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Sample records for spin relaxation processes

  1. Relaxation times of the two-phonon processes with spin-flip and spin-conserving in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zi-Wu, E-mail: zwwang@semi.ac.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Department of Physics, Tianjin University, Tianjin 300072 (China); Liu, Lei [Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215125 (China); Li, Shu-Shen [Institute of Semiconductor, CAS, Beijing 100083 (China)

    2014-04-07

    We perform a theoretical investigation on the two-phonon processes of the spin-flip and spin-conserving relaxation in quantum dots in the frame of the Huang-Rhys' lattice relaxation model. We find that the relaxation time of the spin-flip is two orders of magnitude longer than that of the spin-conserving, which is in agreement with previous experimental measurements. Moreover, the opposite variational trends of the relaxation time as a function of the energy separation for two-phonon processes are obtained in different temperature regime. The relaxation times display the oscillatory behaviors at the demarcation point with increasing magnetic field, where the energy separation matches the optical phonon energy and results in the optical phonon resonance. These results are useful in understanding the intraband levels' relaxation in quantum dots and could be helpful in designing photoelectric and spin-memory devices.

  2. Relaxation of the electron spin in quantum dots via one- and two-phonon processes

    International Nuclear Information System (INIS)

    Calero, C.; Chudnovsky, E.M.; Garanin, D.A.

    2007-01-01

    We have studied direct and Raman processes of the decay of electron spin states in a quantum dot via radiation of phonons corresponding to elastic twists. Universal dependence of the spin relaxation rate on the strength and direction of the magnetic field has been obtained in terms of the electron gyromagnetic tensor and macroscopic elastic constants of the solid

  3. Relaxation of the electron spin in quantum dots via one- and two-phonon processes

    Energy Technology Data Exchange (ETDEWEB)

    Calero, C. [Department of Physics and Astronomy, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589 (United States)]. E-mail: carlos.calero-borrallo@lehman.cuny.edu; Chudnovsky, E.M. [Department of Physics and Astronomy, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589 (United States); Garanin, D.A. [Department of Physics and Astronomy, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589 (United States)

    2007-09-15

    We have studied direct and Raman processes of the decay of electron spin states in a quantum dot via radiation of phonons corresponding to elastic twists. Universal dependence of the spin relaxation rate on the strength and direction of the magnetic field has been obtained in terms of the electron gyromagnetic tensor and macroscopic elastic constants of the solid.

  4. Nuclear Spin Relaxation

    Indian Academy of Sciences (India)

    IAS Admin

    In the context of nuclear magnetic resonance (NMR), the term relaxation indicates the process by which the magnetic atomic nuclei reach thermal equilibrium with the chaotic molecular environment. In NMR, this process can be very slow, requiring between a fraction of a second to many minutes, depending on the.

  5. A post-processing method for multiexponential spin-spin relaxation analysis of MRI signals

    Energy Technology Data Exchange (ETDEWEB)

    Gensanne, D [Laboratoire de Chimie Bioinorganique Medicale, Imagerie therapeutique et diagnostique, CNRS FR 2599, Universite Paul Sabatier, 118, route de Narbonne, 31062 Toulouse Cedex (France); Josse, G [Centre Europeen de Recherche et d' Evaluation sur la Peau et les Epitheliums de Revetement, Institut de Recherche Pierre Fabre, 2, rue Viguerie, BP 3071 31025 Toulouse Cedex 3 (France); Lagarde, J M [Centre Europeen de Recherche et d' Evaluation sur la Peau et les Epitheliums de Revetement, Institut de Recherche Pierre Fabre, 2, rue Viguerie, BP 3071 31025 Toulouse Cedex 3 (France); Vincensini, D [Laboratoire de Chimie Bioinorganique Medicale, Imagerie therapeutique et diagnostique, CNRS FR 2599, Universite Paul Sabatier, 118, route de Narbonne, 31062 Toulouse Cedex (France)

    2005-08-21

    Quantitative MR imaging is a potential tool for tissue characterization; in particular, proton density and proton relaxation times can be derived from MR signal analysis. However, MR image noise affects the accuracy of measurements and the number of tissue parameters that can be reliably estimated. Filtering can be used to limit image noise; however this reduces spatial resolution. In this work we studied, using both simulations and experiments, a filter called a 'selective blurring filter'. Compared to other classical filters, this filter achieves the best compromise between spatial resolution and noise reduction. The filter was specifically used to reliably determine the bi-component transverse relaxation of protons in adipose tissue. Long and short relaxation times and the relative proton fraction of each component were obtained with a degree of uncertainty of less than 10% and an accuracy of 95%.

  6. Muon spin relaxation in random spin systems

    International Nuclear Information System (INIS)

    Toshimitsu Yamazaki

    1981-01-01

    The longitudinal relaxation function Gsub(z)(t) of the positive muon can reflect dynamical characters of local field in a unique way even when the correlation time is longer than the Larmor period of local field. This method has been applied to studies of spin dynamics in spin glass systems, revealing sharp but continuous temperature dependence of the correlation time. Its principle and applications are reviewed. (author)

  7. Spin relaxation in disordered media

    International Nuclear Information System (INIS)

    Dzheparov, F S

    2011-01-01

    A review is given on theoretical grounds and typical experimental appearances of spin dynamics and relaxation in solids containing randomly distributed nuclear and/or electronic spins. Brief content is as follows. Disordered and magnetically diluted systems. General outlines of the spin transport theory. Random walks in disordered systems (RWDS). Observable values in phase spin relaxation, free induction decay (FID). Interrelation of longitudinal and transversal relaxation related to dynamics of occupancies and phases. Occupation number representation for equations of motion. Continuum media approximation and inapplicability of moment expansions. Long-range transitions vs percolation theory. Concentration expansion as a general constructive basis for analytical methods. Scaling properties of propagators. Singular point. Dynamical and kinematical memory in RWDS. Ways of regrouping of concentration expansions. CTRW and semi-phenomenology. Coherent medium approximation for nuclear relaxation via paramagnetic impurities. Combining of memory functions and cumulant expansions for calculation of FID. Path integral representations for RWDS. Numerical simulations of RWDS. Spin dynamics in magnetically diluted systems with low Zeeman and medium low dipole temperatures. Cluster expansions, regularization of dipole interactions and spectral dynamics.

  8. Spin-lattice relaxation of individual solid-state spins

    Science.gov (United States)

    Norambuena, A.; Muñoz, E.; Dinani, H. T.; Jarmola, A.; Maletinsky, P.; Budker, D.; Maze, J. R.

    2018-03-01

    Understanding the effect of vibrations on the relaxation process of individual spins is crucial for implementing nanosystems for quantum information and quantum metrology applications. In this work, we present a theoretical microscopic model to describe the spin-lattice relaxation of individual electronic spins associated to negatively charged nitrogen-vacancy centers in diamond, although our results can be extended to other spin-boson systems. Starting from a general spin-lattice interaction Hamiltonian, we provide a detailed description and solution of the quantum master equation of an electronic spin-one system coupled to a phononic bath in thermal equilibrium. Special attention is given to the dynamics of one-phonon processes below 1 K where our results agree with recent experimental findings and analytically describe the temperature and magnetic-field scaling. At higher temperatures, linear and second-order terms in the interaction Hamiltonian are considered and the temperature scaling is discussed for acoustic and quasilocalized phonons when appropriate. Our results, in addition to confirming a T5 temperature dependence of the longitudinal relaxation rate at higher temperatures, in agreement with experimental observations, provide a theoretical background for modeling the spin-lattice relaxation at a wide range of temperatures where different temperature scalings might be expected.

  9. Electron spin-lattice relaxation in fractals

    International Nuclear Information System (INIS)

    Shrivastava, K.N.

    1986-08-01

    We have developed the theory of the spin-fracton interaction for paramagnetic ions in fractal structures. The interaction is exponentially damped by the self-similarity length of the fractal and by the range dimensionality d Φ . The relaxation time of the spin due to the absorption and emission of the fracton has been calculated for a general dimensionality called the Raman dimensionality d R , which for the fractons differs from the Hausdorff (fractal) dimensionality, D, as well as from the Euclidean dimensionality, d. The exponent of the energy level separation in the relaxation rate varies with d R d Φ /D. We have calculated the spin relaxation rate due to a new type of Raman process in which one fracton is absorbed to affect a spin transition from one electronic level to another and later another fracton is emitted along with a spin transition such that the difference in the energies of the two fractons is equal to the electronic energy level separation. The temperature and the dimensionality dependence of such a process has been found in several approximations. In one of the approximations where the van Vleck relaxation rate for a spin in a crystal is known to vary with temperature as T 9 , our calculated variation for fractals turns out to be T 6.6 , whereas the experimental value for Fe 3+ in frozen solutions of myoglobin azide is T 6.3 . Since we used d R =4/3 and the fracton range dimensionality d Φ =D/1.8, we expect to measure the dimensionalities of the problem by measuring the temperature dependence of the relaxation times. We have also calculated the shift of the paramagnetic resonance transition for a spin in a fractal for general dimensionalities. (author)

  10. Cross relaxation in nitroxide spin labels

    DEFF Research Database (Denmark)

    Marsh, Derek

    2016-01-01

    Cross relaxation, and mI-dependence of the intrinsic electron spin-lattice relaxation rate We, are incorporated explicitly into the rate equations for the electron-spin population differences that govern the saturation behaviour of 14N- and 15N-nitroxide spin labels. Both prove important in spin......-label EPR and ELDOR, particularly for saturation recovery studies. Neither for saturation recovery, nor for CW-saturation EPR and CW-ELDOR, can cross relaxation be described simply by increasing the value of We, the intrinsic spin-lattice relaxation rate. Independence of the saturation recovery rates from...... the hyperfine line pumped or observed follows directly from solution of the rate equations including cross relaxation, even when the intrinsic spin-lattice relaxation rate We is mI-dependent....

  11. Spin relaxation of iron in mixed state hemoproteins

    International Nuclear Information System (INIS)

    Wajnberg, E.; Kalinowski, H.J.; Bemski, G.; Helman, J.S.

    1984-01-01

    In pure states hemoproteins the relaxation of iron depends on its spin state. It is found that in both mixed state met-hemoglobin and met-myoglobin, the low and high spin states relax through an Orbach-like process. Also, very short (approx. 1 ns) and temperature independent transverse relaxation times T 2 were estimated. This peculiar behaviour of the relaxation may result from the unusual electronic structure of mixed state hemoproteins that allows thermal equilibrium and interconversion of the spin states. (Author) [pt

  12. Universal Mechanism of Spin Relaxation in Solids

    Science.gov (United States)

    Chudnovsky, Eugene

    2006-03-01

    Conventional elastic theory ignores internal local twists and torques. Meantime, spin-lattice relaxation is inherently coupled with local elastic twists through conservation of the total angular momentum (spin + lattice). This coupling gives universal lower bound (free of fitting parameters) on the relaxation of the atomic or molecular spin in a solid [1] and on the relaxation of the electron spin in a quantum dot [2]. [1] E. M. Chudnovsky, D. A. Garanin, and R. Schilling, Phys. Rev. B 72, 094426 (2005). [2] C. Calero, E. M. Chudnovsky, and D. A. Garanin, Phys. Rev. Lett. 95, 166603 (2005).

  13. Spin transport and relaxation in graphene

    International Nuclear Information System (INIS)

    Han Wei; McCreary, K.M.; Pi, K.; Wang, W.H.; Li Yan; Wen, H.; Chen, J.R.; Kawakami, R.K.

    2012-01-01

    We review our recent work on spin injection, transport and relaxation in graphene. The spin injection and transport in single layer graphene (SLG) were investigated using nonlocal magnetoresistance (MR) measurements. Spin injection was performed using either transparent contacts (Co/SLG) or tunneling contacts (Co/MgO/SLG). With tunneling contacts, the nonlocal MR was increased by a factor of ∼1000 and the spin injection/detection efficiency was greatly enhanced from ∼1% (transparent contacts) to ∼30%. Spin relaxation was investigated on graphene spin valves using nonlocal Hanle measurements. For transparent contacts, the spin lifetime was in the range of 50-100 ps. The effects of surface chemical doping showed that for spin lifetimes in the order of 100 ps, charged impurity scattering (Au) was not the dominant mechanism for spin relaxation. While using tunneling contacts to suppress the contact-induced spin relaxation, we observed the spin lifetimes as long as 771 ps at room temperature, 1.2 ns at 4 K in SLG, and 6.2 ns at 20 K in bilayer graphene (BLG). Furthermore, contrasting spin relaxation behaviors were observed in SLG and BLG. We found that Elliot-Yafet spin relaxation dominated in SLG at low temperatures whereas Dyakonov-Perel spin relaxation dominated in BLG at low temperatures. Gate tunable spin transport was studied using the SLG property of gate tunable conductivity and incorporating different types of contacts (transparent and tunneling contacts). Consistent with theoretical predictions, the nonlocal MR was proportional to the SLG conductivity for transparent contacts and varied inversely with the SLG conductivity for tunneling contacts. Finally, bipolar spin transport in SLG was studied and an electron-hole asymmetry was observed for SLG spin valves with transparent contacts, in which nonlocal MR was roughly independent of DC bias current for electrons, but varied significantly with DC bias current for holes. These results are very important for

  14. Abrupt relaxation in high-spin molecules

    International Nuclear Information System (INIS)

    Chang, C.-R.; Cheng, T.C.

    2000-01-01

    Mean-field model suggests that the rate of resonant quantum tunneling in high-spin molecules is not only field-dependent but also time-dependent. The relaxation-assisted resonant tunneling in high-spin molecules produces an abrupt magnetization change during relaxation. When the applied field is very close to the resonant field, a time-dependent interaction field gradually shifts the energies of different collective spin states, and magnetization tunneling is observed as two energies of the spin states coincide

  15. Spin-flip relaxation via optical phonon scattering in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zi-Wu, E-mail: zwwang@semi.ac.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Department of Physics, Tianjin University, Tianjin 300072 (China); Liu, Lei [Suzhou Institute of Nano-tech and Nano-bionics, CAS, Suzhou 215125 (China); Li, Shu-Shen [Institute of Semiconductor, CAS, Beijing 100083 (China)

    2013-12-14

    Based on the spin-orbit coupling admixture mechanism, we theoretically investigate the spin-flip relaxation via optical phonon scattering in quantum dots by considering the effect of lattice relaxation due to the electron-acoustic phonon deformation potential coupling. The relaxation rate displays a cusp-like structure (or a spin hot spot) that becomes more clearly with increasing temperature. We also calculate the relaxation rate of the spin-conserving process, which follows a Gaussian form and is several orders of magnitude larger than that of spin-flip process. Moreover, we find that the relaxation rate displays the oscillatory behavior due to the interplay effects between the magnetic and spatial confinement for the spin-flip process not for the spin-conserving process. The trends of increasing and decreasing temperature dependence of the relaxation rates for two relaxation processes are obtained in the present model.

  16. Nuclear spin relaxation of methane in solid xenon

    Science.gov (United States)

    Sugimoto, Takeru; Arakawa, Ichiro; Yamakawa, Koichiro

    2018-03-01

    Nuclear spin relaxation of methane in solid xenon has been studied by infrared spectroscopy. From the analysis of the temporal changes of the rovibrational peaks, the rates of the nuclear spin relaxation of I = 2 ← 1 correlated to the rotational relaxation of J = 0 ← 1 were obtained at temperatures of 5.1-11.5 K. On the basis of the temperature dependence of the relaxation rate, the activation energy of the indirect two-phonon process was determined to be 50 ± 6 K, which is in good agreement with the rotational transition energies of J = 2 ← 1 and J = 3 ← 1. Taking into account this result and the spin degeneracy, we argue that the lowest J = 3 level in which the I = 1 and I = 2 states are degenerate acts as the intermediate point of the indirect process.

  17. Mechanisms of relaxation and spin decoherence in nanomagnets

    Science.gov (United States)

    van Tol, Johan

    Relaxation in spin systems is of great interest with respect to various possible applications like quantum information processing and storage, spintronics, and dynamic nuclear polarization (DNP). The implementation of high frequencies and fields is crucial in the study of systems with large zero-field splitting or large interactions, as for example molecular magnets and low dimensional magnetic materials. Here we will focus on the implementation of pulsed Electron Paramagnetic Resonance (ERP) at multiple frequencies of 10, 95, 120, 240, and 336 GHz, and the relaxation and decoherence processes as a function of magnetic field and temperature. Firstly, at higher frequencies the direct single-phonon spin-lattice relaxation (SLR) is considerably enhanced, and will more often than not be the dominant relaxation mechanism at low temperatures, and can be much faster than at lower fields and frequencies. In principle the measurement of the SLR rates as a function of the frequency provides a means to map the phonon density of states. Secondly, the high electron spin polarization at high fields has a strong influence on the spin fluctuations in relatively concentrated spin systems, and the contribution of the electron-electron dipolar interactions to the coherence rate can be partially quenched at low temperatures. This not only allows the study of relatively concentrated spin systems by pulsed EPR (as for example magnetic nanoparticles and molecular magnets), it enables the separation of the contribution of the fluctuations of the electron spin system from other decoherence mechanisms. Besides choice of temperature and field, several strategies in sample design, pulse sequences, or clock transitions can be employed to extend the coherence time in nanomagnets. A review will be given of the decoherence mechanisms with an attempt at a quantitative comparison of experimental rates with theory.

  18. Spin-Spin Cross Relaxation in Single-Molecule Magnets

    Science.gov (United States)

    Wernsdorfer, W.; Bhaduri, S.; Tiron, R.; Hendrickson, D. N.; Christou, G.

    2002-10-01

    The one-body tunnel picture of single-molecule magnets (SMMs) is not always sufficient to explain the measured tunnel transitions. An improvement to the picture is proposed by including also two-body tunnel transitions such as spin-spin cross relaxation (SSCR) which are mediated by dipolar and weak superexchange interactions between molecules. A Mn4 SMM is used as a model system. At certain external fields, SSCRs lead to additional quantum resonances which show up in hysteresis loop measurements as well-defined steps. A simple model is used to explain quantitatively all observed transitions.

  19. Relaxation of coupled nuclear spin systems

    International Nuclear Information System (INIS)

    Koenigsberger, E.

    1985-05-01

    The subject of the present work is the relaxation behaviour of scalarly coupled spin-1/2 systems. In the theoretical part the semiclassical Redfield equations are used. Dipolar (D), Chemical Shift Anisotropy (CSA) and Random Field (RF) interactions are considered as relaxation mechanisms. Cross correlations of dipolar interactions of different nuclei pairs and those between the D and the CSA mechanisms are important. The model of anisotropic molecular rotational relaxation and the extreme narrowing approximation are used to obtain the spectral density functions. The longitudinal relaxation data are analyzed into normal modes following Werbelow and Grant. The time evolution of normal modes is derived for the AX system with D-CSA cross terms. In the experimental part the hypothesis of dimerization in the cinnamic acid and the methyl cinnamate - AMX systems with DD cross terms - is corroborated by T 1 -time measurements and a calculation of the diffusion constants. In pentachlorobenzene - an AX system - taking into account of D-CSA cross terms enables the complete determination of movements anosotropy and the determination of the sign of the indirect coupling constant 1 Jsub(CH). (G.Q.)

  20. Relaxations in spin glasses: Similarities and differences from ordinary glasses

    International Nuclear Information System (INIS)

    Ngai, K.L.; Rajagopal, A.K.; Huang, C.Y.

    1984-01-01

    Relaxation phenomena have become a major concern in the physics of spin glasses. There are certain resemblances of these relaxation properties to those of ordinary glasses. In this work, we compare the relaxation properties of spin glasses near the freezing temperature with those of glasses near the glass transition temperature. There are similarities between the two types of glasses. Moreover, the relaxation properties of many glasses and spin glasses are in conformity with two coupled ''universality'' relations predicted by a recent model of relaxations in condensed matter

  1. Spin relaxation in quantum dots: Role of the phonon modulated spin-orbit interaction

    Science.gov (United States)

    Alcalde, A. M.; Romano, C. L.; Sanz, L.; Marques, G. E.

    2010-01-01

    We calculate the spin relaxation rates in a parabolic InSb quantum dots due to the spin interaction with acoustical phonons. We considered the deformation potential mechanism as the dominant electron-phonon coupling in the Pavlov-Firsov spin-phonon Hamiltonian. We analyze the behavior of the spin relaxation rates as a function of an external magnetic field and mean quantum dot radius. Effects of the spin admixture due to Dresselhaus contribution to spin-orbit interaction are also discussed.

  2. Spin-lattice relaxation of magnetic centers in molecular crystals at low temperature

    OpenAIRE

    Ho, Le Tuan Anh; Chibotaru, Liviu F.

    2017-01-01

    We study the spin-phonon relaxation rate of both Kramers and non-Kramers molecular magnets in strongly diluted samples at low temperature. Using the "rotational" contribution to the spin-phonon Hamiltonian, universal formulae for the relaxation rate are obtained. Intriguingly, these formulae are all entirely expressed via measurable or \\emph{ab initio} computable physical quantities. Moreover, they are also independent of the energy gaps to excited states involved in the relaxation process. T...

  3. Semiclassical treatment of transport and spin relaxation in spin-orbit coupled systems

    Energy Technology Data Exchange (ETDEWEB)

    Lueffe, Matthias Clemens

    2012-02-10

    The coupling of orbital motion and spin, as derived from the relativistic Dirac equation, plays an important role not only in the atomic spectra but as well in solid state physics. Spin-orbit interactions are fundamental for the young research field of semiconductor spintronics, which is inspired by the idea to use the electron's spin instead of its charge for fast and power saving information processing in the future. However, on the route towards a functional spin transistor there is still some groundwork to be done, e.g., concerning the detailed understanding of spin relaxation in semiconductors. The first part of the present thesis can be placed in this context. We have investigated the processes contributing to the relaxation of a particularly long-lived spin-density wave, which can exist in semiconductor heterostructures with Dresselhaus and Rashba spin-orbit coupling of precisely the same magnitude. We have used a semiclassical spindiffusion equation to study the influence of the Coulomb interaction on the lifetime of this persistent spin helix. We have thus established that, in the presence of perturbations that violate the special symmetry of the problem, electron-electron scattering can have an impact on the relaxation of the spin helix. The resulting temperature-dependent lifetime reproduces the experimentally observed one in a satisfactory manner. It turns out that cubic Dresselhaus spin-orbit coupling is the most important symmetry-breaking element. The Coulomb interaction affects the dynamics of the persistent spin helix also via an Hartree-Fock exchange field. As a consequence, the individual spins precess about the vector of the surrounding local spin density, thus causing a nonlinear dynamics. We have shown that, for an experimentally accessible degree of initial spin polarization, characteristic non-linear effects such as a dramatic increase of lifetime and the appearance of higher harmonics can be expected. Another fascinating solid

  4. Spin relaxation near the metal-insulator transition: dominance of the Dresselhaus spin-orbit coupling.

    Science.gov (United States)

    Intronati, Guido A; Tamborenea, Pablo I; Weinmann, Dietmar; Jalabert, Rodolfo A

    2012-01-06

    We identify the Dresselhaus spin-orbit coupling as the source of the dominant spin-relaxation mechanism in the impurity band of a wide class of n-doped zinc blende semiconductors. The Dresselhaus hopping terms are derived and incorporated into a tight-binding model of impurity sites, and they are shown to unexpectedly dominate the spin relaxation, leading to spin-relaxation times in good agreement with experimental values. This conclusion is drawn from two complementary approaches: an analytical diffusive-evolution calculation and a numerical finite-size scaling study of the spin-relaxation time.

  5. Picosecond spin relaxation in low-temperature-grown GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Uemura, M.; Honda, K.; Yasue, Y.; Tackeuchi, A., E-mail: atacke@waseda.jp [Department of Applied Physics, Waseda University, Tokyo 169-8555 (Japan); Lu, S. L.; Dai, P. [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Science, Suzhou (China)

    2014-03-24

    The spin relaxation process of low-temperature-grown GaAs is investigated by spin-dependent pump and probe reflectance measurements with a sub-picosecond time resolution. Two very short carrier lifetimes of 2.0 ps and 28 ps, which can be attributed to nonradiative recombinations related to defects, are observed at 10 K. The observed spin polarization shows double exponential decay with spin relaxation times of 46.2 ps (8.0 ps) and 509 ps (60 ps) at 10 K (200 K). The observed picosecond spin relaxation, which is considerably shorter than that of conventional GaAs, indicates the strong relevance of the Elliott-Yafet process as the spin relaxation mechanism. For the first (second) spin relaxation component, the temperature and carrier density dependences of the spin relaxation time indicate that the Bir-Aronov-Pikus process is also effective at temperatures between 10 K and 77 K, and that the D'yakonov-Perel’ process is effective between 125 K (77 K) and 200 K.

  6. Nuclear spin-lattice relaxation in carbon nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Panich, A.M., E-mail: pan@bgu.ac.i [Department of Physics, Ben-Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105 (Israel); Sergeev, N.A. [Institute of Physics, University of Szczecin, 70-451 Szczecin (Poland)

    2010-04-15

    Interpretation of nuclear spin-lattice relaxation data in the carbon nanostructures is usually based on the analysis of fluctuations of dipole-dipole interactions of nuclear spins and anisotropic electron-nuclear interactions responsible for chemical shielding, which are caused by molecular dynamics. However, many nanocarbon systems such as fullerene and nanotube derivatives, nanodiamonds and carbon onions reveal noticeable amount of paramagnetic defects with unpaired electrons originating from dangling bonds. The interaction between nuclear and electron spins strongly influences the nuclear spin-lattice relaxation, but usually is not taken into account, thus the relaxation data are not correctly interpreted. Here we report on the temperature dependent NMR spectra and spin-lattice relaxation measurements of intercalated fullerenes C{sub 60}(MF{sub 6}){sub 2} (M=As and Sb), where nuclear relaxation is caused by both molecular rotation and interaction between nuclei and unpaired electron spins. We present a detailed theoretical analysis of the spin-lattice relaxation data taking into account both these contributions. Good agreement between the experimental data and calculations is obtained. The developed approach would be useful in interpreting the NMR relaxation data in different nanostructures and their intercalation compounds.

  7. THEORY OF RELAXATION PROCESSES IN FERROMAGNETIC INSULATORS

    Science.gov (United States)

    Contents: Simplified description of ferromagnetic relaxation Detailed treatment of magnons Relaxation frequency calculations Summary of relaxation processes in YIG Summary of experimental results for YIG

  8. PREFACE: Muon spin rotation, relaxation or resonance

    Science.gov (United States)

    Heffner, Robert H.; Nagamine, Kanetada

    2004-10-01

    To a particle physicist a muon is a member of the lepton family, a heavy electron possessing a mass of about 1/9 that of a proton and a spin of 1/2, which interacts with surrounding atoms and molecules electromagnetically. Since its discovery in 1937, the muon has been put to many uses, from tests of special relativity to deep inelastic scattering, from studies of nuclei to tests of weak interactions and quantum electrodynamics, and most recently, as a radiographic tool to see inside heavy objects and volcanoes. In 1957 Richard Garwin and collaborators, while conducting experiments at the Columbia University cyclotron to search for parity violation, discovered that spin-polarized muons injected into materials might be useful to probe internal magnetic fields. This eventually gave birth to the modern field of muSR, which stands for muon spin rotation, relaxation or resonance, and is the subject of this special issue of Journal of Physics: Condensed Matter. Muons are produced in accelerators when high energy protons (generally >500 MeV) strike a target like graphite, producing pions which subsequently decay into muons. Most experiments carried out today use relatively low-energy (~4 MeV), positively-charged muons coming from pions decaying at rest in the skin of the production target. These muons have 100% spin polarization, a range in typical materials of about 180 mg cm-2, and are ideal for experiments in condensed matter physics and chemistry. Negatively-charged muons are also occasionally used to study such things as muonic atoms and muon-catalysed fusion. The muSR technique provides a local probe of internal magnetic fields and is highly complementary to inelastic neutron scattering and nuclear magnetic resonance, for example. There are four primary muSR facilities in the world today: ISIS (Didcot, UK), KEK (Tsukuba, Japan), PSI (Villigen, Switzerland) and TRIUMF (Vancouver, Canada), serving about 500 researchers world-wide. A new facility, JPARC (Tokai, Japan

  9. Electrical detection of spin current and spin relaxation in nonmagnetic semiconductors

    International Nuclear Information System (INIS)

    Miah, M Idrish

    2008-01-01

    We report an electrical method for the detection of spin current and spin relaxation in nonmagnetic semiconductors. Optically polarized spins are dragged by an electric field in GaAs. We use the anomalous Hall effect for the detection of spin current and spin relaxation. It is found that the effect depends on the electric field and doping density as well as on temperature, but not on the excitation power. A calculation for the effect is performed using the measured spin polarization by a pump-probe experiment. The results are also discussed in comparison with a quantitative evaluation of the spin lifetimes of the photogenerated electrons under drift in GaAs

  10. Electrical detection of spin current and spin relaxation in nonmagnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M Idrish [Nanoscale Science and Technology Centre and School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)], E-mail: m.miah@griffith.edu.au

    2008-09-21

    We report an electrical method for the detection of spin current and spin relaxation in nonmagnetic semiconductors. Optically polarized spins are dragged by an electric field in GaAs. We use the anomalous Hall effect for the detection of spin current and spin relaxation. It is found that the effect depends on the electric field and doping density as well as on temperature, but not on the excitation power. A calculation for the effect is performed using the measured spin polarization by a pump-probe experiment. The results are also discussed in comparison with a quantitative evaluation of the spin lifetimes of the photogenerated electrons under drift in GaAs.

  11. Nuclear spin-lattice relaxation in nitroxide spin-label EPR

    DEFF Research Database (Denmark)

    Marsh, Derek

    2016-01-01

    that the definition of nitrogen nuclear relaxation rate Wn commonly used in the CW-EPR literature for 14N-nitroxyl spin labels is inconsistent with that currently adopted in time-resolved EPR measurements of saturation recovery. Redefinition of the normalised 14N spin-lattice relaxation rate, b = Wn/(2We), preserves...... of spin-lattice relaxation in this three-level system. Expressions for CW-saturation EPR with the revised definitions are summarised. Data on nitrogen nuclear spin-lattice relaxation times are compiled according to the three-level scheme for 14N-relaxation: T1 n = 1/Wn. Results are compared and contrasted...... the expressions used for CW-EPR, whilst rendering them consistent with expressions for saturation recovery rates in pulsed EPR. Furthermore, values routinely quoted for nuclear relaxation times that are deduced from EPR spectral diffusion rates in 14N-nitroxyl spin labels do not accord with conventional analysis...

  12. Nuclear spin relaxation in liquids theory, experiments, and applications

    CERN Document Server

    Kowalewski, Jozef

    2006-01-01

    Nuclear magnetic resonance (NMR) is widely used across many fields because of the rich data it produces, and some of the most valuable data come from the study of nuclear spin relaxation in solution. While described to varying degrees in all major NMR books, spin relaxation is often perceived as a difficult, if not obscure, topic, and an accessible, cohesive treatment has been nearly impossible to find.Collecting relaxation theory, experimental techniques, and illustrative applications into a single volume, this book clarifies the nature of the phenomenon, shows how to study it, and explains why such studies are worthwhile. Coverage ranges from basic to rigorous theory and from simple to sophisticated experimental methods, and the level of detail is somewhat greater than most other NMR texts. Topics include cross-relaxation, multispin phenomena, relaxation studies of molecular dynamics and structure, and special topics such as relaxation in systems with quadrupolar nuclei and paramagnetic systems.Avoiding ove...

  13. Observations of exciton and carrier spin relaxation in Be doped p-type GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Asaka, Naohiro; Harasawa, Ryo; Tackeuchi, Atsushi, E-mail: atacke@waseda.jp [Department of Applied Physics, Waseda University, Shinjuku, Tokyo 169-8555 (Japan); Lu, Shulong; Dai, Pan [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Dushu Lake Higher Education Town, Ruoshui Road 398, Suzhou Industrial Park, Suzhou 215028 (China)

    2014-03-17

    We have investigated the exciton and carrier spin relaxation in Be-doped p-type GaAs. Time-resolved spin-dependent photoluminescence (PL) measurements revealed spin relaxation behaviors between 10 and 100 K. Two PL peaks were observed at 1.511 eV (peak 1) and 1.497 eV (peak 2) at 10 K, and are attributed to the recombination of excitons bound to neutral Be acceptors (peak 1) and the band-to-acceptor transition (peak 2). The spin relaxation times of both PL peaks were measured to be 1.3–3.1 ns at 10–100 K, and found to originate from common electron spin relaxation. The observed existence of a carrier density dependence of the spin relaxation time at 10–77 K indicates that the Bir-Aronov-Pikus process is the dominant spin relaxation mechanism.

  14. Intrinsic spin-relaxation induced negative tunnel magnetoresistance in a single-molecule magnet

    Science.gov (United States)

    Xie, Haiqing; Wang, Qiang; Xue, Hai-Bin; Jiao, HuJun; Liang, J.-Q.

    2013-06-01

    We investigate theoretically the effects of intrinsic spin-relaxation on the spin-dependent transport through a single-molecule magnet (SMM), which is weakly coupled to ferromagnetic leads. The tunnel magnetoresistance (TMR) is obtained by means of the rate-equation approach including not only the sequential but also the cotunneling processes. It is shown that the TMR is strongly suppressed by the fast spin-relaxation in the sequential region and can vary from a large positive to slight negative value in the cotunneling region. Moreover, with an external magnetic field along the easy-axis of SMM, a large negative TMR is found when the relaxation strength increases. Finally, in the high bias voltage limit the TMR for the negative bias is slightly larger than its characteristic value of the sequential region; however, it can become negative for the positive bias caused by the fast spin-relaxation.

  15. Two-channel model for spin-relaxation noise

    Science.gov (United States)

    Omar, S.; van Wees, B. J.; Vera-Marun, I. J.

    2017-12-01

    We develop a two-channel resistor model for simulating spin transport with general applicability. Using this model, for the case of graphene as a prototypical material, we calculate the spin signal consistent with experimental values. Using the same model we also simulate the charge and spin-dependent 1 /f noise, both in the local and nonlocal four-probe measurement schemes, and identify the noise from the spin-relaxation resistances as the major source of spin-dependent 1 /f noise.

  16. Relaxation of nuclear spin on holes in semiconductors

    International Nuclear Information System (INIS)

    Gr'ncharova, E.I.; Perel', V.I.

    1977-01-01

    The longitudienal relaxation time T 1 of nuclear spins due to dipole-dipole interaction with holes in semiconductors is calculated. Expressions for T 1 in cubic and uniaxial semiconductors are obtained for non-degenerate and degenerate cases. On the basis of comparison with available experimental data for silicon the agreement with the theoretical results is obtained. It is demonstrated that in uniaxial semiconductors the time of relaxation on holes for a nuclear spin directed along the c axis is considerably greater than that for a spin in the normal direction

  17. Field dependence of the electron spin relaxation in quantum dots.

    Science.gov (United States)

    Calero, Carlos; Chudnovsky, E M; Garanin, D A

    2005-10-14

    The interaction of the electron spin with local elastic twists due to transverse phonons is studied. The universal dependence of the spin-relaxation rate on the strength and direction of the magnetic field is obtained in terms of the electron gyromagnetic tensor and macroscopic elastic constants of the solid. The theory contains no unknown parameters and it can be easily tested in experiment. At high magnetic field it provides a parameter-free lower bound on the electron spin relaxation in quantum dots.

  18. Electron spin relaxation in cryptochrome-based magnetoreception

    DEFF Research Database (Denmark)

    Kattnig, Daniel R; Solov'yov, Ilia A; Hore, P J

    2016-01-01

    The magnetic compass sense of migratory birds is thought to rely on magnetically sensitive radical pairs formed photochemically in cryptochrome proteins in the retina. An important requirement of this hypothesis is that electron spin relaxation is slow enough for the Earth's magnetic field to have...... this question for a structurally characterized model cryptochrome expected to share many properties with the putative avian receptor protein. To this end we combine all-atom molecular dynamics simulations, Bloch-Redfield relaxation theory and spin dynamics calculations to assess the effects of spin relaxation...... on the performance of the protein as a compass sensor. Both flavin-tryptophan and flavin-Z˙ radical pairs are studied (Z˙ is a radical with no hyperfine interactions). Relaxation is considered to arise from modulation of hyperfine interactions by librational motions of the radicals and fluctuations in certain...

  19. Relaxation processes in Aeolian transport

    Directory of Open Access Journals (Sweden)

    Selmani Houssem

    2017-01-01

    Full Text Available We investigate experimentally the relaxation process toward the equilibrium regime of saltation transport in the context of spatial inhomogeneous conditions. The relaxation length associated to this process is an important length in aeolian transport. This length stands for the distance needed for the particle flux to adapt to a change in flow conditions or in the boundary conditions at the bed. Predicting the value of this length under given conditions of transport remains an open and important issue. We conducted wind tunnel experiments to document the influence of the upstream particle flux and wind speed on the relaxation process toward the saturated transport state. In the absence of upstream particle flux, data show that the relaxation length is independent of the wind strength (except close to the threshold of transport. In contrast, in the case of a finite upstream flux, the relaxation length exhibits a clear increase with increasing air flow velocity. Moreover, in the latter the relaxation is clearly non-monotonic and presents an overshoot.

  20. Influence of intrinsic spin-flip processes on spin-polarized transport through quantum dots in the cotunneling regime

    International Nuclear Information System (INIS)

    Weymann, I.; Barnas, J.

    2006-01-01

    The influence of intrinsic spin relaxation on spin-polarized cotunneling through quantum dots coupled to ferromagnetic leads is analyzed theoretically. It is shown that the zero bias anomaly, which occurs due to the interplay of single-barrier and double-barrier cotunneling processes, becomes suppressed by spin relaxation processes on the dot. Diode-like features of the transport characteristics in the cotunneling regime have been found in asymmetrical systems. These features are also suppressed by the spin relaxation processes

  1. Use of the Strong Collision Model to Calculate Spin Relaxation

    Science.gov (United States)

    Wang, D.; Chow, K. H.; Smadella, M.; Hossain, M. D.; MacFarlane, W. A.; Morris, G. D.; Ofer, O.; Morenzoni, E.; Salman, Z.; Saadaoui, H.; Song, Q.; Kiefl, R. F.

    The strong collision model is used to calculate spin relaxation of a muon or polarized radioactive nucleus in contact with a fluctuating environment. We show that on a time scale much longer than the mean time between collisions (fluctuations) the longitudinal polarization decays exponentially with a relaxation rate equal to a sum of Lorentzians-one for each frequency component in the static polarization function ps(t).

  2. Magnetization relaxation in spin glasses above transition point

    International Nuclear Information System (INIS)

    Zajtsev, I.A.; Minakov, A.A.; Galonzka, R.R.

    1988-01-01

    Magnetization relaxation of Cd 0.6 Zn 0.4 Cr 2 Se 4 and Cd 0.6 Mn 0.4 Te monocrystalline samples with T g =21 K and T g =12 K respectively and magnetic colloid is investigated. It is shown that magnetization inexponential relaxation detected experimentally in spin and dipole glasses is essentially higher than T g temperature transition. It is found that at temperatures higher than T g the essential difference is observed in behaviour of spin glasses with different Z and disorder types

  3. Long Spin-Relaxation Times in a Transition-Metal Atom in Direct Contact to a Metal Substrate.

    Science.gov (United States)

    Hermenau, Jan; Ternes, Markus; Steinbrecher, Manuel; Wiesendanger, Roland; Wiebe, Jens

    2018-03-14

    Long spin-relaxation times are a prerequisite for the use of spins in data storage or nanospintronics technologies. An atomic-scale solid-state realization of such a system is the spin of a transition-metal atom adsorbed on a suitable substrate. For the case of a metallic substrate, which enables the direct addressing of the spin by conduction electrons, the experimentally measured lifetimes reported to date are on the order of only hundreds of femtoseconds. Here, we show that the spin states of iron atoms adsorbed directly on a conductive platinum substrate have a surprisingly long spin-relaxation time in the nanosecond regime, which is comparable to that of a transition metal atom decoupled from the substrate electrons by a thin decoupling layer. The combination of long spin-relaxation times and strong coupling to conduction electrons implies the possibility to use flexible coupling schemes to process the spin information.

  4. Long Spin-Relaxation Times in a Transition-Metal Atom in Direct Contact to a Metal Substrate

    Science.gov (United States)

    Hermenau, Jan; Ternes, Markus; Steinbrecher, Manuel; Wiesendanger, Roland; Wiebe, Jens

    2018-03-01

    Long spin relaxation times are a prerequisite for the use of spins in data storage or nanospintronics technologies. An atomic-scale solid-state realization of such a system is the spin of a transition metal atom adsorbed on a suitable substrate. For the case of a metallic substrate, which enables directly addressing the spin by conduction electrons, the experimentally measured lifetimes reported to date are on the order of only hundreds of femtoseconds. Here, we show that the spin states of iron atoms adsorbed directly on a conductive platinum substrate have an astonishingly long spin relaxation time in the nanosecond regime, which is comparable to that of a transition metal atom decoupled from the substrate electrons by a thin decoupling layer. The combination of long spin relaxation times and strong coupling to conduction electrons implies the possibility to use flexible coupling schemes in order to process the spin-information.

  5. Spin-lattice relaxation of magnetic centers in molecular crystals at low temperature

    Science.gov (United States)

    Ho, Le Tuan Anh; Chibotaru, Liviu F.

    2018-01-01

    We study the spin-phonon relaxation rate of both Kramers and non-Kramers molecular magnets in strongly diluted samples at low temperature. Using the "rotational" contribution to the spin-phonon Hamiltonian, universal formulas for the relaxation rate are obtained. Intriguingly, these formulas are all entirely expressed via measurable or ab initio computable physical quantities. Moreover, they are also independent of the energy gaps to excited states involved in the relaxation process. These obtained expressions for direct and Raman processes offer an easy way to determine the lowest limit of the spin-phonon relaxation of any spin system based on magnetic properties of the ground doublet only. In addition, some intriguing properties of Raman process are also found. Particularly, Raman process in Kramers system is found dependent on the magnetic field's orientation but independent of its magnitude, meanwhile, the same process in non-Kramers system is significantly reduced out of resonance, i.e., for an applied external field. Interestingly, Raman process is demonstrated to vary as T9 for both systems. Application of the theory to a recently investigated cobalt(II) complex shows that it can provide a reasonably good description for the relaxation. Based on these findings, a strategy in developing efficient single-molecule magnets by enhancing the mechanical rigidity of the molecular unit is proposed.

