2016-12-01

The Peltier effect modulates the temperature of a junction comprising two different conductors in response to charge currents across the junction, which is used in solid-state heat pumps and temperature controllers in electronics. Recently, in spintronics, a spin counterpart of the Peltier effect was observed. The `spin Peltier effect' modulates the temperature of a magnetic junction in response to spin currents. Here we report thermal imaging of the spin Peltier effect; using active thermography technique, we visualize the temperature modulation induced by spin currents injected into a magnetic insulator from an adjacent metal. The thermal images reveal characteristic distribution of spin-current-induced heat sources, resulting in the temperature change confined only in the vicinity of the metal/insulator interface. This finding allows us to estimate the actual magnitude of the temperature modulation induced by the spin Peltier effect, which is more than one order of magnitude greater than previously believed.

Inverse spin-valve effect in nanoscale Si-based spin-valve devices

NASA Astrophysics Data System (ADS)

Hiep, Duong Dinh; Tanaka, Masaaki; Hai, Pham Nam

2017-12-01

We investigated the spin-valve effect in nano-scale silicon (Si)-based spin-valve devices using a Fe/MgO/Ge spin injector/detector deposited on Si by molecular beam epitaxy. For a device with a 20 nm Si channel, we observed clear magnetoresistance up to 3% at low temperature when a magnetic field was applied in the film plane along the Si channel transport direction. A large spin-dependent output voltage of 20 mV was observed at a bias voltage of 0.9 V at 15 K, which is among the highest values in lateral spin-valve devices reported so far. Furthermore, we observed that the sign of the spin-valve effect is reversed at low temperatures, suggesting the possibility of a spin-blockade effect of defect states in the MgO/Ge tunneling barrier.

Radiation reaction for spinning bodies in effective field theory. I. Spin-orbit effects

NASA Astrophysics Data System (ADS)

Maia, Natália T.; Galley, Chad R.; Leibovich, Adam K.; Porto, Rafael A.

2017-10-01

We compute the leading post-Newtonian (PN) contributions at linear order in the spin to the radiation-reaction acceleration and spin evolution for binary systems, which enter at fourth PN order. The calculation is carried out, from first principles, using the effective field theory framework for spinning compact objects, in both the Newton-Wigner and covariant spin supplementary conditions. A nontrivial consistency check is performed on our results by showing that the energy loss induced by the resulting radiation-reaction force is equivalent to the total emitted power in the far zone, up to so-called "Schott terms." We also find that, at this order, the radiation reaction has no net effect on the evolution of the spins. The spin-spin contributions to radiation reaction are reported in a companion paper.

Spin-Hall effect and emergent antiferromagnetic phase transition in n-Si

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

Spin current experiences minimal dephasing and scattering in Si due to small spin-orbit coupling and spin-lattice interactions is the primary source of spin relaxation. We hypothesize that if the specimen dimension is of the same order as the spin diffusion length then spin polarization will lead to non-equilibrium spin accumulation and emergent phase transition. In n-Si, spin diffusion length has been reported up to 6 μm. The spin accumulation in Si will modify the thermal transport behavior of Si, which can be detected with thermal characterization. In this study, we report observation of spin-Hall effect and emergent antiferromagnetic phase transition behavior using magneto-electro-thermal transport characterization. The freestanding Pd (1 nm)/Ni80Fe20 (75 nm)/MgO (1 nm)/n-Si (2 μm) thin film specimen exhibits a magnetic field dependent thermal transport and spin-Hall magnetoresistance behavior attributed to Rashba effect. An emergent phase transition is discovered using self-heating 3ω method, which shows a diverging behavior at 270 K as a function of temperature similar to a second order phase transition. We propose that spin-Hall effect leads to the spin accumulation and resulting emergent antiferromagnetic phase transition. We propose that the length scale for Rashba effect can be equal to the spin diffusion length and two-dimensional electron gas is not essential for it. The emergent antiferromagnetic phase transition is attributed to the site inversion asymmetry in diamond cubic Si lattice.

Spin effects induced by thermal perturbation in a normal metal/magnetic insulator system

NASA Astrophysics Data System (ADS)

Lyapilin, I. I.; Okorokov, M. S.; Ustinov, V. V.

2015-05-01

Using one of the methods of quantum nonequilibrium statistical physics, we have investigated the spin transport transverse to the normal metal/ferromagnetic insulator interface in hybrid nanostructures. An approximation of the effective parameters, when each of the interacting subsystems (electron spin, magnon, and phonon) is characterized by its own effective temperature, has been considered. The generalized Bloch equations which describe the spin-wave current propagation in the dielectric have been derived. Finally, two sides of the spin transport "coin" have been revealed: the diffusive nature of the magnon motion and magnon relaxation processes, responsible for the spin pumping, and the spin-torque effect.

Intrinsic Spin-Hall Effect in n-Doped Bulk GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-01-15

We show that the bulk Dresselhauss (k{sup 3}) spin-orbit coupling term leads to an intrinsic spin-Hall effect in n-doped bulk GaAs, but without the appearance of uniform magnetization. The spin-Hall effect in strained and unstrained bulk GaAs has been recently observed experimentally by Kato et. al. [1]. We show that the experimental result is quantitatively consistent with the intrinsic spin-Hall effect due to the Dresselhauss term, when lifetime broadening is taken into account. On the other hand, extrinsic contribution to the spin-Hall effect is several orders of magnitude smaller than the observed effect.

Absence of anomalous Nernst effect in spin Seebeck effect of Pt/YIG

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miao, B. F., E-mail: bfmiao@nju.edu.cn; Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218; Huang, S. Y.

2016-01-15

The Pt/YIG structure has been widely used to study spin Seebeck effect (SSE), inverse spin Hall effect, and other pure spin current phenomena. However, the magnetic proximity effect in Pt when in contact with YIG, and the potential anomalous Nernst effect (ANE) may compromise the spin current phenomena in Pt/YIG. By inserting a Cu layer of various thicknesses between Pt and YIG, we have separated the signals from the SSE and that of the ANE. It is demonstrated that the thermal voltage in Pt/YIG mainly comes from spin current due to the longitudinal SSE with negligible contribution from the ANE.

Coexistence of Velocity Renormalization and Ferrimagnetic Fluctuation in the Organic Dirac Electron System α-(BEDT-TTF)2I3

NASA Astrophysics Data System (ADS)

Matsuno, Genki; Kobayashi, Akito

2018-05-01

We evaluate the uniform spin susceptibility in an extended Hubbard model describing α-(BEDT-TTF)2I3. Employing the Fock-type self-energy with the long-range Coulomb interaction and the random phase approximation with the on-site Coulomb interaction, it is clarified that the characteristic energy scales at which ferrimagnetic fluctuation and velocity renormalization emerge are different. This is why these phenomena coexist while the ferrimagnetic fluctuation is disturbed by the velocity renormalization. In addition, it is found that screening effect to the self-energy is irrelevant in the presence of a strong on-site Coulomb interaction U.

Endohedral fullerenes contaning transition-metal clusters

NASA Astrophysics Data System (ADS)

Bhusal, Shusil; Basurto, Luis; Zope, Rajendra; Baruah, Tunna

We report detailed investigation of structural, electronic, and spectroscopic properties of VSc2N-containing fullerenes in the size range C68 - C96. First, the candidate structures of the ground state are obtained using a systematic approach in which a large number of isomers of endohedral fullerenes were screened for their energetic stability. Stability of some of the most promising isomers were further studied using density functional theory at the all-electron level using large polarized Gaussian basis sets. The effect of the V doping is examined on the structure, spin states and the magnetic properties of the endohedral fullerenes. De-SC0002168, NSF-DMR 125302, DE-SC0006818.

Building Complex Kondo Impurities by Manipulating Entangled Spin Chains.

PubMed

Choi, Deung-Jang; Robles, Roberto; Yan, Shichao; Burgess, Jacob A J; Rolf-Pissarczyk, Steffen; Gauyacq, Jean-Pierre; Lorente, Nicolás; Ternes, Markus; Loth, Sebastian

2017-10-11

The creation of molecule-like structures in which magnetic atoms interact controllably is full of potential for the study of complex or strongly correlated systems. Here, we create spin chains in which a strongly correlated Kondo state emerges from magnetic coupling of transition-metal atoms. We build chains up to ten atoms in length by placing Fe and Mn atoms on a Cu 2 N surface with a scanning tunneling microscope. The atoms couple antiferromagnetically via superexchange interaction through the nitrogen atom network of the surface. The emergent Kondo resonance is spatially distributed along the chain. Its strength can be controlled by mixing atoms of different transition metal elements and manipulating their spatial distribution. We show that the Kondo screening of the full chain by the electrons of the nonmagnetic substrate depends on the interatomic entanglement of the spins in the chain, demonstrating the prerequisites to build and probe spatially extended strongly correlated nanostructures.

Thermally driven spin-Seebeck transport in chiral dsDNA-based molecular devices

NASA Astrophysics Data System (ADS)

Nian, L. L.; Zhang, Rong; Tang, F. R.; Tang, Jun; Bai, Long

2018-03-01

By employing the nonequilibrium Green's function technique, we study the thermal-induced spin-Seebeck transport through a chiral double-stranded DNA (dsDNA) connected to a normal-metal and a ferromagnetic lead. How the main parameters of the dsDNA-based system influence the spin-Seebeck transport is analyzed at length, and the thermally created charge (spin-related) current displays the rectification effect and the negative differential thermal conductance feature. More importantly, the spin current exhibits the rectification behavior of the spin-Seebeck effect; even the perfect spin-Seebeck effect can be obtained with the null charge current. Thus, the chiral dsDNA-based system can act as a spin(charge)-Seebeck diode, spin(charge)-Seebeck switch, and spin(charge)-Seebeck transistor. Our results provide new ways to design spin caloritronic devices based on dsDNA or other organic molecules.

Peculiarities of magnetic and spin effects in a biradical/stable radical complex (three-spin system). Theory and comparison with experiment.

PubMed

Magin, Ilya M; Purtov, Petr A; Kruppa, Alexander I; Leshina, Tatiana V

2005-08-25

The field dependencies of biradical recombination probability in the presence of paramagnetic species with spins S(3) = 1 and S(3) = (1)/(2) have been calculated in the framework of the density matrix formalism. To describe the effect of the "third" spin on the spin evolution in biradical, we have also considered the spin exchange interaction between the added spin and one of the paramagnetic biradical centers. A characteristic feature of the calculated field dependencies is the existence of several extrema with positions and magnitudes depending on the signs and values of the exchange integrals in the system. The method proposed can be used to describe the effect of spin catalysis. It is shown that for the system with the third spin S(3) = 1 spin catalysis manifests itself stronger than in the case of spin S(3) = (1)/(2). The dependence of spin catalysis efficiency on the exchange interaction with the third spin has an extremum with position independent of the value of the spin added.

Intrinsic anharmonic effects on the phonon frequencies and effective spin-spin interactions in a quantum simulator made from trapped ions in a linear Paul trap

NASA Astrophysics Data System (ADS)

McAneny, M.; Freericks, J. K.

2014-11-01

The Coulomb repulsion between ions in a linear Paul trap gives rise to anharmonic terms in the potential energy when expanded about the equilibrium positions. We examine the effect of these anharmonic terms on the accuracy of a quantum simulator made from trapped ions. To be concrete, we consider a linear chain of Yb171+ ions stabilized close to the zigzag transition. We find that for typical experimental temperatures, frequencies change by no more than a factor of 0.01 % due to the anharmonic couplings. Furthermore, shifts in the effective spin-spin interactions (driven by a spin-dependent optical dipole force) are also, in general, less than 0.01 % for detunings to the blue of the transverse center-of-mass frequency. However, detuning the spin interactions near other frequencies can lead to non-negligible anharmonic contributions to the effective spin-spin interactions. We also examine an odd behavior exhibited by the harmonic spin-spin interactions for a range of intermediate detunings, where nearest-neighbor spins with a larger spatial separation on the ion chain interact more strongly than nearest neighbors with a smaller spatial separation.

Spin pumping and inverse Rashba-Edelstein effect in NiFe/Ag/Bi and NiFe/Ag/Sb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wei, E-mail: zwei@anl.gov; Jungfleisch, Matthias B.; Jiang, Wanjun

2015-05-07

The Rashba effect is an interaction between the spin and the momentum of electrons induced by the spin-orbit coupling in surface or interface states. We measured the inverse Rashba-Edelstein effect via spin pumping in Ag/Bi and Ag/Sb interfaces. The spin current is injected from the ferromagnetic resonance of a NiFe layer towards the Rashba interfaces, where it is further converted into a charge current. Using spin pumping theory, we quantify the conversion parameter of spin to charge current to be 0.11 ± 0.02 nm for Ag/Bi and a factor of ten smaller for Ag/Sb. The relative strength of the effect is in agreementmore » with spectroscopic measurements and first principles calculations. We also vary the interlayer materials to study the voltage output in relation to the change of the effective spin mixing conductance. The spin pumping experiment offers a straight-forward approach of using spin current as an efficient probe for detecting interface Rashba splitting.« less

Dyakonov-Perel Effect on Spin Dephasing in n-Type GaAs

NASA Technical Reports Server (NTRS)

Ning, C. Z.; Wu, M. W.

2003-01-01

A paper presents a study of the contribution of the Dyakonov-Perel (DP) effect to spin dephasing in electron-donor-doped bulk GaAs in the presence of an applied steady, moderate magnetic field perpendicular to the growth axis of the GaAs crystal. (The DP effect is an electron-wave-vector-dependent spin-state splitting of the conduction band, caused by a spin/orbit interaction in a crystal without an inversion center.) The applicable Bloch equations of kinetics were constructed to include terms accounting for longitudinal optical and acoustic phonon scattering as well as impurity scattering. The contributions of the aforementioned scattering mechanisms to spin-dephasing time in the presence of DP effect were examined by solving the equations numerically. Spin-dephasing time was obtained from the temporal evolution of the incoherently summed spin coherence. Effects of temperature, impurity level, magnetic field, and electron density on spin-dephasing time were investigated. Spin-dephasing time was found to increase with increasing magnetic field. Contrary to predictions of previous simplified treatments of the DP effect, spin-dephasing time was found to increase with temperature in the presence of impurity scattering. These results were found to agree qualitatively with results of recent experiments.

Spin pumping and inverse Rashba-Edelstein effect in NiFe/Ag/Bi and NiFe/Ag/Sb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wei; Jungfleisch, Matthias B.; Jiang, Wanjun

2015-03-20

The Rashba effect is an interaction between the spin and the momentum of electrons induced by the spin-orbit coupling in surface or interface states. Here, we measured the inverse Rashba-Edelstein effect via spin pumping in Ag/Bi and Ag/Sb interfaces. The spin current is injected from the ferromagnetic resonance of a NiFe layer towards the Rashba interfaces, where it is further converted into a charge current. While using spin pumping theory, we quantify the conversion parameter of spin to charge current to be 0.11 ± 0.02 nm for Ag/Bi and a factor of ten smaller for Ag/Sb. Furthermore, the relative strengthmore » of the effect is in agreement with spectroscopic measurements and first principles calculations. The spin pumping experiment offers a straight-forward approach of using spin current as an efficient probe for detecting interface Rashba splitting.« less

Effect of quantum tunneling on spin Hall magnetoresistance

NASA Astrophysics Data System (ADS)

Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk

2017-02-01

We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.

Spin valve effect of the interfacial spin accumulation in yttrium iron garnet/platinum bilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Lichuan; Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716; Zhang, Dainan

2014-09-29

We report the spin valve effect in yttrium iron garnet/platinum (YIG/Pt) bilayers. The spin Hall effect (SHE) generates spin accumulation at the YIG/Pt interface and can be opened/closed by magnetization switching in the electrical insulator YIG. The interfacial spin accumulation was measured in both YIG/Pt and YIG/Cu/Pt structures using a planar Hall configuration. The spin valve effect remained, even after a 2 nm thick Cu layer was inserted between the YIG and Pt layers, which aimed to exclude the induced magnetization at the YIG/Pt interface. The transverse Hall voltage and switching field were dependent on the applied charge current density. Themore » origin of this behavior can be explained by the SHE induced torque exerted on the domain wall, caused by the transfer of the spin angular momentum from the spin-polarized current to the YIG magnetic moment.« less

Spin-orbit proximity effect in graphene

NASA Astrophysics Data System (ADS)

Avsar, A.; Tan, J. Y.; Taychatanapat, T.; Balakrishnan, J.; Koon, G. K. W.; Yeo, Y.; Lahiri, J.; Carvalho, A.; Rodin, A. S.; O'Farrell, E. C. T.; Eda, G.; Castro Neto, A. H.; Özyilmaz, B.

2014-09-01

The development of spintronics devices relies on efficient generation of spin-polarized currents and their electric-field-controlled manipulation. While observation of exceptionally long spin relaxation lengths makes graphene an intriguing material for spintronics studies, electric field modulation of spin currents is almost impossible due to negligible intrinsic spin-orbit coupling of graphene. In this work, we create an artificial interface between monolayer graphene and few-layer semiconducting tungsten disulphide. In these devices, we observe that graphene acquires spin-orbit coupling up to 17 meV, three orders of magnitude higher than its intrinsic value, without modifying the structure of the graphene. The proximity spin-orbit coupling leads to the spin Hall effect even at room temperature, and opens the door to spin field effect transistors. We show that intrinsic defects in tungsten disulphide play an important role in this proximity effect and that graphene can act as a probe to detect defects in semiconducting surfaces.

Crossover to the anomalous quantum regime in the extrinsic spin Hall effect of graphene

NASA Astrophysics Data System (ADS)

Ferreira, Aires; Milletari, Mirco

Recent reports of spin-orbit coupling enhancement in chemically modified graphene have opened doors to studies of the spin Hall effect with massless chiral fermions. Here, we theoretically investigate the interaction and impurity density dependence of the extrinsic spin Hall effect in spin-orbit coupled graphene. We present a nonperturbative quantum diagrammatic calculation of the spin Hall response function in the strong-coupling regime that incorporates skew scattering and anomalous impurity density-independent contributions on equal footing. The spin Hall conductivity dependence on Fermi energy and electron-impurity interaction strength reveals the existence of experimentally accessible regions where anomalous quantum processes dominate. Our findings suggest that spin-orbit-coupled graphene is an ideal model system for probing the competition between semiclassical and bona fide quantum scattering mechanisms underlying the spin Hall effect. A.F. gratefully acknowledges the financial support of the Royal Society (U.K.).

Direct observation of spin-layer locking by local Rashba effect in monolayer semiconducting PtSe2 film.

PubMed

Yao, Wei; Wang, Eryin; Huang, Huaqing; Deng, Ke; Yan, Mingzhe; Zhang, Kenan; Miyamoto, Koji; Okuda, Taichi; Li, Linfei; Wang, Yeliang; Gao, Hongjun; Liu, Chaoxing; Duan, Wenhui; Zhou, Shuyun

2017-01-31

The generally accepted view that spin polarization in non-magnetic solids is induced by the asymmetry of the global crystal space group has limited the search for spintronics materials mainly to non-centrosymmetric materials. In recent times it has been suggested that spin polarization originates fundamentally from local atomic site asymmetries and therefore centrosymmetric materials may exhibit previously overlooked spin polarizations. Here, by using spin- and angle-resolved photoemission spectroscopy, we report the observation of helical spin texture in monolayer, centrosymmetric and semiconducting PtSe 2 film without the characteristic spin splitting in conventional Rashba effect (R-1). First-principles calculations and effective analytical model analysis suggest local dipole induced Rashba effect (R-2) with spin-layer locking: opposite spins are degenerate in energy, while spatially separated in the top and bottom Se layers. These results not only enrich our understanding of the spin polarization physics but also may find applications in electrically tunable spintronics.

Spin power and efficiency in an Aharnov-Bohm ring with an embedded magnetic impurity quantum dot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Xi; Guo, Yong, E-mail: guoy66@tsinghua.edu.cn; Collaborative Innovation Center of Quantum Matter, Beijing

2015-05-11

Spin thermoelectric effects in an Aharnov-Bohm ring with a magnetic impurity quantum dot (QD) are theoretically investigated by using the nonequilibrium Green's function method. It is found that due to the exchange coupling between the impurity and the electrons in QD, spin output power, and efficiency can be significant and be further modulated by the gate voltage. The spin thermoelectric effect can be modulated effectively by adjusting the Rashba spin-orbit interaction (RSOI) and the magnetic flux. The spin power and efficiency show zigzag oscillations, and thus spin thermoelectric effect can be switched by adjusting the magnetic flux phase factor andmore » RSOI ones. In addition, the spin efficiency can be significantly enhanced by the coexistence of the RSOI and the magnetic flux, and the maximal value of normalized spin efficiency η{sub max}/η{sub C} = 0.35 is obtained. Our results show that such a QD ring device may be used as a manipulative spin thermoelectric generator.« less

Y{sub 3}Fe{sub 5}O{sub 12} spin pumping for quantitative understanding of pure spin transport and spin Hall effect in a broad range of materials (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Chunhui; Wang, Hailong; Hammel, P. Chris

2015-05-07

Using Y{sub 3}Fe{sub 5}O{sub 12} (YIG) thin films grown by our sputtering technique, we study dynamic spin transport in nonmagnetic, ferromagnetic, and antiferromagnetic (AF) materials by ferromagnetic resonance spin pumping. From both inverse spin Hall effect and damping enhancement, we determine the spin mixing conductance and spin Hall angle in many metals. Surprisingly, we observe robust spin conduction in AF insulators excited by an adjacent YIG at resonance. This demonstrates that YIG spin pumping is a powerful and versatile tool for understanding spin Hall physics, spin-orbit coupling, and magnetization dynamics in a broad range of materials.

Spin-Swapping Transport and Torques in Ultrathin Magnetic Bilayers

NASA Astrophysics Data System (ADS)

Saidaoui, Hamed Ben Mohamed; Manchon, A.

2016-07-01

Planar spin transport in disordered ultrathin magnetic bilayers comprising a ferromagnet and a normal metal (typically used for spin pumping, spin Seebeck and spin-orbit torque experiments) is investigated theoretically. Using a tight-binding model that puts the extrinsic spin Hall effect and spin swapping on equal footing, we show that the nature of spin-orbit coupled transport dramatically depends on the ratio between the layer thickness d and the mean free path λ . While the spin Hall effect dominates in the diffusive limit (d ≫λ ), spin swapping dominates in the Knudsen regime (d ≲λ ). A remarkable consequence is that spin swapping induces a substantial fieldlike torque in the Knudsen regime.

Thermoelectric spin voltage in graphene

NASA Astrophysics Data System (ADS)

Sierra, Juan F.; Neumann, Ingmar; Cuppens, Jo; Raes, Bart; Costache, Marius V.; Valenzuela, Sergio O.

2018-02-01

In recent years, new spin-dependent thermal effects have been discovered in ferromagnets, stimulating a growing interest in spin caloritronics, a field that exploits the interaction between spin and heat currents1,2. Amongst the most intriguing phenomena is the spin Seebeck effect3-5, in which a thermal gradient gives rise to spin currents that are detected through the inverse spin Hall effect6-8. Non-magnetic materials such as graphene are also relevant for spin caloritronics, thanks to efficient spin transport9-11, energy-dependent carrier mobility and unique density of states12,13. Here, we propose and demonstrate that a carrier thermal gradient in a graphene lateral spin valve can lead to a large increase of the spin voltage near to the graphene charge neutrality point. Such an increase results from a thermoelectric spin voltage, which is analogous to the voltage in a thermocouple and that can be enhanced by the presence of hot carriers generated by an applied current14-17. These results could prove crucial to drive graphene spintronic devices and, in particular, to sustain pure spin signals with thermal gradients and to tune the remote spin accumulation by varying the spin-injection bias.

Research of spin-orbit interaction in organic conjugated polymers

NASA Astrophysics Data System (ADS)

Li, H.; Zhou, M. Y.; Wu, S. Y.; Liang, X. R.

2017-06-01

The effect of spin-orbit interaction on the one-dimensional organic polymer was investigated theoretically. Spin-orbital interaction led to the spatial separation of energy band but did not eliminate spin degeneration, which was different from energy level splitting in the Zeeman Effect. Spin-orbit interaction had little effect on the energy band structure, charge density, and lattice position, etc.; Spin precession was obtained when a polaron was transported along the polymer chain, which theoretically proved that it was feasible to control the spin precession of polaron in organic polymers by the use of external electric field.

Absence of anomalous Nernst effect in spin Seebeck effect of Pt/YIG

DOE PAGES

Miao, B. F.; Huang, S. Y.; Qu, D.; ...

2016-01-29

The Pt/YIG structure has been widely used to study spin Seebeck effect (SSE), inverse spin Hall effect, and other pure spin current phenomena. However, the magnetic proximity effect in Pt when in contact with YIG, and the potential anomalous Nernst effect (ANE) may compromise the spin current phenomena in Pt/YIG. By inserting a Cu layer of various thicknesses between Pt and YIG, we have separated the signals from the SSE and that of the ANE. Here, it is demonstrated that the thermal voltage in Pt/YIG mainly comes from spin current due to the longitudinal SSE with negligible contribution from themore » ANE.« less

Strong Intrinsic Spin Hall Effect in the TaAs Family of Weyl Semimetals

NASA Astrophysics Data System (ADS)

Sun, Yan; Zhang, Yang; Felser, Claudia; Yan, Binghai

2016-09-01

Since their discovery, topological insulators are expected to be ideal spintronic materials owing to the spin currents carried by surface states with spin-momentum locking. However, the bulk doping problem remains an obstacle that hinders such an application. In this work, we predict that a newly discovered family of topological materials, the Weyl semimetals, exhibits a large intrinsic spin Hall effect that can be utilized to generate and detect spin currents. Our ab initio calculations reveal a large spin Hall conductivity in the TaAs family of Weyl materials. Considering the low charge conductivity of semimetals, Weyl semimetals are believed to present a larger spin Hall angle (the ratio of the spin Hall conductivity over the charge conductivity) than that of conventional spin Hall systems such as the 4 d and 5 d transition metals. The spin Hall effect originates intrinsically from the bulk band structure of Weyl semimetals, which exhibit a large Berry curvature and spin-orbit coupling, so the bulk carrier problem in the topological insulators is naturally avoided. Our work not only paves the way for employing Weyl semimetals in spintronics, but also proposes a new guideline for searching for the spin Hall effect in various topological materials.

Psychometric properties of the Japanese version of the Social Phobia Inventory.

PubMed

Nagata, Toshihiko; Nakajima, Takenori; Teo, Alan R; Yamada, Hisashi; Yoshimura, Chiho

2013-04-01

The aim of the current study was to study the psychometric properties of the Japanese version of the Social Phobia Inventory (SPIN-J) among Japanese subjects with social anxiety disorder (SAD). The sample consisted of 86 subjects with SAD and 86 controls. Diagnosis was based on a modified version of the Structured Clinical Interview for the DSM-IV. In addition to the SPIN-J, clinician-administered and self-rating scales, including the Japanese versions of the Liebowitz Social Anxiety Scale, the Social Phobia Scale, and the Social Interaction Anxiety Scale, were used. The SPIN-J showed adequate internal consistency (0.82-0.96) for the total and subscales. Correlations between the SPIN-J and the Liebowitz Social Anxiety Scale, the Social Phobia Scale, and the Social Interaction Anxiety Scale ranged from 0.83 to 0.89 and indicated adequate concurrent validity. A cut-off point of 22 between subjects with SAD and controls showed a sensitivity of 96.5% and specificity of 87.2%, indicating robust discriminant validity. The SPIN-J showed adequate reliability and validity for use as a screening tool for social anxiety disorder in Japanese clinical settings. © 2013 The Authors. Psychiatry and Clinical Neurosciences © 2013 Japanese Society of Psychiatry and Neurology.

Edge-defect induced spin-dependent Seebeck effect and spin figure of merit in graphene nanoribbons.

PubMed

Liu, Qing-Bo; Wu, Dan-Dan; Fu, Hua-Hua

2017-10-11

By using the first-principle calculations combined with the non-equilibrium Green's function approach, we have studied spin caloritronic properties of graphene nanoribbons (GNRs) with different edge defects. The theoretical results show that the edge-defected GNRs with sawtooth shapes can exhibit spin-dependent currents with opposite flowing directions by applying temperature gradients, indicating the occurrence of the spin-dependent Seebeck effect (SDSE). The edge defects bring about two opposite effects on the thermal spin currents: the enhancement of the symmetry of thermal spin-dependent currents, which contributes to the realization of pure thermal spin currents, and the decreasing of the spin thermoelectric conversion efficiency of the devices. It is fortunate that applying a gate voltage is an efficient route to optimize these two opposite spin thermoelectric properties towards realistic device applications. Moreover, due to the existence of spin-splitting band gaps, the edge-defected GNRs can be designed as spin-dependent Seebeck diodes and rectifiers, indicating that the edge-defected GNRs are potential candidates for room-temperature spin caloritronic devices.

Electrical control of antiferromagnetic metal up to 15 nm

NASA Astrophysics Data System (ADS)

Zhang, PengXiang; Yin, GuFan; Wang, YuYan; Cui, Bin; Pan, Feng; Song, Cheng

2016-08-01

Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in [Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction, the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.

Micro- and macrostructural characterization of polyvinylpirrolidone rotary-spun fibers.

PubMed

Sebe, István; Kállai-Szabó, Barnabás; Kovács, Krisztián Norbert; Szabadi, Enikő; Zelkó, Romána

2015-01-01

The application of high-speed rotary spinning can offer a useful mean for either preparation of fibrous intermediate for conventional dosage forms or drug delivery systems. Polyvinylpyrrolidone (PVP) and poly(vinylpyrrolidone-vinylacetate) (PVP VA) micro- and nanofibers of different polymer concentrations and solvent ratios were prepared with a high-speed rotary spinning technique. In order to study the influence of parameters that enable successful fiber production from polymeric viscous solutions, a complex micro- and macrostructural screening method was implemented. The obtained fiber mats were subjected to detailed morphological analysis using scanning electron microscope (SEM), and rheological measurements while the microstructural changes of fiber samples, based on the free volume changes, was analyzed by positron annihilation lifetime spectroscopy (PALS) and compared with their mechanical characteristics. The plasticizing effect of water tracked by ortho-positronium lifetime changes in relation to the mechanical properties of fibers. A concentration range of polyvinylpyrrolidone solutions was defined for the preparation of fibers of optimum fiber morphology and mechanical properties. The method enabled fiber formulation of advantageous functionality-related properties for further formulation of solid dosage forms.

Collisional spin-oriented Sherman function in electron-hole semiconductor plasmas: Landau damping effect

NASA Astrophysics Data System (ADS)

Lee, Myoung-Jae; Jung, Young-Dae

2018-04-01

The influence of Landau damping on the spin-oriented collisional asymmetry is investigated in electron-hole semiconductor plasmas. The analytical expressions of the spin-singlet and the spin-triplet scattering amplitudes as well as the spin-oriented asymmetry Sherman function are obtained as functions of the scattering angle, the Landau parameter, the effective Debye length, and the collision energy. It is found that the Landau damping effect enhances the spin-singlet and spin-triplet scattering amplitudes in the forward and back scattering domains, respectively. It is also found that the Sherman function increases with an increase in the Landau parameter. In addition, the spin-singlet scattering process is found to be dominant rather than the spin-triplet scattering process in the high collision energy domain.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fajardo, E. A.; Zülicke, U.; Winkler, R.

We discuss the universal spin dynamics in quasi-one-dimensional systems including the real spin in narrow-gap semiconductors like InAs and InSb, the valley pseudospin in staggered single-layer graphene, and the combination of real spin and valley pseudospin characterizing single-layer transition metal dichalcogenides (TMDCs) such as MoS2, WS2, MoS2, and WSe2. All these systems can be described by the same Dirac-like Hamiltonian. Spin-dependent observable effects in one of these systems thus have counterparts in each of the other systems. Effects discussed in more detail include equilibrium spin currents, current-induced spin polarization (Edelstein effect), and spin currents generated via adiabatic spin pumping. Ourmore » work also suggests that a long-debated spin-dependent correction to the position operator in single-band models should be absent.« less

Electrical Control of Metallic Heavy-Metal-Ferromagnet Interfacial States

NASA Astrophysics Data System (ADS)

Bi, Chong; Sun, Congli; Xu, Meng; Newhouse-Illige, Ty; Voyles, Paul M.; Wang, Weigang

2017-09-01

Voltage-control effects provide an energy-efficient means of tailoring material properties, especially in highly integrated nanoscale devices. However, only insulating and semiconducting systems can be controlled so far. In metallic systems, there is no electric field due to electron screening effects and thus no such control effect exists. Here, we demonstrate that metallic systems can also be controlled electrically through ionic rather than electronic effects. In a Pt /Co structure, the control of the metallic Pt /Co interface can lead to unprecedented control effects on the magnetic properties of the entire structure. Consequently, the magnetization and perpendicular magnetic anisotropy of the Co layer can be independently manipulated to any desired state, the efficient spin toques can be enhanced about 3.5 times, and the switching current can be reduced about one order of magnitude. This ability to control a metallic system may be extended to control other physical phenomena.

Spintronics: spin accumulation in mesoscopic systems.

PubMed

Johnson, Mark

2002-04-25

In spintronics, in which use is made of the spin degree of freedom of the electron, issues concerning electrical spin injection and detection of electron spin diffusion are fundamentally important. Jedema et al. describe a magneto-resistance study in which they claim to have observed spin accumulation in a mesoscopic copper wire, but their one-dimensional model ignores two-dimensional spin-diffusion effects, which casts doubt on their analysis. A two-dimensional vector formalism of spin transport is called for to model spin-injection experiments, and the identification of spurious background resistance effects is crucial.

Non-metal spintronics: study of spin-dependent transport in InSb- and InAs-based nanopatterned heterostructures

NASA Astrophysics Data System (ADS)

Heremans, J. J.; Chen, Hong; Peters, J. A.; Goel, N.; Chung, S. J.; Santos, M. B.; van Roy, W.; Borghs, G.

2006-03-01

Spin-orbit interaction in semiconductor heterostructures can lead to various spin-dependent electronic transport effects without the presence of magnetic materials. Mesoscopic samples were fabricated on InSb/InAlSb and InAs/AlGaSb two-dimensional electron systems, where spin-orbit interaction is strong. In mesoscopic devices, the effects of spin-orbit interaction are not averaged out over the geometry, and lead to observable electronic properties. We experimentally demonstrate spin-split ballistic transport and the creation of fully spin-polarized electron beams using spin-dependent reflection geometries and transverse magnetic focusing geometries. Spin-dependent transport properties in the semiconductor materials are also investigated using antidot lattices. Spin-orbit interaction effects in high-mobility semiconductor devices may be utilized toward the design of novel spintronics implementations. We acknowledge NSF DMR-0094055 (JJH), DMR-0080054, DMR-0209371 (MBS).

Theory for cross effect dynamic nuclear polarization under magic-angle spinning in solid state nuclear magnetic resonance: the importance of level crossings.

PubMed

Thurber, Kent R; Tycko, Robert

2012-08-28

We present theoretical calculations of dynamic nuclear polarization (DNP) due to the cross effect in nuclear magnetic resonance under magic-angle spinning (MAS). Using a three-spin model (two electrons and one nucleus), cross effect DNP with MAS for electron spins with a large g-anisotropy can be seen as a series of spin transitions at avoided crossings of the energy levels, with varying degrees of adiabaticity. If the electron spin-lattice relaxation time T(1e) is large relative to the MAS rotation period, the cross effect can happen as two separate events: (i) partial saturation of one electron spin by the applied microwaves as one electron spin resonance (ESR) frequency crosses the microwave frequency and (ii) flip of all three spins, when the difference of the two ESR frequencies crosses the nuclear frequency, which transfers polarization to the nuclear spin if the two electron spins have different polarizations. In addition, adiabatic level crossings at which the two ESR frequencies become equal serve to maintain non-uniform saturation across the ESR line. We present analytical results based on the Landau-Zener theory of adiabatic transitions, as well as numerical quantum mechanical calculations for the evolution of the time-dependent three-spin system. These calculations provide insight into the dependence of cross effect DNP on various experimental parameters, including MAS frequency, microwave field strength, spin relaxation rates, hyperfine and electron-electron dipole coupling strengths, and the nature of the biradical dopants.

Enhancing Spin Filters by Use of Bulk Inversion Asymmetry

NASA Technical Reports Server (NTRS)

Ting, David; Cartoixa,Xavier

2007-01-01

Theoretical calculations have shown that the degrees of spin polarization in proposed nonmagnetic semiconductor resonant tunneling spin filters could be increased through exploitation of bulk inversion asymmetry (BIA). These enhancements would be effected through suitable orientation of spin collectors (or spin-polarization- inducing lateral electric fields), as described below. Spin filters -- more precisely, sources of spin-polarized electron currents -- have been sought for research on, and development of, the emerging technological discipline of spintronics (spin-transport electronics). The proposed spin filters were to be based on the Rashba effect, which is an energy splitting of what would otherwise be degenerate quantum states, caused by a spinorbit interaction in conjunction with a structural-inversion asymmetry (SIA) in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. In a spin filter, the spin-polarized currents produced by the Rashba effect would be extracted by quantum-mechanical resonant tunneling.

Magnetoresistance effect of heat generation in a single-molecular spin-valve

NASA Astrophysics Data System (ADS)

Jiang, Feng; Yan, Yonghong; Wang, Shikuan; Yan, Yijing

2016-02-01

Based on non-equilibrium Green's functions' theory and small polaron transformation's technology, we study the heat generation by current through a single-molecular spin-valve. Numerical results indicate that the variation of spin polarization degree can change heat generation effectively, the spin-valve effect happens not only in electrical current but also in heat generation when Coulomb repulsion in quantum dot is smaller than phonon frequency and interestingly, when Coulomb repulsion is larger than phonon frequency, the inverse spin-valve effect appears by sweeping gate voltage and is enlarged with bias increasing. The inverse spin-valve effect will induce the unique heat magnetoresistance effect, which can be modulated from heat-resistance to heat-gain by gate voltage easily.

Separating inverse spin Hall voltage and spin rectification voltage by inverting spin injection direction

NASA Astrophysics Data System (ADS)

Zhang, Wenxu; Peng, Bin; Han, Fangbin; Wang, Qiuru; Soh, Wee Tee; Ong, Chong Kim; Zhang, Wanli

2016-03-01

We develop a method for universally resolving the important issue of separating the inverse spin Hall effect (ISHE) from the spin rectification effect (SRE) signal. This method is based on the consideration that the two effects depend on the spin injection direction: The ISHE is an odd function of the spin injection direction while the SRE is independent on it. Thus, the inversion of the spin injection direction changes the ISHE voltage signal, while the SRE voltage remains. It applies generally to analyzing the different voltage contributions without fitting them to special line shapes. This fast and simple method can be used in a wide frequency range and has the flexibility of sample preparation.

Free-Spinning-Tunnel Investigation to Determine the Effect of Spin-Recovery Rockets and Thrust Simulation on the Recovery Characteristics of a 1/21-Scale Model of the Chance Vought F7U-3 Airplane, TED No. NACA AD 3103

NASA Technical Reports Server (NTRS)

Burk, Sanger H., Jr.; Healy, Frederick M.

1955-01-01

An investigation of a l/21-scale model of the Chance Vought F7U-3 airplane in the co&at-load- condition has been conducted in the Langley 20-foot free-spinning tunnel, The recovery characteristics of the model were determined by use of spin-recovery rockets for the erect and inverted spinning condition. The rockets were so placed as to provide either a yawing or rolling moment about the model center of gravity. Also included in the investigation were tests to determine the effect of simulated engine thrust on the recovery characteristics of the model. On the basis of model tests, recoveries from erect and inverted spins were satisfactory when a yawing moment of 22,200 foot-pounds (full scale) was provided against the spin by rockets attached to the wing tips; the anti-spin yawing moment was applied for approximately 9 seconds, (full scale). Satisfactory recoveries were obtained from erect spins when a rolling moment of 22,200 foot-pounds (full scale) was provided with the spin (rolls right wing down in right spin). Although the inverted spin was satisfactorily terminated when a rolling moment of equal magnitude was provided, a roll rocket was not considered to be an optimum spin-recovery device to effect recoveries from inverted spins for this airplane because of resulting gyrations during spin recovery. Simulation of engine thrust had no apparent effect on the spin recovery characteristics.

Spin diffusion and torques in disordered antiferromagnets

NASA Astrophysics Data System (ADS)

Manchon, Aurelien

2017-03-01

We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.

Interface-induced phenomena in magnetism

DOE PAGES

Hellman, Frances; Hoffmann, Axel; Tserkovnyak, Yaroslav; ...

2017-06-05

Our article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important conceptsmore » include spin accumulation, spin currents, spin transfer torque, and spin pumping. We provide an overview for the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. Our article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.« less

Interface-Induced Phenomena in Magnetism

PubMed Central

Hoffmann, Axel; Tserkovnyak, Yaroslav; Beach, Geoffrey S. D.; Fullerton, Eric E.; Leighton, Chris; MacDonald, Allan H.; Ralph, Daniel C.; Arena, Dario A.; Dürr, Hermann A.; Fischer, Peter; Grollier, Julie; Heremans, Joseph P.; Jungwirth, Tomas; Kimel, Alexey V.; Koopmans, Bert; Krivorotov, Ilya N.; May, Steven J.; Petford-Long, Amanda K.; Rondinelli, James M.; Samarth, Nitin; Schuller, Ivan K.; Slavin, Andrei N.; Stiles, Mark D.; Tchernyshyov, Oleg; Thiaville, André; Zink, Barry L.

2017-01-01

This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes. PMID:28890576

Scaling Behavior of the Spin Pumping Effect in Ferromagnet-Platinum Bilayers

NASA Astrophysics Data System (ADS)

Czeschka, F. D.; Dreher, L.; Brandt, M. S.; Weiler, M.; Althammer, M.; Imort, I.-M.; Reiss, G.; Thomas, A.; Schoch, W.; Limmer, W.; Huebl, H.; Gross, R.; Goennenwein, S. T. B.

2011-07-01

We systematically measured the dc voltage VISH induced by spin pumping together with the inverse spin Hall effect in ferromagnet-platinum bilayer films. In all our samples, comprising ferromagnetic 3d transition metals, Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, VISH invariably has the same polarity, and scales with the magnetization precession cone angle. These findings, together with the spin mixing conductance derived from the experimental data, quantitatively corroborate the present theoretical understanding of spin pumping in combination with the inverse spin Hall effect.

Longitudinal spin dynamics in nickel fluorosilicate

NASA Astrophysics Data System (ADS)

Galkina, E. G.; Ivanov, B. A.; Butrim, V. I.

2014-07-01

The presence of single-ion anisotropy leads to the appearance of the effect of quantum spin reduction. As a consequence, purely longitudinal magnetization dynamics arises, which involves coupled oscillations of the mean spin modulus and the quadrupole mean values constructed on spin operators. In nickel fluorosilicate, the effect of quantum spin reduction may be controlled by changing pressure. The study of nonlinear longitudinal spin dynamics and the analysis of possible photomagnetic effects showed that this compound is a convenient model system to implement switching of the magnetization direction by femtosecond laser pulses.

Direct observation of the orbital spin Kondo effect in gallium arsenide quantum dots

NASA Astrophysics Data System (ADS)

Shang, Ru-Nan; Zhang, Ting; Cao, Gang; Li, Hai-Ou; Xiao, Ming; Guo, Guang-Can; Guo, Guo-Ping

2018-02-01

Besides the spin Kondo effect, other degrees of freedom can give rise to the pseudospin Kondo effect. We report a direct observation of the orbital spin Kondo effect in a series-coupled gallium arsenide (GaAs) double quantum dot device where orbital degrees act as pseudospin. Electron occupation in both dots induces a pseudospin Kondo effect. In a region of one net spin impurity, complete spectra with three resonance peaks are observed. Furthermore, we observe a pseudo-Zeeman effect and demonstrate its electrical controllability for the artificial pseudospin in this orbital spin Kondo process via gate voltage control. The fourfold degeneracy point is realized at a specific value supplemented by spin degeneracy, indicating a transition from the SU(2) to the SU(4) Kondo effect.

Thermal spin filtering effect and giant magnetoresistance of half-metallic graphene nanoribbon co-doped with non-metallic Nitrogen and Boron

NASA Astrophysics Data System (ADS)

Huang, Hai; Zheng, Anmin; Gao, Guoying; Yao, Kailun

2018-03-01

Ab initio calculations based on density functional theory and non-equilibrium Green's function are performed to investigate the thermal spin transport properties of single-hydrogen-saturated zigzag graphene nanoribbon co-doped with non-metallic Nitrogen and Boron in parallel and anti-parallel spin configurations. The results show that the doped graphene nanoribbon is a full half-metal. The two-probe system based on the doped graphene nanoribbon exhibits various excellent spin transport properties, including the spin-filtering effect, the spin Seebeck effect, the single-spin negative differential thermal resistance effect and the sign-reversible giant magnetoresistance feature. Excellently, the spin-filtering efficiency can reach nearly 100% in the parallel configuration and the magnetoresistance ratio can be up to -1.5 × 1010% by modulating the electrode temperature and temperature gradient. Our findings indicate that the metal-free doped graphene nanoribbon would be a promising candidate for spin caloritronic applications.

Spin injection and detection via the anomalous spin Hall effect of a ferromagnetic metal

NASA Astrophysics Data System (ADS)

Das, K. S.; Schoemaker, W. Y.; van Wees, B. J.; Vera-Marun, I. J.

2017-12-01

We report a spin injection and detection mechanism via the anomalous Hall effect in a ferromagnetic metal. The anomalous spin Hall effect (ASHE) refers to the transverse spin current generated within the ferromagnet. We utilize the ASHE and its reciprocal effect to electrically inject and detect magnons in a magnetic insulator (yttrium iron garnet) in a nonlocal geometry. Our experiments reveal that permalloy has a comparable spin injection and detection efficiency to that of platinum, owing to the ASHE. We also demonstrate the tunability of the ASHE via the orientation of the permalloy magnetization, thus creating possibilities for spintronic applications.

Theory of Direct Optical Measurement of Pure Spin Currents in Direct-gap Semiconductors

NASA Astrophysics Data System (ADS)

Wang, Jing; Liu, Ren-Bao; Zhu, Bang-Fen

2010-01-01

We predict that a pure spin current in a semiconductor may lead to the optical circular birefingence effect without invoking magnetization. This effect may be exploited for a direct, non-destructive measurement of the pure spin current. We derive the effective coupling between a pure spin current and a polarized light beam, and point out that it originates from the inherent spin-orbit coupling in the valence bands, rather than the Rashba or Dresselhaus effects due to inversion asymmetries. The Faraday rotation angle in GaAs is estimated, which indicates that this spin current optical birefringence is experimentally observable.

Analytical theory and possible detection of the ac quantum spin Hall effect

DOE PAGES

Deng, W. Y.; Ren, Y. J.; Lin, Z. X.; ...

2017-07-11

Here, we develop an analytical theory of the low-frequency ac quantum spin Hall (QSH) effect based upon the scattering matrix formalism. It is shown that the ac QSH effect can be interpreted as a bulk quantum pumping effect. When the electron spin is conserved, the integer-quantized ac spin Hall conductivity can be linked to the winding numbers of the reflection matrices in the electrodes, which also equal to the bulk spin Chern numbers of the QSH material. Furthermore, a possible experimental scheme by using ferromagnetic metals as electrodes is proposed to detect the topological ac spin current by electrical means.

First example of a high-level correlated calculation of the indirect spin-spin coupling constants involving tellurium: tellurophene and divinyl telluride.

PubMed

Rusakov, Yury Yu; Krivdin, Leonid B; Østerstrøm, Freja F; Sauer, Stephan P A; Potapov, Vladimir A; Amosova, Svetlana V

2013-08-21

This paper documents the very first example of a high-level correlated calculation of spin-spin coupling constants involving tellurium taking into account relativistic effects, vibrational corrections and solvent effects for medium sized organotellurium molecules. The (125)Te-(1)H spin-spin coupling constants of tellurophene and divinyl telluride were calculated at the SOPPA and DFT levels, in good agreement with experimental data. A new full-electron basis set, av3z-J, for tellurium derived from the "relativistic" Dyall's basis set, dyall.av3z, and specifically optimized for the correlated calculations of spin-spin coupling constants involving tellurium was developed. The SOPPA method shows a much better performance compared to DFT, if relativistic effects calculated within the ZORA scheme are taken into account. Vibrational and solvent corrections are next to negligible, while conformational averaging is of prime importance in the calculation of (125)Te-(1)H spin-spin couplings. Based on the performed calculations at the SOPPA(CCSD) level, a marked stereospecificity of geminal and vicinal (125)Te-(1)H spin-spin coupling constants originating in the orientational lone pair effect of tellurium has been established, which opens a new guideline in organotellurium stereochemistry.

An electronegativity-induced spin repulsion effect.