  6. Detailed mechanisms of1H spin-lattice relaxation in ammonium dihydrogen phosphate confirmed by magic angle spinning.

    Science.gov (United States)

    Hayashi, Shigenobu; Jimura, Keiko

    2017-10-01

    Mechanisms of the 1 H spin-lattice relaxation in NH 4 H 2 PO 4 were studied in detail by use of the effect of magic angle spinning on the relaxation. The acid and the ammonium protons have different relaxation times at the spinning rates higher than 10 kHz due to suppression of spin diffusion between the two kinds of protons. The intrinsic relaxation times not affected by the spin diffusion and the spin-diffusion assisted relaxation times were evaluated separately, taking into consideration temperature dependence. Both mechanisms contribute to the 1 H relaxation of the acid protons comparatively. The spin-diffusion assisted relaxation mechanism was suppressed to the level lower than the experimental errors at the spinning rate of 30 kHz. Copyright © 2017 Elsevier Inc. All rights reserved.

  7. The spin lattice relaxation of 8Li in simple metals

    Science.gov (United States)

    Hossain, M. D.; Saadaoui, H.; Parolin, T. J.; Song, Q.; Wang, D.; Smadella, M.; Chow, K. H.; Egilmez, M.; Fan, I.; Kiefl, R. F.; Kreitzman, S. R.; Levy, C. D. P.; Morris, G. D.; Pearson, M. R.; Salman, Z.; MacFarlane, W. A.

    2009-04-01

    We report the modification to the linear temperature dependence of the Korringa nuclear spin-lattice relaxation rate of an implanted NMR probe in silver, as it makes a thermally activated site change. We develop a simple model of this phenomenon, which is found in a number of metals including Au and Nb.

  8. Universal Behavior of Spin Dipolar Relaxation in Atomic Condensates

    Science.gov (United States)

    Deng, Yuangang; Zhou, Yiquan; Deng, Min; Liu, Qi; Tey, Mengkhoon; Gao, Bo; You, Li

    2017-04-01

    The dipolar relaxation of atomic spinor condensates is studied in terms of the semi-analytical scattering wave functions by utilizing the quantum-defect theory. At nonzero magnetic fields, inelastic dipolar relaxation of exothermic reaction leads to loss of the atomic population. By tuning the bias field, we find that the dipolar relaxation rate exhibits a universal behavior involving a unique dip and peak structure, different from the commonly referenced result based on the Born or the distortedwave Born approximations. The positions for the dip and the peak are shown to be determined dominantly by the short-range s-wave scattering length and the Van der Waals radius, independent of the dipolar interaction strength of ultracold atoms. This is confirmed by the precision measured dipolar relaxation decay rate for both spin-polarized atomic coherent spin states and twin-Fock states of F = 1 87 Rb BoseEinstein condensates. We observe the dipolar relaxation suppression as predicted by our theory for the large bias field, a feature not previously studied experimentally. Our results implicate the possibility of extracting the short-range scattering length and the Van der Waals dispersion coefficient from spin dipolar decay measurements.

  9. Nuclear paramagnetic spin relaxation theory. Paramagnetic spin probes in homogeneous and micro-heterogeneous solutions

    International Nuclear Information System (INIS)

    Westlund, P.O.

    1994-01-01

    Specific mechanisms of relaxation encountered in paramagnetic systems are described: the T1-NMRD curve and the paramagnetically enhanced nuclear spin relaxation (PER) are first discussed and a general theory of PER is proposed (nuclear paramagnetic spin relaxation theory, lattice operators, decomposition approximation, general expression of dipolar correlation functions for slow tumbling complexes, low-field approach). Numerically calculated NMRD curves are described (reorientation model, pseudo-rotation models, vibration models). Experimental studies are then analyzed: NMRD studies of paramagnetic species in an aqueous system, paramagnetic hydrated metal ions in poly-electrolytes and biochemical systems, lyotropic liquid crystalline phases, polymer solutions. 19 fig., 60 ref

  10. Superionic phase transitions and nuclear spin phonon relaxation by Raman processes in Me3H(SeO4)2 (Me = Na, K, and Rb) single crystals by 1H and Me NMR

    International Nuclear Information System (INIS)

    Lim, Ae Ran

    2007-01-01

    Me 3 H(SeO 4 ) 2 (Me = Na, K, and Rb) single crystals were grown by the slow evaporation method, and the relaxation times of the 1 H and Me nuclei in these crystals were investigated using FT NMR spectrometry. The 1 H T 1 NMR results for K 3 H(SeO 4 ) 2 and Rb 3 H(SeO 4 ) 2 single crystals were very different from those for Na 3 H(SeO 4 ) 2 crystals. Short 1 H relaxation times were found for K 3 H(SeO 4 ) 2 and Rb 3 H(SeO 4 ) 2 at high temperatures, but not for Na 3 H(SeO 4 ) 2 , which are attributed to the destruction and reconstruction of hydrogen bonds; thus K 3 H(SeO 4 ) 2 and Rb 3 H(SeO 4 ) 2 have superionic phases, whereas Na 3 H(SeO 4 ) 2 does not. The temperature dependence of the relaxation rate for the 23 Na nucleus in Na 3 H(SeO 4 ) 2 crystals was in accord with a Raman process for nuclear spin-lattice relaxation (T 1 -1 ∝T 2 . In contrast, the spin-lattice relaxation rates for the 39 K and 87 Rb nuclei in K 3 H(SeO 4 ) 2 and Rb 3 H(SeO 4 ) 2 single crystals exhibited a very strong temperature dependence, T 1 -1 ∝T 7 . The motions giving rise to this strong temperature dependence may be related to the high electrical conductivities of these crystals at high temperatures

  11. Resonant Scattering by Magnetic Impurities as a Model for Spin Relaxation in Bilayer Graphene.

    Science.gov (United States)

    Kochan, Denis; Irmer, Susanne; Gmitra, Martin; Fabian, Jaroslav

    2015-11-06

    We propose that the observed spin relaxation in bilayer graphene is due to resonant scattering by magnetic impurities. We analyze a resonant scattering model due to adatoms on both dimer and nondimer sites, finding that only the former give narrow resonances at the charge neutrality point. Opposite to single-layer graphene, the measured spin-relaxation rate in the graphene bilayer increases with carrier density. Although it has been commonly argued that a different mechanism must be at play for the two structures, our model explains this behavior rather naturally in terms of different broadening scales for the same underlying resonant processes. Not only do our results-using robust and first-principles inspired parameters-agree with experiment, they also predict an experimentally testable sharp decrease of the spin-relaxation rate at high carrier densities.

  12. Relaxation of an Isolated Dipolar-Interacting Rydberg Quantum Spin System

    Science.gov (United States)

    Orioli, A. Piñeiro; Signoles, A.; Wildhagen, H.; Günter, G.; Berges, J.; Whitlock, S.; Weidemüller, M.

    2018-02-01

    How do isolated quantum systems approach an equilibrium state? We experimentally and theoretically address this question for a prototypical spin system formed by ultracold atoms prepared in two Rydberg states with different orbital angular momenta. By coupling these states with a resonant microwave driving, we realize a dipolar X Y spin-1 /2 model in an external field. Starting from a spin-polarized state, we suddenly switch on the external field and monitor the subsequent many-body dynamics. Our key observation is density dependent relaxation of the total magnetization much faster than typical decoherence rates. To determine the processes governing this relaxation, we employ different theoretical approaches that treat quantum effects on initial conditions and dynamical laws separately. This allows us to identify an intrinsically quantum component to the relaxation attributed to primordial quantum fluctuations.

  13. Measurements of spin-lattice relaxation time in mixed alkali halide crystals

    International Nuclear Information System (INIS)

    Tannus, A.

    1983-01-01

    Using magneto-optic techniques the ground state spin-lattice relaxation times (T1) of 'F' centers in mixed Alkali Halide cristals (KCl-KBr), was studied. A computer assisted system to optically measure short relaxation times (approx. = 1mS), was described. The technique is based on the measurement of the Magnetic Circular Dicroism (MCD) presented by F centers. The T1 magnetic field dependency at 2 K (up to 65 KGauss), was obtained as well as the MCD spectra for different relative concentration at the mixed matrices. The theory developed by Panepucci and Mollenauer for F centers spin-lattice relaxation in pure matrices was modified to explain the behaviour of T1 in mixed cristals. The Direct Process results (T approx. = 2.0 K) compared against that theory shows that the main relaxation mecanism, up to 25 KGauss, continues to be phonon modulation of the hiperfine iteraction between F electrons and surrounding nuclei. (Author) [pt

  14. Electric field dependence of the spin relaxation anisotropy in (111) GaAs/AlGaAs quantum wells

    International Nuclear Information System (INIS)

    Balocchi, A; Amand, T; Renucci, P; Duong, Q H; Marie, X; Wang, G; Liu, B L

    2013-01-01

    Time-resolved optical spectroscopy experiments in (111)-oriented GaAs/AlGaAs quantum wells (QWs) show a strong electric field dependence of the conduction electron spin relaxation anisotropy. This results from the interplay between the Dresselhaus and Rashba spin splitting in this system with C 3v symmetry. By varying the electric field applied perpendicular to the QW plane from 20 to 50 kV cm −1 the anisotropy of the spin relaxation time parallel (τ s ∥ ) and perpendicular (τ s ⊥ ) to the growth axis can be first canceled and eventually inversed with respect to the one usually observed in III–V zinc-blende QW (τ s ⊥ = 2τ s ∥ ). This dependence stems from the nonlinear contributions of the k-dependent conduction band spin splitting terms which begin to play the dominant spin relaxing role while the linear Dresselhaus terms are compensated by the Rashba ones through the applied bias. A spin density matrix model for the conduction band spin splitting including both linear and cubic terms of the Dresselhaus Hamiltonian is used which allows a quantitative description of the measured electric field dependence of the spin relaxation anisotropy. The existence of an isotropic point where the spin relaxation tensor reduces to a scalar is predicted and confirmed experimentally. The spin splitting compensation electric field and collision processes type in the QW can be likewise directly extracted from the model without complementary measurements. (paper)

  15. Spin relaxation through lateral spin transport in heavily doped n -type silicon

    Science.gov (United States)

    Ishikawa, M.; Oka, T.; Fujita, Y.; Sugiyama, H.; Saito, Y.; Hamaya, K.

    2017-03-01

    We experimentally study temperature-dependent spin relaxation including lateral spin diffusion in heavily doped n -type silicon (n+-Si ) layers by measuring nonlocal magnetoresistance in small-sized CoFe/MgO/Si lateral spin-valve (LSV) devices. Even at room temperature, we observe large spin signals, 50-fold the magnitude of those in previous works on n+-Si . By measuring spin signals in LSVs with various center-to-center distances between contacts, we reliably evaluate the temperature-dependent spin diffusion length (λSi) and spin lifetime (τSi). We find that the temperature dependence of τSi is affected by that of the diffusion constant in the n+-Si layers, meaning that it is important to understand the temperature dependence of the channel mobility. A possible origin of the temperature dependence of τSi is discussed in terms of the recent theories by Dery and co-workers.

  16. Intersubband spin relaxation mechanism in n-doped[110] GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Schmid, Lena; Chen, Shijian; Doehrmann, Stefanie; Oertel, Stefan; Huebner, Jens; Oestreich, Michael [Institute for Solid State Physics, Gottfried Wilhelm Leibniz University Hannover, Appelstr. 2, 30167 Hannover (Germany); Schuh, Dieter; Wegscheider, Werner [Institute of Experimental and Applied Physics, University of Regensburg, Universitaetsstrasse 31, 93040 Regensburg (Germany)

    2008-07-01

    The intersubband spin relaxation mechanism most likely represents the major spin dephasing channel in room temperature applications based upon heterostructures in (110) oriented GaAs for spins oriented along the growth direction. The electron spin relaxation time {tau}{sub s} in n-doped (110)GaAs/AlGaAs quantum wells is investigated by time- and polarisation-resolved photoluminescence measurements in dependence on the subband energy splitting and subband occupancy. The influence by the subband energy splitting on {tau}{sub s} is deduced from well width dependent measurements, whereas different occupancies are adjusted by different sample temperatures. The n-doping suppresses the spin dephasing influence of holes created by the optical excitation. The (110) structure suppresses the Dyakonov-Perel relaxation mechanism for spins pointing in growth direction. Therefore the resulting spin relaxation times are long even at room temperature and the intersubband spin relaxation mechanism becomes the dominating spin relaxation mechanism.

  17. Spin dynamics of the itinerant helimagnet MnSi studied by positive muon spin relaxation

    International Nuclear Information System (INIS)

    Kadono, R.; Matsuzaki, T.; Yamazaki, T.; Kreitzman, S.R.; Brewer, J.H.

    1990-03-01

    The local magnetic fields and spin dynamics of the itinerant helimagnet MnSi(T c ≅ 29.5 K) have been studied experimentally using positive muon spin rotation/relaxation (μ + SR) methods. In the ordered phase (T c ), zero-field μSR was used to measure the hyperfine fields at the muon sites as well as the muon spin-lattice relaxation time T 1 μ . Two magnetically inequivalent interstitial μ + sites were found with hyperfine coupling constants A hf (1) = -3.94 kOe/μ B and A hf (2) = -6.94 kOe/μ B , respectively. In the paramagnetic phase (T > T c ), the muon-nuclear spin double relaxation technique was used to simultaneously but independently determine the spin-lattice relaxation time T 1 Mn of 55 Mn spins and that of positive muons (T 1 μ ) over a wide temperature range (T c 1 Mn and T 1 μ in both phases shows systematic deviations from the predictions of self-consistent renormalization (SCR) theory. (author)

  18. Logarithmically Slow Relaxation in Quasiperiodically Driven Random Spin Chains

    Science.gov (United States)

    Dumitrescu, Philipp T.; Vasseur, Romain; Potter, Andrew C.

    2018-02-01

    We simulate the dynamics of a disordered interacting spin chain subject to a quasiperiodic time-dependent drive, corresponding to a stroboscopic Fibonacci sequence of two distinct Hamiltonians. Exploiting the recursive drive structure, we can efficiently simulate exponentially long times. After an initial transient, the system exhibits a long-lived glassy regime characterized by a logarithmically slow growth of entanglement and decay of correlations analogous to the dynamics at the many-body delocalization transition. Ultimately, at long time scales, which diverge exponentially for weak or rapid drives, the system thermalizes to infinite temperature. The slow relaxation enables metastable dynamical phases, exemplified by a "time quasicrystal" in which spins exhibit persistent oscillations with a distinct quasiperiodic pattern from that of the drive. We show that in contrast with Floquet systems, a high-frequency expansion strictly breaks down above fourth order, and fails to produce an effective static Hamiltonian that would capture the prethermal glassy relaxation.

  19. Muon spin relaxation in ferromagnetic PdMn

    International Nuclear Information System (INIS)

    Dodds, S.A.; Gist, G.A.; Heffner, R.H.; Leon, M.; MacLaughlin, D.E.; Mydosh, J.A.; Nieuwenhuys, G.J.; Schillaci, M.E.

    1983-01-01

    Positive-muon (μ + ) spin relaxation experiments have been carried out in the dilute ferromagnetic alloy Pd + 2 at % Mn (T/sub c/ = 5.8 0 K). In the paramagnetic state the inhomogeneous μ + linewidth is proportional to the bulk magnetization. Below T/sub c/ the μ + linewidth and the width of the μ + local field distribution in zero applied field are both in qualitative accord with the Sherrington-Kirkpatrick theory of disordered magnets

  20. Possible spin frustration in Nd2Ti2O7 probed by muon spin relaxation.

    Science.gov (United States)

    Guo, Hanjie; Xing, Hui; Tong, Jun; Tao, Qian; Watanabe, Isao; Xu, Zhu-an

    2014-10-29

    Muon spin relaxation on Nd2Ti2O7 (NTO) and NdLaTi2O7 (NLTO) compounds are presented. The time spectra for both compounds are as expected for the paramagnetic state at high temperatures, but deviate from the exponential function below around 100 K. Firstly, the muon spin relaxation rate increases with decreasing temperature and then levels off below around 10 K, which is reminiscent of the frustrated systems. An enhancement of the relaxation rate by a longitudinal field in the paramagnetic state is observed for NTO and eliminated by a magnetic dilution for the NLTO sample. This suggests that the spectral density is modified by a magnetic dilution and thus indicates that the spins behave cooperatively rather than individually. The zero-field measurement at 0.3 K indicates that the magnetic ground state for NTO is ferromagnetic.

  1. Spin relaxation mechanism in graphene: resonant scattering by magnetic impurities.

    Science.gov (United States)

    Kochan, Denis; Gmitra, Martin; Fabian, Jaroslav

    2014-03-21

    We propose that the observed small (100 ps) spin relaxation time in graphene is due to resonant scattering by local magnetic moments. At resonances, magnetic moments behave as spin hot spots: the spin-flip scattering rates are as large as the spin-conserving ones, as long as the exchange interaction is greater than the resonance width. Smearing of the resonance peaks by the presence of electron-hole puddles gives quantitative agreement with experiment, for about 1 ppm of local moments. Although magnetic moments can come from a variety of sources, we specifically consider hydrogen adatoms, which are also resonant scatterers. The same mechanism would also work in the presence of a strong local spin-orbit interaction, but this would require heavy adatoms on graphene or a much greater coverage density of light adatoms. To make our mechanism more transparent, we also introduce toy atomic chain models for resonant scattering of electrons in the presence of a local magnetic moment and Rashba spin-orbit interaction.

  2. Muon spin relaxation studies in strongly correlated electron systems

    Science.gov (United States)

    Uemura, Y. J.; Luke, G. M.

    1993-05-01

    We describe recent progress of muon spin relaxation (μSR) studies in heavy-fermion (HF) and other strongly correlated electron systems. Measurements of the magnetic field penetration depth λ in HF superconductors UPt 3, URu 2Si 2, UPd 2Al 3 and U 2PtC 2 have revealed that these systems are characterized by large ratios Tc/ TF = 0.1-0.01 of Tc vs Fermi temperature TF derived from λ. This feature is common to high- Tc cuprate and other exotic superconductors. Zero-field μSR studies of magnetic order have elucidated a cross-over from spin glass ordering to nonmagnetic ground states in the ‘quadrupolar Kondo regime’ of (Y 1- xU x)Pd 3, and also suggested a possibility of incommensurate spin-density-wave (SDW) ordering in UNi 2Al 3.

  3. Muon spin-relaxation measurements of spin-correlation decay in spin-glass AgMn

    International Nuclear Information System (INIS)

    Heffner, R.H.; Cooke, D.W.; Leon, M.; Schillaci, M.E.; MacLaughlin, D.E.; Gupta, L.C.

    1983-01-01

    The field (H) dependence of the muon longitudinal spin-lattice relaxation rate well below the spin-glass temperature in AgMn is found to obey an algebraic form given by (H)/sup nu-1/, with nu = 0.54 +- 0.05. This suggests that Mn spin correlations decay with time as t - /sup nu/, in agreement with mean field theories of spin-glass dynamics which yield nu less than or equal to 0.5. Near the glass temperature the agreement between the data and theory is not as good

  4. Spin Relaxation Time in InAlAs/AlGaAs Quantum Dots

    Directory of Open Access Journals (Sweden)

    N. Sellami

    2014-05-01

    Full Text Available We report systematic temperature dependent measurements of spin relaxation time in self-assembled In0.72Al0.28As/Al0.28Ga0.72As quantum dots by continuous-wave photoluminescence. The degree of circular polarization decreases as a function of temperature. The spin relaxation time tS is deduced from the circular polarization degree using a three dimensional pseudo- spin precession model. The spin relaxation time decreases rapidly from few hundred picoseconds at 10 K to few tens picoseconds at 85 K. This large change of the spin relaxation time is explained in terms of acoustic phonon emission mechanism.

  5. Contact induced spin relaxation in graphene spin valves with Al2O3 and MgO tunnel barriers

    Directory of Open Access Journals (Sweden)

    Walid Amamou

    2016-03-01

    Full Text Available We investigate spin relaxation in graphene by systematically comparing the roles of spin absorption, other contact-induced effects (e.g., fringe fields, and bulk spin relaxation for graphene spin valves with MgO barriers, Al2O3 barriers, and transparent contacts. We obtain effective spin lifetimes by fitting the Hanle spin precession data with two models that include or exclude the effect of spin absorption. Results indicate that additional contact-induced spin relaxation other than spin absorption dominates the contact effect. For tunneling contacts, we find reasonable agreement between the two models with median discrepancy of ∼20% for MgO and ∼10% for Al2O3.

  6. Large spin relaxation anisotropy and valley-Zeeman spin-orbit coupling in WSe2/graphene/h -BN heterostructures

    Science.gov (United States)

    Zihlmann, Simon; Cummings, Aron W.; Garcia, Jose H.; Kedves, Máté; Watanabe, Kenji; Taniguchi, Takashi; Schönenberger, Christian; Makk, Péter

    2018-02-01

    Large spin-orbital proximity effects have been predicted in graphene interfaced with a transition-metal dichalcogenide layer. Whereas clear evidence for an enhanced spin-orbit coupling has been found at large carrier densities, the type of spin-orbit coupling and its relaxation mechanism remained unknown. We show an increased spin-orbit coupling close to the charge neutrality point in graphene, where topological states are expected to appear. Single-layer graphene encapsulated between the transition-metal dichalcogenide WSe2 and h -BN is found to exhibit exceptional quality with mobilities as high as 1 ×105 cm2 V-1 s-1. At the same time clear weak antilocalization indicates strong spin-orbit coupling, and a large spin relaxation anisotropy due to the presence of a dominating symmetric spin-orbit coupling is found. Doping-dependent measurements show that the spin relaxation of the in-plane spins is largely dominated by a valley-Zeeman spin-orbit coupling and that the intrinsic spin-orbit coupling plays a minor role in spin relaxation. The strong spin-valley coupling opens new possibilities in exploring spin and valley degree of freedom in graphene with the realization of new concepts in spin manipulation.

  7. Spin-lattice relaxation in phosphorescent triplet state molecules

    International Nuclear Information System (INIS)

    Verbeek, P.J.F.

    1979-01-01

    The present thesis contains the results of a study of spin-lattice relaxation (SLR) in the photo-excited triplet state of aromatic molecules, dissolved in a molecular host crystal. It appears that SLR in phosphorescent triplet state molecules often is related to the presence of so-called (pseudo) localized phonons in the molecular mixed crystals. These local phonons can be thought to correspond with vibrations (librations) of the guest molecule in the force field of the surrounding host molecules. Since the intermolecular forces are relatively weak, the frequencies corresponding with these vibrations are relatively low and usually are of the order of 10-30 cm -1 . (Auth.)

  8. Nuclear spin relaxation/resonance of 8Li in Al

    Science.gov (United States)

    Wang, D.; Salman, Z.; Chow, K. H.; Fan, I.; Hossain, M. D.; Keeler, T. A.; Kiefl, R. F.; Levy, C. D. P.; Mansour, A. I.; Morris, G. D.; Pearson, M. R.; Parolin, T. J.; Saadaoui, H.; Smadella, M.; Song, Q.; MacFarlane, W. A.

    2009-04-01

    A low energy beam of spin polarized 8Li has been used to study the behaviour of isolated 8Li implanted into a 150 nm thick film of Al on an MgO substrate. The spin relaxation rate 1/T1 and β-NMR lineshape were measured as a function of temperature in a large magnetic field of 4.1 T. The resonances from different sites are unresolved due to the large nuclear dipolar interaction with the host 27Al magnetic dipole moments. Nevertheless the temperature variation of the site averaged 1/T1 and Knight shift show evidence for a transition between the octahedral O and substitutional S sites at about 150 K, as observed in other fcc metals.

  9. Application of spin-exchange relaxation-free magnetometry to the Cosmic Axion Spin Precession Experiment

    Science.gov (United States)

    Wang, Tao; Kimball, Derek F. Jackson; Sushkov, Alexander O.; Aybas, Deniz; Blanchard, John W.; Centers, Gary; Kelley, Sean R. O.'; Wickenbrock, Arne; Fang, Jiancheng; Budker, Dmitry

    2018-03-01

    The Cosmic Axion Spin Precession Experiment (CASPEr) seeks to measure oscillating torques on nuclear spins caused by axion or axion-like-particle (ALP) dark matter via nuclear magnetic resonance (NMR) techniques. A sample spin-polarized along a leading magnetic field experiences a resonance when the Larmor frequency matches the axion/ALP Compton frequency, generating precessing transverse nuclear magnetization. Here we demonstrate a Spin-Exchange Relaxation-Free (SERF) magnetometer with sensitivity ≈ 1 fT /√{ Hz } and an effective sensing volume of 0.1 cm3 that may be useful for NMR detection in CASPEr. A potential drawback of SERF-magnetometer-based NMR detection is the SERF's limited dynamic range. Use of a magnetic flux transformer to suppress the leading magnetic field is considered as a potential method to expand the SERF's dynamic range in order to probe higher axion/ALP Compton frequencies.

  10. A fast determination method for transverse relaxation of spin-exchange-relaxation-free magnetometer

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Jixi, E-mail: lujixi@buaa.edu.cn; Qian, Zheng; Fang, Jiancheng [School of Instrument Science and Opto-Electronics Engineering, Beihang University, Beijing 100191 (China)

    2015-04-15

    We propose a fast and accurate determination method for transverse relaxation of the spin-exchange-relaxation-free (SERF) magnetometer. This method is based on the measurement of magnetic resonance linewidth via a chirped magnetic field excitation and the amplitude spectrum analysis. Compared with the frequency sweeping via separate sinusoidal excitation, our method can realize linewidth determination within only few seconds and meanwhile obtain good frequency resolution. Therefore, it can avoid the drift error in long term measurement and improve the accuracy of the determination. As the magnetic resonance frequency of the SERF magnetometer is very low, we include the effect of the negative resonance frequency caused by the chirp and achieve the coefficient of determination of the fitting results better than 0.998 with 95% confidence bounds to the theoretical equation. The experimental results are in good agreement with our theoretical analysis.

  11. Spin relaxation and antisymmetric exchange in n-doped III-V semiconductors

    Science.gov (United States)

    Gor'kov, L. P.; Krotkov, P. L.

    2003-01-01

    Recently, Kavokin [Phys. Rev. B 64, 075305 (2001)] suggested that the Dzyaloshinskii-Moriya interaction between localized electrons governs slow spin relaxation in n-doped GaAs in the regime close to the metal-insulator transition. We derive the correct spin Hamiltonian and apply it to the determination of spin dephasing time using the method of moments expansion. Our estimates would give longer than the observed values of the spin-relaxation time.

  12. Electron Tunneling in Lithium Ammonia Solutions Probed by Frequency-Dependent Electron-Spin Relaxation Studies

    Science.gov (United States)

    Maeda, Kiminori; Lodge, Matthew T.J.; Harmer, Jeffrey; Freed, Jack H.; Edwards, Peter P.

    2012-01-01

    Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multi-exponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10)×10−12 s over a temperature range 230–290K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a timescale of ca. 10−13 s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential

  13. Electron tunneling in lithium-ammonia solutions probed by frequency-dependent electron spin relaxation studies.

    Science.gov (United States)

    Maeda, Kiminori; Lodge, Matthew T J; Harmer, Jeffrey; Freed, Jack H; Edwards, Peter P

    2012-06-06

    Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T(1)) and spin-spin (T(2)) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multiexponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1-10) × 10(-12) s over a temperature range 230-290 K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a time scale of ∼10(-13) s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great

  14. Calculation of the electron spin relaxation time in a quantum limit using a state-independent projection reduction method

    Science.gov (United States)

    Kang, Nam Lyong

    2018-02-01

    A new formula for determining the electron spin relaxation time in a system of electrons interacting with acoustic deformation phonons through phonon-modulated spin–orbit coupling is derived using the state-independent projection reduction method. The spin flip and conserving processes are explained in an organized manner because the obtained results properly contain the distribution functions for electrons and phonons. The electron spin relaxation time is calculated directly from the lineshape function without calculating the magnetic susceptibility. The temperature (T) and magnetic field (B) dependences of the electron spin relaxation time (T 1) in Si are shown by T 1 ≈ T ‑1.55 and T 1 ≈ B ‑1.96 in the quantum limit, respectively.

  15. Resonances in field-cycling NMR on molecular crystals. (reversible) Spin dynamics or (irreversible) relaxation?; Resonanzen in Field-Cycling-NMR an Molekuelkristallen. (reversible) Spindynamik oder (irreversible) Relaxation?

    Energy Technology Data Exchange (ETDEWEB)

    Tacke, Christian

    2015-07-01

    Multi spin systems with spin 1/2 nuclei and dipolar coupled quadrupolar nuclei can show so called ''quadrupolar dips''. There are two main reasons for this behavior: polarization transfer and relaxation. They look quite alike and without additional research cannot be differentiated easily in most cases. These two phenomena have quite different physical and theoretical backgrounds. For no or very slow dynamics, polarization transfer will take place, which is energy conserving inside the spin system. This effect can entirely be described using quantum mechanics on the spin system. Detailed knowledge about the crystallography is needed, because this affects the relevant hamiltonians directly. For systems with fast enough dynamics, relaxation takes over, and the energy flows from the spin system to the lattice; thus a more complex theoretical description is needed. This description has to include a dynamic model, usually in the form of a spectral density function. Both models should include detailed modelling of the complete spin system. A software library was developed to be able to model complex spin systems. It allows to simulate polarization transfer or relaxation effects. NMR measurements were performed on the protonic conductor K{sub 3}H(SO{sub 4}){sub 2}. A single crystal shows sharp quadrupolar dips at room temperature. Dynamics could be excluded using relaxation measurements and literature values. Thus, a polarization transfer analysis was used to describe those dips with good agreement. As a second system, imidazolium based molecular crystals were analyzed. The quadrupolar dips were expected to be caused by polarization transfer; this was carefully analyzed and found not to be true. A relaxation based analysis shows good agreement with the measured data in the high temperature area. It leverages a two step spectral density function, which indicates two distinct dynamic processes happening in this system.

  16. Probing the Nuclear Spin-Lattice Relaxation Time at the Nanoscale

    NARCIS (Netherlands)

    Wagenaar, J.C.; Den Haan, A. M J; de Voogd, J.M.; Bossoni, L; de Jong, T.A.; de Wit, M.; Bastiaans, K. M.; Thoen, D.J.; Endo, A.; Klapwijk, T.M.; Zaanen, J.; Oosterkamp, TH

    2016-01-01

    Nuclear spin-lattice relaxation times are measured on copper using magnetic-resonance force microscopy performed at temperatures down to 42 mK. The low temperature is verified by comparison with the Korringa relation. Measuring spin-lattice relaxation times locally at very low temperatures opens up

  17. Electron spin relaxation in organic semiconductors probed through {mu}SR

    Energy Technology Data Exchange (ETDEWEB)

    Nuccio, L; Willis, M; Drew, A J [Queen Mary University of London, Department of Physics, Mile End Road, London, E1 4NS (United Kingdom); Schulz, L; Bernhard, C [Department of Physics and FriMat, University of Fribourg, Ch. du Musee 3, 1700 Fribourg, CH (Germany); Pratt, F L [ISIS Muon Facility, Rutherford Appleton Laboratory, Didcot, OX11 0QX (United Kingdom); Heeney, M; Stingelin, N, E-mail: l.nuccio@qmul.ac.uk [Centre for Plastic Electronics, Imperial College London, Exhibition Road, London, SW7 2AZ, London (United Kingdom)

    2011-04-01

    Muon spin spectroscopy and in particular the avoided level crossing technique is introduced, with the aim of showing it as a very sensitive local probe for electron spin relaxation in organic semiconductors. Avoided level crossing data on TMS-pentacene at different temperatures are presented, and they are analysed to extract the electron spin relaxation rate, that is shown to increase on increasing the temperature from 0.02 MHz to 0.33 MHz at 3 K and 300 K respectively.

  18. Nuclear magnetic relaxation by the dipolar EMOR mechanism: Multi-spin systems

    Science.gov (United States)

    Chang, Zhiwei; Halle, Bertil

    2017-08-01

    In aqueous systems with immobilized macromolecules, including biological tissues, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. Starting from the stochastic Liouville equation, we have previously developed a rigorous EMOR relaxation theory for dipole-coupled two-spin and three-spin systems. Here, we extend the stochastic Liouville theory to four-spin systems and use these exact results as a guide for constructing an approximate multi-spin theory, valid for spin systems of arbitrary size. This so-called generalized stochastic Redfield equation (GSRE) theory includes the effects of longitudinal-transverse cross-mode relaxation, which gives rise to an inverted step in the relaxation dispersion profile, and coherent spin mode transfer among solid-like spins, which may be regarded as generalized spin diffusion. The GSRE theory is compared to an existing theory, based on the extended Solomon equations, which does not incorporate these phenomena. Relaxation dispersion profiles are computed from the GSRE theory for systems of up to 16 protons, taken from protein crystal structures. These profiles span the range from the motional narrowing limit, where the coherent mode transfer plays a major role, to the ultra-slow motion limit, where the zero-field rate is closely related to the strong-collision limit of the dipolar relaxation rate. Although a quantitative analysis of experimental data is beyond the scope of this work, it is clear from the magnitude of the predicted relaxation rate and the shape of the relaxation dispersion profile that the dipolar EMOR mechanism is the principal cause of water-1H low-field longitudinal relaxation in aqueous systems of immobilized macromolecules, including soft biological tissues. The relaxation theory developed here therefore provides a basis for molecular-level interpretation of endogenous soft

  19. Spin-Relaxation Anisotropy in a GaAs Quantum Dot

    NARCIS (Netherlands)

    Scarlino, P.; Kawakami, E.; Stano, P.; Shafiei, M.; Reichl, C.; Wegscheider, W.; Vandersypen, L.M.K.

    2014-01-01

    We report that the electron spin-relaxation time T1 in a GaAs quantum dot with a spin-1/2 ground state has a 180° periodicity in the orientation of the in-plane magnetic field. This periodicity has been predicted for circular dots as being due to the interplay of Rashba and Dresselhaus spin orbit

  20. Low-frequency spin dynamics and NMR spin-lattice relaxation in antiferromagnetic rings

    Science.gov (United States)

    Itou, T.; Sagane, T.; Oyamada, A.; Maegawa, S.; Igarashi, S.; Yukawa, Y.

    2011-01-01

    We develop a general theory of the spin dynamics of Heisenberg antiferromagnetic rings (HAFRs) that explains the mechanism of NMR spin-lattice relaxation at low temperatures. In HAFRs, the imaginary parts of the q-summed dynamic spin susceptibilities parallel and perpendicular to an applied static field, χsum∥″(ω) and χsum⊥″(ω), are composed of the sum of many slightly broadened δ-functional modes at many frequencies. The NMR relaxation is caused by the quasielastic mode in χsum∥″(ω) at around zero frequency. This quasielastic mode is characterized by two physical quantities, intensity P0∥ and frequency width Γ0∥. Although P0∥ has to date been assumed to be identical to the uniform static susceptibility, we point out that the two quantities are not identical. Without making this unreliable assumption for P0∥, we demonstrate experimentally how P0∥ and Γ0∥ behave, by analyzing the NMR relaxation rates of two different nuclei, H1 and C13, in a real HAFR. This analysis is more rigorous and thus can be used to estimate Γ0∥ and P0∥ more precisely than previously possible. We find that the temperature dependence of P0∥ exhibits activation-type behavior reflecting the first excitation gap. We also find that Γ0∥ decreases monotonically on cooling but saturates to a nonzero value at zero temperature. This strongly suggests that Γ0∥ is dominated not only by the electron-phonon interactions but also by internanomagnet dipole interactions, which have been neglected to date.

  1. Spin-relaxation time in the impurity band of wurtzite semiconductors

    Science.gov (United States)

    Tamborenea, Pablo I.; Wellens, Thomas; Weinmann, Dietmar; Jalabert, Rodolfo A.

    2017-09-01

    The spin-relaxation time for electrons in the impurity band of semiconductors with wurtzite crystal structure is determined. The effective Dresselhaus spin-orbit interaction Hamiltonian is taken as the source of the spin relaxation at low temperature and for doping densities corresponding to the metallic side of the metal-insulator transition. The spin-flip hopping matrix elements between impurity states are calculated and used to set up a tight-binding Hamiltonian that incorporates the symmetries of wurtzite semiconductors. The spin-relaxation time is obtained from a semiclassical model of spin diffusion, as well as from a microscopic self-consistent diagrammatic theory of spin and charge diffusion in doped semiconductors. Estimates are provided for particularly important materials. The theoretical spin-relaxation times compare favorably with the corresponding low-temperature measurements in GaN and ZnO. For InN and AlN we predict that tuning of the spin-orbit coupling constant induced by an external potential leads to a potentially dramatic increase of the spin-relaxation time related to the mechanism under study.

  2. Relaxation processes connected with electron localization

    International Nuclear Information System (INIS)

    The paper reviews a series of recent theoretical papers worked out in the Institute of Applied Radiation Chemistry, Lodz. Poland. These papers are mainly devoted to various relaxation processes connected with electron localization in irradiated disordered media as well as to the construction of the models of trapped or solvated electron. The models reviewed in this paper (the first part of the review) concern: (1) electron trap relaxation via electron tunnelling followed by molecular reorientation: (2) molecular structure of alcohol-hydrocarbon mixtures and electron localization in these matrices: (3) the glass relaxation effect on trapped electron reactions. (author)

  3. Spin-Spin Relaxation and Karyagin-Gol'danskii Effect in FeCl3·6H2O

    DEFF Research Database (Denmark)

    Thrane, N.; Trumpy, Georg

    1970-01-01

    . Qualitatively, the experimental results can be explained by a combination of a temperature-and magnetic-field-dependent spin-spin relaxation and the Karyagin-Gol'danskii effect. This implies that the zero-field splitting is about 20°K between the lowest-lying Kramers doublet, found to be the |±1 / 2...

  4. Low-field cross spin relaxation of L8i in superconducting NbSe2

    Science.gov (United States)

    Hossain, M. D.; Salman, Z.; Wang, D.; Chow, K. H.; Kreitzman, S.; Keeler, T. A.; Levy, C. D. P.; Macfarlane, W. A.; Miller, R. I.; Morris, G. D.; Parolin, T. J.; Pearson, M.; Saadaoui, H.; Kiefl, R. F.

    2009-04-01

    A low energy beam of spin polarized L8i has been used to investigate nuclear spin relaxation in the multiband superconductor NbSe2 . In low magnetic fields there is significant cross relaxation between the L8i and the host N93b spins, which is driven by low frequency fluctuations in the nuclear magnetic dipolar interaction. The rate of cross relaxation is strongly field dependent and thus the 1/T1 spin relaxation rate of the L8i is a sensitive monitor of the static local magnetic field B just below the surface. This in turn is used to determine the absolute value of the magnetic penetration depth λ in the Meissner state. The temperature variations in 1/T1 and λ are consistent with a wide distribution of superconducting gaps expected for a multiband superconductor.

  5. β -detected NMR spin relaxation in a thin film heterostructure of ferromagnetic EuO

    Science.gov (United States)

    MacFarlane, W. A.; Song, Q.; Ingle, N. J. C.; Chow, K. H.; Egilmez, M.; Fan, I.; Hossain, M. D.; Kiefl, R. F.; Levy, C. D. P.; Morris, G. D.; Parolin, T. J.; Pearson, M. R.; Saadaoui, H.; Salman, Z.; Wang, D.

    2015-08-01

    We present β -detected NMR measurements of the spin-lattice relaxation of +8Li implanted into an epitaxial heterostructure based on a 100 nm thick film of ferromagnetic (FM) EuO as a function of temperature through its FM transition. In the FM state, the spin-lattice relaxation rate follows the same temperature dependence, determined by magnon scattering mechanisms, observed in the bulk by 153Eu NMR, but above 40 K, the signal is wiped out. We also find that +8Li stopped in material adjacent to the magnetic layer exhibits spin relaxation related to the critical slowing of the Eu spins. A particularly strong relaxation in the Au overlayer suggests an unusual strong nonlocal coupling mechanism to 8Li in the metal.

  6. A statistical correlation investigation for the role of surface spins to the spin relaxation of nitrogen vacancy centers

    Energy Technology Data Exchange (ETDEWEB)

    Song, Xuerui; Zhang, Jian; Feng, Fupan; Wang, Junfeng; Zhang, Wenlong; Lou, Liren; Zhu, Wei; Wang, Guanzhong, E-mail: gzwang@ustc.edu.cn [Hefei National Laboratory for Physical Science at Microscale, and Department of Physics, University of Science and Technology of China, Hefei, Anhui, 230026 (China)

    2014-04-15

    We investigated the influence of spins on surface of nanodiamonds (NDs) to the longitudinal relaxation time (T{sub 1}) and transverse relaxation time (T{sub 2}) of nitrogen vacancy (NV) centers in ND. A spherical model of the NDs was suggested to account for the experimental results of T{sub 1} and T{sub 2}, and the density of surface spins was roughly estimated based on the statistical analysis of experimental results of 72 NDs containing a single NV center. For NDs studied here, the T{sub 1} of NV center inside is highly dependent to the surface spins of the NDs. However, for the T{sub 2} of NV center, intrinsic contributions must be much pronounced than that by surface spins. In other words, T{sub 1} of an NV center in NDs is more sensitive to the change of the surface spin density than T{sub 2}.

  7. A statistical correlation investigation for the role of surface spins to the spin relaxation of nitrogen vacancy centers

    Directory of Open Access Journals (Sweden)

    Xuerui Song

    2014-04-01

    Full Text Available We investigated the influence of spins on surface of nanodiamonds (NDs to the longitudinal relaxation time (T1 and transverse relaxation time (T2 of nitrogen vacancy (NV centers in ND. A spherical model of the NDs was suggested to account for the experimental results of T1 and T2, and the density of surface spins was roughly estimated based on the statistical analysis of experimental results of 72 NDs containing a single NV center. For NDs studied here, the T1 of NV center inside is highly dependent to the surface spins of the NDs. However, for the T2 of NV center, intrinsic contributions must be much pronounced than that by surface spins. In other words, T1 of an NV center in NDs is more sensitive to the change of the surface spin density than T2.

  8. Exchange-mediated spin-lattice relaxation of Fe3+ ions in borate glasses.

    Science.gov (United States)

    Misra, Sushil K; Pilbrow, John R

    2007-03-01

    Spin-lattice relaxation times (T1) of two borate glasses doped with different concentrations of Fe2O3 were measured using the Electron Spin-Echo (ESE) technique at X-band (9.630 GHz) in the temperature range 2-6K. In comparison with a previous investigation of Fe3+-doped silicate glasses, the relaxation rates were comparable and differed by no more than a factor of two. The data presented here extend those previously reported for borate glasses in the 10-250K range but measured using the amplitude-modulation technique. The T1 values were found to depend on temperature (T) as T(n) with n approximately 1 for the 1% and 0.1% Fe2O3-doped glass samples. These results are consistent with spin-lattice relaxation as effected by exchange interaction of a Fe3+ spin exchange-coupled to another Fe3+ spin in an amorphous material.

  9. Generalized extended Navier-Stokes theory: multiscale spin relaxation in molecular fluids.

    Science.gov (United States)

    Hansen, J S

    2013-09-01

    This paper studies the relaxation of the molecular spin angular velocity in the framework of generalized extended Navier-Stokes theory. Using molecular dynamics simulations, it is shown that for uncharged diatomic molecules the relaxation time decreases with increasing molecular moment of inertia per unit mass. In the regime of large moment of inertia the fast relaxation is wave-vector independent and dominated by the coupling between spin and the fluid streaming velocity, whereas for small inertia the relaxation is slow and spin diffusion plays a significant role. The fast wave-vector-independent relaxation is also observed for highly packed systems. The transverse and longitudinal spin modes have, to a good approximation, identical relaxation, indicating that the longitudinal and transverse spin viscosities have same value. The relaxation is also shown to be isomorphic invariant. Finally, the effect of the coupling in the zero frequency and wave-vector limit is quantified by a characteristic length scale; if the system dimension is comparable to this length the coupling must be included into the fluid dynamical description. It is found that the length scale is independent of moment of inertia but dependent on the state point.

  10. Electron spin-relaxation via vibronic level of nickel (I) and nickel (III) cyanide complexes in NaCl single crystals.

    Science.gov (United States)

    Vugman, N V; de Araújo, M B; Pinhal, N M; Magon, C J; da Costa Filho, A J

    2004-05-01

    Electron spin-lattice relaxation rates for the low spin [Ni(CN)(4)](1-) and [Ni(CN)(4)](3-) complexes in NaCl host lattice were measured by the inversion recovery technique in the temperature range 7-50K. The data for both paramagnetic species fit very well to a relaxation process involving localized anharmonic vibration modes, also responsible for the g-tensor temperature dependence.

  11. Generalized extended Navier-Stokes theory: Multiscale spin relaxation in molecular fluids

    DEFF Research Database (Denmark)

    Hansen, Jesper Schmidt

    2013-01-01

    This paper studies the relaxation of the molecular spin angular velocity in the framework of generalized extended Navier-Stokes theory. Using molecular dynamics simulations, it is shown that for uncharged diatomic molecules the relaxation time decreases with increasing molecular moment of inertia...

  12. 55Mn nuclear spin relaxation and lifetime of magnons in MnF2 near the spin-flop transition

    International Nuclear Information System (INIS)

    Boucher, J.P.; King, A.R.

    1977-01-01

    A divergence in the nuclear relaxation rate (T 1 -1 ) of 55 Mn is observed in MnF 2 when the magnetic field approaches the field of the spin-flop transition (H=92.94Oe). The field dependence of T 1 -1 at 4.2 and 2K was studied together with its temperature dependence at 92.4 and 85 kOe. Near the transition, T 1 -1 is governed, below 8K, by the processes induced by the dipolar coupling and, above 8K, by those induced by exchange interactions. On the contrary, in weaker fields (H=85Oe), the only exchange induced processes are important [fr

  13. The spin relaxation of nitrogen donors in 6H SiC crystals as studied by the electron spin echo method

    Science.gov (United States)

    Savchenko, D.; Shanina, B.; Kalabukhova, E.; Pöppl, A.; Lančok, J.; Mokhov, E.

    2016-04-01

    We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by the Lely method and by the sublimation "sandwich method" (SSM) with a donor concentration of about 1017 cm-3 at T = 10-40 K. The donor electrons of the N donors substituting quasi-cubic "k1" and "k2" sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1-1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T9, respectively. The character of the temperature dependence of the T1-1 for the donor electrons of N substituting hexagonal ("h") site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm-1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed.

  14. Phonon-bottlenecked spin relaxation of Er3+:Y2SiO5 at sub-kelvin temperatures

    Science.gov (United States)

    Budoyo, Rangga P.; Kakuyanagi, Kosuke; Toida, Hiraku; Matsuzaki, Yuichiro; Munro, William J.; Yamaguchi, Hiroshi; Saito, Shiro

    2018-04-01

    We report on electron spin relaxation measurements of Er3+ dopants in a Y2SiO5 crystal using an electron paramagnetic resonance spectrometer based on a Josephson bifurcation amplifier. We observed the change in the induced flux as a function of time for two spin transitions (at different crystallographic sites) after an excitation microwave pulse or a change in the static magnetic field. Low-microwave-power measurements showed relaxation times of approximately 10 h at 20 mK, and 1/T 1 followed a T 2 dependence between 30 and 200 mK. We observed no difference in behavior between the two transitions. The microwave power and temperature dependences suggest that a phonon-bottleneck-like process limits relaxation.

  15. Spin dynamics of the positive muon radicals in the presence of rapid electron spin exchange: frequency shift and relaxation

    International Nuclear Information System (INIS)

    Senba, Masayoshi; British Columbia Univ., Vancouver, BC

    1991-01-01

    The spin dynamics of the positive muon in a muonium-like radical has been investigated in the case where the unpaired electron of the radical undergoes rapid spin flip collisions. If the spin flip rate λ SF is much faster than the hyperfine frequency of the radical, the behaviour of the muon spin is very similar to that of a positive muon in diamagnetic environments. It has been shown that in a transverse field, the relaxation rate and precession frequency of the apparent diamagnetic muon are related to the time evolution function of the muon spin in muonium. The relaxation rate of such an apparent diamagnetic signal has a characteristic field dependence which is very sensitive to the hyperfine frequency of the radical. The fractional frequency shift with respect to the positive muon precession frequency (ω D -ω μ )/ω μ is shown to be field-dependent, in contrast to the case of Knight shifts in metals. The field dependence of the relaxation and frequency shift will provide a tool to distinguish experimentally the muon in a radical which behaves like a free positive muon from a genuine diamagnetic muon. This work can be applied to a variety of fields involving muonium and hydrogen, such as spin dynamic in the gas phase and the muonium-like (hydrogen-like) states in semiconductors. The case where the muon undergoes both spin flip and charge transfer collisions is also discussed. (author)

  16. The eigenmode perspective of NMR spin relaxation in proteins

    Energy Technology Data Exchange (ETDEWEB)

    Shapiro, Yury E., E-mail: shapiro@nmrsgi4.ls.biu.ac.il, E-mail: eva.meirovitch@biu.ac.il; Meirovitch, Eva, E-mail: shapiro@nmrsgi4.ls.biu.ac.il, E-mail: eva.meirovitch@biu.ac.il [The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900-02 (Israel)

    2013-12-14

    We developed in recent years the two-body (protein and probe) coupled-rotator slowly relaxing local structure (SRLS) approach for elucidating protein dynamics from NMR spin relaxation. So far we used as descriptors the set of physical parameters that enter the SRLS model. They include the global (protein-related) diffusion tensor, D{sub 1}, the local (probe-related) diffusion tensor, D{sub 2}, and the local coupling/ordering potential, u. As common in analyzes based on mesoscopic dynamic models, these parameters have been determined with data-fitting techniques. In this study, we describe structural dynamics in terms of the eigenmodes comprising the SRLS time correlation functions (TCFs) generated by using the best-fit parameters as input to the Smoluchowski equation. An eigenmode is a weighted exponential with decay constant given by an eigenvalue of the Smoluchowski operator, and weighting factor determined by the corresponding eigenvector. Obviously, both quantities depend on the SRLS parameters as determined by the SRLS model. Unlike the set of best-fit parameters, the eigenmodes represent patterns of motion of the probe-protein system. The following new information is obtained for the typical probe, the {sup 15}N−{sup 1}H bond. Two eigenmodes, associated with the protein and the probe, dominate when the time scale separation is large (i.e., D{sub 2} ≫ D{sub 1}), the tensorial properties are simple, and the local potential is either very strong or very weak. When the potential exceeds these limits while the remaining conditions are preserved, new eigenmodes arise. The multi-exponentiality of the TCFs is associated in this case with the restricted nature of the local motion. When the time scale separation is no longer large, the rotational degrees of freedom of the protein and the probe become statistically dependent (coupled dynamically). The multi-exponentiality of the TCFs is associated in this case with the restricted nature of both the local and the

  17. The eigenmode perspective of NMR spin relaxation in proteins

    Science.gov (United States)

    Shapiro, Yury E.; Meirovitch, Eva

    2013-12-01

    We developed in recent years the two-body (protein and probe) coupled-rotator slowly relaxing local structure (SRLS) approach for elucidating protein dynamics from NMR spin relaxation. So far we used as descriptors the set of physical parameters that enter the SRLS model. They include the global (protein-related) diffusion tensor, D1, the local (probe-related) diffusion tensor, D2, and the local coupling/ordering potential, u. As common in analyzes based on mesoscopic dynamic models, these parameters have been determined with data-fitting techniques. In this study, we describe structural dynamics in terms of the eigenmodes comprising the SRLS time correlation functions (TCFs) generated by using the best-fit parameters as input to the Smoluchowski equation. An eigenmode is a weighted exponential with decay constant given by an eigenvalue of the Smoluchowski operator, and weighting factor determined by the corresponding eigenvector. Obviously, both quantities depend on the SRLS parameters as determined by the SRLS model. Unlike the set of best-fit parameters, the eigenmodes represent patterns of motion of the probe-protein system. The following new information is obtained for the typical probe, the 15N-1H bond. Two eigenmodes, associated with the protein and the probe, dominate when the time scale separation is large (i.e., D2 ≫ D1), the tensorial properties are simple, and the local potential is either very strong or very weak. When the potential exceeds these limits while the remaining conditions are preserved, new eigenmodes arise. The multi-exponentiality of the TCFs is associated in this case with the restricted nature of the local motion. When the time scale separation is no longer large, the rotational degrees of freedom of the protein and the probe become statistically dependent (coupled dynamically). The multi-exponentiality of the TCFs is associated in this case with the restricted nature of both the local and the global motion. The effects of local

  18. Spin relaxation in InGaN quantum disks in GaN nanowires

    KAUST Repository

    Banerjee, Animesh

    2011-12-14

    The spin relaxation time of photoinduced conduction electrons has been measured in InGaN quantum disks in GaN nanowires as a function of temperature and In composition in the disks. The relaxation times are of the order of ∼100 ps at 300 K and are weakly dependent on temperature. Theoretical considerations show that the Elliott-Yafet scattering mechanism is essentially absent in these materials and the results are interpreted in terms of the D\\'yakonov-Perel\\' relaxation mechanism in the presence of Rashba spin-orbit coupling of the wurtzite structure. The calculated spin relaxation times are in good agreement with the measured values. © 2011 American Chemical Society.

  19. Spin lattice relaxation of 8Li in a ferromagnetic EuO epitaxial thin film

    Science.gov (United States)

    Song, Q.; Chow, K. H.; Egilmez, M.; Fan, I.; Hossain, M. D.; Kiefl, R. F.; Kreitzman, S. R.; Levy, C. D. P.; Morris, G. D.; Parolin, T. J.; Pearson, M. R.; Salman, Z.; Saadaoui, H.; Smadella, M.; Wang, D.; Ingle, N. J. C.; MacFarlane, W. A.

    2009-04-01

    We inject a low energy spin polarized Li+8 beam into an epitaxially grown multilayer film consisting of Au(20 nm)/EuO(100 nm)/ LaAlO3, and investigate the nuclear spin relaxation at 3.33 T. The relaxation varies with implantation energy below 28 keV as the fraction of the probe Li8 stopping in each layer changes. We attribute the fast relaxating component to the EuO, while the much slower relaxation has contributions from both the Au and the substrate. However, fast relaxation is still observed at the lowest implantation energy where all the Li8 stops in the Au capping layer. This may be due to a proximity effect from the EuO.

  20. Spin lattice relaxation of {sup 8}Li in a ferromagnetic EuO epitaxial thin film

    Energy Technology Data Exchange (ETDEWEB)

    Song, Q., E-mail: susan@phas.ubc.c [Department of Physics, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Chow, K.H.; Egilmez, M.; Fan, I. [Department of Physics, University of Alberta, Edmonton, AB, T6G 2G7 (Canada); Hossain, M.D. [Department of Physics, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Kiefl, R.F. [Department of Physics, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Canadian Institute of Advanced Research (Canada); Kreitzman, S.R.; Levy, C.D.P.; Morris, G.D. [TRIMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Parolin, T.J. [Chemistry Department, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Pearson, M.R. [TRIMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Salman, Z. [TRIMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Physics Department, Oxford University, Parks Road, Oxford, OX1 3PU (United Kingdom); Saadaoui, H.; Smadella, M.; Wang, D. [Department of Physics, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Ingle, N.J.C. [AMPEL, University of British Columbia, Vancouver (Canada); MacFarlane, W.A. [Chemistry Department, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada)

    2009-04-15

    We inject a low energy spin polarized {sup 8}Li{sup +} beam into an epitaxially grown multilayer film consisting of Au(20 nm)/EuO(100 nm)/LaAlO{sub 3}, and investigate the nuclear spin relaxation at 3.33 T. The relaxation varies with implantation energy below 28 keV as the fraction of the probe {sup 8}Li stopping in each layer changes. We attribute the fast relaxating component to the EuO, while the much slower relaxation has contributions from both the Au and the substrate. However, fast relaxation is still observed at the lowest implantation energy where all the {sup 8}Li stops in the Au capping layer. This may be due to a proximity effect from the EuO.

  1. Far-from-Equilibrium Field Theory of Many-Body Quantum Spin Systems: Prethermalization and Relaxation of Spin Spiral States in Three Dimensions

    Directory of Open Access Journals (Sweden)

    Mehrtash Babadi

    2015-10-01

    Full Text Available We study theoretically the far-from-equilibrium relaxation dynamics of spin spiral states in the three-dimensional isotropic Heisenberg model. The investigated problem serves as an archetype for understanding quantum dynamics of isolated many-body systems in the vicinity of a spontaneously broken continuous symmetry. We present a field-theoretical formalism that systematically improves on the mean field for describing the real-time quantum dynamics of generic spin-1/2 systems. This is achieved by mapping spins to Majorana fermions followed by a 1/N expansion of the resulting two-particle-irreducible effective action. Our analysis reveals rich fluctuation-induced relaxation dynamics in the unitary evolution of spin spiral states. In particular, we find the sudden appearance of long-lived prethermalized plateaus with diverging lifetimes as the spiral winding is tuned toward the thermodynamically stable ferro- or antiferromagnetic phases. The emerging prethermalized states are characterized by different bosonic modes being thermally populated at different effective temperatures and by a hierarchical relaxation process reminiscent of glassy systems. Spin-spin correlators found by solving the nonequilibrium Bethe-Salpeter equation provide further insight into the dynamic formation of correlations, the fate of unstable collective modes, and the emergence of fluctuation-dissipation relations. Our predictions can be verified experimentally using recent realizations of spin spiral states with ultracold atoms in a quantum gas microscope [S. Hild et al., Phys. Rev. Lett. 113, 147205 (2014PRLTAO0031-900710.1103/PhysRevLett.113.147205].

  2. Spin-lattice relaxation times and knight shift in InSb and InAs

    International Nuclear Information System (INIS)

    Braun, P.; Grande, S.

    1976-01-01

    For a dominant contact interaction between nuclei and conduction electrons the relaxation rate is deduced. The extreme cases of degenerate and non-degenerate semiconductors are separately discussed. At strong degeneracy the product of the Knight shift and relaxation time gives the Korringa relation for metals. Measurements of the NMR spin-lattice relaxation times of 115 InSb and 115 InAs were made between 4.2 and 300 K for strongly degenerated samples. The different relaxation mechanisms are discussed and the experimental and theoretical results are compared. (author)

  3. High field electron-spin transport and observation of the Dyakonov-Perel spin relaxation of drifting electrons in low temperature-grown gallium arsenide

    International Nuclear Information System (INIS)

    Miah, M. Idrish

    2008-01-01

    High field electron-spin transport in low temperature-grown gallium arsenide is studied. We generate electron spins in the samples by optical pumping. During transport, we observe the Dyakonov-Perel (DP) [M.I. Dyakonov, V.I. Perel, Zh. Eksp. Teor. Fiz. 60 (1971) 1954] spin relaxation of the drifting electrons. The results are discussed and are compared with those obtained in calculations of the DP spin relaxation frequency of the hot electrons. A good agreement is obtained

  4. High field electron-spin transport and observation of the Dyakonov-Perel spin relaxation of drifting electrons in low temperature-grown gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M. Idrish [Nanoscale Science and Technology Centre, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong-4331 (Bangladesh)], E-mail: m.miah@griffith.edu.au

    2008-11-17

    High field electron-spin transport in low temperature-grown gallium arsenide is studied. We generate electron spins in the samples by optical pumping. During transport, we observe the Dyakonov-Perel (DP) [M.I. Dyakonov, V.I. Perel, Zh. Eksp. Teor. Fiz. 60 (1971) 1954] spin relaxation of the drifting electrons. The results are discussed and are compared with those obtained in calculations of the DP spin relaxation frequency of the hot electrons. A good agreement is obtained.

  5. NMR relaxation in spin ice at low temperature due to diffusing emergent monopoles

    Science.gov (United States)

    Henley, Christopher L.

    2013-03-01

    At low temperatures, spin dynamics in ideal spin ice is due mainly to dilute, thermally excited magnetic ``monopole'' excitations. I consider how these will affect the longitudinal (T1) and dephasing (T2) relaxation functions of a nuclear spin in the spin-ice pyrochlore Dy2Ti2O4. Up to the time scale for nearby monopoles to be rearranged, a stretched-exponential form of the relaxation functions is expected, due to averaging over nuclei that have different local environments. ror the dephasing (T2) relaxation, the power of time in the stretched exponential is 3/2 in the case of diffusing monopoles, but 1/2 in the case of fixed, fluctuating magnetic impurities. The flip rate and density of fluctuating spins (whatever their nature) can be extracted from the measured relaxation times T1 and T2, and from known parameters. However, the actual experimental relaxation measured by Kitagawa and Takigawa becomes temperature independent in the very low T limit, and the T2 has a power t 1 / 2 in the exponential, neither of which can be explained by monopoles. I suggest the very low T behavior could be due to magnetic impurities on the (normally nonmagnetic) Ti sites. Supported by NSF grant DMR-1005466.

  6. Spin-spin cross relaxation and spin-Hamiltonian spectroscopy by optical pumping of Pr/sup 3+/:LaF3

    International Nuclear Information System (INIS)

    Lukac, M.; Otto, F.W.; Hahn, E.L.

    1989-01-01

    We report the observation of an anticrossing in solid-state laser spectroscopy produced by cross relaxation. Spin-spin cross relaxation between the /sup 141/Pr- and /sup 19/F-spin reservoirs in Pr/sup 3+/:LaF 3 and its influence on the /sup 141/Pr NMR spectrum is detected by means of optical pumping. The technique employed combines optical pumping and hole burning with either external magnetic field sweep or rf resonance saturation in order to produce slow transient changes in resonant laser transmission. At a certain value of the external Zeeman field, where the energy-level splittings of Pr and F spins match, a level repulsion and discontinuity of the Pr/sup 3+/ NMR lines is observed. This effect is interpreted as the ''anticrossing'' of the combined Pr-F spin-spin reservoir energy states. The Zeeman-quadrupole-Hamiltonian spectrum of the hyperfine optical ground states of Pr/sup 3+/:LaF 3 is mapped out over a wide range of Zeeman magnetic fields. A new scheme is proposed for dynamic polarization of nuclei by means of optical pumping, based on resonant cross relaxation between rare spins and spin reservoirs

  7. Spin relaxation and the Kondo effect in transition metal dichalcogenide monolayers

    International Nuclear Information System (INIS)

    Rostami, Habib; Moghaddam, Ali G; Asgari, Reza

    2016-01-01

    We investigate the spin relaxation and Kondo resistivity caused by magnetic impurities in doped transition metal dichalcogenide monolayers. We show that momentum and spin relaxation times, due to the exchange interaction by magnetic impurities, are much longer when the Fermi level is inside the spin-split region of the valence band. In contrast to the spin relaxation, we find that the dependence of Kondo temperature T K on the doping is not strongly affected by the spin–orbit induced splitting, although only one of the spin species are present at each valley. This result, which is obtained using both perturbation theory and the poor man’s scaling methods, originates from the intervalley spin-flip scattering in the spin-split region. We further demonstrate the decline in the conductivity with temperatures close to T K , which can vary with the doping. Our findings reveal the qualitative difference with the Kondo physics in conventional metallic systems and other Dirac materials. (paper)

  8. Mn-based hard magnets with small saturation magnetization and low spin relaxation for spintronics

    International Nuclear Information System (INIS)

    Mizukami, S.; Sakuma, A.; Sugihara, A.; Suzuki, K.Z.; Ranjbar, R.

    2016-01-01

    The pursuit of high saturation magnetization is an important area of hard magnetic materials research. However, spintronics requires hard magnets exhibiting small saturation magnetization and low spin relaxation. Mn-based alloys that are composed of Mn and light group III and/or group IV elements exhibit such properties and may belong to a new category of magnetic materials. In this article, we review the magnetic properties of Mn-based hard magnet films. In particular, we focus on low spin relaxation as a new viewpoint for hard magnets, and we discuss the origin of their extraordinary magnetism in terms of their unique electronic structures.

  9. Optimal Configuration for Relaxation Times Estimation in Complex Spin Echo Imaging

    Directory of Open Access Journals (Sweden)

    Fabio Baselice

    2014-01-01

    Full Text Available Many pathologies can be identified by evaluating differences raised in the physical parameters of involved tissues. In a Magnetic Resonance Imaging (MRI framework, spin-lattice T1 and spin-spin T2 relaxation time parameters play a major role in such an identification. In this manuscript, a theoretical study related to the evaluation of the achievable performances in the estimation of relaxation times in MRI is proposed. After a discussion about the considered acquisition model, an analysis on the ideal imaging acquisition parameters in the case of spin echo sequences, i.e., echo and repetition times, is conducted. In particular, the aim of the manuscript consists in providing an empirical rule for optimal imaging parameter identification with respect to the tissues under investigation. Theoretical results are validated on different datasets in order to show the effectiveness of the presented study and of the proposed methodology.

  10. NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning

    Energy Technology Data Exchange (ETDEWEB)

    Shmyreva, Anna A. [Center for Magnetic Resonance, St. Petersburg State University, St. Petersburg 198504 (Russian Federation); Safdari, Majid; Furó, István [Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm (Sweden); Dvinskikh, Sergey V., E-mail: sergeid@kth.se [Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm (Sweden); Laboratory of Biomolecular NMR, St. Petersburg State University, St. Petersburg 199034 (Russian Federation)

    2016-06-14

    Orders of magnitude decrease of {sup 207}Pb and {sup 199}Hg NMR longitudinal relaxation times T{sub 1} upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX{sub 2} (Me = Pb, Hg and X = Cl, Br, I). In lead(II) halides, the most dramatic decrease of T{sub 1} relative to that in a static sample is in PbI{sub 2}, while it is smaller but still significant in PbBr{sub 2}, and not detectable in PbCl{sub 2}. The effect is magnetic-field dependent but independent of the spinning speed in the range 200–15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.

  11. Matrix-assisted relaxation in Fe(phen)2(NCS)2 spin-crossover microparticles, experimental and theoretical investigations

    International Nuclear Information System (INIS)

    Enachescu, Cristian; Stancu, Alexandru; Tanasa, Radu; Tissot, Antoine; Laisney, Jérôme; Boillot, Marie-Laure

    2016-01-01

    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.

  12. The spin lattice relaxation of {sup 8}Li in simple metals

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, M.D.; Saadaoui, H. [Department of Physics, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Parolin, T.J. [Chemistry Department, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Song, Q.; Wang, D.; Smadella, M. [Department of Physics, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Chow, K.H.; Egilmez, M.; Fan, I. [Department of Physics, University of Alberta, Edmonton, AB, T6G 2G7 (Canada); Kiefl, R.F. [Department of Physics, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Canadian Institute of Advanced Research (Canada); Kreitzman, S.R.; Levy, C.D.P.; Morris, G.D.; Pearson, M.R. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Salman, Z. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU (United Kingdom); MacFarlane, W.A., E-mail: wam@chem.ubc.c [Chemistry Department, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada)

    2009-04-15

    We report the modification to the linear temperature dependence of the Korringa nuclear spin-lattice relaxation rate of an implanted NMR probe in silver, as it makes a thermally activated site change. We develop a simple model of this phenomenon, which is found in a number of metals including Au and Nb.

  13. Thermal conduction effects in spin-lattice relaxation experiments on ytterbium chloride hexahydrate

    NARCIS (Netherlands)

    Flokstra, Jakob; Gerritsma, G.J.; Blokhuis, A.C.

    1979-01-01

    The anomalous behaviour of the spin-lattice relaxation observed for single crystals of ytterbium chloride hexahydrate at fields stronger than 5 kOe is due to the poor heat transfer in the liquid-helium bath. The thermal conduction effects can be explained by means of a thermal conduction model for

  14. Criteria for accurate determination of the magnon relaxation length from the nonlocal spin Seebeck effect

    NARCIS (Netherlands)

    Shan, Juan; Cornelissen, Ludo Johannes; Liu, Jing; Ben Youssef, J.; Liang, Lei; van Wees, Bart

    2017-01-01

    The nonlocal transport of thermally generated magnons not only unveils the underlying mechanism of the spin Seebeck effect, but also allows for the extraction of the magnon relaxation length (λm) in a magnetic material, the average distance over which thermal magnons can propagate. In this study, we

  15. Direct and two-phonon Orbach-Aminov type spin-lattice relaxation in molecular magnet V15

    Science.gov (United States)

    Tarantul, Alex; Tsukerblat, Boris

    2011-10-01

    In this article we propose a model of spin-phonon relaxation in K6[VIV 15As6O42(H2O)]-8H2O, the so called V15 cluster exhibiting the unique layered magnetic structure. The work is motivated by the recent observation of the Rabi oscillation [1] in this system and aimed to elucidate the role of spin-phonon interaction as a source of decoherence. The spin-phonon coupling is assumed to appear as a result of the modulation of the isotropic and antisymmetric (Dzyaloshinsky-Moriya) exchange interactions in the central triangular layer of vanadium ions by the acoustic lattice vibrations. The relaxation rates are estimated within the Debye model for the lattice vibrations. Within the pseudo-angular momentum representation the selection rules for the direct (one-phonon) transitions between Zeeman levels are derived and a special role of the antisymmetric exchange is underlined. The probabilities of the two-phonon Orbach-Aminov type processes are evaluated as well, while the Raman type relaxation is shown to have a negligible importance at low temperatures at which the Rabi oscillations have been detected.

  16. Muon Spin Relaxation Evidence for the U(1) Quantum Spin-Liquid Ground State in the Triangular Antiferromagnet YbMgGaO_{4}.

    Science.gov (United States)

    Li, Yuesheng; Adroja, Devashibhai; Biswas, Pabitra K; Baker, Peter J; Zhang, Qian; Liu, Juanjuan; Tsirlin, Alexander A; Gegenwart, Philipp; Zhang, Qingming

    2016-08-26

    Muon spin relaxation (μSR) experiments on single crystals of the structurally perfect triangular antiferromagnet YbMgGaO_{4} indicate the absence of both static long-range magnetic order and spin freezing down to 0.048 K in a zero field. Below 0.4 K, the μ^{+} spin relaxation rates, which are proportional to the dynamic correlation function of the Yb^{3+} spins, exhibit temperature-independent plateaus. All these μSR results unequivocally support the formation of a gapless U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO_{4}.

  17. A new problem in the correlation of nuclear-spin relaxation and ionic conductivity in superionic glasses

    Science.gov (United States)

    Tatsumisago, M.; Angell, C. A.; Martin, S. W.

    1992-11-01

    Following the recent resolution of the longstanding problem of reconciling constant frequency nuclear-spin lattice relaxation (SLR) activation energies and d.c. conductivity activity energies in ion conducting glasses, we point out a new problem which seems not to have been discussed previously. We report conductivity data measured at a series of fixed frequencies and variable temperatures on a lithium chloroborate glass and compare them with SLR data on identically prepared samples, also using different fixed frequencies. While phenomenological similarities due to comparable departures from exponential relaxation are found in each case, pronounced differences in the most probable relaxation times themselves are observed. The conductivity relaxation at 500 K occurs on a time scale shorter by some 2 orders of magnitude than the 7Li SLR correlation, and has a significantly lower activation energy. We show from a literature review that this distinction is a common but unreported finding for highly decoupled (fast-ion conducting) systems, and that an inverse relationship is found in supercoupled salt/polymer ``solid'' electrolytes. In fast-ion conducting glasses, the slower SLR process would imply special features in the fast-ion motion which permit spin correlations to survive many more successive ion displacements than previously expected. It is conjectured that the SLR in superionic glasses depends on the existence of a class of low-lying traps infrequently visited by migrating ions.

  18. Spin diffusion and1H spin-lattice relaxation in Cs2(HSO4)(H2PO4) containing a small amount of ammonium ions.

    Science.gov (United States)

    Hayashi, Shigenobu; Jimura, Keiko

    2017-11-01

    Inorganic solid acid salts with hydrogen bond networks frequently show very long spin-lattice relaxation times even for 1 H because the hydrogen bonds suppress motions. In the present work, the 1 H spin-lattice relaxation in Cs 2 (HSO 4 )(H 2 PO 4 ) containing a small amount of ammonium ions were studied in detail by use of the effect of magic angle spinning (MAS) on the relaxation. The 1 H spin-lattice relaxation times of the acid protons decrease with increase in the content of ammonium ions. Reorientation of the NH 4 group fluctuates the dipole-dipole interaction and relaxes the ammonium protons as well as the acid protons. The 1 H relaxation times of the acid protons are a little bit longer than those of the ammonium protons at the MAS rate of 8 kHz. The spinning at 50 kHz makes the relaxation times of the acid protons longer and those of the ammonium protons shorter. Spin diffusion between the acid and the ammonium protons averages partially the 1 H relaxation of the acid and the ammonium protons at the MAS rate of 8 kHz. The spin diffusion is suppressed completely at the MAS rate of 50 kHz. Spin diffusion between the acid protons is not suppressed at the MAS rate of 50 kHz. The acid protons always show the same relaxation times. The intrinsic relaxation times not affected by spin diffusion are evaluated quantitatively for both the acid and the ammonium protons. Those values are independent of the ammonium content. Contribution of the spin diffusion between the acid and the ammonium protons to the relaxation is estimated quantitatively. Using those parameters, the effect of ammonium ions on the 1 H spin-lattice relaxation can be predicted. The 1 H spin-lattice relaxation is a sensitive tool to study the distribution of ammonium ions in solids. Copyright © 2017 Elsevier Inc. All rights reserved.

  19. Quantum mechanical alternative to Arrhenius equation in the interpretation of proton spin-lattice relaxation data for the methyl groups in solids

    KAUST Repository

    Bernatowicz, Piotr

    2015-10-01

    Theory of nuclear spin-lattice relaxation in methyl groups in solids has been a recurring problem in nuclear magnetic resonance (NMR) spectroscopy. The current view is that, except for extreme cases of low torsional barriers where special quantum effects are at stake, the relaxation behaviour of the nuclear spins in methyl groups is controlled by thermally activated classical jumps of the methyl group between its three orientations. The temperature effects on the relaxation rates can be modelled by Arrhenius behaviour of the correlation time of the jump process. The entire variety of relaxation effects in protonated methyl groups has recently been given a consistently quantum mechanical explanation not invoking the jump model regardless of the temperature range. It exploits the damped quantum rotation (DQR) theory originally developed to describe NMR line shape effects for hindered methyl groups. In the DQR model, the incoherent dynamics of the methyl group include two quantum rate, i.e., coherence-damping processes. For proton relaxation only one of these processes is relevant. In this paper, temperature-dependent proton spin-lattice relaxation data for the methyl groups in polycrystalline methyltriphenyl silane and methyltriphenyl germanium, both deuterated in aromatic positions, are reported and interpreted in terms of the DQR model. A comparison with the conventional approach exploiting the phenomenological Arrhenius equation is made. The present observations provide further indications that incoherent motions of molecular moieties in condensed phase can retain quantum character over much broad temperature range than is commonly thought.

  20. Electronic Relaxation Processes of Transition Metal Atoms in Helium Nanodroplets

    Science.gov (United States)

    Kautsch, Andreas; Lindebner, Friedrich; Koch, Markus; Ernst, Wolfgang E.

    2014-06-01

    Spectroscopy of doped superfluid helium nanodroplets (He_N) gives information about the influence of this cold, chemically inert, and least interacting matrix environment on the excitation and relaxation dynamics of dopant atoms and molecules. We present the results from laser induced fluorescence (LIF), photoionization (PI), and mass spectroscopy of Cr and Cu doped He_N. From these results, we can draw a comprehensive picture of the complex behavior of such transition metal atoms in He_N upon photo-excitation. The strong Cr and Cu ground state transitions show an excitation blueshift and broadening with respect to the bare atom transitions which can be taken as indication for the solvation inside the droplet. From the originally excited states the atoms relax to energetically lower states and are ejected from the He_N. The relaxation processes include bare atom spin-forbidden transitions, which clearly bears the signature of the He_N influence. Two-color resonant two-photon ionization (2CR2PI) also shows the formation of bare atoms and small Cr-He_n and Cu-He_n clusters in their ground and metastable states ^c. Currently, Cr dimer excitation studies are in progress and a brief outlook on the available results will be given. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, 2011. A. Kautsch, M. Koch, and W. E. Ernst, J. Phys. Chem. A, 117 (2013) 9621-9625, DOI: 10.1021/jp312336m F. Lindebner, A. Kautsch, M. Koch, and W. E. Ernst, Int. J. Mass Spectrom. (2014) in press, DOI: 10.1016/j.ijms.2013.12.022 M. Koch, A. Kautsch, F. Lackner, and W. E. Ernst, submitted to J. Phys. Chem. A

  1. Nuclear magnetic relaxation by the dipolar EMOR mechanism: General theory with applications to two-spin systems.

    Science.gov (United States)

    Chang, Zhiwei; Halle, Bertil

    2016-02-28

    In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. We have embarked on a systematic program to develop, from the stochastic Liouville equation, a general and rigorous theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole coupling strengths, and Larmor frequencies. Here, we present a general theoretical framework applicable to spin systems of arbitrary size with symmetric or asymmetric exchange. So far, the dipolar EMOR theory is only available for a two-spin system with symmetric exchange. Asymmetric exchange, when the spin system is fragmented by the exchange, introduces new and unexpected phenomena. Notably, the anisotropic dipole couplings of non-exchanging spins break the axial symmetry in spin Liouville space, thereby opening up new relaxation channels in the locally anisotropic sites, including longitudinal-transverse cross relaxation. Such cross-mode relaxation operates only at low fields; at higher fields it becomes nonsecular, leading to an unusual inverted relaxation dispersion that splits the extreme-narrowing regime into two sub-regimes. The general dipolar EMOR theory is illustrated here by a detailed analysis of the asymmetric two-spin case, for which we present relaxation dispersion profiles over a wide range of conditions as well as analytical results for integral relaxation rates and time-dependent spin modes in the zero-field and motional-narrowing regimes. The general theoretical framework presented here will enable a quantitative analysis of frequency-dependent water-proton longitudinal relaxation in model systems with immobilized macromolecules and, ultimately, will provide a rigorous link between relaxation-based magnetic resonance image contrast and molecular parameters.

  2. An inversion-relaxation approach for sampling stationary points of spin model Hamiltonians

    International Nuclear Information System (INIS)

    Hughes, Ciaran; Mehta, Dhagash; Wales, David J.

    2014-01-01

    Sampling the stationary points of a complicated potential energy landscape is a challenging problem. Here, we introduce a sampling method based on relaxation from stationary points of the highest index of the Hessian matrix. We illustrate how this approach can find all the stationary points for potentials or Hamiltonians bounded from above, which includes a large class of important spin models, and we show that it is far more efficient than previous methods. For potentials unbounded from above, the relaxation part of the method is still efficient in finding minima and transition states, which are usually the primary focus of attention for atomistic systems

  3. The impact of structural relaxation on spin polarization and magnetization reversal of individual nano structures studied by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Sander, Dirk; Phark, Soo-Hyon; Corbetta, Marco; Fischer, Jeison A; Oka, Hirofumi; Kirschner, Jürgen

    2014-10-01

    The application of low temperature spin-polarized scanning tunneling microscopy and spectroscopy in magnetic fields for the quantitative characterization of spin polarization, magnetization reversal and magnetic anisotropy of individual nano structures is reviewed. We find that structural relaxation, spin polarization and magnetic anisotropy vary on the nm scale near the border of a bilayer Co island on Cu(1 1 1). This relaxation is lifted by perimetric decoration with Fe. We discuss the role of spatial variations of the spin-dependent electronic properties within and at the edge of a single nano structure for its magnetic properties.

  4. Dynamical transition in molecular glasses and proteins observed by spin relaxation of nitroxide spin probes and labels

    Science.gov (United States)

    Golysheva, Elena A.; Shevelev, Georgiy Yu.; Dzuba, Sergei A.

    2017-08-01

    In glassy substances and biological media, dynamical transitions are observed in neutron scattering that manifests itself as deviations of the translational mean-squared displacement, , of hydrogen atoms from harmonic dynamics. In biological media, the deviation occurs at two temperature intervals, at ˜100-150 K and at ˜170-230 K, and it is attributed to the motion of methyl groups in the former case and to the transition from harmonic to anharmonic or diffusive motions in the latter case. In this work, electron spin echo (ESE) spectroscopy—a pulsed version of electron paramagnetic resonance—is applied to study the spin relaxation of nitroxide spin probes and labels introduced in molecular glass former o-terphenyl and in protein lysozyme. The anisotropic contribution to the rate of the two-pulse ESE decay, ΔW, is induced by spin relaxation appearing because of restricted orientational stochastic molecular motion; it is proportional to τc, where is the mean-squared angle of reorientation of the nitroxide molecule around the equilibrium position and τc is the correlation time of reorientation. The ESE time window allows us to study motions with τc τc temperature dependence shows a transition near 240 K, which is in agreement with the literature data on . For spin probes of essentially different size, the obtained data were found to be close, which evidences that motion is cooperative, involving a nanocluster of several neighboring molecules. For the dry lysozyme, the τc values below 260 K were found to linearly depend on the temperature in the same way as it was observed in neutron scattering for . As spin relaxation is influenced only by stochastic motion, the harmonic motions seen in ESE must be overdamped. In the hydrated lysozyme, ESE data show transitions near 130 K for all nitroxides, near 160 K for the probe located in the hydration layer, and near 180 K for the label in the protein interior. For this system, the two latter transitions are not

  5. TU-EF-BRA-02: Longitudinal Proton Spin Relaxation and T1-Imaging

    Energy Technology Data Exchange (ETDEWEB)

    Lemen, L. [Univ Cincinnati (United States)

    2015-06-15

    can be introduced with either of two approaches. In the first, one thinks (loosely) of the nuclei of hydrogen atoms as (rotating and charged and therefore) magnetic objects, whose spin-axes tend to align in a strong external magnetic field, much like a compass needle. As with the Bohr atom, this spin-up/spin-down picture is a highly abridged version of the full quantum mechanical treatment, but still it leads to some useful, legitimate pictures of the NMR process occurring within a voxel: When RF photons of the correct (Larmor) frequency elevate protons in a fixed magnetic field out of their lower-energy spin state into the upper, the NMR phenomenon is indicated by the detectable absorption of RF power. With the addition of a linear gradient field along a multi-voxel, one-dimensional patient/phantom, as well, we can determine the water content of each compartment – an example of a real MRI study, albeit in 1D. Part I concludes with a discussion of the net magnetization at position x, m0(x), under conditions of dynamic thermal equilibrium, which leads into: Part II. Net Voxel Magnetization, m(x,t); T1-MRI; The MRI Device (Lemen), investigates the biophysics of the form of proton spin relaxation process characterized by the time T1. It then moves on to the creation of an MR image that displays the spatial variation in the values of this clinically relevant parameter, again in 1D. Finally, the design and workings of a clinical MRI machine are sketched, in preparation for: Part III. ‘Classical’ NMR; FID Imaging in 1D via k-Space (Yanasak) presents the second standard approach to NMR and MRI, the classical model. It focuses on the time dependence of the net nuclear magnetization, m(x,t), the overall magnetic field generated by the cohort of protons in the voxel at position x. Quite remarkably, this nuclear net magnetization itself acts in a strong magnetic field like a gyroscope in a gravitational field. This tack is better for explaining Free Induction Decay (FID

  6. TU-EF-BRA-02: Longitudinal Proton Spin Relaxation and T1-Imaging

    International Nuclear Information System (INIS)

    Lemen, L.