PubMed

Stirling, Andras; Pasquarello, Alfredo

2005-09-22

We present a spin delocalization effect in radical Si-containing systems, featuring a heteroatom of high electronegativity (such as N, O, or Cl) bonded to the unsaturated Si atom. We find that the higher the electronegativity of the heteroatom, the more the localized spin shifts away from the unsaturated Si atom and the heteroatom toward saturated Si neighbors. We demonstrate that this spin repulsion toward saturated Si atoms is induced by the electronegativity difference between the Si atom and the heteroatoms. We present a simple molecular-orbital-based mechanism which fully explains the structural and electronic effects. We contrast the present spin delocalization mechanism with the classical hyperconjugation in organic chemistry. The most important consequences of this spin redistribution are the electron-spin-resonance activity of the saturated Si neighbors and the enhanced stability of the radical centers. We predict a similar effect for Ge radicals and discuss why organic systems based on carbon do not feature such spin repulsion.

Dynamic generation of spin-wave currents in hybrid structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lyapilin, I. I.; Okorokov, M. S., E-mail: Okorokovmike@gmail.com

2016-11-15

Spin transport through the interface in a semiconductor/ferromagnetic insulator hybrid structure is studied by the nonequilibrium statistical operator method under conditions of the spin Seebeck effect. The effective parameter approach in which each examined subsystem (conduction electrons, magnons, phonons) is characterized by its specific effective temperature is considered. The effect of the resonant (electric dipole) excitation of the spin electronic subsystem of conduction electrons on spin-wave current excitation in a ferromagnetic insulator is considered. The macroscopic equations describing the spin-wave current caused by both resonant excitation of the spin system of conduction electrons and the presence of a nonuniform temperaturemore » field in the ferromagnetic insulator are derived taking into account both the resonance-diffusion propagation of magnons and their relaxation processes. It is shown that spin-wave current excitation is also of resonant nature under the given conditions.« less

Spin-charge coupled dynamics driven by a time-dependent magnetization

NASA Astrophysics Data System (ADS)

Tölle, Sebastian; Eckern, Ulrich; Gorini, Cosimo

2017-03-01

The spin-charge coupled dynamics in a thin, magnetized metallic system are investigated. The effective driving force acting on the charge carriers is generated by a dynamical magnetic texture, which can be induced, e.g., by a magnetic material in contact with a normal-metal system. We consider a general inversion-asymmetric substrate/normal-metal/magnet structure, which, by specifying the precise nature of each layer, can mimic various experimentally employed setups. Inversion symmetry breaking gives rise to an effective Rashba spin-orbit interaction. We derive general spin-charge kinetic equations which show that such spin-orbit interaction, together with anisotropic Elliott-Yafet spin relaxation, yields significant corrections to the magnetization-induced dynamics. In particular, we present a consistent treatment of the spin density and spin current contributions to the equations of motion, inter alia, identifying a term in the effective force which appears due to a spin current polarized parallel to the magnetization. This "inverse-spin-filter" contribution depends markedly on the parameter which describes the anisotropy in spin relaxation. To further highlight the physical meaning of the different contributions, the spin-pumping configuration of typical experimental setups is analyzed in detail. In the two-dimensional limit the buildup of dc voltage is dominated by the spin-galvanic (inverse Edelstein) effect. A measuring scheme that could isolate this contribution is discussed.

Experimental evidences of a large extrinsic spin Hall effect in AuW alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laczkowski, P.; Rojas-Sánchez, J.-C.; INAC/SP2M, CEA-Université Joseph Fourier, F-38054 Grenoble

2014-04-07

We report an experimental study of a gold-tungsten alloy (7 at. % W concentration in Au host) displaying remarkable properties for spintronics applications using both magneto-transport in lateral spin valve devices and spin-pumping with inverse spin Hall effect experiments. A very large spin Hall angle of about 10% is consistently found using both techniques with the reliable spin diffusion length of 2 nm estimated by the spin sink experiments in the lateral spin valves. With its chemical stability, high resistivity, and small induced damping, this AuW alloy may find applications in the nearest future.

Coriolis effect and spin Hall effect of light in an inhomogeneous chiral medium.

PubMed

Zhang, Yongliang; Shi, Lina; Xie, Changqing

2016-07-01

We theoretically investigate the spin Hall effect of spinning light in an inhomogeneous chiral medium. The Hamiltonian equations of the photon are analytically obtained within eikonal approximation in the noninertial orthogonal frame. Besides the usual spin curvature coupling, the chiral parameter enters the Hamiltonian as a spin-torsion-like interaction. We reveal that both terms have parallel geometric origins as the Coriolis terms of Maxwell's equations in nontrivial frames.

Non-Markovian spin-resolved counting statistics and an anomalous relation between autocorrelations and cross correlations in a three-terminal quantum dot

NASA Astrophysics Data System (ADS)

Luo, JunYan; Yan, Yiying; Huang, Yixiao; Yu, Li; He, Xiao-Ling; Jiao, HuJun

2017-01-01

We investigate the noise correlations of spin and charge currents through an electron spin resonance (ESR)-pumped quantum dot, which is tunnel coupled to three electrodes maintained at an equivalent chemical potential. A recursive scheme is employed with inclusion of the spin degrees of freedom to account for the spin-resolved counting statistics in the presence of non-Markovian effects due to coupling with a dissipative heat bath. For symmetric spin-up and spin-down tunneling rates, an ESR-induced spin flip mechanism generates a pure spin current without an accompanying net charge current. The stochastic tunneling of spin carriers, however, produces universal shot noises of both charge and spin currents, revealing the effective charge and spin units of quasiparticles in transport. In the case of very asymmetric tunneling rates for opposite spins, an anomalous relationship between noise autocorrelations and cross correlations is revealed, where super-Poissonian autocorrelation is observed in spite of a negative cross correlation. Remarkably, with strong dissipation strength, non-Markovian memory effects give rise to a positive cross correlation of the charge current in the absence of a super-Poissonian autocorrelation. These unique noise features may offer essential methods for exploiting internal spin dynamics and various quasiparticle tunneling processes in mesoscopic transport.

Antiferromagnetic spin Seebeck effect.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Stephen M.; Zhang, Wei; KC, Amit

2016-03-03

We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in themore » spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.« less

Antiferromagnetic Spin Seebeck Effect

NASA Astrophysics Data System (ADS)

Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

2016-03-01

We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2 . A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30 nm )/Pt (4 nm) grown by molecular beam epitaxy on a MgF2 (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9 T ) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

Hf thickness dependence of spin-orbit torques in Hf/CoFeB/MgO heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramaswamy, Rajagopalan; Qiu, Xuepeng; Dutta, Tanmay

We have studied the spin-orbit torques in perpendicularly magnetized Hf/CoFeB/MgO system, by systematically varying the thickness of Hf underlayer. We have observed a sign change of effective fields between Hf thicknesses of 1.75 and 2 nm, indicating that competing mechanisms, such as the Rashba and spin Hall effects, contribute to spin-orbit torques in our system. For larger Hf thicknesses (>2 nm), both the components of spin-orbit torques arise predominantly from the bulk spin Hall effect. We have also confirmed these results using spin-orbit torque induced magnetization switching measurements. Our results could be helpful in designing Hf based SOT devices.

One-electron versus electron-electron interaction contributions to the spin-spin coupling mechanism in nuclear magnetic resonance spectroscopy: Analysis of basic electronic effects

NASA Astrophysics Data System (ADS)

Gräfenstein, Jürgen; Cremer, Dieter

2004-12-01

For the first time, the nuclear magnetic resonance (NMR) spin-spin coupling mechanism is decomposed into one-electron and electron-electron interaction contributions to demonstrate that spin-information transport between different orbitals is not exclusively an electron-exchange phenomenon. This is done using coupled perturbed density-functional theory in conjunction with the recently developed J-OC-PSP [=J-OC-OC-PSP: Decomposition of J into orbital contributions using orbital currents and partial spin polarization)] method. One-orbital contributions comprise Ramsey response and self-exchange effects and the two-orbital contributions describe first-order delocalization and steric exchange. The two-orbital effects can be characterized as external orbital, echo, and spin transport contributions. A relationship of these electronic effects to zeroth-order orbital theory is demonstrated and their sign and magnitude predicted using simple models and graphical representations of first order orbitals. In the case of methane the two NMR spin-spin coupling constants result from totally different Fermi contact coupling mechanisms. 1J(C,H) is the result of the Ramsey response and the self-exchange of the bond orbital diminished by external first-order delocalization external one-orbital effects whereas 2J(H,H) spin-spin coupling is almost exclusively mitigated by a two-orbital steric exchange effect. From this analysis, a series of prediction can be made how geometrical deformations, electron lone pairs, and substituent effects lead to a change in the values of 1J(C,H) and 2J(H,H), respectively, for hydrocarbons.

An experimental study of the effect of tail configuration on the spinning characteristics of general aviation aircraft. M.S. Thesis; [static wind tunnel force measurements

NASA Technical Reports Server (NTRS)

Ballin, M. G.

1982-01-01

The feasibility of using static wind tunnel tests to obtain information about spin damping characteristics of an isolated general aviation aircraft tail was investigated. A representative tail section was oriented to the tunnel free streamline at angles simulating an equilibrium spin. A full range of normally encountered spin conditions was employed. Results of parametric studies performed to determine the effect of spin damping on several tail design parameters show satisfactory agreement with NASA rotary balance tests. Wing and body interference effects are present in the NASA studies at steep spin attitudes, but agreement improves with increasing pitch angle and spin rate, suggesting that rotational flow effects are minimal. Vertical position of the horizontal stabilizer is found to be a primary parameter affecting yaw damping, and horizontal tail chordwise position induces a substantial effect on pitching moment.

Spin memory effect for compact binaries in the post-Newtonian approximation

NASA Astrophysics Data System (ADS)

Nichols, David A.

2017-04-01

The spin memory effect is a recently predicted relativistic phenomenon in asymptotically flat spacetimes that become nonradiative infinitely far in the past and future. Between these early and late times, the magnetic-parity part of the time integral of the gravitational-wave strain can undergo a nonzero change; this difference is the spin memory effect. Families of freely falling observers around an isolated source can measure this effect, in principle, and fluxes of angular momentum per unit solid angle (or changes in superspin charges) generate the effect. The spin memory effect had not been computed explicitly for astrophysical sources of gravitational waves, such as compact binaries. In this paper, we compute the spin memory in terms of a set of radiative multipole moments of the gravitational-wave strain. The result of this calculation allows us to establish the following results about the spin memory: (i) We find that the accumulation of the spin memory behaves in a qualitatively different way from that of the displacement memory effect for nonspinning, quasicircular compact binaries in the post-Newtonian approximation: the spin memory undergoes a large secular growth over the duration of the inspiral, whereas for the displacement effect this increase is small. (ii) The rate at which the spin memory grows is equivalent to a nonlinear, but nonoscillatory and nonhereditary effect in the gravitational waveform that had been previously calculated for nonspinning, quasicircular compact binaries. (iii) This rate of buildup of the spin memory could potentially be detected by future gravitational-wave detectors by carefully combining the measured waveforms from hundreds of gravitational-wave detections of compact binaries.

Spin-Mechatronics

NASA Astrophysics Data System (ADS)

Matsuo, Mamoru; Saitoh, Eiji; Maekawa, Sadamichi

2017-01-01

We investigate the interconversion phenomena between spin and mechanical angular momentum in moving objects. In particular, the recent results on spin manipulation and spin-current generation by mechanical motion are examined. In accelerating systems, spin-dependent gauge fields emerge, which enable the conversion from mechanical angular momentum into spins. Such a spin-mechanical effect is predicted by quantum theory in a non-inertial frame. Experiments which confirm the effect, i.e., the resonance frequency shift in nuclear magnetic resonance, the stray field measurement of rotating metals, and electric voltage generation in liquid metals, are discussed.

Extrinsic spin Nernst effect from first principles.

PubMed

Tauber, Katarina; Gradhand, Martin; Fedorov, Dmitry V; Mertig, Ingrid

2012-07-13

We present an ab initio description of the thermal transport phenomenon called the spin Nernst effect. It refers to generation of a spin accumulation or a pure spin current transverse to an applied temperature gradient. This is similar to the intensively studied spin Hall effect described by intrinsic and extrinsic mechanisms due to an applied electric field. Analogously, several contributions are present for the spin Nernst effect. Here we investigate the extrinsic skew scattering mechanism which is dominant in the limit of dilute alloys. Our calculations are based on a fully relativistic Korringa-Kohn-Rostoker method and a solution of the linearized Boltzmann equation. As a first application, we consider a Cu host with Au, Ti, and Bi impurities.

Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton.

PubMed

Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

2015-05-22

Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology.

Electron spin dynamics and optical orientation of Mn2+ ions in GaAs

NASA Astrophysics Data System (ADS)

Akimov, I. A.; Dzhioev, R. I.; Korenev, V. L.; Kusrayev, Yu. G.; Sapega, V. F.; Yakovlev, D. R.; Bayer, M.

2013-04-01

We present an overview of spin-related phenomena in GaAs doped with low concentration of Mn-acceptors (below 1018 cm-3). We use the combination of different experimental techniques such as spin-flip Raman scattering and time-resolved photoluminescence. This allows to evaluate the time evolution of both electron and Mn spins. We show that optical orientation of Mn ions is possible under application of weak magnetic field, which is required to suppress the manganese spin relaxation. The optically oriented Mn2+ ions maintain the spin and return part of the polarization back to the electron spin system providing a long-lived electron spin memory. This leads to a bunch of spectacular effects such as non-exponential electron spin decay and spin precession in the effective exchange fields.

Spin imbalance effect on the Larkin-Ovchinnikov-Fulde-Ferrel state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshii, Ryosuke; Tsuchiya, Shunji; Research and Education Center for Natural Sciences, Keio University, 4-1-1 Hiyoshi, Kanagawa 223-8521

2011-07-01

We study spin imbalance effects on the Larkin-Ovchinnikov-Fulde-Ferrel (LOFF) state relevant for superconductors under a strong magnetic field and spin polarized ultracold Fermi gas. We obtain the exact solution for the condensates with arbitrary spin imbalance and the fermion spectrum perturbatively in the presence of small spin imbalance. We also obtain fermion zero mode exactly without perturbation theory.

Numerical relativity simulations of precessing binary neutron star mergers

NASA Astrophysics Data System (ADS)

Dietrich, Tim; Bernuzzi, Sebastiano; Brügmann, Bernd; Ujevic, Maximiliano; Tichy, Wolfgang

2018-03-01

We present the first set of numerical relativity simulations of binary neutron mergers that include spin precession effects and are evolved with multiple resolutions. Our simulations employ consistent initial data in general relativity with different spin configurations and dimensionless spin magnitudes ˜0.1 . They start at a gravitational-wave frequency of ˜392 Hz and cover more than 1 precession period and about 15 orbits up to merger. We discuss the spin precession dynamics by analyzing coordinate trajectories, quasilocal spin measurements, and energetics, by comparing spin aligned, antialigned, and irrotational configurations. Gravitational waveforms from different spin configuration are compared by calculating the mismatch between pairs of waveforms in the late inspiral. We find that precession effects are not distinguishable from nonprecessing configurations with aligned spins for approximately face-on binaries, while the latter are distinguishable from nonspinning configurations. Spin precession effects are instead clearly visible for approximately edge-on binaries. For the parameters considered here, precession does not significantly affect the characteristic postmerger gravitational-wave frequencies nor the mass ejection. Our results pave the way for the modeling of spin precession effects in the gravitational waveform from binary neutron star events.

Interfacial spin-filter assisted spin transfer torque effect in Co/BeO/Co magnetic tunnel junction

NASA Astrophysics Data System (ADS)

Tang, Y.-H.; Chu, F.-C.

2015-03-01

The first-principles calculation is employed to demonstrate the spin-selective transport properties and the non-collinear spin-transfer torque (STT) effect in the newly proposed Co/BeO/Co magnetic tunnel junction. The subtle spin-polarized charge transfer solely at O/Co interface gives rise to the interfacial spin-filter (ISF) effect, which can be simulated within the tight binding model to verify the general expression of STT. This allows us to predict the asymmetric bias behavior of non-collinear STT directly via the interplay between the first-principles calculated spin current densities in collinear magnetic configurations. We believe that the ISF effect, introduced by the combination between wurtzite-BeO barrier and the fcc-Co electrode, may open a new and promising route in semiconductor-based spintronics applications.

Spin Seebeck effect and thermoelectric phenomena in superconducting hybrids with magnetic textures or spin-orbit coupling

PubMed Central

Bathen, Marianne Etzelmüller; Linder, Jacob

2017-01-01

We theoretically consider the spin Seebeck effect, the charge Seebeck coefficient, and the thermoelectric figure of merit in superconducting hybrid structures including either magnetic textures or intrinsic spin-orbit coupling. We demonstrate that large magnitudes for all these quantities are obtainable in Josephson-based systems with either zero or a small externally applied magnetic field. This provides an alternative to the thermoelectric effects generated in high-field (~1 T) superconducting hybrid systems, which were recently experimentally demonstrated. The systems studied contain either conical ferromagnets, spin-active interfaces, or spin-orbit coupling. We present a framework for calculating the linear thermoelectric response for both spin and charge of a system upon applying temperature and voltage gradients based on quasiclassical theory which allows for arbitrary spin-dependent textures and fields to be conveniently incorporated. PMID:28139667

Spin Seebeck effect and thermoelectric phenomena in superconducting hybrids with magnetic textures or spin-orbit coupling.

PubMed

Bathen, Marianne Etzelmüller; Linder, Jacob

2017-01-31

We theoretically consider the spin Seebeck effect, the charge Seebeck coefficient, and the thermoelectric figure of merit in superconducting hybrid structures including either magnetic textures or intrinsic spin-orbit coupling. We demonstrate that large magnitudes for all these quantities are obtainable in Josephson-based systems with either zero or a small externally applied magnetic field. This provides an alternative to the thermoelectric effects generated in high-field (~1 T) superconducting hybrid systems, which were recently experimentally demonstrated. The systems studied contain either conical ferromagnets, spin-active interfaces, or spin-orbit coupling. We present a framework for calculating the linear thermoelectric response for both spin and charge of a system upon applying temperature and voltage gradients based on quasiclassical theory which allows for arbitrary spin-dependent textures and fields to be conveniently incorporated.

The spin-temperature theory of dynamic nuclear polarization and nuclear spin-lattice relaxation

NASA Technical Reports Server (NTRS)

Byvik, C. E.; Wollan, D. S.

1974-01-01

A detailed derivation of the equations governing dynamic nuclear polarization (DNP) and nuclear spin lattice relaxation by use of the spin temperature theory has been carried to second order in a perturbation expansion of the density matrix. Nuclear spin diffusion in the rapid diffusion limit and the effects of the coupling of the electron dipole-dipole reservoir (EDDR) with the nuclear spins are incorporated. The complete expression for the dynamic nuclear polarization has been derived and then examined in detail for the limit of well resolved solid effect transitions. Exactly at the solid effect transition peaks, the conventional solid-effect DNP results are obtained, but with EDDR effects on the nuclear relaxation and DNP leakage factor included. Explicit EDDR contributions to DNP are discussed, and a new DNP effect is predicted.

Demonstration of an adaptive response to preconditioning Frankliniella occidentalis (Pergande) to sublethal doses of spinosad: a hormetic-dose response.

PubMed

Gong, Youhui; Xu, Baoyun; Zhang, Youjun; Gao, Xiwu; Wu, Qingjun

2015-07-01

Sublethal doses of some insecticides have been reported to either stimulate or reduce the survival and fecundity of insects. Many sublethal-effect studies have been conducted after exposure of only one generation to sublethal insecticides, and there is little information about the sublethal effects on insects after long-term exposure to sublethal insecticides. In this study, changes in biological characteristics were investigated in spinosad-susceptible (Spin-S) and sublethal-spinosad-treated (Spin-Sub) strains of Frankliniella occidentalis (Pergande) after exposure to their corresponding sublethal concentrations of spinosad. The results showed that for the Spin-S strain, the LC10 concentration of spinosad slightly affected the biotic fitness both in parents and offspring of F. occidentalis. The LC25 concentration of spinosad prolonged the development time, reduced the fecundity, and significantly reduced the intrinsic rate of increase, the net reproductive rate and the finite rate of increase in the Spin-S strain. However, the negative effects were not as pronounced in the offspring (F1 generation) as in the parent generation. For the Spin-Sub strain, the LC10 and LC25 concentrations of spinosad had little negative effect on the development and fecundity, and no significant difference was found between the effects of the LC10 and LC25 treatments on the Spin-Sub strain. The Spin-Sub strain exhibited a shorter developmental time, and larger intrinsic rates of increase and net reproductive rates, compared with the corresponding treatments of the Spin-S strain. These findings combined with our previous studies suggest that the biotic fitness increased in the Spin-Sub strain and the strain became more adaptable to sublethal doses of spinosad, compared with the Spin-S strain. Physiological and biochemical adaptation may contribute to these changes after long treatment times at sublethal doses.

Adding Liquid Payloads Effects to the 6-DOF Trajectory of Spinning Projectiles

DTIC Science & Technology

2010-03-01

Adding Liquid Payloads Effects to the 6-DOF Trajectory of Spinning Projectiles by Gene R. Cooper ARL-TR-5118 March 2010...Liquid Payloads Effects to the 6-DOF Trajectory of Spinning Projectiles Gene R. Cooper Weapons and Materials Research Directorate, ARL...September 2007 4. TITLE AND SUBTITLE Adding Liquid Payloads Effects to the 6-DOF Trajectory of Spinning Projectiles 5a. CONTRACT NUMBER 5b. GRANT

Unique spin-polarized transmission effects in a QD ring structure

NASA Astrophysics Data System (ADS)

Hedin, Eric; Joe, Yong

2010-10-01

Spintronics is an emerging field in which the spin of the electron is used for switching purposes and to communicate information. In order to obtain spin-polarized electron transmission, the Zeeman effect is employed to produce spin-split energy states in quantum dots which are embedded in the arms of a mesoscopic Aharonov-Bohm (AB) ring heterostructure. The Zeeman splitting of the QD energy levels can be induced by a parallel magnetic field, or by a perpendicular field which also produces AB-effects. The combination of these effects on the transmission resonances of the structure is studied analytically and several parameter regimes are identified which produce a high degree of spin-polarized output. Contour and line plots of the weighted spin polarization as a function of electron energy and magnetic field are presented to visualize the degree of spin-polarization. Taking advantage of these unique parameter regimes shows the potential promise of such devices for producing spin-polarized currents.

Rydberg-Ritz analysis and quantum defects for Rb and Cs atoms on helium nanodroplets

NASA Astrophysics Data System (ADS)

Lackner, Florian; Krois, Günter; Ernst, Wolfgang E.

2013-08-01

A Rydberg-Ritz approach is used for the interpretation of Rb-He? and Cs-He? Rydberg states and Rydberg series. Variations of the quantum defects within a Rydberg series give insight into the interaction between the alkali atom's valence electron and the superfluid helium droplet. A screening of the valence electron from the alkali atom core by the helium droplet is observed for high Rydberg states. For states with lower principal quantum number, the effect decreases and the quantum defects are found to lie closer to free atom values, indicating an increased probability for the electron to be found inside the alkali atom core. An investigation of the spin-orbit splitting of the Cs-He? nP(2Π) components reveals that the splitting of the lowest 2Π states is more atom-like [Hund's case (c) coupling] than at higher n states [Hund's case (a) coupling]. In addition, we report a detailed study of the droplet size dependence of Ak-He? Rydberg series on the example of the Rb-He? D(Δ) series. Higher Rydberg states of this series are strongly redshifted, which is also related to the screening effect.

Tunable spin splitting and spin lifetime in polar WSTe monolayer

NASA Astrophysics Data System (ADS)

Adhib Ulil Absor, Moh.; Kotaka, Hiroki; Ishii, Fumiyuki; Saito, Mineo

2018-04-01

The established spin splitting with out-of-plane Zeeman spin polarizations in the monolayer (ML) of transition metal dichalcogenides (TMDs) is dictated by inversion symmetry breaking together with mirror symmetry in the surface plane. Here, by density functional theory calculations, we find that mirror symmetry breaking in the polar WSTe ML leads to large spin splitting exhibiting in-plane Rashba spin polarizations. We also find that the interplay between the out-of-plane Zeeman- and in-plane Rashba spin-polarized states sensitively affects the spin lifetime, which can be effectively controlled by in-plane strain. In addition, the tunability of spin splitting using an external electric field is also demonstrated. Our study clarifies that the use of in-plane strain and an external electric field is effective for tuning the spin splitting and spin lifetime of the polar WSTe ML; thus, it is useful for designing spintronic devices.

STM studies of an atomic-scale gate electrode formed by a single charged vacancy in GaAs

NASA Astrophysics Data System (ADS)

Lee, Donghun; Daughton, David; Gupta, Jay

2009-03-01

Electric-field control of spin-spin interactions at the atomic level is desirable for the realization of spintronics and spin-based quantum computation. Here we demonstrate the realization of an atomic-scale gate electrode formed by a single charged vacancy on the GaAs(110) surface[1]. We can position these vacancies with atomic precision using the tip of a home-built, low temperature STM. Tunneling spectroscopy of single Mn acceptors is used to quantify the electrostatic field as a function of distance from the vacancy. Single Mn acceptors are formed by substituting Mn adatoms for Ga atoms in the first layer of the p-GaAs(110) surface[2]. Depending on the distance, the in-gap resonance of single Mn acceptors can shift as much as 200meV. Our data indicate that the electrostatic field decays according to a screened Coulomb potential. The charge state of the vacancy can be switched to neutral, as evidenced by the Mn resonance returning to its unperturbed position. Reversible control of the local electric field as well as charged states of defects in semiconductors can open new insights such as realizing an atomic-scale gate control and studying spin-spin interactions in semiconductors. http://www.physics.ohio-state.edu/sim jgupta [1] D. Lee and J.A. Gupta (in preparation) [2] D. Kitchen et al., Nature 442, 436-439 (2006)

Spin-independent transparency of pure spin current at normal/ferromagnetic metal interface

NASA Astrophysics Data System (ADS)

Hao, Runrun; Zhong, Hai; Kang, Yun; Tian, Yufei; Yan, Shishen; Liu, Guolei; Han, Guangbing; Yu, Shuyun; Mei, Liangmo; Kang, Shishou

2018-03-01

The spin transparency at the normal/ferromagnetic metal (NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect (SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect (ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents ({{\\boldsymbol{σ }}}sc}), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe20Ni80 (Py) than that of Ni is obtained from the nonlocal voltage measurements. Project supported by the National Basic Research Program of China (Grant No. 2015CB921502), the National Natural Science Foundation of China (Grant Nos. 11474184 and 11627805), the 111 Project, China (Grant No. B13029), and the Fundamental Research Funds of Shandong University, China.

Curvature-enhanced Spin-orbit Coupling and Spinterface Effect in Fullerene-based Spin Valves

PubMed Central

Liang, Shiheng; Geng, Rugang; Yang, Baishun; Zhao, Wenbo; Chandra Subedi, Ram; Li, Xiaoguang; Han, Xiufeng; Nguyen, Tho Duc

2016-01-01

We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface. PMID:26786047

Curvature-enhanced Spin-orbit Coupling and Spinterface Effect in Fullerene-based Spin Valves

NASA Astrophysics Data System (ADS)

Liang, Shiheng; Geng, Rugang; Yang, Baishun; Zhao, Wenbo; Chandra Subedi, Ram; Li, Xiaoguang; Han, Xiufeng; Nguyen, Tho Duc

2016-01-01

We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface.

Evidence for phonon skew scattering in the spin Hall effect of platinum

NASA Astrophysics Data System (ADS)

Karnad, G. V.; Gorini, C.; Lee, K.; Schulz, T.; Lo Conte, R.; Wells, A. W. J.; Han, D.-S.; Shahbazi, K.; Kim, J.-S.; Moore, T. A.; Swagten, H. J. M.; Eckern, U.; Raimondi, R.; Kläui, M.

2018-03-01

We measure and analyze the effective spin Hall angle of platinum in the low-residual resistivity regime by second-harmonic measurements of the spin-orbit torques for a multilayer of Pt |Co | AlOx . An angular-dependent study of the torques allows us to extract the effective spin Hall angle responsible for the damping-like torque in the system. We observe a strikingly nonmonotonic and reproducible temperature dependence of the torques. This behavior is compatible with recent theoretical predictions which include both intrinsic and extrinsic (impurities and phonons) contributions to the spin Hall effect at finite temperatures.

Spin caloritronics, origin and outlook

NASA Astrophysics Data System (ADS)

Yu, Haiming; Brechet, Sylvain D.; Ansermet, Jean-Philippe

2017-03-01

Spin caloritronics refers to research efforts in spintronics when a heat current plays a role. In this review, we start out by reviewing the predictions that can be drawn from the thermodynamics of irreversible processes. This serves as a conceptual framework in which to analyze the interplay of charge, spin and heat transport. This formalism predicts tensorial relations between vectorial quantities such as currents and gradients of chemical potentials or of temperature. Transverse effects such as the Nernst or Hall effects are predicted on the basis that these tensors can include an anti-symmetric contribution, which can be written with a vectorial cross-product. The local symmetry of the system may determine the direction of the vector defining such transverse effects, such as the surface of an isotropic medium. By including magnetization as state field in the thermodynamic description, spin currents appear naturally from the continuity equation for the magnetization, and dissipative spin torques are derived, which are charge-driven or heat-driven. Thermodynamics does not give the strength of these effects, but may provide relationships between them. Based on this framework, the review proceeds by showing how these effects have been observed in various systems. Spintronics has become a vast field of research, and the experiments highlighted in this review pertain only to heat effects on transport and magnetization dynamics, such as magneto-thermoelectric power, or the spin-dependence of the Seebeck effect, the spin-dependence of the Peltier effect, the spin Seebeck effect, the magnetic Seebeck effect, or the Nernst effect. The review concludes by pointing out predicted effects that are yet to be verified experimentally, and in what novel materials the standard thermal spin effects could be investigated.

Magneto-optical studies of quantum dots

NASA Astrophysics Data System (ADS)

Russ, Andreas Hans

Significant effort in condensed matter physics has recently been devoted to the field of "spintronics" which seeks to utilize the spin degree of freedom of electrons. Unlike conventional electronics that rely on the electron charge, devices exploiting their spin have the potential to yield new and novel technological applications, including spin transistors, spin filters, and spin-based memory devices. Any such application has the following essential requirements: 1) Efficient electrical injection of spin-polarized carriers; 2) Long spin lifetimes; 3) Ability to control and manipulate electron spins; 4) Effective detection of spin-polarized carriers. Recent work has demonstrated efficient electrical injection from ferromagnetic contacts such as Fe and MnAs, utilizing a spin-Light Emitting Diode (spin-LED) as a method of detection. Semiconductor quantum dots (QDs) are attractive candidates for satisfying requirements 2 and 3 as their zero dimensionality significantly suppresses many spin-flip mechanisms leading to long spin coherence times, as well as enabling the localization and manipulation of a controlled number of electrons and holes. This thesis is composed of three projects that are all based on the optical properties of QD structures including: I) Intershell exchange between spin-polarized electrons occupying adjacent shells in InAs QDs; II) Spin-polarized multiexitons in InAs QDs in the presence of spin-orbit interactions; III) The optical Aharonov-Bohm effect in AlxGa1-xAs/AlyGa1-yAs quantum wells (QWs). In the following we introduce some of the basic optical properties of quantum dots, describe the main tool (spin-LED) employed in this thesis to inject and detect spins in these QDs, and conclude with the optical Aharonov-Bohm effect (OAB) in type-II QDs.

Widespread spin polarization effects in photoemission from topological insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jozwiak, C.; Chen, Y. L.; Fedorov, A. V.

2011-06-22

High-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi{sub 2}Se{sub 3} using a recently developed high-efficiency spectrometer. The topological surface state's helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations ofmore » photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.« less

Characterizing Active Pharmaceutical Ingredient Binding to Human Serum Albumin by Spin-Labeling and EPR Spectroscopy.

PubMed

Hauenschild, Till; Reichenwallner, Jörg; Enkelmann, Volker; Hinderberger, Dariush

2016-08-26

Drug binding to human serum albumin (HSA) has been characterized by a spin-labeling and continuous-wave (CW) EPR spectroscopic approach. Specifically, the contribution of functional groups (FGs) in a compound on its albumin-binding capabilities is quantitatively described. Molecules from different drug classes are labeled with EPR-active nitroxide radicals (spin-labeled pharmaceuticals (SLPs)) and in a screening approach CW-EPR spectroscopy is used to investigate HSA binding under physiological conditions and at varying ratios of SLP to protein. Spectral simulations of the CW-EPR spectra allow extraction of association constants (KA ) and the maximum number (n) of binding sites per protein. By comparison of data from 23 SLPs, the mechanisms of drug-protein association and the impact of chemical modifications at individual positions on drug uptake can be rationalized. Furthermore, new drug modifications with predictable protein binding tendency may be envisaged. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spin-Hall effect in the scattering of structured light from plasmonic nanowire.

PubMed

Sharma, Deepak K; Kumar, Vijay; Vasista, Adarsh B; Chaubey, Shailendra K; Kumar, G V Pavan

2018-06-01

Spin-orbit interactions are subwavelength phenomena that can potentially lead to numerous device-related applications in nanophotonics. Here, we report the spin-Hall effect in the forward scattering of Hermite-Gaussian (HG) and Gaussian beams from a plasmonic nanowire. Asymmetric scattered radiation distribution was observed for circularly polarized beams. Asymmetry in the scattered radiation distribution changes the sign when the polarization handedness inverts. We found a significant enhancement in the spin-Hall effect for a HG beam compared to a Gaussian beam for constant input power. The difference between scattered powers perpendicular to the long axis of the plasmonic nanowire was used to quantify the enhancement. In addition, the nodal line of the HG beam acts as the marker for the spin-Hall shift. Numerical calculations corroborate experimental observations and suggest that the spin flow component of the Poynting vector associated with the circular polarization is responsible for the spin-Hall effect and its enhancement.

Spin-Hall effect in the scattering of structured light from plasmonic nanowire

NASA Astrophysics Data System (ADS)

Sharma, Deepak K.; Kumar, Vijay; Vasista, Adarsh B.; Chaubey, Shailendra K.; Kumar, G. V. Pavan

2018-06-01

Spin-orbit interactions are subwavelength phenomena which can potentially lead to numerous device related applications in nanophotonics. Here, we report Spin-Hall effect in the forward scattering of Hermite-Gaussian and Gaussian beams from a plasmonic nanowire. Asymmetric scattered radiation distribution was observed for circularly polarized beams. Asymmetry in the scattered radiation distribution changes the sign when the polarization handedness inverts. We found a significant enhancement in the Spin-Hall effect for Hermite-Gaussian beam as compared to Gaussian beam for constant input power. The difference between scattered powers perpendicular to the long axis of the plasmonic nanowire was used to quantify the enhancement. In addition to it, nodal line of HG beam acts as the marker for the Spin-Hall shift. Numerical calculations corroborate experimental observations and suggest that the Spin flow component of Poynting vector associated with the circular polarization is responsible for the Spin-Hall effect and its enhancement.

Quasiparticle-mediated spin Hall effect in a superconductor.

PubMed

Wakamura, T; Akaike, H; Omori, Y; Niimi, Y; Takahashi, S; Fujimaki, A; Maekawa, S; Otani, Y

2015-07-01

In some materials the competition between superconductivity and magnetism brings about a variety of unique phenomena such as the coexistence of superconductivity and magnetism in heavy-fermion superconductors or spin-triplet supercurrent in ferromagnetic Josephson junctions. Recent observations of spin-charge separation in a lateral spin valve with a superconductor evidence that these remarkable properties are applicable to spintronics, although there are still few works exploring this possibility. Here, we report the experimental observation of the quasiparticle-mediated spin Hall effect in a superconductor, NbN. This compound exhibits the inverse spin Hall (ISH) effect even below the superconducting transition temperature. Surprisingly, the ISH signal increases by more than 2,000 times compared with that in the normal state with a decrease of the injected spin current. The effect disappears when the distance between the voltage probes becomes larger than the charge imbalance length, corroborating that the huge ISH signals measured are mediated by quasiparticles.

Thickness dependence and the role of spin transfer torque in nonlinear giant magnetoresistance of permalloy dual spin valves

NASA Astrophysics Data System (ADS)

Banerjee, N.; Aziz, A.; Ali, M.; Robinson, J. W. A.; Hickey, B. J.; Blamire, M. G.

2010-12-01

The recent discovery of nonlinear current-dependent magnetoresistance in dual spin valve devices [A. Aziz, O. P. Wessely, M. Ali, D. M. Edwards, C. H. Marrows, B. J. Hickey, and M. G. Blamire, Phys. Rev. Lett. 103, 237203 (2009)10.1103/PhysRevLett.103.237203] opens up the possibility for distinct physics which extends the standard model of giant magnetoresistance. When the outer ferromagnetic layers of a dual spin valve are antiparallel, the resulting accumulation of spin in the middle ferromagnetic layer strongly modifies its bulk and interfacial spin asymmetry and resistance. Here, we report experimental evidence of the role of bulk spin accumulation in this nonlinear effect and show that interfacial spin accumulation alone cannot account for the observed dependence of the effect on the thickness of the middle ferromagnetic layer. It is also shown that spin torque acting on the middle ferromagnetic layer combined with the nonlinear effect might be useful in understanding the dynamical features associated with the nonlinear behavior.

Catalystlike effect of orbital angular momentum on the conversion of transverse to three-dimensional spin states within tightly focused radially polarized beams

NASA Astrophysics Data System (ADS)

Han, Lei; Liu, Sheng; Li, Peng; Zhang, Yi; Cheng, Huachao; Zhao, Jianlin

2018-05-01

We report on the catalystlike effect of orbital angular momentum (OAM) on local spin-state conversion within the tightly focused radially polarized beams associated with optical spin-orbit interaction. It is theoretically demonstrated that the incident OAM can lead to a conversion of purely transverse spin state to a three-dimensional spin state on the focal plane. This conversion can be conveniently manipulated by altering the sign and value of the OAM. By comparing the total OAM and spin angular momentum (SAM) on the incident plane to those on the focal plane, it is indicated that the incident OAM have no participation in the angular momentum intertransfer, and just play a role as a catalyst of local SAM conversion. Such an effect of OAM sheds new light on the optical spin-orbit interaction in tight-focusing processes. The resultant three-dimensional spin states may provide more degrees of freedom in optical manipulation and spin-dependent directive coupling.

Modulation of spin dynamics via voltage control of spin-lattice coupling in multiferroics

DOE PAGES

Zhu, Mingmin; Zhou, Ziyao; Peng, Bin; ...

2017-02-03

Our work aims at magnonics manipulation by the magnetoelectric coupling effect and is motivated by the most recent progresses in both magnonics (spin dynamics) and multiferroics fields. Here, voltage control of magnonics, particularly the surface spin waves, is achieved in La 0.7Sr 0.3MnO 3/0.7Pb(Mg 1/3Nb 2/3)O 3-0.3PbTiO 3 multiferroic heterostructures. With the electron spin resonance method, a large 135 Oe shift of surface spin wave resonance (≈7 times greater than conventional voltage-induced ferromagnetic resonance shift of 20 Oe) is determined. A model of the spin-lattice coupling effect, i.e., varying exchange stiffness due to voltage-induced anisotropic lattice changes, has been establishedmore » to explain experiment results with good agreement. In addition, an “on” and “off” spin wave state switch near the critical angle upon applying a voltage is created. The modulation of spin dynamics by spin-lattice coupling effect provides a platform for realizing energy-efficient, tunable magnonics devices.« less

Spin Seebeck devices using local on-chip heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Stephen M.; Fradin, Frank Y.; Hoffman, Jason

2015-05-07

A micro-patterned spin Seebeck device is fabricated using an on-chip heater. Current is driven through a Au heater layer electrically isolated from a bilayer consisting of Fe3O4 (insulating ferrimagnet) and a spin detector layer. It is shown that through this method it is possible to measure the longitudinal spin Seebeck effect (SSE) for small area magnetic devices, equivalent to traditional macroscopic SSE experiments. Using a lock-in detection technique, it is possible to more sensitively characterize both the SSE and the anomalous Nernst effect (ANE), as well as the inverse spin Hall effect in various spin detector materials. By using themore » spin detector layer as a thermometer, we can obtain a value for the temperature gradient across the device. These results are well matched to values obtained through electromagnetic/thermal modeling of the device structure and with large area spin Seebeck measurements.« less

Spin Seebeck devices using local on-chip heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Stephen M., E-mail: swu@anl.gov; Fradin, Frank Y.; Hoffman, Jason

2015-05-07

A micro-patterned spin Seebeck device is fabricated using an on-chip heater. Current is driven through a Au heater layer electrically isolated from a bilayer consisting of Fe{sub 3}O{sub 4} (insulating ferrimagnet) and a spin detector layer. It is shown that through this method it is possible to measure the longitudinal spin Seebeck effect (SSE) for small area magnetic devices, equivalent to traditional macroscopic SSE experiments. Using a lock-in detection technique, it is possible to more sensitively characterize both the SSE and the anomalous Nernst effect (ANE), as well as the inverse spin Hall effect in various spin detector materials. Bymore » using the spin detector layer as a thermometer, we can obtain a value for the temperature gradient across the device. These results are well matched to values obtained through electromagnetic/thermal modeling of the device structure and with large area spin Seebeck measurements.« less

Spin Funneling for Enhanced Spin Injection into Ferromagnets

PubMed Central

Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo

2016-01-01

It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory. PMID:27374496

Spin Funneling for Enhanced Spin Injection into Ferromagnets

NASA Astrophysics Data System (ADS)

Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo

2016-07-01

It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory.

Magnon Hall effect without Dzyaloshinskii-Moriya interaction.

PubMed

Owerre, S A

2017-01-25

Topological magnon bands and magnon Hall effect in insulating collinear ferromagnets are induced by the Dzyaloshinskii-Moriya interaction (DMI) even at zero magnetic field. In the geometrically frustrated star lattice, a coplanar/noncollinear [Formula: see text] magnetic ordering may be present due to spin frustration. This magnetic structure, however, does not exhibit topological magnon effects even with DMI in contrast to collinear ferromagnets. We show that a magnetic field applied perpendicular to the star plane induces a non-coplanar spin configuration with nonzero spin scalar chirality, which provides topological effects without the need of DMI. The non-coplanar spin texture originates from the topology of the spin configurations and does not need the presence of DMI or magnetic ordering, which suggests that this phenomenon may be present in the chiral spin liquid phases of frustrated magnetic systems. We propose that these anomalous topological magnon effects can be accessible in polymeric iron (III) acetate-a star-lattice antiferromagnet with both spin frustration and long-range magnetic ordering.

The effect of inertia on the Dirac electron, the spin Hall current and the momentum space Berry curvature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chowdhury, Debashree, E-mail: debashreephys@gmail.com; Basu, B., E-mail: sribbasu@gmail.com

2013-02-15

We have studied the spin dependent force and the associated momentum space Berry curvature in an accelerating system. The results are derived by taking into consideration the non-relativistic limit of a generally covariant Dirac equation with an electromagnetic field present, where the methodology of the Foldy-Wouthuysen transformation is applied to achieve the non-relativistic limit. Spin currents appear due to the combined action of the external electric field, the crystal field and the induced inertial electric field via the total effective spin-orbit interaction. In an accelerating frame, the crucial role of momentum space Berry curvature in the spin dynamics has alsomore » been addressed from the perspective of spin Hall conductivity. For time dependent acceleration, the expression for the spin polarization has been derived. - Highlights: Black-Right-Pointing-Pointer We study the effect of acceleration on the Dirac electron in the presence of an electromagnetic field, where the acceleration induces an electric field. Black-Right-Pointing-Pointer Spin currents appear due to the total effective electric field via the total spin-orbit interaction. Black-Right-Pointing-Pointer We derive the expression for the spin dependent force and the spin Hall current, which is zero for a particular acceleration. Black-Right-Pointing-Pointer The role of the momentum space Berry curvature in an accelerating system is discussed. Black-Right-Pointing-Pointer An expression for the spin polarization for time dependent acceleration is derived.« less

Deficiency of the bulk spin Hall effect model for spin-orbit torques in magnetic-insulator/heavy-metal heterostructures

NASA Astrophysics Data System (ADS)

Li, Junxue; Yu, Guoqiang; Tang, Chi; Liu, Yizhou; Shi, Zhong; Liu, Yawen; Navabi, Aryan; Aldosary, Mohammed; Shao, Qiming; Wang, Kang L.; Lake, Roger; Shi, Jing

2017-06-01

Electrical currents in a magnetic-insulator/heavy-metal heterostructure can induce two simultaneous effects, namely, spin Hall magnetoresistance (SMR) on the heavy-metal side and spin-orbit torques (SOTs) on the magnetic-insulator side. Within the framework of a pure spin current model based on the bulk spin Hall effect (SHE), the ratio of the spin Hall-induced anomalous Hall effect (SH-AHE) to SMR should be equal to the ratio of the fieldlike torque (FLT) to the dampinglike torque (DLT). We perform a quantitative study of SMR, SH-AHE, and SOTs in a series of thulium iron garnet/platinum or T m3F e5O12/Pt heterostructures with different T m3F e5O12 thicknesses, where T m3F e5O12 is a ferrimagnetic insulator with perpendicular magnetic anisotropy. We find the ratio between the measured effective fields of FLT and DLT is at least two times larger than the ratio of the SH-AHE to SMR. In addition, the bulk SHE model grossly underestimates the spin-torque efficiency of FLT. Our results reveal deficiencies of the bulk SHE model and also address the importance of interfacial effects such as the Rashba and magnetic proximity effects in magnetic-insulator/heavy-metal heterostructures.

Modelling magnetic anisotropy of single-chain magnets in |d/J| ≥ 1 regime

NASA Astrophysics Data System (ADS)

Haldar, Sumit; Raghunathan, Rajamani; Sutter, Jean-Pascal; Ramasesha, S.

2017-11-01

Single-molecule magnets (SMMs) with single-ion anisotropies comparable to exchange interactions J between spins have recently been synthesised. Here, we provide theoretical insights into the magnetism of such systems. We study spin chains with site-spins, s = 1, 3/2 and 2 and strength of on-site anisotropy comparable to the exchange constants between the spins. We find that large on-site anisotropies lead to crossing of the states with different MS values in the same spin manifold to which they belong in the absence of anisotropy. When on-site anisotropy is increased further, we also find that the MS states of the higher energy spin states descend below the MS states of the ground spin manifold. Giant spin in this limit is no longer conserved and describing the axial and rhombic anisotropies of the molecule, DM and EM, respectively, is not possible. However, the giant spin of the low-lying large MS states is very nearly an integer and, using this spin value, it is possible to construct an effective spin-Hamiltonian and compute the molecular magnetic anisotropy constants DM and EM. We report effect of finite sizes, rotations of site anisotropies and chain dimerisation on the effective anisotropy of the spin chains.

Spin-tunnel investigation of a 1/15-scale model of an Australian trainer airplane

NASA Technical Reports Server (NTRS)

Bowman, James S., Jr.; Whipple, Raymond D.; White, William L.

1987-01-01

An investigation was conducted in the Langley Spin Tunnel of the spin and spin-recovery characteristics of a 1/15-scale model of an Australian trainer airplane. The invesigation included erect and inverted spins; configuration variables such as a long tail, fuselage strakes, 20 deg. elevator cutouts, and rudder modifications; and determination of the parachute size for emergency spin recovery. Also included in the investigation were wing leading-edge modifications to evaluate Reynolds number effects. Results indicate that the basic configuration will spin erect at an angle of attack of about 63 deg. at about 2 to 2.3 seconds per turn. Recovery from this spin was unsatisfactory by rudder reversal or by rudder reversal and ailerons deflected to full with the spin. The elevators had a pronounced effect on the recovery characteristics. The elevators-down position was very adverse to recoveries, whereas the elevators-up position provided favorable recovery effects. Moving the vertical tail aft (producing a long tail configuration) improved the spin characteristics, but the recoveries were still considered marginal. An extension to the basic rudder chord and length made a significant improvement in the spin and recovery characteristics. Satisfactory recoveries were obtained by deflecting the rudder to full against the spin and the elevators and ailerons to neutral.

Effects of discontinuous drooped wing leading-edge modifications on the spinning characteristics of a low-wing general aviation airplane

NASA Technical Reports Server (NTRS)

Dicarlo, D. J.; Stough, H. P., III; Patton, J. M., Jr.

1980-01-01

Wind tunnel and flight tests were conducted to determine the effects of several discontinuous drooped wing leading-edge configurations on the spinning characteristics of a light, single-engine, low-wing research airplane. Particular emphasis was placed on the identification of modifications which would improve the spinning characteristics. The spanwise length of a discontinuous outboard droop was varied and several additional inboard segments were added to determine the influence of such leading-edge configurations on the spin behavior. Results of the study indicated that the use of only the discontinuous outboard droop, over a specific spanwise area, was most effective towards improving spin and spin recovery characteristics, whereas the segmented configurations having both inboard and outboard droop exhibited a tendency to enter a flat spin.