    2015-01-01

    can be introduced with either of two approaches. In the first, one thinks (loosely) of the nuclei of hydrogen atoms as (rotating and charged and therefore) magnetic objects, whose spin-axes tend to align in a strong external magnetic field, much like a compass needle. As with the Bohr atom, this spin-up/spin-down picture is a highly abridged version of the full quantum mechanical treatment, but still it leads to some useful, legitimate pictures of the NMR process occurring within a voxel: When RF photons of the correct (Larmor) frequency elevate protons in a fixed magnetic field out of their lower-energy spin state into the upper, the NMR phenomenon is indicated by the detectable absorption of RF power. With the addition of a linear gradient field along a multi-voxel, one-dimensional patient/phantom, as well, we can determine the water content of each compartment – an example of a real MRI study, albeit in 1D. Part I concludes with a discussion of the net magnetization at position x, m0(x), under conditions of dynamic thermal equilibrium, which leads into: Part II. Net Voxel Magnetization, m(x,t); T1-MRI; The MRI Device (Lemen), investigates the biophysics of the form of proton spin relaxation process characterized by the time T1. It then moves on to the creation of an MR image that displays the spatial variation in the values of this clinically relevant parameter, again in 1D. Finally, the design and workings of a clinical MRI machine are sketched, in preparation for: Part III. ‘Classical’ NMR; FID Imaging in 1D via k-Space (Yanasak) presents the second standard approach to NMR and MRI, the classical model. It focuses on the time dependence of the net nuclear magnetization, m(x,t), the overall magnetic field generated by the cohort of protons in the voxel at position x. Quite remarkably, this nuclear net magnetization itself acts in a strong magnetic field like a gyroscope in a gravitational field. This tack is better for explaining Free Induction Decay (FID

  7. Quantitative study of optical pumping in the presence of spin-exchange relaxation

    Science.gov (United States)

    Shi, Yongqi; Scholtes, Theo; Grujić, Zoran D.; Lebedev, Victor; Dolgovskiy, Vladimir; Weis, Antoine

    2018-01-01

    We have performed quantitative measurements of the variation of the on-resonance absorption coefficients κ0 of the four hyperfine components of the Cs D1 transition as a function of laser power P , for pumping with linearly and with circularly polarized light. Sublevel populations derived from rate equations assuming isotropic population relaxation (at a rate γ1) yield algebraic κ0(P ) dependences that do not reproduce the experimental findings from Cs vapor in a paraffin-coated cell. However, numerical results that consider spin-exchange relaxation (at a rate γse) and isotropic relaxation fit the experimental data perfectly well. The fit parameters, viz., the absolute value of κ0, the optical pumping saturation power Psat, and the ratio γse/γ1 , are well described by the experimental conditions and yield absolute values for γ1 and γse. The latter is consistent with the previously published Cs-Cs spin-exchange relaxation cross section.

  8. Optically-detected spin-echo method for relaxation times measurements in a Rb atomic vapor

    Science.gov (United States)

    Gharavipour, M.; Affolderbach, C.; Gruet, F.; Radojičić, I. S.; Krmpot, A. J.; Jelenković, B. M.; Mileti, G.

    2017-06-01

    We introduce and demonstrate an experimental method, optically-detected spin-echo (ODSE), to measure ground-state relaxation times of a rubidium (Rb) atomic vapor held in a glass cell with buffer-gas. The work is motivated by our studies on high-performance Rb atomic clocks, where both population and coherence relaxation times (T 1 and T 2, respectively) of the ‘clock transition’ (52S1/2 | {F}g = 1,{m}F=0> ≤ftrightarrow | {F}g=2,{m}F=0> ) are relevant. Our ODSE method is inspired by classical nuclear magnetic resonance spin-echo method, combined with optical detection. In contrast to other existing methods, like continuous-wave double-resonance (CW-DR) and Ramsey-DR, principles of the ODSE method allow suppression of decoherence arising from the inhomogeneity of the static magnetic field across the vapor cell, thus enabling measurements of intrinsic relaxation rates, as properties of the cell alone. Our experimental result for the coherence relaxation time, specific for the clock transition, measured with the ODSE method is in good agreement with the theoretical prediction, and the ODSE results are validated by comparison to those obtained with Franzen, CW-DR and Ramsey-DR methods. The method is of interest for a wide variety of quantum optics experiments with optical signal readout.

  9. Spin-spin cross-relaxation of optically-excited rare-earth ions in crystals

    International Nuclear Information System (INIS)

    Otto, F.W.; D'Amato, F.X.; Hahn, E.L.; Lukas, M.

    1986-01-01

    A laser saturation grating experiment is applied for the measurement of electron hyperfine state spin orientation diffusion among Tm +2 impurity ion hyperfine ground states in SrF 2 . A strong laser pulse at λ 1 produces a spatial grating of excited spin states followed by a probe at λ 2 . The probe transmission intensity is to assess diffusion of non-equilibrium spin population into regions not excited by the pulse at λ 1 . In a second experiment, a field sweep laser hole burning method enables measurement of Pr +3 optical ion hyperfine coupling of optical ground states to the reservoir of F nuclear moments in LaF 3 by level crossing. A related procedure with external RF resonance sweep excitation maps out the nuclear Zeeman-electric quadrupole coupled spectrum of Pr +3 over a wide range by monitoring laser beam transmission absorption

  10. NMR water-proton spin-lattice relaxation time of human red blood cells and red blood cell suspensions

    International Nuclear Information System (INIS)

    Sullivan, S.G.; Rosenthal, J.S.; Winston, A.; Stern, A.

    1988-01-01

    NMR water-proton spin-lattice relaxation times were studied as probes of water structure in human red blood cells and red blood cell suspensions. Normal saline had a relaxation time of about 3000 ms while packed red blood cells had a relaxation time of about 500 ms. The relaxation time of a red blood cell suspension at 50% hematocrit was about 750 ms showing that surface charges and polar groups of the red cell membrane effectively structure extracellular water. Incubation of red cells in hypotonic saline increases relaxation time whereas hypertonic saline decreases relaxation time. Relaxation times varied independently of mean corpuscular volume and mean corpuscular hemoglobin concentration in a sample population. Studies with lysates and resealed membrane ghosts show that hemoglobin is very effective in lowering water-proton relaxation time whereas resealed membrane ghosts in the absence of hemoglobin are less effective than intact red cells. 9 refs.; 3 figs.; 1 table

  11. Evaluation of biexponential relaxation processes by magnetic resonance imaging. A phantom study

    DEFF Research Database (Denmark)

    Kjaer, L; Thomsen, C; Larsson, H B

    1988-01-01

    Despite the complexity of biologic tissues, a monoexponential behaviour is usually assumed when estimating relaxation processes in vivo by magnetic resonance imaging (MRI). This study was designed to evaluate the potential of biexponential decomposition of T1 and T2 relaxation curves obtained at 1.......5 tesla (T). Measurements were performed on a phantom of bicompartmental perspex boxes with combinations of different CuSO4 concentrations. T1 determination was based on a 12-points partial saturation inversion recovery pulse sequence. T2 determination was provided by a multiple spin echo sequence with 32...

  12. Spin Canting and Magnetic Relaxation Phenomena in Mn0.25Zn0.75Fe2O4

    DEFF Research Database (Denmark)

    Anhøj, T. A.; Olsen, Brian Bilenberg; Thomsen, Benjamin

    2003-01-01

    affected by transverse relaxation at relatively low temperatures. A third group of 13-site ions has negligible canting at low temperatures and these ions are only slightly affected by relaxation below 60 K. At low temperatures the material can be described as a cluster spin glass. Above 60 K part...

  13. Spin-orbit relaxation of Cl(2P½) and F(2P½) in a gas of H2

    NARCIS (Netherlands)

    Abrahamsson, E.; Groenenboom, G.C.; Krems, R.V.

    2007-01-01

    The authors present quantum scattering calculations of rate coefficients for the spin-orbit relaxation of F(P-2(1/2)) atoms in a gas of H-2 molecules and Cl(P-2(1/2)) atoms in a gas of H-2 and D-2 molecules. Their calculation of the thermally averaged rate coefficient for the electronic relaxation

  14. Spin-lattice relaxation within a dimerized Ising chain in a magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Erdem, Rıza, E-mail: rerdem@akdeniz.edu.tr, E-mail: rerdem29@hotmail.com [Department of Physics, Akdeniz University, 07058 Antalya (Turkey); Gülpınar, Gül [Department of Physics, Dokuz Eylül University, 35160 İzmir (Turkey); Yalçın, Orhan [Department of Physics, Niğde University, 51240 Niğde (Turkey); Pawlak, Andrzej [Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61–614 Poznań (Poland)

    2014-07-21

    A qualitative study of the spin-lattice relaxation within a dimerized Ising chain in a magnetic field is presented. We have first determined the time dependence of the deviation of the lattice distortion parameter δΔ from the equilibrium state within framework of a technique combining the statistical equilibrium theory based on the transfer matrix method and the linear theory of irreversible thermodynamics. We have shown that the time dependence of the lattice distortion parameter is characterized by a single time constant (τ) which diverges around the critical point in both dimerized (Δ≠0) and uniform (Δ=0) phase regions. When the temperature and magnetic field are fixed to certain values, the time τ depends only on exchange coupling between the spins. It is a characteristic time associated with the long wavelength fluctuations of distortion. We have also taken into account the effects of spatial fluctuations on the relaxation time using the full Landau-Ginzburg free energy functional. We have found an explicit expression for the relaxation time as a function of temperature, coupling constant and wave vector (q) and shown that the critical mode corresponds to the case q=0. Finally, our results are found to be in good qualitative agreement with the results obtained in recent experimental study on synchrotron x-ray scattering and muon spin relaxation in diluted material Cu{sub 1−y}Mg{sub y}GeO{sub 3} where the composition y is very close to 0.0209. These results can be considered as natural extensions of some previous works on static aspects of the problem.

  15. The effect of a broad activation energy distribution on deuteron spin-lattice relaxation.

    Science.gov (United States)

    Ylinen, E E; Punkkinen, M; Birczyński, A; Lalowicz, Z T

    2015-10-01

    Deuteron NMR spectra and spin-lattice relaxation were studied experimentally in zeolite NaY(2.4) samples containing 100% or 200% of CD3OH or CD3OD molecules of the total coverage of Na atoms in the temperature range 20-150K. The activation energies describing the methyl and hydroxyl motions show broad distributions. The relaxation data were interpreted by improving a recent model (Stoch et al., 2013 [16]) in which the nonexponential relaxation curves are at first described by a sum of three exponentials with adjustable relaxation rates and weights. Then a broad distribution of activation energies (the mean activation energy A0 and the width σ) was assumed for each essentially different methyl and hydroxyl position. The correlation times were calculated from the Arrhenius equation (containing the pre-exponential factor τ0), individual relaxation rates computed and classified into three classes, and finally initial relaxation rates and weights for each class formed. These were compared with experimental data, motional parameters changed slightly and new improved rates and weights for each class calculated, etc. This method was improved by deriving for the deuterons of the A and E species methyl groups relaxation rates, which depend explicitly on the tunnel frequency ωt. The temperature dependence of ωt and of the low-temperature correlation time were obtained by using the solutions of the Mathieu equation for a threefold potential. These dependencies were included in the simulations and as the result sets of A0, σ and τ0 obtained, which describe the methyl and hydroxyl motions in different positions in zeolite. Copyright © 2015 Elsevier Inc. All rights reserved.

  16. Collisional Penrose process with spinning particles

    Science.gov (United States)

    Mukherjee, Sajal

    2018-03-01

    In this article, we have investigated collisional Penrose process (CPP) using spinning particles in a Kerr spacetime. Recent studies have shown that the collision between two spinning particles can produce a significantly high energy in the center of mass frame. Here, we explicitly compute the energy extraction and efficiency as measured by an observer at infinity. We consider the colliding particles as well as the escaping particles may contain spins. It has been shown that the energy extraction is larger than the non-spinning case and also their possibility to escape to infinity is wider than the geodesics.

  17. Formation of local spin-state concentration waves during the relaxation from a photoinduced state in a spin-crossover polymer.

    Science.gov (United States)

    Mariette, Céline; Trzop, Elzbieta; Zerdane, Serhane; Fertey, Pierre; Zhang, Daopeng; Valverde-Muñoz, Francisco J; Real, José Antonio; Collet, Eric

    2017-08-01

    The complex relaxation from the photoinduced high-spin phase (PIHS) to the low-spin phase of the bimetallic two-dimensional coordination spin-crossover polymer [Fe[(Hg(SCN) 3 ) 2 ](4,4'-bipy) 2 ] n is reported. During the thermal relaxation, commensurate and incommensurate spin-state concentration waves (SSCWs) form. However, contrary to the steps forming at thermal equilibrium, associated with long-range SSCW order, the SSCWs forming during the relaxation from the PIHS phase correspond to short-range order, revealed by diffuse X-ray scattering. This is interpreted as resulting from the competition between the two types of SSCW order and another structural symmetry breaking, due to ligand ordering, occurring at low temperature and precluding long-range SSCW order.

  18. Models for multiple relaxation processes in collagen fiber

    Indian Academy of Sciences (India)

    ... originate from stress strain induced changes in hydrogen bond network whereas the other seems to be more strongly coupled to salt like bridges and electrostatic interactions. Urea alters the activation energy for one relaxation step while pH and solvent dielectric constant alter the relaxation behavior one set of processes.

  19. Near-threshold photoionization of the Xe 3d spin-orbit doublet: Relativistic, relaxation, and intershell interaction effects

    International Nuclear Information System (INIS)

    Radojevic, V.; Davidovic, D.M.; Amusia, M.Ya.

    2003-01-01

    Results of calculations of the near-threshold photoionization of the xenon 3d spin-orbit doublet are reported. Our theoretical analysis is undertaken in order to interpret and enlighten the very detailed measurements of this process [A. Kivimaeki et al., Phys. Rev. A 63, 012716 (2001)], which revealed a previously unobserved interesting feature--an additional broad maximum--in the partial xenon 3d 5/2 cross section. This double maximum was not produced by earlier calculations, except in the recent study by Amusia et al. [Phys. Rev. Lett. 88, 093002 (2002)], which, in contrast to the present one, is not ab initio and relativistic in character. The partial photoionization cross sections of 3d 5/2 and 3d 3/2 subshells, photoelectron anisotropy parameters, and spin-polarization parameters that were so far not studied either experimentally or theoretically are calculated. Many-electron correlations, relativistic effects, and relaxation effects of the ionic core in the ionization process are taken into account by using the relativistic random-phase approximation, modified to include the relaxation of the considered subshell

  20. Magnetic properties and proton spin-lattice relaxation in molecular clusters

    International Nuclear Information System (INIS)

    Allalen, M.

    2006-01-01

    In this work we studied magnetic properties of molecular magnets of the new heteropolyanion {Cu 20 }, dodecanuclear cluster {Ni 12 }, and the heterometallic {Cr 7 M} wheels, in which one of the Cr III ions of Cr 8 has been replaced by a Fe, Cu, Zn, Ni, ion with this extra-spin acts as local probe for the spin dynamics. Such systems have been synthesized recently and they are well described using the Heisenberg spin Hamiltonian with a Zeeman term of an applied magnetic field along the z-axis. Using the numerical exact diagonalization method, we have calculated the energy spectrum and the eigenstates for different compounds, and we have used them for reexamining the available experimental susceptibility data to determine the values of exchange parameters. We have studied the thermodynamic properties such magnetization, susceptibility, heat-capacity. At low temperature regions molecular magnets act as individual quantum nanomagnets and can display super-paramagnetic phenomena like macroscopic quantum tunneling, ground state degeneracy, level-crossing. A crucial issue for understanding these phenomena is the coupling between magnetic molecular levels and the environment such as nuclear spins. We have modeled the behavior of the proton spin lattice relaxation rate as a function of applied magnetic field for low temperatures as it is measured in Nuclear Magnetic Resonance (NMR) experiments. (orig.)

  1. Investigation of proton spin relaxation in water with dispersed silicon nanoparticles for potential magnetic resonance imaging applications

    Science.gov (United States)

    Kargina, Yu. V.; Gongalsky, M. B.; Perepukhov, A. M.; Gippius, A. A.; Minnekhanov, A. A.; Zvereva, E. A.; Maximychev, A. V.; Timoshenko, V. Yu.

    2018-03-01

    Porous and nonporous silicon (Si) nanoparticles (NPs) prepared by ball-milling of electrochemically etched porous Si layers and crystalline Si wafers were studied as potential agents for enhancement of the proton spin relaxation in aqueous media. While nonporous Si NPs did not significantly influence the spin relaxation, the porous ones resulted in strong shortening of the transverse relaxation times. In order to investigate an effect of the electron spin density in porous Si NPs on the proton spin relaxation, we use thermal annealing of the NPs in vacuum or in air. The transverse relaxation rate of about 0.5 l/(g s) was achieved for microporous Si NPs, which were thermally annealing in vacuum to obtain the electron spin density of the order of 1017 g-1. The transverse relaxation rate was found to be almost proportional to the concentration of porous Si NPs in the range from 0.1 to 20 g/l. The obtained results are discussed in view of possible biomedical applications of Si NPs as contrast agents for magnetic resonance imaging.

  2. Insight into lithium transport in lithium nitridometallate battery materials from muon spin relaxation.

    Science.gov (United States)

    Powell, Andrew S; Stoeva, Zlatka; Lord, James S; Smith, Ronald I; Gregory, Duncan H; Titman, Jeremy J

    2013-01-21

    Muon spin relaxation and powder neutron diffraction have been combined to study three lithium cobalt nitride battery materials. Neutron diffraction shows that these retain the P6/mmm space group of Li(3)N with Co located only on Li(1) sites. The lattice parameters vary smoothly with the degree of metal substitution, such that the [Li(2)N] layers expand while the layer separation contracts, as observed previously for similar series of Cu- and Ni-substituted materials. However, in contrast to the latter, the Li(3-x-y)Co(x)N phases exhibit Curie-Weiss paramagnetism and this prevents the use of nuclear magnetic resonance to measure Li(+) transport parameters. Therefore, muon spin relaxation has been employed here as an alternative technique to obtain quantitative information about Li(+) diffusion. Muon spin relaxation shows that Li(+) diffusion in Li(3-x-y)Co(x)N is anisotropic with transport confined to the [Li(2)N] plane at low temperature and exchange between Li(1) and Li(2) sites dominant at high temperature. By a comparison with previous studies some general trends have been established across a range of Cu-, Ni- and Co-substituted materials. For intra-layer diffusion E(a) decreases as metal substitution increases and the corresponding expansion of the layers results in a more open pathway for Li(+) diffusion. However, an optimal value of x is found with a ≈ 3.69 Å after which the concomitant contraction in layer spacing reduces the polarizability of the lattice framework.

  3. Nuclear spin relaxation/resonance of {sup 8}Li in Al

    Energy Technology Data Exchange (ETDEWEB)

    Wang, D. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Salman, Z. [Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU (United Kingdom); ISIS Facility, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX (United Kingdom); Chow, K.H.; Fan, I. [Department of Physics, University of Alberta, Edmonton, AB, T6G 2G7 (Canada); Hossain, M.D.; Keeler, T.A. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Kiefl, R.F., E-mail: kiefl@triumf.c [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Canadian Institute for Advanced Research (Canada); Levy, C.D.P. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Mansour, A.I. [Department of Physics, University of Alberta, Edmonton, AB, T6G 2G7 (Canada); Morris, G.D.; Pearson, M.R. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Parolin, T.J. [Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z3 (Canada); Saadaoui, H.; Smadella, M.; Song, Q. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); MacFarlane, W.A. [Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z3 (Canada)

    2009-04-15

    A low energy beam of spin polarized {sup 8}Li has been used to study the behaviour of isolated {sup 8}Li implanted into a 150 nm thick film of Al on an MgO substrate. The spin relaxation rate 1/T{sub 1} and beta-NMR lineshape were measured as a function of temperature in a large magnetic field of 4.1 T. The resonances from different sites are unresolved due to the large nuclear dipolar interaction with the host {sup 27}Al magnetic dipole moments. Nevertheless the temperature variation of the site averaged 1/T{sub 1} and Knight shift show evidence for a transition between the octahedral O and substitutional S sites at about 150 K, as observed in other fcc metals.

  4. Coexisting static magnetic ordering and superconductivity in CeCu2.1Si2 found by muon spin relaxation

    Science.gov (United States)

    Uemura, Y. J.; Kossler, W. J.; Yu, X. H.; Schone, H. E.; Kempton, J. R.; Stronach, C. E.; Barth, S.; Gygax, F. N.; Hitti, B.; Schenck, A.

    1988-01-01

    Zero- and longitudinal-field muon spin relaxation measurements on a heavy fermion system CeCu2.1 Si2 have revealed an onset of static magnetic ordering below T(M) approximately 0.8 K, which coexists with superconductivity below T(c) = 0.7 K. The line shapes of the observed muon spin depolarization functions suggest an ordering in either spin glass or incommensurate spin-density-wave state, with a small averaged static moment of the order of 0.1 micro-B per formula unit at T approaches 0.

  5. Theory of relaxation phenomena in a spin-3/2 Ising system near the second-order phase transition temperature

    International Nuclear Information System (INIS)

    Keskin, Mustafa; Canko, Osman

    2005-01-01

    The relaxation behavior of the spin-3/2 Ising model Hamiltonian with bilinear and biquadratic interactions near the second-order phase transition temperature or critical temperature is studied by means of the Onsager's theory of irreversible thermodynamics or the Onsager reciprocity theorem (ORT). First, we give the equilibrium case briefly within the molecular-field approximation in order to study the relaxation behavior by using the ORT. Then, the ORT is applied to the model and the kinetic equations are obtained. By solving these equations, three relaxation times are calculated and examined for temperatures near the second-order phase transition temperature. It is found that one of the relaxation times goes to infinity near the critical temperature on either side, the second relaxation time makes a cusp at the critical temperature and third one behaves very differently in which it terminates at the critical temperature while approaching it, then showing a 'flatness' property and then decreases. We also study the influences of the Onsager rate coefficients on the relaxation times. The behavior of these relaxation times is discussed and compared with the spin-1/2 and spin-1 Ising systems

  6. Unconventional superconductivity in Y5Rh6Sn18 probed by muon spin relaxation.

    Science.gov (United States)

    Bhattacharyya, Amitava; Adroja, Devashibhai; Kase, Naoki; Hillier, Adrian; Akimitsu, Jun; Strydom, Andre

    2015-08-19

    Conventional superconductors are robust diamagnets that expel magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high-temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor Y5Rh6Sn18 ( TC= 3.0 K). The electronic heat capacity of Y5Rh6Sn18 shows a T(3) dependence below Tc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu5Rh6Sn18 which is a strong coupling s-wave superconductor. The temperature dependence of the deduced superfluid in density Y5Rh6Sn18 is consistent with a BCS s-wave gap function, while the zero-field muon spin relaxation measurements strongly evidences unconventional superconductivity through a spontaneous appearance of an internal magnetic field below the superconducting transition temperature, signifying that the superconducting state is categorized by the broken time-reversal symmetry.

  7. Magnetization and 13C NMR spin-lattice relaxation of nanodiamond powder

    Energy Technology Data Exchange (ETDEWEB)

    Levin, E.M.; Fang, X.W.; Bud' ko, S.L.; Straszheim, W.E.; McCallum, R.W.; Schmidt-Rohr, K.

    2008-02-15

    The bulk magnetization at temperatures of 1.8-400 K and in magnetic fields up to 70 kOe, the ambient temperature {sup 13}C NMR spin-lattice relaxation, T{sub 1,c}, and the elemental composition of three nanodiamond powder samples have been studied. The total magnetization of nanodiamond can be explained in terms of contributions from (1) the diamagnetic effect of carbon, (2) the paramagnetic effect of unpaired electrons present in nanodiamond grains, and (3) ferromagnetic-like and (4) superparamagnetic contributions from Fe-containing particles detected in spatially resolved energy-dispersive spectroscopy. Contributions (1) and (2) are intrinsic to nanodiamond, while contributions (3) and (4) arise from impurities naturally present in detonation nanodiamond samples. {sup 13}C NMR T{sub 1,c} relaxation would be unaffected by the presence of the ferromagnetic particles with the bulk magnetization of {approx} 0.01 emu/g at 300 K. Thus, a reduction of T{sub 1,c} by 3 orders of magnitude compared to natural and synthetic microdiamonds confirms the presence of unpaired electrons in the nanodiamond grains. The spin concentration in nanodiamond powder corresponds to {approx}30 unpaired electrons per {approx}4.6 nm diameter nanodiamond grain.

  8. Slow spin relaxation induced by magnetic field in [NdCo(bpdo)(H2O)4(CN)6]⋅3H2O.

    Science.gov (United States)

    Vrábel, P; Orendáč, M; Orendáčová, A; Čižmár, E; Tarasenko, R; Zvyagin, S; Wosnitza, J; Prokleška, J; Sechovský, V; Pavlík, V; Gao, S

    2013-05-08

    We report on a comprehensive investigation of the magnetic properties of [NdCo(bpdo)(H2O)4(CN)6]⋅3H2O (bpdo=4, 4'-bipyridine-N,N'-dioxide) by use of electron paramagnetic resonance, magnetization, specific heat and susceptibility measurements. The studied material was identified as a magnet with an effective spin S = 1/2 and a weak exchange interaction J/kB = 25 mK. The ac susceptibility studies conducted at audio frequencies and at temperatures from 1.8 to 9 K revealed that the application of a static magnetic field induces a slow spin relaxation. It is suggested that the relaxation in the magnetic field appears due to an Orbach-like process between the two lowest doublet energy states of the magnetic Nd(3+) ion. The appearance of the slow relaxation in a magnetic field cannot be associated with a resonant phonon trapping. The obtained results suggest that the relaxation is influenced by nuclear spin driven quantum tunnelling which is suppressed by external magnetic field.

  9. Spin-polarization dependent carrier recombination dynamics and spin relaxation mechanism in asymmetrically doped (110) n-GaAs quantum wells

    Science.gov (United States)

    Teng, Lihua; Jiang, Tianran; Wang, Xia; Lai, Tianshu

    2018-05-01

    Carrier recombination and electron spin relaxation dynamics in asymmetric n-doped (110) GaAs/AlGaAs quantum wells are investigated with time-resolved pump-probe spectroscopy. The experiment results reveal that the measured carrier recombination time depends strongly on the polarization of pump pulse. With the same pump photon flux densities, the recombination time of spin-polarized carriers is always longer than that of the spin-balanced carriers except at low pump photon flux densities, this anomaly originates from the polarization-sensitive nonlinear absorption effect. Differing from the traditional views, in the low carrier density regime, the D'yakonov-Perel' (DP) mechanism can be more important than the Bir-Aronov-Pikus (BAP) mechanism, since the DP mechanism takes effect, the spin relaxation time in (110) GaAs QWs is shortened obviously via asymmetric doping.

  10. Solute-Vacancy Clustering In Al-Mg-Si Alloys Studied By Muon Spin Relaxation Technique

    Directory of Open Access Journals (Sweden)

    Nishimura K.

    2015-06-01

    Full Text Available Zero-field muon spin relaxation experiments were carried out with Al-1.6%Mg2Si, Al-0.5%Mg, and Al-0.5%Si alloys. Observed relaxation spectra were compared with the calculated relaxation functions based on the Monte Carlo simulation to extract the dipolar width (Δ, trapping (νt, and detrapping rates (νd, with the initially trapped muon fraction (P0. The fitting analysis has elucidated that the muon trapping rates depended on the heat treatment and solute concentrations. The dissolved Mg in Al dominated the νt at lower temperatures below 120 K, therefore the similar temperature variations of νt were observed with the samples mixed with Mg. The νt around 200 K remarkably reflected the heat treatment effect on the samples, and the largest νt value was found with the sample annealed at 100°C among Al-1.6%Mg2Si alloys. The as-quenched Al-0.5%Si sample showed significant νt values between 80 and 280 K relating with Si-vacancy clusters, but such clusters disappeared with the natural aged Al-0.5%Si sample.

  11. Spin versus helicity in processes involving transversity

    CERN Document Server

    Mekhfi, Mustapha

    2011-01-01

    We construct the spin formalism in order to deal in a direct and natural way with processes involving transversity which are now of increasing popularity. The helicity formalism which is more appropriate for collision processes of definite helicity has been so far used also to manage processes with transversity, but at the price of computing numerous helicity amplitudes generally involving unnecessary kinematical variables.In a second step we work out the correspondence between both formalisms and retrieve in another way all results of the helicity formalism but in simpler forms.We then compute certain processes for comparison.A special process:the quark dipole magnetic moment is shown to be exclusively treated within the spin formalism as it is directly related to the transverse spin of the quark inside the baryon.

  12. Optical Transient-Grating Measurements of Spin Diffusion and Relaxation in a Two-Dimensional Electron Gas

    International Nuclear Information System (INIS)

    Weber, Christopher P.

    2005-01-01

    Spin diffusion in n-GaAs quantum wells, as measured by our optical transient-grating technique, is strongly suppressed relative to that of charge. Over a broad range of temperatures and dopings, the suppression of Ds relative to Dc agrees quantitatively with the prediction of ''spin Coulomb dra'' theory, which takes into account the exchange of spin in electron-electron collisions. Moreover, the spin-diffusion length, Ls, is a nearly constant 1 micrometer over the same range of T and n, despite Ds's varying by nearly two orders of magnitude. This constancy supports the D'yakonov-Perel'-Kachorovskii model of spin relaxation through interrupted precessional dephasing in the spin-orbit field

  13. Optical Transient-Grating Measurements of Spin Diffusion andRelaxation in a Two-Dimensional Electron Gas

    Energy Technology Data Exchange (ETDEWEB)

    Weber, Christopher Phillip [Univ. of California, Berkeley, CA (United States)

    2005-01-01

    Spin diffusion in n-GaAs quantum wells, as measured by our optical transient-grating technique, is strongly suppressed relative to that of charge. Over a broad range of temperatures and dopings, the suppression of Ds relative to Dc agrees quantitatively with the prediction of ''spin Coulomb dra'' theory, which takes into account the exchange of spin in electron-electron collisions. Moreover, the spin-diffusion length, Ls, is a nearly constant 1 micrometer over the same range of T and n, despite Ds's varying by nearly two orders of magnitude. This constancy supports the D'yakonov-Perel'-Kachorovskii model of spin relaxation through interrupted precessional dephasing in the spin-orbit field.

  14. Electron spin-lattice relaxation of the S0 state of the oxygen-evolving complex in photosystem II and of dinuclear manganese model complexes.

    Science.gov (United States)

    Kulik, L V; Lubitz, W; Messinger, J

    2005-07-05

    The temperature dependence of the electron spin-lattice relaxation time T1 was measured for the S0 state of the oxygen-evolving complex (OEC) in photosystem II and for two dinuclear manganese model complexes by pulse EPR using the inversion-recovery method. For [Mn(III)Mn(IV)(mu-O)2 bipy4]ClO4, the Raman relaxation process dominates at temperatures below 50 K. In contrast, Orbach type relaxation was found for [Mn(II)Mn(III)(mu-OH)(mu-piv)2(Me3 tacn)2](ClO4)2 between 4.3 and 9 K. For the latter complex, an energy separation of 24.7-28.0 cm(-1) between the ground and the first excited electronic state was determined. In the S0 state of photosystem II, the T1 relaxation times were measured in the range of 4.3-6.5 K. A comparison with the relaxation data (rate and pre-exponential factor) of the two model complexes and of the S2 state of photosystem II indicates that the Orbach relaxation process is dominant for the S0 state and that its first excited state lies 21.7 +/- 0.4 cm(-1) above its ground state. The results are discussed with respect to the structure of the OEC in photosystem II.

  15. Interaction study of polyisobutylene with paraffins by NMR using the evaluation of spin-lattice relaxation times for hydrogen nuclei

    International Nuclear Information System (INIS)

    Marques, Rosana G.G.; Tavares, Maria I.B.

    2001-01-01

    The evaluation of spin-lattice relaxation times of 1 H for polyisobutylene/paraffin systems, were obtained using the classic inversion recovery technique, and also through Cross Polarization Magic Angle Spinning (CP/MAS) techniques varying the contact time and also by the delayed contact time pulse sequence. NMR results showed that the polyisobutylene/paraffin systems in which high molecular weight paraffins were used, is heterogeneous. However, for paraffins with low molecular weight, the system presents good homogeneity. (author)

  16. Matrix-assisted relaxation in Fe(phen){sub 2}(NCS){sub 2} spin-crossover microparticles, experimental and theoretical investigations

    Energy Technology Data Exchange (ETDEWEB)

    Enachescu, Cristian, E-mail: cristian.enachescu@uaic.ro; Stancu, Alexandru [Faculty of Physics, “Alexandru Ioan Cuza” University, 700506 Iasi (Romania); Tanasa, Radu [Faculty of Physics, “Alexandru Ioan Cuza” University, 700506 Iasi (Romania); Department of Engineering, University of Cambridge, CB2 1PZ Cambridge (United Kingdom); Tissot, Antoine [Institut de Chimie Moléculaire et des Matériaux d' Orsay, Université Paris Sud, Université Paris-Saclay, CNRS, 91405 Orsay (France); Institut Lavoisier de Versailles, UMR 8180, CNRS, Université de Versailles-Saint Quentin en Yvelines, 78035 Versailles (France); Laisney, Jérôme; Boillot, Marie-Laure, E-mail: marie-laure.boillot@u-psud.fr [Institut de Chimie Moléculaire et des Matériaux d' Orsay, Université Paris Sud, Université Paris-Saclay, CNRS, 91405 Orsay (France)

    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 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.

  17. Muon spin relaxation study of spin dynamics in the extended kagome systems YBaCo4O7 +δ (δ =0 ,0.1 )

    Science.gov (United States)

    Lee, S.; Lee, Wonjun; Lee, K. J.; Kim, ByungJun; Suh, B. J.; Zheng, H.; Mitchell, J. F.; Choi, K.-Y.

    2018-03-01

    We present muon spin relaxation (μ SR ) measurements of the extended kagome systems YBaCo4O7 +δ (δ =0 ,0.1 ), comprising two interpenetrating kagome sublattice of Co (I) 3 + (S =3 /2 ) and a triangle sublattice of Co (II) 2 + (S =2 ). The zero- and longitudinal-field μ SR spectra of the stoichiometric compound YBaCo4O7 unveil that the triangular subsystem orders at TN=101 K. In contrast, the muon spin relaxation rate pertaining to the kagome subsystem shows persistent spin dynamics down to T =20 K and then a sublinear decrease λ (T ) ˜T0.66 (5 ) on cooling towards T =4 K. In addition, the introduction of interstitial oxygen (δ =0.1 ) is found to drastically affect the magnetism. For the fast-cooling experiment (>10 K/min), YBaCo4O7.1 enters a regime characterized by persistent spin dynamics below 90 K. For the slow-cooling experiment (1 K/min), evidence is obtained for the phase separation into interstitial oxygen-poor and oxygen-rich regions with distinct correlation times. The observed temperature, cooling rate, and oxygen content dependencies of spin dynamics are discussed in terms of a broad range of spin-spin correlation times, relying on a different degree of frustration between the kagome and triangle sublattices as well as of oxygen migration.

  18. Relaxation cracking in the process industry, an underestimated problem

    Energy Technology Data Exchange (ETDEWEB)

    Wortel, J.C. van [TNO Institute of Industrial Technology, Apeldoorn (Netherlands)

    1998-12-31

    Austenitic components, operating between 500 and 750 deg C, can fail within 1 year service while the ordinary mechanical properties after failure are still within the code requirements. The intergranular brittle failures are situated in the welded or cold deformed areas. This type of cracking has many names, showing the uncertainty concerning the mechanism for the (catastrophical) failures. A just finished investigation showed that it is a relaxation crack problem, introduced by manufacturing processes, especially welding and cold rolling. Cracking/failures can be expected after only 0.1- 0.2 % relaxation strain. These low strain values can already be generated during relaxation of the welding stresses. Especially coarse grained `age hardening` materials are susceptible. Stabilising and Postweld Heat Treatments are very effective to avoid relaxation crack problems during operation. After these heat treatments the components can withstand more than 2 % relaxation strain. At temperatures between 500 and 750 deg C relaxation cracking is the predominant factor for the safety and lifetime of welded austenitic components. (orig.) 12 refs.

  19. The Effect of Phonon Relaxation Process on Absorption Spectra ...

    African Journals Online (AJOL)

    In this work we study the effect of phonon relaxation process on the absorption spectra using the Green's function technique. The Green's function technique which is widely used in many particle problems is used to solve the Kubo formula which describes the optical absorption process. Finally the configurational diagram is ...

  20. Relaxation theory of spin-3/2 Ising system near phase transition temperatures

    International Nuclear Information System (INIS)

    Canko, Osman; Keskin, Mustafa

    2010-01-01

    Dynamics of a spin-3/2 Ising system Hamiltonian with bilinear and biquadratic nearest-neighbour exchange interactions is studied by a simple method in which the statistical equilibrium theory is combined with the Onsager's theory of irreversible thermodynamics. First, the equilibrium behaviour of the model in the molecular-field approximation is given briefly in order to obtain the phase transition temperatures, i.e. the first- and second-order and the tricritical points. Then, the Onsager theory is applied to the model and the kinetic or rate equations are obtained. By solving these equations three relaxation times are calculated and their behaviours are examined for temperatures near the phase transition points. Moreover, the z dynamic critical exponent is calculated and compared with the z values obtained for different systems experimentally and theoretically, and they are found to be in good agrement. (general)

  1. Study of the operation temperature in the spin-exchange relaxation free magnetometer

    International Nuclear Information System (INIS)

    Fang, Jiancheng; Li, Rujie; Duan, Lihong; Chen, Yao; Quan, Wei

    2015-01-01

    We study the influence of the cell temperature on the sensitivity of the spin-exchange relaxation free (SERF) magnetometer and analyze the possibility of operating at a low temperature. Utilizing a 25 × 25 × 25 mm 3 Cs vapor cell with a heating temperature of 85  ∘ C, which is almost half of the value of potassium, we obtain a linewidth of 1.37 Hz and achieve a magnetic field sensitivity of 55 fT/Hz 1/2 in a single channel. Theoretical analysis shows that fundamental sensitivity limits of this device with an active volume of 1 cm 3 could approach 1 fT/Hz 1/2 . Taking advantage of the higher saturated vapor pressure, SERF magnetometer based on Cs opens up the possibility for low cost and portable sensors and is particularly appropriate for lower temperature applications

  2. Study of the operation temperature in the spin-exchange relaxation free magnetometer

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Jiancheng; Li, Rujie, E-mail: lirujie@buaa.edu.cn; Duan, Lihong; Chen, Yao; Quan, Wei [School of Instrument Science and Opto-Electronics Engineering, Beihang University, Beijing 100191 (China)

    2015-07-15

    We study the influence of the cell temperature on the sensitivity of the spin-exchange relaxation free (SERF) magnetometer and analyze the possibility of operating at a low temperature. Utilizing a 25 × 25 × 25 mm{sup 3} Cs vapor cell with a heating temperature of 85 {sup ∘}C, which is almost half of the value of potassium, we obtain a linewidth of 1.37 Hz and achieve a magnetic field sensitivity of 55 fT/Hz{sup 1/2} in a single channel. Theoretical analysis shows that fundamental sensitivity limits of this device with an active volume of 1 cm{sup 3} could approach 1 fT/Hz{sup 1/2}. Taking advantage of the higher saturated vapor pressure, SERF magnetometer based on Cs opens up the possibility for low cost and portable sensors and is particularly appropriate for lower temperature applications.

  3. Gaussian signal relaxation around spin echoes: Implications for precise reversible transverse relaxation quantification of pulmonary tissue at 1.5 and 3 Tesla.

    Science.gov (United States)

    Zapp, Jascha; Domsch, Sebastian; Weingärtner, Sebastian; Schad, Lothar R

    2017-05-01

    To characterize the reversible transverse relaxation in pulmonary tissue and to study the benefit of a quadratic exponential (Gaussian) model over the commonly used linear exponential model for increased quantification precision. A point-resolved spectroscopy sequence was used for comprehensive sampling of the relaxation around spin echoes. Measurements were performed in an ex vivo tissue sample and in healthy volunteers at 1.5 Tesla (T) and 3 T. The goodness of fit using χred2 and the precision of the fitted relaxation time by means of its confidence interval were compared between the two relaxation models. The Gaussian model provides enhanced descriptions of pulmonary relaxation with lower χred2 by average factors of 4 ex vivo and 3 in volunteers. The Gaussian model indicates higher sensitivity to tissue structure alteration with increased precision of reversible transverse relaxation time measurements also by average factors of 4 ex vivo and 3 in volunteers. The mean relaxation times of the Gaussian model in volunteers are T2,G' = (1.97 ± 0.27) msec at 1.5 T and T2,G' = (0.83 ± 0.21) msec at 3 T. Pulmonary signal relaxation was found to be accurately modeled as Gaussian, providing a potential biomarker T2,G' with high sensitivity. Magn Reson Med 77:1938-1945, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  4. Organic light-emitting devices using spin-dependent processes

    Science.gov (United States)

    Vardeny, Z. Valy; Wohlgenannt, Markus

    2010-03-23

    The maximum luminous efficiency of organic light-emitting materials is increased through spin-dependent processing. The technique is applicable to all electro-luminescent processes in which light is produced by singlet exciton decay, and all devices which use such effects, including LEDs, super-radiant devices, amplified stimulated emission devices, lasers, other optical microcavity devices, electrically pumped optical amplifiers, and phosphorescence (Ph) based light emitting devices. In preferred embodiments, the emissive material is doped with an impurity, or otherwise modified, to increase the spin-lattice relaxation rate (i.e., decrease the spin-lattice time), and hence raise the efficiency of the device. The material may be a polymer, oligomer, small molecule, single crystal, molecular crystal, or fullerene. The impurity is preferably a magnetic or paramagnetic substance. The invention is applicable to IR, UV, and other electromagnetic radiation generation and is thus not limited to the visible region of the spectrum. The methods of the invention may also be combined with other techniques used to improve device performance.

  5. Spin relaxation studies of Li+ion dynamics in polymer gel electrolytes.

    Science.gov (United States)

    Brinkkötter, M; Gouverneur, M; Sebastião, P J; Vaca Chávez, F; Schönhoff, M

    2017-03-08

    Two ternary polymer gel electrolyte systems are compared, containing either polyethylene oxide (PEO) or the poly-ionic liquid poly(diallyldimethylammonium) bis(trifluoromethyl sulfonyl)imide (PDADMA-TFSI). Both gel types are based on the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl sulfonyl)imide (P 14 TFSI) and LiTFSI. We study the influence of the polymers on the local lithium ion dynamics at different polymer concentrations using 7 Li spin-lattice relaxation data in dependence on frequency and temperature. In all cases the relaxation rates are well described by the Cole-Davidson motional model with Arrhenius dependence of the correlation time and a temperature dependent quadrupole coupling constant. For both polymers the correlation times are found to increase with polymer concentration. The activation energy of local motions slightly increases with increasing PEO concentration, and slightly decreases with increasing PDADMA-TFSI concentration. Thus the local Li + motion is reduced by the presence of either polymer; however, the reduction is less effective in the PDADMA + samples. We thus conclude that mechanical stabilization of a liquid electrolyte by a polymer can be achieved at a lower decrease of Li + motion when a cationic polymer is used instead of PEO.

  6. Solid state proton spin-lattice relaxation in four structurally related organic molecules

    International Nuclear Information System (INIS)

    Beckmann, Peter A.; Burbank, Kendra S.; Lau, Matty M.W.; Ree, Jessica N.; Weber, Tracy L.

    2003-01-01

    We report and interpret the temperature dependence of the proton spin-lattice relaxation rate at 8.50 and 22.5 MHz in four polycrystalline solids composed of structurally related molecules: 2-ethylanthracene, 2-t-butylanthracene, 2-ethylanthraquinone, and 2-t-butylanthraquinone. We have been unable to grow single crystals and therefore do not know the crystal structures. Hence, we use the NMR relaxometry data to make predictions about the solid state structures. As expected, we are able to conclude that the ethyl groups do not reorient in the solid state but that the t-butyl groups do. The anthraquinones have a ''simpler'' structure than the anthracenes. The best dynamical models suggest that there is a unique crystallographic site for the t-butyl groups in 2-t-butylanthraquinone and two sites, each with half the molecules, for the ethyl groups in 2-ethylanthraquinone. There are also two sites in 2-ethylanthracene, but with unequal weights, suggesting four sites in the unit cell with lower symmetry than the two anthraquinones. Finally, the observed relaxation rate data in 2-t-butylanthracene is very complex and its interpretation demonstrates the uniqueness problem that arises in interpreting relaxometry data without the knowledge of the crystal structure

  7. Anisotropic Rotational Diffusion Studied by Nuclear Spin Relaxation and Molecular Dynamics Simulation: An Undergraduate Physical Chemistry Laboratory

    Science.gov (United States)

    Fuson, Michael M.

    2017-01-01

    Laboratories studying the anisotropic rotational diffusion of bromobenzene using nuclear spin relaxation and molecular dynamics simulations are described. For many undergraduates, visualizing molecular motion is challenging. Undergraduates rarely encounter laboratories that directly assess molecular motion, and so the concept remains an…

  8. Planar quark diagrams and binary spin processes

    International Nuclear Information System (INIS)

    Grigoryan, A.A.; Ivanov, N.Ya.

    1986-01-01

    Contributions of planar diagrams to the binary scattering processes are analyzed. The analysis is based on the predictions of quark-gluon picture of strong interactions for the coupling of reggeons with quarks as well as on the SU(6)-classification of hadrons. The dependence of contributions of nonplanar corrections on spins and quark composition of interacting particles is discussed

  9. Measurements of the nuclear spin-spin relaxation times for commensurate {sup 3}He-Ne films adsorbed on hexagonal boron nitride

    Energy Technology Data Exchange (ETDEWEB)

    Parks, C; Sullivan, N S [Department of Physics, University of Florida, Gainesville, FL 32611 (United States); Stachowiak, P [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, 50-950 Wroclaw (Poland)], E-mail: Sullivan@phys.ufl.edu

    2009-02-01

    Measurements of the {sup 3}He nuclear spin-spin relaxation time, T{sub 2}, have been carried out for commensurate layers of {sup 3}He-Ne mixtures adsorbed on hexagonal boron nitride for temperatures 0.2< T <10 K. A temperature independent relaxation is observed at low temperatures and is interpreted in terms of the effective exchange frequencies for {sup 3}He particle exchange on the surface. The results show a strong dependence on the fraction of neon in the adsorbed layer. This variation is discussed in terms of a multiple spin exchange model for {sup 3}He in a monolayer. The contributions to T{sub 2} from different components of the exchange, 2-spin exchange (J{sub 2}), 3-spin exchange (J{sub 3}), 4-spin exchange (J{sub 4}) and higher exchange permutations depend on the {sup 3}He coverage and thus permit the separation of the amplitudes of the different exchange rates, and in particular allow one to deduce the relative strengths of 2-atom and 3-atom exchange where other methods are sensitive only to the effective two-particle term J{sub eff} = J{sub 2} - 2J{sub 3}.

  10. Coherence and relaxation in energy transfer processes in condensed phases

    International Nuclear Information System (INIS)

    Shelby, R.M.

    1978-03-01

    Investigations of electronic triplet and vibrational energy transfer dynamics and relaxation processes are presented. Emphasis is placed on understanding the role of coherence and interactions which tend to destroy the coherence. In the case of triplet excitons at low temperatures, the importance of coherence in energy migration can be established, and the average coherence parameters can be experimentally determined. In the case of vibrational excitations, both picosecond spectroscopic studies of vibrational relaxation and spontaneous Raman spectroscopy are used to characterize the dynamics and give increased insight into the nature of the mechanisms responsible for vibrational dephasing. The design and operation of the picosecond apparatus used in these experiments is also described

  11. An approach to the magnetic relaxation processes in lithium ferrites

    International Nuclear Information System (INIS)

    Torres, C.; Gonzalez Arias, A.; Hernandez-Gomez, P.; Francisco, C. de; Alejos, O.; Munoz, J.M.; Zazo, M.

    2007-01-01

    The relaxation of the initial magnetic permeability has been measured in polycrystalline Li x Fe 3- x O 4 samples, with x ranging from 0 to 0.5, by means of the magnetic disaccommodation (DA) technique. We have found that there is no abrupt transition for a given composition, but there is a progressive modification of the characteristic relaxation processes of magnetite. These results have been interpreted on the basis of the increasing amount of Li ions in the spinel lattice and hence, the resulting modifications on their proximities

  12. Electronic relaxation processes in poly(p-phenylene)

    International Nuclear Information System (INIS)

    Butlers, P.I.; Knoblikh, G.

    1987-01-01

    Results of an experimental study of the electronic relaxation processes in X-irradiated solid films of poly(p-phenylene) (PPP) by the fractional glow technique are presented. The obtained results suggest two temperature regions of the relaxation: a low-temperature region (T 170 K) where the interpolaron hopping occurs, and a high-temperature one (T 170 K) where the relaxation is due to thermally activated interchain polaron hopping which results in the formation and radiative recombination of the self-localized (polaronic) exciton. The activation energy and the frequency factor of the interchain polaron hopp in the PPP have the values about 0.65 eV and 5x10 13 s -1 , respectively

  13. Local spin dynamics at low temperature in the slowly relaxing molecular chain [Dy(hfac)3(NIT(C6H4OPh))]: A μ{sup +} spin relaxation study

    Energy Technology Data Exchange (ETDEWEB)

    Arosio, Paolo, E-mail: paolo.arosio@guest.unimi.it; Orsini, Francesco [Department of Physics, Università degli Studi di Milano, and INSTM, Milano (Italy); Corti, Maurizio [Department of Physics, Università degli Studi di Pavia and INSTM, Pavia (Italy); Mariani, Manuel [Department of Physics and Astronomy, Università degli Studi di Bologna, Bologna (Italy); Bogani, Lapo [Physikalisches Institut, Universität Stuttgart, Stuttgart (Germany); Caneschi, Andrea [INSTM and Department of Chemistry, University of Florence, Firenze (Italy); Lago, Jorge [Departamento de Quimica Inorganica, Universidad del Pais Vasco, Bilbao (Spain); Lascialfari, Alessandro [Department of Physics, Università degli Studi di Milano, and INSTM, Milano (Italy); Centro S3, Istituto Nanoscienze - CNR, Modena (Italy)

    2015-05-07

    The spin dynamics of the molecular magnetic chain [Dy(hfac){sub 3}(NIT(C{sub 6}H{sub 4}OPh))] were investigated by means of the Muon Spin Relaxation (μ{sup +}SR) technique. This system consists of a magnetic lattice of alternating Dy(III) ions and radical spins, and exhibits single-chain-magnet behavior. The magnetic properties of [Dy(hfac){sub 3}(NIT(C{sub 6}H{sub 4}OPh))] have been studied by measuring the magnetization vs. temperature at different applied magnetic fields (H = 5, 3500, and 16500 Oe) and by performing μ{sup +}SR experiments vs. temperature in zero field and in a longitudinal applied magnetic field H = 3500 Oe. The muon asymmetry P(t) was fitted by the sum of three components, two stretched-exponential decays with fast and intermediate relaxation times, and a third slow exponential decay. The temperature dependence of the spin dynamics has been determined by analyzing the muon longitudinal relaxation rate λ{sub interm}(T), associated with the intermediate relaxing component. The experimental λ{sub interm}(T) data were fitted with a corrected phenomenological Bloembergen-Purcell-Pound law by using a distribution of thermally activated correlation times, which average to τ = τ{sub 0} exp(Δ/k{sub B}T), corresponding to a distribution of energy barriers Δ. The correlation times can be associated with the spin freezing that occurs when the system condenses in the ground state.

  14. NMR spin relaxation in proteins: The patterns of motion that dissipate power to the bath

    Science.gov (United States)

    Shapiro, Yury E.; Meirovitch, Eva

    2014-04-01

    We developed in recent years the two-body coupled-rotator slowly relaxing local structure (SRLS) approach for the analysis of NMR relaxation in proteins. The two bodies/rotators are the protein (diffusion tensor D1) and the spin-bearing probe, e.g., the 15N-1H bond (diffusion tensor, D2), coupled by a local potential (u). A Smoluchowski equation is solved to yield the generic time correlation functions (TCFs), which are sums of weighted exponentials (eigenmodes). By Fourier transformation one obtains the generic spectral density functions (SDFs) which underlie the experimental relaxation parameters. The typical paradigm is to characterize structural dynamics in terms of the best-fit values of D1, D2, and u. Additional approaches we pursued employ the SRLS TCFs, SDFs, or eigenmodes as descriptors. In this study we develop yet another perspective. We consider the SDF as function of the angular velocity associated with the fluctuating fields underlying NMR relaxation. A parameter called j-fraction, which represents the relative contribution of eigenmode, i, to a given value of the SDF function at a specific frequency, ω, is defined. j-fraction profiles of the dominant eigenmodes are derived for 0 ≤ ω ≤ 1012 rad/s. They reveal which patterns of motion actuate power dissipation at given ω-values, what are their rates, and what is their relative contribution. Simulations are carried out to determine the effect of timescale separation, D1/D2, axial potential strength, and local diffusion axiality. For D1/D2 ≤ 0.01 and strong local potential of 15 kBT, power is dissipated by global diffusion, renormalized (by the strong potential) local diffusion, and probe diffusion on the surface of a cone (to be called cone diffusion). For D1/D2 = 0.1, power is dissipated by mixed eigenmodes largely of a global-diffusion-type or cone-diffusion-type, and a nearly bare renormalized-local-diffusion eigenmode. For D1/D2 > 0.1, most eigenmodes are of a mixed type. The analysis is

  15. Spin Liquid State in the 3D Frustrated Antiferromagnet PbCuTe_{2}O_{6}: NMR and Muon Spin Relaxation Studies.

    Science.gov (United States)

    Khuntia, P; Bert, F; Mendels, P; Koteswararao, B; Mahajan, A V; Baenitz, M; Chou, F C; Baines, C; Amato, A; Furukawa, Y

    2016-03-11

    PbCuTe_{2}O_{6} is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu^{2+} ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T_{1} NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.

  16. Off-centre dynamic Jahn-Teller effect studied by electron spin relaxation of Cu2+ ions in SrF2 crystal

    International Nuclear Information System (INIS)

    Hoffmann, S.K.

    2000-01-01

    Temperature cw-EPR and pulsed EPR electron spin echo experiments were performed for a low concentration of Cu 2+ ions in cubic SrF 2 crystals. The well resolved EPR spectrum at low temperatures (below 30 K) with parameters g parallel = 2.493, g perpendicular = 2.083, A parallel = 121, A perpendicular = 8.7, A parallel ( 19 F) = 135, A parallel ( 19 F) = 33.0 (A-values in 10 -4 cm -1 ) is transformed continuously into a single broad line above 225 K on heating, due to the g-factor shift and EPR line broadening. These data along with the angular variation EPR data are described in terms of a pseudo-Jahn-Teller effect of (T 2g +A 2u )x(a 1g +e g +t 1u ) type producing six off-centre positions of the Cu 2+ ion in the fluorine cube. Above 30 K a two-step averaging g -factor process occurs and is governed by vibronic dynamics between potential wells of the off-centre positions. This dynamics governs the electron spin relaxation in the whole temperature range. The electron spin-lattice relaxation rate 1/T 1 grows rapidly by six orders of magnitude in the temperature range 30-100 K and is determined by the Orbach-type process with excitations to two excited vibronic levels of energy 83 and 174 cm -1 . For higher temperatures the relaxation is dominated by overbarrier jumps leading to the isotropic EPR spectrum above 225 K. The phase memory time T M has the rigid lattice value 3.5 μs determined by nuclear spectral diffusion and its temperature variation is governed by the vibronic dynamics indicating that the excitations between vibronic levels produce a dephasing of the electron spin precessional motion. (author)

  17. Energy relaxation between low lying tunnel split spin-states of the single molecule magnet Ni4

    Science.gov (United States)

    de Loubens, G.; Chaves-O'Flynn, G. D.; Kent, A. D.; Ramsey, C.; Del Barco, E.; Beedle, C.; Hendrickson, D. N.

    2007-03-01

    We have developed integrated magnetic sensors to study quantum tunneling of magnetization (QTM) in single molecule magnet (SMMs) single crystals. These sensors incorporate a microstrip resonator (30 GHz) and a micro-Hall effect magnetometer. They have been used to investigate the relaxation rates between the 2 lowest lying tunnel split spin-states of the SMM Ni4 (S=4). EPR spectroscopy at 30 GHz and 0.4 K and concurrent magnetization measurements of several Ni4 single crystals are presented. EPR enables measurement of the energy splitting between the 2 lowest lying superposition states as a function of the longitudinal and transverse fields. The energy relaxation rate is determined in two ways. First, in cw microwave experiments the change in spin-population together with the microwave absorption directly gives the relaxation time from energy conservation in steady-state. Second, direct time-resolved measurements of the magnetization with pulsed microwave radiation have been performed. The relaxation time is found to vary by several orders of magnitude in different crystals, from a few seconds down to smaller than 100 μs. We discuss this and the form of the relaxation found for different crystals and pulse conditions.

  18. Proton Relaxation and Spin Label Studies of Papaverine Localization in Ionic Micelles

    Science.gov (United States)

    Yushmanov, V. E.; Imasato, H.; Perussi, J. R.; Tabak, M.

    The localization of papaverine (PAV) in micelles of zwitterionic N-hexadecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (HPS), cationic cetyltrimethylammonium chloride (CTAC), and anionic sodium dodecyl sulfate (SDS) in D 2O was studied by 1H NMR and ESR in the presence and absence of 5-doxyl- or 12-doxyl-stearic acid. PAV, surfactants, and spin probes are characterized by restricted anisotropic motion in micelles. The rotational correlation time of doxyl fragment was in the range of 0.2 to 0.5 nanoseconds. Binding of PAV to micelles decreases the mobility of both probes, suggesting the localization of PAV inside the hydrophobic part of micelles near the micelle-water interface. According to the NOE data, the methoxy groups of PAV are located in the vicinity of the nitrogen atom in CTAC and HPS micelles, the methoxy groups of the PAV heterocycle being immersed slightly deeper inside the micelle. The T1 relaxation enhancements by two different spin probes show that the H5 and methoxy substituents of the PAV heterocycle are in close proximity to the α-CH 2 of acyl chains in all types of micelles, whereas H3 and H12 are the most distant from the α-CH 2. No significant differences were found for the protonated and neutral PAV in SDS micelles at pD 4.9 and 11.2. These data show that the geometry of the PAV-micelle complex is practically independent of the PAV charge and surfactant headgroup.

  19. Photoluminescence quenching and enhanced spin relaxation in Fe doped ZnO nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Ovhal, Manoj M.; Santhosh Kumar, A. [Department of Materials Engineering, Defence Institute of Advanced Technology, Girinagar, Pune 411025 (India); Khullar, Prerna [School of Materials Science and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India); Kumar, Manjeet [Department of Materials Engineering, Defence Institute of Advanced Technology, Girinagar, Pune 411025 (India); Abhyankar, A.C., E-mail: ashutoshabhyankar@gmail.com [Department of Materials Engineering, Defence Institute of Advanced Technology, Girinagar, Pune 411025 (India)

    2017-07-01

    Cost-effective ultrasonically assisted precipitation method is utilized to synthesize Zinc oxide (ZnO) nanoparticles (NPs) at room temperature and the effect of Iron (Fe) doping on structural, optical and spin relaxation properties also presented. As-synthesized pure and Fe doped ZnO NPs possess a perfect hexagonal growth habit of wurtzite zinc oxide, along the (101) direction of preference. With Fe doping, ‘c/a’ ratio and compressive lattice strain in ZnO NPs are found to reduce and increase, respectively. Raman studies demonstrate that the E{sub 1} longitudinal optical (LO) vibrational mode is very weak in pure which remarkably enhanced with Fe doping into ZnO NPs. The direct band gap energy (E{sub g}) of the ZnO NPs has been increased from 3.02 eV to 3.11 eV with Fe doping. A slight red-shift observed with strong green emission band, in photoluminescence spectra, is strongly quenched in 6 wt.% Fe doped ZnO NPs. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) reveals spherical shape of ZnO NPs with 60–70 nm, which reduces substantially on Fe doping. The energy dispersive X-ray spectrum and elemental mapping confirms the homogeneous distribution of Fe in ZnO NPs. Moreover, the specific relaxation rate (R{sub 2sp} = 1/T{sub 2}) has been measured using Carr-Purcell-Meiboom-Gill (CPMG) method and found to be maximum in 6 wt.% Fe doped ZnO NPs. Further, the correlation of structural, optical and dynamic properties is proposed. - Highlights: • Pure ZnO and Fe doped ZnO NPs were successfully prepared by cost effective ultrasonically assisted precipitation method. • The optical band gap of ZnO has been enhanced form 3.02–3.11 eV with Fe doping. • PL quenching behaviour has been observed with Fe{sup 3+} ions substitution in ZnO lattice. • Specific relaxation rate (R{sub 2sp} = 1/T{sub 2}) has been varied with Fe doping and found to be maximum in 6 wt.% Fe doped ZnO NPs.

  20. Muon spin relaxation study of Zr(H2PO4)(PO4).2H2O.

    Science.gov (United States)

    Clayden, Nigel J; Cottrell, Stephen P

    2006-07-14

    Muon spin relaxation has been used to study the muon dynamics in the layered zirconium phosphate Zr(H(2)PO(4))(PO(4)).2H(2)O as a function of temperature. Radiofrequency decoupling was used to establish the origin of the local dipolar field as coupling with (1)H spins. Muons were trapped at two sites, one identified as HMuO and the other consistent with PO-Mu on the basis of their zero-field second moments. Although a small decrease in the local nuclear dipolar field was seen with temperature, the muons remained essentially static over the temperature range 20-300 K.

  1. Electron spin-lattice relaxation of low-symmetry Ni.sup.2+./sup. centers in LiF

    Czech Academy of Sciences Publication Activity Database

    Azamat, Dmitry; Badalyan, A. G.; Dejneka, Alexandr; Jastrabík, Lubomír; Lančok, Ján

    2014-01-01

    Roč. 104, č. 25 (2014), "252902-1"-"252902-4" ISSN 0003-6951 R&D Projects: GA MŠk(CZ) LM2011029; GA TA ČR TA01010517; GA ČR GAP108/12/1941 Grant - others:SAFMAT(XE) CZ.2.16/3.1.00/22132 Institutional support: RVO:68378271 Keywords : Ni 2+ centers * LiF single crystals * electron spin-lattice relaxation * electron spin echo technique Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.302, year: 2014

  2. Spin time-relaxation within strongly coupled paramagnetic systems exhibiting paramagnetic-ferrimagnetic transitions

    CERN Document Server

    Chahid, M

    2000-01-01

    The purpose of the present work is a quantitative study of the spin time relaxation within superweak ferrimagnetic materials exhibiting a paramagnetic-ferrimagnetic transition, when the temperature is changed from an initial value T sub i to a final one T sub f very close to the critical temperature T sub c. From a magnetic point of view, the material under investigation is considered to be made of two strongly coupled paramagnetic sublattices of respective moments phi (cursive,open) Greek and psi. Calculations are made within a Landau mean-field theory, whose free energy involves, in addition to quadratic and quartic terms in both moments phi (cursive,open) Greek and psi, a lowest-order coupling - Cphi (cursive,open) Greek psi, where C<0 stands for the coupling constant measuring the interaction between the two sublattices. We first determine the time dependence of the shifts of the order parameters delta phi (cursive,open) Greek and delta psi from the equilibrium state. We find that this time dependence ...

  3. Suppression of vapor cell temperature error for spin-exchange-relaxation-free magnetometer

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Jixi, E-mail: lujixi@buaa.edu.cn; Qian, Zheng; Fang, Jiancheng; Quan, Wei [School of Instrument Science and Opto-Electronics Engineering, Beihang University, Beijing 100191 (China)

    2015-08-15

    This paper presents a method to reduce the vapor cell temperature error of the spin-exchange-relaxation-free (SERF) magnetometer. The fluctuation of cell temperature can induce variations of the optical rotation angle, resulting in a scale factor error of the SERF magnetometer. In order to suppress this error, we employ the variation of the probe beam absorption to offset the variation of the optical rotation angle. The theoretical discussion of our method indicates that the scale factor error introduced by the fluctuation of the cell temperature could be suppressed by setting the optical depth close to one. In our experiment, we adjust the probe frequency to obtain various optical depths and then measure the variation of scale factor with respect to the corresponding cell temperature changes. Our experimental results show a good agreement with our theoretical analysis. Under our experimental condition, the error has been reduced significantly compared with those when the probe wavelength is adjusted to maximize the probe signal. The cost of this method is the reduction of the scale factor of the magnetometer. However, according to our analysis, it only has minor effect on the sensitivity under proper operating parameters.

  4. Proton spin lattice relaxation studies in lithium ammonium sulfate LiNH4SO4

    International Nuclear Information System (INIS)

    Shenoy, R.K.; Ramakrishna, J.

    1979-01-01

    Lithium ammonium sulfate (LAS) undergoes a phase transition at Tsub(c1) = 459.5deg K from a paraelectric phase (phase 1) to a ferroelectric phase (phase II) and again at Tsub(c2) = 283deg K to a polar ferroelastic phase (phase III). Proton spin lattice relaxation investigations in the temperature range 480-77deg K at 10 MHz show discontinuous changes in Tsub(1) at the transition temperatures, indicating first order phase transitions. The absence of the slow motion region (ωsub(not)tausub(not)>>1) shows that the ammonium ions are reorienting fast enough to keep the resonance absorption line narrow down to liquid nitrogen temperatures. The possibility of a second minimum and a low activation energy, Esub(a) = 2.659 kcal/mole, in phase III suggest the possibility of tunnelling of the protons at low temperatures. The nature of the transitions have been discussed in the light of the available literature. The unusually high activation energy, Esub(a) = 17.845 kcal/mole, in the paraelectric phase has been attributed to the possible diffusion of protons. (auth.)

  5. Spin-lattice relaxation attenuation coefficients for on-line nuclear orientation experiments

    CERN Document Server

    Vénos, D; Severijns, N

    2003-01-01

    In on-line nuclear orientation experiments the relaxation process is of great importance. During implantation of the radioactive beam, the nuclear sublevel populations attain a secular equilibrium. For this case secular orientation parameters are introduced: B sublambda(sec)=rho sublambda B sublambda(th). Previously attenuation coefficients rho sublambda have already been tabulated, but only for lambda=2,4. In the last few years the number of nuclear orientation experiments in which beta or alpha particles are studied has increased. For these experiments the terms with lambda=1,3,6, and 8 are also necessary. Therefore, we have calculated the values of rho sublambda in full scope.

  6. Microscopic dynamics and relaxation processes in liquid hydrogen fluoride

    International Nuclear Information System (INIS)

    Angelini, R.; Giura, P.; Monaco, G.; Sette, F.; Fioretto, D.; Ruocco, G.

    2004-01-01

    Inelastic x-ray scattering and Brillouin light scattering measurements of the dynamic structure factor of liquid hydrogen fluoride have been performed in the temperature range T=214-283 K. The data, analyzed using a viscoelastic model with a two time-scale memory function, show a positive dispersion of the sound velocity c(Q) between the low frequency value c 0 (Q) and the high frequency value c ∞α (Q). This finding confirms the existence of a structural (α) relaxation directly related to the dynamical organization of the hydrogen bonds network of the system. The activation energy E a of the process has been extracted by the analysis of the temperature behavior of the relaxation time τ α (T) that follows an Arrhenius law. The obtained value for E a , when compared with that observed in another hydrogen bond liquid as water, suggests that the main parameter governing the α-relaxation process is the number of hydrogen bonds per molecule

  7. PREFACE: 13th International Conference on Muon Spin Rotation, Relaxation and Resonance

    Science.gov (United States)

    2014-12-01

    The 13th International Conference on Muon Spin Rotation, Relaxation and Resonance (μSR2014) organized by the Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute in collaboration with the University of Zurich and the University of Fribourg, was held in Grindelwald, Switzerland from 1st to 6th June 2014. The conference provided a forum for researchers from around the world with interests in the applications of μSR to study a wide range of topics including condensed matter physics, materials and molecular sciences, chemistry and biology. Polarized muons provide a unique and versatile probe of matter, enabling studies at the atomic level of electronic structure and dynamics in a wide range of systems. The conference was the thirteenth in a series, which began in Rorschach in 1978 and it took place for the third time in Switzerland. The previous conferences were held in Cancun, Mexico (2011), Tsukuba, Japan (2008), Oxford, UK (2005), Williamsburg, USA (2002), Les Diablerets, Switzerland (1999), Nikko, Japan (1996), Maui, USA (1993), Oxford, UK (1990), Uppsala, Sweden (1986), Shimoda, Japan (1983), Vancouver, Canada (1980), and Rorschach, Switzerland (1978). These conference proceedings contain 67 refereed publications from presentations covering magnetism, superconductivity, chemistry, semiconductors, biophysics and techniques. The conference logo, displayed in the front pages of these proceedings, represents both the location of μSR2014 in the Alps and the muon-spin rotation technique. The silhouette represents the famous local mountains Eiger, Mönch and Jungfrau as drawn by the Swiss painter Ferdinand Hodler and the apple with arrow is at the same time a citation of the Wilhelm Tell legend and a remembrance of the key role played by the muon spin and the asymmetric muon decay (which for the highest positron energy has an apple like shape). More than 160 participants (including 32 registered as students and 13 as accompanying persons) from 19 countries

  8. Heteronuclear relaxation in time-dependent spin systems: 15N-T1ρ dispersion during adiabatic fast passage

    International Nuclear Information System (INIS)

    Konrat, Robert; Tollinger, Martin

    1999-01-01

    A novel NMR experiment comprising adiabatic fast passage techniques for the measurement of heteronuclear self-relaxation rates in fully 15N-enriched proteins is described. Heteronuclear self-relaxation is monitored by performing adiabatic fast passage (AFP) experiments at variable adiabaticity (e.g., variation of RF spin-lock field intensity). The experiment encompasses gradient- selection and sensitivity-enhancement. It is shown that transverse relaxation rates derived with this method are in good agreement with the ones measured by the classical Carr-Purcell-Meiboom-Gill (CPMG) sequences. An application of this method to the study of the carboxyl-terminal LIM domain of quail cysteine and glycine-rich protein qCRP2(LIM2) is presented

  9. Cross-Correlated Relaxation of Dipolar Coupling and Chemical-Shift Anisotropy in Magic-Angle Spinning R1ρ NMR Measurements: Application to Protein Backbone Dynamics Measurements

    Science.gov (United States)

    Kurauskas, Vilius; Weber, Emmanuelle; Hessel, Audrey; Ayala, Isabel; Marion, Dominique; Schanda, Paul

    2016-01-01

    Transverse relaxation rate measurements in MAS solid-state NMR provide information about molecular motions occurring on nanoseconds-to-milliseconds (ns-ms) time scales. The measurement of heteronuclear (13C, 15N) relaxation rate constants in the presence of a spin-lock radio-frequency field (R1ρ relaxation) provides access to such motions, and an increasing number of studies involving R1ρ relaxation in proteins has been reported. However, two factors that influence the observed relaxation rate constants have so far been neglected, namely (i) the role of CSA/dipolar cross-correlated relaxation (CCR), and (ii) the impact of fast proton spin flips (i.e. proton spin diffusion and relaxation). We show that CSA/D CCR in R1ρ experiments is measurable, and that this cross-correlated relaxation rate constant depends on ns-ms motions, and can thus itself provide insight into dynamics. We find that proton spin-diffusion attenuates this cross-correlated relaxation, due to its decoupling effect on the doublet components. For measurements of dynamics, the use of R1ρ rate constants has practical advantages over the use of CCR rates, and the present manuscript reveals factors that have so far been disregarded and which are important for accurate measurements and interpretation. PMID:27500976

  10. Relaxation processes and physical aging in metallic glasses

    Science.gov (United States)

    Ruta, B.; Pineda, E.; Evenson, Z.

    2017-12-01

    Since their discovery in the 1960s, metallic glasses have continuously attracted much interest across the physics and materials science communities. In the forefront are their unique properties, which hold the alluring promise of broad application in fields as diverse as medicine, environmental science and engineering. However, a major obstacle to their wide-spread commercial use is their inherent temporal instability arising from underlying relaxation processes that can dramatically alter their physical properties. The result is a physical aging process which can bring about degradation of mechanical properties, namely through embrittlement and catastrophic mechanical failure. Understanding and controlling the effects of aging will play a decisive role in our on-going endeavor to advance the use of metallic glasses as structural materials, as well as in the more general comprehension of out-of-equilibrium dynamics in complex systems. This review presents an overview of the current state of the art in the experimental advances probing physical aging and relaxation processes in metallic glasses. Similarities and differences between other hard and soft matter glasses are highlighted. The topic is discussed in a multiscale approach, first presenting the key features obtained in macroscopic studies, then connecting them to recent novel microscopic investigations. Particular emphasis is put on the occurrence of distinct relaxation processes beyond the main structural process in viscous metallic melts and their fate upon entering the glassy state, trying to disentangle results and formalisms employed by the different groups of the glass-science community. A microscopic viewpoint is presented, in which physical aging manifests itself in irreversible atomic-scale processes such as avalanches and intermittent dynamics, ascribed to the existence of a plethora of metastable glassy states across a complex energy landscape. Future experimental challenges and the comparison with

  11. Thermal relaxation and heat transport in spin ice Dy{sub 2}Ti{sub 2}O{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Klemke, Bastian; Meissner, M.; Tennant, D.A. [Helmholtz-Zentrum Berlin (Germany); Technische Universitaet Berlin (Germany); Strehlow, P. [Technische Universitaet Berlin (Germany); Physikalisch Technische Bundesanstalt, Institut Berlin (Germany); Kiefer, K. [Helmholtz-Zentrum Berlin (Germany); Grigera, S.A. [School of Physics and Astronomy, St. Andrews (United Kingdom); Instituto de Fisica de Liquidos y Sistemas Biologicos, CONICET, UNLP, La Plata (Argentina)

    2011-07-01

    The thermal properties of single crystalline Dy{sub 2}Ti{sub 2}O{sub 7} have been studied at temperature below 30 K and magnetic fields applied along [110] direction up to 1.5 T. Based on a thermodynamic field theory (TFT) various heat relaxation and thermal transport measurements were analysed. So we were able to present not only the heat capacity of Dy{sub 2}Ti{sub 2}O{sub 7}, but also for the first time the different contributions of the magnetic excitations and their corresponding relaxation times in the spin ice phase. In addition, the thermal conductivity and the shortest relaxation time were determined by thermodynamic analysis of steady state heat transport measurements. Finally, we were able to reproduce the temperature profiles recorded in heat pulse experiments on the basis of TFT using the previously determined heat capacity and thermal conductivity data without additional parameters. Thus, TFT has been proved to be thermodynamically consistent in describing three thermal transport experiments on different time scales. The observed temperature and field dependencies of heat capacity contributions and relaxation times indicate the magnetic excitations in the spin ice Dy{sub 2}Ti{sub 2}O{sub 7} as thermally activated monopole-antimonopole defects.

  12. Relaxation theory of the electronic spin of a complexed paramagnetic metal ion in solution beyond the Redfield limit

    Science.gov (United States)

    Fries, Pascal H.; Belorizky, Elie

    2007-05-01

    The relaxation of the electronic spin S of a paramagnetic metal ion with fully quenched orbital angular momentum in its ground state is investigated in an external magnetic field through a systematic study of the time correlation functions governing the evolution of the statistical operator (density matrix). Let ω0 be the Larmor angular frequency of S. When the relaxation is induced by a time-fluctuating perturbing Hamiltonian ℏH1(t ) of time correlation τc, it is demonstrated that after a transient period the standard Redfield approximation is relevant to calculate the evolution of the populations of the spin states if ∥H1∥2τc2/(1+ω02τc2)≪1 and that this transient period becomes shorter than τc at sufficiently high field for a zero-field splitting perturbing Hamiltonian. This property, proven analytically and confirmed by numerical simulation, explains the surprising success of several simple expressions of the longitudinal electronic relaxation rate 1/T1e derived from the Redfield approximation well beyond its expected validity range ∥H1∥τc≪1. It has favorable practical consequences on the interpretation of the paramagnetic relaxation enhancement of nuclei used for structural and dynamic studies.

  13. Measuring gas temperature during spin-exchange optical pumping process

    Science.gov (United States)

    Normand, E.; Jiang, C. Y.; Brown, D. R.; Robertson, L.; Crow, L.; Tong, X.

    2016-04-01

    The gas temperature inside a Spin-Exchange Optical Pumping (SEOP) laser-pumping polarized 3He cell has long been a mystery. Different experimental methods were employed to measure this temperature but all were based on either modelling or indirect measurement. To date there has not been any direct experimental measurement of this quantity. Here we present the first direct measurement using neutron transmission to accurately determine the number density of 3He, the temperature is obtained using the ideal gas law. Our result showed a surprisingly high gas temperature of 380°C, compared to the 245°C of the 3He cell wall temperature and 178°C of the optical pumping oven temperature. This experiment result may be used to further investigate the unsolved puzzle of the "X-factor" in the SEOP process which places an upper bound to the 3He polarization that can be achieved. Additional spin relaxation mechanisms might exist due to the high gas temperature, which could explain the origin of the X-factor.

  14. A Block-Asynchronous Relaxation Method for Graphics Processing Units

    Energy Technology Data Exchange (ETDEWEB)

    Antz, Hartwig [Karlsruhe Inst. of Technology (KIT) (Germany); Tomov, Stanimire [Univ. of Tennessee, Knoxville, TN (United States); Dongarra, Jack [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Manchester (United Kingdom); Heuveline, Vincent [Karlsruhe Inst. of Technology (KIT) (Germany)

    2011-11-30

    In this paper, we analyze the potential of asynchronous relaxation methods on Graphics Processing Units (GPUs). For this purpose, we developed a set of asynchronous iteration algorithms in CUDA and compared them with a parallel implementation of synchronous relaxation methods on CPU-based systems. For a set of test matrices taken from the University of Florida Matrix Collection we monitor the convergence behavior, the average iteration time and the total time-to-solution time. Analyzing the results, we observe that even for our most basic asynchronous relaxation scheme, despite its lower convergence rate compared to the Gauss-Seidel relaxation (that we expected), the asynchronous iteration running on GPUs is still able to provide solution approximations of certain accuracy in considerably shorter time then Gauss- Seidel running on CPUs. Hence, it overcompensates for the slower convergence by exploiting the scalability and the good fit of the asynchronous schemes for the highly parallel GPU architectures. Further, enhancing the most basic asynchronous approach with hybrid schemes – using multiple iterations within the ”subdomain” handled by a GPU thread block and Jacobi-like asynchronous updates across the ”boundaries”, subject to tuning various parameters – we manage to not only recover the loss of global convergence but often accelerate convergence of up to two times (compared to the effective but difficult to parallelize Gauss-Seidel type of schemes), while keeping the execution time of a global iteration practically the same. This shows the high potential of the asynchronous methods not only as a stand alone numerical solver for linear systems of equations fulfilling certain convergence conditions but more importantly as a smoother in multigrid methods. Due to the explosion of parallelism in todays architecture designs, the significance and the need for asynchronous methods, as the ones described in this work, is expected to grow.

  15. Static magnetic ordering of CeCu2.1Si2 found by muon spin relaxation

    Science.gov (United States)

    Uemura, Y. J.; Kossler, W. J.; Yu, X. H.; Schone, H. E.; Kempton, J. R.; Stronach, C. E.; Barth, S.; Gygax, F. N.; Hitti, B.; Schenck, A.

    1988-01-01

    Zero- and longitudinal-field muon spin relaxation measurements on a polycrystal sample of a heavy fermion superconductor CeCu2.1 Si2 (T(c) = 0.7 K) have revealed an onset of static magnetic ordering below T approximately 0.8 K. The line shapes of the observed spectra in zero field indicate a wide distribution of static random local fields at muon sites, suggesting that the ordering is either spin glass or incommensurate spin-density-wave state. The observed width of the random local field at T = 0.05 K corresponds to a small averaged static moment of the order of 0.1 micro-B per formula unit.

  16. NMR spin relaxation in proteins: The patterns of motion that dissipate power to the bath

    Energy Technology Data Exchange (ETDEWEB)

    Shapiro, Yury E., E-mail: eva.meirovitch@biu.ac.il, E-mail: yuryeshapiro@gmail.com; Meirovitch, Eva, E-mail: eva.meirovitch@biu.ac.il, E-mail: yuryeshapiro@gmail.com [The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900-02 (Israel)

    2014-04-21

    We developed in recent years the two-body coupled-rotator slowly relaxing local structure (SRLS) approach for the analysis of NMR relaxation in proteins. The two bodies/rotators are the protein (diffusion tensor D{sub 1}) and the spin-bearing probe, e.g., the {sup 15}N−{sup 1}H bond (diffusion tensor, D{sub 2}), coupled by a local potential (u). A Smoluchowski equation is solved to yield the generic time correlation functions (TCFs), which are sums of weighted exponentials (eigenmodes). By Fourier transformation one obtains the generic spectral density functions (SDFs) which underlie the experimental relaxation parameters. The typical paradigm is to characterize structural dynamics in terms of the best-fit values of D{sub 1}, D{sub 2}, and u. Additional approaches we pursued employ the SRLS TCFs, SDFs, or eigenmodes as descriptors. In this study we develop yet another perspective. We consider the SDF as function of the angular velocity associated with the fluctuating fields underlying NMR relaxation. A parameter called j-fraction, which represents the relative contribution of eigenmode, i, to a given value of the SDF function at a specific frequency, ω, is defined. j-fraction profiles of the dominant eigenmodes are derived for 0 ≤ ω ≤ 10{sup 12} rad/s. They reveal which patterns of motion actuate power dissipation at given ω-values, what are their rates, and what is their relative contribution. Simulations are carried out to determine the effect of timescale separation, D{sub 1}/D{sub 2}, axial potential strength, and local diffusion axiality. For D{sub 1}/D{sub 2} ≤ 0.01 and strong local potential of 15 k{sub B}T, power is dissipated by global diffusion, renormalized (by the strong potential) local diffusion, and probe diffusion on the surface of a cone (to be called cone diffusion). For D{sub 1}/D{sub 2} = 0.1, power is dissipated by mixed eigenmodes largely of a global-diffusion-type or cone-diffusion-type, and a nearly bare renormalized

  17. Spin structure of nucleon in QCD: inclusive and exclusive processes

    International Nuclear Information System (INIS)

    Teryaev, O.V.

    2001-01-01

    There are two basically independent ways to describe the nucleon spin structure. One is related to quark and gluon spins and another one to their total angular momenta. The latter spin structure may be studied, in principle, in hard exclusive processes

  18. [Brain activity during different stages of the relaxation process].

    Science.gov (United States)

    gorev, A S; Kovaleva, A V; Panova, E N; Gorbacheva, A K

    2012-01-01

    A group of adults participated in experiment in which they were asked to reach relaxed state by using relaxation techniques (active relaxation) and to maintain this state without any technique (passive relaxation). Some changes of EEG-characteristics during relaxation were analyzed. This experiment includes four situations (different functional states): baselinel, active relaxation, passive relaxation, baseline2. EEG was recorded from 10 cortical leads: O1, O2, TPO (left and right), P3, P4, C3, C4, F3 and F4. A comparative EEG analysis was done for 10 frequency bands from 5 to 40 Hz. In each experimental situation we revealed general trends for EEG parameters and also some specific changes in EEG, which characterized brain organization during passive and active relaxed states.

  19. The spin relaxation of nitrogen donors in 6H SiC crystals as studied by the electron spin echo method

    Czech Academy of Sciences Publication Activity Database

    Savchenko, Dariia; Shanina, B.; Kalabukhova, E.; Pöppl, A.; Lančok, Ján; Mokhov, E.

    2016-01-01

    Roč. 119, č. 13 (2016), 1-7, č. článku 135706. ISSN 0021-8979 R&D Projects: GA ČR GP13-06697P; GA MŠk LO1409; GA MŠk LM2015088 Grant - others:SAFMAT(XE) CZ.2.16/3.1.00/22132 Institutional support: RVO:68378271 Keywords : electron spin resonance * SiC * nitrogen donors * relaxation times Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.068, year: 2016

  20. Shape Control of Vesicle by Reverse Process Method of Relaxation

    Science.gov (United States)

    Kohyama, Tamotsu

    2018-03-01

    We consider a reverse process of relaxation and obtain a necessary condition under which the reverse process proceeds. Applying this method to fluid vesicle dynamics, which is derived by Onsager's variational principle, we derive the necessary equations for spontaneous curvature and anisotropic bending rigidity distributions that are induced by the proteins attached to the membrane of the vesicle. Numerical schemes to obtain the distributions of the protein properties are proposed and applied to spheroid vesicles. It is shown that proteins with an anisotropic spontaneous curvature deviator are effective in forming a long prolate spheroid. We conclude that the proposed method may become a useful tool to study the protein distribution in the membrane of a vesicle with a measured shape.