Spin supercurrent and effect of quantum phase transition in the two-dimensional XY model

NASA Astrophysics Data System (ADS)

Lima, L. S.

2018-04-01

We have verified the influence of quantum phase transition on spin transport in the spin-1 two-dimensional XY model on the square lattice, with easy plane, single ion and exchange anisotropy. We analyze the effect of the phase transition from the Néel phase to the paramagnetic phase on the AC spin conductivity. Our results show a bit influence of the quantum phase transition on the conductivity. We also obtain a conventional spin transport for ω > 0 and an ideal spin transport in the limit of DC conductivity and therefore, a superfluid spin transport for the DC current in this limit. We have made the diagrammatic expansion for the Green-function with objective to include the effect exciton-exciton scattering on the results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, C.; Kewisch, J.; Huang, H.

At RHIC, the spin polarization is preserved with a pair of Siberian snakes on the oppo- site sides in each ring. The polarized proton beam with finite spin tune spread might cross spin resonances multiple times in two cases, one is when beam going through strong spin intrinsic resonances during acceleration, the other is when sweeping spin flipper’ frequency across the spin tune to flip the direction of spin polarization. The consequence is loss of spin polarization in both cases. Therefore, a scheme of min- imizing the spin tune spread by matching the dispersion primes at the two snakes wasmore » introduced based on the fact that the spin tune spread is proportional to the difference of dispersion primes at the two snakes. The scheme was implemented at fixed energies for the spin flipper study and during beam acceleration for better spin polarization transmission efficiency. The effect of minimizing the spin tune spread by matching the dispersion primes was observed and confirmed experimentally. The principle of minimizing the spin tune spread by matching the dispersion primes, the impact on the beam optics, and the effect of a narrower spin tune spread are presented in this report.« less

Quantum dynamics of nuclear spins and spin relaxation in organic semiconductors

NASA Astrophysics Data System (ADS)

Mkhitaryan, V. V.; Dobrovitski, V. V.

2017-06-01

We investigate the role of the nuclear-spin quantum dynamics in hyperfine-induced spin relaxation of hopping carriers in organic semiconductors. The fast-hopping regime, when the carrier spin does not rotate much between subsequent hops, is typical for organic semiconductors possessing long spin coherence times. We consider this regime and focus on a carrier random-walk diffusion in one dimension, where the effect of the nuclear-spin dynamics is expected to be the strongest. Exact numerical simulations of spin systems with up to 25 nuclear spins are performed using the Suzuki-Trotter decomposition of the evolution operator. Larger nuclear-spin systems are modeled utilizing the spin-coherent state P -representation approach developed earlier. We find that the nuclear-spin dynamics strongly influences the carrier spin relaxation at long times. If the random walk is restricted to a small area, it leads to the quenching of carrier spin polarization at a nonzero value at long times. If the random walk is unrestricted, the carrier spin polarization acquires a long-time tail, decaying as 1 /√{t } . Based on the numerical results, we devise a simple formula describing the effect quantitatively.

Spin-dependent Peltier effect in 3D topological insulators

NASA Astrophysics Data System (ADS)

Sengupta, Parijat; Kubis, Tillmann; Povolotskyi, Michael; Klimeck, Gerhard

2013-03-01

The Peltier effect represents the heat carrying capacity of a certain material when current passes through it. When two materials with different Peltier coefficients are placed together, the Peltier effect causes heat to flow either towards or away from the interface between them. This work utilizes the spin-polarized property of 3D topological insulator (TI) surface states to describe the transport of heat through the spin-up and spin-down channels. It has been observed that the spin channels are able to carry heat independently of each other. Spin currents can therefore be employed to supply or extract heat from an interface between materials with spin-dependent Peltier coefficients. The device is composed of a thin film of Bi2Se3 sandwiched between two layers of Bi2Te3. The thin film of Bi2Se3serves both as a normal and topological insulator. It is a normal insulator when its surfaces overlap to produce a finite band-gap. Using an external gate, Bi2Se3 film can be again tuned in to a TI. Sufficiently thick Bi2Te3 always retain TI behavior. Spin-dependent Peltier coefficients are obtained and the spin Nernst effect in TIs is shown by controlling the temperature gradient to convert charge current to spin current.

A study of environmental effects on galaxy spin using MaNGA data

NASA Astrophysics Data System (ADS)

Lee, Jong Chul; Hwang, Ho Seong; Chung, Haeun

2018-06-01

We investigate environmental effects on galaxy spin using the recent public data of Mapping Nearby Galaxies at APO (MaNGA) integral field spectroscopic survey containing ˜2800 galaxies. We measure the spin parameter of 1830 galaxies through the analysis of two-dimensional stellar kinematic maps within the effective radii, and obtain their large-scale (background mass density from 20 nearby galaxies) and small-scale (distance to and morphology of the nearest neighbour galaxy) environmental parameters for 1529 and 1767 galaxies, respectively. We first examine the mass dependence of galaxy spin, and find that the spin parameter of early-type galaxies decreases with stellar mass at log (M*/M⊙) ≳ 10, consistent with the results from previous studies. We then divide the galaxies into three subsamples using their stellar masses to minimize the mass effects on galaxy spin. The spin parameters of galaxies in each subsample do not change with background mass density, but do change with distance to and morphology of the nearest neighbour. In particular, the spin parameter of late-type galaxies decreases as early-type neighbours approach within the virial radius. These results suggest that the large-scale environments hardly affect the galaxy spin, but the small-scale environments such as hydrodynamic galaxy-galaxy interactions can play a substantial role in determining galaxy spin.

A hyperpolarized equilibrium for magnetic resonance

PubMed Central

Hövener, Jan-Bernd; Schwaderlapp, Niels; Lickert, Thomas; Duckett, Simon B.; Mewis, Ryan E.; Highton, Louise A. R.; Kenny, Stephen M.; Green, Gary G. R.; Leibfritz, Dieter; Korvink, Jan G.; Hennig, Jürgen; von Elverfeldt, Dominik

2013-01-01

Nuclear magnetic resonance spectroscopy and imaging (MRI) play an indispensable role in science and healthcare but use only a tiny fraction of their potential. No more than ≈10 p.p.m. of all 1H nuclei are effectively detected in a 3-Tesla clinical MRI system. Thus, a vast array of new applications lays dormant, awaiting improved sensitivity. Here we demonstrate the continuous polarization of small molecules in solution to a level that cannot be achieved in a viable magnet. The magnetization does not decay and is effectively reinitialized within seconds after being measured. This effect depends on the long-lived, entangled spin-order of parahydrogen and an exchange reaction in a low magnetic field of 10−3 Tesla. We demonstrate the potential of this method by fast MRI and envision the catalysis of new applications such as cancer screening or indeed low-field MRI for routine use and remote application. PMID:24336292

A hyperpolarized equilibrium for magnetic resonance.

PubMed

Hövener, Jan-Bernd; Schwaderlapp, Niels; Lickert, Thomas; Duckett, Simon B; Mewis, Ryan E; Highton, Louise A R; Kenny, Stephen M; Green, Gary G R; Leibfritz, Dieter; Korvink, Jan G; Hennig, Jürgen; von Elverfeldt, Dominik

2013-01-01

Nuclear magnetic resonance spectroscopy and imaging (MRI) play an indispensable role in science and healthcare but use only a tiny fraction of their potential. No more than ≈10 p.p.m. of all ¹H nuclei are effectively detected in a 3-Tesla clinical MRI system. Thus, a vast array of new applications lays dormant, awaiting improved sensitivity. Here we demonstrate the continuous polarization of small molecules in solution to a level that cannot be achieved in a viable magnet. The magnetization does not decay and is effectively reinitialized within seconds after being measured. This effect depends on the long-lived, entangled spin-order of parahydrogen and an exchange reaction in a low magnetic field of 10⁻³ Tesla. We demonstrate the potential of this method by fast MRI and envision the catalysis of new applications such as cancer screening or indeed low-field MRI for routine use and remote application.

Spin decoherence of InAs surface electrons by transition metal ions

NASA Astrophysics Data System (ADS)

Zhang, Yao; Soghomonian, V.; Heremans, J. J.

2018-04-01

Spin interactions between a two-dimensional electron system at the InAs surface and transition metal ions, Fe3 +, Co2 +, and Ni2 +, deposited on the InAs surface, are probed by antilocalization measurements. The spin-dependent quantum interference phenomena underlying the quantum transport phenomenon of antilocalization render the technique sensitive to the spin states of the transition metal ions on the surface. The experiments yield data on the magnitude and temperature dependence of the electrons' inelastic scattering rates, spin-orbit scattering rates, and magnetic spin-flip rates as influenced by Fe3 +, Co2 +, and Ni2 +. A high magnetic spin-flip rate is shown to mask the effects of spin-orbit interaction, while the spin-flip rate is shown to scale with the effective magnetic moment of the surface species. The spin-flip rates and their dependence on temperature yield information about the spin states of the transition metal ions at the surface, and in the case of Co2 + suggest either a spin transition or formation of a spin-glass system.

Met Éireann high resolution reanalysis for Ireland

NASA Astrophysics Data System (ADS)

Gleeson, Emily; Whelan, Eoin; Hanley, John

2017-03-01

The Irish Meteorological Service, Met Éireann, has carried out a 35-year very high resolution (2.5 km horizontal grid) regional climate reanalysis for Ireland using the ALADIN-HIRLAM numerical weather prediction system. This article provides an overview of the reanalysis, called MÉRA, as well as a preliminary analysis of surface parameters including screen level temperature, 10 m wind speeds, mean sea-level pressure (MSLP), soil temperatures, soil moisture and 24 h rainfall accumulations. The quality of the 3-D variational data assimilation used in the reanalysis is also assessed. Preliminary analysis shows that it takes almost 12 months to spin up the deep soil in terms of moisture, justifying the choice of running year-long spin up periods. Overall, the model performed consistently over the time period. Small biases were found in screen-level temperatures (less than -0.5 °C), MSLP (within 0.5 hPa) and 10 m wind speed (up to 0.5 m s-1) Soil temperatures are well represented by the model. 24 h accumulations of precipitation generally exhibit a small positive bias of ˜ 1 mm per day and negative biases over mountains due to a mismatch between the model orography and the geography of the region. MÉRA outperforms the ERA-Interim reanalysis, particularly in terms of standard deviations in screen-level temperatures and surface winds. This dataset is the first of its kind for Ireland that will be made publically available during spring 2017.

Boson-mediated quantum spin simulators in transverse fields: X Y model and spin-boson entanglement

NASA Astrophysics Data System (ADS)

Wall, Michael L.; Safavi-Naini, Arghavan; Rey, Ana Maria

2017-01-01

The coupling of spins to long-wavelength bosonic modes is a prominent means to engineer long-range spin-spin interactions, and has been realized in a variety of platforms, such as atoms in optical cavities and trapped ions. To date, much of the experimental focus has been on the realization of long-range Ising models, but generalizations to other spin models are highly desirable. In this work, we explore a previously unappreciated connection between the realization of an X Y model by off-resonant driving of a single sideband of boson excitation (i.e., a single-beam Mølmer-Sørensen scheme) and a boson-mediated Ising simulator in the presence of a transverse field. In particular, we show that these two schemes have the same effective Hamiltonian in suitably defined rotating frames, and analyze the emergent effective X Y spin model through a truncated Magnus series and numerical simulations. In addition to X Y spin-spin interactions that can be nonperturbatively renormalized from the naive Ising spin-spin coupling constants, we find an effective transverse field that is dependent on the thermal energy of the bosons, as well as other spin-boson couplings that cause spin-boson entanglement not to vanish at any time. In the case of a boson-mediated Ising simulator with transverse field, we discuss the crossover from transverse field Ising-like to X Y -like spin behavior as a function of field strength.

A qualitative study of spin polarization effect in defect tuned Co/graphene/Co nanostructures

NASA Astrophysics Data System (ADS)

Mandal, Sumit; Saha, Shyamal K.

2014-10-01

Theoretical reports predict that in contact with a ferromagnetic giant spin, spin polarization evolves in defective graphene since defects in graphene act as local spin moments. We have synthesized different Co/graphene/Co nano spin valve like structures tuning the degree of defect applying ultrasonic vibration and characterized them by Raman spectroscopy. Initially with increasing ID/IG ratio in Raman spectra, antiferromagnetic coupling between the Co nanosheets on either sides of graphene enhances leading to betterment in spin transport through graphene. But for highest ID/IG, a totally new phenomenon called antiferro quadrupolar ordering (AFQ) takes place which eventually reduces the spin polarization effect.

Transmutation of skyrmions to half-solitons driven by the nonlinear optical spin Hall effect.

PubMed

Flayac, H; Solnyshkov, D D; Shelykh, I A; Malpuech, G

2013-01-04

We show that the spin domains, generated in the linear optical spin Hall effect by the analog of spin-orbit interaction for exciton polaritons, are associated with the formation of a Skyrmion lattice. In the nonlinear regime, the spin anisotropy of the polariton-polariton interactions results in a spatial compression of the domains and in a transmutation of the Skyrmions into oblique half-solitons. This phase transition is associated with both the focusing of the spin currents and the emergence of a strongly anisotropic emission pattern.

Electrical detection of magnetization dynamics via spin rectification effects

NASA Astrophysics Data System (ADS)

Harder, Michael; Gui, Yongsheng; Hu, Can-Ming

2016-11-01

The purpose of this article is to review the current status of a frontier in dynamic spintronics and contemporary magnetism, in which much progress has been made in the past decade, based on the creation of a variety of micro and nanostructured devices that enable electrical detection of magnetization dynamics. The primary focus is on the physics of spin rectification effects, which are well suited for studying magnetization dynamics and spin transport in a variety of magnetic materials and spintronic devices. Intended to be intelligible to a broad audience, the paper begins with a pedagogical introduction, comparing the methods of electrical detection of charge and spin dynamics in semiconductors and magnetic materials respectively. After that it provides a comprehensive account of the theoretical study of both the angular dependence and line shape of electrically detected ferromagnetic resonance (FMR), which is summarized in a handbook format easy to be used for analysing experimental data. We then review and examine the similarity and differences of various spin rectification effects found in ferromagnetic films, magnetic bilayers and magnetic tunnel junctions, including a discussion of how to properly distinguish spin rectification from the spin pumping/inverse spin Hall effect generated voltage. After this we review the broad applications of rectification effects for studying spin waves, nonlinear dynamics, domain wall dynamics, spin current, and microwave imaging. We also discuss spin rectification in ferromagnetic semiconductors. The paper concludes with both historical and future perspectives, by summarizing and comparing three generations of FMR spectroscopy which have been developed for studying magnetization dynamics.

Spin Hall effect and Landau spectrum of Dirac electrons in bismuth

NASA Astrophysics Data System (ADS)

Fuseya, Yuki

2015-03-01

Bismuth has played an important role in solid-state physics. Many key phenomena were first discovered in bismuth, such as diamagnetism, Seebeck, Nernst, Shubnikov-de Haas, and de Haas-van Alphen effects. These phenomena result from particular electronic states of bismuth. The strong spin-orbit interaction (~ 1.5eV) causes strong spin-dependent interband couplings resulting in an anomalous spin magnetic moment. We investigate the spin Hall effect and the angular dependent Landau spectrum of bismuth paying special attention to the effect of the anomalous spin magnetic moment. It is shown that the spin Hall insulator is possible and there is a fundamental relationship between the spin Hall conductivity and orbital diamagnetism in the insulating state of the Dirac electrons. Based on this theoretical finding, the magnitude of spin Hall conductivity is estimated for bismuth by that of orbital susceptibility. The magnitude of spin Hall conductivity turns out to be as large as 104Ω-1 cm-1, which is about 100 times larger than that of Pt. It is also shown that the ratio of the Zeeman splitting to the cyclotron energy, which reflects the effect of crystalline spin-orbit interaction, for holes at the T-point can be larger than 1.0 (the maximum of previous theories) and exhibit strong angular dependence, which gives a possible solution to the long-standing mystery of holes at the T-point. In collaboration with Masao Ogata, Hidetoshi Fukuyama, Zengwei Zhu, Benoît Fauqué, Woun Kang, and Kamran Behnia. Supported by JSPS (KAKENHI 24244053, 25870231, and 13428660).

Proposed new test of spin effects in general relativity.

PubMed

O'Connell, R F

2004-08-20

The recent discovery of a double-pulsar PSR J0737-3039A/B provides an opportunity of unequivocally observing, for the first time, spin effects in general relativity. Existing efforts involve detection of the precession of the spinning body itself. However, for a close binary system, spin effects on the orbit may also be discernible. Not only do they add to the advance of the periastron (by an amount which is small compared to the conventional contribution) but they also give rise to a precession of the orbit about the spin direction. The measurement of such an effect would also give information on the moment of inertia of pulsars.

Photonic spin Hall effect enabled refractive index sensor using weak measurements.

PubMed

Zhou, Xinxing; Sheng, Lijuan; Ling, Xiaohui

2018-01-19

In this work, we theoretically propose an optical biosensor (consists of a BK7 glass, a metal film, and a graphene sheet) based on photonic spin Hall effect (SHE). We establish a quantitative relationship between the spin-dependent shift in photonic SHE and the refractive index of sensing medium. It is found that, by considering the surface plasmon resonance effect, the refractive index variations owing to the adsorption of biomolecules in sensing medium can effectively change the spin-dependent displacements. Remarkably, using the weak measurement method, this tiny spin-dependent shifts can be detected with a desirable accuracy so that the corresponding biomolecules concentration can be determined.

Polar-core spin vortex of quasi-2D ferromagnetic spin-1 condensate in a flat-bottomed optical trap with a weak magnetic field

NASA Astrophysics Data System (ADS)

Zheng, Gong-Ping; Li, Pin; Li, Ting; Xue, Ya-Jie

2018-02-01

Motivated by the recent experiments realized in a flat-bottomed optical trap (Navon et al., 2015; Chomaz et al., 2015), we study the ground state of polar-core spin vortex of quasi-2D ferromagnetic spin-1 condensate in a finite-size homogeneous trap with a weak magnetic field. The exact spatial distribution of local spin is obtained with a variational method. Unlike the fully-magnetized planar spin texture with a zero-spin core, which was schematically demonstrated in previous studies for the ideal polar-core spin vortex in a homogeneous trap with infinitely large boundary, some plateaus and two-cores structure emerge in the distribution curves of spin magnitude in the polar-core spin vortex we obtained for the larger effective spin-dependent interaction. More importantly, the spin values of the plateaus are not 1 as expected in the fully-magnetized spin texture, except for the sufficiently large spin-dependent interaction and the weak-magnetic-field limit. We attribute the decrease of spin value to the effect of finite size of the system. The spin values of the plateaus can be controlled by the quadratic Zeeman energy q of the weak magnetic field, which decreases with the increase of q.

Detection of single electron spin resonance in a double quantum dota)

NASA Astrophysics Data System (ADS)

Koppens, F. H. L.; Buizert, C.; Vink, I. T.; Nowack, K. C.; Meunier, T.; Kouwenhoven, L. P.; Vandersypen, L. M. K.

2007-04-01

Spin-dependent transport measurements through a double quantum dot are a valuable tool for detecting both the coherent evolution of the spin state of a single electron, as well as the hybridization of two-electron spin states. In this article, we discuss a model that describes the transport cycle in this regime, including the effects of an oscillating magnetic field (causing electron spin resonance) and the effective nuclear fields on the spin states in the two dots. We numerically calculate the current flow due to the induced spin flips via electron spin resonance, and we study the detector efficiency for a range of parameters. The experimental data are compared with the model and we find a reasonable agreement.

Modulating effect of new potential antimelanomic agents, spin-labeled triazenes and nitrosoureas on the DOPA-oxidase activity of tyrosinase.

PubMed

Gadjeva, V; Zheleva, A; Raikova, E

1999-07-01

The modulating effect of newly synthesized alkylating spin labeled triazene and spin labeled nitrosourea derivatives on the DOPA-oxidase activity of mushroom tyrosinase has been investigated by Bumett's spectrophotometric method (Burnett et al., 1967). All spin labeled triazenes have exhibited activating effect on DOPA-oxidase activity of tyrosinase, whereas clinically used triazene (DTIC), which does not contain nitroxide moiety, have showed inhibiting effect. At the same experimental conditions the spin labeled aminoacid nitrosoureas have showed dual effect - activating, in the beginning of the enzyme reaction and inhibiting later on. It is deduced that the activating effect of the spin labeled compounds is due to the nitroxide moiety and the inhibiting effect of all compounds depends on their half-life time. This study might contribute to make more clear the mechanism of action of the new compounds and on the other hand would come in quite useful as a preliminary prognosis for their antimelanomic activity.

Effect of asymmetric interface on charge and spin transport across two dimensional electron gas with Dresselhaus spin-orbit coupling/ferromagnet junction

NASA Astrophysics Data System (ADS)

Srisongmuang, B.; Pasanai, K.

2018-04-01

We theoretically studied the effect of interfacial scattering on the transport of charge and spin across the junction of a two-dimensional electron gas with Dresselhaus spin-orbit coupling and ferromagnetic material junction, via the conductance (G) and the spin-polarization of the conductance spectra (P) using the scattering method. At the interface, not only were the effects of spin-conserving (Z0) and spin-flip scattering (Zf) considered, but also the interfacial Rashba spin-orbit coupling scattering (ZRSOC) , which was caused by the asymmetry of the interface, was taken into account, and all of them were modeled by the delta potential. It was found that G was suppressed with increasing Z0 , as expected. Interestingly, a particular value of Zf can cause G and P to reach a maximum value. In particular, ZRSOC plays a crucial role to reduce G and P in the metallic limit, but its influence on the tunneling limit was quite weak. On the other hand, the effect of ZRSOC was diminished in the tunneling limit of the magnetic junction.

Understanding asteroid collisional history through experimental and numerical studies

NASA Technical Reports Server (NTRS)

Davis, Donald R.; Ryan, Eileen V.; Weidenschilling, S. J.

1991-01-01

Asteroids can lose angular momentum due to so called splash effect, the analog to the drain effect for cratering impacts. Numerical code with the splash effect incorporated was applied to study the simultaneous evolution of asteroid sized and spins. Results are presented on the spin changes of asteroids due to various physical effects that are incorporated in the described model. The goal was to understand the interplay between the evolution of sizes and spins over a wide and plausible range of model parameters. A single starting population was used both for size distribution and the spin distribution of asteroids and the changes in the spins were calculated over solar system history for different model parameters. It is shown that there is a strong coupling between the size and spin evolution, that the observed relative spindown of asteroids approximately 100 km diameter is likely to be the result of the angular momentum splash effect.

Understanding asteroid collisional history through experimental and numerical studies

NASA Astrophysics Data System (ADS)

Davis, Donald R.; Ryan, Eileen V.; Weidenschilling, S. J.

1991-06-01

Asteroids can lose angular momentum due to so called splash effect, the analog to the drain effect for cratering impacts. Numerical code with the splash effect incorporated was applied to study the simultaneous evolution of asteroid sized and spins. Results are presented on the spin changes of asteroids due to various physical effects that are incorporated in the described model. The goal was to understand the interplay between the evolution of sizes and spins over a wide and plausible range of model parameters. A single starting population was used both for size distribution and the spin distribution of asteroids and the changes in the spins were calculated over solar system history for different model parameters. It is shown that there is a strong coupling between the size and spin evolution, that the observed relative spindown of asteroids approximately 100 km diameter is likely to be the result of the angular momentum splash effect.

Thermal spin current generation and spin transport in Pt/magnetic-insulator/Py heterostructures

NASA Astrophysics Data System (ADS)

Chen, Ching-Tzu; Safranski, Christopher; Krivorotov, Ilya; Sun, Jonathan

Magnetic insulators can transmit spin current via magnon propagation while blocking charge current. Furthermore, under Joule heating, magnon flow as a result of the spin Seeback effect can generate additional spin current. Incorporating magnetic insulators in a spin-orbit torque magnetoresistive memory device can potentially yield high switching efficiencies. Here we report the DC magneto-transport studies of these two effects in Pt/magnetic-insulator/Py heterostructures, using ferrimagnetic CoFexOy (CFO) and antiferromagnet NiO as the model magnetic insulators. We observe the presence and absence of the inverse spin-Hall signals from the thermal spin current in Pt/CFO/Py and Pt/NiO/Py structures. These results are consistent with our spin-torque FMR linewidths in comparison. We will also report investigations into the magnetic field-angle dependence of these observations.

Optimal Charge-to-Spin Conversion in Graphene on Transition-Metal Dichalcogenides

NASA Astrophysics Data System (ADS)

Offidani, Manuel; Milletarı, Mirco; Raimondi, Roberto; Ferreira, Aires

2017-11-01

When graphene is placed on a monolayer of semiconducting transition metal dichalcogenide (TMD) its band structure develops rich spin textures due to proximity spin-orbital effects with interfacial breaking of inversion symmetry. In this work, we show that the characteristic spin winding of low-energy states in graphene on a TMD monolayer enables current-driven spin polarization, a phenomenon known as the inverse spin galvanic effect (ISGE). By introducing a proper figure of merit, we quantify the efficiency of charge-to-spin conversion and show it is close to unity when the Fermi level approaches the spin minority band. Remarkably, at high electronic density, even though subbands with opposite spin helicities are occupied, the efficiency decays only algebraically. The giant ISGE predicted for graphene on TMD monolayers is robust against disorder and remains large at room temperature.

The Enhancement of spin Hall torque efficiency and Reduction of Gilbert damping in spin Hall metal/normal metal/ferromagnetic trilayers

NASA Astrophysics Data System (ADS)

Nguyen, Minh-Hai; Pai, Chi-Feng; Ralph, Daniel C.; Buhrman, Robert A.

2015-03-01

The spin Hall effect (SHE) in ferromagnet/heavy metal bilayer structures has been demonstrated to be a powerful means for producing pure spin currents and for exerting spin-orbit damping-like and field-like torques on the ferromagnetic layer. Large spin Hall (SH) angles have been reported for Pt, beta-Ta and beta-W films and have been utilized to achieve magnetic switching of in-plane and out-of-plane magnetized nanomagnets, spin torque auto-oscillators, and the control of high velocity domain wall motion. For many of the proposed applications of the SHE it is also important to achieve an effective Gilbert damping parameter that is as low as possible. In general the spin orbit torques and the effective damping are predicted to depend directly on the spin-mixing conductance of the SH metal/ferromagnet interface. This opens up the possibility of tuning these properties with the insertion of a very thin layer of another metal between the SH metal and the ferromagnet. Here we will report on experiments with such trilayer structures in which we have observed both a large enhancement of the spin Hall torque efficiency and a significant reduction in the effective Gilbert damping. Our results indicate that there is considerable opportunity to optimize the effectiveness and energy efficiency of the damping-like torque through engineering of such trilayer structures. Supported in part by NSF and Samsung Electronics Corporation.

Antisymmetric Spin-Orbit Coupling in a d-p Model on a Zigzag Chain

DOE PAGES

Sugita, Yusuke; Hayami, Satoru; Motome, Yukitoshi

2015-12-29

In this paper, we theoretically investigate how an antisymmetric spin-orbit coupling emerges in electrons moving on lattice structures which are centrosymmetric but break the spatial inversion symme- try at atomic positions. We construct an effective d-p model on the simplest lattice structure, a zigzag chain of edge-sharing octahedra, with taking into account the crystalline electric field, the spin-orbit coupling, and on-site and inter-site d-p hybridizations. We show that an effective antisymmetric spin-orbit coupling arises in the sublattice-dependent form, which results in a hidden spin polarization in the band structure. Finally, we explicitly derive the effective antisymmetric spin-orbit coupling for dmore » electrons, which not only explains the hidden spin polarization but also indicates how to enhance it.« less

Antisymmetric Spin-Orbit Coupling in a d-p Model on a Zigzag Chain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugita, Yusuke; Hayami, Satoru; Motome, Yukitoshi

In this paper, we theoretically investigate how an antisymmetric spin-orbit coupling emerges in electrons moving on lattice structures which are centrosymmetric but break the spatial inversion symme- try at atomic positions. We construct an effective d-p model on the simplest lattice structure, a zigzag chain of edge-sharing octahedra, with taking into account the crystalline electric field, the spin-orbit coupling, and on-site and inter-site d-p hybridizations. We show that an effective antisymmetric spin-orbit coupling arises in the sublattice-dependent form, which results in a hidden spin polarization in the band structure. Finally, we explicitly derive the effective antisymmetric spin-orbit coupling for dmore » electrons, which not only explains the hidden spin polarization but also indicates how to enhance it.« less

Unambiguous separation of the inverse spin Hall and anomalous Nernst effects within a ferromagnetic metal using the spin Seebeck effect

DOE PAGES

Wu, Stephen M.; Hoffman, Jason; Pearson, John E.; ...

2014-09-05

In this paper, the longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe 3O 4 with the ferromagnetic metal Co 0.2Fe 0.6B 0.2 (CoFeB) as the spin detector. By using a non-magnetic spacer material between the two materials (Ti), it is possible to decouple the two ferromagnetic materials and directly observe pure spin flow from Fe 3O 4 into CoFeB. It is shown that in a single ferromagnetic metal, the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur simultaneously with opposite polarity. Using this and the large difference in the coercive fields between themore » two magnets, it is possible to unambiguously separate the contributions of the spin Seebeck effect from the ANE and observe the degree to which each effect contributes to the total response. Finally, these experiments show conclusively that the ISHE and ANE in CoFeB are separate phenomena with different origins and can coexist in the same material with opposite response to a thermal gradient.« less

Unambiguous separation of the inverse spin Hall and anomalous Nernst effects within a ferromagnetic metal using the spin Seebeck effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Stephen M., E-mail: swu@anl.gov; Hoffman, Jason; Pearson, John E.

2014-09-01

The longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe{sub 3}O{sub 4} with the ferromagnetic metal Co{sub 0.2}Fe{sub 0.6}B{sub 0.2} (CoFeB) as the spin detector. By using a non-magnetic spacer material between the two materials (Ti), it is possible to decouple the two ferromagnetic materials and directly observe pure spin flow from Fe{sub 3}O{sub 4} into CoFeB. It is shown that in a single ferromagnetic metal, the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur simultaneously with opposite polarity. Using this and the large difference in the coercive fields between the two magnets, itmore » is possible to unambiguously separate the contributions of the spin Seebeck effect from the ANE and observe the degree to which each effect contributes to the total response. These experiments show conclusively that the ISHE and ANE in CoFeB are separate phenomena with different origins and can coexist in the same material with opposite response to a thermal gradient.« less

Generation and detection of dissipationless spin current in a MgO/Si bilayer

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

Spintronics is an analogue to electronics where the spin of the electron rather than its charge is functionally controlled for devices. The generation and detection of spin current without ferromagnetic or exotic/scarce materials are two of the biggest challenges for spintronics devices. In this study, we report a solution to the two problems of spin current generation and detection in Si. Using non-local measurement, we experimentally demonstrate the generation of helical dissipationless spin current using the spin-Hall effect. Contrary to the theoretical prediction, we observe the spin-Hall effect in both n-doped and p-doped Si. The helical spin current is attributed to the site-inversion asymmetry of the diamond cubic lattice of Si and structure inversion asymmetry in a MgO/Si bilayer. The spin to charge conversion in Si is insignificant due to weak spin-orbit coupling. For the efficient detection of spin current, we report spin to charge conversion at the MgO (1 nm)/Si (2 µm) (p-doped and n-doped) thin film interface due to Rashba spin-orbit coupling. We detected the spin current at a distance of  >100 µm, which is an order of magnitude larger than the longest spin diffusion length measured using spin injection techniques. The existence of spin current in Si is verified from the coercivity reduction in a Co/Pd multilayer due to spin-orbit torque generated by spin current from Si.

Nuclear spin dependence of time reversal invariance violating effects in neutron scattering

NASA Astrophysics Data System (ADS)

Gudkov, Vladimir; Shimizu, Hirohiko M.

2018-06-01

The spin structure of parity violating and time reversal invariance violating effects in neutron scattering is discussed. The explicit relations between these effects are presented in terms of functions nuclear spins and neutron partial widths of p -wave resonances.

Free radical scavenging activities measured by electron spin resonance spectroscopy and B16 cell antiproliferative behaviors of seven plants.

PubMed

Calliste, C A; Trouillas, P; Allais, D P; Simon, A; Duroux, J L

2001-07-01

In an effort to discover new antioxidant natural compounds, seven plants that grow in France (most of them in the Limousin countryside) were screened. Among these plants, was the extensively studied Vitis vinifera as reference. For each plant, sequential percolation was realized with five solvents of increasing polarities (hexane, chloroform, ethyl acetate, methanol, and water). Free radical scavenging activities were examined in different systems using electron spin resonance (ESR) spectroscopy. These assays were based on the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH), the hydroxyl radicals generated by a Fenton reaction, and the superoxide radicals generated by the X/XO system. Antiproliferative behavior was studied on B16 melanoma cells. ESR results showed that three plants (Castanea sativa, Filipendula ulmaria, and Betula pendula) possessed, for the most polar fractions (presence of phenolic compounds), high antioxidant activities in comparison with the Vitis vinifera reference. Gentiana lutea was the only one that presented a hydroxyl scavenging activity for the ethyl acetate and chloroform fractions. The antiproliferative test results showed that the same three plants are the most effective, but for the apolar fractions (chloroform and hexane).

Full superconducting dome of strong Ising protection in gated monolayer WS2.

PubMed

Lu, Jianming; Zheliuk, Oleksandr; Chen, Qihong; Leermakers, Inge; Hussey, Nigel E; Zeitler, Uli; Ye, Jianting

2018-04-03

Many recent studies show that superconductivity not only exists in atomically thin monolayers but can exhibit enhanced properties such as a higher transition temperature and a stronger critical field. Nevertheless, besides being unstable in air, the weak tunability in these intrinsically metallic monolayers has limited the exploration of monolayer superconductivity, hindering their potential in electronic applications (e.g., superconductor-semiconductor hybrid devices). Here we show that using field effect gating, we can induce superconductivity in monolayer WS 2 grown by chemical vapor deposition, a typical ambient-stable semiconducting transition metal dichalcogenide (TMD), and we are able to access a complete set of competing electronic phases over an unprecedented doping range from band insulator, superconductor, to a reentrant insulator at high doping. Throughout the superconducting dome, the Cooper pair spin is pinned by a strong internal spin-orbit interaction, making this material arguably the most resilient superconductor in the external magnetic field. The reentrant insulating state at positive high gating voltages is attributed to localization induced by the characteristically weak screening of the monolayer, providing insight into many dome-like superconducting phases observed in field-induced quasi-2D superconductors.

Separation of spin Seebeck effect and anomalous Nernst effect in Co/Cu/YIG

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Dai; State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433; Li, Yufan

2015-05-25

The spin Seebeck effect (SSE) and Anomalous Nernst effect (ANE) have been observed in Co/Cu/YIG (yttrium iron garnet) multi-layer structure, where the ferromagnetic insulator YIG acts as the pure spin injector and the ferromagnetic metal Co layer acts as the spin current detector. With the insertion of 5 nm Cu layer, the two ferromagnetic layers are decoupled, thus allowing unambiguous separation of the SSE and ANE contributions under the same experimental conditions in the same sample.

Separation of spin Seebeck effect and anomalous Nernst effect in Co/Cu/YIG

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Dai; Li, Yufan; Qu, D.

2015-05-25

The spin Seebeck effect (SSE) and Anomalous Nernst effect (ANE) have been observed in Co/Cu/YIG (yttrium iron garnet) multi-layer structure, where the ferromagnetic insulator YIG acts as the pure spin injector and the ferromagnetic metal Co layer acts as the spin current detector. With the insertion of 5 nm Cu layer, the two ferromagnetic layers are decoupled, thus allowing unambiguous separation of the SSE and ANE contributions under the same experimental conditions in the same sample.

Spin transport in lateral structures with semiconducting channel

NASA Astrophysics Data System (ADS)

Zainuddin, Abu Naser

Spintronics is an emerging field of electronics with the potential to be used in future integrated circuits. Spintronic devices are already making their mark in storage technologies in recent times and there are proposals for using spintronic effects in logic technologies as well. So far, major improvement in spintronic effects, for example, the `spin-valve' effect, is being achieved in metals or insulators as channel materials. But not much progress is made in semiconductors owing to the difficulty in injecting spins into them, which has only very recently been overcome with the combined efforts of many research groups around the world. The key motivations for semiconductor spintronics are their ease in integration with the existing semiconductor technology along with the gate controllability. At present semiconductor based spintronic devices are mostly lateral and are showing a very poor performance compared to their metal or insulator based vertical counterparts. The objective of this thesis is to analyze these devices based on spin-transport models and simulations. At first a lateral spin-valve device is modeled with the spin-diffusion equation based semiclassical approach. Identifying the important issues regarding the device performance, a compact circuit equivalent model is presented which would help to improve the device design. It is found that the regions outside the current path also have a significant influence on the device performance under certain conditions, which is ordinarily neglected when only charge transport is considered. Next, a modified spin-valve structure is studied where the spin signal is controlled with a gate in between the injecting and detecting contacts. The gate is used to modulate the rashba spin-orbit coupling of the channel which, in turn, modulates the spin-valve signal. The idea of gate controlled spin manipulation was originally proposed by Datta and Das back in 1990 and is called 'Datta-Das' effect. In this thesis, we have extended the model described in the original proposal to include the influence of channel dimensions on the nature of electron flow and the contact dimensions on the magnitude and phase of the spin-valve signal. In order to capture the spin-orbit effect a non-equilibrium Green's function (NEGF) based quantum transport model for spin-valve device have been developed which is also explained with simple theoretical treatment based on stationary phase approximation. The model is also compared against a recent experiment that demonstrated such gate modulated spin-valve effect. This thesis also evaluates the possibility of gate controlled magnetization reversal or spin-torque effect as a means to validate this, so called, 'Datta-Das' effect on a more solid footing. Finally, the scope for utilizing topological insulator material in semiconductor spintronics is discussed as a possible future work for this thesis.

Physics and application of persistent spin helix state in semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Kohda, Makoto; Salis, Gian

2017-07-01

In order to utilize the spin degree of freedom in semiconductors, control of spin states and transfer of the spin information are fundamental requirements for future spintronic devices and quantum computing. Spin orbit (SO) interaction generates an effective magnetic field for moving electrons and enables spin generation, spin manipulation and spin detection without using external magnetic field and magnetic materials. However, spin relaxation also takes place due to a momentum dependent SO-induced effective magnetic field. As a result, SO interaction is considered to be a double-edged sword facilitating spin control but preventing spin transport over long distances. The persistent spin helix (PSH) state solves this problem since uniaxial alignment of the SO field with SU(2) symmetry enables the suppression of spin relaxation while spin precession can still be controlled. Consequently, understanding the PSH becomes an important step towards future spintronic technologies for classical and quantum applications. Here, we review recent progress of PSH in semiconductor heterostructures and its device application. Fundamental physics of SO interaction and the conditions of a PSH state in semiconductor heterostructures are discussed. We introduce experimental techniques to observe a PSH and explain both optical and electrical measurements for detecting a long spin relaxation time and the formation of a helical spin texture. After emphasizing the bulk Dresselhaus SO coefficient γ, the application of PSH states for spin transistors and logic circuits are discussed.

Nonlinear spin current generation in noncentrosymmetric spin-orbit coupled systems

NASA Astrophysics Data System (ADS)

Hamamoto, Keita; Ezawa, Motohiko; Kim, Kun Woo; Morimoto, Takahiro; Nagaosa, Naoto

2017-06-01

Spin current plays a central role in spintronics. In particular, finding more efficient ways to generate spin current has been an important issue and has been studied actively. For example, representative methods of spin-current generation include spin-polarized current injections from ferromagnetic metals, the spin Hall effect, and the spin battery. Here, we theoretically propose a mechanism of spin-current generation based on nonlinear phenomena. By using Boltzmann transport theory, we show that a simple application of the electric field E induces spin current proportional to E2 in noncentrosymmetric spin-orbit coupled systems. We demonstrate that the nonlinear spin current of the proposed mechanism is supported in the surface state of three-dimensional topological insulators and two-dimensional semiconductors with the Rashba and/or Dresselhaus interaction. In the latter case, the angular dependence of the nonlinear spin current can be manipulated by the direction of the electric field and by the ratio of the Rashba and Dresselhaus interactions. We find that the magnitude of the spin current largely exceeds those in the previous methods for a reasonable magnitude of the electric field. Furthermore, we show that application of ac electric fields (e.g., terahertz light) leads to the rectifying effect of the spin current, where dc spin current is generated. These findings will pave a route to manipulate the spin current in noncentrosymmetric crystals.

Effect of capping layer on spin-orbit torques

NASA Astrophysics Data System (ADS)

Sun, Chi; Siu, Zhuo Bin; Tan, Seng Ghee; Yang, Hyunsoo; Jalil, Mansoor B. A.

2018-04-01

In order to enhance the magnitude of spin-orbit torque (SOT), considerable experimental works have been devoted to studying the thickness dependence of the different layers in multilayers consisting of heavy metal (HM), ferromagnet (FM), and capping layers. Here, we present a theoretical model based on the spin-drift-diffusion formalism to investigate the effect of the capping layer properties such as its thickness on the SOT observed in experiments. It is found that the spin Hall-induced SOT can be significantly enhanced by incorporating a capping layer with an opposite spin Hall angle to that of the HM layer. The spin Hall torque can be maximized by tuning the capping layer thickness. However, in the absence of the spin Hall effect (SHE) in the capping layer, the torque decreases monotonically with the capping layer thickness. Conversely, the spin Hall torque is found to decrease monotonically with the FM layer thickness, irrespective of the presence or absence of the SHE in the capping layer. All these trends are in correspondence with experimental observations. Finally, our model suggests that capping layers with a long spin diffusion length and high resistivity would also enhance the spin Hall torque.

Proton transport through aqueous Nafion membrane

NASA Astrophysics Data System (ADS)

Son, D. N.; Kasai, H.

2009-08-01

We introduce a new model for proton transport through a single proton-conducting channel of an aqueous Nafion membrane based on a mechanism in which protons move under electrostatic effect provided by the sulfonate ( SO3 -groups of the Nafion side chains, the spin effect of active components, the hydrogen bonding effect with water molecules, and the screening effect of water media. This model can describe the proton transport within various levels of humidification ranging from the low humidity to the high humidity as a function of operating temperature. At low humidity, this model approaches to the so-called surface mechanism, while at high humidity, it approaches the well-known Grotthuss one. Proton motion is considered as the transfer from cluster to cluster under a potential energy. A proton-proton interaction is comprised in the calculation. Using Green function method, we obtained the proton current as a function of the Nafion membrane temperature. We found that the lower the temperature, the higher the proton current transfer through the Nafion membrane in low temperatures compared to the critical point 10K, which separates magnetic regime from non-magnetic regime. The increasing of proton current at very low temperatures is attributed to the spin effect. As the membrane temperature is higher than 40 ° C , the decreasing of proton current is attributed to the loss of water uptake and the polymer contraction. The results of this study are qualitatively in good agreement with experiments. The expression for the critical temperature is also presented as a function of structural and tunable parameters, and interpreted by experimental data. in here

Theory of in-plane current induced spin torque in metal/ferromagnet bilayers

NASA Astrophysics Data System (ADS)

Sakanashi, Kohei; Sigrist, Manfred; Chen, Wei

2018-05-01

Using a semiclassical approach that simultaneously incorporates the spin Hall effect (SHE), spin diffusion, quantum well states, and interface spin–orbit coupling (SOC), we address the interplay of these mechanisms as the origin of the spin–orbit torque (SOT) induced by in-plane currents, as observed in the normal metal/ferromagnetic metal bilayer thin films. Focusing on the bilayers with a ferromagnet much thinner than its spin diffusion length, such as Pt/Co with  ∼10 nm thickness, our approach addresses simultaneously the two contributions to the SOT, namely the spin-transfer torque (SHE-STT) due to SHE-induced spin injection, and the inverse spin Galvanic effect spin–orbit torque (ISGE-SOT) due to SOC-induced spin accumulation. The SOC produces an effective magnetic field at the interface, hence it modifies the angular momentum conservation expected for the SHE-STT. The SHE-induced spin voltage and the interface spin current are mutually dependent and, hence, are solved in a self-consistent manner. The result suggests that the SHE-STT and ISGE-SOT are of the same order of magnitude, and the spin transport mediated by the quantum well states may be an important mechanism for the experimentally observed rapid variation of the SOT with respect to the thickness of the ferromagnet.

Distinguishing spin-aligned and isotropic black hole populations with gravitational waves.

PubMed

Farr, Will M; Stevenson, Simon; Miller, M Coleman; Mandel, Ilya; Farr, Ben; Vecchio, Alberto

2017-08-23

The direct detection of gravitational waves from merging binary black holes opens up a window into the environments in which binary black holes form. One signature of such environments is the angular distribution of the black hole spins. Binary systems that formed through dynamical interactions between already-compact objects are expected to have isotropic spin orientations (that is, the spins of the black holes are randomly oriented with respect to the orbit of the binary system), whereas those that formed from pairs of stars born together are more likely to have spins that are preferentially aligned with the orbit. The best-measured combination of spin parameters for each of the four likely binary black hole detections GW150914, LVT151012, GW151226 and GW170104 is the 'effective' spin. Here we report that, if the magnitudes of the black hole spins are allowed to extend to high values, the effective spins for these systems indicate a 0.015 odds ratio against an aligned angular distribution compared to an isotropic one. When considering the effect of ten additional detections, this odds ratio decreases to 2.9 × 10 -7 against alignment. The existing preference for either an isotropic spin distribution or low spin magnitudes for the observed systems will be confirmed (or overturned) confidently in the near future.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haidar, S. M., E-mail: haidar@imr.tohoku.ac.jp; Iguchi, R.; Yagmur, A.

We have investigated dc voltage generation induced by ferromagnetic resonance in a Co{sub 75}Fe{sub 25}/Pt film. In order to reduce rectification effects of anisotropic magnetoresistance and the planar Hall effect, which may be observed simultaneously with the inverse spin Hall effect, we selected Co{sub 75}Fe{sub 25} with extremely small anisotropic magnetoresistance as a spin injector. Using the difference in the spectral shape of voltage and in the angle dependence of in-plane magnetization among the effects, we demonstrated that the generated dc voltage is governed by the inverse spin Hall effect induced by spin pumping.

Coalescence of two spinning black holes: An effective one-body approach

NASA Astrophysics Data System (ADS)

Damour, Thibault

2001-12-01

We generalize to the case of spinning black holes a recently introduced ``effective one-body'' approach to the general relativistic dynamics of binary systems. We show how to approximately map the conservative part of the third post-Newtonian (3PN) dynamics of two spinning black holes of masses m1, m2 and spins S1, S2 onto the dynamics of a non-spinning particle of mass μ≡m1m2/(m1+m2) in a certain effective metric geffμν(xλM,ν,a) which can be viewed either as a spin deformation [with the deformation parameter a≡Seff/M] of the recently constructed 3PN effective metric geffμν(xλM,ν), or as a ν deformation [with the comparable-mass deformation parameter ν≡m1m2/(m1+m2)2] of a Kerr metric of mass M≡m1+m2 and (effective) spin Seff≡[1+3m2/(4m1)]S1+[1+3m1/(4m2)]S2. The combination of the effective one-body approach, and of a Padé definition of the crucial effective radial functions, is shown to define a dynamics with much improved post-Newtonian convergence properties, even for black hole separations of the order of 6 GM/c2. The complete (conservative) phase-space evolution equations of binary spinning black hole systems are written down and their exact and approximate first integrals are discussed. This leads to the approximate existence of a two-parameter family of ``spherical orbits'' (with constant radius), and of a corresponding one-parameter family of ``last stable spherical orbits'' (LSSO). These orbits are of special interest for forthcoming LIGO-VIRGO-GEO gravitational wave observations. The binding energy and total angular momentum of LSSO's are studied in some detail. It is argued that for most (but not all) of the parameter space of two spinning holes the approximate (leading-order) effective one-body approach introduced here gives a reliable analytical tool for describing the dynamics of the last orbits before coalescence. This tool predicts, in a quantitative way, how certain spin orientations increase the binding energy of the LSSO. This leads to a detection bias, in LIGO-VIRGO-GEO observations, favoring spinning black hole systems, and makes it urgent to complete the conservative effective one-body dynamics given here by adding (resummed) radiation reaction effects, and by constructing gravitational waveform templates that include spin effects. Finally, our approach predicts that the spin of the final hole formed by the coalescence of two arbitrarily spinning holes never approaches extremality.