  1. Sound therapy induced relaxation: down regulating stress processes and pathologies.

    Science.gov (United States)

    Salamon, Elliott; Kim, Minsun; Beaulieu, John; Stefano, George B

    2003-05-01

    The use of music as a means of inducing positive emotions and subsequent relaxation has been studied extensively by researchers. A great deal of this research has centered on the use of music as a means of reducing feelings of anxiety and stress as well as aiding in the relief of numerous pathologies. The precise mechanism responsible for these mediated effects has never been truly determined. In the current report we propose that nitric oxide (NO) is the molecule chiefly responsible for these physiological and psychological relaxing effects. Furthermore this molecules importance extends beyond the mechanistic, and is required for the development of the very process that it mediates. Nitric oxide has been determined to aid in the development of the auditory system and participate in cochlear blood flow. We show that NO is additionally responsible for the induced exhibited physiological effects. We proceed to outline the precise neurochemical pathway leading to these effects. Furthermore we explore the interrelationship between the varying emotion centers within the central nervous system and explain how the introduction of music can mediate its effects via NO coupled to these complex pathways.

  2. Electron spin echo study of the E'-center phase relaxation in γ-irradiated quartz glass

    International Nuclear Information System (INIS)

    Dudkin, V.I.; Petrun'kin, V.Yu.; Rubinov, S.V.; Uspenskij, L.I.

    1986-01-01

    Experimental studies of phase relaxation of E'-centres in γ-irradiated quartz glass are conducted by the method of electron spin echo (ESE) for different concentrations of paramagnetic centres. Contribution of mechanisms of spectral and prompt diffusion to kinetics of amplitude drop of echo signal is proved to reduce with growth of delay time between exciting microwave pulse that results in increase of phase memory time at large delays. The mentioned property can be used in electric controlled delay lines on the base of ESE

  3. Design and commissioning of a high magnetic field muon spin relaxation spectrometer at the ISIS pulsed neutron and muon source.

    Science.gov (United States)

    Lord, J S; McKenzie, I; Baker, P J; Blundell, S J; Cottrell, S P; Giblin, S R; Good, J; Hillier, A D; Holsman, B H; King, P J C; Lancaster, T; Mitchell, R; Nightingale, J B; Owczarkowski, M; Poli, S; Pratt, F L; Rhodes, N J; Scheuermann, R; Salman, Z

    2011-07-01

    The high magnetic field (HiFi) muon instrument at the ISIS pulsed neutron and muon source is a state-of-the-art spectrometer designed to provide applied magnetic fields up to 5 T for muon studies of condensed matter and molecular systems. The spectrometer is optimised for time-differential muon spin relaxation studies at a pulsed muon source. We describe the challenges involved in its design and construction, detailing, in particular, the magnet and detector performance. Commissioning experiments have been conducted and the results are presented to demonstrate the scientific capabilities of the new instrument.

  4. On the invariance of spatially inhomogeneous relaxation processes

    Energy Technology Data Exchange (ETDEWEB)

    Eliazar, Iddo [Department of Technology Management, Holon Institute of Technology, PO Box 305, Holon 58102 (Israel); Benichou, Olivier, E-mail: eliazar@post.tau.ac.il, E-mail: benichou@lptmc.jussieu.fr [UPMC Universite de Paris 06, UMR 7600 Laboratoire de Physique Theorique de la Matiere Condensee, 4 Place Jussieu, F-75005 Paris (France)

    2012-01-13

    We consider a general relaxation model based on an ensemble of particles propagating randomly in a general space. The particles' trajectories are independent and identically distributed copies of an arbitrary random spatial curve, and each particle has its own parameter triplet: initiation epoch, velocity and relaxation coefficient. The relaxation rate of each particle is dynamic-depending on its spatial location and quantified by an arbitrary spatial 'landscape function'. We study the relaxation rate of the entire ensemble and characterize the class of Poissonian randomizations of the particles' parameters that render the ensemble's relaxation rate invariant with respect to both the particles' trajectories and the landscape function. The invariant relaxation rates turn out to be governed by power laws and display a statistical behavior analogous to anomalous diffusion. Applications range from chemical reactions to target search and intelligence sifting. (paper)

  5. Anomalous relaxation and self-organization in nonequilibrium processes

    International Nuclear Information System (INIS)

    Fatkullin, Ibrahim; Kladko, Konstantin; Mitkov, Igor; Bishop, A. R.

    2001-01-01

    We study thermal relaxation in ordered arrays of coupled nonlinear elements with external driving. We find that our model exhibits dynamic self-organization manifested in a universal stretched-exponential form of relaxation. We identify two types of self-organization, cooperative and anticooperative, which lead to fast and slow relaxation, respectively. We give a qualitative explanation for the behavior of the stretched exponent in different parameter ranges. We emphasize that this is a system exhibiting stretched-exponential relaxation without explicit disorder or frustration

  6. Molecular motions in thermotropic liquid crystals studied by NMR spin-lattice relaxation

    International Nuclear Information System (INIS)

    Zamar, R.C.; Gonzalez, C.E.; Mensio, O.

    1998-01-01

    Nuclear magnetic resonance relaxation experiments with field cycling techniques proved to be a valuable tool for studying molecular motions in liquid crystals, allowing a very broad Larmor frequency variation, sufficient to separate the cooperative motions from the liquid like molecular diffusion. In new experiments combining NMR field cycling with the Jeener-Broekaert order-transfer pulse sequence, it is possible to measure the dipolar order relaxation time (T 1D ), in addition to the conventional Zeeman relaxation time (T 1Z ) in a frequency range of several decades. When applying this technique to nematic thermotropic liquid crystals, T 1D showed to depend almost exclusively on the order fluctuation of the director mechanism in the whole frequency range. This unique characteristic of T 1D makes dipolar order relaxation experiments specially useful for studying the frequency and temperature dependence of the spectral properties of the collective motions. (author)

  7. Temperature dependence of electron spin-lattice relaxation of radiation-produced silver atoms in polycrystalline aqueous and glassy organic matrices. Importance of relaxation by tunneling modes in disordered matrices

    International Nuclear Information System (INIS)

    Michalik, J.; Kevan, L.

    1978-01-01

    The electron spin-lattice relaxation of trapped silver atoms in polycrystalline ice matrices and in methanol, ethanol, propylene carbonate, and 2-methyltetrahydrofuran organic glasses has been directly studied as a function of temperature by the saturation-recovery method. Below 40 K the dominant electron spin-lattice relaxation mechanism involves modulation of the electron nuclear dipolar interaction with nuclei in the radical's environment by tunneling of those nuclei between two nearly equal energy configurations. This relaxation mechanism occurs with high efficiency, has a characteristic linear temperature dependence, and is typically found in highly disordered matrices. The efficiency of this relaxation mechanism seems to decrease with decreasing polarity of the matrix. Deuteration experiments show that the tunneling nuclei are protons and in methanol it is shown that the methyl protons have more tunneling modes available than the hydroxyl protons. In polycrystalline ice matrices silver atoms can be stabilized with two different orientations of surrounding water molecules; the efficiency of the tunneling relaxation reflects this difference. From these and previous results on tunneling relaxation of trapped electrons in glassy matrices it appears that tunneling relaxation may be used to distinguish models with different geometrical configurations and to determine the relative rigidity of such configurations around trapped radicals in disordered solids. (author)

  8. Continuous relaxation time spectrum of α-process in glass-like B2O3

    International Nuclear Information System (INIS)

    Bartenev, G.M.; Lomovskij, V.A.

    1991-01-01

    α-process of relaxation of glass-like B 2 O 3 was investigated in a wide temperature range. Continuous spectrum of relaxation times H(τ) for this process was constructed, using data of dynamic methods of investigation. It is shown that increase of temperature of α-process investigation leads to change of glass-like BaO 3 structure in such a way, that H(τ) spectrum tends to the maxwell one with a unit relaxation time

  9. Spin dynamics of Mn12-acetate in the thermally activated tunneling regime: ac susceptibility and magnetization relaxation

    Science.gov (United States)

    Pohjola, Teemu; Schoeller, Herbert

    2000-12-01

    In this work, we study the spin dynamics of Mn12-acetate molecules in the regime of thermally assisted tunneling. In particular, we describe the system in the presence of a strong transverse magnetic field. Similar to recent experiments, the relaxation time/rate is found to display a series of resonances; their Lorentzian shape is found to stem from the tunneling. The dynamic susceptibility χ(ω) is calculated starting from the microscopic Hamiltonian and the resonant structure manifests itself also in χ(ω). Similar to recent results reported on another molecular magnet, Fe8, we find oscillations of the relaxation rate as a function of the transverse magnetic field when the field is directed along a hard axis of the molecules. This phenomenon is attributed to the interference of the geometrical or Berry phase. We propose susceptibility experiments to be carried out for strong transverse magnetic fields to study these oscillations and for a better resolution of the sharp satellite peaks in the relaxation rates.

  10. Electron spin relaxation can enhance the performance of a cryptochrome-based magnetic compass sensor

    DEFF Research Database (Denmark)

    Kattnig, Daniel R; Sowa, Jakub K; Solov'yov, Ilia A

    2016-01-01

    The radical pair model of the avian magnetoreceptor relies on long-lived electron spin coherence. Dephasing, resulting from interactions of the spins with their fluctuating environment, is generally assumed to degrade the sensitivity of this compass to the direction of the Earth's magnetic field...... to an Earth-strength magnetic field. Supported by calculations using toy radical pair models, we argue that these enhancements could be consistent with the molecular dynamics and magnetic interactions in avian cryptochromes....

  11. Spin structure in high energy processes: Proceedings

    Energy Technology Data Exchange (ETDEWEB)

    DePorcel, L.; Dunwoodie, C. [eds.

    1994-12-01

    This report contains papers as the following topics: Spin, Mass, and Symmetry; physics with polarized Z{sup 0}s; spin and precision electroweak physics; polarized electron sources; polarization phenomena in quantum chromodynamics; polarized lepton-nucleon scattering; polarized targets in high energy physics; spin dynamics in storage rings and linear accelerators; spin formalism and applications to new physics searches; precision electroweak physics at LEP; recent results on heavy flavor physics from LEP experiments using 1990--1992 data; precise measurement of the left-right cross section asymmetry in Z boson production by electron-positron collisions; preliminary results on heavy flavor physics at SLD; QCD tests with SLD and polarized beams; recent results from TRISTAN at KEK; recent B physics results from CLEO; searching for the H dibaryon at Brookhaven; recent results from the compton observatory; the spin structure of the deuteron; spin structure of the neutron ({sup 3}HE) and the Bjoerken sum rule; a consumer`s guide to lattice QCD results; top ten models constrained by b {yields} sy; a review of the Fermilab fixed target program; results from the D0 experiment; results from CDF at FNAL; quantum-mechanical suppression of bremsstrahlung; report from the ZEUS collaboration at HERA; physics from the first year of H1 at HERA, and hard diffraction. These papers have been cataloged separately elsewhere.

  12. Spin structure in high energy processes: Proceedings

    International Nuclear Information System (INIS)

    DePorcel, L.; Dunwoodie, C.

    1994-12-01

    This report contains papers as the following topics: Spin, Mass, and Symmetry; physics with polarized Z 0 s; spin and precision electroweak physics; polarized electron sources; polarization phenomena in quantum chromodynamics; polarized lepton-nucleon scattering; polarized targets in high energy physics; spin dynamics in storage rings and linear accelerators; spin formalism and applications to new physics searches; precision electroweak physics at LEP; recent results on heavy flavor physics from LEP experiments using 1990--1992 data; precise measurement of the left-right cross section asymmetry in Z boson production by electron-positron collisions; preliminary results on heavy flavor physics at SLD; QCD tests with SLD and polarized beams; recent results from TRISTAN at KEK; recent B physics results from CLEO; searching for the H dibaryon at Brookhaven; recent results from the compton observatory; the spin structure of the deuteron; spin structure of the neutron ( 3 HE) and the Bjoerken sum rule; a consumer's guide to lattice QCD results; top ten models constrained by b → sy; a review of the Fermilab fixed target program; results from the D0 experiment; results from CDF at FNAL; quantum-mechanical suppression of bremsstrahlung; report from the ZEUS collaboration at HERA; physics from the first year of H1 at HERA, and hard diffraction. These papers have been cataloged separately elsewhere

  13. Stretched exponential relaxation processes in hydrogenated amorphous and polymorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Morigaki, Kazuo [Department of Electrical and Digital-System Engineering, Hiroshima Institute of Technology, Miyake, Saeki-ku, Hiroshima 731-5193 (Japan); Hikita, Harumi [Physics Laboratory, Meikai University, Urayasu, Chiba 279-8550 (Japan)

    2011-09-15

    Stretched exponential relaxation has been observed in various phenomena of hydrogenated amorphous silicon (a-Si:H) and hydrogenated polymorphous silicon (pm-Si:H). As an example, we take light-induced defect creation in a-Si:H and pm-Si:H, in which defect-creation process and defect-annihilation process via hydrogen movement play important roles. We have performed the Monte Carlo simulation for hydrogen movement. Hydrogen movement exhibits anomalous diffusion. In our model of light-induced defect creation in a-Si:H, a pair of two types of dangling bonds, i.e., a normal dangling bond and a hydrogen-related dangling bond, that is a dangling bond having hydrogen in the nearby site, are created under illumination, and hydrogen dissociated from the hydrogen-related dangling bond terminates a normal dangling bond via hydrogen movement. The amorphous network reflects on the dispersive parameter of the stretched exponential function in the light-induced defect creation. We discuss this issue, taking into account the difference in the amorphous network between a-Si:H and pm-Si:H (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Lattice Distortion Mediated Paramagnetic Relaxation in High-Spin High-Symmetry Molecular Magnets

    Science.gov (United States)

    Garg, Anupam

    1998-08-01

    Field-dependent maxima in the relaxation rate of the magnetic molecules Mn12-Ac and Fe8-tacn have commonly been ascribed to some resonant tunneling phenomena. We argue instead that the relaxation is purely due to phonons. The rate maxima arise because of a Jahn-Teller-like distortion caused by the coupling of phonons to degenerate Zeeman levels of the molecule at the top of the barrier. The binding energy of the distorted intermediate states lowers the barrier height and increases the relaxation rate. A nonperturbative calculation of this effect is carried out for a model system. An approximate result for the field variation near a maximum is found to agree reasonably with experiment.

  15. Relaxation process of self-trapping exciton in C60

    International Nuclear Information System (INIS)

    Sun, X.; Zhang, G.P.; Ma, Y.S.; Fu, R.L.

    1995-09-01

    When C 60 is photoexcited, a self-trapping exciton (STE) is formed. The bond structure is distorted while the states A 1u and A 2u are pulled into the energy gap from HOMO and LUMO respectively. A dynamical scheme is employed to simulate the relaxation of STE. The evolutions of both bond structure and electronic states show that the relaxation time for STE is about 100 fs. It is noticed that this relaxation time is much shorter than that of the charge transfer in C 60 , and the origin for this big difference is discussed. (author). 13 refs, 4 figs

  16. Formation and relaxation processes of photoinduced defects in a Ge-doped SiO2 glass

    International Nuclear Information System (INIS)

    Yamaguchi, M.; Saito, K.; Ikushima, A.J.

    2002-01-01

    The defect centers induced by ArF laser irradiation in Ge-doped SiO 2 have been investigated by the electron-spin resonance method. In order to observe formation and relaxation processes of the defects, step annealing has been carried out after the irradiation at 77 K. The thermally induced decay of the self-trapped hole (STH) and formation of the so-called Ge(2) centers have been observed with increasing temperature. The result suggests that the holes are transferred from the STH to the Ge(2)

  17. Some kinetic and spectroscopic evidence on intramolecular relaxation processes in polyatomic molecules

    International Nuclear Information System (INIS)

    Quack, M.

    1983-01-01

    The description and definition of intramolecular vibrational relaxation processes is discussed within the framework of the quantum mechanical and statistical mechanical equations of motion. The evidence from quite different experimental sources is summarized under the common aspect of vibrational relaxation. Although much of the evidence remains ambiguous, there is good indication that a localized vibrational excitation relaxes typically in 0.1 to 10 picoseconds, which is long compared to many optical and reactive processes

  18. A cluster expansion for interacting spin-flip processes

    Directory of Open Access Journals (Sweden)

    Campanino Massimo

    2017-01-01

    Full Text Available We consider a system of spin flip processes, one-for each point of ℤ${\\mathbb Z}$, interacting through an Ising type interaction. We construct a cluster expansion and prove that it is convergent when the intensity h of the spin-flip processes is sufficiently high. The system is relevant in the study of the ground state of a quantum Ising process with transverse magnetic field.

  19. Cadmium-113 NMR spin-lattice relaxation and exchange kinetics in concanavalin A: A double saturation transfer experiment

    Science.gov (United States)

    Ellis, Paul D.; Yang, Ping P.; Palmert, Allen R.

    The field dependence of the 113Cd relaxation rate in cadmium-substituted Concanavalin A was investigated at three magnetic field strengths, 2.3, 4.7, and 9.4 T. Because of the anomalously large relaxation rate observed for the resonance corresponding to free cadmium in the system and our prior knowledge that cadmium is undergoing chemical exchange in this system, a detailed analysis was undertaken of the relaxation data obtained at 9.4 T to investigate the relative importance of chemical exchange dynamics upon the observed relaxation time constants. The differential equations for the resulting restricted three-site exchange network can be solved in closed form by employing a double saturation transfer experiment in conjunction with a saturation-recovery T1 experiment. The analysis of these data demonstrate that chemical exchange processes contribute 14, 75, and 20% to the observed relaxation time constants for the 113Cd resonances for the S1 site, free cadmium and the S2 site respectively. If the possibility of exchange contributions to the NOE were ignored, then the observed field dependence of T1 could not be discussed in terms of conventional single correlation time theories of relaxation. In this case the data could be discussed in terms of correlation times involving overall motion of the protein coupled with correlation times describing "internal motions." These internal motions may be the result of the formation of "abortive" complexes with exogenous ligands for those metalloproteins where the metal can be readily removed from the protein. However, for Con A, it is shown that the weak field dependence observed for the heteronuclear NOE is not due to internal motions, but rather to exchange processes.

  20. Muonium spin exchange as a Poisson process: magnetic field dependence in transverse fields

    International Nuclear Information System (INIS)

    Senba, Masayoshi; British Columbia Univ., Vancouver, BC

    1993-01-01

    The muonium spin exchange has been investigated as a function of transverse magnetic field strength, where the Poisson nature of collisions is exploited to simplify the calculation. In intermediate fields where the so-called two-frequency muonium signal is observed, the muonium relaxation due to spin exchange is 1.5 times faster than in low fields. In even higher fields, the observed relaxation rate drops back to the low field value. Since the relaxation rate due to a chemical reaction is field independent, such a distinct field dependence in spin exchange can be used in distinguishing experimentally spin exchange from chemical reactions. The time evolution of the muon spin polarization in the presence of muonium spin exchange has been expressed in a simple analytical closed form. (author)

  1. Surface dependent structural phase transition in SrTiO 3 observed with spin relaxation of 8Li

    Science.gov (United States)

    Smadella, M.; Salman, Z.; Chow, K. H.; Egilmez, M.; Fan, I.; Hossain, M. D.; Kiefl, R. F.; Kreitzman, S. R.; Levy, C. D. P.; MacFarlane, W. A.; Mansour, A. I.; Morris, G. D.; Parolin, T. J.; Pearson, M.; Saadaoui, H.; Song, Q.; Wang, D.

    2009-04-01

    We investigate the 105 K structural phase transition in SrTiO 3 using depth controlled measurements of the spin relaxation of 8Li. The measurements were performed in zero external magnetic field and rely on the local electric field gradient (EFG) at the crystalline implantation site of the 8Li ( I=2) to hold the nuclear polarization. The tetragonal distortion accompanying the phase transition modifies the EFG in some 8Li implantation sites, resulting in an observable loss of 8Li polarization. This loss of polarization begins at a temperature T*=150 K, indicating there is some loss of cubic symmetry well above the bulk transition. We find that the value of T* is unaffected by the range of implantation depths available (10-150 nm); however, the temperature dependence of the polarization depends on the surface preparation of the SrTiO 3 sample.

  2. Surface dependent structural phase transition in SrTiO{sub 3} observed with spin relaxation of {sup 8}Li

    Energy Technology Data Exchange (ETDEWEB)

    Smadella, M. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Salman, Z. [Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU (United Kingdom); ISIS Facility, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX (United Kingdom); Chow, K.H.; Egilmez, M.; Fan, I. [Department of Physics, University of Alberta, Edmonton, AB, T6G 2G7 (Canada); Hossain, M.D. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Kiefl, R.F., E-mail: kiefl@triumf.c [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Canadian Institute for Advanced Research (Canada); Kreitzman, S.R.; Levy, C.D.P. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); MacFarlane, W.A. [Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z3 (Canada); Mansour, A.I. [Department of Physics, University of Alberta, Edmonton, AB, T6G 2G7 (Canada); Morris, G.D. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Parolin, T.J. [Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z3 (Canada); Pearson, M. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Saadaoui, H.; Song, Q.; Wang, D. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada)

    2009-04-15

    We investigate the 105 K structural phase transition in SrTiO{sub 3} using depth controlled measurements of the spin relaxation of {sup 8}Li. The measurements were performed in zero external magnetic field and rely on the local electric field gradient (EFG) at the crystalline implantation site of the {sup 8}Li (I=2) to hold the nuclear polarization. The tetragonal distortion accompanying the phase transition modifies the EFG in some {sup 8}Li implantation sites, resulting in an observable loss of {sup 8}Li polarization. This loss of polarization begins at a temperature T{sup *}=150K, indicating there is some loss of cubic symmetry well above the bulk transition. We find that the value of T{sup *} is unaffected by the range of implantation depths available (10-150 nm); however, the temperature dependence of the polarization depends on the surface preparation of the SrTiO{sub 3} sample.

  3. Pairwise NMR experiments for the determination of protein backbone dihedral angle Φ based on cross-correlated spin relaxation

    International Nuclear Information System (INIS)

    Takahashi, Hideo; Shimada, Ichio

    2007-01-01

    Novel cross-correlated spin relaxation (CCR) experiments are described, which measure pairwise CCR rates for obtaining peptide dihedral angles Φ. The experiments utilize intra-HNCA type coherence transfer to refocus 2-bond J NCα coupling evolution and generate the N (i)-C α (i) or C'(i-1)-C α (i) multiple quantum coherences which are required for measuring the desired CCR rates. The contribution from other coherences is also discussed and an appropriate setting of the evolution delays is presented. These CCR experiments were applied to 15 N- and 13 C-labeled human ubiquitin. The relevant CCR rates showed a high degree of correlation with the Φ angles observed in the X-ray structure. By utilizing these CCR experiments in combination with those previously established for obtaining dihedral angle Ψ, we can determine high resolution structures of peptides that bind weakly to large target molecules

  4. Pseudogap Behavior of the Nuclear Spin-Lattice Relaxation Rate in FeSe Probed by 77Se-NMR

    Science.gov (United States)

    Shi, Anlu; Arai, Takeshi; Kitagawa, Shunsaku; Yamanaka, Takayoshi; Ishida, Kenji; Böhmer, Anna E.; Meingast, Christoph; Wolf, Thomas; Hirata, Michihiro; Sasaki, Takahiko

    2018-01-01

    We conducted 77Se-nuclear magnetic resonance studies of the iron-based superconductor FeSe in magnetic fields of 0.6 to 19 T to investigate the superconducting and normal-state properties. The nuclear spin-lattice relaxation rate divided by the temperature (T1T)-1 increases below the structural transition temperature Ts but starts to be suppressed below T*, well above the superconducting transition temperature Tc(H), resulting in a broad maximum of (T1T)-1 at Tp(H). This is similar to the pseudogap behavior in optimally doped cuprate superconductors. Because T* and Tp(H) decrease in the same manner as Tc(H) with increasing H, the pseudogap behavior in FeSe is ascribed to superconducting fluctuations, which presumably originate from the theoretically predicted preformed pair above Tc(H).

  5. Duchenne muscular dystrophy carriers. Proton spin-lattice relaxation times of skeletal muscles on magnetic resonance imaging

    Energy Technology Data Exchange (ETDEWEB)

    Matsumura, K.; Nakano, I. (Shimoshizu National Hospital, Chiba (Japan). Dept. of Neurology); Fukuda, N.; Ikehira, H.; Tateno, Y. (National Inst. of Radiological Sciences, Chiba (Japan). Div. of Clinical Research); Aoki, Y. (National Inst. of Radiological Sciences, Chiba (Japan))

    1989-11-01

    By means of magnetic resonance imaging (MRI), the proton spin-lattice relaxation times (T1 values) of the skeletal muscles were measured in Duchenne muscular dystrophy (DMD) carriers and normal controls. The bound water fraction (BWF) was calculated from the T1 values obtained, according to the fast proton diffusion model. In the DMD carriers, T1 values of the gluteus maximus and quadriceps femoris muscles were significantly higher, and BWFs of these muscles were significantly lower than in normal control. Degenerative muscular changes accompanied by interstitial edema were presumed responsible for this abnormality. No correlation was observed between the muscle T1 and serum creatine kinase values. The present study showed that MRI could be a useful method for studying the dynamic state of water in both normal and pathological skeletal muscles. Its possible utility for DMD carrier detection was discussed briefly. (orig.).

  6. Characterization of Chemical Exchange Using Relaxation Dispersion of Hyperpolarized Nuclear Spins.

    Science.gov (United States)

    Liu, Mengxiao; Kim, Yaewon; Hilty, Christian

    2017-09-05

    Chemical exchange phenomena are ubiquitous in macromolecules, which undergo conformational change or ligand complexation. NMR relaxation dispersion (RD) spectroscopy based on a Carr-Purcell-Meiboom-Gill pulse sequence is widely applied to identify the exchange and measure the lifetime of intermediate states on the millisecond time scale. Advances in hyperpolarization methods improve the applicability of NMR spectroscopy when rapid acquisitions or low concentrations are required, through an increase in signal strength by several orders of magnitude. Here, we demonstrate the measurement of chemical exchange from a single aliquot of a ligand hyperpolarized by dissolution dynamic nuclear polarization (D-DNP). Transverse relaxation rates are measured simultaneously at different pulsing delays by dual-channel 19 F NMR spectroscopy. This two-point measurement is shown to allow the determination of the exchange term in the relaxation rate expression. For the ligand 4-(trifluoromethyl)benzene-1-carboximidamide binding to the protein trypsin, the exchange term is found to be equal within error limits in neutral and acidic environments from D-DNP NMR spectroscopy, corresponding to a pre-equilibrium of trypsin deprotonation. This finding illustrates the capability for determination of binding mechanisms using D-DNP RD. Taking advantage of hyperpolarization, the ligand concentration in the exchange measurements can reach on the order of tens of μM and protein concentration can be below 1 μM, i.e., conditions typically accessible in drug discovery.

  7. Perspectives of using spin waves for computing and signal processing

    Energy Technology Data Exchange (ETDEWEB)

    Csaba, György, E-mail: gcsaba@gmail.com [Center for Nano Science and Technology, University of Notre Dame (United States); Faculty for Information Technology and Bionics, Pázmány Péter Catholic University (Hungary); Papp, Ádám [Center for Nano Science and Technology, University of Notre Dame (United States); Faculty for Information Technology and Bionics, Pázmány Péter Catholic University (Hungary); Porod, Wolfgang [Center for Nano Science and Technology, University of Notre Dame (United States)

    2017-05-03

    Highlights: • We give an overview of spin wave-based computing with emphasis on non-Boolean signal processors. • Spin waves can combine the best of electronics and photonics and do it in an on-chip and integrable way. • Copying successful approaches from microelectronics may not be the best way toward spin-wave based computing. • Practical devices can be constructed by minimizing the number of required magneto-electric interconnections. - Abstract: Almost all the world's information is processed and transmitted by either electric currents or photons. Now they may get a serious contender: spin-wave-based devices may just perform some information-processing tasks in a lot more efficient and practical way. In this article, we give an engineering perspective of the potential of spin-wave-based devices. After reviewing various flavors for spin-wave-based processing devices, we argue that the niche for spin-wave-based devices is low-power, compact and high-speed signal-processing devices, where most traditional electronics show poor performance.

  8. Perspectives of using spin waves for computing and signal processing

    International Nuclear Information System (INIS)

    Csaba, György; Papp, Ádám; Porod, Wolfgang

    2017-01-01

    Highlights: • We give an overview of spin wave-based computing with emphasis on non-Boolean signal processors. • Spin waves can combine the best of electronics and photonics and do it in an on-chip and integrable way. • Copying successful approaches from microelectronics may not be the best way toward spin-wave based computing. • Practical devices can be constructed by minimizing the number of required magneto-electric interconnections. - Abstract: Almost all the world's information is processed and transmitted by either electric currents or photons. Now they may get a serious contender: spin-wave-based devices may just perform some information-processing tasks in a lot more efficient and practical way. In this article, we give an engineering perspective of the potential of spin-wave-based devices. After reviewing various flavors for spin-wave-based processing devices, we argue that the niche for spin-wave-based devices is low-power, compact and high-speed signal-processing devices, where most traditional electronics show poor performance.

  9. Studies of a Large Odd-Numbered Odd-Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8 Mn.

    Science.gov (United States)

    Baker, Michael L; Lancaster, Tom; Chiesa, Alessandro; Amoretti, Giuseppe; Baker, Peter J; Barker, Claire; Blundell, Stephen J; Carretta, Stefano; Collison, David; Güdel, Hans U; Guidi, Tatiana; McInnes, Eric J L; Möller, Johannes S; Mutka, Hannu; Ollivier, Jacques; Pratt, Francis L; Santini, Paolo; Tuna, Floriana; Tregenna-Piggott, Philip L W; Vitorica-Yrezabal, Iñigo J; Timco, Grigore A; Winpenny, Richard E P

    2016-01-26

    The spin dynamics of Cr8 Mn, a nine-membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8 Mn is a rare example of a large odd-membered AF ring, and has an odd-number of 3d-electrons present. Odd-membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated-spin ground states. The chemical synthesis and structures of two Cr8 Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground-spin-state crossing from S=1/2 to S=3/2 in Cr8 Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin-pair correlations and scalar-spin chirality, shows a non-collinear spin structure that fluctuates between non-planar states of opposite chiralities. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Electron Spin Relaxation Can Enhance the Performance of a Cryptochrome-Based Magnetic Compass Sensor

    Science.gov (United States)

    2016-08-19

    2016 PUBLISHED 9 June 2016 Original content from this workmay be used under the terms of the Creative CommonsAttribution 3.0 licence . Any further...24], is normally expected to attenuate the sensitivity of the compass by destroying the spin coherence that is essential for its operation [35]. It...μT) and the symmetry axis of the hyperfine tensor. qF ( )S was determined using the equation ofmotion for the radical pair density operator , r̂ ( )t

  11. Coulomb collisional relaxation process of ion beams in magnetized plasmas

    OpenAIRE

    Nishimura, Y.

    2010-01-01

    An orbit following code is developed to calculate ion beam trajectories in magnetized plasmas. The equation of motion (the Newton's equation) is solved including the Lorentz force term and Coulomb collisional relaxation term. Furthermore, a new algorithm is introduced by applying perturbation method regarding the collision term as a small term. The reduction of computation time is suggested.

  12. Magnetic field penetration depth of La(1.85)Sr(0.15)CuO4 measured by muon spin relaxation

    Science.gov (United States)

    Kossler, W. J.; Kempton, J. R.; Yu, X. H.; Schone, H. E.; Uemura, Y. J.

    1987-01-01

    Muon-spin-relaxation measurements have been performed on a high-Tc superconductor La(1.85)Sr(0.15)CuO4. In an external transverse magnetic field of 500 G, a magnetic field penetration depth of 2000 A at T = 10 K has been determined from the muon-spin-relaxation rate which increased with decreasing temperature below Tc. From this depth and the Pauli susceptibility, the superconducting carrier density is estimated at 3 x 10 to the 21st per cu cm. The zero-field relaxation rates above and below Tc were equal, which suggests that the superconducting state in this sample is not associated with detectable static magnetic ordering.

  13. Electron spin resonance studies on reduction process of nitroxyl spin radicals used in molecular imaging

    Energy Technology Data Exchange (ETDEWEB)

    Dhas, M. Kumara; Benial, A. Milton Franklin, E-mail: miltonfranklin@yahoo.com [Department of Physics, NMSSVN College, Nagamalai, Madurai-625019, Tamilnadu (India); Jawahar, A. [Department of Chemistry, NMSSVN College, Nagamalai, Madurai-625019, Tamilnadu (India)

    2014-04-24

    The Electron spin resonance studies on the reduction process of nitroxyl spin probes were carried out for 1mM {sup 14}N labeled nitroxyl radicals in pure water and 1 mM concentration of ascorbic acid as a function of time. The electron spin resonance parameters such as signal intensity ratio, line width, g-value, hyperfine coupling constant and rotational correlation time were determined. The half life time was estimated for 1mM {sup 14}N labeled nitroxyl radicals in 1 mM concentration of ascorbic acid. The ESR study reveals that the TEMPONE has narrowest line width and fast tumbling motion compared with TEMPO and TEMPOL. From the results, TEMPONE has long half life time and high stability compared with TEMPO and TEMPOL radical. Therefore, this study reveals that the TEMPONE radical can act as a good redox sensitive spin probe for molecular imaging.

  14. Electron spin resonance studies on reduction process of nitroxyl spin radicals used in molecular imaging

    Science.gov (United States)

    Dhas, M. Kumara; Jawahar, A.; Benial, A. Milton Franklin

    2014-04-01

    The Electron spin resonance studies on the reduction process of nitroxyl spin probes were carried out for 1mM 14N labeled nitroxyl radicals in pure water and 1 mM concentration of ascorbic acid as a function of time. The electron spin resonance parameters such as signal intensity ratio, line width, g-value, hyperfine coupling constant and rotational correlation time were determined. The half life time was estimated for 1mM 14N labeled nitroxyl radicals in 1 mM concentration of ascorbic acid. The ESR study reveals that the TEMPONE has narrowest line width and fast tumbling motion compared with TEMPO and TEMPOL. From the results, TEMPONE has long half life time and high stability compared with TEMPO and TEMPOL radical. Therefore, this study reveals that the TEMPONE radical can act as a good redox sensitive spin probe for molecular imaging.

  15. Active site dynamics in NADH oxidase from Thermus thermophilus studied by NMR spin relaxation

    International Nuclear Information System (INIS)

    Miletti, Teresa; Farber, Patrick J.; Mittermaier, Anthony

    2011-01-01

    We have characterized the backbone dynamics of NADH oxidase from Thermus thermophilus (NOX) using a recently-developed suite of NMR experiments designed to isolate exchange broadening, together with 15 N R 1 , R 1ρ , and { 1 H}- 15 N steady-state NOE relaxation measurements performed at 11.7 and 18.8 T. NOX is a 54 kDa homodimeric enzyme that belongs to a family of structurally homologous flavin reductases and nitroreductases with many potential biotechnology applications. Prior studies have suggested that flexibility is involved in the catalytic mechanism of the enzyme. The active site residue W47 was previously identified as being particularly important, as its level of solvent exposure correlates with enzyme activity, and it was observed to undergo “gating” motions in computer simulations. The NMR data are consistent with these findings. Signals from W47 are dynamically broadened beyond detection and several other residues in the active site have significant R ex contributions to transverse relaxation rates. In addition, the backbone of S193, whose side chain hydroxyl proton hydrogen bonds directly with the FMN cofactor, exhibits extensive mobility on the ns–ps timescale. We hypothesize that these motions may facilitate structural rearrangements of the active site that allow NOX to accept both FMN and FAD as cofactors.

  16. Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

    DEFF Research Database (Denmark)

    Zhang, Wenkai; Kjær, Kasper Skov; Alonso-Mori, Roberto

    2017-01-01

    iron complexes with four cyanide (CN-;) ligands and one 2,2′-bipyridine (bpy) ligand. This enables MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL......) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN)4(bpy)]2-. The two experimental techniques are highly complementary; the time-resolved UV...

  17. Membrane docking geometry of GRP1 PH domain bound to a target lipid bilayer: an EPR site-directed spin-labeling and relaxation study.

    Directory of Open Access Journals (Sweden)

    Huai-Chun Chen

    Full Text Available The second messenger lipid PIP(3 (phosphatidylinositol-3,4,5-trisphosphate is generated by the lipid kinase PI3K (phosphoinositide-3-kinase in the inner leaflet of the plasma membrane, where it regulates a broad array of cell processes by recruiting multiple signaling proteins containing PIP(3-specific pleckstrin homology (PH domains to the membrane surface. Despite the broad importance of PIP(3-specific PH domains, the membrane docking geometry of a PH domain bound to its target PIP(3 lipid on a bilayer surface has not yet been experimentally determined. The present study employs EPR site-directed spin labeling and relaxation methods to elucidate the membrane docking geometry of GRP1 PH domain bound to bilayer-embedded PIP(3. The model target bilayer contains the neutral background lipid PC and both essential targeting lipids: (i PIP(3 target lipid that provides specificity and affinity, and (ii PS facilitator lipid that enhances the PIP(3 on-rate via an electrostatic search mechanism. The EPR approach measures membrane depth parameters for 18 function-retaining spin labels coupled to the PH domain, and for calibration spin labels coupled to phospholipids. The resulting depth parameters, together with the known high resolution structure of the co-complex between GRP1 PH domain and the PIP(3 headgroup, provide sufficient constraints to define an optimized, self-consistent membrane docking geometry. In this optimized geometry the PH domain engulfs the PIP(3 headgroup with minimal bilayer penetration, yielding the shallowest membrane position yet described for a lipid binding domain. This binding interaction displaces the PIP(3 headgroup from its lowest energy position and orientation in the bilayer, but the headgroup remains within its energetically accessible depth and angular ranges. Finally, the optimized docking geometry explains previous biophysical findings including mutations observed to disrupt membrane binding, and the rapid lateral

  18. Algorithm for capturing primary relaxation processes in excitable gases by two-frequency acoustic measurements

    International Nuclear Information System (INIS)

    Zhang, Ke-Sheng; Wang, Shu; Zhu, Ming; Ding, Yi

    2013-01-01

    It is still a challenge to employ the acoustic method to investigate the molecular relaxation phenomena in excitable gases. Here we present an algorithm to capture the primary relaxation processes by only measuring the sound absorption and sound speed of two operating frequencies at a single pressure, without the necessity of detecting the gas density. This algorithm is developed from the fact that the frequency-dependent sound absorption curve due to a single-relaxation process can be reconstructed from the two values of the relaxation frequency and the maximum relaxational absorption, and they can be synthesized by the acoustic measurements at two frequencies. Moreover, by acquiring the high-frequency sound speed, those two synthesized values can be used to reconstruct the sound dispersion curve. The simulations demonstrate the validity of the proposed algorithm and its robustness against errors of acoustic measurements. (paper)

  19. Reconstruction of mono-vacancies in carbon nanotubes: Atomic relaxation vs. spin polarization

    International Nuclear Information System (INIS)

    Berber, S.; Oshiyama, A.

    2006-01-01

    We have investigated the reconstruction of mono-vacancies in carbon nanotubes using density functional theory (DFT) geometry optimization and electronic structure calculations, employing a numerical basis set. We considered mono-vacancies in achiral nanotubes with diameter range ∼4-9A. Contrary to previous tight-binding calculations, our results indicate that mono-vacancies could have several metastable geometries, confirming the previous plane-wave DFT results. Formation energy of mono-vacancies is 4.5-5.5eV, increasing with increasing tube diameter. Net magnetic moment decreases from ideal mono-vacancy value after reconstruction, reflecting the reduction of the number of dangling bonds. In spite of the existence of a dangling bond, ground state of mono-vacancies in semiconducting tubes have no spin polarization. Metallic carbon nanotubes show net magnetic moment for most stable structure of mono-vacancy, except for very small diameter tubes

  20. Spin Hall and spin swapping torques in diffusive ferromagnets

    KAUST Repository

    Pauyac, C. O.

    2017-12-08

    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 precessional effects displays a complex spatial dependence that can be exploited to generate torques and nucleate/propagate domain walls in centrosymmetric geometries without use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.

  1. Relaxation process of coherent transients in the presence of an adjacent strongly driven transition

    International Nuclear Information System (INIS)

    Feng Xiaomin; Yang Lijun; Li Xiaoli; Zhang Lianshui; Han Li; Guo Qinglin; Fu Guangsheng

    2007-01-01

    Coherent transient occurs when a two-level transition is subjected to pulsed laser excitation. The relaxation process of coherent transient depends on both the longitudinal and transverse relaxation parameters of the two-level transition, which is related to the population and coherence decay rates. In this paper we study relaxation process of a new type coherent transients observed by applying a pulsed laser excitation to a two-level transition in the presence of a second strong continuous-wave (cw) coherent field coupling one of the two levels to a third level, that is, in a three-level double-resonance configuration. The relaxation process of coherent transients is studied as a function of relaxation parameters of both the two-level transition excited by the pulsed laser field and the transition coupled by the cw laser field. It is shown that by involving a third level with coherent field the relaxation process of coherent transients of a two-level transition can be modified. Our study illustrates a new way of controlling relaxation process of coherent transients in a two-level transition by a second coherent laser and this has important implication for quantum information storage and quantum computing

  2. Nuclear spin relaxation of 8Li in a thin film of La 0.67Ca 0.33MnO 3

    Science.gov (United States)

    Miller, R. I.; Arseneau, D.; Chow, K. H.; Daviel, S.; Engelbertz, A.; Hossain, MD.; Keeler, T.; Kiefl, R. F.; Kreitzman, S.; Levy, C. D. P.; Morales, P.; Morris, G. D.; MacFarlane, W. A.; Parolin, T. J.; Poutissou, R.; Saadaoui, H.; Salman, Z.; Wang, D.; Wei, J. Y. T.