Assessment of bilayer silicene to probe as quantum spin and valley Hall effect

NASA Astrophysics Data System (ADS)

Rehman, Majeed Ur; Qiao, Zhenhua

2018-02-01

Silicene takes precedence over graphene due to its buckling type structure and strong spin orbit coupling. Motivated by these properties, we study the silicene bilayer in the presence of applied perpendicular electric field and intrinsic spin orbit coupling to probe as quantum spin/valley Hall effect. Using analytical approach, we calculate the spin Chern-number of bilayer silicene and then compare it with monolayer silicene. We reveal that bilayer silicene hosts double spin Chern-number as compared to single layer silicene and therefore accordingly has twice as many edge states in contrast to single layer silicene. In addition, we investigate the combined effect of intrinsic spin orbit coupling and the external electric field, we find that bilayer silicene, likewise single layer silicene, goes through a phase transitions from a quantum spin Hall state to a quantum valley Hall state when the strength of the applied electric field exceeds the intrinsic spin orbit coupling strength. We believe that the results and outcomes obtained for bilayer silicene are experimentally more accessible as compared to bilayer graphene, because of strong SO coupling in bilayer silicene.

Non-perturbative calculation of orbital and spin effects in molecules subject to non-uniform magnetic fields

NASA Astrophysics Data System (ADS)

Sen, Sangita; Tellgren, Erik I.

2018-05-01

External non-uniform magnetic fields acting on molecules induce non-collinear spin densities and spin-symmetry breaking. This necessitates a general two-component Pauli spinor representation. In this paper, we report the implementation of a general Hartree-Fock method, without any spin constraints, for non-perturbative calculations with finite non-uniform fields. London atomic orbitals are used to ensure faster basis convergence as well as invariance under constant gauge shifts of the magnetic vector potential. The implementation has been applied to investigate the joint orbital and spin response to a field gradient—quantified through the anapole moments—of a set of small molecules. The relative contributions of orbital and spin-Zeeman interaction terms have been studied both theoretically and computationally. Spin effects are stronger and show a general paramagnetic behavior for closed shell molecules while orbital effects can have either direction. Basis set convergence and size effects of anapole susceptibility tensors have been reported. The relation of the mixed anapole susceptibility tensor to chirality is also demonstrated.

Coriolis effect in optics: unified geometric phase and spin-Hall effect.

PubMed

Bliokh, Konstantin Y; Gorodetski, Yuri; Kleiner, Vladimir; Hasman, Erez

2008-07-18

We examine the spin-orbit coupling effects that appear when a wave carrying intrinsic angular momentum interacts with a medium. The Berry phase is shown to be a manifestation of the Coriolis effect in a noninertial reference frame attached to the wave. In the most general case, when both the direction of propagation and the state of the wave are varied, the phase is given by a simple expression that unifies the spin redirection Berry phase and the Pancharatnam-Berry phase. The theory is supported by the experiment demonstrating the spin-orbit coupling of electromagnetic waves via a surface plasmon nanostructure. The measurements verify the unified geometric phase, demonstrated by the observed polarization-dependent shift (spin-Hall effect) of the waves.

Modulated spin orbit torque in a Pt/Co/Pt/YIG multilayer by nonequilibrium proximity effect

NASA Astrophysics Data System (ADS)

Liu, Q. B.; Meng, K. K.; Cai, Y. Z.; Qian, X. H.; Wu, Y. C.; Zheng, S. Q.; Jiang, Y.

2018-01-01

We have compared the spin orbit torque (SOT) induced magnetization switching in Pt/Co/Pt/Y3Fe5O12 (YIG) and Pt/Co/Pt/SiO2 multilayers. The critical switching current in Pt/Co/Pt/YIG is almost half of that in Pt/Co/Pt/SiO2. Through harmonic measurements, we demonstrated the enhancement of the effective spin Hall angle in Pt/Co/Pt/YIG. The increased efficiency of SOT is ascribed to the nonequilibrium proximity effect at the Pt/YIG interface, which suppresses the spin current reflection and enhances the effective spin accumulation at the Co/Pt interface. Our method can effectively reduce the switching current density and provide another way to modulate SOT.

Time-domain detection of current controlled magnetization damping in Pt/Ni{sub 81}Fe{sub 19} bilayer and determination of Pt spin Hall angle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ganguly, A.; Haldar, A.; Sinha, J.

2014-09-15

The effect of spin torque from the spin Hall effect in Pt/Ni{sub 81}Fe{sub 19} rectangular bilayer film was investigated using time-resolved magneto-optical Kerr microscopy. Current flow through the stack resulted in a linear variation of effective damping up to ±7%, attributed to spin current injection from the Pt into the Ni{sub 81}Fe{sub 19}. The spin Hall angle of Pt was estimated as 0.11 ± 0.03. The modulation of the damping depended on the angle between the current and the bias magnetic field. These results demonstrate the importance of optical detection of precessional magnetization dynamics for studying spin transfer torque due to spinmore » Hall effect.« less

Free-Spinning-Tunnel Investigation of a 0.034-Scale Model of the Production Version of the Chance Vought F7U-3 Airplane, TED No. NACA AD 3103

NASA Technical Reports Server (NTRS)

Klinar, Walter J.; Healy, Frederick M.

1955-01-01

An investigation of a 0.034-scale model of the production version of the Chance Vought F7U-3 airplane has been conducted in the Langley 20-foot free-spinning tunnel. The inverted and erect spin and recovery characteristics of the model were determined for the combat loading with the model in the clean condition and the effect of extending slats was investigated. A brief investigation of pilot ejection was also performed. The results indicate that the inverted spin-recovery characteristics of the airplane will be satisfactory by full rudder reversal. If the rudders can only be neutralized because of high pedal forces in the inverted spins, satisfactory recovery will be obtained if the auxiliary rudders can be moved to neutral or against the spin provided the stick is held full forward. Optimum control technique for satisfactory recovery from erect spins will be full rudder reversal in conjunction with aileron movement to full with the spin (stick right in a right spin). Extension of the slats will have a slightly adverse effect on recoveries from (1 inverted spins but will have a favorable effect on recoveries from erect spins. The results of brief tests indicate that if a pilot is ejected during a spin while a spin-recovery parachute is extended and fully inflated, he will probably clear the tail parachute.

The enhanced spin-polarized transport behaviors through cobalt benzene-porphyrin-benzene molecular junctions: the effect of functional groups

NASA Astrophysics Data System (ADS)

Cheng, Jue-Fei; Zhou, Liping; Wen, Zhongqian; Yan, Qiang; Han, Qin; Gao, Lei

2017-05-01

The modification effects of the groups amino (NH2) and nitro (NO2) on the spin polarized transport properties of the cobalt benzene-porphyrin-benzene (Co-BPB) molecule coupled to gold (Au) nanowire electrodes are investigated by the nonequilibrium Green’s function method combined with the density functional theory. The calculation results show that functional groups can lead to the significant spin-filter effect, enhanced low-bias negative differential resistance (NDR) behavior and novel reverse rectifying effect in Co-BPB molecular junction. The locations and types of functional groups have distinct influences on spin-polarized transport performances. The configuration with NH2 group substituting H atom in central porphyrin ring has larger spin-down current compared to that with NO2 substitution. And Co-BPB molecule junction with NH2 group substituting H atom in side benzene ring shows reverse rectifying effect. Detailed analyses confirm that NH2 and NO2 group substitution change the spin-polarized transferred charge, which makes the highest occupied molecular orbitals (HOMO) of spin-down channel of Co-BPB closer to the Fermi level. And the shift of HOMO strengthens the spin-polarized coupling between the molecular orbitals and the electrodes, leading to the enhanced spin-polarized behavior. Our findings might be useful in the design of multi-functional molecular devices in the future.

Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB6

PubMed Central

Song, Qi; Mi, Jian; Zhao, Dan; Su, Tang; Yuan, Wei; Xing, Wenyu; Chen, Yangyang; Wang, Tianyu; Wu, Tao; Chen, Xian Hui; Xie, X. C.; Zhang, Chi; Shi, Jing; Han, Wei

2016-01-01

There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin–momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observe the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Furthermore, the magnetic field angle dependence of the spin signal is consistent with spin–momentum locking property of surface states of SmB6. PMID:27834378

Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB 6

DOE PAGES

Song, Qi; Mi, Jian; Zhao, Dan; ...

2016-11-11

There has been considerable interest in exploiting the spin degrees of freedom of electrons for potential information storage and computing technologies. Topological insulators (TIs), a class of quantum materials, have special gapless edge/surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction. This spin–momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, the spin injection in pure surface states of TI is very challenging because of the coexistence of the highly conducting bulk states. Here, we experimentally demonstrate the spin injection and observemore » the inverse Edelstein effect in the surface states of a topological Kondo insulator, SmB 6. At low temperatures when only surface carriers are present, a clear spin signal is observed. Moreover, the magnetic field angle dependence of the spin signal is consistent with spin–momentum locking property of surface states of SmB6.« less

Relativistic effects on the bonding and properties of the hydrides of platinum

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.

1993-01-01

The ground state of PtH2 and several low-lying states of PtH(+) and PtH have been studied at the all-electron self-consistent-field level of theory to examine the importance of relativistic effects. The results of calculations based on Dirac-Hartree-Fock theory, nonrelativistic theory, and the spin-free no-pair relativistic approximation of Hess are compared to separate the effects of the spin-free terms and the spin-orbit terms of the Hamiltonian on the relativistic corrections to the molecular properties. Comparison is also made between first-order perturbation theory including the one-electron spin-free terms and the method of Hess to determine the size of effects beyond first order. It is found that the spin-orbit interaction significantly affects the properties and energetics of these molecules because of the participation of the Pt 5d orbitals in the bonding, and that effects beyond first order in perturbation theory are large. Any treatment of Pt compounds will have to include both the spin-free and spin-orbit interactions for an accurate description.

Magnetoelectric Effect in a Spin-State Transition System

NASA Astrophysics Data System (ADS)

Naka, Makoto; Mizoguchi, Eriko; Nasu, Joji; Ishihara, Sumio

2018-06-01

Magnetic, dielectric, and magnetoelectric properties in a spin-state transition system are examined, motivated by the recent discovery of multiferroic behavior in a cobalt oxide. We construct an effective model Hamiltonian on the basis of the two-orbital Hubbard model, in which the spin-state degrees of freedom in magnetic ions couple with ferroelectric-type lattice distortions. A phase transition occurs from the high-temperature low-spin phase to the low-temperature high-spin ferroelectric phase with an accompanying increase in spin entropy. The calculated results are consistent with the experimental pressure-temperature phase diagram. We predict the magnetic-field induced electric polarization in the low-spin paraelectric phase near the ferroelectric phase boundary.

Effect of inertia properties on attitude stability of nonrigid spin-stabilized spacecraft

NASA Technical Reports Server (NTRS)

Lang, W. E.; Young, J. P.

1974-01-01

The phenomenon of energy dissipation in spinning spacecraft is discussed with particular reference to its dependence on spacecraft inertia properties. Specific dissipation mechanisms are identified. The effect of external environmental factors on spin stability is also discussed. Generalized curves are presented relating system stability to the principal inertia ratio for various forms of energy dissipation. Dual-spin systems and the effect of lateral inertia asymmetry are also reviewed.

TMRG studies on spin alignment in molecule-based ferrimagnetics [rapid communication

NASA Astrophysics Data System (ADS)

Liu, Q. M.; Yao, K. L.; Liu, Z. L.

2005-05-01

A physical picture of spin alignment in organic molecule-based ferrimagnets is presented from studying the thermal effective magnetic moment of the sublattice by use of the transfer matrix renormalization group. We conclude that the classical antiparallel spin alignment is not the most stable state. The three-spin system tends to parallel alignment when the exchange interaction between the biradical and the monoradical molecules is much weaker than that within the biradical, which can result in the decrease of the effective magnetic moment upon lowering the temperature. More importantly, we give the theoretical evidence that even the antiparallel spin alignment in the biradical monoradical alternating chain does not necessarily lead to ferrimagnetic spin ordering due to the formation of the spin singlet pairs, which suppresses the ferrimagnetic spin alignment.

Orbital and spin dynamics of intraband electrons in quantum rings driven by twisted light.

PubMed

Quinteiro, G F; Tamborenea, P I; Berakdar, J

2011-12-19

We theoretically investigate the effect that twisted light has on the orbital and spin dynamics of electrons in quantum rings possessing sizable Rashba spin-orbit interaction. The system Hamiltonian for such a strongly inhomogeneous light field exhibits terms which induce both spin-conserving and spin-flip processes. We analyze the dynamics in terms of the perturbation introduced by a weak light field on the Rasha electronic states, and describe the effects that the orbital angular momentum as well as the inhomogeneous character of the beam have on the orbital and the spin dynamics.

Optical pumping of electron and nuclear spin in a negatively-charged quantum dot

NASA Astrophysics Data System (ADS)

Bracker, Allan; Gershoni, David; Korenev, Vladimir

2005-03-01

We report optical pumping of electron and nuclear spins in an individual negatively-charged quantum dot. With a bias-controlled heterostructure, we inject one electron into the quantum dot. Intense laser excitation produces negative photoluminescence polarization, which is easily erased by the Hanle effect, demonstrating optical pumping of a long-lived resident electron. The electron spin lifetime is consistent with the influence of nuclear spin fluctuations. Measuring the Overhauser effect in high magnetic fields, we observe a high degree of nuclear spin polarization, which is closely correlated to electron spin pumping.

Nuclear spin nanomagnet in an optically excited quantum dot.

PubMed

Korenev, V L

2007-12-21

Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins-the nuclear spin nanomagnet.

Antiferromagnetic domain wall as spin wave polarizer

NASA Astrophysics Data System (ADS)

Lan, Jin; Yu, Weichao; Xiao, Jiang

Spin waves are collective excitations of local magnetizations that can effectively propagate information even in magnetic insulators. In antiferromagnet, spin waves are endowed with additional polarization freedom. Here we propose that the antiferromagnetic domain wall can act as a spin wave polarizer, which perfectly passes one linearly polarized spin wave while substantially reflects the perpendicular one. We show that the polarizing effect lies in the suppression of one linear polarization inside domain wall, in close analogy to the wire-grid optical polarizer. Our finding opens up new possibilities in magnonic processing by harnessing spin wave polarization in antiferromagnet.

Effect of electron spin-spin interaction on level crossings and spin flips in a spin-triplet system

NASA Astrophysics Data System (ADS)

Jia, Wei; Hu, Fang-Qi; Wu, Ning; Zhao, Qing

2017-12-01

We study level crossings and spin flips in a system consisting of a spin-1 (an electron spin triplet) coupled to a nuclear spin of arbitrary size K , in the presence of a uniform magnetic field and the electron spin-spin interaction within the triplet. Through an analytical diagonalization based on the SU (3 ) Lie algebra, we find that the electron spin-spin interaction not only removes the curious degeneracy which appears in the absence of the interaction, but also produces some level anticrossings (LACs) for strong interactions. The real-time dynamics of the system shows that periodic spin flips occur at the LACs for arbitrary K , which might provide an option for nuclear or electron spin polarization.

Resonant spin Hall effect in two dimensional electron gas

NASA Astrophysics Data System (ADS)

Shen, Shun-Qing

2005-03-01

Remarkable phenomena have been observed in 2DEG over last two decades, most notably, the discovery of integer and fractional quantum Hall effect. The study of spin transport provides a good opportunity to explore spin physics in two-dimensional electron gas (2DEG) with spin-orbit coupling and other interaction. It is already known that the spin-orbit coupling leads to a zero-field spin splitting, and competes with the Zeeman spin splitting if the system is subjected to a magnetic field perpendicular to the plane of 2DEG. The result can be detected as beating of the Shubnikov-de Haas oscillation. Very recently the speaker and his collaborators studied transport properties of a two-dimensional electron system with Rashba spin-orbit coupling in a perpendicular magnetic field. The spin-orbit coupling competes with the Zeeman splitting to generate additional degeneracies between different Landau levels at certain magnetic fields. It is predicted theoretically that this degeneracy, if occurring at the Fermi level, gives rise to a resonant spin Hall conductance, whose height is divergent as 1/T and whose weight is divergent as -lnT at low temperatures. The charge Hall conductance changes by 2e^2/h instead of e^2/h as the magnetic field changes through the resonant point. The speaker will address the resonance condition, symmetries in the spin-orbit coupling, the singularity of magnetic susceptibility, nonlinear electric field effect, the edge effect and the disorder effect due to impurities. This work was supported by the Research Grants Council of Hong Kong under Grant No.: HKU 7088/01P. *S. Q. Shen, M. Ma, X. C. Xie, and F. C. Zhang, Phys. Rev. Lett. 92, 256603 (2004) *S. Q. Shen, Y. J. Bao, M. Ma, X. C. Xie, and F. C. Zhang, cond-mat/0410169

Hyperfine interaction and its effects on spin dynamics in organic solids

NASA Astrophysics Data System (ADS)

Yu, Z. G.; Ding, Feizhi; Wang, Haobin

2013-05-01

Hyperfine interaction (HFI) and spin-orbit coupling are two major sources that affect electron spin dynamics. Here we present a systematic study of the HFI and its role in organic spintronic applications. For electron spin dynamics in disordered π-conjugated organics, the HFI can be characterized by an effective magnetic field whose modular square is a weighted sum of contact and dipolar contributions. We determine the effective HFI fields of some common π-conjugated organics studied in the literature via first-principles calculations. Most of them are found to be less than 2 mT. While the H atoms are the major source of the HFI in organics containing only the C and H atoms, many organics contain other nuclear spins, such as Al and N in tris-(8-hydroxyquinoline) aluminum, that contribute to the total HFI. Consequently, the deuteration effect on the HFI in the latter may be much weaker than in the former. The HFI gives rise to multiple resonance peaks in electron spin resonance. In disordered organic solids, these individual resonances are unresolved, leading to a broad peak whose width is proportional to the effective HFI field. As electrons hop among adjacent organic molecules, they experience a randomly varying local HFI field, inducing electron spin relaxation and diffusion. This is analyzed rigorously based on master equations. Electron spin relaxation undergoes a crossover along the ratio between the electron hopping rate η¯ and the Larmor frequency Ω of the HFI field. The spin relaxation rate increases (decreases) with η¯ when η¯≪Ω (η¯≫Ω). A coherent beating of electron spin at Ω is possible when the external field is small compared to the HFI. In this regime, the magnetic field is found to enhance the spin relaxation.

Perspective: Interface generation of spin-orbit torques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.

We present that most of the modern spintronics developments rely on the manipulation of magnetization states via electric currents, which started with the discovery of spin transfer torque effects 20 years ago. By now, it has been realized that spin-orbit coupling provides a particularly efficient pathway for generating spin torques from charge currents. At the same time, spin-orbit effects can be enhanced at interfaces, which opens up novel device concepts. Here, we discuss two examples of such interfacial spin-orbit torques, namely, systems with inherently two-dimensional materials and metallic bilayers with strong Rashba spin-orbit coupling at their interfaces. We show howmore » ferromagnetic resonance excited by spin-orbit torques can provide information about the underlying mechanisms. In addition, this article provides a brief overview of recent developments with respect to interfacial spin-orbit torques and an outlook of still open questions.« less

Perspective: Interface generation of spin-orbit torques

DOE PAGES

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

2016-11-14

We present that most of the modern spintronics developments rely on the manipulation of magnetization states via electric currents, which started with the discovery of spin transfer torque effects 20 years ago. By now, it has been realized that spin-orbit coupling provides a particularly efficient pathway for generating spin torques from charge currents. At the same time, spin-orbit effects can be enhanced at interfaces, which opens up novel device concepts. Here, we discuss two examples of such interfacial spin-orbit torques, namely, systems with inherently two-dimensional materials and metallic bilayers with strong Rashba spin-orbit coupling at their interfaces. We show howmore » ferromagnetic resonance excited by spin-orbit torques can provide information about the underlying mechanisms. In addition, this article provides a brief overview of recent developments with respect to interfacial spin-orbit torques and an outlook of still open questions.« less

Complex Terahertz and Direct Current Inverse Spin Hall Effect in YIG/Cu1-xIrx Bilayers Across a Wide Concentration Range.

PubMed

Cramer, Joel; Seifert, Tom; Kronenberg, Alexander; Fuhrmann, Felix; Jakob, Gerhard; Jourdan, Martin; Kampfrath, Tobias; Kläui, Mathias

2018-02-14

We measure the inverse spin Hall effect of Cu 1-x Ir x thin films on yttrium iron garnet over a wide range of Ir concentrations (0.05 ⩽ x ⩽ 0.7). Spin currents are triggered through the spin Seebeck effect, either by a continuous (dc) temperature gradient or by ultrafast optical heating of the metal layer. The spin Hall current is detected by electrical contacts or measurement of the emitted terahertz radiation. With both approaches, we reveal the same Ir concentration dependence that follows a novel complex, nonmonotonous behavior as compared to previous studies. For small Ir concentrations a signal minimum is observed, whereas a pronounced maximum appears near the equiatomic composition. We identify this behavior as originating from the interplay of different spin Hall mechanisms as well as a concentration-dependent variation of the integrated spin current density in Cu 1-x Ir x . The coinciding results obtained for dc and ultrafast stimuli provide further support that the spin Seebeck effect extends to terahertz frequencies, thus enabling a transfer of established spintronic measurement schemes into the terahertz regime. Our findings also show that the studied material allows for efficient spin-to-charge conversion even on ultrafast time scales.

Ensemble control of Kondo screening in molecular adsorbates

DOE PAGES

Maughan, Bret; Zahl, Percy; Sutter, Peter; ...

2017-04-06

Switching the magnetic properties of organic semiconductors on a metal surface has thus far largely been limited to molecule-by-molecule tip-induced transformations in scanned probe experiments. Here we demonstrate with molecular resolution that collective control of activated Kondo screening can be achieved in thin-films of the organic semiconductor titanyl phthalocyanine on Cu(110) to obtain tunable concentrations of Kondo impurities. Using low-temperature scanning tunneling microscopy and spectroscopy, we show that a thermally activated molecular distortion dramatically shifts surface–molecule coupling and enables ensemble-level control of Kondo screening in the interfacial spin system. This is accompanied by the formation of a temperature-dependent Abrikosov–Suhl–Kondo resonancemore » in the local density of states of the activated molecules. This enables coverage-dependent control over activation to the Kondo screening state. Finally, our study thus advances the versatility of molecular switching for Kondo physics and opens new avenues for scalable bottom-up tailoring of the electronic structure and magnetic texture of organic semiconductor interfaces at the nanoscale.« less

Quantum phase transitions in effective spin-ladder models for graphene zigzag nanoribbons

NASA Astrophysics Data System (ADS)

Koop, Cornelie; Wessel, Stefan

2017-10-01

We examine the magnetic correlations in quantum spin models that were derived recently as effective low-energy theories for electronic correlation effects on the edge states of graphene nanoribbons. For this purpose, we employ quantum Monte Carlo simulations to access the large-distance properties, accounting for quantum fluctuations beyond mean-field-theory approaches to edge magnetism. For certain chiral nanoribbons, antiferromagnetic interedge couplings were previously found to induce a gapped quantum disordered ground state of the effective spin model. We find that the extended nature of the intraedge couplings in the effective spin model for zigzag nanoribbons leads to a quantum phase transition at a large, finite value of the interedge coupling. This quantum critical point separates the quantum disordered region from a gapless phase of stable edge magnetism at weak intraedge coupling, which includes the ground states of spin-ladder models for wide zigzag nanoribbons. To study the quantum critical behavior, the effective spin model can be related to a model of two antiferromagnetically coupled Haldane-Shastry spin-half chains with long-ranged ferromagnetic intrachain couplings. The results for the critical exponents are compared also to several recent renormalization-group calculations for related long-ranged interacting quantum systems.

Thermoelastic enhancement of the magnonic spin Seebeck effect in thin films and bulk samples

NASA Astrophysics Data System (ADS)

Chotorlishvili, L.; Wang, X.-G.; Toklikishvili, Z.; Berakdar, J.

2018-04-01

A nonuniform temperature profile may generate a pure spin current in magnetic films, as observed, for instance, in the spin Seebeck effect. In addition, thermally induced elastic deformations may set in that could affect the spin current. A self-consistent theory of the magnonic spin Seebeck effect including thermally activated magnetoelastic effects is presented, and analytical expressions for the thermally activated deformation tensor and dispersion relations for coupled magnetoelastic modes are obtained. We derive analytical results for bulk (three-dimensional) systems and thin magnetic (two-dimensional) films. We observe that the displacement vector and the deformation tensor in bulk systems decay asymptotically as u ˜1 /R2 and ɛ ˜1 /R3 , respectively, while the decays in thin magnetic films proceed slower, following u ˜1 /R and ɛ ˜1 /R2 . The dispersion relations evidence a strong anisotropy in the magnetic excitations. We observe that a thermoelastic steady-state deformation may lead to both an enchantment and a reduction of the gap in the magnonic spectrum. The reduction of the gap increases the number of magnons contributing to the spin Seebeck effect and offers new possibilities for the thermoelastic control of the spin Seebeck effect.

Spin current and second harmonic generation in non-collinear magnetic systems: the hydrodynamic model

NASA Astrophysics Data System (ADS)

Karashtin, E. A.; Fraerman, A. A.

2018-04-01

We report a theoretical study of the second harmonic generation in a noncollinearly magnetized conductive medium with equilibrium spin current. The hydrodynamic model is used to unravel the mechanism of a novel effect of the double frequency signal generation that is attributed to the spin current. According to our calculations, this second harmonic response appears due to the ‘non-adiabatic’ spin polarization of the conduction electrons induced by the oscillations in the non-uniform magnetization forced by the electric field of the electromagnetic wave. Together with the linear velocity response this leads to the generation of the double frequency spin current. This spin current is converted to the electric current via the inverse spin Hall effect, and the double-frequency electric current emits the second harmonic radiation. Possible experiment for detection of the new second harmonic effect is proposed.

Chemical potential of quasi-equilibrium magnon gas driven by pure spin current.

PubMed

Demidov, V E; Urazhdin, S; Divinskiy, B; Bessonov, V D; Rinkevich, A B; Ustinov, V V; Demokritov, S O

2017-11-17

Pure spin currents provide the possibility to control the magnetization state of conducting and insulating magnetic materials. They allow one to increase or reduce the density of magnons, and achieve coherent dynamic states of magnetization reminiscent of the Bose-Einstein condensation. However, until now there was no direct evidence that the state of the magnon gas subjected to spin current can be treated thermodynamically. Here, we show experimentally that the spin current generated by the spin-Hall effect drives the magnon gas into a quasi-equilibrium state that can be described by the Bose-Einstein statistics. The magnon population function is characterized either by an increased effective chemical potential or by a reduced effective temperature, depending on the spin current polarization. In the former case, the chemical potential can closely approach, at large driving currents, the lowest-energy magnon state, indicating the possibility of spin current-driven Bose-Einstein condensation.

A separation of antiferromagnetic spin motion modes in the training effect of exchange biased Co/CoO film with in-plane anisotropy

NASA Astrophysics Data System (ADS)

Wu, R.; Yun, C.; Ding, S. L.; Wen, X.; Liu, S. Q.; Wang, C. S.; Han, J. Z.; Du, H. L.; Yang, J. B.

2016-08-01

The motion of antiferromagnetic interfacial spins is investigated through the temperature evolution of training effect in a Co/CoO film with in-plane biaxial anisotropy. Significant differences in the training effect and its temperature dependence are observed in the magnetic easy axis and hard axis (HA) and ascribed to the different motion modes of antiferromagnetic interfacial spins, the collective spin cluster rotation (CSR) and the single spin reversal (SSR), caused by different magnetization reversal modes of ferromagnetic layer. These motion modes of antiferromagnetic spins are successfully separated using a combination of an exponential function and a classic n-1/2 function. A larger CSR to SSR ratio and a shorter lifetime of CSR found in the HA indicates that the domain rotation in the ferromagnetic layer tends to activate and accelerate a CSR mode in the antiferromagnetic spins.

Tunneling Anomalous and Spin Hall Effects.

PubMed

Matos-Abiague, A; Fabian, J

2015-07-31

We predict, theoretically, the existence of the anomalous Hall effect when a tunneling current flows through a tunnel junction in which only one of the electrodes is magnetic. The interfacial spin-orbit coupling present in the barrier region induces a spin-dependent momentum filtering in the directions perpendicular to the tunneling current, resulting in a skew tunneling even in the absence of impurities. This produces an anomalous Hall conductance and spin Hall currents in the nonmagnetic electrode when a bias voltage is applied across the tunneling heterojunction. If the barrier is composed of a noncentrosymmetric material, the anomalous Hall conductance and spin Hall currents become anisotropic with respect to both the magnetization and crystallographic directions, allowing us to separate this interfacial phenomenon from the bulk anomalous and spin Hall contributions. The proposed effect should be useful for proving and quantifying the interfacial spin-orbit fields in metallic and metal-semiconductor systems.

Bogoliubov theory and Lee-Huang-Yang corrections in spin-1 and spin-2 Bose-Einstein condensates in the presence of the quadratic Zeeman effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uchino, Shun; Kobayashi, Michikazu; Ueda, Masahito

2010-06-15

We develop Bogoliubov theory of spin-1 and spin-2 Bose-Einstein condensates (BECs) in the presence of a quadratic Zeeman effect, and derive the Lee-Huang-Yang (LHY) corrections to the ground-state energy, pressure, sound velocity, and quantum depletion. We investigate all the phases of spin-1 and spin-2 BECs that can be realized experimentally. We also examine the stability of each phase against quantum fluctuations and the quadratic Zeeman effect. Furthermore, we discuss a relationship between the number of symmetry generators that are spontaneously broken and that of Nambu-Goldstone (NG) modes. It is found that in the spin-2 nematic phase there are special Bogoliubovmore » modes that have gapless linear dispersion relations but do not belong to the NG modes.« less

Nuclear spin dependence of time reversal invariance violating effects in neutron scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gudkov, Vladimir; Shimizu, Hirohiko M.

In this study, the spin structure of parity violating and time reversal invariance violating effects in neutron scattering is discussed. The explicit relations between these effects are presented in terms of functions nuclear spins and neutron partial widths of p-wave resonances.

Nuclear spin dependence of time reversal invariance violating effects in neutron scattering

DOE PAGES

Gudkov, Vladimir; Shimizu, Hirohiko M.

2018-06-11

In this study, the spin structure of parity violating and time reversal invariance violating effects in neutron scattering is discussed. The explicit relations between these effects are presented in terms of functions nuclear spins and neutron partial widths of p-wave resonances.

Bipolar magnetic semiconductor in silicene nanoribbons

NASA Astrophysics Data System (ADS)

Farghadan, Rouhollah

2017-08-01

A theoretical study was presented on generation of spin polarization in silicene nanoribbons using the single-band tight-binding approximation and the non-equilibrium Green's function formalism. We focused on the effect of electric and exchange magnetic fields on the spin-filter capabilities of zigzag-edge silicene nanoribbons in the presence of the intrinsic spin-orbit interaction. The results show that a robust bipolar magnetic semiconductor with controllable spin-flip and spin-conserved gaps can be obtained when exchange magnetic and electric field strengths are both larger than the intrinsic spin-orbit interaction. Therefore, zigzag silicene nanoribbons could act as bipolar and perfect spin filter devices with a large spin-polarized current and a reversible spin polarization in the vicinity of the Fermi energy. We also investigated the effect of edge roughness and found that the bipolar magnetic semiconductor features are robust against edge disorder in silicene nanoribbon junctions. These results may be useful in multifunctional spin devices based on silicene nanoribbons.

Determination of the spin Hall angle in single-crystalline Pt films from spin pumping experiments

NASA Astrophysics Data System (ADS)

Keller, Sascha; Mihalceanu, Laura; Schweizer, Matthias R.; Lang, Philipp; Heinz, Björn; Geilen, Moritz; Brächer, Thomas; Pirro, Philipp; Meyer, Thomas; Conca, Andres; Karfaridis, Dimitrios; Vourlias, George; Kehagias, Thomas; Hillebrands, Burkard; Papaioannou, Evangelos Th

2018-05-01

We report on the determination of the spin Hall angle in ultra-clean, defect-reduced epitaxial Pt films. By applying vector network analyzer ferromagnetic resonance spectroscopy to a series of single crystalline Fe (12 nm) /Pt (t Pt) bilayers we determine the real part of the spin mixing conductance (4.4 ± 0.2) × 1019 m‑2 and reveal a very small spin diffusion length in the epitaxial Pt (1.1 ± 0.1) nm film. We investigate the spin pumping and ISHE in a stripe microstucture excited by a microwave coplanar waveguide antenna. By using their different angular dependencies, we distinguish between spin rectification effects and the inverse spin Hall effect. The relatively large value of the spin Hall angle (5.7 ± 1.4)% shows that ultra-clean e-beam evaporated non-magnetic materials can also have a comparable spin-to-charge current conversion efficiency as sputtered high resistivity layers.

Flight investigation of the effect of tail configuration on stall, spin, and recovery characteristics of a low-wing general aviation research airplane

NASA Technical Reports Server (NTRS)

Stough, H. Paul, III; Patton, James M., Jr.; Sliwa, Steven M.

1987-01-01

Flight tests were performed to investigate the stall, spin, and recovery characteristics of a low-wing, single-engine, light airplane with four interchangeable tail configurations. The four tail configurations were evaluated for effects of varying mass distribution, center-of-gravity position, and control inputs. The airplane tended to roll-off at the stall. Variations in tail configuration produced spins ranging from 40 deg to 60 deg angle of attack and turn rates of about 145 to 208 deg/sec. Some unrecoverable flat spins were encountered which required use of the airplane spin chute for recovery. For recoverable spins, antispin rudder followed by forward wheel with ailerons centered provided the quickest spin recovery. The moderate spin modes agreed very well with those predicted from spin-tunnel model tests, however, the flat spin was at a lower angle of attack and a slower rotation rate than indicated by the model tests.

Housing flexibility effects on rotor stability

NASA Technical Reports Server (NTRS)

Davis, L. B.; Wolfe, E. A.; Beatty, R. F.

1985-01-01

Preliminary rotordynamic evaluations are performed with a housing stiffness assumption that is typically determined only after the hardware is built. In addressing rotor stability, a rigid housing assumption was shown to predict an instability at a lower spin speed than a comparable flexible housing analysis. This rigid housing assumption therefore provides a conservative estimate of the stability threshold speed. A flexible housing appears to act as an energy absorber and dissipated some of the destabilizing force. The fact that a flexible housing is usually asymmetric and considerably heavier than the rotor was related to this apparent increase in rotor stability. Rigid housing analysis is proposed as a valuable screening criteria and may save time and money in construction of elaborate housing finite element models for linear stability analyses.

Electron acceleration in quantum plasma with spin-up and spin-down exchange interaction

NASA Astrophysics Data System (ADS)

Kumar, Punit; Singh, Shiv; Ahmad, Nafees

2018-05-01

Electron acceleration by ponderomotive force of an intense circularly polarized laser pulse in high density magnetized quantum plasma with two different spin states embedded in external static magnetic field. The basic mechanism involves electron acceleration by axial gradient in the ponderomotive potential of laser. The effects of Bohm potential, fermi pressure and intrinsic spin of electron have been taken into account. A simple solution for ponderomotive electron acceleration has been established and effect of spin polarization is analyzed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshizumi, K.; Sasaki, A.; Kohda, M.

We demonstrate gate-controlled switching between persistent spin helix (PSH) state and inverse PSH state, which are detected by quantum interference effect on magneto-conductance. These special symmetric spin states showing weak localization effect give rise to a long spin coherence when the strength of Rashba spin-orbit interaction (SOI) is close to that of Dresselhaus SOI. Furthermore, in the middle of two persistent spin helix states, where the Rashba SOI can be negligible, the bulk Dresselhaus SOI parameter in a modulation doped InGaAs/InAlAs quantum well is determined.

Inverse spin Hall effect by spin injection

NASA Astrophysics Data System (ADS)

Liu, S. Y.; Horing, Norman J. M.; Lei, X. L.

2007-09-01

Motivated by a recent experiment [S. O. Valenzuela and M. Tinkham, Nature (London) 442, 176 (2006)], the authors present a quantitative microscopic theory to investigate the inverse spin-Hall effect with spin injection into aluminum considering both intrinsic and extrinsic spin-orbit couplings using the orthogonalized-plane-wave method. Their theoretical results are in good agreement with the experimental data. It is also clear that the magnitude of the anomalous Hall resistivity is mainly due to contributions from extrinsic skew scattering.

Nano-oxide-layer insertion and specular effects in spin valves: Experiment and theory

NASA Astrophysics Data System (ADS)

Wang, L.; Qiu, J. J.; McMahon, W. J.; Li, K. B.; Wu, Y. H.

2004-06-01

We report a systematic study of NOL (nano-oxide-layer) insertion and specular effects on the giant magnetoresistance (GMR) of single, synthetic, and dual spin valves, using a semiclassical Boltzmann theory. It is confirmed that the GMR ratio is enhanced by NOL insertion inside the pinned layer or after the free layer. The enhancements are primarily due to the contribution of the majority carriers. The NOL insertions inside the inactive layers of spin valves such as the seed, under, and capping layers reduce the GMR ratio. Though introducing a NOL before or after the Cu spacer would, in principle, significantly suppress the GMR ratio due to the blocking effect or the average effect of different spin channels, large positive or negative (inverse) GMR is found by assuming spin-dependent NOL specular reflections. We have also demonstrated that specular reflection, even beyond a capping layer, may result in reduction of GMR. Upon appropriate NOL insertion, the amplitude of curve of GMR versus thickness of individual layer of spin valves may be generally enhanced, but the shape may change, depending on whether the distance of the NOL to the layer is small or large (distance effect). Finally, it is found that most results obtained for the single realistic spin valves are applicable to synthetic and dual spin valves.

Spin-Driven Emergent Antiferromagnetism and Metal-Insulator Transition in Nanoscale p-Si

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

The entanglement of the charge, spin and orbital degrees of freedom can give rise to emergent behavior especially in thin films, surfaces and interfaces. Often, materials that exhibit those properties require large spin orbit coupling. We hypothesize that the emergent behavior can also occur due to spin, electron and phonon interactions in widely studied simple materials such as Si. That is, large intrinsic spin-orbit coupling is not an essential requirement for emergent behavior. The central hypothesis is that when one of the specimen dimensions is of the same order (or smaller) as the spin diffusion length, then non-equilibrium spin accumulation due to spin injection or spin-Hall effect (SHE) will lead to emergent phase transformations in the non-ferromagnetic semiconductors. In this experimental work, we report spin mediated emergent antiferromagnetism and metal insulator transition in a Pd (1 nm)/Ni81Fe19 (25 nm)/MgO (1 nm)/p-Si (~400 nm) thin film specimen. The spin-Hall effect in p-Si, observed through Rashba spin-orbit coupling mediated spin-Hall magnetoresistance behavior, is proposed to cause the spin accumulation and resulting emergent behavior. The phase transition is discovered from the diverging behavior in longitudinal third harmonic voltage, which is related to the thermal conductivity and heat capacity.

Temperature dependence of spin-orbit torques in Pt/Co/Pt multilayers

NASA Astrophysics Data System (ADS)

Chen, Shiwei; Li, Dong; Cui, Baoshan; Xi, Li; Si, Mingsu; Yang, Dezheng; Xue, Desheng

2018-03-01

We studied the current-induced spin-orbit torques in a perpendicularly magnetized Pt (1 nm)/Co (0.8 nm)/Pt (5 nm) heterojunction by harmonic Hall voltage measurements. Owing to similar Pt/Co/Pt interfaces, the spin-orbit torques originated from the Rashba effect are reduced, but the contribution from the spin Hall effect is still retained because of asymmetrical Pt thicknesses. When the temperature increases from 50 to 300 K, two orthogonal components of the effective field, induced by spin-orbit torques, reveal opposite temperature dependencies: the field-like term (transverse effective field) decreases from 2.3 to 2.1 (10-6 Oe (A cm-2)-1), whereas the damping-like term (longitudinal effective field) increases from 3.7 to 4.8 (10-6 Oe (A cm-2)-1). It is noticed that the damping-like term, usually smaller than the field-like term in the similar Pt/Co interfaces, is twice as large as the field-like term. As a result, the damping-like spin-orbit torque reaches an efficiency of 0.15 at 300 K. Such a temperature-dependent damping-like term in a Pt/Co/Pt heterojunction can efficiently reduce the switching current density which is 2.30  ×  106 A cm-2 at 300 K, providing an opportunity to further improve and understand spin-orbit torques induced by spin Hall effect.

Spin-Dependent Phenomena in Graphene

DTIC Science & Technology

2012-03-15

scattering on spin relaxation: By investigating the effect of gold dopants on spin transport, we concluded that charged impurity scattering is not...transport in graphene spin valves consisting of an ultrathin sheet of graphene (single or bilayer) contacted by ferromagnetic cobalt electrodes...workfunction cannot explain the observed behavior. The second effect was that the mobility was reduced by the transition metal dopants , as indicated by

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawahara, Hajime, E-mail: divrot@gmail.com

We consider the effect of planetary spin on the planetary radial velocity (PRV) in dayside spectra of exoplanets. To understand the spin effect qualitatively, we derive an analytic formula of the intensity-weighted radial velocity from the planetary surface on the following assumptions: (1) constant and solid rotation without precession, (2) stable and uniform distribution of molecules/atoms, (3) emission models from the dayside hemisphere, and (4) a circular orbit. On these assumptions, we find that the curve of the PRV is distorted by the planetary spin and this anomaly is characterized by the spin radial velocity at the equator and amore » projected angle on a celestial plane between the spin axis and the axis of orbital motion {lambda}{sub p} in a manner analogous to the Rossiter-McLaughlin effect. The latter can constrain the planetary obliquity. Creating mock PRV data with 3 km s{sup -1} accuracy, we demonstrate how {lambda}{sub p} and the spin radial velocity at the equator are estimated. We find that the stringent constraint of eccentricity is crucial to detect the spin effect. Though our formula is still qualitative, we conclude that the PRV in the dayside spectra will be a powerful means for constraining the planetary spin.« less

Spin transport across antiferromagnets induced by the spin Seebeck effect

NASA Astrophysics Data System (ADS)

Cramer, Joel; Ritzmann, Ulrike; Dong, Bo-Wen; Jaiswal, Samridh; Qiu, Zhiyong; Saitoh, Eiji; Nowak, Ulrich; Kläui, Mathias

2018-04-01

For prospective spintronics devices based on the propagation of pure spin currents, antiferromagnets are an interesting class of materials that potentially entail a number of advantages as compared to ferromagnets. Here, we present a detailed theoretical study of magnonic spin current transport in ferromagnetic-antiferromagnetic multilayers by using atomistic spin dynamics simulations. The relevant length scales of magnonic spin transport in antiferromagnets are determined. We demonstrate the transfer of angular momentum from a ferromagnet into an antiferromagnet due to the excitation of only one magnon branch in the antiferromagnet. As an experimental system, we ascertain the transport across an antiferromagnet in Y3Fe5O12 |Ir20Mn80|Pt heterostructures. We determine the spin transport signals for spin currents generated in the Y3Fe5O12 by the spin Seebeck effect and compare to measurements of the spin Hall magnetoresistance in the heterostructure stack. By means of temperature-dependent and thickness-dependent measurements, we deduce conclusions on the spin transport mechanism across Ir20Mn80 and furthermore correlate it to its paramagnetic-antiferromagnetic phase transition.

New opportunities at the frontiers of spintronics

DOE PAGES

Hoffmann, Axel; Bader, Sam D.

2015-10-05

The field of spintronics, or magnetic electronics, is maturing and giving rise to new subfields. These new directions involve the study of collective spin excitations and couplings of the spin system to additional degrees of freedom of a material, as well as metastable phenomena due to perturbations that drive the system far from equilibrium. The interactions lead to possibilities for future applications within the realm of energy-efficient information technologies. Examples discussed herein include research opportunities associated with (i) various spin-orbit couplings, such as spin Hall effects, (ii) couplings to the thermal bath of a system, such as in spin Seebeckmore » effects, (iii) spin-spin couplings, such as via induced and interacting magnon excitations, and (iv) spin-photon couplings, such as in ultra-fast magnetization switching due to coherent photon pulses. These four basic frontier areas of research are giving rise to new applied disciplines known as spin-orbitronics, spin-caloritronics, magnonics, and spin-photonics, respectively. These topics are highlighted in order to stimulate interest in the new directions that spintronics research is taking, and to identify open issues to pursue.« less

Free-Spinning-Tunnel Investigation of a 1/28-Scale Model of the North American FJ-4 Airplane with External Fuel Tanks, TED No. NACA AD 3112

NASA Technical Reports Server (NTRS)

Healy, Frederick M.

1958-01-01

A supplementary investigation to determine the effect of external fuel tanks on the spin and recovery characteristics of a l/28-scale model of the North American FJ-4 airplane has been conducted in the Langley 20-foot free-spinning tunnel. The model had been extensively tested previously (NACA Research Memorandum SL38A29) and therefore only brief tests were made to evaluate the effect of tank installation. Erect spin tests of the model indicate that flat-type spins-are more prevalent with 200-gallon external fuel tanks than with tanks not installed. The recovery technique determined for spins without tanks, rudder reversal to full against the spin accompanied by simultaneous movement of ailerons to full with the spin, is recommended for spins encountered with external tanks installed. If inverted spins are encountered with external tanks installed, the tanks should be jettisoned and recovery attempted by rudder reversal to full against the spin with ailerons maintained at neutral.

Density and spin modes in imbalanced normal Fermi gases from collisionless to hydrodynamic regime

NASA Astrophysics Data System (ADS)

Narushima, Masato; Watabe, Shohei; Nikuni, Tetsuro

2018-03-01

We study the mass- and population-imbalance effect on density (in-phase) and spin (out-of-phase) collective modes in a two-component normal Fermi gas. By calculating the eigenmodes of the linearized Boltzmann equation as well as the density/spin dynamic structure factor, we show that mass- and population-imbalance effects offer a variety of collective mode crossover behaviors from collisionless to hydrodynamic regimes. The mass-imbalance effect shifts the crossover regime to the higher-temperature, and a significant peak of the spin dynamic structure factor emerges only in the collisionless regime. This is in contrast to the case of mass- and population-balanced normal Fermi gases, where the spin dynamic response is always absent. Although the population-imbalance effect does not shift the crossover regime, the spin dynamic structure factor survives both in the collisionless and hydrodynamic regimes.

New pathways towards efficient metallic spin Hall spintronics

DOE PAGES

Jungfleisch, Matthias Benjamin; Zhang, Wei; Jiang, Wanjun; ...

2015-11-16

Spin Hall effects (SHEs) interconvert spin- and charge currents due to spin- orbit interaction, which enables convenient electrical generation and detection of diffusive spin currents and even collective spin excitations in magnetic solids. Here, we review recent experimental efforts exploring efficient spin Hall detector materials as well as new approaches to drive collective magnetization dynamics and to manipulate spin textures by SHEs. As a result, these studies are also expected to impact practical spintronics applications beyond their significance in fundamental research.

Next-to-next-to-leading order gravitational spin-squared potential via the effective field theory for spinning objects in the post-Newtonian scheme

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levi, Michele; Steinhoff, Jan, E-mail: michele.levi@upmc.fr, E-mail: jan.steinhoff@aei.mpg.de

2016-01-01

The next-to-next-to-leading order spin-squared interaction potential for generic compact binaries is derived for the first time via the effective field theory for gravitating spinning objects in the post-Newtonian scheme. The spin-squared sector is an intricate one, as it requires the consideration of the point particle action beyond minimal coupling, and mainly involves the spin-squared worldline couplings, which are quite complex, compared to the worldline couplings from the minimal coupling part of the action. This sector also involves the linear in spin couplings, as we go up in the nonlinearity of the interaction, and in the loop order. Hence, there ismore » an excessive increase in the number of Feynman diagrams, of which more are higher loop ones. We provide all the Feynman diagrams and their values. The beneficial ''nonrelativistic gravitational'' fields are employed in the computation. This spin-squared correction, which enters at the fourth post-Newtonian order for rapidly rotating compact objects, completes the conservative sector up to the fourth post-Newtonian accuracy. The robustness of the effective field theory for gravitating spinning objects is shown here once again, as demonstrated in a recent series of papers by the authors, which obtained all spin dependent sectors, required up to the fourth post-Newtonian accuracy. The effective field theory of spinning objects allows to directly obtain the equations of motion, and the Hamiltonians, and these will be derived for the potential obtained here in a forthcoming paper.« less

Spin-Wave Chirality and Its Manifestations in Antiferromagnets

NASA Astrophysics Data System (ADS)

Proskurin, Igor; Stamps, Robert L.; Ovchinnikov, Alexander S.; Kishine, Jun-ichiro

2017-10-01

As first demonstrated by Tang and Cohen in chiral optics, the asymmetry in the rate of electromagnetic energy absorption between left and right enantiomers is determined by an optical chirality density. Here, we demonstrate that this effect can exist in magnetic spin systems. By constructing a formal analogy with electrodynamics, we show that in antiferromagnets with broken chiral symmetry, the asymmetry in local spin-wave energy absorption is proportional to a spin-wave chirality density, which is a direct counterpart of optical zilch. We propose that injection of a pure spin current into an antiferromagnet may serve as a chiral symmetry breaking mechanism, since its effect in the spin-wave approximation can be expressed in terms of additional Lifshitz invariants. We use linear response theory to show that the spin current induces a nonequilibrium spin-wave chirality density.