    2006-03-01

    We report β-NMR measurements of the nuclear spin relaxation rate (1/T1) in a thin film of La 0.67Ca 0.33MnO 3 (LCMO) using a low-energy beam of spin-polarized 8Li. In a small magnetic field of 150 G, there is a broad peak in 1/T1 near the Curie temperature (Tc=259 K) and a dramatic decrease in 1/T1 at lower temperatures. This is attributed to a critical slowing down of the spin fluctuations near Tc and freezing of the magnetic excitations at low temperatures, respectively. In addition, there is a small amplitude, slow relaxing component at high temperatures, which we attribute to 8Li in the SrTiO 3 substrate. There is an indication that the spin relaxation rate in the substrate is also peaked at Tc due to close proximity to the magnetic film. These results establish that low-energy β-NMR can be used as a probe of magnetic fluctuations in magnetic thin films over a wide range of temperatures.

  3. Determination of proton transverse relaxation times in homonuclear-coupled Spin Systems

    Science.gov (United States)

    Gochin, Miriam

    A new method is described for obtaining proton transverse relaxation times in homonuclear-coupled systems. The oscillatory effect of the coupling on the T2 decay was removed by using the attached heteronucleus as a filter. A BIRD pulse (J. R. Garbow, D. P. Weitekamp, and A. Pines, Chem. Phys. Lett.93, 504, 1982) was applied in the center of the T2 decay period, causing protons directly and remotely connected to the heteronucleus to be decoupled from each other. Protons directly bound to the heteronucleus were inverted, leaving remote protons unaffected. Thus the method works well in natural-abundance 13C and 15N systems or for 15N-enriched biological materials, where no NN connectivities exist. The importance of obtaining proton T2 values pertains to their usefulness and sensitivity in quantitating structure and mobility in molecules. Sequences for obtaining proton T2 values were described and demonstrated on formate, alcohol, and gramicidin S. The accuracy of the measured T2 as a function of X-nucleus offset and heteronuclear coupling constant was assessed.

  4. I. Advances in NMR Signal Processing. II. Spin Dynamics in Quantum Dissipative Systems

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Yung-Ya [Univ. of California, Berkeley, CA (United States)

    1998-11-01

    Part I. Advances in IVMR Signal Processing. Improvements of sensitivity and resolution are two major objects in the development of NMR/MRI. A signal enhancement method is first presented which recovers signal from noise by a judicious combination of a priordmowledge to define the desired feasible solutions and a set theoretic estimation for restoring signal properties that have been lost due to noise contamination. The effect of noise can be significantly mitigated through the process of iteratively modifying the noisy data set to the smallest degree necessary so that it possesses a collection of prescribed properties and also lies closest to the original data set. A novel detection-estimation scheme is then introduced to analyze noisy and/or strongly damped or truncated FIDs. Based on exponential modeling, the number of signals is detected based on information estimated using the matrix pencil method. theory and the spectral parameters are Part II. Spin Dynamics in body dipole-coupled systems Quantum Dissipative Systems. Spin dynamics in manyconstitutes one of the most fundamental problems in magnetic resonance and condensed-matter physics. Its many-spin nature precludes any rigorous treatment. ‘Therefore, the spin-boson model is adopted to describe in the rotating frame the influence of the dipolar local fields on a tagged spin. Based on the polaronic transform and a perturbation treatment, an analytical solution is derived, suggesting the existence of self-trapped states in the. strong coupling limit, i.e., when transverse local field >> longitudinal local field. Such nonlinear phenomena originate from the joint action of the lattice fluctuations and the reaction field. Under semiclassical approximation, it is found that the main effect of the reaction field is the renormalization of the Hamiltonian of interest. Its direct consequence is the two-step relaxation process: the spin is initially localized in a quasiequilibrium state, which is later detrapped by

  5. Effect of spatial spin modulation on relaxation and NMR frequencies of sup 5 sup 7 Fe nuclei in ferroelectric antiferromagnetic BiFeO sub 3

    CERN Document Server

    Zalessky, A V; Zvezdin, A K; Gippius, A A; Morozova, E N; Khozeev, D F; Bush, A S; Pokatilov, V S

    2002-01-01

    The NMR spectra on the iron nuclei in the BiFeO sub 3 antiferromagnetic sample enriched by the sup 5 sup 7 Fe (95.43%) with the spatially-modulated magnetic structure are studied. It is established that the cycloid-type spin modulation in the BiFeO sub 3 produces spatial modulation of the nuclear spin-spin relaxation velocity and leads to the spectral nonuniform widening of the NMR local line. It is determined also that the local magnetic moments of the iron ions on various cycloid sections differently depend on temperature which testifies to different character of the spin waves excitation. The analogy of the experimental results with the NMR regularities in the Bloch wall is discussed

  6. In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Jiancheng; Wang, Tao, E-mail: wangtaowt@aspe.buaa.edu.cn; Quan, Wei; Yuan, Heng; Li, Yang [School of Instrument Science and Opto-Electronics Engineering, Beihang University, Beijing 100191 (China); Zhang, Hong; Zou, Sheng [School of Instrument Science and Engineering, Southeast University, Nanjing 210096 (China)

    2014-06-15

    A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz{sup 1/2}, which was mainly dominated by the noise of the magnetic shield.

  7. Rotational dynamics in supercooled water from nuclear spin relaxation and molecular simulations.

    Science.gov (United States)

    Qvist, Johan; Mattea, Carlos; Sunde, Erik P; Halle, Bertil

    2012-05-28

    Structural dynamics in liquid water slow down dramatically in the supercooled regime. To shed further light on the origin of this super-Arrhenius temperature dependence, we report high-precision (17)O and (2)H NMR relaxation data for H(2)O and D(2)O, respectively, down to 37 K below the equilibrium freezing point. With the aid of molecular dynamics (MD) simulations, we provide a detailed analysis of the rotational motions probed by the NMR experiments. The NMR-derived rotational correlation time τ(R) is the integral of a time correlation function (TCF) that, after a subpicosecond librational decay, can be described as a sum of two exponentials. Using a coarse-graining algorithm to map the MD trajectory on a continuous-time random walk (CTRW) in angular space, we show that the slowest TCF component can be attributed to large-angle molecular jumps. The mean jump angle is ∼48° at all temperatures and the waiting time distribution is non-exponential, implying dynamical heterogeneity. We have previously used an analogous CTRW model to analyze quasielastic neutron scattering data from supercooled water. Although the translational and rotational waiting times are of similar magnitude, most translational jumps are not synchronized with a rotational jump of the same molecule. The rotational waiting time has a stronger temperature dependence than the translation one, consistent with the strong increase of the experimentally derived product τ(R) D(T) at low temperatures. The present CTRW jump model is related to, but differs in essential ways from the extended jump model proposed by Laage and co-workers. Our analysis traces the super-Arrhenius temperature dependence of τ(R) to the rotational waiting time. We present arguments against interpreting this temperature dependence in terms of mode-coupling theory or in terms of mixture models of water structure.

  8. Protrusion of the Rod Electrode in the Electro spinning Process

    International Nuclear Information System (INIS)

    Valtera, J.; Komarek, J.; Skrivanek, J.; Zabka, P.; Beran, J.; Vyslouzilova, L.; Lukas, D.

    2015-01-01

    The paper focuses on the influence of the protrusion of the rod electrode on critical voltage in the DC electro spinning process. On the testing and industrial DC electro spinning devices, electrodes of any kind are extended towards the counter electrode. This provides the maximal, that is, supercritical, electric field intensity on the spinning-electrode orifice that is found to be higher than on the other supplementary parts. The principal study and experiments with basic apparatus were carried out and presented by Taylor in 1966. This study is focused on the arrangement closely related to the design of the real electro spinning device with respect to the safety and technological aspects. Results of the carried out experiments of the rod spinning-electrode are compared with the electrostatic simulation and analytical calculation. The presented effect of the electrode protrusion on the potential difference and the critical field strength introduces valuable information for the designers of electro spinning machines as well as for the setting up of the optimal technological parameters for producing modern nonwoven textile products.

  9. Anomalous 125Te Nuclear Spin Relaxation Coincident with Charge Kondo Behavior in Superconducting Pb1-xTlxTe

    Science.gov (United States)

    Mukuda, Hidekazu; Matsumura, Takashi; Maki, Shota; Yashima, Mitsuharu; Kitaoka, Yoshio; Miyake, Kazumasa; Murakami, Hironaru; Giraldo-Gallo, Paula; Geball, Theodore H.; Fisher, Ian R.

    2018-02-01

    We report the results of a 125Te NMR study of single crystalline Pb1-xTlxTe (x = 0, 0.35, 1.0%) as a window on the novel electronic states associated with the thallium impurities in PbTe. The Knight shift is enhanced as x increases, corresponding to an increase in the average density of states (DOS) coupled to a strong spatial variation in the local DOS surrounding each Tl dopant. Remarkably, for the superconducting composition (x = 1.0%), the 125Te nuclear spin relaxation rate (1/T1T) for Te ions that are close to the Tl dopants is unexpectedly enhanced in the normal state below a characteristic temperature of ˜10 K, below which the resistivity experiences an upturn. Such a simultaneous upturn in both the resistivity and (1/T1T) was not suppressed in the high magnetic field. We suggest that these observations are consistently accounted for by dynamical charge fluctuations in the absence of paramagnetism, which is anticipated by the charge Kondo scenario associated with the Tl dopants. In contrast, such anomalies were not detected in the non-superconducting samples (x = 0 and 0.35%), suggesting a connection between dynamical valence fluctuations and the occurrence of superconductivity in Pb1-xTlxTe.

  10. Spin wave relaxation and magnetic properties in [M/Cu] super-lattices; M=Fe, Co and Ni

    International Nuclear Information System (INIS)

    Fahmi, A.; Qachaou, A.

    2009-01-01

    In this work, we study the elementary excitations and magnetic properties of the [M/Cu] super-lattices with: M=Fe, Co and Ni, represented by a Heisenberg ferromagnetic system with N atomic planes. The nearest neighbour (NN), next nearest neighbour (NNN) exchange, dipolar interactions and surface anisotropy effects are taken into account and the Hamiltonian is studied in the framework of the linear spin wave theory. In the presence of the exchange alone, the excitation spectrum E(k) and the magnetization z >/S analytical expressions are obtained using the Green's function formalism. The obtained relaxation time of the magnon populations is nearly the same in the Fe and Co-based super-lattices, while these magnetic excitations would last much longer in the Ni-based super lattice. A numerical study of the surface anisotropy and long-ranged dipolar interaction combined effects are also reported. The exchange integral values deduced from a comparison with experience for the three super-lattices are coherent.

  11. Accuracy enhancement of magnetic field distribution measurements within a large cell spin-exchange relaxation-free magnetometer

    Science.gov (United States)

    Gusarov, Alexander; Ben-Amar Baranga, Andrei; Levron, David; Shuker, Reuben

    2018-04-01

    The factorial design technique is implemented to achieve greater accuracy in the determination of magnetic field distribution within a single cell of spin-exchange relaxation-free atomic magnetometer. Three-dimensional magnetic field distribution within a single vapor cell can be found by consecutively pumping, layer by layer, all the cell volumes perpendicular to the probe laser beam, detected by a photodiode array. Thus each element of the array collects information about the magnetic field in the small volume (voxel) which forms when the corresponding part of the probe beam and optically pumped layer cross. One of the most effective ways to enhance measurement accuracy is repeated pumping of the layers and averaging the measured results. However, the measurement time is multiplied several times due to the repeated scanning of the cell volume. The suggested technique enables increased measurement accuracy of each voxel while preserving the number of measurements. Magnetic field distribution is determined by the illumination of the cell layers one by one or simultaneously, according to a special algorithm, with subsequent multifactorial analysis of the obtained results.

  12. Screening of point charge impurities in highly anisotropic metals: application to mu+-spin relaxation in underdoped cuprate superconductors.

    Science.gov (United States)

    Shekhter, Arkady; Shu, Lei; Aji, Vivek; MacLaughlin, D E; Varma, C M

    2008-11-28

    We calculate the screening charge density distribution due to a point charge, such as that of a positive muon (mu+), placed between the planes of a highly anisotropic layered metal. In underdoped hole cuprates the screening charge converts the charge density in the metallic-plane unit cells in the vicinity of the mu+ to nearly its value in the insulating state. The current-loop-ordered state observed by polarized neutron diffraction then vanishes in such cells, and also in nearby cells over a distance of order the intrinsic correlation length of the loop-ordered state. This strongly suppresses the magnetic field at the mu+ site. We estimate this suppressed field in underdoped YBa2Cu3O6+x and La2-xSrxCuO4, and find consistency with the observed approximately 0.2 G field in the former case and the observed upper bound of approximately 0.2 G in the latter case. This resolves the controversy between the neutron diffraction and mu-spin relaxation experiments.

  13. Linear scaling between momentum and spin scattering in graphene

    NARCIS (Netherlands)

    Jozsa, C.; Maassen, T.; Popinciuc, M.; Zomer, P. J.; Veligura, A.; Jonkman, H. T.; van Wees, B. J.

    2009-01-01

    Spin transport in graphene carries the potential of a long spin-diffusion length at room temperature. However, extrinsic relaxation processes limit the current experimental values to 1-2 mu m. We present Hanle spin precession measurements in gated lateral spin valve devices in the low to high (up to

  14. CdZnTe quantum dots study: energy and phase relaxation process

    International Nuclear Information System (INIS)

    Viale, Yannick

    2004-01-01

    We present a study of the electron-hole pair energy and phase relaxation processes in a CdTe/ZnTe heterostructure, in which quantum dots are embedded. CdZnTe quantum wells with a high Zinc concentration, separated by ZnTe barriers, contain islands with a high cadmium concentration. In photoluminescence excitation spectroscopy experiments, we evidence two types of electron hole pair relaxation processes. After being excited in the CdZnTe quantum well, the pairs relax their energy by emitting a cascade of longitudinal optical phonons until they are trapped in the quantum dots. Before their radiative recombination follows an intra-dot relaxation, which is attributed to a lattice polarization mechanism of the quantum dots. It is related to the coupling between the electronic and the vibrational states. Both relaxation mechanisms are reinforced by the strong polar character of the chemical bond in II-VI compounds. Time resolved measurements of transmission variations in a pump-probe configuration allowed us to investigate the population dynamics of the electron-hole pairs during the relaxation process. We observe a relaxation time of about 2 ps for the longitudinal phonon emission cascade in the quantum well before a saturation of the quantum dot transition. We also measured an intra-box relaxation time of 25 ps. The comparison of various cascades allows us to estimate the emission time of a longitudinal optical phonon in the quantum well to be about 100 fs. In four waves mixing experiments, we observe oscillations that we attribute to quantum beats between excitonic and bi-excitonic transitions. The dephasing times that we measure as function of the density of photons shows that excitons are strongly localized in the quantum dots. The excitonic dephasing time is much shorter than the radiative lifetime and is thus controlled by the intra-dot relaxation time. (author) [fr

  15. Comparison of the Magnetic Anisotropy and Spin Relaxation Phenomenon of Dinuclear Terbium(III) Phthalocyaninato Single-Molecule Magnets Using the Geometric Spin Arrangement.

    Science.gov (United States)

    Morita, Takaumi; Damjanović, Marko; Katoh, Keiichi; Kitagawa, Yasutaka; Yasuda, Nobuhiro; Lan, Yanhua; Wernsdorfer, Wolfgang; Breedlove, Brian K; Enders, Markus; Yamashita, Masahiro

    2018-02-28

    Herein we report the synthesis and characterization of a dinuclear Tb III single-molecule magnet (SMM) with two [TbPc 2 ] 0 units connected via a fused-phthalocyaninato ligand. The stable and robust complex [(obPc)Tb(Fused-Pc)Tb(obPc)] (1) was characterized by using synchrotron radiation measurements and other spectroscopic techniques (ESI-MS, FT-IR, UV). The magnetic couplings between the Tb III ions and the two π radicals present in 1 were explored by means of density functional theory (DFT). Direct and alternating current magnetic susceptibility measurements were conducted on magnetically diluted and nondiluted samples of 1, indicating this compound to be an SMM with improved properties compared to those of the well-known [TbPc 2 ] -/0/+ and the axially symmetric dinuclear Tb III phthalocyaninato triple-decker complex (Tb 2 (obPc) 3 ). Assuming that the probability of quantum tunneling of the magnetization (QTM) occurring in one TbPc 2 unit is P QTM , the probability of QTM simultaneously occurring in 1 is P QTM 2 , meaning that QTM is effectively suppressed. Furthermore, nondiluted samples of 1 underwent slow magnetic relaxation times (τ ≈ 1000 s at 0.1 K), and the blocking temperature (T B ) was determined to be ca. 16 K with an energy barrier for spin reversal (U eff ) of 588 cm -1 (847 K) due to D 4d geometry and weak inter- and intramolecular magnetic interactions as an exchange bias (H bias ), reducing QTM. Four hyperfine steps were observed by micro-SQUID measurement. Furthermore, solution NMR measurements (one-dimensional, two-dimensional, and dynamic) were done on 1, which led to the determination of the high rotation barrier (83 ± 10 kJ/mol) of the obPc ligand. A comparison with previously reported Tb III triple-decker compounds shows that ambient temperature NMR measurements can indicate improvements in the design of coordination environments for SMMs. A large U eff causes strong uniaxial magnetic anisotropy in 1, leading to a χ ax value (1.39

  16. Near-Surface Structural Phase Transition of SrTiO3 Studied with Zero-Field β-Detected Nuclear Spin Relaxation and Resonance

    Science.gov (United States)

    Salman, Z.; Kiefl, R. F.; Chow, K. H.; Hossain, M. D.; Keeler, T. A.; Kreitzman, S. R.; Levy, C. D. P.; Miller, R. I.; Parolin, T. J.; Pearson, M. R.; Saadaoui, H.; Schultz, J. D.; Smadella, M.; Wang, D.; Macfarlane, W. A.

    2006-04-01

    We demonstrate that zero-field β-detected nuclear quadrupole resonance and spin relaxation of low energy Li8 can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO3 single crystal occurs at Tc˜150K, i.e., ˜45K higher than Tcbulk, and that the tetragonal domains formed below Tc are randomly oriented.

  17. Direct simulation Monte Carlo modeling of relaxation processes in polyatomic gases

    Science.gov (United States)

    Pfeiffer, M.; Nizenkov, P.; Mirza, A.; Fasoulas, S.

    2016-02-01

    Relaxation processes of polyatomic molecules are modeled and implemented in an in-house Direct Simulation Monte Carlo code in order to enable the simulation of atmospheric entry maneuvers at Mars and Saturn's Titan. The description of rotational and vibrational relaxation processes is derived from basic quantum-mechanics using a rigid rotator and a simple harmonic oscillator, respectively. Strategies regarding the vibrational relaxation process are investigated, where good agreement for the relaxation time according to the Landau-Teller expression is found for both methods, the established prohibiting double relaxation method and the new proposed multi-mode relaxation. Differences and applications areas of these two methods are discussed. Consequently, two numerical methods used for sampling of energy values from multi-dimensional distribution functions are compared. The proposed random-walk Metropolis algorithm enables the efficient treatment of multiple vibrational modes within a time step with reasonable computational effort. The implemented model is verified and validated by means of simple reservoir simulations and the comparison to experimental measurements of a hypersonic, carbon-dioxide flow around a flat-faced cylinder.

  18. Probing of structural relaxation times in the glassy state of sucrose and trehalose based on dynamical properties of two secondary relaxation processes

    International Nuclear Information System (INIS)

    Kaminski, K.; Adrjanowicz, K.; Paluch, M.; Kaminska, E.

    2011-01-01

    Time-dependent isothermal dielectric measurements were carried out deeply in the glassy state on two very important saccharides: sucrose and trehalose. In both compounds two prominent secondary relaxation processes were identified. The faster one is an inherent feature of the whole family of carbohydrates. The slower one can also be detected in oligo- and polysaccharides. It was shown earlier that the β process is the Johari-Goldstein (JG) relaxation coupled to motions of the glycosidic linkage, while the γ relaxation originates from motions of the exocyclic hydroxymethyl unit. Recently, it was shown that the JG relaxation process can be used to determine structural relaxation times in the glassy state [R. Casalini and C. M. Roland, Phys. Rev. Lett. 102, 035701 (2009)]. In this paper we present the results of an analysis of the data obtained during aging using two independent approaches. The first was proposed by Casalini and Roland, and the second one is based on the variation of the dielectric strength of the secondary relaxation process during aging [J. K. Vij and G. Power, J. Non-Cryst. Solids 357, 783 (2011)]. Surprisingly, we found that the estimated structural relaxation times in the glassy state of both saccharides are almost the same, independent of the type of secondary mode. This finding calls into question the common view that secondary modes of intramolecular origin do not provide information about the dynamics of the glassy state.

  19. Analysis of the kinetics of the fragile fracture process in Mo monocrystals in quasi-relaxation

    International Nuclear Information System (INIS)

    Tamayo Meza, Pedro; Bautista Godinez, Eric Gustavo; Yermishkin, Viacheslav

    2008-01-01

    The method of quasi-relaxation, generally known as the force relaxation method, has been widely applied in the study of elementary dislocational processes. It is essential for the study and analysis of thermoactivated mechanisms, for the determination of the energy of interaction between dislocations and inclusions, in the definition of the dislocational constants, to predict the development of creep, and even for the study of fracture kinetics. For the first time the use of the quasi-relaxation method for evaluating the fragile fracture tendency was presented in the work. However, as usually carried out, the use of mass specimens and the development of a considerable plastic deformation in the vertex of the crack-notch sample limits the possibilities for this method. Many studies analyze the theoretical aspects of the fracture process, and the obtention of reliable quantitative information about the behavior of the dislocation based on an analytical description of the process, and how and when it influences the conditions under which the final catastrophic fracture occurs. This work proposes a new method to analyze the effect of a tension concentrator on the surface of Mo monocrystal specimens. The relaxation of the force and the increase in the crack opening is related to the development of the plastic zone in its vertex with the help of the Irwin correction. During the relaxation, the crack-groove grows until it attains the length of the plastic zone. Specimens with and without force concentrators were tested in quasi-relaxation. The cracks appearing under these conditions are analyzed using a scanning electron microscopy (SEM). The crack appearing in the specimens under load conditions, whose development produced heavy force relaxation, allowed the force relaxation value to be defined and compared in the specimens with and without tension concentrators (au)

  20. Lattice dynamics, phase transitions and spin relaxation in [Fe(C{sub 5}H{sub 5}){sub 2}] PF{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Herber, R. H.; Felner, I.; Nowik, I., E-mail: nowik@vms.huji.ac.il [The Hebrew University, Racah Institute of Physics (Israel)

    2016-12-15

    The organometallic compound ferrocenium hexafluorophosphate, [Fe(C{sub 5}H{sub 5}){sub 2}] PF{sub 6}, has been studied by Mössbauer spectroscopy in the past, mainly to determine the crystal structure at high temperatures. Here we present studies at 95 K to 305 K and analyze the spectra in terms of spin relaxation theory which yields accurately the hyperfine interaction parameters and the spin-spin and spin-lattice relaxation rates in this paramagnetic compound. The spectral area under the resonance curve yields the recoil free fraction and thus the mean square of the vibration amplitude . One observes a large discontinuity in the slope of versus T at 210 K, indicative of a phase transition. The analysis of the spectra proves that the quadrupole interaction is small but certainly negative, ½e{sup 2}qQ = -0.12(2) mm/s, and causes the asymmetry observed in the spectra. The detailed analysis yields also, for the first time, the fluctuating effective magnetic hyperfine field, H {sub eff} = 180(50) kOe.

  1. Physical processes in spin polarized plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Kulsrud, R.M.; Valeo, E.J.; Cowley, S.

    1984-05-01

    If the plasma in a nuclear fusion reactor is polarized, the nuclear reactions are modified in such a way as to enhance the reactor performance. We calculate in detail the modification of these nuclear reactions by different modes of polarization of the nuclear fuel. We also consider in detail the various physical processes that can lead to depolarization and show that they are by and large slow enough that a high degree of polarization can be maintained.

  2. Viscoelastic characterization of compacted pharmaceutical excipient materials by analysis of frequency-dependent mechanical relaxation processes

    Science.gov (United States)

    Welch, K.; Mousavi, S.; Lundberg, B.; Strømme, M.

    2005-09-01

    A newly developed method for determining the frequency-dependent complex Young's modulus was employed to analyze the mechanical response of compacted microcrystalline cellulose, sorbitol, ethyl cellulose and starch for frequencies up to 20 kHz. A Debye-like relaxation was observed in all the studied pharmaceutical excipient materials and a comparison with corresponding dielectric spectroscopy data was made. The location in frequency of the relaxation peak was shown to correlate to the measured tensile strength of the tablets, and the relaxation was interpreted as the vibrational response of the interparticle hydrogen and van der Waals bindings in the tablets. Further, the measured relaxation strength, holding information about the energy loss involved in the relaxation processes, showed that the weakest material in terms of tensile strength, starch, is the material among the four tested ones that is able to absorb the most energy within its structure when exposed to external perturbations inducing vibrations in the studied frequency range. The results indicate that mechanical relaxation analysis performed over relatively broad frequency ranges should be useful for predicting material properties of importance for the functionality of a material in applications such as, e.g., drug delivery, drug storage and handling, and also for clarifying the origin of hitherto unexplained molecular processes.

  3. Real-time observation of cascaded electronic relaxation processes in p-Fluorotoluene

    Science.gov (United States)

    Hao, Qiaoli; Deng, Xulan; Long, Jinyou; Wang, Yanmei; Abulimiti, Bumaliya; Zhang, Bing

    2017-08-01

    Ultrafast electronic relaxation processes following two photoexcitation of 400 nm in p-Fluorotoluene (pFT) have been investigated utilizing time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Cascaded electronic relaxation processes started from the electronically excited S2 state are directly imaged in real time and well characterized by two distinct time constants of 85 ± 10 fs and 2.4 ± 0.3 ps. The rapid component corresponds to the lifetime of the initially excited S2 state, including the structure relaxation from the Franck-Condon region to the conical intersection of S2/S1 and the subsequent internal conversion to the highly excited S1 state. While, the slower relaxation constant is attributed to the further internal conversion to the high levels of S0 from the secondarily populated S1 locating in the channel three region. Moreover, dynamical differences with benzene and toluene of analogous structures, including, specifically, the slightly slower relaxation rate of S2 and the evidently faster decay of S1, are also presented and tentatively interpreted as the substituent effects. In addition, photoelectron kinetic energy and angular distributions reveal the feature of accidental resonances with low-lying Rydberg states (the 3p, 4s and 4p states) during the multi-photon ionization process, providing totally unexpected but very interesting information for pFT.

  4. Nuclear Spin Relaxation

    Indian Academy of Sciences (India)

    IAS Admin

    Nuclei occur in many different species, called nuclides, which are defined by the numbers of protons and neutrons they contain. The chemical nature of an atom is defined by the number of protons in its nucleus. For example, all atoms of carbon have six protons in the nucleus, and all atoms of hydrogen have a single proton ...

  5. Energy thresholds of discrete breathers in thermal equilibrium and relaxation processes.

    Science.gov (United States)

    Ming, Yi; Ling, Dong-Bo; Li, Hui-Min; Ding, Ze-Jun

    2017-06-01

    So far, only the energy thresholds of single discrete breathers in nonlinear Hamiltonian systems have been analytically obtained. In this work, the energy thresholds of discrete breathers in thermal equilibrium and the energy thresholds of long-lived discrete breathers which can remain after a long time relaxation are analytically estimated for nonlinear chains. These energy thresholds are size dependent. The energy thresholds of discrete breathers in thermal equilibrium are the same as the previous analytical results for single discrete breathers. The energy thresholds of long-lived discrete breathers in relaxation processes are different from the previous results for single discrete breathers but agree well with the published numerical results known to us. Because real systems are either in thermal equilibrium or in relaxation processes, the obtained results could be important for experimental detection of discrete breathers.

  6. Atomistic simulation of processes in Ni-base alloys with account for local relaxations

    International Nuclear Information System (INIS)

    Bursik, Jiri

    2007-01-01

    Ordering in Ni-base superalloys is the crucial process controlling the development of the characteristic two-phase microstructure and subsequently the mechanical properties. Systems containing up to six alloying elements typical of advanced Ni-based superalloys are modelled in this work using a Monte Carlo approach with phenomenological Lennard-Jones pair potentials and interactions up to the third coordination sphere. Three-dimensional crystal block is used with over 10 5 atoms. Molecular dynamics approach is used to relax local atomic positions in course of ordering processes under applied stress. The importance of taking into account both relaxation of modelled block dimensions and relaxation of local atomic positions is discussed

  7. Effects of distribution function nonequilibrium tails on relaxation and transfer processes in rarefied gases

    International Nuclear Information System (INIS)

    Grigoryev, Yu.N.; Mikhalitsyn, A.N.; Yanenko, N.N.

    1984-01-01

    Quantitative characteristics of the nonmonotone relaxation process are studied in a gas of pseudo-Maxwell molecules. Basic results are obtained by a direct numerical integration of the nonlinear Boltzmann equation. The evolution of initial distributions being finite or having exponential asymptotics of tails was researched. In particular, initial data obtained by selective excitation (absorption) against the Maxwell background encountered in laser physics problems have been considered. It is shown that under conditions of a developed effect of nonmonotone relaxation the overpopulation in the velocity range 4 <= upsilon <= 10 exceeds on the average 2-3 times the equilibrium value. For the given particles energy the excitation is preserved during t = 5/6 and the total relaxation time of the overpopulation wave reaches t asymptotically equals 20. The amplitudes and the relaxation time of overpopulation in the ''cupola'' region of distribution are substantially lower than in the case of a developed effect in the tail. The influence of the effect on the kinetics of threshold chemical reaction is studied. From the results it follows that in the process of nonmonotone relaxation the mean rates of binary threshold reactions can exceed more than twice the equilibrium values. This estimate is valid for all power like intermolecular repulsive potentials from the pseudo-Maxwell model up to rigid spheres. Time intervals over which the mean reaction rate exceeds considerably the equilibrium one make from 5 to 15 mean free path times increasing with the decrease in the potential ''rigidity''. (author)

  8. The Stress Relaxation Process in Sutures Tied with a Surgeon's Knot in a Simulated Biological Environment.

    Science.gov (United States)

    Liber-Kneć, Aneta; Łagan, Sylwia

    2016-01-01

    The exact characteristics of sutures are not only the basis for selecting from among different types of suture, but also provide the necessary information for the design of new surgical sutures. Apart from information relating to the breaking load of a suture reported in pharmacopoeias, the viscoelastic properties of sutures can be an additional selection criterium - one that influences stitching quality, especially when there is a risk of wound dehiscence. The aim of the study was to assess the stress relaxation process for 3 polymeric sutures in an environment simulating the conditions in a living organism and (for comparison) in room conditions. Stress relaxation testing was carried out on 3 polymeric sutures: polypropylene (PP), polydioxanone (PDS) and polyglycolic acid (PGA). To identify the mechanical properties of the sutures, uniaxial tensile tests were conducted according to the Polish Pharmacopoeia. The relaxation test was carried out in room conditions and in the bath simulating a biological environment. The sutures being tested were tied with a surgeon's knot. The PP suture exhibited the greatest stress relaxation (18% of the initial stress in room conditions and 21% of the initial stress in the bath). The PGA suture exhibited the least stress relaxation (approximately 60% of the initial stress in room conditions and 59% of the initial stress in the bath). The PDS suture was tested at a lower strain level and showed stress relaxation similar to the PGA suture (approximately 63% of the initial stress in room conditions and 55% in the bath). Multifilament braided absorbable (PGA) sutures and monofilament absorbable (PDS) sutures had a higher stress relaxation ratio over time than monofilament non-absorbable (PP) sutures. These findings may indicate higher stress maintained over time in PDS and PGA sutures, and thus higher tension at wound edges, sufficient to resist wound dehiscence.

  9. Competition between domain walls and the reverse magnetization in the magnetic relaxation of a Pt/Co/Ir/Co/Pt spin switcher

    Science.gov (United States)

    Morgunov, R. B.; L'vova, G. L.; Hamadeh, A.; Mangin, S.

    2018-01-01

    A multilayer Pt/Co/Ir/Co/Pt/GaAs heterostructures demonstrates a long term (to several hours) magnetic relaxation between two stable states of the magnetization of the system. The magnetization reversal of the heterostructure layers occurs both due to the formation of nuclei of the reverse magnetization domains and as a result of their further growth by means of motion of domain walls. The competition between two these processes provides a nonexponential character of the magnetic relaxation. At 300 K, the contributions of these processes to the relaxation are commensurable, while, at temperatures lower than 200 K, the contribution of the nucleation is suppressed and the magnetic relaxation occurs as a result of motion of the domain walls.

  10. Relaxation processes in a lower disorder order transition diblock copolymer

    International Nuclear Information System (INIS)

    Sanz, Alejandro; Ezquerra, Tiberio A.; Nogales, Aurora; Hernández, Rebeca; Sprung, Michael

    2015-01-01

    The dynamics of lower disorder-order temperature diblock copolymer leading to phase separation has been observed by X ray photon correlation spectroscopy. Two different modes have been characterized. A non-diffusive mode appears at temperatures below the disorder to order transition, which can be associated to compositional fluctuations, that becomes slower as the interaction parameter increases, in a similar way to the one observed for diblock copolymers exhibiting phase separation upon cooling. At temperatures above the disorder to order transition T ODT , the dynamics becomes diffusive, indicating that after phase separation in Lower Disorder-Order Transition (LDOT) diblock copolymers, the diffusion of chain segments across the interface is the governing dynamics. As the segregation is stronger, the diffusive process becomes slower. Both observed modes have been predicted by the theory describing upper order-disorder transition systems, assuming incompressibility. However, the present results indicate that the existence of these two modes is more universal as they are present also in compressible diblock copolymers exhibiting a lower disorder-order transition. No such a theory describing the dynamics in LDOT block copolymers is available, and these experimental results may offer some hints to understanding the dynamics in these systems. The dynamics has also been studied in the ordered state, and for the present system, the non-diffusive mode disappears and only a diffusive mode is observed. This mode is related to the transport of segment in the interphase, due to the weak segregation on this system

  11. Relaxation processes in a lower disorder order transition diblock copolymer

    Energy Technology Data Exchange (ETDEWEB)

    Sanz, Alejandro; Ezquerra, Tiberio A.; Nogales, Aurora, E-mail: aurora.nogales@csic.es [Instituto de Estructura de la Materia, IEM-CSIC. C/ Serrano 121, Madrid 28006 (Spain); Hernández, Rebeca [Instituto de Ciencia y Tecnología de Polímeros, ICTP-CSIC. C/ Juan de la Cierva 3, Madrid 28006 (Spain); Sprung, Michael [Petra III at DESY, Notkestr. 85, 22607 Hamburg (Germany)

    2015-02-14

    The dynamics of lower disorder-order temperature diblock copolymer leading to phase separation has been observed by X ray photon correlation spectroscopy. Two different modes have been characterized. A non-diffusive mode appears at temperatures below the disorder to order transition, which can be associated to compositional fluctuations, that becomes slower as the interaction parameter increases, in a similar way to the one observed for diblock copolymers exhibiting phase separation upon cooling. At temperatures above the disorder to order transition T{sub ODT}, the dynamics becomes diffusive, indicating that after phase separation in Lower Disorder-Order Transition (LDOT) diblock copolymers, the diffusion of chain segments across the interface is the governing dynamics. As the segregation is stronger, the diffusive process becomes slower. Both observed modes have been predicted by the theory describing upper order-disorder transition systems, assuming incompressibility. However, the present results indicate that the existence of these two modes is more universal as they are present also in compressible diblock copolymers exhibiting a lower disorder-order transition. No such a theory describing the dynamics in LDOT block copolymers is available, and these experimental results may offer some hints to understanding the dynamics in these systems. The dynamics has also been studied in the ordered state, and for the present system, the non-diffusive mode disappears and only a diffusive mode is observed. This mode is related to the transport of segment in the interphase, due to the weak segregation on this system.

  12. Quantum information processing with electronic and nuclear spins in semiconductors

    Science.gov (United States)

    Klimov, Paul Victor

    Traditional electronic and communication devices operate by processing binary information encoded as bits. Such digital devices have led to the most advanced technologies that we encounter in our everyday lives and they influence virtually every aspect of our society. Nonetheless, there exists a much richer way to encode and process information. By encoding information in quantum mechanical states as qubits, phenomena such as coherence and entanglement can be harnessed to execute tasks that are intractable to digital devices. Under this paradigm, it should be possible to realize quantum computers, quantum communication networks and quantum sensors that outperform their classical counterparts. The electronic spin states of color-center defects in the semiconductor silicon carbide have recently emerged as promising qubit candidates. They have long-lived quantum coherence up to room temperature, they can be controlled with mature magnetic resonance techniques, and they have a built-in optical interface operating near the telecommunication bands. In this thesis I will present two of our contributions to this field. The first is the electric-field control of electron spin qubits. This development lays foundation for quantum electronics that operate via electrical gating, much like traditional electronics. The second is the universal control and entanglement of electron and nuclear spin qubits in an ensemble under ambient conditions. This development lays foundation for quantum devices that have a built-in redundancy and can operate in real-world conditions. Both developments represent important steps towards practical quantum devices in an electronic grade material.

  13. A carbon-13 NMR spin-lattice relaxation study of the molecular conformation of the nootropic drug 2-oxopyrrolidin-1-ylacetamide

    Science.gov (United States)

    Baldo, M.; Grassi, A.; Guidoni, L.; Nicolini, M.; Pappalardo, G. C.; Viti, V.

    The spin-lattice relaxation times ( T1) of carbon-13 resonances of the drug 2-oxopyrrolidin- 1-ylacetamide ( 2OPYAC) were determined in CDCl 3 + DMSO and H 2O solutions to investigate the internal conformational flexibility. The measured T1s for the hydrogen-bearing carbon atoms of the 2-pyrrolidone ring fragment were diagnostic of a rigid conformation with respect to the acetamide linked moiety. The model of anisotropic reorientation of a rigid body was used to analyse the measured relaxation data in terms of a single conformation. Owing to the small number of T1 data available the fitting procedure for each of the possible conformations failed. The structure corresponding to the rigid conformation was therefore considered to be the one that is strongly stabilized by internal hydrogen bonding as predicted on the basis of theoretical MO ab initio quantum chemical calculations.

  14. Decay of Metastable State with Account of Agglomeration and Relaxation Processes

    Directory of Open Access Journals (Sweden)

    Victor Kurasov

    2016-01-01

    Full Text Available Theoretical description of the metastable phase decay kinetics in the presence of specific connections between the embryos of small sizes has been given. The theory of the decay kinetics in the presence of relaxation processes is constructed in analytical manner. The m-mers nucleation is investigated and the global kinetics of decay is also constructed in this case analytically.

  15. Non-equilibrium reacting gas flows kinetic theory of transport and relaxation processes

    CERN Document Server

    Nagnibeda, Ekaterina; Nagnibeda, Ekaterina

    2009-01-01

    This volume develops the kinetic theory of transport phenomena and relaxation processes in the flows of reacting gas mixtures. The theory is applied to the modeling of non-equilibrium flows behind strong shock waves, in the boundary layer, and in nozzles.

  16. Near-surface structural phase transition of SrTiO3 studied with zero-field beta-detected nuclear spin relaxation and resonance.

    Science.gov (United States)

    Salman, Z; Kiefl, R F; Chow, K H; Hossain, M D; Keeler, T A; Kreitzman, S R; Levy, C D P; Miller, R I; Parolin, T J; Pearson, M R; Saadaoui, H; Schultz, J D; Smadella, M; Wang, D; MacFarlane, W A

    2006-04-14

    We demonstrate that zero-field beta-detected nuclear quadrupole resonance and spin relaxation of low energy (8)Li can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO(3) single crystal occurs at T(c) approximately 150K, i.e., approximately 45K higher than T(c)bulk, and that the tetragonal domains formed below T(c) are randomly oriented.

  17. $^{11}$B and $^{27}$Al NMR spin-lattice relaxation and Knight shift study of Mg$_{1-x}$Al$_x$B$_2$. Evidence for anisotropic Fermi surface

    OpenAIRE

    Papavassiliou, G.; Pissas, M.; Karayanni, M.; Fardis, M.; Koutandos, S.; Prassides, K.

    2002-01-01

    We report a detailed study of $^{11}$B and $^{27}$Al NMR spin-lattice relaxation rates ($1/T_1$), as well as of $^{27}$Al Knight shift (K) of Mg$_{1-x}$Al$_x$B$_2$, $0\\leq x\\leq 1$. The obtained ($1/T_1T$) and K vs. x plots are in excellent agreement with ab initio calculations. This asserts experimentally the prediction that the Fermi surface is highly anisotropic, consisting mainly of hole-type 2-D cylindrical sheets from bonding $2p_{x,y}$ boron orbitals. It is also shown that the density ...

  18. Quasistatic internal magnetic field detected in the pseudogap phase of Bi2 +xSr2 -xCaCu2O8 +δ by muon spin relaxation

    Science.gov (United States)

    Pal, A.; Dunsiger, S. R.; Akintola, K.; Fang, A. C. Y.; Elhosary, A.; Ishikado, M.; Eisaki, H.; Sonier, J. E.

    2018-02-01

    We report muon spin relaxation (μ SR ) measurements of optimally doped and overdoped Bi2 +xSr2 -xCaCu2O8 +δ single crystals that reveal the presence of a weak temperature-dependent quasistatic internal magnetic field of electronic origin in the superconducting and pseudogap (PG) phases. In both samples the internal magnetic field persists up to 160 K, but muon diffusion prevents following the evolution of the field to higher temperatures. We consider the evidence from our measurements in support of PG order parameter candidates, namely, electronic loop currents and magnetoelectric quadrupoles.

  19. Muon-spin relaxation study of the double perovskite insulators Sr2 BOsO6 (B  =  Fe, Y, ln).

    Science.gov (United States)

    Williams, R C; Xiao, F; Thomas, I O; Clark, S J; Lancaster, T; Cornish, G A; Blundell, S J; Hayes, W; Paul, A K; Felser, C; Jansen, M

    2016-02-24

    We present the results of zero-field muon-spin relaxation measurements made on the double perovskite insulators Sr2 BOsO6 (B = Fe,Y, In). Spontaneous muon-spin precession indicative of quasistatic long range magnetic ordering is observed in Sr2FeOsO6 within the AF1 antiferromagnetic phase for temperatures below [Formula: see text] K. Upon cooling below T2≈67 K the oscillations cease to be resolvable owing to the coexistence of the AF1 and AF2 phases, which leads to a broader range of internal magnetic fields. Using density functional calculations we identify a candidate muon stopping site within the unit cell, which dipole field simulations show to be consistent with the proposed magnetic structure. The possibility of incommensurate magnetic ordering is discussed for temperatures below TN = 53 K and 25 K for Sr2YOsO6 and Sr2InOsO6, respectively.