Optically Induced Nuclear Spin Polarization in the Quantum Hall Regime: The Effect of Electron Spin Polarization through Exciton and Trion Excitations.

PubMed

Akiba, K; Kanasugi, S; Yuge, T; Nagase, K; Hirayama, Y

2015-07-10

We study nuclear spin polarization in the quantum Hall regime through the optically pumped electron spin polarization in the lowest Landau level. The nuclear spin polarization is measured as a nuclear magnetic field B(N) by means of the sensitive resistive detection. We find the dependence of B(N) on the filling factor nonmonotonic. The comprehensive measurements of B(N) with the help of the circularly polarized photoluminescence measurements indicate the participation of the photoexcited complexes, i.e., the exciton and trion (charged exciton), in nuclear spin polarization. On the basis of a novel estimation method of the equilibrium electron spin polarization, we analyze the experimental data and conclude that the filling factor dependence of B(N) is understood by the effect of electron spin polarization through excitons and trions.

Driving magnetization dynamics with interfacial spin-orbit torques (Conference Presentation)

NASA Astrophysics Data System (ADS)

Hoffmann, Axel F.; Zhang, Wei; Sklenar, Joseph; Jungfleisch, Matthias Benjamin; Jiang, Wanjun; Hsu, Bo; Xiao, Jiao; Pearson, John E.; Fradin, Frank Y.; Liu, Yaohua; Ketterson, John B.; Yang, Zheng

2016-10-01

Bulk spin Hall effects are well know to provide spin orbit torques, which can be used to drive magnetization dynamics [1]. But one of the reoccurring questions is to what extend spin orbit torques may also originate at the interface between materials with strong spin orbit coupling and the ferromagnets. Using spin torque driven ferromagnetic resonance we show for two systems, where interfacial torques dominate, that they can be large enough to be practically useful. First, we show spin transfer torque driven magnetization dynamics based on Rashba-Edelstein effects at the Bi/Ag interface [2]. Second, we will show that combining permalloy with monolayer MoS2 gives rise to sizable spin-orbit torques. Given the monolayer nature of MoS2 it is clear that bilk spin Hall effects are negligible and therefore the spin transfer torques are completely interfacial in nature. Interestingly the spin orbit torques with MoS2 show a distinct dependence on the orientation of the magnetization in the permalloy, and become strongly enhanced, when the magnetization is pointing perpendicular to the interfacial plane. This work was supported by the U.S. Department of Energy, Office of Science, Materials Science and Engineering Division. [1] A. Hoffmann, IEEE Trans. Mag. 49, 5172 (2013). [2] W. Zhang et al., J. Appl. Phys. 117, 17C727 (2015). [3] M. B. Jungfleisch et al., arXiv:1508.01410.

Towards electrical spin injection into LaAlO3-SrTiO3.

PubMed

Bibes, M; Reyren, N; Lesne, E; George, J-M; Deranlot, C; Collin, S; Barthélémy, A; Jaffrès, H

2012-10-28

Future spintronics devices will be built from elemental blocks allowing the electrical injection, propagation, manipulation and detection of spin-based information. Owing to their remarkable multi-functional and strongly correlated character, oxide materials already provide such building blocks for charge-based devices such as ferroelectric field-effect transistors (FETs), as well as for spin-based two-terminal devices such as magnetic tunnel junctions, with giant responses in both cases. Until now, the lack of suitable channel materials and the uncertainty of spin-injection conditions in these compounds had however prevented the exploration of similar giant responses in oxide-based lateral spin transport structures. In this paper, we discuss the potential of oxide-based spin FETs and report magnetotransport data that suggest electrical spin injection into the LaAlO(3)-SrTiO(3) interface system. In a local, three-terminal measurement scheme, we analyse the voltage variation associated with the precession of the injected spin accumulation driven by perpendicular or longitudinal magnetic fields (Hanle and 'inverted' Hanle effects). The spin accumulation signal appears to be much larger than expected, probably owing to amplification effects by resonant tunnelling through localized states in the LaAlO(3). We give perspectives on how to achieve direct spin injection with increased detection efficiency, as well on the implementation of efficient top gating schemes for spin manipulation.

Graphene-based half-metal and spin-semiconductor for spintronic applications.

PubMed

Qi, Jingshan; Chen, Xiaofang; Hu, Kaige; Feng, Ji

2016-03-31

In this letter we propose a strategy to make graphene become a half-metal or spin-semiconductor by combining the magnetic proximity effects and sublattice symmetry breaking in graphone/graphene and graphone/graphene/BN heterostructures. Exchange interactions lift the spin degeneracy and sublattice symmetry breaking opens a band gap in graphene. More interestingly, the gap opening depends on the spin direction and the competition between the sublattice asymmetry and exchange field determines the system is a half-metal or a spin-semiconductor. By first-principles calculations and a low-energy effective model analysis, we elucidate the underlying physical mechanism of spin-dependent gap opening and spin degeneracy splitting. This offers an alternative practical platform for graphene-based spintronics.

Stability of standing spin wave in permalloy thin film studied by anisotropic magnetoresistance effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamanoi, K.; Yokotani, Y.; Cui, X.

2015-12-21

We have investigated the stability for the resonant spin precession under the strong microwave magnetic field by a specially developed detection method using the anisotropic magnetoresistance effect. The electrically separated excitation and detection circuits enable us to investigate the influence of the heating effect and the nonuniform spin dynamics independently. The large detecting current is found to induce the field shift of the resonant spectra because of the Joule heating. From the microwave power dependence, we found that the linear response regime for the standing spin wave is larger than that for the ferromagnetic resonance. This robust characteristic of themore » standing spin wave is an important advantage for the high power operation of the spin-wave device.« less

Spin-Dependent Transport through Chiral Molecules Studied by Spin-Dependent Electrochemistry

PubMed Central

2016-01-01

Conspectus Molecular spintronics (spin + electronics), which aims to exploit both the spin degree of freedom and the electron charge in molecular devices, has recently received massive attention. Our recent experiments on molecular spintronics employ chiral molecules which have the unexpected property of acting as spin filters, by way of an effect we call “chiral-induced spin selectivity” (CISS). In this Account, we discuss new types of spin-dependent electrochemistry measurements and their use to probe the spin-dependent charge transport properties of nonmagnetic chiral conductive polymers and biomolecules, such as oligopeptides, L/D cysteine, cytochrome c, bacteriorhodopsin (bR), and oligopeptide-CdSe nanoparticles (NPs) hybrid structures. Spin-dependent electrochemical measurements were carried out by employing ferromagnetic electrodes modified with chiral molecules used as the working electrode. Redox probes were used either in solution or when directly attached to the ferromagnetic electrodes. During the electrochemical measurements, the ferromagnetic electrode was magnetized either with its magnetic moment pointing “UP” or “DOWN” using a permanent magnet (H = 0.5 T), placed underneath the chemically modified ferromagnetic electrodes. The spin polarization of the current was found to be in the range of 5–30%, even in the case of small chiral molecules. Chiral films of the l- and d-cysteine tethered with a redox-active dye, toludin blue O, show spin polarizarion that depends on the chirality. Because the nickel electrodes are susceptible to corrosion, we explored the effect of coating them with a thin gold overlayer. The effect of the gold layer on the spin polarization of the electrons ejected from the electrode was investigated. In addition, the role of the structure of the protein on the spin selective transport was also studied as a function of bias voltage and the effect of protein denaturation was revealed. In addition to “dark” measurements, we also describe photoelectrochemical measurements in which light is used to affect the spin selective electron transport through the chiral molecules. We describe how the excitation of a chromophore (such as CdSe nanoparticles), which is attached to a chiral working electrode, can flip the preferred spin orientation of the photocurrent, when measured under the identical conditions. Thus, chirality-induced spin polarization, when combined with light and magnetic field effects, opens new avenues for the study of the spin transport properties of chiral molecules and biomolecules and for creating new types of spintronic devices in which light and molecular chirality provide new functions and properties. PMID:27797176

Classical spin glass system in external field with taking into account relaxation effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gevorkyan, A. S., E-mail: g_ashot@sci.am; Abajyan, H. G.

2013-08-15

We study statistical properties of disordered spin systems under the influence of an external field with taking into account relaxation effects. For description of system the spatial 1D Heisenberg spin-glass Hamiltonian is used. In addition, we suppose that interactions occur between nearest-neighboring spins and they are random. Exact solutions which define angular configuration of the spin in nodes were obtained from the equations of stationary points of Hamiltonian and the corresponding conditions for the energy local minimum. On the basis of these recurrent solutions an effective parallel algorithm is developed for simulation of stabile spin-chains of an arbitrary length. Itmore » is shown that by way of an independent order of N{sup 2} numerical simulations (where N is number of spin in each chain) it is possible to generate ensemble of spin-chains, which is completely ergodic which is equivalent to full self-averaging of spin-chains' vector polarization. Distributions of different parameters (energy, average polarization by coordinates, and spin-spin interaction constant) of unperturbed system are calculated. In particular, analytically is proved and numerically is shown, that for the Heisenberg nearest-neighboring Hamiltonian model, the distribution of spin-spin interaction constants as opposed to widely used Gauss-Edwards-Anderson distribution satisfies Levy alpha-stable distribution law. This distribution is nonanalytic function and does not have variance. In the work we have in detail studied critical properties of an ensemble depending on value of external field parameters (from amplitude and frequency) and have shown that even at weak external fields the spin-glass systemis strongly frustrated. It is shown that frustrations have fractal behavior, they are selfsimilar and do not disappear at scale decreasing of area. By the numerical computation is shown that the average polarization of spin-glass on a different coordinates can have values which can lead to catastrophes in the equation ofClausius-Mossotti for dielectric constant. In other words, for some values of external field parameter, a critical phenomenon occurs in the system which is impossible to describe by the real-valued Heisenberg spin-glass Hamiltonian. For the solution of this problem at first the complex-valued disordered Hamiltonian is used. Physically this type of extension of Hamiltonian allows to consider relaxation effects which occur in the system under the influence of an external field. On the basis of developed approach an effective parallel algorithm is developed for simulation of statistic parameters of spin-glass system under the influence of an external field.« less

Modeling the Stability of Topological Matter in Optical Lattices

DTIC Science & Technology

2013-05-18

that vortex attachment to each particle helps screen the otherwise strong inter- particle repulsion by tuning the size of correlation holes. Figure 3...electric and ferromagnetic order in complex multiferroic materi - als presents a set of compelling fundamental condensed matter physics problems with... particle interactions and heating. I will examine interacting atoms in square optical lattices with spin orbit coupling, and more generally, gauge fields

Spin Seebeck effect and thermal colossal magnetoresistance in Christmas-tree silicene nanoribbons

NASA Astrophysics Data System (ADS)

Gao, Xiu-Jin; Zhao, Peng; Chen, Gang

2018-05-01

Based on the density functional theory and nonequilibrium Green's function method, we investigate the electronic structures and thermal spin transport properties of Christmas-tree silicene nanoribbons (CSiNRs). The results show that CSiNRs have ferromagnetic ground state with high Curie temperature far above the room temperature. Obvious spin Seebeck effect with spin-up and spin-down currents flowing in opposite directions by a temperature gradient can be observed in these systems. Furthermore, a thermal colossal magnetoresistance up to 109% can be realized by tuning the external magnetic field. The results show that CSiNRs hold great potential in designing spin caloritronic devices.

Parity Anomaly and Spin Transmutation in Quantum Spin Hall Josephson Junctions.

PubMed

Peng, Yang; Vinkler-Aviv, Yuval; Brouwer, Piet W; Glazman, Leonid I; von Oppen, Felix

2016-12-23

We study the Josephson effect in a quantum spin Hall system coupled to a localized magnetic impurity. As a consequence of the fermion parity anomaly, the spin of the combined system of impurity and spin-Hall edge alternates between half-integer and integer values when the superconducting phase difference across the junction advances by 2π. This leads to characteristic differences in the splittings of the spin multiplets by exchange coupling and single-ion anisotropy at phase differences, for which time-reversal symmetry is preserved. We discuss the resulting 8π-periodic (or Z_{4}) fractional Josephson effect in the context of recent experiments.

Effect of the δ-potential on spin-dependent electron tunneling in double barrier semiconductor heterostructure

NASA Astrophysics Data System (ADS)

Chandrasekar, L. Bruno; Gnanasekar, K.; Karunakaran, M.

2018-06-01

The effect of δ-potential was studied in GaAs/Ga0.6Al0·4As double barrier heterostructure with Dresselhaus spin-orbit interaction. The role of barrier height and position of the δ- potential in the well region was analysed on spin-dependent electron tunneling using transfer matrix method. The spin-separation between spin-resonances on energy scale depends on both height and position of the δ- potential, whereas the tunneling life time of electrons highly influenced by the position of the δ- potential and not on the height. These results might be helpful for the fabrication of spin-filters.

Exact Mapping from Many-Spin Hamiltonians to Giant-Spin Hamiltonians.

PubMed

Ghassemi Tabrizi, Shadan; Arbuznikov, Alexei V; Kaupp, Martin

2018-03-26

Thermodynamic and spectroscopic data of exchange-coupled molecular spin clusters (e.g. single-molecule magnets) are routinely interpreted in terms of two different models: the many-spin Hamiltonian (MSH) explicitly considers couplings between individual spin centers, while the giant-spin Hamiltonian (GSH) treats the system as a single collective spin. When isotropic exchange coupling is weak, the physical compatibility between both spin Hamiltonian models becomes a serious concern, due to mixing of spin multiplets by local zero-field splitting (ZFS) interactions ('S-mixing'). Until now, this effect, which makes the mapping MSH→GSH ('spin projection') non-trivial, had only been treated perturbationally (up to third order), with obvious limitations. Here, based on exact diagonalization of the MSH, canonical effective Hamiltonian theory is applied to construct a GSH that exactly matches the energies of the relevant (2S+1) states comprising an effective spin multiplet. For comparison, a recently developed strategy for the unique derivation of effective ('pseudospin') Hamiltonians, now routinely employed in ab initio calculations of mononuclear systems, is adapted to the problem of spin projection. Expansion of the zero-field Hamiltonian and the magnetic moment in terms of irreducible tensor operators (or Stevens operators) yields terms of all ranks k (up to k=2S) in the effective spin. Calculations employing published MSH parameters illustrate exact spin projection for the well-investigated [Ni(hmp)(dmb)Cl] 4 ('Ni 4 ') single-molecule magnet, which displays weak isotropic exchange (dmb=3,3-dimethyl-1-butanol, hmp - is the anion of 2-hydroxymethylpyridine). The performance of the resulting GSH in finite field is assessed in terms of EPR resonances and diabolical points. The large tunnel splitting in the M=± 4 ground doublet of the S=4 multiplet, responsible for fast tunneling in Ni 4 , is attributed to a Stevens operator with eightfold rotational symmetry, marking the first quantification of a k=8 term in a spin cluster. The unique and exact mapping MSH→GSH should be of general importance for weakly-coupled systems; it represents a mandatory ultimate step for comparing theoretical predictions (e.g. from quantum-chemical calculations) to ZFS, hyperfine or g-tensors from spectral fittings. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of electrically induced refraction and absorption on the measurement of spin current by pockels effect in GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Houquan; She, Weilong, E-mail: shewl@mail.sysu.edu.cn

2015-03-14

The pockels effect could be utilized to measure spin current in semiconductors for linear electro-optic coefficient can be induced by spin current. When dc electric field is applied, the carriers will shift in k space, which could lead to the change of refraction and absorption coefficients. In this paper, we investigate the influence of the induced change of the refraction and absorption coefficients on the measurement of spin current by pockels effect in GaAs.

Spin Currents and Ferromagnetic Resonance in Magnetic Thin Films

NASA Astrophysics Data System (ADS)

Ellsworth, David

Spin currents represent a new and exciting phenomenon. There is both a wealth of new physics to be discovered and understood, and many appealing devices which may result from this area of research. To fully realize the potential of this discipline it is necessary to develop new methods for realizing spin currents and explore new materials which may be suitable for spin current applications. Spin currents are an inherently dynamic phenomenon involving the transfer of angular momentum within and between different thin films. In order to understand and optimize such devices the dynamics of magnetization must be determined. This dissertation reports on novel approaches for spin current generation utilizing the magnetic insulators yttrium iron garnet (YIG) and M-type barium hexagonal ferrite (BaM). First, the light-induced spin Seebeck effect is reported for the first time in YIG. Additionally, the first measurement of the spin Seebeck effect without an external magnetic field is demonstrated. To accomplish this the self-biased BaM thin films are utilized. Second, a new method for the generation of spin currents is presented: the photo-spin-voltaic effect. In this new phenomenon, a spin current may be generated by photons in a non-magnetic metal that is in close proximity to a magnetic insulator. On exposure to light, there occurs a light induced, spin-dependent excitation of electrons in a few platinum layers near the metal/magnetic insulator interface. This excitation gives rise to a pure spin current which flows in the metal. This new effect is explored in detail and extensive measurements are carried out to confirm the photonic origin of the photo-spin-voltaic effect and exclude competing effects. In addition to the spin current measurements, magnetization dynamics were probed in thin films using ferromagnetic resonance (FMR). In order to determine the optimal material configuration for magnetic recording write heads, FMR measurements were used to perform damping studies on a set of FeCo samples with different numbers of lamination layers. The use of lamination layers has the potential to tune the damping in such films, while leaving the other magnetic properties unchanged. Finally, the sensitivity of the vector network analyzer FMR technique was improved. The use of field modulation and lock-in detection, along with the background subtraction of a Mach-Zehnder microwave interferometer working as a notch filter, is able to increase the sensitivity and lower the background noise of this measurement technique. This improved system opens the possibility of probing previously difficult samples with extremely low signals.

Observation of spinon spin currents in one-dimensional spin liquid

NASA Astrophysics Data System (ADS)

Hirobe, Daichi; Sato, Masahiro; Kawamata, Takayuki; Shiomi, Yuki; Uchida, Ken-Ichi; Iguchi, Ryo; Koike, Yoji; Maekawa, Sadamichi; Saitoh, Eiji

To date, two types of spin current have been explored experimentally: conduction-electron spin current and spin-wave spin current. Here, we newly present spinon spin current in quantum spin liquid. An archetype of quantum spin liquid is realized in one-dimensional spin-1/2 chains with the spins coupled via antiferromagnetic interaction. Elementary excitation in such a system is known as a spinon. Theories have predicted that the correlation of spinons reaches over a long distance. This suggests that spin current may propagate via one-dimensional spinons even in spin liquid states. In this talk, we report the experimental observation that a spin liquid in a spin-1/2 quantum chain generates and conveys spin current, which is attributed to spinon spin current. This is demonstrated by observing an anisotropic negative spin Seebeck effect along the spin chains in Sr2CuO3. The results show that spin current can flow via quantum fluctuation in spite of the absence of magnetic order, suggesting that a variety of quantum spin systems can be applied to spintronics. Spin Quantum Rectification Project, ERATO, JST, Japan; PRESTO, JST, Japan.

The effect of spin in swing bowling in cricket: model trajectories for spin alone

NASA Astrophysics Data System (ADS)

Robinson, Garry; Robinson, Ian

2015-02-01

In ‘swing’ bowling, as employed by fast and fast-medium bowlers in cricket, back-spin along the line of the seam is normally applied in order to keep the seam vertical and to provide stability against ‘wobble’ of the seam. Whilst spin is normally thought of as primarily being the slow bowler's domain, the spin applied by the swing bowler has the side-effect of generating a lift or Magnus force. This force, depending on the orientation of the seam and hence that of the back-spin, can have a side-ways component as well as the expected vertical ‘lift’ component. The effect of the spin itself, in influencing the trajectory of the fast bowler's delivery, is normally not considered, presumably being thought of as negligible. The purpose of this paper is to investigate, using calculated model trajectories, the amount of side-ways movement due to the spin and to see how this predicted movement compares with the total observed side-ways movement. The size of the vertical lift component is also estimated. It is found that, although the spin is an essential part of the successful swing bowler's delivery, the amount of side-ways movement due to the spin itself amounts to a few centimetres or so, and is therefore small, but perhaps not negligible, compared to the total amount of side-ways movement observed. The spin does, however, provide a considerable amount of lift compared to the equivalent delivery bowled without spin, altering the point of pitching by up to 3 m, a very large amount indeed. Thus, for example, bowling a ball with the seam pointing directly down the pitch and not designed to swing side-ways at all, but with the amount of back-spin varied, could provide a very powerful additional weapon in the fast bowler's arsenal. So-called ‘sling bowlers’, who use a very low arm action, can take advantage of spin since effectively they can apply side-spin to the ball, giving rise to a large side-ways movement, ˜ 20{}^\\circ cm or more, which certainly is significant. For a given amount of spin the amount of side-ways movement increases as the bowler's delivery arm becomes more horizontal. This technique could also be exploited by normal spin bowlers as well as swing bowlers.

Langmuir instability in partially spin polarized bounded degenerate plasma

NASA Astrophysics Data System (ADS)

Iqbal, Z.; Jamil, M.; Murtaza, G.

2018-04-01

Some new features of waves inside the cylindrical waveguide on employing the separated spin evolution quantum hydrodynamic model are evoked. Primarily, the instability of Langmuir wave due to the electron beam in a partially spin polarized degenerate plasma considering a nano-cylindrical geometry is discussed. Besides, the evolution of a new spin-dependent wave (spin electron acoustic wave) due to electron spin polarization effects in the real wave spectrum is elaborated. Analyzing the growth rate, it is found that in the absence of Bohm potential, the electron spin effects or exchange interaction reduce the growth rate as well as k-domain but the inclusion of Bohm potential increases both the growth rate and k-domain. Further, we investigate the geometry effects expressed by R and pon and find that they have opposite effects on the growth rate and k-domain of the instability. Additionally, how the other parameters like electron beam density or streaming speed of beam electrons influence the growth rate is also investigated. This study may find its applications for the signal analysis in solid state devices at nanoscales.

Emergent spin electromagnetism induced by magnetization textures in the presence of spin-orbit interaction (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tatara, Gen, E-mail: gen.tatara@riken.jp; Nakabayashi, Noriyuki; Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 Japan

2014-05-07

Emergent electromagnetic field which couples to electron's spin in ferromagnetic metals is theoretically studied. Rashba spin-orbit interaction induces spin electromagnetic field which is in the linear order in gradient of magnetization texture. The Rashba-induced effective electric and magnetic fields satisfy in the absence of spin relaxation the Maxwell's equations as in the charge-based electromagnetism. When spin relaxation is taken into account besides spin dynamics, a monopole current emerges generating spin motive force via the Faraday's induction law. The monopole is expected to play an important role in spin-charge conversion and in the integration of spintronics into electronics.

Modeling all-electrical detection of the inverse Edelstein effect by spin-polarized tunneling in a topological-insulator/ferromagnetic-metal heterostructure

NASA Astrophysics Data System (ADS)

Dey, Rik; Register, Leonard F.; Banerjee, Sanjay K.

2018-04-01

The spin-momentum locking of the surface states in a three-dimensional topological insulator (TI) allows a charge current on the surface of the TI induced by an applied spin current onto the surface, which is known as the inverse Edelstein effect (IEE), that could be achieved either by injecting pure spin current by spin-pumping from a ferromagnetic metal (FM) layer or by injecting spin-polarized charge current by direct tunneling of electrons from the FM to the TI. Here, we present a theory of the observed IEE effect in a TI-FM heterostructure for the spin-polarized tunneling experiments. If an electrical current is passed from the FM to the surface of the TI, because of density-of-states polarization of the FM, an effective imbalance of spin-polarized electrons occurs on the surface of the TI. Due to the spin-momentum helical locking of the surface states in the TI, a difference of transverse charge accumulation appears on the TI surface in a direction orthogonal to the direction of the magnetization of the FM, which is measured as a voltage difference. Here, we derive the two-dimensional transport equations of electrons on the surface of a diffusive TI, coupled to a FM, starting from the quantum kinetic equation, and analytically solve the equations for a rectangular geometry to calculate the voltage difference.

Screening molecular associations with lipid membranes using natural abundance 13C cross-polarization magic-angle spinning NMR and principal component analysis.

PubMed

Middleton, David A; Hughes, Eleri; Madine, Jillian

2004-08-11

We describe an NMR approach for detecting the interactions between phospholipid membranes and proteins, peptides, or small molecules. First, 1H-13C dipolar coupling profiles are obtained from hydrated lipid samples at natural isotope abundance using cross-polarization magic-angle spinning NMR methods. Principal component analysis of dipolar coupling profiles for synthetic lipid membranes in the presence of a range of biologically active additives reveals clusters that relate to different modes of interaction of the additives with the lipid bilayer. Finally, by representing profiles from multiple samples in the form of contour plots, it is possible to reveal statistically significant changes in dipolar couplings, which reflect perturbations in the lipid molecules at the membrane surface or within the hydrophobic interior.

Exchange-Dominated Pure Spin Current Transport in Alq3 Molecules.

PubMed

Jiang, S W; Liu, S; Wang, P; Luan, Z Z; Tao, X D; Ding, H F; Wu, D

2015-08-21

We address the controversy over the spin transport mechanism in Alq3 utilizing spin pumping in the Y3Fe5O12/Alq3/Pd system. An unusual angular dependence of the inverse spin Hall effect is found. It, however, disappears when the microwave magnetic field is fully in the sample plane, excluding the presence of the Hanle effect. Together with the quantitative temperature-dependent measurements, these results provide compelling evidence that the pure spin current transport in Alq3 is dominated by the exchange-mediated mechanism.

Exploratory study of the effects of wing-leading-edge modifications on the stall/spin behavior of a light general aviation airplane

NASA Technical Reports Server (NTRS)

1979-01-01

Configurations with full-span and segmented leading-edge flaps and full-span and segmented leading-edge droop were tested. Studies were conducted with wind-tunnel models, with an outdoor radio-controlled model, and with a full-scale airplane. Results show that wing-leading-edge modifications can produce large effects on stall/spin characteristics, particularly on spin resistance. One outboard wing-leading-edge modification tested significantly improved lateral stability at stall, spin resistance, and developed spin characteristics.

Spin-Triplet Pairing Induced by Spin-Singlet Interactions in Noncentrosymmetric Superconductors

NASA Astrophysics Data System (ADS)

Matsuzaki, Tomoaki; Shimahara, Hiroshi

2017-02-01

In noncentrosymmetric superconductors, we examine the effect of the difference between the intraband and interband interactions, which becomes more important when the band splitting increases. We define the difference ΔVμ between their coupling constants, i.e., that between the intraband and interband hopping energies of intraband Cooper pairs. Here, the subscript μ of ΔVμ indicates that the interactions scatter the spin-singlet and spin-triplet pairs when μ = 0 and μ = 1,2,3, respectively. It is shown that the strong antisymmetric spin-orbit interaction reverses the target spin parity of the interaction: it converts the spin-singlet and spin-triplet interactions represented by ΔV0 and ΔVμ>0 into effective spin-triplet and spin-singlet pairing interactions, respectively. Hence, for example, triplet pairing can be induced solely by the singlet interaction ΔV0. We name the pairing symmetry of the system after that of the intraband Cooper pair wave function, but with an odd-parity phase factor excluded. The pairing symmetry must then be even, even for the triplet component, and the following results are obtained. When ΔVμ is small, the spin-triplet p-wave interactions induce spin-triplet s-wave and spin-triplet d-wave pairings in the regions where the repulsive singlet s-wave interaction is weak and strong, respectively. When ΔV0 is large, a repulsive interband spin-singlet interaction can stabilize spin-triplet pairing. When the Rashba interaction is adopted for the spin-orbit interaction, the spin-triplet pairing interactions mediated by transverse magnetic fluctuations do not contribute to triplet pairing.

Calculation of spin-densities within the context of density functional theory. The crucial role of the correlation functional

NASA Astrophysics Data System (ADS)

Filatov, Michael; Cremer, Dieter

2005-09-01

It is demonstrated that the LYP correlation functional is not suited to be used for the calculation of electron spin resonance hyperfine structure (HFS) constants, nuclear magnetic resonance spin-spin coupling constants, magnetic, shieldings and other properties that require a balanced account of opposite- and equal-spin correlation, especially in the core region. In the case of the HFS constants of alkali atoms, LYP exaggerates opposite-spin correlation effects thus invoking too strong in-out correlation effects, an exaggerated spin-polarization pattern in the core shells of the atoms, and, consequently, too large HFS constants. Any correlation functional that provides a balanced account of opposite- and equal-spin correlation leads to improved HFS constants, which is proven by comparing results obtained with the LYP and the PW91 correlation functional. It is suggested that specific response properties are calculated with the PW91 rather than the LYP correlation functional.

Dynamical spin accumulation in large-spin magnetic molecules

NASA Astrophysics Data System (ADS)

Płomińska, Anna; Weymann, Ireneusz; Misiorny, Maciej

2018-01-01

The frequency-dependent transport through a nanodevice containing a large-spin magnetic molecule is studied theoretically in the Kondo regime. Specifically, the effect of magnetic anisotropy on dynamical spin accumulation is of primary interest. Such accumulation arises due to finite components of frequency-dependent conductance that are off diagonal in spin. Here, employing the Kubo formalism and the numerical renormalization group method, we demonstrate that the dynamical transport properties strongly depend on the relative orientation of spin moments in electrodes of the device, as well as on intrinsic parameters of the molecule. In particular, the effect of dynamical spin accumulation is found to be greatly affected by the type of magnetic anisotropy exhibited by the molecule, and it develops for frequencies corresponding to the Kondo temperature. For the parallel magnetic configuration of the device, the presence of dynamical spin accumulation is conditioned by the interplay of ferromagnetic-lead-induced exchange field and the Kondo correlations.

Resonant Tunneling Spin Pump

NASA Technical Reports Server (NTRS)

Ting, David Z.

2007-01-01

The resonant tunneling spin pump is a proposed semiconductor device that would generate spin-polarized electron currents. The resonant tunneling spin pump would be a purely electrical device in the sense that it would not contain any magnetic material and would not rely on an applied magnetic field. Also, unlike prior sources of spin-polarized electron currents, the proposed device would not depend on a source of circularly polarized light. The proposed semiconductor electron-spin filters would exploit the Rashba effect, which can induce energy splitting in what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. Theoretical studies have suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling.

Persistent spin helix manipulation by optical doping of a CdTe quantum well

NASA Astrophysics Data System (ADS)

Passmann, F.; Anghel, S.; Tischler, T.; Poshakinskiy, A. V.; Tarasenko, S. A.; Karczewski, G.; Wojtowicz, T.; Bristow, A. D.; Betz, M.

2018-05-01

Time-resolved Kerr-rotation microscopy explores the influence of optical doping on the persistent spin helix in a [001]-grown CdTe quantum well at cryogenic temperatures. Electron spin-diffusion dynamics reveal a momentum-dependent effective magnetic field providing SU(2) spin-rotation symmetry, consistent with kinetic theory. The Dresselhaus and Rashba spin-orbit coupling parameters are extracted independently from rotating the spin helix with external magnetic fields applied parallel and perpendicular to the effective magnetic field. Most importantly, a nonuniform spatiotemporal precession pattern is observed. The kinetic-theory framework of spin diffusion allows for modeling of this finding by incorporating the photocarrier density into the Rashba (α) and the Dresselhaus (β3) parameters. Corresponding calculations are further validated by an excitation-density-dependent measurement. This work shows universality of the persistent spin helix by its observation in a II-VI compound and the ability to fine-tune it by optical doping.

Matrix-assisted relaxation in Fe(phen)2(NCS)2 spin-crossover microparticles, experimental and theoretical investigations

NASA Astrophysics Data System (ADS)

Enachescu, Cristian; Tanasa, Radu; Stancu, Alexandru; Tissot, Antoine; Laisney, Jérôme; Boillot, Marie-Laure

2016-07-01

In this study, we present the influence of the embedding matrix on the relaxation of Fe(phen)2(NCS)2 (phen = 1,10-phenanthroline) spin-transition microparticles as revealed by experiments and provide an explanation within the framework of an elastic model based on a Monte-Carlo method. Experiments show that the shape of the high-spin → low-spin relaxation curves is drastically changed when the particles are dispersed in glycerol. This effect was considered in the model by means of interactions between the microparticles and the matrix. A faster start of the relaxation for microparticles embedded in glycerol is due to an initial positive local pressure acting on the edge spin-crossover molecules from the matrix side. This local pressure diminishes and eventually becomes negative during relaxation, as an effect of the decrease of the volume of spin-crossover microparticles from high-spin to low-spin.

Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a W /Co40Fe40B20/MgO Structure with Perpendicular Magnetic Anisotropy

NASA Astrophysics Data System (ADS)

Hao, Qiang; Xiao, Gang

2015-03-01

We obtain robust perpendicular magnetic anisotropy in a β -W /Co40Fe40B20/MgO structure without the need of any insertion layer between W and Co40Fe40B20 . This is achieved within a broad range of W thicknesses (3.0-9.0 nm), using a simple fabrication technique. We determine the spin Hall angle (0.40) and spin-diffusion length for the bulk β form of tungsten with a large spin-orbit coupling. As a result of the giant spin Hall effect in β -W and careful magnetic annealing, we significantly reduce the critical current density for the spin-transfer-torque-induced magnetic switching in Co40Fe40B20 . The elemental β -W is a superior candidate for magnetic memory and spin-logic applications.

Free-Spinning-Tunnel Tests of a 1/24-Scale Model of the Grumman XF9F-2 Airplane, TED No. NACA DE 317

NASA Technical Reports Server (NTRS)

Berman, Theodore

1948-01-01

An investigation of the spin and recovery characteristics of a scale model of the Grumman XF9F-2 airplane has been conducted in the Langley 20-foot free-spinning tunnel. The effects of control settings and movements on the erect and inverted spin and recovery characteristics of the model in the flight loading were determined. The investigation also included spin-recovery-parachute, pilot-escape, and rudder-pedal- . force tests. The recovery characteristics of the model were satisfactory for all configurations tested. Spins for the normal control configuration were oscillatory in roll and yaw. Deflecting the leading-edge flaps or the dive brakes did not change the spin and recovery characteristics of the model noticeably. A 10.0-foot tail parachute or a 6.0-foot wing-tip parachute (drag coefficient of 0.75) was found to be effective for recoveries from demonstration spins. The rudder forces in the spin appeared to be within the capabilities of the pilot.

Spin- and Valley-Dependent Electronic Structure in Silicene Under Periodic Potentials

NASA Astrophysics Data System (ADS)

Lu, Wei-Tao; Li, Yun-Fang; Tian, Hong-Yu

2018-03-01

We study the spin- and valley-dependent energy band and transport property of silicene under a periodic potential, where both spin and valley degeneracies are lifted. It is found that the Dirac point, miniband, band gap, anisotropic velocity, and conductance strongly depend on the spin and valley indices. The extra Dirac points appear as the voltage potential increases, the critical values of which are different for electron with different spins and valleys. Interestingly, the velocity is greatly suppressed due to the electric field and exchange field, other than the gapless graphene. It is possible to achieve an excellent collimation effect for a specific spin near a specific valley. The spin- and valley-dependent band structure can be used to adjust the transport, and perfect transmissions are observed at Dirac points. Therefore, a remarkable spin and valley polarization is achieved which can be switched effectively by the structural parameters. Importantly, the spin and valley polarizations are greatly enhanced by the disorder of the periodic potential.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

NASA Astrophysics Data System (ADS)

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M. D.

2017-09-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal-metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces.

PubMed

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M D

2017-09-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

PubMed Central

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M. D.

2017-01-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism. PMID:29333523

A model of spin crossover in manganese(III) compounds: effects of intra- and intercenter interactions.

PubMed

Klokishner, Sophia I; Roman, Marianna A; Reu, Oleg S

2011-11-21

A microscopic approach to the problem of cooperative spin crossover in the [MnL2]NO3 crystal, which contains Mn(III) ions as structural units, is elaborated on, and the main mechanisms governing this effect are revealed. The proposed model also takes into account the splitting of the low-spin 3T1 (t(2)(4)) and high-spin 5E (t(2)(3)e) terms by the low-symmetry crystal field. The low-spin → high-spin transition has been considered as a cooperative phenomenon driven by interaction of the electronic shells of the Mn(III) ions with the all-around full-symmetric deformation that is extended over the crystal lattice via the acoustic phonon field. The model well explains the observed thermal dependencies of the magnetic susceptibility and the effective magnetic moment.

Effect of a Phonon Bottleneck on Exciton and Spin Generation in Self-Assembled In1 -xGaxAs Quantum Dots

NASA Astrophysics Data System (ADS)

Huang, Y. Q.; Buyanova, I. A.; Yang, X. J.; Murayama, A.; Chen, W. M.

2018-04-01

We provide direct experimental evidence for the effect of a phonon bottleneck on exciton and spin generation in self-assembled In0.5Ga0.5As quantum dots (QDs). With the aid of tunable laser spectroscopy, we resolve and identify efficient exciton generation channels in the QDs mediated by longitudinal-optical (LO) phonons from an otherwise inhomogeneously broadened QD emission background that suffers from the phonon bottleneck effect in exciton generation. Spin-generation efficiency is found to be enhanced under the LO-assisted excitation condition due to suppressed spin relaxation accompanying accelerated exciton generation. These findings underline the importance of fine-tuning QD energy levels that will benefit potential spin-optoelectronic applications of QDs by reducing spin loss due to the phonon bottleneck.

Collective Yu-Shiba-Rusinov states in magnetic clusters at superconducting surfaces

NASA Astrophysics Data System (ADS)

Körber, Simon; Trauzettel, Björn; Kashuba, Oleksiy

2018-05-01

We study the properties of collective Yu-Shiba-Rusinov (YSR) states generated by multiple magnetic adatoms (clusters) placed on the surface of a superconductor. For magnetic clusters with equal distances between their constituents, we demonstrate the formation of effectively spin-unpolarized YSR states with subgap energies independent of the spin configuration of the magnetic impurities. We solve the problem analytically for arbitrary spin structure and analyze both spin-polarized (dispersive energy levels) and spin-unpolarized (pinned energy levels) solutions. While the energies of the spin-polarized solutions can be characterized solely by the net magnetic moment of the cluster, the wave functions of the spin-unpolarized solutions effectively decouple from it. This decoupling makes them stable against thermal fluctuation and detectable in scanning tunneling microscopy experiments.

Control by substrate of the cytochrome p450-dependent redox machinery: mechanistic insights.

PubMed

Hlavica, Peter

2007-08-01

Based on initial studies with bacterial CYP101A1, a popular concept emerged predicting that substrate-induced low-to-high spin conversion of P450s is universally associated with shifts of the midpoint potential to a more positive value to maximize rates of electron transfer and metabolic turnover. However, evaluation of the plethora of observations with pro- and eukaryotic hemoproteins suggests a caveat as to generalization of this principle. Thus, some P450s are inherently high-spin, so that there is no need for a supportive substrate-triggered impulse to electron flow. With other enzymes, high-spin content is not consonant with reductive activity, and spin transition as such is not essential to sustaining substrate oxidation. Also, with certain proteins the low-spin conformer is reduced as swift as the high-spin entity. Moreover, there is not regularly a linear relationship between high-spin level and anodic shift of the reduction potential. Similarly, in given cases turnover may proceed despite insignificant or even lacking substrate-provoked alterations in the redox behaviour. Thus, folding of the disparate and sometimes conflicting data into a harmonized overall picture is a lingering problem. Apart from direct perturbation of the electrochemical properties, substrate docking may entail changes in enzyme conformation such as to favour productive complexation with redox partners or modulate electron transfer conduits within preformed donor/acceptor adducts, resulting in elevated ease of flow of reducing equivalents. Substrate-steered ordering of the oligomeric aggregation state of P450s is likely to impose steric constraints on heterodimers, causing one component to more readily align with electron carriers. Careful uncovering of electrochemical mechanisms in these systems will be fruitful to tailoring of novel bioenergetic machines and redox chains via redox-inspired protein engineering or molecular Lego, capable of generating products of interest or degrading toxic pollutants. Finally, availability of P450 nanobiochips for high-throughput screening of substrate libraries might expedite drug development.

Recent advancements in 2D-materials interface based magnetic junctions for spintronics

NASA Astrophysics Data System (ADS)

Iqbal, Muhammad Zahir; Qureshi, Nabeel Anwar; Hussain, Ghulam

2018-07-01

Two-dimensional (2D) materials comprising of graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs) have revealed fascinating properties in various spintronic architectures. Here, we review spin valve effect in lateral and vertical magnetic junctions incorporating 2D materials as non-magnetic layer between ferromagnetic (FM) electrodes. The magnetic field dependent spin transport properties are studied by measuring non-local resistance (RNL) and relative magnetoresistance ratio (MR) for lateral and vertical structures, respectively. The review consists of (i) studying spin lifetimes and spin diffusion length thereby exploring the effect of tunneling and transparent contacts in lateral spin valve structures, temperature dependence, gate tunability and contrasting mechanisms of spin relaxation in single layer graphene (SLG) and bilayer graphene (BLG) devices. (ii) Perpendicular spin valve devices are thoroughly investigated thereby studying the role of different 2D materials in vertical spin dynamics. The dependence of spin valve signal on interface quality, temperature and various other parameters is also investigated. Furthermore, the spin reversal in graphene-hBN hybrid system is examined on the basis of Julliere model.

Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain

PubMed Central

Chekhovich, E.A.; Hopkinson, M.; Skolnick, M.S.; Tartakovskii, A.I.

2015-01-01

Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear–nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we report direct measurement of nuclear spin bath coherence in individual self-assembled InGaAs/GaAs quantum dots: spin-echo coherence times in the range 1.2–4.5 ms are found. Based on these values, we demonstrate that strain-induced quadrupolar interactions make nuclear spin fluctuations much slower compared with lattice-matched GaAs/AlGaAs structures. Our findings demonstrate that quadrupolar effects can potentially be used to engineer optically active III-V semiconductor spin-qubits with a nearly noise-free nuclear spin bath, previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling are challenging. PMID:25704639

Spinning Characteristics of the XN2Y-1 Airplane Obtained from the Spinning Balance and Compared with Results from the Spinning Tunnel and from Flight Tests

NASA Technical Reports Server (NTRS)

Bamber, M J; House, R O

1937-01-01

Report presents the results of tests of a 1/10-scale model of the XN2Y-1 airplane tested in the NACA 5-foot vertical wind tunnel in which the six components of forces and moments were measured. The model was tested in 17 attitudes in which the full-scale airplane had been observed to spin, in order to determine the effects of scale, tunnel, and interference. In addition, a series of tests was made to cover the range of angles of attack, angles of sideslip, rates of rotation, and control setting likely to be encountered by a spinning airplane. The data were used to estimate the probable attitudes in steady spins of an airplane in flight and of a model in the free-spinning tunnel. The estimated attitudes of steady spin were compared with attitudes measured in flight and in the spinning tunnel. The results indicate that corrections for certain scale and tunnel effects are necessary to estimate full-scale spinning attitudes from model results.

Free-Spinning-Tunnel Investigation of a 1/24-Scale Model of the Grumman F9F-6 Airplane TED No. NACA DE 364

NASA Technical Reports Server (NTRS)

Klinar, Walter J.; Healy, Frederick M.

1952-01-01

An investigation of a 1/24-scale model of the Grumman F9F-6 airplane has been conducted in the Langley 20-foot free-spinning tunnel. The erect and inverted spin and recovery characteristics of the model were determined for the normal flight loading with the model in the clean condition. The effect of loading variations was investigated briefly. Spin-recovery parachute tests were also performed. The results indicate that erect spins obtained on the airplane in the clean condition will be satisfactorily terminated for all loading conditions provided full rudder reversal is accompanied by moving the ailerons and flaperons (lateral controls) to full with the spin (stick right in a right spin). Inverted spins should be satisfactorily terminated by full reversal of the rudder alone. The model tests indicate that an 11.4-foot (laid-out-flat diameter) tail parachute (drag coefficient approximately 0.73) should be effective as an emergency spin-recovery device during demonstration spins of the airplane provided the towline is attached above the horizontal stabilizer.

Detection of Short-Waved Spin Waves in Individual Microscopic Spin-Wave Waveguides Using the Inverse Spin Hall Effect.

PubMed

Brächer, T; Fabre, M; Meyer, T; Fischer, T; Auffret, S; Boulle, O; Ebels, U; Pirro, P; Gaudin, G

2017-12-13

The miniaturization of complementary metal-oxide-semiconductor (CMOS) devices becomes increasingly difficult due to fundamental limitations and the increase of leakage currents. Large research efforts are devoted to find alternative concepts that allow for a larger data-density and lower power consumption than conventional semiconductor approaches. Spin waves have been identified as a potential technology that can complement and outperform CMOS in complex logic applications, profiting from the fact that these waves enable wave computing on the nanoscale. The practical application of spin waves, however, requires the demonstration of scalable, CMOS compatible spin-wave detection schemes in material systems compatible with standard spintronics as well as semiconductor circuitry. Here, we report on the wave-vector independent detection of short-waved spin waves with wavelengths down to 150 nm by the inverse spin Hall effect in spin-wave waveguides made from ultrathin Ta/Co 8 Fe 72 B 20 /MgO. These findings open up the path for miniaturized scalable interconnects between spin waves and CMOS and the use of ultrathin films made from standard spintronic materials in magnonics.

Strong-coupling induced damping of spin-echo modulations in magic-angle-spinning NMR: Implications for J coupling measurements in disordered solids

NASA Astrophysics Data System (ADS)

Guerry, Paul; Brown, Steven P.; Smith, Mark E.

2017-10-01

In the context of improving J coupling measurements in disordered solids, strong coupling effects have been investigated in the spin-echo and refocused INADEQUATE spin-echo (REINE) modulations of three- and four-spin systems under magic-angle-spinning (MAS), using density matrix simulations and solid-state NMR experiments on a cadmium phosphate glass. Analytical models are developed for the different modulation regimes, which are shown to be distinguishable in practice using Akaike's information criterion. REINE modulations are shown to be free of the damping that occurs for spin-echo modulations when the observed spin has the same isotropic chemical shift as its neighbour. Damping also occurs when the observed spin is bonded to a strongly-coupled pair. For mid-chain units, the presence of both direct and relayed damping makes both REINE and spin-echo modulations impossible to interpret quantitatively. We nonetheless outline how a qualitative comparison of the modulation curves can provide valuable information on disordered networks, possibly also pertaining to dynamic effects therein.

Half-metallic superconducting triplet spin multivalves

NASA Astrophysics Data System (ADS)

Alidoust, Mohammad; Halterman, Klaus

2018-02-01

We study spin switching effects in finite-size superconducting multivalve structures. We examine F1F2SF3 and F1F2SF3F4 hybrids where a singlet superconductor (S) layer is sandwiched among ferromagnet (F) layers with differing thicknesses and magnetization orientations. Our results reveal a considerable number of experimentally viable spin-valve configurations that lead to on-off switching of the superconducting state. For S widths on the order of the superconducting coherence length ξ0, noncollinear magnetization orientations in adjacent F layers with multiple spin axes leads to a rich variety of triplet spin-valve effects. Motivated by recent experiments, we focus on samples where the magnetizations in the F1 and F4 layers exist in a fully spin-polarized half-metallic phase, and calculate the superconducting transition temperature, spatially and energy resolved density of states, and the spin-singlet and spin-triplet superconducting correlations. Our findings demonstrate that superconductivity in these devices can be completely switched on or off over a wide range of magnetization misalignment angles due to the generation of equal-spin and opposite-spin triplet pairings.

Spin relaxation in graphene nanoribbons in the presence of substrate surface roughness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chaghazardi, Zahra; Faez, Rahim; Touski, Shoeib Babaee

2016-08-07

In this work, spin transport in corrugated armchair graphene nanoribbons (AGNRs) is studied. We survey combined effects of spin-orbit interaction and surface roughness, employing the non-equilibrium Green's function formalism and multi-orbitals tight-binding model. Rough substrate surfaces have been statistically generated and the hopping parameters are modulated based on the bending and distance of corrugated carbon atoms. The effects of surface roughness parameters, such as roughness amplitude and correlation length, on spin transport in AGNRs are studied. The increase of surface roughness amplitude results in the coupling of σ and π bands in neighboring atoms, leading to larger spin flipping ratemore » and therefore reduction of the spin-polarization, whereas a longer correlation length makes AGNR surface smoother and increases spin-polarization. Moreover, spin diffusion length of carriers is extracted and its dependency on the roughness parameters is investigated. In agreement with experimental data, the spin diffusion length for various substrate ranges between 2 and 340 μm. Our results indicate the importance of surface roughness on spin-transport in graphene.« less

Spin-orbit coupling effects in zinc-blende InSb and wurtzite InAs nanowires: Realistic calculations with multiband k .p method

NASA Astrophysics Data System (ADS)

Campos, Tiago; Faria Junior, Paulo E.; Gmitra, Martin; Sipahi, Guilherme M.; Fabian, Jaroslav

2018-06-01

A systematic numerical investigation of spin-orbit fields in the conduction bands of III-V semiconductor nanowires is performed. Zinc-blende (ZB) InSb nanowires are considered along [001], [011], and [111] directions, while wurtzite (WZ) InAs nanowires are studied along [0001] and [10 1 ¯0 ] or [11 2 ¯0 ] directions. Robust multiband k .p Hamiltonians are solved by using plane-wave expansions of real-space parameters. In all cases, the linear and cubic spin-orbit coupling parameters are extracted for nanowire widths from 30 to 100 nm. Typical spin-orbit energies are on the μ eV scale, except for WZ InAs nanowires grown along [10 1 ¯0 ] or [11 2 ¯0 ] , in which the spin-orbit energy is about meV, largely independent of the wire diameter. Significant spin-orbit coupling is obtained by applying a transverse electric field, causing the Rashba effect. For an electric field of about 4 mV/nm, the obtained spin-orbit energies are about 1 meV for both materials in all investigated growth directions. The most favorable system, in which the spin-orbit effects are maximal, are WZ InAs nanowires grown along [1010] or [11 2 ¯0 ] since here spin-orbit energies are giant (meV) already in the absence of electric field. The least favorable are InAs WZ nanowires grown along [0001] since here even the electric field does not increase the spin-orbit energies beyond 0.1 meV. The presented results should be useful for investigations of optical orientation, spin transport, weak localization, and superconducting proximity effects in semiconductor nanowires.

Kondo physics in non-local metallic spin transport devices.

PubMed

O'Brien, L; Erickson, M J; Spivak, D; Ambaye, H; Goyette, R J; Lauter, V; Crowell, P A; Leighton, C

2014-05-29

The non-local spin-valve is pivotal in spintronics, enabling separation of charge and spin currents, disruptive potential applications and the study of pressing problems in the physics of spin injection and relaxation. Primary among these problems is the perplexing non-monotonicity in the temperature-dependent spin accumulation in non-local ferromagnetic/non-magnetic metal structures, where the spin signal decreases at low temperatures. Here we show that this effect is strongly correlated with the ability of the ferromagnetic to form dilute local magnetic moments in the NM. This we achieve by studying a significantly expanded range of ferromagnetic/non-magnetic combinations. We argue that local moments, formed by ferromagnetic/non-magnetic interdiffusion, suppress the injected spin polarization and diffusion length via a manifestation of the Kondo effect, thus explaining all observations. We further show that this suppression can be completely quenched, even at interfaces that are highly susceptible to the effect, by insertion of a thin non-moment-supporting interlayer.

A separation of antiferromagnetic spin motion modes in the training effect of exchange biased Co/CoO film with in-plane anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, R.; Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS; Yun, C.

2016-08-07

The motion of antiferromagnetic interfacial spins is investigated through the temperature evolution of training effect in a Co/CoO film with in-plane biaxial anisotropy. Significant differences in the training effect and its temperature dependence are observed in the magnetic easy axis and hard axis (HA) and ascribed to the different motion modes of antiferromagnetic interfacial spins, the collective spin cluster rotation (CSR) and the single spin reversal (SSR), caused by different magnetization reversal modes of ferromagnetic layer. These motion modes of antiferromagnetic spins are successfully separated using a combination of an exponential function and a classic n{sup −1/2} function. A largermore » CSR to SSR ratio and a shorter lifetime of CSR found in the HA indicates that the domain rotation in the ferromagnetic layer tends to activate and accelerate a CSR mode in the antiferromagnetic spins.« less

Rashba effect and enriched spin-valley coupling in Ga X /M X2 (M = Mo, W; X = S, Se, Te) heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Qingyun; Schwingenschlögl, Udo

2018-04-01

Using first-principles calculations, we investigate the electronic properties of the two-dimensional Ga X /MX 2 (M = Mo, W; X = S, Se, Te) heterostructures. Orbital hybridization between Ga X and MX 2 is found to result in Rashba splitting at the valence-band edge around the Γ point, which grows for increasing strength of the spin-orbit coupling in the p orbitals of the chalcogenide atoms. The location of the valence-band maximum in the Brillouin zone can be tuned by strain and application of an out-of-plane electric field. The coexistence of Rashba splitting (in-plane spin direction) and band splitting at the K and K' valleys (out-of-plane spin direction) makes Ga X /MX 2 heterostructures interesting for spintronics and valleytronics. They are promising candidates for two-dimensional spin-field-effect transistors and spin-valley Hall effect devices. Our findings shed light on the spin-valley coupling in van der Waals heterostructures.

Driving and detecting ferromagnetic resonance in insulators with the spin Hall effect

DOE PAGES

Sklenar, Joseph; Zhang, Wei; Jungfleisch, Matthias B.; ...

2015-11-06

We demonstrate the generation and detection of spin-torque ferromagnetic resonance in Pt/Y 3Fe 5O 12 (YIG) bilayers. A unique attribute of this system is that the spin Hall effect lies at the heart of both the generation and detection processes and no charge current is passing through the insulating magnetic layer. When the YIG undergoes resonance, a dc voltage is detected longitudinally along the Pt that can be described by two components. One is the mixing of the spin Hall magnetoresistance with the microwave current. The other results from spin pumping into the Pt being converted to a dc currentmore » through the inverse spin Hall effect. The voltage is measured with applied magnetic field directions that range in-plane to nearly perpendicular. In conclusion, we find that for magnetic fields that are mostly out-of-plane, an imaginary component of the spin mixing conductance is required to model our data.« less

Equilibrium charge fluctuations of a charge detector and its effect on a nearby quantum dot

NASA Astrophysics Data System (ADS)

Ruiz-Tijerina, David; Vernek, Edson; Ulloa, Sergio

2014-03-01

We study the Kondo state of a spin-1/2 quantum dot (QD), in close proximity to a quantum point contact (QPC) charge detector near the conductance regime of the 0.7 anomaly. The electrostatic coupling between the QD and QPC introduces a remote gate on the QD level, which varies with the QPC gate voltage. Furthermore, models for the 0.7 anomaly [Y. Meir et al., PRL 89,196802(2002)] suggest that the QPC lodges a Kondo-screened level with charge-correlated hybridization, which may be also affected by capacitive coupling to the QD, giving rise to a competition between the two Kondo ground states. We model the QD-QPC system as two capacitively-coupled Kondo impurities, and explore the zero-bias transport of both the QD and the QPC for different local gate voltages and coupling strengths, using the numerical renormalization group and variational methods. We find that the capacitive coupling produces a remote gating effect, non-monotonic in the gate voltages, which reduces the gate voltage window for Kondo screening in either impurity, and which can also drive a quantum phase transition out of the Kondo regime. Our study is carried out for intermediate coupling strengths, and as such is highly relevant to experiments; particularly, to recent studies of decoherence effects on QDs. Supported by MWN/CIAM and NSF PIRE.

Spin-Hall nano-oscillator with oblique magnetization and Dzyaloshinskii-Moriya interaction as generator of skyrmions and nonreciprocal spin-waves

PubMed Central

Giordano, A.; Verba, R.; Zivieri, R.; Laudani, A.; Puliafito, V.; Gubbiotti, G.; Tomasello, R.; Siracusano, G.; Azzerboni, B.; Carpentieri, M.; Slavin, A.; Finocchio, G.

2016-01-01

Spin-Hall oscillators (SHO) are promising sources of spin-wave signals for magnonics applications, and can serve as building blocks for magnonic logic in ultralow power computation devices. Thin magnetic layers used as “free” layers in SHO are in contact with heavy metals having large spin-orbital interaction, and, therefore, could be subject to the spin-Hall effect (SHE) and the interfacial Dzyaloshinskii-Moriya interaction (i-DMI), which may lead to the nonreciprocity of the excited spin waves and other unusual effects. Here, we analytically and micromagnetically study magnetization dynamics excited in an SHO with oblique magnetization when the SHE and i-DMI act simultaneously. Our key results are: (i) excitation of nonreciprocal spin-waves propagating perpendicularly to the in-plane projection of the static magnetization; (ii) skyrmions generation by pure spin-current; (iii) excitation of a new spin-wave mode with a spiral spatial profile originating from a gyrotropic rotation of a dynamical skyrmion. These results demonstrate that SHOs can be used as generators of magnetic skyrmions and different types of propagating spin-waves for magnetic data storage and signal processing applications. PMID:27786261

All-Electrical Spin Field Effect Transistor in van der Waals Heterostructures at Room Temperature

NASA Astrophysics Data System (ADS)

Dankert, André; Dash, Saroj

Spintronics aims to exploit the spin degree of freedom in solid state devices for data storage and information processing. Its fundamental concepts (creation, manipulation and detection of spin polarization) have been demonstrated in semiconductors and spin transistor structures using electrical and optical methods. However, an unsolved challenge is the realization of all-electrical methods to control the spin polarization in a transistor manner at ambient temperatures. Here we combine graphene and molybdenum disulfide (MoS2) in a van der Waals heterostructure to realize a spin field-effect transistor (spin-FET) at room temperature. These two-dimensional crystals offer a unique platform due to their contrasting properties, such as weak spin-orbit coupling (SOC) in graphene and strong SOC in MoS2. The gate-tuning of the Schottky barrier at the MoS2/graphene interface and MoS2 channel yields spins to interact with high SOC material and allows us to control the spin polarization and lifetime. This all-electrical spin-FET at room temperature is a substantial step in the field of spintronics and opens a new platform for testing a plethora of exotic physical phenomena, which can be key building blocks in future device architectures.

Spin-orbit coupling, electron transport and pairing instabilities in two-dimensional square structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocharian, Armen N.; Fernando, Gayanath W.; Fang, Kun

Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges andmore » opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters) engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.« less

Heat-driven spin torques in antiferromagnets

NASA Astrophysics Data System (ADS)

Białek, Marcin; Bréchet, Sylvain; Ansermet, Jean-Philippe

2018-04-01

Heat-driven magnetization damping, which is a linear function of a temperature gradient, is predicted in antiferromagnets by considering the sublattice dynamics subjected to a heat-driven spin torque. This points to the possibility of achieving spin torque oscillator behavior. The model is based on the magnetic Seebeck effect acting on sublattices which are exchange coupled. The heat-driven spin torque is estimated and the feasibility of detecting this effect is discussed.

Anisotropic in-plane spin splitting in an asymmetric (001) GaAs/AlGaAs quantum well

PubMed Central

2011-01-01

The in-plane spin splitting of conduction-band electron has been investigated in an asymmetric (001) GaAs/AlxGa1-xAs quantum well by time-resolved Kerr rotation technique under a transverse magnetic field. The distinctive anisotropy of the spin splitting was observed while the temperature is below approximately 200 K. This anisotropy emerges from the combined effect of Dresselhaus spin-orbit coupling plus asymmetric potential gradients. We also exploit the temperature dependence of spin-splitting energy. Both the anisotropy of spin splitting and the in-plane effective g-factor decrease with increasing temperature. PACS: 78.47.jm, 71.70.Ej, 75.75.+a, 72.25.Fe, PMID:21888636

Spin Nernst effect of magnons in collinear antiferromagnets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Ran; Okamoto, Satoshi; Xiao, Di

2016-11-15

In a collinear antiferromagnet with easy-axis anisotropy, symmetry guarantees that the spin wave modes are doubly degenerate. The two modes carry opposite spin angular momentum and exhibit opposite chirality. Using a honeycomb antiferromagnet in the presence of the Dzyaloshinskii-Moriya interaction, we show that a longitudinal temperature gradient can drive the two modes to opposite transverse directions, realizing a spin Nernst effect of magnons with vanishing thermal Hall current. We find that magnons around themore » $$\\Gamma$$ point and the $K$ point contribute oppositely to the transverse spin transport, and their competition leads to a sign change of the spin Nernst coefficient at finite temperature. As a result, possible material candidates are discussed.« less

Antiresonance induced spin-polarized current generation

NASA Astrophysics Data System (ADS)

Yin, Sun; Min, Wen-Jing; Gao, Kun; Xie, Shi-Jie; Liu, De-Sheng

2011-12-01

According to the one-dimensional antiresonance effect (Wang X R, Wang Y and Sun Z Z 2003 Phys. Rev. B 65 193402), we propose a possible spin-polarized current generation device. Our proposed model consists of one chain and an impurity coupling to the chain. The energy level of the impurity can be occupied by an electron with a specific spin, and the electron with such a spin is blocked because of the antiresonance effect. Based on this phenomenon our model can generate the spin-polarized current flowing through the chain due to different polarization rates. On the other hand, the device can also be used to measure the generated spin accumulation. Our model is feasible with today's technology.

Kondo Physics at Interfaces in Metallic Non-Local Spin Transport Devices

NASA Astrophysics Data System (ADS)

Leighton, Chris

2015-03-01

Despite the maturity of metallic spintronics there remain large gaps in our understanding of spin transport in metals, particularly with injection of spins across ferromagnetic/non-magnetic (FM/NM) interfaces, and their subsequent diffusion and relaxation. Unresolved issues include the limits of applicability of Elliott-Yafet spin relaxation, quantification of the influence of defects, surfaces, and interfaces on spin relaxation at nanoscopic dimensions, and the importance of magnetic and spin-orbit scattering. The non-local spin-valve is an enabling device in this context as, in addition to offering potentially disruptive applications, it allows for the separation of charge and spin currents. One particularly perplexing issue in metallic non-local spin valves is the widely observed non-monotonicity in the T-dependent spin accumulation, where the spin signal actually decreases at low T, in contrast to simple expectations. In this work, by studying an expanded range of FM/NM combinations (encompassing Ni80Fe20, Ni, Fe, Co, Cu, and Al), we demonstrate that this effect is not a property of a given FM or NM, but rather of the FM/NM pair. The non-monotonicity is in fact strongly correlated with the ability of the FM to form a dilute local magnetic moment in the NM. We show that local moments, resulting in this case from the ppm-level tail of the FM/NM interdiffusion profile, suppress the injected spin polarization and diffusion length via a novel manifestation of the Kondo effect, explaining all observations associated with the low T downturn in spin accumulation. We further show: (a) that this effect can be promoted by thermal annealing, at which point the conventional charge transport Kondo effect is simultaneously detected in the NM, and (b) that this suppression in spin accumulation can be quenched, even at interfaces that are highly susceptible to the effect, by insertion of a thin non-moment-supporting interlayer. Important implications for room temperature devices will be discussed. Work supported by: Seagate Technology, NSF MRSEC (DMR-0819885), Marie Curie International Outgoing Fellowship, 7th European Community Framework Programme (No. 299376). Work at SNS, ORNL, supported by DOE. Work in collaboration with: L. O'Brien, J. Watts, D. Spivak, M. Erickson, H. Ambaye, R.J. Goyette, V. Lauter, P.A. Crowell.

Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO{sub 2}/NiFe trilayers near simultaneous ferromagnetic resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soh, Wee Tee, E-mail: a0046479@u.nus.edu; Ong, C. K.; Peng, Bin

2015-08-15

The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-localmore » SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO{sub 2} spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.« less

Pure spin current manipulation in antiferromagnetically exchange coupled heterostructures

NASA Astrophysics Data System (ADS)

Avilés-Félix, L.; Butera, A.; González-Chávez, D. E.; Sommer, R. L.; Gómez, J. E.

2018-03-01

We present a model to describe the spin currents generated by ferromagnet/spacer/ferromagnet exchange coupled trilayer systems and heavy metal layers with strong spin-orbit coupling. By exploiting the magnitude of the exchange coupling (oscillatory RKKY-like coupling) and the spin-flop transition in the magnetization process, it has been possible to produce spin currents polarized in arbitrary directions. The spin-flop transition of the trilayer system originates pure spin currents whose polarization vector depends on the exchange field and the magnetization equilibrium angles. We also discuss a protocol to control the polarization sign of the pure spin current injected into the metallic layer by changing the initial conditions of magnetization of the ferromagnetic layers previously to the spin pumping and inverse spin Hall effect experiments. The small differences in the ferromagnetic layers lead to a change in the magnetization vector rotation that permits the control of the sign of the induced voltage components due to the inverse spin Hall effect. Our results can lead to important advances in hybrid spintronic devices with new functionalities, particularly, the ability to control microscopic parameters such as the polarization direction and the sign of the pure spin current through the variation of macroscopic parameters, such as the external magnetic field or the thickness of the spacer in antiferromagnetic exchange coupled systems.

Magnon Mode Selective Spin Transport in Compensated Ferrimagnets.

PubMed

Cramer, Joel; Guo, Er-Jia; Geprägs, Stephan; Kehlberger, Andreas; Ivanov, Yurii P; Ganzhorn, Kathrin; Della Coletta, Francesco; Althammer, Matthias; Huebl, Hans; Gross, Rudolf; Kosel, Jürgen; Kläui, Mathias; Goennenwein, Sebastian T B

2017-06-14

We investigate the generation of magnonic thermal spin currents and their mode selective spin transport across interfaces in insulating, compensated ferrimagnet/normal metal bilayer systems. The spin Seebeck effect signal exhibits a nonmonotonic temperature dependence with two sign changes of the detected voltage signals. Using different ferrimagnetic garnets, we demonstrate the universality of the observed complex temperature dependence of the spin Seebeck effect. To understand its origin, we systematically vary the interface between the ferrimagnetic garnet and the metallic layer, and by using different metal layers we establish that interface effects play a dominating role. They do not only modify the magnitude of the spin Seebeck effect signal but in particular also alter its temperature dependence. By varying the temperature, we can select the dominating magnon mode and we analyze our results to reveal the mode selective interface transmission probabilities for different magnon modes and interfaces. The comparison of selected systems reveals semiquantitative details of the interfacial coupling depending on the materials involved, supported by the obtained field dependence of the signal.

Quantum dust magnetosonic waves with spin and exchange correlation effects

NASA Astrophysics Data System (ADS)

Maroof, R.; Mushtaq, A.; Qamar, A.

2016-01-01

Dust magnetosonic waves are studied in degenerate dusty plasmas with spin and exchange correlation effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, spin magnetization energy, and exchange correlation, a generalized dispersion relation is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. The exchange-correlation potentials are used, based on the adiabatic local-density approximation, and can be described as a function of the electron density. For three different values of angle, the dispersion relation is reduced to three different modes under the low frequency magnetohydrodynamic assumptions. It is found that the effects of quantum corrections in the presence of dust concentration significantly modify the dispersive properties of these modes. The results are useful for understanding numerous collective phenomena in quantum plasmas, such as those in compact astrophysical objects (e.g., the cores of white dwarf stars and giant planets) and in plasma-assisted nanotechnology (e.g., quantum diodes, quantum free-electron lasers, etc.).

Internet-delivered cognitive-behavioral therapy for social anxiety disorder in Romania: a randomized controlled trial.

PubMed

Tulbure, Bogdan Tudor; Szentagotai, Aurora; David, Oana; Ștefan, Simona; Månsson, Kristoffer N T; David, Daniel; Andersson, Gerhard

2015-01-01

Internet-based cognitive-behavioral therapy (iCBT) for social anxiety disorder has been found effective, as attested by independently conducted randomized controlled trials in four languages. The study aim is to test the efficacy of an iCBT program in a culture where it was not tested before (i.e. Romania). Participants (n = 76) were recruited, screened and randomized to either a nine-week guided iCBT or a wait-list control group in April and May 2012. Self-report measures were collected before (April 2012) and after the intervention (July 2012), as well as six months later (January 2013). Although social anxiety was assessed with multiple measures, the Liebowitz Social Anxiety Scale - Self Report version (LSAS-SR) and Social Phobia Inventory (SPIN) were used as the primary outcome measures. A significant difference with a large between-group effect size in favor of iCBT was found (Cohen's d = 1.19 for LSAS-SR and d = 1.27 for SPIN). Recovery rates show that 36.8% (n = 14) in the treatment group score below the SPIN clinical cut-off compared to only 2.6% (n = 1) in the wait-list control group. Post-intervention clinical interviews also revealed that 34.2% (n = 13) of the treatment group was completely recovered (full remission) while additionally 36.8% (n = 14) retained some social anxiety symptoms (partial remission). However, an important study limitation is that post-intervention interviewers were not blinded to the study conditions. The program also effectively reduced depression and dysfunctional thinking (between-group Cohen's d = 0.84 for depression and d = 0.63 for dysfunctional thinking). Moreover, the iCBT intervention appears to have a long-term impact for participants' functioning, as the treatment gains were maintained six months later. Internet-delivered interventions display a high potential to quickly and widely disseminate effective evidence-based programs around the world. This study provides support for guided iCBT as a promising treatment approach in Romania. ClinicalTrials.gov NCT01557894.

Internet-Delivered Cognitive-Behavioral Therapy for Social Anxiety Disorder in Romania: A Randomized Controlled Trial

PubMed Central

Tulbure, Bogdan Tudor; Szentagotai, Aurora; David, Oana; Ștefan, Simona; Månsson, Kristoffer N. T.; David, Daniel; Andersson, Gerhard

2015-01-01

Background and Aims Internet-based cognitive-behavioral therapy (iCBT) for social anxiety disorder has been found effective, as attested by independently conducted randomized controlled trials in four languages. The study aim is to test the efficacy of an iCBT program in a culture where it was not tested before (i.e. Romania). Methods Participants (n = 76) were recruited, screened and randomized to either a nine-week guided iCBT or a wait-list control group in April and May 2012. Self-report measures were collected before (April 2012) and after the intervention (July 2012), as well as six months later (January 2013). Although social anxiety was assessed with multiple measures, the Liebowitz Social Anxiety Scale - Self Report version (LSAS-SR) and Social Phobia Inventory (SPIN) were used as the primary outcome measures. Results A significant difference with a large between-group effect size in favor of iCBT was found (Cohen´s d = 1.19 for LSAS-SR and d = 1.27 for SPIN). Recovery rates show that 36.8% (n = 14) in the treatment group score below the SPIN clinical cut-off compared to only 2.6% (n = 1) in the wait-list control group. Post-intervention clinical interviews also revealed that 34.2% (n = 13) of the treatment group was completely recovered (full remission) while additionally 36.8% (n = 14) retained some social anxiety symptoms (partial remission). However, an important study limitation is that post-intervention interviewers were not blinded to the study conditions. The program also effectively reduced depression and dysfunctional thinking (between-group Cohen´s d = 0.84 for depression and d = 0.63 for dysfunctional thinking). Moreover, the iCBT intervention appears to have a long-term impact for participants’ functioning, as the treatment gains were maintained six months later. Conclusions Internet-delivered interventions display a high potential to quickly and widely disseminate effective evidence-based programs around the world. This study provides support for guided iCBT as a promising treatment approach in Romania. Trial Registration ClinicalTrials.gov NCT01557894 PMID:25938241

Unusual negative permeability of single magnetic nanowire excited by the spin transfer torque effect

NASA Astrophysics Data System (ADS)

Han, Mangui; Zhou, Wu

2018-07-01

Due to the effect of spin transfer torque, negative imaginary parts of permeability (μ″ < 0) are reported in a ferromagnetic nanowire. It is found that negative μ″ values are resulted from the interaction of spin polarized conduction electrons with the spatially non-uniform distributed magnetic moments at both ends of nanowires. The results are well explained from the effect of spin transfer torque on the precession of magnetization under the excitation of both the pulsed magnetic field and static electric field.

Effect of multiple spin species on spherical shell neutron transmission analysis

NASA Technical Reports Server (NTRS)

Semler, T. T.

1972-01-01

A series of Monte Carlo calculations were performed in order to evaluate the effect of separated against merged spin statistics on the analysis of spherical shell neutron transmission experiments for gold. It is shown that the use of separated spin statistics results in larger average capture cross sections of gold at 24 KeV. This effect is explained by stronger windows in the total cross section caused by the interference between potential and J(+) resonances and by J(+) and J(-) resonance overlap allowed by the use of separated spin statistics.

Spin-dependent transport and current modulation in a current-in-plane spin-valve field-effect transistor

NASA Astrophysics Data System (ADS)

Kanaki, Toshiki; Koyama, Tomohiro; Chiba, Daichi; Ohya, Shinobu; Tanaka, Masaaki

2016-10-01

We propose a current-in-plane spin-valve field-effect transistor (CIP-SV-FET), which is composed of a ferromagnet/nonferromagnet/ferromagnet trilayer structure and a gate electrode. This is a promising device alternative to spin metal-oxide-semiconductor field-effect transistors. Here, we fabricate a ferromagnetic-semiconductor GaMnAs-based CIP-SV-FET and demonstrate its basic operation of the resistance modulation both by the magnetization configuration and by the gate electric field. Furthermore, we present the electric-field-assisted magnetization reversal in this device.

Entanglement distribution in star network based on spin chain in diamond

NASA Astrophysics Data System (ADS)

Zhu, Yuan-Ming; Ma, Lei

2018-06-01

After star network of spins was proposed, generating entanglement directly through spin interactions between distant parties became possible. We propose an architecture which involves coupled spin chains based on nitrogen-vacancy centers and nitrogen defect spins to expand star network. The numerical analysis shows that the maximally achievable entanglement Em exponentially decays with the length of spin chains M and spin noise. The entanglement capability of this configuration under the effect of disorder and spin loss is also studied. Moreover, it is shown that with this kind of architecture, star network of spins is feasible in measurement of magnetic-field gradient.

Thermoelectronic transport through spin-crossover single molecule Fe[(H2Bpz2)2bipy

NASA Astrophysics Data System (ADS)

Liu, N.; Zhu, L.; Yao, K. L.

2018-04-01

By means of density functional theory combined with the method of Keldysh nonequilibrium Green’s function, the thermal transport properties of high- and low-spin states of mononuclear FeII molecules with spin-crossover characteristics are studied. It is found that the high-spin molecular junction has a larger current than the low-spin one, producing thermally-induced switching effect. Furthermore, for high spin state molecule, the spin-up thermo-current is strongly blocked, thus achieving a pure thermo spin current. The enhanced Seebeck coefficient and the figure of merit value of high-spin state indicate that it is an ideal candidate for thermoelectric applications.

Quantum spin circulator in Y junctions of Heisenberg chains

NASA Astrophysics Data System (ADS)

Buccheri, Francesco; Egger, Reinhold; Pereira, Rodrigo G.; Ramos, Flávia B.

2018-06-01

We show that a quantum spin circulator, a nonreciprocal device that routes spin currents without any charge transport, can be achieved in Y junctions of identical spin-1 /2 Heisenberg chains coupled by a chiral three-spin interaction. Using bosonization, boundary conformal field theory, and density matrix renormalization group simulations, we find that a chiral fixed point with maximally asymmetric spin conductance arises at a critical point separating a regime of disconnected chains from a spin-only version of the three-channel Kondo effect. We argue that networks of spin-chain Y junctions provide a controllable approach to construct long-sought chiral spin-liquid phases.

Effective S =2 antiferromagnetic spin chain in the salt (o -MePy-V)FeCl4

NASA Astrophysics Data System (ADS)

Iwasaki, Y.; Kida, T.; Hagiwara, M.; Kawakami, T.; Hosokoshi, Y.; Tamekuni, Y.; Yamaguchi, H.

2018-02-01

We present a model compound for the S =2 antiferromagnetic (AF) spin chain composed of the salt (o -MePy-V ) FeCl4 . Ab initio molecular-orbital calculations indicate the formation of a partially stacked two-dimensional (2D) spin model comprising five types of exchange interactions between S =1 /2 and S =5 /2 spins, which locate on verdazyl radical and Fe ion, respectively. The magnetic properties of the synthesized crystals indicate that the dominant interaction between the S =1 /2 and S =5 /2 spins stabilizes an S =2 spin in the low-temperature region, and an effective S =2 AF chain is formed for T ≪10 K and H <4 T. We explain the magnetization curve and electron-spin-resonance modes quantitatively based on the S =2 AF chain. At higher fields above quantitatively 4 T, the magnetization curve assumes two-thirds of the full saturation value for fields between 4 and 20 T, and approaches saturation at ˜40 T. The spin model in the high-field region can be considered as a quasi-2D S =1 /2 honeycomb lattice under an effective internal field caused by the fully polarized S =5 /2 spin.

Effective Hamiltonians for correlated narrow energy band systems and magnetic insulators: Role of spin-orbit interactions in metal-insulator transitions and magnetic phase transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborty, Subrata; Vijay, Amrendra, E-mail: avijay@iitm.ac.in

Using a second-quantized many-electron Hamiltonian, we obtain (a) an effective Hamiltonian suitable for materials whose electronic properties are governed by a set of strongly correlated bands in a narrow energy range and (b) an effective spin-only Hamiltonian for magnetic materials. The present Hamiltonians faithfully include phonon and spin-related interactions as well as the external fields to study the electromagnetic response properties of complex materials and they, in appropriate limits, reduce to the model Hamiltonians due to Hubbard and Heisenberg. With the Hamiltonian for narrow-band strongly correlated materials, we show that the spin-orbit interaction provides a mechanism for metal-insulator transition, whichmore » is distinct from the Mott-Hubbard (driven by the electron correlation) and the Anderson mechanism (driven by the disorder). Next, with the spin-only Hamiltonian, we demonstrate the spin-orbit interaction to be a reason for the existence of antiferromagnetic phase in materials which are characterized by a positive isotropic spin-exchange energy. This is distinct from the Néel-VanVleck-Anderson paradigm which posits a negative spin-exchange for the existence of antiferromagnetism. We also find that the Néel temperature increases as the absolute value of the spin-orbit coupling increases.« less

Decoherence and fluctuation dynamics of the quantum dot nuclear spin bath probed by nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Chekhovich, Evgeny A.

2017-06-01

Dynamics of nuclear spin decoherence and nuclear spin flip-flops in self-assembled InGaAs/GaAs quantum dots are studied experimentally using optically detected nuclear magnetic resonance (NMR). Nuclear spin-echo decay times are found to be in the range 1-4 ms. This is a factor of ~3 longer than in strain-free GaAs/AlGaAs structures and is shown to result from strain-induced quadrupolar effects that suppress nuclear spin flip-flops. The correlation times of the flip-flops are examined using a novel frequency-comb NMR technique and are found to exceed 1 s, a factor of ~1000 longer than in strain-free structures. These findings complement recent studies of electron spin coherence and reveal the paradoxical dual role of the quadrupolar effects in self-assembled quantum dots: large increase of the nuclear spin bath coherence and at the same time significant reduction of the electron spin-qubit coherence. Approaches to increasing electron spin coherence are discussed. In particular the nanohole filled GaAs/AlGaAs quantum dots are an attractive option: while their optical quality matches the self-assembled dots the quadrupolar effects measured in NMR spectra are a factor of 1000 smaller.

A spin labelling study of immunomodulating peptidoglycan monomer and adamantyltripeptides entrapped into liposomes.

PubMed

Frkanec, Ruza; Noethig-Laslo, Vesna; Vranesić, Branka; Mirosavljević, Krunoslav; Tomasić, Jelka

2003-04-01

The interaction of immunostimulating compounds, the peptidoglycan monomer (PGM) and structurally related adamantyltripeptides (AdTP1 and AdTP2), respectively, with phospholipids in liposomal bilayers were investigated by electron paramagnetic resonance spectroscopy. (1). The fatty acids bearing the nitroxide spin label at different positions along the acyl chain were used to investigate the interaction of tested compounds with negatively charged multilamellar liposomes. Electron spin resonance (ESR) spectra were studied at 290 and 310 K. The entrapment of the adamantyltripeptides affected the motional properties of all spin labelled lipids, while the entrapment of PGM had no effect. (2). Spin labelled PGM was prepared and the novel compound bearing the spin label attached via the amino group of diaminopimelic acid was chromatographically purified and chemically characterized. The rotational correlation time of the spin labelled molecule dissolved in buffer at pH 7.4 was studied as a function of temperature. The conformational change was observed above 300 K. The same effect was observed with the spin labelled PGM incorporated into liposomes. Such effect was not observed when the spin labelled PGM was studied at alkaline pH, probably due to the hydrolysis of PGM molecule. The study of possible interaction with liposomal membrane is relevant to the use of tested compounds incorporated into liposomes, as adjuvants in vivo.

The spin-Hall effect and spin-orbit torques in epitaxial Co2FeAl/platinum bilayers

NASA Astrophysics Data System (ADS)

Peterson, T. A.; Liu, C.; McFadden, T.; Palmstrøm, C. J.; Crowell, P. A.

We have performed magnetoresistance measurements on epitaxially grown Co2FeAl/platinum (CFA/Pt) ultrathin ferromagnet/heavy metal bilayers to study the spin-Hall effect in Pt and the accompanying spin-orbit torque (SOT) exerted on the magnetic CFA layer. Specifically, we measure the spin-Hall magnetoresistance in the Pt layer by changing the orientation of the CFA magnetization with respect to the spin current orientation created in the Pt, and we determine the SOT efficiency using a second-harmonic detection technique. Because the latter of the two measurements is proportional to the spin-Hall ratio θSHE while the former is proportional to θSHE2, we are able to extract the bare Pt spin-Hall ratio with no assumptions about the CFA/Pt interface spin mixing conductance. Furthermore, by varying the Pt thickness we show that the results are consistent with resistivity-independent spin-Hall conductivity. Finally, the two measurements in combination allow us to infer a spin-mixing conductance at the CFA/Pt interface of 2 +/- 1 ×1015Ω-1m-2 . The combination of spin-Hall magnetoresistance and SOT measurements allows for a determination of the spin-mixing conductance using only low-frequency transport techniques. This work was supported by STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

Topological states of matter in two-dimensional fermionic systems

NASA Astrophysics Data System (ADS)

Beugeling, W.

2012-09-01

Topological states of matter in two-dimensional systems are characterised by the different properties of the edges and the bulk of the system: The edges conduct electrical current while the bulk is insulating. The first well-known example is the quantum Hall effect, which is induced by a perpendicular magnetic field that generates chiral edge channels along which the current propagates. Each channel contributes one quantum to the Hall conductivity. Due to the chirality, i.e., all currents propagate in the same direction, backscattering due to impurities is absent, and the Hall conductivity carried by the edge states is therefore protected from perturbations. Another example is the quantum spin Hall effect, induced by intrinsic spin-orbit coupling in absence of a magnetic field. There the edge states are helical, i.e., spin up and down currents propagate oppositely. In this case, the spin Hall conductivity is quantized, and it is protected by time-reversal symmetry from backscattering due to impurities. In Chapter 2 of the thesis, I discuss the combined effect of the magnetic field and intrinsic spin-orbit coupling. In addition, I discuss the influence of the Rashba spin-orbit coupling and of the Zeeman effect. In particular, I show that in absence of magnetic impurities, a weaker form of the quantum spin Hall state persists in the presence of a magnetic field. In addition, I show that the intrinsic spin-orbit coupling and the Zeeman effect act similarly in the low-flux limit. I furthermore analyse the phase transitions induced by intrinsic spin-orbit coupling at a fixed magnetic field, thereby explaining the change of the Hall and spin Hall conductivities at the transition. I also study the subtle interplay between the effects of the different terms in the Hamiltonian. In Chapter 3, I investigate an effective model for HgTe quantum wells doped with Mn ions. Without doping, HgTe quantum wells may exhibit the quantum spin Hall effect, depending on the thickness of the well. The doping with Mn ions modifies the behaviour of the system in two ways: First, the quantum spin Hall gap is reduced in size, and secondly, the system becomes paramagnetic. The latter effect causes a bending of the Landau levels, which is responsible for reentrant behaviour of the (spin) Hall conductivity. I investigate the different types of reentrant behaviour, and I estimate the experimental resolvability of this effect. In Chapter 4, I present a framework to describe the fractional quantum Hall effect in systems with multiple internal degrees of freedom, e.g., spin or pseudospin. This framework describes the so-called flux attachment in terms of a Chern-Simons theory in Hamiltonian form, proposed earlier for systems without internal degrees of freedom. Here, I show a generalization of these results, by replacing the number of attached flux quanta by a matrix. In particular, the plasma analogy proposed by Laughlin still applies, and Kohn’s theorem remains valid. I also show that the results remain valid when the flux-attachment matrix is singular.

Dynamics of antiferromagnetic skyrmion driven by the spin Hall effect

NASA Astrophysics Data System (ADS)

Jin, Chendong; Song, Chengkun; Wang, Jianbo; Liu, Qingfang

2016-10-01

Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its property of topological protection. Our results present the understanding of antiferromagnetic skyrmion motion driven by the spin Hall effect and may also contribute to the development of antiferromagnetic skyrmion-based racetrack memories.

Dynamical Jahn-Teller effect of fullerene anions

NASA Astrophysics Data System (ADS)

Liu, Dan; Iwahara, Naoya; Chibotaru, Liviu F.

2018-03-01

The dynamical Jahn-Teller effect of C60n - anions (n =1 -5) is studied using the numerical diagonalization of the linear pn⊗8 d Jahn-Teller Hamiltonian with the currently established coupling parameters. It is found that in all anions the Jahn-Teller effect stabilizes the low-spin states, resulting in the violation of Hund's rule. The energy gain due to the Jahn-Teller dynamics is found to be comparable to the static Jahn-Teller stabilization. The Jahn-Teller dynamics influences the thermodynamic properties via strong variation of the density of vibronic states with energy. Thus the large vibronic entropy in the low-spin states enhances the effective spin gap of C603 - quenching the spin crossover. From the calculations of the effective spin gap as a function of the Hund's rule coupling, we found that the latter should amount 40 ±5 meV in order to cope with the violation of Hund's rule and to reproduce the large spin gap. With the obtained numerical solutions, the matrix elements of electronic operators for the low-lying vibronic levels and the vibronic reduction factors are calculated for all anions.

Measurement of cross relaxation between two selected nuclei by synchronous nutation of magnetization in nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Burghardt, Irene; Konrat, Robert; Boulat, Benoit; Vincent, Sébastien J. F.; Bodenhausen, Geoffrey

1993-01-01

A novel technique is described that allows one to measure cross-relaxation rates (Overhauser effects) between two selected nuclei in high-resolution NMR. The two chosen sites are irradiated simultaneously with the sidebands of an amplitude-modulated radio-frequency field, so that their magnetization vectors are forced to undergo a simultaneous motion, which is referred to as ``synchronous nutation.'' From the time-dependence observed for different initial conditions, one may derive cross-relaxation rates, and hence determine internuclear distances. The scalar interactions between the selected spins and other spins belonging to the same coupling network are effectively decoupled. Furthermore, cross relaxation to other spins in the environment does not affect the transient response of the selected spins, which are therefore in effect isolated from their environment in terms of dipolar interactions. The method is particularly suitable to study cases where normal Overhauser effects are perturbed by spin-diffusion effects due to the presence of further spins. The technique is applied to the protein bovine pancreatic trypsin inhibitor.

Correlation between amplitude of spin accumulation signals investigated by Hanle effect measurement and effective junction barrier height in CoFe/MgO/n{sup +}-Si junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saito, Y., E-mail: yoshiaki.saito@toshiba.co.jp; Ishikawa, M.; Sugiyama, H.

2015-05-07

Correlation between the amplitude of the spin accumulation signals and the effective barrier height estimated from the slope of the log (RA) - t{sub MgO} plot (RA: resistance area product, t{sub MgO}: thickness of MgO tunnel barrier) in CoFe/MgO/n{sup +}-Si junctions was investigated. The amplitude of spin accumulation signals increases with increasing effective barrier heights. This increase of the amplitude of spin accumulation is originated from the increase of the spin polarization (P{sub Si}) in Si. The estimated absolute values of P{sub Si} using three-terminal Hanle signals are consistent with those estimated by four-terminal nonlocal-magnetoresistance (MR) and two-terminal local-MR. Tomore » demonstrate large spin accumulation in Si bulk band and enhance the local-MR through Si channel, these results indicate that the increase of the effective barrier height at ferromagnet/(tunnel barrier)/n{sup +}-Si junction electrode is important.« less

Model Development for Graphene Spintronics

DTIC Science & Technology

2015-09-21

structure near the dirac point. Scattering was evaluated in born approximation. Screening and transport were treated semi-classically...requested and granted by the cognizant office, and the program ran through 25 May 2015. Graphene is a promising material for electronic and spintronic...of an insulating material such as Al2O3, to enable efficient spin injection. The graphene layer is beneath the tunnel barrier, followed by SiO2 (on

Magnetoelectric Andreev Effect due to Proximity-Induced Nonunitary Triplet Superconductivity in Helical Metals

NASA Astrophysics Data System (ADS)

Tkachov, G.

2017-01-01

Noncentrosymmetric superconductors exhibit the magnetoelectric effect, which manifests itself in the appearance of the magnetic spin polarization in response to a dissipationless electric current (supercurrent). While much attention has been dedicated to the thermodynamic version of this phenomenon (Edelstein effect), nonequilibrium transport magnetoelectric effects have not been explored yet. We propose the magnetoelectric Andreev effect (MAE), which consists in the generation of spin-polarized triplet Andreev conductance by an electric supercurrent. The MAE stems from the spin polarization of the Cooper-pair condensate due to a supercurrent-induced nonunitary triplet pairing. We propose the realization of such a nonunitary pairing and MAE in superconducting proximity structures based on two-dimensional helical metals—strongly spin-orbit-coupled electronic systems with the Dirac spectrum such as the topological surface states. Our results uncover an unexplored route towards electrically controlled superconducting spintronics and are a smoking gun for induced unconventional superconductivity in spin-orbit-coupled materials.

Thermally driven anomalous Hall effect transitions in FeRh

NASA Astrophysics Data System (ADS)

Popescu, Adrian; Rodriguez-Lopez, Pablo; Haney, Paul M.; Woods, Lilia M.

2018-04-01

Materials exhibiting controllable magnetic phase transitions are currently in demand for many spintronics applications. Here, we investigate from first principles the electronic structure and intrinsic anomalous Hall, spin Hall, and anomalous Nernst response properties of the FeRh metallic alloy which undergoes a thermally driven antiferromagnetic-to-ferromagnetic phase transition. We show that the energy band structures and underlying Berry curvatures have important signatures in the various Hall effects. Specifically, the suppression of the anomalous Hall and Nernst effects in the antiferromagnetic state and a sign change in the spin Hall conductivity across the transition are found. It is suggested that the FeRh can be used as a spin current detector capable of differentiating the spin Hall effect from other anomalous transverse effects. The implications of this material and its thermally driven phases as a spin current detection scheme are also discussed.

Spin-orbit-torque driven magnetoimpedance in Pt-layer/magnetic-ribbon heterostructures

NASA Astrophysics Data System (ADS)

Hajiali, M. R.; Mohseni, S. Morteza; Jamilpanah, L.; Hamdi, M.; Roozmeh, S. E.; Mohseni, S. Majid

2017-11-01

When a flow of electrons passes through a paramagnetic layer with strong spin-orbit-coupling such as platinum (Pt), a net spin current is produced via the spin Hall effect (SHE). This spin current can exert a torque on the magnetization of an adjacent ferromagnetic layer which can be probed via magnetization dynamic responses, e.g., spin-torque ferromagnetic resonance. Nevertheless, that effect in the lower frequency magnetization dynamic regime where the skin effect occurs in high permeability ferromagnetic conductors, namely, the magneto-impedance (MI) effect, can be fundamentally important, and has not been studied so far. Here, by utilizing the MI effect in the magnetic-ribbon/Pt heterostructure with high transvers magnetic permeability that allows the ac current effectively confined at the skin depth of ˜100 nm thickness, the effect of spin-orbit-torque (SOT) induced by the SHE probed via the MI measurement is investigated. We observed a systematic MI frequency shift that increases by increasing the applied current amplitude and thickness of the Pt layer (varying from 0 nm to 20 nm). In addition, the role of the Pt layer in the ribbon/Pt heterostructure is evaluated with the ferromagnetic resonance effect representing a standard Gilbert damping increase as a result of the presence of the SHE. Our results unveil the role of SOT in dynamic control of the transverse magnetic permeability probed by impedance spectroscopy as a useful and valuable technique for detection of future SHE devices.

Associating Specific Materials with Topological Insulation Behavior

NASA Astrophysics Data System (ADS)

Zhang, Xiuwen

2014-03-01

The first-principles (a) total-energy/stability calculations combined with (b) electronic structure calculations of band inversion, spin-polarization and topological invariants (Z2) has led to the design and prediction of specific materials that are topological insulators in this study. We classify bulk materials into four types of band-inversion behaviors (TI-1, TI-2, BI-3, BI-4), based on the number of band inversions and their distributions on various time reversal invariant k points. Depending on the inversion type in bulk, the corresponding surface states have different protections e.g., protected by time reversal symmetry (in TI-1 materials), spatial symmetry (in TI-2), or not protected (in BI-3, BI-4). Subject 1 Discovery of new TI by screening materials for a Z2 metric: Such high-throughput search in the framework of Inverse Design methodology predicts a few previously undocumented materials that are TI-1 in their ground state crystal structure. We also predict dozens of materials that are TI-1 however in structures that are not ground states (e.g. perovskite structure of II-Bi-O3). Subject 2 Design Principle to increase the gap of TI-1 materials: In HgTe-like cubic topological materials, the insulating gap is zero since the spin-orbit splitting is positive and so a 4-fold half-filled p-like band is near the Fermi level. By design of hybridization of d-orbitals into the p-like bands, one can create negative spin-orbit splitting and so a finite insulating gap. Subject 3 Unconventional spin textures of TI surface states: Despite the fact that one of our predicted TI-1 KBaBi has inversion symmetry in the bulk-a fact that that would preclude bulk spin polarization-we find a Dresselhaus-like spin texture with non-helical spin texture. This originates from the local spin polarization, anchored on the atomic sites with inversion asymmetric point groups, that is compensated due to global inversion symmetry in bulk. In collaboration with: Jun-Wei Luo, Qihang Liu, Julien Vidal, and Alex Zunger, and supported in part by National Science Foundation DMREF. X.Z. acknowledges the administrative support of REMRSEC at Colorado School of Mines, Golden, Colorado.

Spin Transport in Nondegenerate Si with a Spin MOSFET Structure at Room Temperature

NASA Astrophysics Data System (ADS)

Sasaki, Tomoyuki; Ando, Yuichiro; Kameno, Makoto; Tahara, Takayuki; Koike, Hayato; Oikawa, Tohru; Suzuki, Toshio; Shiraishi, Masashi

2014-09-01

Spin transport in nondegenerate semiconductors is expected to pave the way to the creation of spin transistors, spin logic devices, and reconfigurable logic circuits, because room-temperature (RT) spin transport in Si has already been achieved. However, RT spin transport has been limited to degenerate Si, which makes it difficult to produce spin-based signals because a gate electric field cannot be used to manipulate such signals. Here, we report the experimental demonstration of spin transport in nondegenerate Si with a spin metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We successfully observe the modulation of the Hanle-type spin-precession signals, which is a characteristic spin dynamics in nondegenerate semiconductors. We obtain long spin transport of more than 20 μm and spin rotation greater than 4π at RT. We also observe gate-induced modulation of spin-transport signals at RT. The modulation of the spin diffusion length as a function of a gate voltage is successfully observed, which we attribute to the Elliott-Yafet spin relaxation mechanism. These achievements are expected to lead to the creation of practical Si-based spin MOSFETs.

Effects of magnetic and nonmagnetic impurities on the spin susceptibility of a noncentrosymmetrical superconductor: Application to CePt3Si

NASA Astrophysics Data System (ADS)

Yavari, H.; Mokhtari, M.; Tamaddonpour, M.

2013-10-01

The combined effect of nonmagnetic and magnetic impurities on the spin susceptibility of a noncentrosymmetrical superconductor by considering a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components is investigated. For clean superconductor CePt3Si, the low-temperature dependence (T →0) of spin susceptibility is linear which suggests that the gap function has line nodes, consistent with our gap model. We will show that in the presence of magnetic impurities the susceptibility does not vanish even in the absence of spin orbit coupling and in the region where the energy gap still is finite, and in the low concentration of magnetic impurities the spin susceptibility at zero temperature is proportional to impurity concentration.

Covariant Conservation Laws and the Spin Hall Effect in Dirac-Rashba Systems

NASA Astrophysics Data System (ADS)

Milletarı, Mirco; Offidani, Manuel; Ferreira, Aires; Raimondi, Roberto

2017-12-01

We present a theoretical analysis of two-dimensional Dirac-Rashba systems in the presence of disorder and external perturbations. We unveil a set of exact symmetry relations (Ward identities) that impose strong constraints on the spin dynamics of Dirac fermions subject to proximity-induced interactions. This allows us to demonstrate that an arbitrary dilute concentration of scalar impurities results in the total suppression of nonequilibrium spin Hall currents when only Rashba spin-orbit coupling is present. Remarkably, a finite spin Hall conductivity is restored when the minimal Dirac-Rashba model is supplemented with a spin-valley interaction. The Ward identities provide a systematic way to predict the emergence of the spin Hall effect in a wider class of Dirac-Rashba systems of experimental relevance and represent an important benchmark for testing the validity of numerical methodologies.

Current-induced spin polarization on metal surfaces probed by spin-polarized positron beam

PubMed Central

Zhang, H. J.; Yamamoto, S.; Fukaya, Y.; Maekawa, M.; Li, H.; Kawasuso, A.; Seki, T.; Saitoh, E.; Takanashi, K.

2014-01-01

Current-induced spin polarization (CISP) on the outermost surfaces of Au, Cu, Pt, Pd, Ta, and W nanoscaled films were studied using a spin-polarized positron beam. The Au and Cu surfaces showed no significant CISP. In contrast, the Pt, Pd, Ta, and W films exhibited large CISP (3~15% per input charge current of 105 A/cm2) and the CISP of Ta and W were opposite to those of Pt and Pd. The sign of the CISP obeys the same rule in spin Hall effect suggesting that the spin-orbit coupling is mainly responsible for the CISP. The magnitude of the CISP is explained by the Rashba-Edelstein mechanism rather than the diffusive spin Hall effect. This settles a controversy, that which of these two mechanisms dominates the large CISP on metal surfaces. PMID:24776781

Terahertz emission from ultrafast spin-charge current at a Rashba interface

NASA Astrophysics Data System (ADS)

Zhang, Qi; Jungfleisch, Matthias Benjamin; Zhang, Wei; Pearson, John E.; Wen, Haidan; Hoffmann, Axel

Ultrafast broadband terahertz (THz) radiation is highly desired in various fields from fundamental research in condensed matter physics to bio-chemical detection. Conventional ultrafast THz sources rely on either nonlinear optical effects or ultrafast charge currents in semiconductors. Recently, however, it was realized that ultrabroad-band THz radiation can be produced highly effectively by novel spintronics-based emitters that also make use of the electron's spin degree of freedom. Those THz-emitters convert a spin current flow into a terahertz electromagnetic pulse via the inverse spin-Hall effect. In contrast to this bulk conversion process, we demonstrate here that a femtosecond spin current pulse launched from a CoFeB layer can also generate terahertz transients efficiently at a two-dimensional Rashba interface between two non-magnetic materials, i.e., Ag/Bi. Those interfaces have been proven to be efficient means for spin- and charge current interconversion.

Electron spin control of optically levitated nanodiamonds in vacuum.

PubMed

Hoang, Thai M; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang

2016-07-19

Electron spins of diamond nitrogen-vacancy (NV) centres are important quantum resources for nanoscale sensing and quantum information. Combining NV spins with levitated optomechanical resonators will provide a hybrid quantum system for novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centres in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this system, we investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centres, indicating potential applications of NV centres in oxygen gas sensing. Our results pave the way towards a levitated spin-optomechanical system for studying macroscopic quantum mechanics.

Ultrafast optical modification of exchange interactions in iron oxides

NASA Astrophysics Data System (ADS)

Mikhaylovskiy, R. V.; Hendry, E.; Secchi, A.; Mentink, J. H.; Eckstein, M.; Wu, A.; Pisarev, R. V.; Kruglyak, V. V.; Katsnelson, M. I.; Rasing, Th.; Kimel, A. V.

2015-09-01

Ultrafast non-thermal manipulation of magnetization by light relies on either indirect coupling of the electric field component of the light with spins via spin-orbit interaction or direct coupling between the magnetic field component and spins. Here we propose a scenario for coupling between the electric field of light and spins via optical modification of the exchange interaction, one of the strongest quantum effects with strength of 103 Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be called inverse magneto-refraction, is allowed in a material of any symmetry. Its existence is corroborated by the experimental observation of terahertz emission by spin resonances optically excited in a broad class of iron oxides with a canted spin configuration. From its strength we estimate that a sub-picosecond modification of the exchange interaction by laser pulses with fluence of about 1 mJ cm-2 acts as a pulsed effective magnetic field of 0.01 Tesla.

Electron spin control of optically levitated nanodiamonds in vacuum

NASA Astrophysics Data System (ADS)

Hoang, Thai M.; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang

2016-07-01

Electron spins of diamond nitrogen-vacancy (NV) centres are important quantum resources for nanoscale sensing and quantum information. Combining NV spins with levitated optomechanical resonators will provide a hybrid quantum system for novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centres in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this system, we investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centres, indicating potential applications of NV centres in oxygen gas sensing. Our results pave the way towards a levitated spin-optomechanical system for studying macroscopic quantum mechanics.

A two-dimensional spin field-effect switch

NASA Astrophysics Data System (ADS)

Casanova, Felix

The integration of the spin degree of freedom in charge-based electronic devices has revolutionised both sensing and memory capability in microelectronics. Further development in spintronic devices requires electrical manipulation of spin current for logic operations. The mainstream approach followed so far, inspired by the seminal proposal of the Datta and Das spin modulator, has relied on the spin-orbit field as a medium for electrical control of the spin state. However, the still standing challenge is to find a material whose spin-orbit coupling (SOC) is weak enough to transport spins over long distances, while also being strong enough to allow their electrical manipulation. In our recent work, we demonstrate a radically different approach by engineering a van der Waals heterostructure from atomically thin crystals, and which combines the superior spin transport properties of graphene with the strong SOC of MoS2, a transition metal dichalcogenide with semiconducting properties. The spin transport in the graphene channel is modulated between ON and OFF states by tuning the spin absorption into the MoS2 layer with a gate electrode. Our demonstration of a spin field-effect switch using two-dimensional (2D) materials identifies a new route towards spin logic operations for beyond CMOS technology. Furthermore, the van der Waals heterostructure at the core of our experiments opens the path for fundamental research of exotic transport properties predicted for transition metal dichalcogenides, in which electrical spin injection has so far been elusive.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tani, Yasuo; Shikoh, Eiji, E-mail: shikoh@elec.eng.osaka-cu.ac.jp; Teki, Yoshio

We report the spin-pump-induced spin transport properties of a pentacene film prepared by thermal evaporation. In a palladium(Pd)/pentacene/Ni{sub 80}Fe{sub 20} tri-layer sample, a pure spin-current is generated in the pentacene layer by the spin-pumping of Ni{sub 80}Fe{sub 20}, which is independent of the conductance mismatch problem in spin injection. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current at room temperature in pentacene films prepared by thermal evaporation.

The effect of fringe fields from patterned magnetic domains on the electroluminescence of organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Harmon, Nicholas J.; Wohlgennant, Markus; Flatté, Michael E.

2016-10-01

Large magnetic field effects, either in conduction or luminescence, have been observed in organic light-emitting diodes (OLEDs) for over a decade now. The physical processes are largely understood when exciton formation and recombination lead to the magnetic field effects. Recently, magnetic field effects in some co-evaporated blends have shown that exciplexes deliver even larger responses. In either case, the magnetic field effects arise from some spin-mixing mechanism and spin-selective processes in either the exciton formation or the exciplex recombination. Precise control of light output is not possible when the spin mixing is either due to hyper-fine fields or differences in the Lande g-factor. We theoretically examine the optical output when a patterned magnetic film is deposited near the OLED. The fringe fields from the magnetic layers supply an additionally source of spin mixing that can be easily controlled. In the absence of other spin mixing mechanisms, the luminescence from exciplexes can be modified by 300%. When other spin-mixing mechanisms are present, fringe fields from remanent magnetic states act as a means to either boost or reduce light emission from those mechanisms. Lastly, we examine the influence of spin decoherence on the optical output.

Artifacts correction for T1rho imaging with constant amplitude spin-lock

NASA Astrophysics Data System (ADS)

Chen, Weitian

2017-01-01

T1rho imaging with constant amplitude spin-lock is prone to artifacts in the presence of B1 RF and B0 field inhomogeneity. Despite significant technological progress, improvements on the robustness of constant amplitude spin-lock are necessary in order to use it for routine clinical practice. This work proposes methods to simultaneously correct for B1 RF and B0 field inhomogeneity in constant amplitude spin-lock. By setting the maximum B1 amplitude of the excitation adiabatic pulses equal to the expected constant amplitude spin-lock frequency, the spins become aligned along the effective field throughout the spin-lock process. This results in T1rho-weighted images free of artifacts, despite the spatial variation of the effective field caused by B1 RF and B0 field inhomogeneity. When the pulse is long, the relaxation effect during the adiabatic half passage may result in a non-negligible error in the mono-exponential relaxation model. A two-acquisition approach is presented to solve this issue. Simulation, phantom, and in-vivo scans demonstrate the proposed methods achieve superior image quality compared to existing methods, and that the two-acquisition method is effective in resolving the relaxation effect during the adiabatic half passage.

Experimental investigation of spin-orbit coupling in n-type PbTe quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peres, M. L.; Monteiro, H. S.; Castro, S. de

2014-03-07

The spin-orbit coupling is studied experimentally in two PbTe quantum wells by means of weak antilocalization effect. Using the Hikami-Larkin-Nagaoka model through a computational global optimization procedure, we extracted the spin-orbit and inelastic scattering times and estimated the strength of the zero field spin-splitting energy Δ{sub so}. The values of Δ{sub so} are linearly dependent on the Fermi wave vector (k{sub F}) confirming theoretical predictions of the existence of large spin-orbit coupling in IV-VI quantum wells originated from pure Rashba effect.

Photon energy dependence of photo-induced inverse spin-Hall effect in Pt/GaAs and Pt/Ge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isella, Giovanni, E-mail: giovanni.isella@polimi.it; Bottegoni, Federico; Ferrari, Alberto

2015-06-08

We report the photon energy dependence of photo-induced inverse spin Hall effect (ISHE) in Pt/GaAs and Pt/Ge Schottky junctions. The experimental results are compared with a spin drift-diffusion model, which highlights the role played by the different spin lifetime in the two semiconductors, in determining the energy dependence of the ISHE signal detected in the Pt layer. The good qualitative agreement between experiments and modelling indicates that photo-induced ISHE can be used as a tool to characterize spin lifetime in semiconductors.

Nuclear Spin Nanomagnet in an Optically Excited Quantum Dot

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2007-12-01

Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins—the nuclear spin nanomagnet.

Rockets for spin recovery

NASA Technical Reports Server (NTRS)

Whipple, R. D.

1980-01-01

The potential effectiveness of rockets as an auxiliary means for an aircraft to effect recovery from spins was investigated. The advances in rocket technology produced by the space effort suggested that currently available systems might obviate many of the problems encountered in earlier rocket systems. A modern fighter configuration known to exhibit a flat spin mode was selected. An analytical study was made of the thrust requirements for a rocket spin recovery system for the subject configuration. These results were then applied to a preliminary systems study of rocket components appropriate to the problem. Subsequent spin tunnel tests were run to evaluate the analytical results.

Numerical investigation of the effect of sphere dimples on the drag crisis and the Magnus effect

NASA Astrophysics Data System (ADS)

Li, Jing; Tsubokura, Makoto; Tsunoda, Masaya

2015-11-01

The present study investigates the flow over a golf ball and a smooth sphere around the critical Reynolds numbers under both stationary and self-spinning conditions by conducting Large-eddy simulations (LES) based on high resolution unstructured grids. For the stationary cases, the present calculation results validate the promotion of the drag crisis at a relatively lower Reynolds number due to the golf ball dimples. It also shows that the golf ball dimples have a limited effect on the time-dependent lateral force development in the subcritical regime, whereas the dimples are beneficial in suppressing the lateral force oscillations in the supercritical regimes. With spin parameter Γ = 0.1, the drag coefficients for the spinning smooth sphere increase slightly in all Reynolds number regimes when compared to the stationary cases, whereas for the spinning golf ball, the drag force decreases in the critical regime and increases in the supercritical regime. For both spinning models, the inverse Magnus effect was reproduced in the critical regime, whereas in the supercritical regime the ordinary Magnus force was generated. Relatively weaker lift forces were also observed in the cases of the spinning golf balls when compared to the spinning smooth spheres.

Monte Carlo simulations of spin transport in a strained nanoscale InGaAs field effect transistor

NASA Astrophysics Data System (ADS)

Thorpe, B.; Kalna, K.; Langbein, F. C.; Schirmer, S.

2017-12-01

Spin-based logic devices could operate at a very high speed with a very low energy consumption and hold significant promise for quantum information processing and metrology. We develop a spintronic device simulator by combining an in-house developed, experimentally verified, ensemble self-consistent Monte Carlo device simulator with spin transport based on a Bloch equation model and a spin-orbit interaction Hamiltonian accounting for Dresselhaus and Rashba couplings. It is employed to simulate a spin field effect transistor operating under externally applied voltages on a gate and a drain. In particular, we simulate electron spin transport in a 25 nm gate length In0.7Ga0.3As metal-oxide-semiconductor field-effect transistor with a CMOS compatible architecture. We observe a non-uniform decay of the net magnetization between the source and the gate and a magnetization recovery effect due to spin refocusing induced by a high electric field between the gate and the drain. We demonstrate a coherent control of the polarization vector of the drain current via the source-drain and gate voltages, and show that the magnetization of the drain current can be increased twofold by the strain induced into the channel.

Voltage Control of Two-Magnon Scattering and Induced Anomalous Magnetoelectric Coupling in Ni-Zn Ferrite.

PubMed

Xue, Xu; Dong, Guohua; Zhou, Ziyao; Xian, Dan; Hu, Zhongqiang; Ren, Wei; Ye, Zuo-Guang; Chen, Wei; Jiang, Zhuang-De; Liu, Ming

2017-12-13

Controlling spin dynamics through modulation of spin interactions in a fast, compact, and energy-efficient way is compelling for its abundant physical phenomena and great application potential in next-generation voltage controllable spintronic devices. In this work, we report electric field manipulation of spin dynamics-the two-magnon scattering (TMS) effect in Ni 0.5 Zn 0.5 Fe 2 O 4 (NZFO)/Pb(Mg 2/3 Nb 1/3 )-PbTiO 3 (PMN-PT) multiferroic heterostructures, which breaks the bottleneck of magnetostatic interaction-based magnetoelectric (ME) coupling in multiferroics. An alternative approach allowing spin-wave damping to be controlled by external electric field accompanied by a significant enhancement of the ME effect has been demonstrated. A two-way modulation of the TMS effect with a large magnetic anisotropy change up to 688 Oe has been obtained, referring to a 24 times ME effect enhancement at the TMS critical angle at room temperature. Furthermore, the anisotropic spin-freezing behaviors of NZFO were first determined via identifying the spatial magnetic anisotropy fluctuations. A large spin-freezing temperature change of 160 K induced by the external electric field was precisely determined by electron spin resonance.

Superconducting quantum spin-Hall systems with giant orbital g-factors

NASA Astrophysics Data System (ADS)

Hankiewicz, Ewelina; Reinthaler, Rolf; Tkachov, Grigory

Topological aspects of superconductivity in quantum spin-Hall systems (QSHSs) such as thin layers of three-dimensional topological insulators (3D Tis) or two-dimensional Tis are in the focus of current research. Here, we describe a novel superconducting quantum spin-Hall effect (quantum spin Hall system in the proximity to the s-wave superconductor and in the orbital in-plane magnetic field), which is protected against elastic backscattering by combined time-reversal and particle-hole symmetry. This effect is characterized by spin-polarized edge states, which can be manipulated in weak magnetic fields due to a giant effective orbital g-factor, allowing the generation of spin currents. The phenomenon provides a novel solution to the outstanding challenge of detecting the spin-polarization of the edge states. Here we propose the detection of the edge polarization in the three-terminal junction using unusual transport properties of superconducting quantum Hall-effect: a non-monotonic excess current and a zero-bias conductance splitting. We thank for the financial support the German Science Foundation (DFG), Grants No HA 5893/4-1 within SPP 1666, HA5893/5-2 within FOR1162 and TK60/1-1 (G.T.), as well the ENB graduate school ``Topological insulators''.

Voltage Control of Two-Magnon Scattering and Induced Anomalous Magnetoelectric Coupling in Ni–Zn Ferrite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Xu; Dong, Guohua; Zhou, Ziyao

2017-12-01

Controlling spin dynamics through modulation of spin interactions in a fast, compact, and energy-efficient way is compelling for its abundant physical phenomena and great application potential in next-generation voltage controllable spintronic devices. In this work, we report electric field manipulation of spin dynamics-the two-magnon scattering (TMS) effect in Ni0.5Zn0.5Fe2O4 (NZFO)/Pb(Mg2/3Nb1/3)-PbTiO3 (PMN-PT) multiferroic heterostructures, which breaks the bottleneck of magnetostatic interaction-based magnetoelectric (ME) coupling in multiferroics. An alternative approach allowing spin-wave damping to be controlled by external electric field accompanied by a significant enhancement of the ME effect has been demonstrated. A two-way modulation of the TMS effect with a largemore » magnetic anisotropy change up to 688 Oe has been obtained, referring to a 24 times ME effect enhancement at the TMS critical angle at room temperature. Furthermore, the anisotropic spin-freezing behaviors of NZFO were first determined via identifying the spatial magnetic anisotropy fluctuations. A large spin-freezing temperature change of 160 K induced by the external electric field was precisely determined by electron spin resonance.« less

Spin-orbit torques in magnetic bilayers

NASA Astrophysics Data System (ADS)

Haney, Paul

2015-03-01

Spintronics aims to utilize the coupling between charge transport and magnetic dynamics to develop improved and novel memory and logic devices. Future progress in spintronics may be enabled by exploiting the spin-orbit coupling present at the interface between thin film ferromagnets and heavy metals. In these systems, applying an in-plane electrical current can induce magnetic dynamics in single domain ferromagnets, or can induce rapid motion of domain wall magnetic textures. There are multiple effects responsible for these dynamics. They include spin-orbit torques and a chiral exchange interaction (the Dzyaloshinskii-Moriya interaction) in the ferromagnet. Both effects arise from the combination of ferromagnetism and spin-orbit coupling present at the interface. There is additionally a torque from the spin current flux impinging on the ferromagnet, arising from the spin hall effect in the heavy metal. Using a combination of approaches, from drift-diffusion to Boltzmann transport to first principles methods, we explore the relative contributions to the dynamics from these different effects. We additionally propose that the transverse spin current is locally enhanced over its bulk value in the vicinity of an interface which is oriented normal to the charge current direction.

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

NASA Astrophysics Data System (ADS)

Miller, Richards; van Schooten, K. J.; Malissa, H.; Joshi, G.; Jamali, S.; Lupton, J. M.; Boehme, C.

2016-12-01

We have studied the role of spin-dependent processes on conductivity in polyfluorene (PFO) thin films by preforming continuous wave (cw) electrically detected magnetic resonance (EDMR) spectroscopy at temperatures between 10 K and room temperature using microwave frequencies between about 1 GHz and 20 GHz, as well as pulsed EDMR at the X band (10 GHz). Variable frequency EDMR allows us to establish the role of spin-orbit coupling in spin-dependent processes whereas pulsed EDMR allows for the observation of coherent spin motion effects. We used PFO for this study in order to allow for the investigation of the effects of microscopic morphological ordering since this material can adopt two distinct intrachain morphologies: an amorphous (glassy) phase, in which monomer units are twisted with respect to each other, and an ordered (β) phase, where all monomers lie within one plane. In thin films of organic light-emitting diodes, the appearance of a particular phase can be controlled by deposition parameters and solvent vapor annealing, and is verified by electroluminescence spectroscopy. Under bipolar charge-carrier injection conditions, we conducted multifrequency cw EDMR, electrically detected Rabi spin-beat experiments, and Hahn echo and inversion-recovery measurements. Coherent echo spectroscopy reveals electrically detected electron-spin-echo envelope modulation due to the coupling of the carrier spins to nearby nuclear spins. Our results demonstrate that, while conformational disorder can influence the observed EDMR signals, including the sign of the current changes on resonance as well as the magnitudes of local hyperfine fields and charge-carrier spin-orbit interactions, it does not qualitatively affect the nature of spin-dependent transitions in this material. In both morphologies, we observe the presence of at least two different spin-dependent recombination processes. At room temperature and 10 K, polaron-pair recombination through weakly spin-spin coupled intermediate charge-carrier pair states is dominant, while at low temperatures, additional signatures of spin-dependent charge transport through the interaction of polarons with triplet excitons are seen in the half-field resonance of a triplet spin-1 species. This additional contribution arises since triplet lifetimes are increased at lower temperatures. We tentatively conclude that spectral broadening induced by hyperfine coupling is slightly weaker in the more ordered β-phase than in the glassy phase since protons are more evenly spaced, whereas broadening effects due to spin-orbit coupling, which impacts the distribution of g -factors, appear to be somewhat more significant in the β-phase.

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

NASA Astrophysics Data System (ADS)

Luengo-Kovac, M.; Huang, S.; Del Gaudio, D.; Occena, J.; Goldman, R. S.; Raimondi, R.; Sih, V.

2017-11-01

The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InxGa1 -xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.

Electronic spin transport in gate-tunable black phosphorus spin valves

NASA Astrophysics Data System (ADS)

Liu, Jiawei; Avsar, Ahmet; Tan, Jun You; Oezyilmaz, Barbaros

High charge mobility, the electric field effect and small spin-orbit coupling make semiconducting black phosphorus (BP) a promising material for spintronics device applications requiring long spin distance spin communication with all rectification and amplification actions. Towards this, we study the all electrical spin injection, transport and detection under non-local spin valve geometry in fully encapsulated ultra-thin BP devices. We observe spin relaxation times as high as 4 ns, with spin relaxation lengths exceeding 6 μm. These values are an order of magnitude higher than what have been measured in typical graphene spin valve devices. Moreover, the spin transport depends strongly on charge carrier concentration and can be manipulated in a spin transistor-like manner by controlling electric field. This behaviour persists even at room temperature. Finally, we will show that similar to its electrical and optical properties, spin transport property is also strongly anisotropic.

TEGA Whirligig Model

NASA Technical Reports Server (NTRS)

2008-01-01

This is a photo of an engineering model of the Thermal and Evolved-Gas Analyzer (TEGA) instrument on board NASA's Phoenix Mars Lander. This view shows a TEGA oven-loading mechanism beneath the input screen. The screen on the 1-and-1/2-inch-wide funnel has been removed in this model to show the whirligig that is suspended from the screw on the shaft. The black hole underneath is the porthole that leads to the oven.

A tiny electric current compresses and releases a spring on the shaft. As the shaft spins, the screw bumps the screen, breaking up clumps of material into fine particles so they pass through the one millimeter-square screen openings. The energy applied to the tapping screen is about 0.02 inch per pound, or the force needed to move a one-pound mass two-hundredths of an inch.

The screw also lifts the three-bladed whirligig so that it jostles fine particles and keeps the oven port open to aid the loading process.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Antiferromagnetic Spin Wave Field-Effect Transistor

DOE PAGES

Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; ...

2016-04-06

In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. In conclusion, our findings open up the exciting possibilitymore » of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.« less

Theory of the Spin Galvanic Effect at Oxide Interfaces

NASA Astrophysics Data System (ADS)

Seibold, Götz; Caprara, Sergio; Grilli, Marco; Raimondi, Roberto

2017-12-01

The spin galvanic effect (SGE) describes the conversion of a nonequilibrium spin polarization into a transverse charge current. Recent experiments have demonstrated a large conversion efficiency for the two-dimensional electron gas formed at the interface between two insulating oxides, LaAlO3 and SrTiO3 . Here, we analyze the SGE for oxide interfaces within a three-band model for the Ti t2 g orbitals which displays an interesting variety of effective spin-orbit couplings in the individual bands that contribute differently to the spin-charge conversion. Our analytical approach is supplemented by a numerical treatment where we also investigate the influence of disorder and temperature, which turns out to be crucial to providing an appropriate description of the experimental data.

Electric field controlled spin interference in a system with Rashba spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ciftja, Orion, E-mail: ogciftja@pvamu.edu

There have been intense research efforts over the last years focused on understanding the Rashba spin-orbit coupling effect from the perspective of possible spintronics applications. An important component of this line of research is aimed at control and manipulation of electron’s spin degrees of freedom in semiconductor quantum dot devices. A promising way to achieve this goal is to make use of the tunable Rashba effect that relies on the spin-orbit interaction in a two-dimensional electron system embedded in a host semiconducting material that lacks inversion-symmetry. This way, the Rashba spin-orbit coupling effect may potentially lead to fabrication of amore » new generation of spintronic devices where control of spin, thus magnetic properties, is achieved via an electric field and not a magnetic field. In this work we investigate theoretically the electron’s spin interference and accumulation process in a Rashba spin-orbit coupled system consisting of a pair of two-dimensional semiconductor quantum dots connected to each other via two conducting semi-circular channels. The strength of the confinement energy on the quantum dots is tuned by gate potentials that allow “leakage” of electrons from one dot to another. While going through the conducting channels, the electrons are spin-orbit coupled to a microscopically generated electric field applied perpendicular to the two-dimensional system. We show that interference of spin wave functions of electrons travelling through the two channels gives rise to interference/conductance patterns that lead to the observation of the geometric Berry’s phase. Achieving a predictable and measurable observation of Berry’s phase allows one to control the spin dynamics of the electrons. It is demonstrated that this system allows use of a microscopically generated electric field to control Berry’s phase, thus, enables one to tune the spin-dependent interference pattern and spintronic properties with no need for injection of spin-polarized electrons.« less

Investigation of Spinning and Tumbling Characteristics of a 1/20-Scale Model of the Consolidated Vultee XFY-1 Airplane in the Free-Spinning Tunnel, TED No. NACA DE 370

NASA Technical Reports Server (NTRS)

Lee, Henry A.

1952-01-01

An investigation has been conducted in the Langley 20-foot free-spinning tunnel on a l/20-scale model of the Consolidated Vultee XFY-1 airplane with a windmilling propeller simulated to determine the effects of control setting and movements upon the erect spin and recovery characteristics for a range of airplane-loading conditions. The effects on the model's spin-recovery characteristics of removing the lower vertical tail, removing the gun pods, and fixing the rudders at neutral were also investigated briefly. The investigation included determination of the size parachute required for emergency recovery from demonstration spins. The tumbling tendencies of the model were also investigated. Brief static force tests were made to determine the aerodynamic characteristics in pitch at high angles of attack. The investigation indicated that the spin and recovery characteristics of the airplane with propeller windmilling will be satisfactory for all loading conditions if recovery is attempted by full rudder reversal accompanied by simultaneous movement of the stick laterally to full with the spin (stick right in a right spin) and longitudinally to neutral. Inverted spins should be satisfactorily terminated by fully reversing the rudder followed immediately by moving the stick laterally towards the forward rudder pedal and longitudinally to neutral. Removal of the gun pods or fixing the rudders at neutral will not adversely affect the airplane's spin-recovery characteristics, but removal of the lower vertical tail will result in unsatisfactory spin-recovery characteristics. The model-test results showed that a 13.3-foot wing-tip conventional parachute (drag coefficient approximately 0.7) should be effective as an emergency spin-recovery device during demonstration spins of the airplane. It was indicated that the airplane should not tumble and that no unusual longitudinal-trim characteristics should be obtained for the center-of-gravity positions investigated.

Relativistic effects on the NMR parameters of Si, Ge, Sn, and Pb alkynyl compounds: Scalar versus spin-orbit effects

NASA Astrophysics Data System (ADS)

Demissie, Taye B.

2017-11-01

The NMR chemical shifts and indirect spin-spin coupling constants of 12 molecules containing 29Si, 73Ge, 119Sn, and 207Pb [X(CCMe)4, Me2X(CCMe)2, and Me3XCCH] are presented. The results are obtained from non-relativistic as well as two- and four-component relativistic density functional theory (DFT) calculations. The scalar and spin-orbit relativistic contributions as well as the total relativistic corrections are determined. The main relativistic effect in these molecules is not due to spin-orbit coupling but rather to the scalar relativistic contraction of the s-shells. The correlation between the calculated and experimental indirect spin-spin coupling constants showed that the four-component relativistic density functional theory (DFT) approach using the Perdew's hybrid scheme exchange-correlation functional (PBE0; using the Perdew-Burke-Ernzerhof exchange and correlation functionals) gives results in good agreement with experimental values. The indirect spin-spin coupling constants calculated using the spin-orbit zeroth order regular approximation together with the hybrid PBE0 functional and the specially designed J-coupling (JCPL) basis sets are in good agreement with the results obtained from the four-component relativistic calculations. For the coupling constants involving the heavy atoms, the relativistic corrections are of the same order of magnitude compared to the non-relativistically calculated results. Based on the comparisons of the calculated results with available experimental values, the best results for all the chemical shifts and non-existing indirect spin-spin coupling constants for all the molecules are reported, hoping that these accurate results will be used to benchmark future DFT calculations. The present study also demonstrates that the four-component relativistic DFT method has reached a level of maturity that makes it a convenient and accurate tool to calculate indirect spin-spin coupling constants of "large" molecular systems involving heavy atoms.

Electrical detection of nuclear spin-echo signals in an electron spin injection system

NASA Astrophysics Data System (ADS)

Lin, Zhichao; Rasly, Mahmoud; Uemura, Tetsuya

2017-06-01

We demonstrated spin echoes of nuclear spins in a spin injection device with a highly polarized spin source by nuclear magnetic resonance (NMR). Efficient spin injection into GaAs from a half-metallic spin source of Co2MnSi enabled efficient dynamic nuclear polarization (DNP) and sensitive detection of NMR signals even at a low magnetic field of ˜0.1 T and a relatively high temperature of 4.2 K. The intrinsic coherence time T2 of 69Ga nuclear spins was evaluated from the spin-echo signals. The relation between T2 and the decay time of the Rabi oscillation suggests that the inhomogeneous effects in our system are not obvious. This study provides an all-electrical NMR system for nuclear-spin-based qubits.

Effect of rare earth metal on the spin-orbit torque in magnetic heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ueda, Kohei; Pai, Chi-Feng; Tan, Aik Jun

2016-06-06

We report the effect of the rare earth metal Gd on current-induced spin-orbit torques (SOTs) in perpendicularly magnetized Pt/Co/Gd heterostructures, characterized using harmonic measurements and spin-torque ferromagnetic resonance (ST-FMR). By varying the Gd metal layer thickness from 0 nm to 8 nm, harmonic measurements reveal a significant enhancement of the effective fields generated from the Slonczewski-like and field-like torques. ST-FMR measurements confirm an enhanced effective spin Hall angle and show a corresponding increase in the magnetic damping constant with increasing Gd thickness. These results suggest that Gd plays an active role in generating SOTs in these heterostructures. Our finding may lead tomore » spin-orbitronics device application such as non-volatile magnetic random access memory, based on rare earth metals.« less

Spin-orbit torque induced magnetic vortex polarity reversal utilizing spin-Hall effect

NASA Astrophysics Data System (ADS)

Li, Cheng; Cai, Li; Liu, Baojun; Yang, Xiaokuo; Cui, Huanqing; Wang, Sen; Wei, Bo

2018-05-01

We propose an effective magnetic vortex polarity reversal scheme that makes use of spin-orbit torque introduced by spin-Hall effect in heavy-metal/ferromagnet multilayers structure, which can result in subnanosecond polarity reversal without endangering the structural stability. Micromagnetic simulations are performed to investigate the spin-Hall effect driven dynamics evolution of magnetic vortex. The mechanism of magnetic vortex polarity reversal is uncovered by a quantitative analysis of exchange energy density, magnetostatic energy density, and their total energy density. The simulation results indicate that the magnetic vortex polarity is reversed through the nucleation-annihilation process of topological vortex-antivortex pair. This scheme is an attractive option for ultra-fast magnetic vortex polarity reversal, which can be used as the guidelines for the choice of polarity reversal scheme in vortex-based random access memory.

Spin Hall Effect and Weak Antilocalization in Graphene/Transition Metal Dichalcogenide Heterostructures.

PubMed

Garcia, Jose H; Cummings, Aron W; Roche, Stephan

2017-08-09

We report on a theoretical study of the spin Hall Effect (SHE) and weak antilocalization (WAL) in graphene/transition metal dichalcogenide (TMDC) heterostructures, computed through efficient real-space quantum transport methods, and using realistic tight-binding models parametrized from ab initio calculations. The graphene/WS 2 system is found to maximize spin proximity effects compared to graphene on MoS 2 , WSe 2 , or MoSe 2 with a crucial role played by disorder, given the disappearance of SHE signals in the presence of strong intervalley scattering. Notably, we found that stronger WAL effects are concomitant with weaker charge-to-spin conversion efficiency. For further experimental studies of graphene/TMDC heterostructures, our findings provide guidelines for reaching the upper limit of spin current formation and for fully harvesting the potential of two-dimensional materials for spintronic applications.

Homogenization of Doppler broadening in spin-noise spectroscopy

NASA Astrophysics Data System (ADS)

Petrov, M. Yu.; Ryzhov, I. I.; Smirnov, D. S.; Belyaev, L. Yu.; Potekhin, R. A.; Glazov, M. M.; Kulyasov, V. N.; Kozlov, G. G.; Aleksandrov, E. B.; Zapasskii, V. S.

2018-03-01

The spin-noise spectroscopy, being a nonperturbative linear optics tool, is still reputed to reveal a number of capabilities specific to nonlinear optics techniques. The effect of the Doppler broadening homogenization discovered in this work essentially widens these unique properties of spin-noise spectroscopy. We investigate spin noise of a classical system—cesium atoms vapor with admixture of buffer gas—by measuring the spin-induced Faraday rotation fluctuations in the region of D 2 line. The line, under our experimental conditions, is strongly inhomogeneously broadened due to the Doppler effect. Despite that, optical spectrum of the spin-noise power has the shape typical for the homogeneously broadened line with a dip at the line center. This fact is in stark contrast with the results of previous studies of inhomogeneous quantum dot ensembles and Doppler broadened atomic systems. In addition, the two-color spin-noise measurements have shown, in a highly spectacular way, that fluctuations of the Faraday rotation within the line are either correlated or anticorrelated depending on whether the two wavelengths lie on the same side or on different sides of the resonance. The experimental data are interpreted in the frame of the developed theoretical model which takes into account both kinetics and spin dynamics of Cs atoms. It is shown that the unexpected behavior of the Faraday rotation noise spectra and effective homogenization of the optical transition in the spin-noise measurements are related to smallness of the momentum relaxation time of the atoms as compared with their spin-relaxation time. Our findings demonstrate abilities of spin-noise spectroscopy for studying dynamic properties of inhomogeneously broadened ensembles of randomly moving spins.

Predicted NMR properties of noble gas hydride cations RgH +

NASA Astrophysics Data System (ADS)

Cukras, Janusz; Sadlej, Joanna

2008-12-01

The NMR shielding constants and, for the first time, the spin-spin coupling constants of Rg and H in RgH + compounds for Rg = Ne, Ar, Kr, Xe have been investigated by non-relativistic Hartree-Fock (HF) and relativistic Dirac-Hartree-Fock (DHF) methods. Electron-correlation effects have been furthermore calculated using SOPPA and CCSD at the non-relativistic level. The correlation effects are large on both parameters and opposite to the relativistic effects. The results indicate that both the relativistic and correlation effects need to be taken into account in a quantitative computations, especially in the case of the spin-spin coupling constants.

Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling

PubMed Central

Hou, Yan-Hua; Yu, Zhenhua

2015-01-01

Successful realization of spin-orbit coupling in atomic gases by the NIST scheme opens the prospect of studying the effects of spin-orbit coupling on many-body physics in an unprecedentedly controllable way. Here we derive the linearized hydrodynamic equations for the normal atomic gases of the spin-orbit coupling by the NIST scheme with zero detuning. We show that the hydrodynamics of the system crucially depends on the momentum susceptibilities which can be modified by the spin-orbit coupling. We reveal the effects of the spin-orbit coupling on the sound velocities and the dipole mode frequency of the gases by applying our formalism to the ideal Fermi gas. We also discuss the generalization of our results to other situations. PMID:26483090

Phase-controllable spin wave generation in iron garnet by linearly polarized light pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshimine, Isao; Iida, Ryugo; Shimura, Tsutomu

A phase-controlled spin wave was non-thermally generated in bismuth-doped rare-earth iron garnet by linearly polarized light pulses. We controlled the initial phase of the spin wave continuously within a range of 180° by changing the polarization azimuth of the excitation light. The azimuth dependences of the initial phase and amplitude of the spin wave were attributed to a combination of the inverse Cotton-Mouton effect and photoinduced magnetic anisotropy. Temporally and spatially resolved spin wave propagation was observed with a CCD camera, and the waveform was in good agreement with calculations. A nonlinear effect of the spin excitation was observed formore » excitation fluences higher than 100 mJ/cm{sup 2}.« less

All-electric spin modulator based on a two-dimensional topological insulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, Xianbo; Ai, Guoping; Liu, Ying

2016-01-18

We propose and investigate a spin modulator device consisting of two ferromagnetic leads connected by a two-dimensional topological insulator as the channel material. It exploits the unique features of the topological spin-helical edge states, such that the injected carriers with a non-collinear spin-polarization direction would travel through both edges and show interference effect. The conductance of the device can be controlled in a simple and all-electric manner by a side-gate voltage, which effectively rotates the spin-polarization of the carrier. At low voltages, the rotation angle is linear in the gate voltage, and the device can function as a good spin-polarizationmore » rotator by replacing the drain electrode with a non-magnetic material.« less

Spin-charge conversion in disordered two-dimensional electron gases lacking inversion symmetry

NASA Astrophysics Data System (ADS)

Huang, Chunli; Milletarı, Mirco; Cazalilla, Miguel A.

2017-11-01

We study the spin-charge conversion mechanisms in a two-dimensional gas of electrons moving in a smooth disorder potential by accounting for both Rashba-type and Mott's skew scattering contributions. We find that the quantum interference effects between spin-flip and skew scattering give rise to anisotropic spin precession scattering (ASP), a direct spin-charge conversion mechanism that was discovered in an earlier study of graphene decorated with adatoms [Huang et al., Phys. Rev. B 94, 085414 (2016), 10.1103/PhysRevB.94.085414]. Our findings suggest that, together with other spin-charge conversion mechanisms such as the inverse galvanic effect, ASP is a fairly universal phenomenon that should be present in disordered two-dimensional systems lacking inversion symmetry.

Skyrmion formation and optical spin-Hall effect in an expanding coherent cloud of indirect excitons.

PubMed

Vishnevsky, D V; Flayac, H; Nalitov, A V; Solnyshkov, D D; Gippius, N A; Malpuech, G

2013-06-14

We provide a theoretical description of the polarization pattern and phase singularities experimentally evidenced recently in a condensate of indirect excitons [H. High et al., Nature 483, 584 (2012)]. We show that the averaging of the electron and hole orbital motion leads to a comparable spin-orbit interaction for both types of carriers. We demonstrate that the interplay between a radial coherent flux of bright indirect excitons and the Dresselhaus spin-orbit interaction results in the formation of spin domains and of topological defects similar to Skyrmions. We reproduce qualitatively all the features of the experimental data and obtain a polarization pattern as in the optical spin-Hall effect despite the different symmetry of the spin-orbit interactions.

Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling.

PubMed

Hou, Yan-Hua; Yu, Zhenhua

2015-10-20

Successful realization of spin-orbit coupling in atomic gases by the NIST scheme opens the prospect of studying the effects of spin-orbit coupling on many-body physics in an unprecedentedly controllable way. Here we derive the linearized hydrodynamic equations for the normal atomic gases of the spin-orbit coupling by the NIST scheme with zero detuning. We show that the hydrodynamics of the system crucially depends on the momentum susceptibilities which can be modified by the spin-orbit coupling. We reveal the effects of the spin-orbit coupling on the sound velocities and the dipole mode frequency of the gases by applying our formalism to the ideal Fermi gas. We also discuss the generalization of our results to other situations.

Electric dipole spin resonance in a quantum spin dimer system driven by magnetoelectric coupling

NASA Astrophysics Data System (ADS)

Kimura, Shojiro; Matsumoto, Masashige; Akaki, Mitsuru; Hagiwara, Masayuki; Kindo, Koichi; Tanaka, Hidekazu

2018-04-01

In this Rapid Communication, we propose a mechanism for electric dipole active spin resonance caused by spin-dependent electric polarization in a quantum spin gapped system. This proposal was successfully confirmed by high-frequency electron spin resonance (ESR) measurements of the quantum spin dimer system KCuCl3. ESR measurements by an illuminating linearly polarized electromagnetic wave reveal that the optical transition between the singlet and triplet states in KCuCl3 is driven by an ac electric field. The selection rule of the observed transition agrees with the calculation by taking into account spin-dependent electric polarization. We suggest that spin-dependent electric polarization is effective in achieving fast control of quantum spins by an ac electric field.

Using Spin to Understand the Formation of LIGO and Virgo’s Black Holes

NASA Astrophysics Data System (ADS)

Farr, Ben; Holz, Daniel E.; Farr, Will M.

2018-02-01

With the growing number of binary black hole (BBH) mergers detected by the Advanced LIGO and Virgo detectors, it is becoming possible to constrain the properties of the underlying population and better understand the formation of these systems. Black hole (BH) spin orientations are one of the cleanest discriminators of formation history, with BHs in dynamically formed binaries in dense stellar environments expected to have spins distributed isotropically, in contrast to isolated populations where stellar evolution is expected to induce spins preferentially aligned with the orbital angular momentum. In this work, we propose a simple, model-agnostic approach to characterizing the spin properties of LIGO/Virgo’s BBH population. Using measurements of the effective spin of the binaries, we introduce a simple parameter to quantify the fraction of the population that is isotropically distributed, regardless of the spin magnitude distribution of the population. Once the orientation characteristics of the population have been determined, we show how measurements of effective spin can be used to directly constrain the BH spin magnitude distribution. We find that most effective spin measurements are too small to be informative, with the first four events showing a slight preference for a population with alignment, with an odds ratio of 1.2. We argue that it will be possible to distinguish symmetric and anti-symmetric populations at high confidence with tens of additional detections, although mixed populations may take significantly longer to disentangle. We also derive BH spin magnitude distributions from LIGO’s first four BBHs under the assumption of aligned or isotropic populations.

Spin-dependent delay time and Hartman effect in asymmetrical graphene barrier under strain

NASA Astrophysics Data System (ADS)

Sattari, Farhad; Mirershadi, Soghra

2018-01-01

We study the spin-dependent tunneling time, including group delay and dwell time, in a graphene based asymmetrical barrier with Rashba spin-orbit interaction in the presence of strain, sandwiched between two normal leads. We find that the spin-dependent tunneling time can be efficiently tuned by the barrier width, and the bias voltage. Moreover, for the zigzag direction strain although the oscillation period of the dwell time does not change, the oscillation amplitude increases by increasing the incident electron angle. It is found that for the armchair direction strain unlike the zigzag direction the group delay time at the normal incidence depends on the spin state of electrons and Hartman effect can be observed. In addition, for the armchair direction strain the spin polarization increases with increasing the RSOI strength and the bias voltage. The magnitude and sign of spin polarization can be manipulated by strain. In particular, by applying an external electric field the efficiency of the spin polarization is improved significantly in strained graphene, and a fully spin-polarized current is generated.

Majorana surface modes of nodal topological pairings in spin-3/2 semimetals

NASA Astrophysics Data System (ADS)

Yang, Wang; Xiang, Tao; Wu, Congjun

2017-10-01

When solid state systems possess active orbital-band structures subject to spin-orbit coupling, their multicomponent electronic structures are often described in terms of effective large-spin fermion models. Their topological structures of superconductivity are beyond the framework of spin singlet and triplet Cooper pairings for spin-1/2 systems. Examples include the half-Heusler compound series of RPtBi, where R stands for a rare-earth element. Their spin-orbit coupled electronic structures are described by the Luttinger-Kohn model with effective spin-3/2 fermions and are characterized by band inversion. Recent experiments provide evidence to unconventional superconductivity in the YPtBi material with nodal spin-septet pairing. We systematically study topological pairing structures in spin-3/2 systems with the cubic group symmetries and calculate the surface Majorana spectra, which exhibit zero energy flat bands, or, cubic dispersion depending on the specific symmetry of the superconducting gap functions. The signatures of these surface states in the quasiparticle interference patterns of tunneling spectroscopy are studied, which can be tested in future experiments.

Two-level system in spin baths: Non-adiabatic dynamics and heat transport

NASA Astrophysics Data System (ADS)

Segal, Dvira

2014-04-01

We study the non-adiabatic dynamics of a two-state subsystem in a bath of independent spins using the non-interacting blip approximation, and derive an exact analytic expression for the relevant memory kernel. We show that in the thermodynamic limit, when the subsystem-bath coupling is diluted (uniformly) over many (infinite) degrees of freedom, our expression reduces to known results, corresponding to the harmonic bath with an effective, temperature-dependent, spectral density function. We then proceed and study the heat current characteristics in the out-of-equilibrium spin-spin-bath model, with a two-state subsystem bridging two thermal spin-baths of different temperatures. We compare the behavior of this model to the case of a spin connecting boson baths, and demonstrate pronounced qualitative differences between the two models. Specifically, we focus on the development of the thermal diode effect, and show that the spin-spin-bath model cannot support it at weak (subsystem-bath) coupling, while in the intermediate-strong coupling regime its rectifying performance outplays the spin-boson model.

Spin-orbit interaction of light on the surface of atomically thin crystals

NASA Astrophysics Data System (ADS)

Zhou, Junxiao; Chen, Shizhen; Zhang, Wenshuai; Luo, Hailu; Wen, Shuangchun

2017-09-01

Two-dimensional (2D) atomic crystals have extraordinary electronic and photonic properties and hold great promise in the applications of photonic and optoelectronics. Here, we review some of our works about the spin-orbit interaction of light on the surface of 2D atomic crystals. First, we propose a general model to describe the spin-orbit interaction of light of the 2D free standing atomic crystal, and find that it is not necessary to involve the effective refractive index to describe the spin-orbit interaction. By developing the quantum weak measurements, we detect the spin-orbit interaction of light in 2D atomic crystals, which can act as a simple method for defining the layer numbers of graphene. Moreover, we find the transverse spin-dependent splitting in the photonic spin Hall effect exhibits a quantized behavior. Furthermore, the spin-orbit interaction of light for the case of air-topological insulator interface can be routed by adjusting the strength of the axion coupling. These basic finding may enhance the comprehension of the spin-orbit interaction, and find the important application in optoelectronic.

Electrical control of flying spin precession in chiral 1D edge states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakajima, Takashi; Komiyama, Susumu; Lin, Kuan-Ting

2013-12-04

Electrical control and detection of spin precession are experimentally demonstrated by using spin-resolved edge states in the integer quantum Hall regime. Spin precession is triggered at a corner of a biased metal gate, where electron orbital motion makes a sharp turn leading to a nonadiabatic change in the effective magnetic field via spin-orbit interaction. The phase of precession is controlled by the group velocity of edge-state electrons tuned by gate bias voltage: Spin-FET-like coherent control of spin precession is thus realized by all-electrical means.

Global Dirac bispinor entanglement under Lorentz boosts

NASA Astrophysics Data System (ADS)

Bittencourt, Victor A. S. V.; Bernardini, Alex E.; Blasone, Massimo

2018-03-01

The effects of Lorentz boosts on the quantum entanglement encoded by a pair of massive spin-1/2 particles are described according to the Lorentz covariant structure described by Dirac bispinors. The quantum system considered incorporates four degrees of freedom: two of them related to the bispinor intrinsic parity and the other two related to the bispinor spin projection, i.e., the Dirac particle helicity. Because of the natural multipartite structure involved, the Meyer-Wallach global measure of entanglement is preliminarily used for computing global quantum correlations, while the entanglement separately encoded by spin degrees of freedom is measured through the negativity of the reduced two-particle spin-spin state. A general framework to compute the changes on quantum entanglement induced by a boost is developed and then specialized to describe three particular antisymmetric two-particle states. According to the results obtained, two-particle spin-spin entanglement cannot be created by the action of a Lorentz boost in a spin-spin separable antisymmetric state. On the other hand, the maximal spin-spin entanglement encoded by antisymmetric superpositions is degraded by Lorentz boosts driven by high-speed frame transformations. Finally, the effects of boosts on chiral states are shown to exhibit interesting invariance properties, which can only be obtained through such a Lorentz covariant formulation of the problem.

Driving spin transition at interface: Role of adsorption configurations

NASA Astrophysics Data System (ADS)

Zhang, Yachao

2018-01-01

A clear insight into the electrical manipulation of molecular spins at interface is crucial to the design of molecule-based spintronic devices. Here we report on the electrically driven spin transition in manganocene physisorbed on a metallic surface in two different adsorption configurations predicted by ab initio techniques, including a Hubbard-U correction at the manganese site and accounting for the long-range van der Waals interactions. We show that the application of an electric field at the interface induces a high-spin to low-spin transition in the flat-lying manganocene, while it could hardly alter the high-spin ground state of the standing-up molecule. This phenomenon cannot be explained by either the molecule-metal charge transfer or the local electron correlation effects. We demonstrate a linear dependence of the intra-molecular spin-state splitting on the energy difference between crystal-field splitting and on-site Coulomb repulsion. After considering the molecule-surface binding energy shifts upon spin transition, we reproduce the obtained spin-state energetics. We find that the configuration-dependent responses of the spin-transition originate from the binding energy shifts instead of the variation of the local ligand field. Through these analyses, we obtain an intuitive understanding of the effects of molecule-surface contact on spin-crossover under electrical bias.

Theory of the inverse spin galvanic effect in quantum wells

NASA Astrophysics Data System (ADS)

Maleki Sheikhabadi, Amin; Miatka, Iryna; Sherman, E. Ya.; Raimondi, Roberto

2018-06-01

The understanding of the fundamentals of spin and charge densities and currents interconversion by spin-orbit coupling can enable efficient applications beyond the possibilities offered by conventional electronics. For this purpose we consider various forms of the frequency-dependent inverse spin galvanic effect in semiconductor quantum wells and epilayers taking into account the cubic in the electron momentum spin-orbit coupling in the Rashba and Dresselhaus forms, concentrating on the current-induced spin polarization (CISP). We find that including the cubic terms qualitatively explains recent findings of the CISP in InGaAs epilayers being the strongest if the internal spin-orbit coupling field is the smallest and vice versa [Norman et al., Phys. Rev. Lett. 112, 056601 (2014), 10.1103/PhysRevLett.112.056601; Luengo-Kovac et al., Phys. Rev. B 96, 195206 (2017), 10.1103/PhysRevB.96.195206], in contrast to the common understanding. Our results provide a promising framework for the control of spin transport in future spintronics devices.

Computations of the chirality-sensitive effect induced by an antisymmetric indirect spin–spin coupling

NASA Astrophysics Data System (ADS)

Garbacz, Piotr

2018-05-01

Results of quantum mechanical computations of the antisymmetric part of the indirect spin-spin coupling tensor, ?, performed using the coupled-cluster method, the second-order polarisation propagator approximation, and the density functional theory for 25 molecules and nearly 100 spin-spin couplings are reported. These results are used for an estimation of the magnitude of the recently proposed liquid-state nuclear magnetic resonance chirality-sensitive effect, which allows to determine the molecular chirality directly, i.e. without the need for the application of any chiral agent. The following were found: (i) the antisymmetry J⋆ is usually larger for the coupling between spins separated by two chemical bonds in comparison with the coupling through one bond, (ii) promising samples are those which contain fluorine, and (iii) the antisymmetry of the spin-spin coupling tensor is of the order of a few hertz for commercially available chemical compounds. Therefore, the relevant property of the experiment, the pseudoscalar Jc, for them is of the order of 1 nHz m/V.

Inverse spin Hall effect from pulsed spin current in organic semiconductors with tunable spin-orbit coupling.

PubMed

Sun, Dali; van Schooten, Kipp J; Kavand, Marzieh; Malissa, Hans; Zhang, Chuang; Groesbeck, Matthew; Boehme, Christoph; Valy Vardeny, Z

2016-08-01

Exploration of spin currents in organic semiconductors (OSECs) induced by resonant microwave absorption in ferromagnetic substrates is appealing for potential spintronics applications. Owing to the inherently weak spin-orbit coupling (SOC) of OSECs, their inverse spin Hall effect (ISHE) response is very subtle; limited by the microwave power applicable under continuous-wave (cw) excitation. Here we introduce a novel approach for generating significant ISHE signals in OSECs using pulsed ferromagnetic resonance, where the ISHE is two to three orders of magnitude larger compared to cw excitation. This strong ISHE enables us to investigate a variety of OSECs ranging from π-conjugated polymers with strong SOC that contain intrachain platinum atoms, to weak SOC polymers, to C60 films, where the SOC is predominantly caused by the curvature of the molecule's surface. The pulsed-ISHE technique offers a robust route for efficient injection and detection schemes of spin currents at room temperature, and paves the way for spin orbitronics in plastic materials.

General theory of feedback control of a nuclear spin ensemble in quantum dots

NASA Astrophysics Data System (ADS)

Yang, Wen; Sham, L. J.

2013-12-01

We present a microscopic theory of the nonequilibrium nuclear spin dynamics driven by the electron and/or hole under continuous-wave pumping in a quantum dot. We show the correlated dynamics of the nuclear spin ensemble and the electron and/or hole under optical excitation as a quantum feedback loop and investigate the dynamics of the many nuclear spins as a nonlinear collective motion. This gives rise to three observable effects: (i) hysteresis, (ii) locking (avoidance) of the pump absorption strength to (from) the natural resonance, and (iii) suppression (amplification) of the fluctuation of weakly polarized nuclear spins, leading to prolonged (shortened) electron-spin coherence time. A single nonlinear feedback function is constructed which determines the different outcomes of the three effects listed above depending on the feedback being negative or positive. The general theory also helps to put in perspective the wide range of existing theories on the problem of a single electron spin in a nuclear spin bath.

Large Spin-Wave Bullet in a Ferrimagnetic Insulator Driven by the Spin Hall Effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jungfleisch, M. B.; Zhang, W.; Sklenar, J.

2016-02-01

Due to its transverse nature, spin Hall effects (SHE) provide the possibility to excite and detect spin currents and magnetization dynamics even in magnetic insulators. Magnetic insulators are outstanding materials for the investigation of nonlinear phenomena and for novel low power spintronics applications because of their extremely low Gilbert damping. Here, we report on the direct imaging of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the ferrimagnetic insulator Y 3Fe 5O 12 based on the excitation and detection by SHEs. The driven spin dynamics in Y 3Fe 5O 12 is directly imaged by spatially-resolved microfocused Brillouin light scattering (BLS) spectroscopy.more » Previously, ST-FMR experiments assumed a uniform precession across the sample, which is not valid in our measurements. A strong spin-wave localization in the center of the sample is observed indicating the formation of a nonlinear, self-localized spin-wave `bullet'.« less

Matrix-assisted relaxation in Fe(phen){sub 2}(NCS){sub 2} spin-crossover microparticles, experimental and theoretical investigations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Enachescu, Cristian, E-mail: cristian.enachescu@uaic.ro; Stancu, Alexandru; Tanasa, Radu

2016-07-18

In this study, we present the influence of the embedding matrix on the relaxation of Fe(phen){sub 2}(NCS){sub 2} (phen = 1,10-phenanthroline) spin-transition microparticles as revealed by experiments and provide an explanation within the framework of an elastic model based on a Monte-Carlo method. Experiments show that the shape of the high-spin → low-spin relaxation curves is drastically changed when the particles are dispersed in glycerol. This effect was considered in the model by means of interactions between the microparticles and the matrix. A faster start of the relaxation for microparticles embedded in glycerol is due to an initial positive local pressure actingmore » on the edge spin-crossover molecules from the matrix side. This local pressure diminishes and eventually becomes negative during relaxation, as an effect of the decrease of the volume of spin-crossover microparticles from high-spin to low-spin.« less

Ab initio model potential calculations on the electronic spectrum of Ni2 + -doped MgO including correlation, spin-orbit and embedding effects

NASA Astrophysics Data System (ADS)

Llusar, Rosa; Casarrubios, Marcos; Barandiarán, Zoila; Seijo, Luis

1996-10-01

An ab initio theoretical study of the optical absorption spectrum of Ni2+-doped MgO has been conducted by means of calculations in a MgO-embedded (NiO6)10-cluster. The calculations include long- and short-range embedding effects of electrostatic and quantum nature brought about by the MgO crystalline lattice, as well as electron correlation and spin-orbit effects within the (NiO6)10- cluster. The spin-orbit calculations have been performed using the spin-orbit-CI WB-AIMP method [Chem. Phys. Lett. 147, 597 (1988); J. Chem. Phys. 102, 8078 (1995)] which has been recently proposed and is applied here for the first time to the field of impurities in crystals. The WB-AIMP method is extended in order to handle correlation effects which, being necessary to produce accurate energy differences between spin-free states, are not needed for the proper calculation of spin-orbit couplings. The extension of the WB-AIMP method, which is also aimed at keeping the size of the spin-orbit-CI within reasonable limits, is based on the use of spin-free-state shifting operators. It is shown that the unreasonable spin-orbit splittings obtained for MgO:Ni2+ in spin-orbit-CI calculations correlating only 8 electrons become correct when the proposed extension is applied, so that the same CI space is used but energy corrections due to correlating up to 26 electrons are included. The results of the ligand field spectrum of MgO:Ni2+ show good overall agreement with the experimental measurements and a reassignment of the observed Eg(b3T1g) excited state is proposed and discussed.

The Consequences of Spin-Orbit Coupling on the 5d3 Electronic Configuration

NASA Astrophysics Data System (ADS)

Christianson, A. D.

The impact of spin-orbit coupling on collective properties of matter is of considerable interest. The most intensively investigated materials in this regard are Iridium-based transition metal oxides which exhibit a host of interesting ground states that originate from a 5d5 Jeff = 1/2 electronic configuration. Moving beyond the Jeff = 1/2 paradigm to other electronic configurations where spin-orbit coupling plays a prominent role is a key objective of ongoing research. Here we focus on several Osmium-based transition metal oxides such as NaOsO3, Cd2Os2O7, Ca3LiOsO6, Sr2ScOsO6, Ba2YOsO6, and Sr2FeOsO6, which are nominally in the 5d3 electronic configuration. Within the LS coupling picture and a strong octahedral crystal field, the 5d3 configuration is expected to be an orbital singlet and spin-orbit effects should be minimal. Nevertheless, our neutron and x-ray scattering investigations of these materials as well as investigations by other groups show dramatic effects of spin-orbit coupling including reduced moment magnetic order, enhanced spin-phonon coupling, and large spin gaps. In particular, the anisotropy induced by spin-orbit coupling tips the balance of the frustrated interactions and drives the selection of particular magnetic ground states. To understand the mechanism driving the spin-orbit effects, we have explored the ground state t2g manifold with resonant inelastic x-ray scattering and observe a spectrum inexplicable by an LS coupling picture. On the other hand, an intermediate coupling approach reveals that the ground state wave function is a J =3/2 configuration which answers the question of how strong spin-orbit coupling effects arise in 5d3 systems.

The effect of engine spin direction on the dynamics of powered two wheelers

NASA Astrophysics Data System (ADS)

Massaro, Matteo; Marconi, Edoardo

2018-04-01

The effect of engine spin direction on the dynamics of powered two wheelers is investigated in terms of steady-state points (equilibria), vibration modes (stability), manoeuvre time (performance/manoeuvrability) and handling. The goal is to assess and quantify the advantage sometimes claimed for the 'counter-rotating' engine configuration, where the engine spins in the opposite direction with respect to wheels, against the 'conventional' configuration, where the engine spins in the same direction of wheels.

Magnetic anisotropy in binuclear complexes in the weak-exchange limit: From the multispin to the giant-spin Hamiltonian

NASA Astrophysics Data System (ADS)

Maurice, Rémi; de Graaf, Coen; Guihéry, Nathalie

2010-06-01

This paper studies the physical basis of the giant-spin Hamiltonian, which is usually used to describe the anisotropy of single-molecule magnets. A rigorous extraction of the model has been performed in the weak-exchange limit of a binuclear centrosymmetric Ni(II) complex, using correlated ab initio calculations and effective Hamiltonian theory. It is shown that the giant-spin Hamiltonian is not appropriate to describe polynuclear complexes as soon as spin mixing becomes non-negligible. A relevant model is proposed involving fourth-order operators, different from the traditionally used Stevens operators. The new giant-spin Hamiltonian correctly reproduces the effects of the spin mixing in the weak-exchange limit. A procedure to switch on and off the spin mixing in the extraction has been implemented in order to separate this effect from other anisotropic effects and to numerically evaluate both contributions to the tunnel splitting. Furthermore, the new giant-spin Hamiltonian has been derived analytically from the multispin Hamiltonian at the second order of perturbation and the theoretical link between the two models is studied to gain understanding concerning the microscopic origin of the fourth-order interaction in terms of axial, rhombic, or mixed (axial-rhombic) character. Finally, an adequate method is proposed to extract the proper magnetic axes frame for polynuclear anisotropic systems.

Training effect in specular spin valves

NASA Astrophysics Data System (ADS)

Ventura, J.; Araujo, J. P.; Sousa, J. B.; Veloso, A.; Freitas, P. P.

2008-05-01

Specular spin valves show an enhanced giant magnetoresistive (GMR) ratio due to specular reflection in nano-oxide layers (NOLs) formed by the partial oxidation of CoFe pinned and free layers. The oxides that form the (pinned layer) NOL were recently shown to antiferromagnetically order at Ttilde 175K . Here, we study the training effect (TE) in MnIr/CoFe/NOL/CoFe/Cu/CoFe/NOL/Ta specular spin valves in the 300-15 K temperature range. The exchange bias direction between the MnIr and CoFe layers impressed during annealing is taken as the positive direction. The training effect is observed in antiferromagnetic (AFM)/ferromagnetic (FM) exchange systems and related to the rearrangement of interfacial AFM spin structure with the number of hysteretic cycles performed (n) , resulting in the decrease of the exchange field (Hexch) . Here, in the studied specular spin valve, TE was only observed for T<175K and is thus related to the pinned layer NOL-AFM ordering and to the evolution of the corresponding spin structure with n . We show that FM spins that are strongly coupled to AFM domains do not align with the applied positive magnetic field (H) , giving rise to a residual MR at H≫0 . Such nonsaturating MR will be related with a spin-glass-like behavior of the interfacial magnetism induced by the nano-oxide layer. The observed dependence of the training effect on the field cooling procedure is also likely associated with the existence of different spin configurations available in the magnetically disordered oxide. Furthermore, anomalous magnetoresistance cycles measured after cooling runs under -500Oe are here related to induced NOL exchange bias/applied magnetic field misalignment. The temperature dependence of the training effect was obtained and fitted by using a recent theoretical model.

Spin current induced by a charged tip in a quantum point contact

NASA Astrophysics Data System (ADS)

Shchamkhalova, B. S.

2017-03-01

We show that the charged tip of the probe microscope, which is widely used in studying the electron transport in low-dimensional systems, induces a spin current. The effect is caused by the spin-orbit interaction arising due to an electric field produced by the charged tip. The tip acts as a spin-flip scatterer giving rise to the spin polarization of the net current and the occurrence of a spin density in the system.

Exchange interactions in transition metal oxides: the role of oxygen spin polarization.

PubMed

Logemann, R; Rudenko, A N; Katsnelson, M I; Kirilyuk, A

2017-08-23

Magnetism of transition metal (TM) oxides is usually described in terms of the Heisenberg model, with orientation-independent interactions between the spins. However, the applicability of such a model is not fully justified for TM oxides because spin polarization of oxygen is usually ignored. In the conventional model based on the Anderson principle, oxygen effects are considered as a property of the TM ion and only TM interactions are relevant. Here, we perform a systematic comparison between two approaches for spin polarization on oxygen in typical TM oxides. To this end, we calculate the exchange interactions in NiO, MnO and hematite (Fe 2 O 3 ) for different magnetic configurations using the magnetic force theorem. We consider the full spin Hamiltonian including oxygen sites, and also derive an effective model where the spin polarization on oxygen renormalizes the exchange interactions between TM sites. Surprisingly, the exchange interactions in NiO depend on the magnetic state if spin polarization on oxygen is neglected, resulting in non-Heisenberg behavior. In contrast, the inclusion of spin polarization in NiO makes the Heisenberg model more applicable. Just the opposite, MnO behaves as a Heisenberg magnet when oxygen spin polarization is neglected, but shows strong non-Heisenberg effects when spin polarization on oxygen is included. In hematite, both models result in non-Heisenberg behavior. The general applicability of the magnetic force theorem as well as the Heisenberg model to TM oxides is discussed.

Organic Spin-Valves and Beyond: Spin Injection and Transport in Organic Semiconductors and the Effect of Interfacial Engineering.

PubMed

Jang, Hyuk-Jae; Richter, Curt A

2017-01-01

Since the first observation of the spin-valve effect through organic semiconductors, efforts to realize novel spintronic technologies based on organic semiconductors have been rapidly growing. However, a complete understanding of spin-polarized carrier injection and transport in organic semiconductors is still lacking and under debate. For example, there is still no clear understanding of major spin-flip mechanisms in organic semiconductors and the role of hybrid metal-organic interfaces in spin injection. Recent findings suggest that organic single crystals can provide spin-transport media with much less structural disorder relative to organic thin films, thus reducing momentum scattering. Additionally, modification of the band energetics, morphology, and even spin magnetic moment at the metal-organic interface by interface engineering can greatly impact the efficiency of spin-polarized carrier injection. Here, progress on efficient spin-polarized carrier injection into organic semiconductors from ferromagnetic metals by using various interface engineering techniques is presented, such as inserting a metallic interlayer, a molecular self-assembled monolayer (SAM), and a ballistic carrier emitter. In addition, efforts to realize long spin transport in single-crystalline organic semiconductors are discussed. The focus here is on understanding and maximizing spin-polarized carrier injection and transport in organic semiconductors and insight is provided for the realization of emerging organic spintronics technologies. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yee, Seonghwan, E-mail: Seonghwan.Yee@Beaumont.edu; Gao, Jia-Hong

Purpose: To investigate whether the direction of spin-lock field, either parallel or antiparallel to the rotating magnetization, has any effect on the spin-lock MRI signal and further on the quantitative measurement of T1ρ, in a clinical 3 T MRI system. Methods: The effects of inverted spin-lock field direction were investigated by acquiring a series of spin-lock MRI signals for an American College of Radiology MRI phantom, while the spin-lock field direction was switched between the parallel and antiparallel directions. The acquisition was performed for different spin-locking methods (i.e., for the single- and dual-field spin-locking methods) and for different levels ofmore » clinically feasible spin-lock field strength, ranging from 100 to 500 Hz, while the spin-lock duration was varied in the range from 0 to 100 ms. Results: When the spin-lock field was inverted into the antiparallel direction, the rate of MRI signal decay was altered and the T1ρ value, when compared to the value for the parallel field, was clearly different. Different degrees of such direction-dependency were observed for different spin-lock field strengths. In addition, the dependency was much smaller when the parallel and the antiparallel fields are mixed together in the dual-field method. Conclusions: The spin-lock field direction could impact the MRI signal and further the T1ρ measurement in a clinical MRI system.« less

Theory of unidirectional magnetoresistance in magnetic heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Steven S.-L.; Vignale, Giovanni

2017-09-01

We present a general drift-diffusion theory beyond linear response to explain the unidirectional magnetoresistance (UMR) observed in recent experiments in various magnetic heterostructures. In general, such nonlinear magnetoresistance may originate from the concerted action of current-induced spin accumulation and spin asymmetry in electron mobility. As a case study, we calculate the UMR in a bilayer system consisting of a heavy-metal (HM) and a ferromagnetic metal (FM), where the spin accumulation is induced via the spin Hall effect in the bulk of the HM layer. Our previous formulation [cf. PRB 94, 140411(R) (2016)] is generalized to include the interface resistance and spin memory loss, which allows us to analyze in details their effects on the UMR. We found that the UMR turns out to be independent of the spin asymmetry of the interfacial resistance, at variance with the linear giant-magnetoresistance (GMR) effect. A linear relation between the UMR and the conductivity-spin asymmetry is revealed, which provides an alternative way to control the sign and magnitude of the UMR and hence may serve as an experimental signature of our proposed mechanism.

Single Spin Superconductivity: Bulk and Junction Effects

NASA Astrophysics Data System (ADS)

Rudd, Robert E.; Pickett, Warren E.

1998-03-01

The Josephson Effect provides a primary signature of single spin superconductivity (SSS), the as yet unobserved superconducting state which was proposed recently(W.E. Pickett, Phys. Rev. Lett. 77), 3185 (1996). as a low temperature phase of half-metallic antiferromagnets.(W.E. Pickett, ``Spin Density Functional Based Search for Half-Metallic Antiferromagnets,'' cond-mat/9709100 (1997).) These materials are insulating in the spin-down channel but are metallic in the spin-up channel. The SSS state is characterized by a unique form of p-wave pairing within a single spin channel.(R.E. Rudd and W.E. Pickett, ``Single Spin Superconductivity:Formulation and Ginzburg-Landau Theory,'' Phys. Rev. B. in press) We develop the theory of a rich variety of Josephson effects that arise due to the form of the SSS order parameter. Tunneling is allowed at a SSS-SSS^' junction depending on the relative orientation of each of their order parameters (SSS and HM AFM). No current flows between an SSS and an s-wave BCS system, which provides a powerful method to distinguish SSS from other superconducting states.

Magnetocrystalline anisotropy in cobalt based magnets: a choice of correlation parameters and the relativistic effects

DOE PAGES

Nguyen, Manh Cuong; Yao, Yongxin; Wang, Cai-Zhuang; ...

2018-05-16

The dependence of the magnetocrystalline anisotropy energy (MAE) in MCo 5 (M = Y, La, Ce, Gd) and CoPt on the Coulomb correlations and strength of spin orbit (SO) interaction within the GGA + U scheme is investigated. A range of parameters suitable for the satisfactory description of key magnetic properties is determined. We show that for a large variation of SO interaction the MAE in these materials can be well described by the traditional second order perturbation theory. We also show that in these materials the MAE can be both proportional and negatively proportional to the orbital moment anisotropymore » (OMA) of Co atoms. Dependence of relativistic effects on Coulomb correlations, applicability of the second order perturbation theory for the description of MAE, and effective screening of the SO interaction in these systems are discussed using a generalized virial theorem. Finally, such determined sets of parameters of Coulomb correlations can be used in much needed large scale atomistic simulations.« less

Magnetocrystalline anisotropy in cobalt based magnets: a choice of correlation parameters and the relativistic effects

NASA Astrophysics Data System (ADS)

Nguyen, Manh Cuong; Yao, Yongxin; Wang, Cai-Zhuang; Ho, Kai-Ming; Antropov, Vladimir P.

2018-05-01

The dependence of the magnetocrystalline anisotropy energy (MAE) in MCo5 (M  =  Y, La, Ce, Gd) and CoPt on the Coulomb correlations and strength of spin orbit (SO) interaction within the GGA  +  U scheme is investigated. A range of parameters suitable for the satisfactory description of key magnetic properties is determined. We show that for a large variation of SO interaction the MAE in these materials can be well described by the traditional second order perturbation theory. We also show that in these materials the MAE can be both proportional and negatively proportional to the orbital moment anisotropy (OMA) of Co atoms. Dependence of relativistic effects on Coulomb correlations, applicability of the second order perturbation theory for the description of MAE, and effective screening of the SO interaction in these systems are discussed using a generalized virial theorem. Such determined sets of parameters of Coulomb correlations can be used in much needed large scale atomistic simulations.

Magnetocrystalline anisotropy in cobalt based magnets: a choice of correlation parameters and the relativistic effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Manh Cuong; Yao, Yongxin; Wang, Cai-Zhuang

The dependence of the magnetocrystalline anisotropy energy (MAE) in MCo 5 (M = Y, La, Ce, Gd) and CoPt on the Coulomb correlations and strength of spin orbit (SO) interaction within the GGA + U scheme is investigated. A range of parameters suitable for the satisfactory description of key magnetic properties is determined. We show that for a large variation of SO interaction the MAE in these materials can be well described by the traditional second order perturbation theory. We also show that in these materials the MAE can be both proportional and negatively proportional to the orbital moment anisotropymore » (OMA) of Co atoms. Dependence of relativistic effects on Coulomb correlations, applicability of the second order perturbation theory for the description of MAE, and effective screening of the SO interaction in these systems are discussed using a generalized virial theorem. Finally, such determined sets of parameters of Coulomb correlations can be used in much needed large scale atomistic simulations.« less

Bending strain engineering in quantum spin hall system for controlling spin currents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Bing; Jin, Kyung-Hwan; Cui, Bin

Quantum spin Hall system can exhibit exotic spin transport phenomena, mediated by its topological edge states. The concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system is demonstrated. Here, we show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. Moreover, the curvedmore » quantum spin Hall system can be achieved by the concept of topological nanomechanical architecture in a controllable way, as demonstrated by the material example of Bi/Cl/Si(111) nanofilm. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics.« less

Bending strain engineering in quantum spin hall system for controlling spin currents

DOE PAGES

Huang, Bing; Jin, Kyung-Hwan; Cui, Bin; ...

2017-06-16

Quantum spin Hall system can exhibit exotic spin transport phenomena, mediated by its topological edge states. The concept of bending strain engineering to tune the spin transport properties of a quantum spin Hall system is demonstrated. Here, we show that bending strain can be used to control the spin orientation of counter-propagating edge states of a quantum spin system to generate a non-zero spin current. This physics mechanism can be applied to effectively tune the spin current and pure spin current decoupled from charge current in a quantum spin Hall system by control of its bending curvature. Moreover, the curvedmore » quantum spin Hall system can be achieved by the concept of topological nanomechanical architecture in a controllable way, as demonstrated by the material example of Bi/Cl/Si(111) nanofilm. This concept of bending strain engineering of spins via topological nanomechanical architecture affords a promising route towards the realization of topological nano-mechanospintronics.« less

Giant magneto-spin-Seebeck effect and magnon transfer torques in insulating spin valves

NASA Astrophysics Data System (ADS)

Cheng, Yihong; Chen, Kai; Zhang, Shufeng

2018-01-01

We theoretically study magnon transport in an insulating spin valve (ISV) made of an antiferromagnetic insulator sandwiched between two ferromagnetic insulator (FI) layers. In the conventional metal-based spin valve, the electron spins propagate between two metallic ferromagnetic layers, giving rise to giant magnetoresistance and spin transfer torque. Here, the incoherent magnons in the ISV serve as angular momentum carriers and are responsible for the angular momentum transport between two FI layers across the antiferromagnetic spacer. We predict two transport phenomena in the presence of the temperature gradient: a giant magneto-spin-Seebeck effect in which the output voltage signal is controlled by the relative orientation of the two FI layers and magnon transfer torque that can be used for switching the magnetization of the FI layers with a temperature gradient of the order of 0.1 Kelvin per nanometer.

Strain and thermally induced magnetic dynamics and spin current in magnetic insulators subject to transient optical grating

NASA Astrophysics Data System (ADS)

Wang, Xi-Guang; Chotorlishvili, Levan; Berakdar, Jamal

2017-07-01

We analyze the magnetic dynamics and particularlythe spin current in an open-circuit ferromagnetic insulator irradiated by two intense, phase-locked laser pulses. The interference of the laser beams generates a transient optical grating and a transient spatio-temporal temperature distribution. Both effects lead to elastic and heat waves at the surface and into the bulk of the sample. The strain induced spin current as well as the thermally induced magnonic spin current are evaluated numerically on the basis of micromagnetic simulations using solutions of the heat equation. We observe that the thermo-elastically induced magnonic spin current propagates on a distance larger than the characteristic size of thermal profile, an effect useful for applications in remote detection of spin caloritronics phenomena. Our findings point out that exploiting strain adds a new twist to heat-assisted magnetic switching and spin-current generation for spintronic applications.

Versatile microwave-driven trapped ion spin system for quantum information processing

PubMed Central

Piltz, Christian; Sriarunothai, Theeraphot; Ivanov, Svetoslav S.; Wölk, Sabine; Wunderlich, Christof

2016-01-01

Using trapped atomic ions, we demonstrate a tailored and versatile effective spin system suitable for quantum simulations and universal quantum computation. By simply applying microwave pulses, selected spins can be decoupled from the remaining system and, thus, can serve as a quantum memory, while simultaneously, other coupled spins perform conditional quantum dynamics. Also, microwave pulses can change the sign of spin-spin couplings, as well as their effective strength, even during the course of a quantum algorithm. Taking advantage of the simultaneous long-range coupling between three spins, a coherent quantum Fourier transform—an essential building block for many quantum algorithms—is efficiently realized. This approach, which is based on microwave-driven trapped ions and is complementary to laser-based methods, opens a new route to overcoming technical and physical challenges in the quest for a quantum simulator and a quantum computer. PMID:27419233

Spin-filtering and giant magnetoresistance effects in polyacetylene-based molecular devices

NASA Astrophysics Data System (ADS)

Chen, Tong; Yan, Shenlang; Xu, Liang; Liu, Desheng; Li, Quan; Wang, Lingling; Long, Mengqiu

2017-07-01

Using the non-equilibrium Green's function formalism in combination with density functional theory, we performed ab initio calculations of spin-dependent electron transport in molecular devices consisting of a polyacetylene (CnHn+1) chain vertically attached to a carbon chain sandwiched between two semi-infinite zigzag-edged graphene nanoribbon electrodes. Spin-charge transport in the device could be modulated to different magnetic configurations by an external magnetic field. The results showed that single spin conduction could be obtained. Specifically, the proposed CnHn+1 devices exhibited several interesting effects, including (dual) spin filtering, spin negative differential resistance, odd-even oscillation, and magnetoresistance (MR). Marked spin polarization with a filtering efficiency of up to 100% over a large bias range was found, and the highest MR ratio for the CnHn+1 junctions reached 4.6 × 104. In addition, the physical mechanisms for these phenomena were also revealed.

Confinement and Diffusion Effects in Dynamical Nuclear Polarization in Low Dimensional Nanostructures

NASA Astrophysics Data System (ADS)

Henriksen, Dan; Tifrea, Ionel

2012-02-01

We investigate the dynamic nuclear polarization as it results from the hyperfine coupling between nonequilibrium electronic spins and nuclear spins in semiconductor nanostructures. The natural confinement provided by low dimensional nanostructures is responsible for an efficient nuclear spin - electron spin hyperfine coupling [1] and for a reduced value of the nuclear spin diffusion constant [2]. In the case of optical pumping, the induced nuclear spin polarization is position dependent even in the presence of nuclear spin diffusion. This effect should be measurable via optically induced nuclear magnetic resonance or time-resolved Faraday rotation experiments. We discuss the implications of our calculations for the case of GaAs quantum well structures.[4pt] [1] I. Tifrea and M. E. Flatt'e, Phys. Rev. B 84, 155319 (2011).[0pt] [2] A. Malinowski and R. T. Harley, Solid State Commun. 114, 419 (2000).

Long tailed trions in monolayer MoS2: Temperature dependent asymmetry and resulting red-shift of trion photoluminescence spectra.

PubMed

Christopher, Jason W; Goldberg, Bennett B; Swan, Anna K

2017-10-25

Monolayer molybdenum disulfide (MoS 2 ) has emerged as a model system for studying many-body physics because the low dimensionality reduces screening leading to tightly bound states stable at room temperature. Further, the many-body states possess a pseudo-spin degree of freedom that corresponds with the two direct-gap valleys of the band structure, which can be optically manipulated. Here we focus on one bound state, the negatively charged trion. Unlike excitons, trions can radiatively decay with non-zero momentum by kicking out an electron, resulting in an asymmetric trion photoluminescence (PL) peak with a long low-energy tail and peak position that differs from the zero momentum trion energy. The asymmetry of the trion PL peak and resulting peak red-shift depends both on the trion size and a temperature-dependent contribution. Ignoring the trion asymmetry will result in over estimating the trion binding energy by nearly 20 meV at room temperature. We analyze the temperature-dependent PL to reveal the effective trion size, consistent with the literature, and the temperature dependence of the band gap and spin-orbit splitting of the valence band. This is the first time the temperature-dependence of the trion PL has been analyzed with such detail in any system.

Why the Heyd-Scuseria-Ernzerhof hybrid functional description of VO2 phases is not correct

NASA Astrophysics Data System (ADS)

Grau-Crespo, Ricardo; Wang, Hao; Schwingenschlögl, Udo

2012-08-01

In contrast with recent claims that the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional can provide a good description of the electronic and magnetic structures of VO2 phases [Eyert, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.107.016401 107, 016401 (2011)], we show here that the HSE lowest-energy solutions for both the low-temperature monoclinic (M1) phase and the high-temperature rutile (R) phase, which are obtained upon inclusion of spin polarization, are at odds with experimental observations. For the M1 phase the ground state is (but should not be) magnetic, while the ground state of the R phase, which is also spin polarized, is not (but should be) metallic. The energy difference between the low-temperature and high-temperature phases has strong discrepancies with the experimental latent heat.

Transversity 2005

NASA Astrophysics Data System (ADS)

Barone, Vincenzo; Ratcliffe, Philip G.

Introduction. Purpose and status of the Italian Transversity Project / F. Bradamante -- Opening lecture. Transversity / M. Anselmino -- Experimental lectures. Azimuthal single-spin asymmetries from polarized and unpolarized hydrogen targets at HERMES / G. Schnell (for the HERMES Collaboration). Collins and Sivers asymmetries on the deuteron from COMPASS data / I. Horn (for the COMPASS Collaboration). First measurement of interference fragmentation on a transversely polarized hydrogen target / P. B. van der Nat (for the HERMES Collaboration). Two-hadron asymmetries at the COMPASS experiment / A. Mielech (for the COMPASS Collaboration). Measurements of chiral-odd fragmentation functions at Belle / R. Seidl ... [et al.]. Lambda asymmetries / A. Ferrero (for the COMPASS Collaboration). Transverse spin at PHENIX: results and prospects / C. Aidala (for the PHENIX Collaboration). Transverse spin and RHIC / L. Bland. Studies of transverse spin effects at JLab / H. Avakian ... [et al.] (for the CLAS Collaboration). Neutron transversity at Jefferson Lab / J. P. Chen ... [et al.] (for the Jefferson Lab Hall A Collaboration). PAX: polarized antiproton experiments / M. Contalbrigo. Single and double spin N-N interactions at GSI / M. Maggiora (for the ASSIA Collaboration). Spin filtering in storage rings / N. N. Nikolaev & F. F. Pavlov -- Theory lectures. Single-spin asymmetries and transversity in QCD / S. J. Brodsky. The relativistic hydrogen atom: a theoretical laboratory for structure functions / X. Artru & K. Benhizia. GPD's and SSA's / M. Burkardt. Time reversal odd distribution functions in chiral models / A. Drago. Soffer bound and transverse spin densities from lattice QCD / M. Diehl ... [et al.]. Single-spin asymmetries and Qiu-Sterman effect(s) / A. Bacchetta. Sivers function: SIDIS data, fits and predictions / M. Anselmino ... [et al.]. Twist-3 effects in semi-inclusive deep inelastic scattering / M. Schlegel, K. Goeke & A. Metz. Quark and gluon Sivers functions / I. Schmidt. Sivers effect in semi-inclusive deeply inelastic scattering and Drell-Yan / J. C. Collins ... [et al.]. Helicity formalism and spin asymmetries in hadronic processes / M. Anselmino ... [et al.]. Including Cahn and Sivers effects into event generators / A. Kotzinian. Comparing extractions of Sivers functions / M. Anselmino ... [et al.]. Anomalous Drell-Yan asymmetry from hadronic or QCD vacuum effects / D. Boer. "T-odd" effects in transverse spin and azimuthal asymmetries in SIDIS / L. P. Gamberg & G. R. Goldstein. T-odd effects in unpolarized Drell-Yan scattering / G. R. Goldstein & L. P. Gamberg. Alternative approaches to transversity: how convenient and feasible are they? / M. Radici. Relations between single and double transverse asymmetries / O. V. Teryaev. Cross sections, error bars and event distributions in simulated Drell-Yan azimuthal asymmetry measurements / A. Bianconi. Next-to-leading order QCD corrections for transversely polarized pp and p¯p collisions / A. Mukherjee, M. Stratmann & W. Vogelsang. Double transverse-spin asymmetries in Drell-Yan and J/[symbol] production from proton-antiproton collisions / M. Guzzi ... [et al.]. The quark-quark correlator: theory and phenomenology / E. Di Salvo. Chiral quark model spin filtering mechanism and hyperon polarization / S. M. Troshin & N. E. Tyurin -- Closing lecture. Where we've been ... and where we're going / G. Bunce.

Spin Current through a Quantum Dot in the Presence of an Oscillating Magnetic Field

NASA Astrophysics Data System (ADS)

Zhang, Ping; Xue, Qi-Kun; Xie, X. C.

2003-11-01

Nonequilibrium spin transport through an interacting quantum dot is analyzed. The coherent spin oscillations in the dot provide a generating source for spin current. In the interacting regime, the Kondo effect is influenced in a significant way by the presence of the processing magnetic field. In particular, when the precession frequency is tuned to resonance between spin-up and spin-down states of the dot, Kondo singularity for each spin splits into a superposition of two resonance peaks. The Kondo-type cotunneling contribution is manifested by a large enhancement of the pumped spin current in the strong coupling low temperature regime.

Nonreciprocal Transverse Photonic Spin and Magnetization-Induced Electromagnetic Spin-Orbit Coupling

PubMed Central

Levy, Miguel; Karki, Dolendra

2017-01-01

We present a formulation of electromagnetic spin-orbit coupling in magneto-optic media, and propose an alternative source of spin-orbit coupling to non-paraxial optics vortices. Our treatment puts forth a formulation of nonreciprocal transverse-spin angular-momentum-density shifts for evanescent waves in magneto-optic waveguide media. It shows that magnetization-induced electromagnetic spin-orbit coupling is possible, and that it leads to unequal spin to orbital angular momentum conversion in magneto-optic media evanescent waves in opposite propagation-directions. Generation of free-space helicoidal beams based on this conversion is shown to be spin-helicity- and magnetization-dependent. We show that transverse-spin to orbital angular momentum coupling into magneto-optic waveguide media engenders spin-helicity-dependent unidirectional propagation. This unidirectional effect produces different orbital angular momenta in opposite directions upon excitation-spin-helicity reversals. PMID:28059120

Laser-induced polarization of a quantum spin system in the steady-state regime

NASA Astrophysics Data System (ADS)

Zvyagin, A. A.

2016-05-01

The effect of the circularly polarized laser field on quantum spin systems in the steady-state regime, in which relaxation plays the central role, has been studied. The dynamical mean-field-like theory predicts several general results for the behavior of the time-average magnetization caused by the laser field. The induced magnetization oscillates with the frequency of the laser field (while Rabi-like oscillations, which modulate the latter in the dynamical regime, are damped by the relaxation in the steady-state regime). At high frequencies, that magnetization is determined by the value to which the relaxation process is directed. At low frequencies the slope of that magnetization as a function of the frequency is determined by the strength of the laser field. The anisotropy determines the resonance behavior of the time-averaged magnetization in both the ferromagnetic and antiferromagnetic cases with nonzero magnetic anisotropy. Nonlinear effects (in the magnitude of the laser field) have been considered. The effect of the laser field on quantum spin systems is maximal in resonance, where the time-averaged magnetization, caused by the laser field, is changed essentially. Out of resonance the changes in the magnetization are relatively small. The resonance effect is caused by the nonzero magnetic anisotropy. The resonance frequency is small (proportional to the anisotropy value) for spin systems with ferromagnetic interactions and enhanced by exchange interactions in the spin systems with antiferromagnetic couplings. We show that it is worthwhile to study the laser-field-induced magnetization of quantum spin systems caused by the high-frequency laser field in the steady-state regime in "easy-axis" antiferromagnetic spin systems (e.g., in Ising-like antiferromagnetic spin-chain materials). The effects of the Dzyaloshinskii-Moriya interaction and the spin-frustration couplings (in the case of the zigzag spin chain) have been analyzed.

Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes

NASA Astrophysics Data System (ADS)

Avsar, Ahmet; Tan, Jun Y.; Kurpas, Marcin; Gmitra, Martin; Watanabe, Kenji; Taniguchi, Takashi; Fabian, Jaroslav; Özyilmaz, Barbaros

2017-09-01

Two-dimensional materials offer new opportunities for both fundamental science and technological applications, by exploiting the electron's spin. Although graphene is very promising for spin communication due to its extraordinary electron mobility, the lack of a bandgap restricts its prospects for semiconducting spin devices such as spin diodes and bipolar spin transistors. The recent emergence of two-dimensional semiconductors could help overcome this basic challenge. In this letter we report an important step towards making two-dimensional semiconductor spin devices. We have fabricated a spin valve based on ultrathin (~5 nm) semiconducting black phosphorus (bP), and established fundamental spin properties of this spin channel material, which supports all electrical spin injection, transport, precession and detection up to room temperature. In the non-local spin valve geometry we measure Hanle spin precession and observe spin relaxation times as high as 4 ns, with spin relaxation lengths exceeding 6 μm. Our experimental results are in a very good agreement with first-principles calculations and demonstrate that the Elliott-Yafet spin relaxation mechanism is dominant. We also show that spin transport in ultrathin bP depends strongly on the charge carrier concentration, and can be manipulated by the electric field effect.

Acoustic parametric pumping of spin waves

NASA Astrophysics Data System (ADS)

Keshtgar, Hedyeh; Zareyan, Malek; Bauer, Gerrit E. W.

2014-11-01

Recent experiments demonstrated generation of spin currents by ultrasound. We can understand this acoustically induced spin pumping in terms of the coupling between magnetization and lattice waves. Here we study the parametric excitation of magnetization by longitudinal acoustic waves and calculate the acoustic threshold power. The induced magnetization dynamics can be detected by the spin pumping into an adjacent normal metal that displays the inverse spin Hall effect.

Multi-scale modeling of spin transport in organic semiconductors

NASA Astrophysics Data System (ADS)

Hemmatiyan, Shayan; Souza, Amaury; Kordt, Pascal; McNellis, Erik; Andrienko, Denis; Sinova, Jairo

In this work, we present our theoretical framework to simulate simultaneously spin and charge transport in amorphous organic semiconductors. By combining several techniques e.g. molecular dynamics, density functional theory and kinetic Monte Carlo, we are be able to study spin transport in the presence of anisotropy, thermal effects, magnetic and electric field effects in a realistic morphologies of amorphous organic systems. We apply our multi-scale approach to investigate the spin transport in amorphous Alq3 (Tris(8-hydroxyquinolinato)aluminum) and address the underlying spin relaxation mechanism in this system as a function of temperature, bias voltage, magnetic field and sample thickness.

Electron spin control of optically levitated nanodiamonds in vacuum

NASA Astrophysics Data System (ADS)

Hoang, Thai; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang

2016-05-01

Electron spins of diamond nitrogen-vacancy (NV) centers are important quantum resources for nanoscale sensing and quantum information. Combining such NV spin systems with levitated optomechanical resonators will provide a hybrid quantum system for many novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centers in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this novel system, we also investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect.

Epitaxy of spin injectors and their application toward spin-polarized lasers

NASA Astrophysics Data System (ADS)

Holub, Michael A.

Spintronics is an emerging; multidisciplinary field which examines the role of electron and nuclear spin in solid-state physics. Recent experiments suggest that the spin degree of freedom may be exploited to enhance the functionality of conventional semi conductor devices. Such endeavors require methods for efficient spin injection; spin transport, and spin detection in semiconductor heterostructures. This dissertation investigates the molecular-beam epitaxial growth and properties of ferromagnetic materials for electrical spin injection. Spin-injecting contacts are incorporated into prototype spintronic devices and their performance is examined. Two classes of materials may be used for spin injection into semiconductors: dilute magnetic semiconductor and ferromagnetic metals. The low-temperature growth and properties of (Al)Gal4nAs and In(Ga)MnAs epilayers and nanostructures are investigated, and a technique for the self-organized growth of Mn-doped InAs quantum dots is developed. The epitaxial growth of (Fe,MnAs)/(Al)GaAs Schottky tunnel barriers for electron spin injection is also investigated. The spin-injection efficiency of these contacts is assessed using a spin-valve or spin-polarized light-emitting diode. Lateral MnAs/GaAs spin-valves where Schottky tunnel barriers enable all-electrical spin injection and detection are grown, fabricated, and characterized. The Rowell criteria confirm that tunneling is the dominant, transport mechanism for the Schottky tunnel contacts. A peak magnetoresistance of 3.6% at 10 K and 1.1% at 125 K are observed for a 0.5 pin channel length spin-valve. Measurements using non-local spin-valves and other control devices verify that spurious contributions from anisotropic magnetoresistance and local Hall effects are negligible. Spin-polarized lasers offer inherent polarization control, reduced chirp, and lower threshold currents and are expected to outperform their charge-based counterparts. Initial efforts to realize a spin-VCSEL utilize (Ga,Mn)As spin aligners for hole spin injection. The polarization of the laser emission is dominated by dichroic absorption in the ferromagnetic (Ga,Mn)As spin-aligner layer, which greatly complicates the verification of spin injection. Significant spin-dependent effects are observed in a spin-VCSEL utilizing epitaxially regrown Fe/AlGaAs Schottky tunnel barriers. A maximum degree of circular polarization of 23% and corresponding threshold current reduction of 11% are measured for a 15 mum Fe spin-VCSEL at 50 K. A cavity spin polarization of 16.8% is estimated from rate equation analysis.

Revisiting spin-lattice relaxation time measurements for dilute spins in high-resolution solid-state NMR spectroscopy

NASA Astrophysics Data System (ADS)

Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua

2016-07-01

Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as 13C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. 13C) and abundant I (e.g. 1H) spins affects the measured T1S values in solid-state NMR in the absence of 1H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance L-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions.

Aging dynamics of quantum spin glasses of rotors

NASA Astrophysics Data System (ADS)

Kennett, Malcolm P.; Chamon, Claudio; Ye, Jinwu

2001-12-01

We study the long time dynamics of quantum spin glasses of rotors using the nonequilibrium Schwinger-Keldysh formalism. These models are known to have a quantum phase transition from a paramagnetic to a spin-glass phase, which we approach by looking at the divergence of the spin-relaxation rate at the transition point. In the aging regime, we determine the dynamical equations governing the time evolution of the spin response and correlation functions, and show that all terms in the equations that arise solely from quantum effects are irrelevant at long times under time reparametrization group (RPG) transformations. At long times, quantum effects enter only through the renormalization of the parameters in the dynamical equations for the classical counterpart of the rotor model. Consequently, quantum effects only modify the out-of-equilibrium fluctuation-dissipation relation (OEFDR), i.e. the ratio X between the temperature and the effective temperature, but not the form of the classical OEFDR.

Neutron beam effects on spin-exchange-polarized 3He.

PubMed

Sharma, M; Babcock, E; Andersen, K H; Barrón-Palos, L; Becker, M; Boag, S; Chen, W C; Chupp, T E; Danagoulian, A; Gentile, T R; Klein, A; Penttila, S; Petoukhov, A; Soldner, T; Tardiff, E R; Walker, T G; Wilburn, W S

2008-08-22

We have observed depolarization effects when high intensity cold neutron beams are incident on alkali-metal spin-exchange-polarized 3He cells used as neutron spin filters. This was first observed as a reduction of the maximum attainable 3He polarization and was attributed to a decrease of alkali-metal polarization, which led us to directly measure alkali-metal polarization and spin relaxation over a range of neutron fluxes at Los Alamos Neutron Science Center and Institute Laue-Langevin. The data reveal a new alkali-metal spin-relaxation mechanism that approximately scales as sqrt[phi_{n}], where phi_{n} is the neutron capture-flux density incident on the cell. This is consistent with an effect proportional to the concentration of electron-ion pairs but is much larger than expected from earlier work.

Topological Phase Transitions in the Photonic Spin Hall Effect

DOE PAGES

Kort-Kamp, Wilton Junior de Melo

2017-10-04

The recent synthesis of two-dimensional staggered materials opens up burgeoning opportunities to study optical spin-orbit interactions in semiconducting Dirac-like systems. In this work, we unveil topological phase transitions in the photonic spin Hall effect in the graphene family materials. It is shown that an external static electric field and a high frequency circularly polarized laser allow for active on-demand manipulation of electromagnetic beam shifts. The spin Hall effect of light presents a rich dependence with radiation degrees of freedom, and material properties, and features nontrivial topological properties. Finally, we discover that photonic Hall shifts are sensitive to spin and valleymore » properties of the charge carriers, providing an unprecedented pathway to investigate spintronics and valleytronics in staggered 2D semiconductors.« less

Effective combined water and sideband suppression for low-speed tissue and in vivo MAS NMR.

PubMed

Mobarhan, Yalda Liaghati; Struppe, Jochem; Fortier-McGill, Blythe; Simpson, André J

2017-08-01

High-resolution magic angle spinning (HR-MAS) NMR is a powerful technique that can provide metabolic profiles and structural constraints on intact biological and environmental samples such as cells, tissues and living organisms. However, centripetal force from fast spinning can lead to a loss of sample integrity. In analyses focusing on structural organization, metabolite compartmentalization or in vivo studies, it is critical to keep the sample intact. As such, there is growing interest in slow spinning studies that preserve sample longevity. In this study, for example, reducing the spinning rate from 2500 to 500 Hz during the analysis of a living freshwater shrimp increased the 100% survivability threshold from ~14 to 40 h. Unfortunately, reducing spinning rate decreases the intensity of the isotropic signals and increases both the intensity and number of spinning sidebands, which mask spectral information. Interestingly, water suppression approaches such as excitation sculpting and W5 WATERGATE, which are effective at higher spinning rates, fail at lower spinning rates (<2500 Hz) while simpler approaches such as presaturation are not able to effectively suppress water when the ratio of water to biomass is very high, as is the case in vivo. As such there is a considerable gap in NMR approaches which can be used to suppress water signals and sidebands in biological samples at lower spinning rates. This research presents simple but practically important sequences that combine PURGE water suppression with both phase-adjusted spinning sidebands and an analogue of TOSS termed TOSS.243. The result is simple and effective water and sideband suppression even in extremely dilute samples in pure water down to ~100 Hz spinning rate. The approach is introduced, described and applied to a range of samples including, ex vivo worm tissue, Daphnia magna (water fleas), and in vivo Hyalella azteca (shrimp).