  20. Relaxation study of a paramagnetic ion by the observation of nuclear resonance signals

    International Nuclear Information System (INIS)

    Landesman, A.

    1960-01-01

    Dynamic polarization of protons in water containing the paramagnetic ion NO(SO 3 ) 2 was studied, both theoretically and experimentally, as a function of magnetic field. The enhancement of the proton polarization depends appreciably on the relaxation process of the electron spin and so enables us to decide which is the real relaxation process. We tried the two following processes: a) The electron spin is coupled with the nitrogen magnetic moment by hyperfine interaction; if this interaction has an anisotropic part, a relaxation process for the electronic spin will result through the Brownian motion of the ion. b) The relaxation of the electron spin takes place through spin-orbit coupling of the electron spin. Experimental results showed that the relaxation took place through the second process with the help of dynamic polarization we were able to study the relaxation of an electron spin in a liquid without using any electron resonance spectrometer, simply by observing the resonance of a nuclear spin coupled with the electron spin. Reprint of a paper published in Le Journal de Physique et le Radium, t. 20, p. 937-948, 1959 [fr

  1. A new parallel algorithm for simulation of spin glasses on scales of space-time periods of external fields with consideration of relaxation effects

    International Nuclear Information System (INIS)

    Gevorkyan, A.S.; Abajyan, H.G.

    2011-01-01

    We have investigated the statistical properties of an ensemble of disordered 1D spatial spin chains (SSCs) of finite length, placed in an external field, with consideration of relaxation effects. The short-range interaction complex-classical Hamiltonian was first used for solving this problem. A system of recurrent equations is obtained on the nodes of the spin-chain lattice. An efficient mathematical algorithm is developed on the basis of these equations with consideration of the advanced Sylvester conditions which allow step by step construct a huge number of stable spin chains in parallel. The distribution functions of different parameters of spin-glass system are constructed from the first principles of the complex classical mechanics by analyzing the calculation results of the 1D SSCs ensemble. It is shown that the behavior of the parameter distributions is quite different depending on the external fields. The energy ensembles and constants of spin-spin interactions are changed smoothly depending on the external field in the limit of statistical equilibrium, while some of them such as the mean value of polarizations of ensemble and parameters of its orderings are frustrated. We have also studied some critical properties of the ensemble of such catastrophes in the Clausius-Mossotti equation depending on the value of the external field. We have shown that the generalized complex-classical approach excludes these catastrophes allowing one to organize continuous parallel computing on the whole region of values of the external field including critical points. A new representation of the partition function based on these investigations is suggested. As opposed to usual definition, this function is a complex one and its derivatives are everywhere defined, including critical points

  2. Relaxation-compensated difference spin diffusion NMR for detecting 13C–13C long-range correlations in proteins and polysaccharides

    International Nuclear Information System (INIS)

    Wang, Tuo; Williams, Jonathan K.; Schmidt-Rohr, Klaus; Hong, Mei

    2015-01-01

    The measurement of long-range distances remains a challenge in solid-state NMR structure determination of biological macromolecules. In 2D and 3D correlation spectra of uniformly 13 C-labeled biomolecules, inter-residue, inter-segmental, and intermolecular 13 C– 13 C cross peaks that provide important long-range distance constraints for three-dimensional structures often overlap with short-range cross peaks that only reflect the covalent structure of the molecule. It is therefore desirable to develop new approaches to obtain spectra containing only long-range cross peaks. Here we show that a relaxation-compensated modification of the commonly used 2D 1 H-driven spin diffusion (PDSD) experiment allows the clean detection of such long-range cross peaks. By adding a z-filter to keep the total z-period of the experiment constant, we compensate for 13 C T 1 relaxation. As a result, the difference spectrum between a long- and a scaled short-mixing time spectrum show only long-range correlation signals. We show that one- and two-bond cross peaks equalize within a few tens of milliseconds. Within ∼200 ms, the intensity equilibrates within an amino acid residue and a monosaccharide to a value that reflects the number of spins in the local network. With T 1 relaxation compensation, at longer mixing times, inter-residue and inter-segmental cross peaks increase in intensity whereas intra-segmental cross-peak intensities remain unchanged relative to each other and can all be subtracted out. Without relaxation compensation, the difference 2D spectra exhibit both negative and positive intensities due to heterogeneous T 1 relaxation in most biomolecules, which can cause peak cancellation. We demonstrate this relaxation-compensated difference PDSD approach on amino acids, monosaccharides, a crystalline model peptide, a membrane-bound peptide and a plant cell wall sample. The resulting difference spectra yield clean multi-bond, inter-residue and intermolecular correlation peaks

  3. Numerical methods for TVD transport and coupled relaxing processes in gases and plasmas

    Science.gov (United States)

    Cambier, Jean-Luc

    1990-01-01

    The construction of second-order upwind schemes for nonequilibrium plasmas, for both one- and two-fluid formulations is demonstrated. Coupled relaxation processes, including ionization kinetics and radiative processes and their algorithms for nonequilibrium, multiple temperature conditions are described as well. The paper applies the numerical techniques on some simple test cases, points out critical problems and their solutions, and makes qualitative comparisons with known results, whenever possible.

  4. Elucidation of Dual Magnetic Relaxation Processes in Dinuclear Dysprosium(III) Phthalocyaninato Triple-Decker Single-Molecule Magnets Depending on the Octacoordination Geometry.

    Science.gov (United States)

    Katoh, Keiichi; Aizawa, Yu; Morita, Takaumi; Breedlove, Brian K; Yamashita, Masahiro

    2017-11-02

    When applying single-molecule magnets (SMMs) to spintronic devices, control of the quantum tunneling of the magnetization (QTM) as well as a spin-lattice interactions are important. Attempts have been made to use not only coordination geometry but also magnetic interactions between SMMs as an exchange bias. In this manuscript, dinuclear dysprosium(III) (Dy III ) SMMs with the same octacoordination geometry undergo dual magnetic relaxation processes at low temperature. In the dinuclear Dy III phthalocyaninato (Pc 2- ) triple-decker type complex [(Pc)Dy(ooPc)Dy(Pc)] (1) (ooPc 2- =2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato) with a square-antiprismatic (SAP) geometry, the ground state is divided by the Zeeman effect, and level intersection occurs when a magnetic field is applied. Due to the ground state properties of 1, since the Zeeman diagram where the levels intersect in an H dc of 2500 Oe, two kinds of QTM and direct processes occur. However, dinuclear Dy III -Pc systems with C 4 geometry, which have a twist angle (ϕ) of less than 45° do not undergo dual magnetic relaxation processes. From magnetic field and temperature dependences, the dual magnetic relaxation processes were clarified. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Polymer dynamics near the surface and in the bulk of poly(tetrafluoroethylene) probed by zero-field muon-spin-relaxation spectroscopy.

    Science.gov (United States)

    McKenzie, Iain; Salman, Zaher; Giblin, Sean R; Han, Yun Yu; Leach, Gary W; Morenzoni, Elvezio; Prokscha, Thomas; Suter, Andreas

    2014-02-01

    The results of many experiments on polymers such as polystyrene indicate that the polymer chains near a free surface exhibit enhanced dynamics when compared with the bulk. We have investigated whether this is the case for poly(tetrafluoroethylene) (PTFE) by using zero-field muon-spin-relaxation spectroscopy to characterize a local probe, the F-Mu(+)-F state, which forms when spin-polarized positive muons are implanted in PTFE. Low-energy muons (implantation energies from 2.0 to 23.0 keV) were used to study the F-Mu(+)-F state between ∼ 23 and 191 nm from the free surface of PTFE. Measurements were also made with surface muons (4.1 MeV) where the mean implantation depth is on the order of ∼ 0.6 mm. The relaxation rate of the F-Mu(+)-F state up to ∼ 150 K was found to be significantly higher for muons implanted at 2.0 keV than for higher implantation energies, which suggests that the polymer chains in a region on the order of a few tens of nanometers from the free surface are more mobile than those in the bulk.

  6. Relaxation processes in optically excites metal clusters; Relaxationsprozesse in optisch angeregten Metallclustern

    Energy Technology Data Exchange (ETDEWEB)

    Stanzel, J.

    2007-08-10

    The present work is concerned with the dynamics of optically excited metal clusters in the gas phase. Small mass-selected gold and tungsten cluster anions (Au{sup -}{sub n}, n=5-8, 14, 20 and W{sup -}{sub n}, n=3-14) are studied using femtosecond time-resolved photoelectron spectroscopy. Depending on the electronic structure in the valence region as well as on the optical excitation energy fundamentally different relaxation processes are observed. In small gold cluster anions excited with 1.56 eV an isolated electronically excited state is populated. The time-dependent measurements are strongly sizedependent and open insights into photoinduced geometry changes of the nuclear framework. Oscillatory vibrational wavepacket motion in Au{sup -}{sub 5}, an extremely longlived ({tau} >90 ns) electronically excited state in Au{sup -}{sub 6} as well as photoinduced melting in Au{sup -}{sub 7} and Au{sup -}{sub 8} is monitored in real time. By increasing the OPTICAL excitation energy to 3.12 eV a completely different scenario is observed. A multitude of electronically excited states can be reached upon optical excitation and as a consequence electronic relaxation processes that take place on a time scale of 1 ps are dominating. This is shown for Au{sup -}{sub 7}, Au{sup -}{sub 14} and Au{sup -}{sub 20}. Compared to gold clusters, tungsten clusters are characterized by a significantly higher electronic density of states in the valence region. Therefore electronic relaxation processes are much more likely and take place on a significantly faster time scale. The fast electronic relaxation processes are distinguished from pure vibrational relaxation. It is shown that already in the four atomic tungsten cluster W{sup -}{sub 4} electronic relaxation processes take place on a time scale of 30 fs. In all investigated tungsten cluster anions (W{sup -}{sub n}, n=3-14) an equilibrium between electronic and vibrational system is reached within around 1 ps after optical excitation which

  7. Virtual processes and superradiance in spin-boson modes

    Energy Technology Data Exchange (ETDEWEB)

    Alcalde, M. Aparicio; Kullock, R.; Svaiter, N.F. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)]. E-mails: aparicio@cbpf.br; rkullock@cbpf.br; nfuxsvai@cbpf.br

    2008-07-01

    We consider spin-boson models composed by a single bosonic mode and an ensemble of N identical two-level atoms. The situation where the coupling between the bosonic mode and the atoms generates real and virtual processes is studied, where the whole system is in thermal equilibrium with a reservoir at temperature {beta}{sup -1}. Phase transitions from ordinary fluorescence to super radiant phase in three different models is investigated. First a model where the coupling between the bosonic mode and the j - th atom is via the pseudo-spin operator {sigma}{sub (j)}{sup z} is studied. Second, we investigate the generalized Dicke model, introducing different coupling constants between the single mode bosonic field and the environment, g{sub 1} and g{sub 2} for rotating and counter-rotating terms, respectively. Finally it is considered a modified version of the generalized Dicke model with intensity-dependent coupling in the rotating terms. In the first model the zero mode contributes to render the canonical entropy a negative quantity for low temperatures. The last two models presents phase transitions, even when only Hamiltonian terms which generates virtual processes are considered. (author)

  8. Virtual processes and superradiance in spin-boson modes

    International Nuclear Information System (INIS)

    Alcalde, M. Aparicio; Kullock, R.; Svaiter, N.F.

    2008-01-01

    We consider spin-boson models composed by a single bosonic mode and an ensemble of N identical two-level atoms. The situation where the coupling between the bosonic mode and the atoms generates real and virtual processes is studied, where the whole system is in thermal equilibrium with a reservoir at temperature β -1 . Phase transitions from ordinary fluorescence to super radiant phase in three different models is investigated. First a model where the coupling between the bosonic mode and the j - th atom is via the pseudo-spin operator σ (j) z is studied. Second, we investigate the generalized Dicke model, introducing different coupling constants between the single mode bosonic field and the environment, g 1 and g 2 for rotating and counter-rotating terms, respectively. Finally it is considered a modified version of the generalized Dicke model with intensity-dependent coupling in the rotating terms. In the first model the zero mode contributes to render the canonical entropy a negative quantity for low temperatures. The last two models presents phase transitions, even when only Hamiltonian terms which generates virtual processes are considered. (author)

  9. Spin-controlled atom-ion chemistry.

    Science.gov (United States)

    Sikorsky, Tomas; Meir, Ziv; Ben-Shlomi, Ruti; Akerman, Nitzan; Ozeri, Roee

    2018-03-02

    Quantum control of chemical reactions is an important goal in chemistry and physics. Ultracold chemical reactions are often controlled by preparing the reactants in specific quantum states. Here we demonstrate spin-controlled atom-ion inelastic (spin-exchange) processes and chemical (charge-exchange) reactions in an ultracold Rb-Sr + mixture. The ion's spin state is controlled by the atomic hyperfine spin state via spin-exchange collisions, which polarize the ion's spin parallel to the atomic spin. We achieve ~ 90% spin polarization due to the absence of strong spin-relaxation channel. Charge-exchange collisions involving electron transfer are only allowed for (RbSr) + colliding in the singlet manifold. Initializing the atoms in various spin states affects the overlap of the collision wave function with the singlet molecular manifold and therefore also the reaction rate. Our observations agree with theoretical predictions.

  10. Stimulated polarization wave process in spin 3/2 chains

    International Nuclear Information System (INIS)

    Furman, G. B.

    2007-01-01

    Stimulated wave of polarization, triggered by a flip of a single spin, presents a simple model of quantum amplification. Recently, it has been demonstrated that, in an idealized one-dimensional Ising spin 1/2 chain with nearest-neighbor interactions and realistic spin 1/2 chain including the natural dipole-dipole interactions, irradiated by a weak resonant transverse field, a wave of flipped spins can be triggered by a single spin flip. Here we focuse on control of polarization wave in chain of spin 3/2, where the nuclear quadrupole interaction is dominant. Results of simulations for 1D spin chains and rings with up to five spins are presented.

  11. Glass transition and relaxation processes of polymers studied by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Uedono, Akira; Tanigawa, Shoichiro [Tsukuba Univ., Ibaraki (Japan). Inst. of Materials Science

    1996-10-01

    The glass transition and relaxation processes of polymers were studied by the positron annihilation technique. A positron implanted into polymers might annihilate from positronium (Ps) states in open spaces. Ps is a bound state between a positron and an electron, and its nonrelativistic quantum mechanics is practically identical to that of a hydrogen atom. The lifetime of Ps can be associated with the size of the open spaces, and the formation probability of Ps provides information of motions of molecules. Since the glass transition or relaxation processes affect behavior of open spaces, one can study these phenomena through the detection of the open spaces using the positron annihilation technique. In the present paper, we report studies of the glass transition and relaxation processes in polyethylene, polypropylene, and polystyrene by measurements of lifetime spectra of positrons and those of Doppler broadening profiles of the annihilation radiation. For these specimens, by measurements of the lifetime of Ps, {tau}{sub 3}, as a function of temperature, the glass transition temperature, T{sub g}, was determined as an onset temperature of the increase in the temperature coefficient of {tau}{sub 3}. Below T{sub g}, local motions of molecules were detected by measurements of the formation probability of Ps. The positron annihilation as a tool for the characterization of polymers was discussed. (author). 51 refs.

  12. Dynamic analysis of spinning solar sails at deployment process

    Directory of Open Access Journals (Sweden)

    Xinxing ZHANG

    2017-10-01

    Full Text Available The spinning deployment process of solar sails is analyzed in this study. A simplified model is established by considering the out-of-plane and in-plane motions of solar sails. The influences of structure parameters, initial conditions, and feedback control parameters are also analyzed. A method to build the geometric model of a solar sail is presented by analyzing the folding process of solar sails. The finite element model of solar sails is then established, which contains continuous cables and sail membranes. The dynamics of the second-stage deployment of solar sails are simulated by using ABAQUS software. The influences of the rotational speed and out-of-plane movement of the hub are analyzed by different tip masses, initial velocities, and control parameters. Compared with the results from theoretical models, simulation results show good agreements.

  13. An Analysis and Modelling of Spinning Process without Wall-Thickness Reduction

    Directory of Open Access Journals (Sweden)

    Jurković, M.

    2006-01-01

    Full Text Available Through the spinning process it is made the different axial-symmetrical parts by acting spinning roller on blank of sheet metal, which is shaped through a chuck. In the paper is shown an analyse of stressed and strained state, as well as forming force components of spinning process. On the ground of experimental results it is made mathematical modelling of spinning forming force. The obtained mathematical model describes enough accurate and reliable (P = 0,98 the spinning forming force.

  14. FACTORS AND MOTIVES FOR THE SPIN-OFF PROCESS

    Directory of Open Access Journals (Sweden)

    Igor B. Khmelev

    2013-01-01

    Full Text Available This article is about the factors that encourage managers to use spin offs as a restructuring tool, and about the main motives of spin-off transactions. Attention is focused on the nature of spin-offs. There is a classification of the driving factors of spin-offs from the theoretical viewpoint and the degree of this question elaboration in economic literature. Four factors are marked: industrial, life cycle, company size and support of the parent company. The basic spin-off motives are pointed in this article.

  15. F center-molecular ion couples in alkali halides: Magneto-optics study (part two). Spin lattice relaxation time and electron spin memory; Studi di magnetoottica sulla coppia centro F-ione molecolare negli alogenuri alcalini: Parte 2. Misura del tempo di rilassamento spin-reticolo e della memoria di spin dell`elettrone nel ciclo ottico

    Energy Technology Data Exchange (ETDEWEB)

    Baldacchini, G.; Botti, S.; Grassano, U.M.; Luty, F.

    1991-10-01

    The spin-lattice relaxation time in the ground state, T/sub 1/, and the spin-mixing parameter during the optical cycle, epsilon, were measured in FH(OH) and FH(CN) centers in various alkali halides (KCl, KBr, KI, CsCl, and CsBr). For a close comparison, all experiments were performed before and after the optical association of the F center and molecular ion. T/sub 1/ becomes shorter before and still more after aggregation with respect to the values measured in the pure crystal, especially at very low magnetic fields. Epsilon decreases a little in crystals doped with OH-, while it increases a lot in crystals doped with CN-. Part of these results can be interpreted within the actual knowledge of the F-center physics. Part have been used to shed some light on the various unknown aspects of the energy transfer between the excited F-center and the molecular ion.

  16. Interaction study of polyisobutylene with paraffins by NMR using the evaluation of spin-lattice relaxation times for hydrogen nuclei; Estudo da interacao do poliisobutileno com parafinas por RMN no estado solido

    Energy Technology Data Exchange (ETDEWEB)

    Marques, Rosana G.G. [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas - CENPES]. E-mail: garrido@cenpes.petrobras.com.br; Tavares, Maria I.B. [Universidade Federal, Rio de Janeiro, RJ (Brazil). Inst. de Macromoleculas]. E-mail: mibt@ima.ufrj.br

    2001-07-01

    The evaluation of spin-lattice relaxation times of {sup 1}H for polyisobutylene/paraffin systems, were obtained using the classic inversion recovery technique, and also through Cross Polarization Magic Angle Spinning (CP/MAS) techniques varying the contact time and also by the delayed contact time pulse sequence. NMR results showed that the polyisobutylene/paraffin systems in which high molecular weight paraffins were used, is heterogeneous. However, for paraffins with low molecular weight, the system presents good homogeneity. (author)

  17. Uncertainty management by relaxation of conflicting constraints in production process scheduling

    Science.gov (United States)

    Dorn, Juergen; Slany, Wolfgang; Stary, Christian

    1992-01-01

    Mathematical-analytical methods as used in Operations Research approaches are often insufficient for scheduling problems. This is due to three reasons: the combinatorial complexity of the search space, conflicting objectives for production optimization, and the uncertainty in the production process. Knowledge-based techniques, especially approximate reasoning and constraint relaxation, are promising ways to overcome these problems. A case study from an industrial CIM environment, namely high-grade steel production, is presented to demonstrate how knowledge-based scheduling with the desired capabilities could work. By using fuzzy set theory, the applied knowledge representation technique covers the uncertainty inherent in the problem domain. Based on this knowledge representation, a classification of jobs according to their importance is defined which is then used for the straightforward generation of a schedule. A control strategy which comprises organizational, spatial, temporal, and chemical constraints is introduced. The strategy supports the dynamic relaxation of conflicting constraints in order to improve tentative schedules.

  18. Simulation study of MHD relaxation and reconnection processes in RFP plasma

    International Nuclear Information System (INIS)

    Kusano, Kanya; Kunimoto, Kaito; Suzuki, Yoshio; Tamano, Teruo; Sato, Tetsuya

    1991-01-01

    The authors have studied several nonlinear processes in RFP plasma through the use of 3D MHD simulations. In particular, they have shed light on: (1) dynamo and self-sustainment in reversed-field pinch (RFP), (2) phase locking process in MHD relaxation, and (3) the heating and acceleration in magnetic reconnection process. First, the contributions of the kink (m = 1) mode (linearly unstable) and of the m = 0 mode (driven by nonlinear coupling) to the dynamo are qualitatively evaluated using a high accuracy simulation. It is found that, if the free energy to drive kink instabilities is as small as that in the actual experimental plasma, the m = 0 modes, driven nonlinearly, play a more important role for the flux generation than the kink modes. Secondly, numerical simulations of the self-sustainment process in a RFP are performed. It is confirmed that the self-sustainment process is a coherent oscillating process composed of the MHD relaxation and the resistive diffusion processes. Toroidal phase locking process of kink modes is numerically observed in simulations of self-reversal and self-sustainment processes. It has characteristics similar to the slinky mode observed in the OHTE experiment. A detailed investigation reveals that nonlinear coupling between the most unstable two kink modes governs the entire dynamics in all kink modes and leads to the phase locking process. They find that reconnection can accelerate plasma over a local Alfven speed. This is a result of the fact that the magnetic field in the downstream area plays a similar role to de Laval nozzle. They also investigate the heating mechanisms in reconnection process. It is revealed that the viscous heating rate is as large as the joule heating rate in the reconnection process. This result implies that the viscous heating in the reconnection process is an important candidate for the mechanism to explain the RFP experiments where the ion temperatures is higher than the electron temperature

  19. NMR spin-lattice relaxation study of 7Li and 93Nb nuclei in Ti- or Fe-doped LiNbO3:Mg single crystals

    Directory of Open Access Journals (Sweden)

    Tae Ho Yeom

    2016-04-01

    Full Text Available In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO3, LiNbO3:Mg, LiNbO3:Mg/Ti, LiNbO3:Mg/Fe, and LiNbO3:Mg/Fe (thermally treated at 500°C single crystals. The results for the LiNbO3:Mg single crystals doped with Fe3+ or Ti3+ are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO3:Mg/Fe single crystals were examined based on the T1 analysis of 7Li and 93Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.

  20. Determination of correlation times from selective and non-selective spin-lattice relaxation rates and their use in drug-drug and drug-albumin interaction studies

    Directory of Open Access Journals (Sweden)

    Tinoco Luzineide Wanderley

    1999-01-01

    Full Text Available The effects of the changes in sample concentration on the NMR chemical shifts and on the selective and non-selective spin-lattice relaxation rates (R1S and R1NS of the three isomers of nitrobenzaldeyde guanyl hydrazone (NBGH pure and with bovine serum albumin (BSA were measured in solution. The results wereused to determine the correlation times (tauc, showing that the degree of intermolecular drug-drug association varies with the nitro group position on the ring and that this degree of association interferes with the interaction of these drugs with BSA. The results suggest that the degree of drug-drug and drug-BSA association are related to the in vitro anti-Trypanosoma cruzi activity of these compounds.

  1. Unconventional Superconductivity in La(7)Ir(3) Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry.

    Science.gov (United States)

    Barker, J A T; Singh, D; Thamizhavel, A; Hillier, A D; Lees, M R; Balakrishnan, G; Paul, D McK; Singh, R P

    2015-12-31

    The superconductivity of the noncentrosymmetric compound La(7)Ir(3) is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature T(c)=2.25  K-a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La(7)Ir(3) may be unconventional and paves the way for further studies of this family of materials.

  2. Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine2(CN2

    Directory of Open Access Journals (Sweden)

    Kasper S. Kjær

    2017-07-01

    Full Text Available We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy2(CN2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2′-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy2(CN2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy2(CN2] complement prior measurement performed on [Fe(bpy3]2+ and [Fe(bpy(CN4]2− in dimethylsulfoxide solution and help complete the chemical series [Fe(bpyN(CN6–2N]2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3d transition metal complexes.

  3. Synthesis, crystal structures, and magnetic properties of cyanide-bridged W(V)Mn(III) anionic coordination polymers containing divalent cationic moieties: slow magnetic relaxations and spin crossover phenomenon.

    Science.gov (United States)

    Yoon, Jung Hee; Lim, Kwang Soo; Ryu, Dae Won; Lee, Woo Ram; Yoon, Sung Won; Suh, Byoung Jin; Hong, Chang Seop

    2014-10-06

    Two trimetallic coordination complexes were prepared by self-assembly of [W(CN)8](3-) and the Mn(III) Schiff base followed by the addition of a Zn(II) or Fe(II) cationic unit. The octacyanotungstate connects neighboring Mn(III) centers to form a one-dimensional chain. The anionic chain requires cationic units of Zn(II) or Fe(II) to maintain charge balance in the structure. The Zn-containing complex shows ferrimagnetic behavior originating from the antiparallel alignment of W(V) and Mn(III) spins within the chain, which leads to slow magnetic relaxation at low temperatures. For the Fe(II)-containing compound, Fe(II) moieties are integrated into the ferrimagnetic chains, altering their spin states depending on the temperature. It appears that the coexistence of high- and low-spin states in the low temperature regime is responsible for the slower and faster relaxations of the magnetization.

  4. Optimizations of spin-exchange relaxation-free magnetometer based on potassium and rubidium hybrid optical pumping

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Jiancheng; Wang, Tao, E-mail: wangtao@buaa.edu.cn; Li, Yang [School of Instrument Science and Opto-Electronics Engineering, Beihang University, Beijing 100191 (China); Zhang, Hong; Zou, Sheng [School of Instrument Science and Engineering, Southeast University, Nanjing 210096 (China)

    2014-12-15

    The hybrid optical pumping atomic magnetometers have not realized its theoretical sensitivity, the optimization is critical for optimal performance. The optimizations proposed in this paper are suitable for hybrid optical pumping atomic magnetometer, which contains two alkali species. To optimize the parameters, the dynamic equations of spin evolution with two alkali species were solved, whose steady-state solution is used to optimize the parameters. The demand of the power of the pump beam is large for hybrid optical pumping. Moreover, the sensitivity of the hybrid optical pumping magnetometer increases with the increase of the power density of the pump beam. The density ratio between the two alkali species is especially important for hybrid optical pumping magnetometer. A simple expression for optimizing the density ratio is proposed in this paper, which can help to determine the mole faction of the alkali atoms in fabricating the hybrid cell before the cell is sealed. The spin-exchange rate between the two alkali species is proportional to the saturated density of the alkali vapor, which is highly dependent on the temperature of the cell. Consequently, the sensitivity of the hybrid optical pumping magnetometer is dependent on the temperature of the cell. We proposed the thermal optimization of the hybrid cell for a hybrid optical pumping magnetometer, which can improve the sensitivity especially when the power of the pump beam is low. With these optimizations, a sensitivity of approximately 5 fT/Hz{sup 1/2} is achieved with gradiometer arrangement.

  5. Optimizations of spin-exchange relaxation-free magnetometer based on potassium and rubidium hybrid optical pumping

    International Nuclear Information System (INIS)

    Fang, Jiancheng; Wang, Tao; Li, Yang; Zhang, Hong; Zou, Sheng

    2014-01-01

    The hybrid optical pumping atomic magnetometers have not realized its theoretical sensitivity, the optimization is critical for optimal performance. The optimizations proposed in this paper are suitable for hybrid optical pumping atomic magnetometer, which contains two alkali species. To optimize the parameters, the dynamic equations of spin evolution with two alkali species were solved, whose steady-state solution is used to optimize the parameters. The demand of the power of the pump beam is large for hybrid optical pumping. Moreover, the sensitivity of the hybrid optical pumping magnetometer increases with the increase of the power density of the pump beam. The density ratio between the two alkali species is especially important for hybrid optical pumping magnetometer. A simple expression for optimizing the density ratio is proposed in this paper, which can help to determine the mole faction of the alkali atoms in fabricating the hybrid cell before the cell is sealed. The spin-exchange rate between the two alkali species is proportional to the saturated density of the alkali vapor, which is highly dependent on the temperature of the cell. Consequently, the sensitivity of the hybrid optical pumping magnetometer is dependent on the temperature of the cell. We proposed the thermal optimization of the hybrid cell for a hybrid optical pumping magnetometer, which can improve the sensitivity especially when the power of the pump beam is low. With these optimizations, a sensitivity of approximately 5 fT/Hz 1/2 is achieved with gradiometer arrangement

  6. Systematic variation of magnetic-field penetration depth in high-Tc superconductors studied by muon-spin relaxation

    Science.gov (United States)

    Uemura, Y. J.; Emery, V. J.; Moodenbaugh, A. R.; Suenaga, M.; Johnston, D. C.

    1988-01-01

    The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 SrO.15 CuO4 in transverse external magnetic fields 1 is approximately 4 kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

  7. Systematic variation of magnetic-field penetration depth in high-T(c) superconductors studied by muon spin relaxation

    Science.gov (United States)

    Uemura, Y. J.; Emery, V. J.; Moodenbaugh, A. R.; Suenaga, M.; Johnston, D. C.; Jacobson, A. J.; Lewandowski, J. T.; Brewer, J. H.; Kiefl, R. F.; Kreitzman, S. R.

    1988-01-01

    The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 Sr0.15 CuO4 in transverse external magnetic fields 1 is approximately 4kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

  8. Three-stage decoherence dynamics of an electron spin qubit in an optically active quantum dot

    Science.gov (United States)

    Bechtold, Alexander; Rauch, Dominik; Li, Fuxiang; Simmet, Tobias; Ardelt, Per-Lennart; Regler, Armin; Müller, Kai; Sinitsyn, Nikolai A.; Finley, Jonathan J.

    2015-12-01

    The control of solid-state qubits requires a detailed understanding of the decoherence mechanisms. Despite considerable progress in uncovering the qubit dynamics in strong magnetic fields, decoherence at very low magnetic fields remains puzzling, and the role of quadrupole coupling of nuclear spins is poorly understood. For spin qubits in semiconductor quantum dots, phenomenological models of decoherence include two basic types of spin relaxation: fast dephasing due to static but randomly distributed hyperfine fields (~2 ns) and a much slower process (>1 μs) of irreversible monotonic relaxation due either to nuclear spin co-flips or other complex many-body interaction effects. Here we show that this is an oversimplification; the spin qubit relaxation is determined by three rather than two distinct stages. The additional stage corresponds to the effect of coherent precession processes that occur in the nuclear spin bath itself, leading to a relatively fast but incomplete non-monotonic relaxation at intermediate timescales (~750 ns).

  9. Understanding charge carrier relaxation processes in terbium arsenide nanoparticles using transient absorption spectroscopy

    Science.gov (United States)

    Vanderhoef, Laura R.

    Erbium arsenide nanoparticles epitaxially grown within III-V semiconductors have been shown to improve the performance of devices for applications ranging from thermoelectrics to THz pulse generation. The small size of rare-earth nanoparticles suggests that interesting electronic properties might emerge as a result of both spatial confinement and surface states. However, ErAs nanoparticles do not exhibit any signs of quantum confinement or an emergent bandgap, and these experimental observations are understood from theory. The incorporation of other rare-earth monopnictide nanoparticles into III-V hosts is a likely path to engineering carrier excitation, relaxation and transport dynamics for optoelectronic device applications. However, the electronic structure of these other rare-earth monopnictide nanoparticles remains poorly understood. The objective of this research is to explore the electronic structure and optical properties of III-V materials containing novel rare-earth monopnictides. We use ultrafast pump-probe spectroscopy to investigate the electronic structure of TbAs nanoparticles in III-V hosts. We start with TbAs:GaAs, which was expected to be similar to ErAs:GaAs. We study the dynamics of carrier relaxation into the TbAs states using optical pump terahertz probe transient absorption spectroscopy. By analyzing how the carrier relaxation rates depend on pump fluence and sample temperature, we conclude that the TbAs states are saturable. Saturable traps suggest the existence of a bandgap for TbAs nanoparticles, in sharp contrast with previous results for ErAs. We then apply the same experimental technique to two samples of TbAs nanoparticles in InGaAs with different concentrations of TbAs. We observe similar relaxation dynamics associated with trap saturation, though the ability to resolve these processes is contingent upon a high enough TbAs concentration in the sample. We have also constructed an optical pump optical probe transient absorption

  10. Influence of relaxation processes on the evaluation of the metastable defect density in Cu(In,Ga)Se{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Maciaszek, M.; Zabierowski, P. [Faculty of Physics, Warsaw University of Technology, Koszykowa 75, Warszawa 00 662 (Poland)

    2016-06-07

    In this contribution, we investigated by means of numerical simulations the influence of relaxation processes related to metastable defects on electrical characteristics of Cu(In,Ga)Se{sub 2}. In particular, we analyzed the relaxation of a metastable state induced by illumination at a fixed temperature as well as the dependence of the hole concentration on the temperature during cooling. The knowledge of these two relaxation processes is crucial in the evaluation of the hole concentration in the relaxed state and after light soaking. We have shown that the distribution of the metastable defects can be considered frozen below 200 K. The hole capture cross section was estimated as ∼3 × 10{sup −15} cm{sup 2}. It was shown that the usually used cooling rates may lead to relevant changes of the hole concentration. We calculated the lower limit of the hole concentration after cooling, and we presented how it depends on densities of shallow acceptors and metastable defects. Moreover, we proposed a method which allows for the evaluation of shallow acceptor and metastable defect densities from two capacitance-voltage profiles measured in the relaxed and light soaking states. Finally, we indicated experimental conditions in which the influence of relaxation processes on the accuracy of this method is the smallest.

  11. Uncovering Molecular Relaxation Processes with Nonlinear Spectroscopies in the Deep UV

    Science.gov (United States)

    West, Brantley Andrew

    Conical intersections mediate internal conversion dynamics that compete with even the fastest nuclear motions in molecular systems. Traditional kinetic models do not apply in this regime of commensurate electronic and nuclear motion because the surroundings do not maintain equilibrium throughout the relaxation process. This dissertation focuses on uncovering the physics associated with vibronic interactions at conical intersections. Of particular interest are coherent nuclear motions driven by steep excited state potential energy gradients. Technical advances have only recently made these dynamics accessible in many systems including DNA nucleobases and cyclic polyene molecules. Optical analogues of multidimensional NMR spectroscopies have recently yielded transformative insight in relaxation processes ranging from energy transfer in photosynthesis to bond making and breaking in liquids. Prior to the start of this research, such experiments had only been conducted at infrared and visible wavelengths. Applications in the ultraviolet were motivated by studies of numerous biological systems (e.g., DNA, proteins), but had been challenged by technical issues. The work presented in this dissertation combines pulse generation techniques developed in the optical physics community with spectroscopic techniques largely pioneered by physical chemists to implement two-dimensional ultraviolet spectroscopy (2DUV). This technique is applied at the shortest wavelengths and with the best signal-to-noise ratios reported to date. Sub-picosecond excited state deactivation processes provide photo stability to the DNA double helix. Vibrational energy transfer from the solute to surrounding solvent enables relaxation of the highly non-equilibrium ground state produced by fast internal conversion. In this dissertation, nonlinear spectroscopies carried out at cryogenic temperatures are used to uncover the particular nuclear modes in the solvent that primarily accept vibrational energy from

  12. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    Science.gov (United States)

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-10-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  13. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes.

    Science.gov (United States)

    Ma, X; Fang, F; Li, Q; Zhu, J; Yang, Y; Wu, Y Z; Zhao, H B; Lüpke, G

    2015-10-28

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  14. Effect of thermal annealing on electron spin relaxation of beryllium-doped In{sub 0.8}Ga{sub 0.2}As{sub 0.45}P{sub 0.55} bulk

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Hao; Harasawa, Ryo; Yasue, Yuya; Aritake, Takanori; Jiang, Canyu; Tackeuchi, Atsushi, E-mail: atacke@waseda.jp [Department of Applied Physics, Waseda University, Shinjuku, Tokyo 169-8555 (Japan); Ji, Lian; Lu, Shulong [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Dushu Lake Higher Education Town, Ruoshui Road 398, Suzhou Industrial Park, Suzhou (China)

    2016-08-15

    The effect of thermal annealing on the electron spin relaxation of beryllium-doped In{sub 0.8}Ga{sub 0.2}As{sub 0.45}P{sub 0.55} bulk was investigated by time-resolved spin-dependent pump and probe reflection measurement with a high time resolution of 200 fs. Three similar InGaAsP samples were examined one of which was annealed at 800 °C for 1 s, one was annealed at 700 °C for 1 s and the other was not annealed after crystal growth by molecular beam epitaxy. Although the carrier lifetimes of the 700 °C-annealed sample and the unannealed sample were similar, that of the 800 °C-annealed sample was extended to 11.6 (10.4) ns at 10 (300) K, which was more than two (four) times those of the other samples. However, interestingly the spin relaxation time of the 800 °C-annealed sample was found to be similar to those of the other two samples. Particularly at room temperature, the spin relaxation times are 143 ps, 147 ps, and 111 ps for the 800 °C-annealed sample, 700 °C-annealed sample, and the unannealed sample, respectively.

  15. Effect of thermal annealing on electron spin relaxation of beryllium-doped In0.8Ga0.2As0.45P0.55 bulk

    Directory of Open Access Journals (Sweden)

    Hao Wu

    2016-08-01

    Full Text Available The effect of thermal annealing on the electron spin relaxation of beryllium-doped In0.8Ga0.2As0.45P0.55 bulk was investigated by time-resolved spin-dependent pump and probe reflection measurement with a high time resolution of 200 fs. Three similar InGaAsP samples were examined one of which was annealed at 800 °C for 1 s, one was annealed at 700 °C for 1 s and the other was not annealed after crystal growth by molecular beam epitaxy. Although the carrier lifetimes of the 700 °C-annealed sample and the unannealed sample were similar, that of the 800 °C-annealed sample was extended to 11.6 (10.4 ns at 10 (300 K, which was more than two (four times those of the other samples. However, interestingly the spin relaxation time of the 800 °C-annealed sample was found to be similar to those of the other two samples. Particularly at room temperature, the spin relaxation times are 143 ps, 147 ps, and 111 ps for the 800 °C-annealed sample, 700 °C-annealed sample, and the unannealed sample, respectively.

  16. Nuclear spin relaxation of {sup 8}Li in a thin film of La{sub 0.67}Ca{sub 0.33}MnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Miller, R.I. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, Canada V6T 2A3 (Canada); Arseneau, D. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Chow, K.H. [Department of Physics, University of Alberta, Edmonton, Alta., T6G 2J1 (Canada); Daviel, S. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Engelbertz, A. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Hossain, MD. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Keeler, T. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Kiefl, R.F. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada)]|[Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada V6T 1Z1 (Canada)]|[Canadian Institute for Advanced Research, Toronto, Ont., Canada M5G 1Z8 (Canada)]. E-mail: kiefl@triumf.ca; Kreitzman, S. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Levy, C.D.P. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Morales, P. [Department of Physics, University of Toronto, Toronto, Ont., M5S 1A7 (Canada); Morris, G.D. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); MacFarlane, W.A. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada): Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Parolin, T.J. [Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Poutissou, R. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Saadaoui, H.; Wang, D. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada); Salman, Z. [TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3 (Canada); Wei, J.Y.T. [Canadian Institute for Advanced Research, Toronto, Ont., M5G 1Z8 (Canada)]|[Department of Physics, University of Toronto, Toronto, Ont., M5S 1A7 (Canada)

    2006-03-31

    We report {beta}-NMR measurements of the nuclear spin relaxation rate (1/T{sub 1}) in a thin film of La{sub 0.67}Ca{sub 0.33}MnO{sub 3} (LCMO) using a low-energy beam of spin-polarized {sup 8}Li. In a small magnetic field of 150G, there is a broad peak in 1/T{sub 1} near the Curie temperature (T{sub c}=259K) and a dramatic decrease in 1/T{sub 1} at lower temperatures. This is attributed to a critical slowing down of the spin fluctuations near T{sub c} and freezing of the magnetic excitations at low temperatures, respectively. In addition, there is a small amplitude, slow relaxing component at high temperatures, which we attribute to {sup 8}Li in the SrTiO{sub 3} substrate. There is an indication that the spin relaxation rate in the substrate is also peaked at T{sub c} due to close proximity to the magnetic film. These results establish that low-energy {beta}-NMR can be used as a probe of magnetic fluctuations in magnetic thin films over a wide range of temperatures.

  17. Molecular interactions in the ionic liquid emim acetate and water binary mixtures probed via NMR spin relaxation and exchange spectroscopy.

    Science.gov (United States)

    Allen, Jesse J; Bowser, Sage R; Damodaran, Krishnan

    2014-05-07

    Interactions of ionic liquids (ILs) with water are of great interest for many potential IL applications. 1-Ethyl-3-methylimidazolium (emim) acetate, in particular, has shown interesting interactions with water including hydrogen bonding and even chemical exchange. Previous studies have shown the unusual behavior of emim acetate when in the presence of 0.43 mole fraction of water, and a combination of NMR techniques is used herein to investigate the emim acetate-water system and the unusual behavior at 0.43 mole fraction of water. NMR relaxometry techniques are used to describe the effects of water on the molecular motion and interactions of emim acetate with water. A discontinuity is seen in nuclear relaxation behavior at the concentration of 0.43 mole fraction of water, and this is attributed to the formation of a hydrogen bonded network. EXSY measurements are used to determine the exchange rates between the H2 emim proton and water, which show a complex dependence on the concentration of the mixture. The findings support and expand our previous results, which suggested the presence of an extended hydrogen bonding network in the emim acetate-water system at concentrations close to 0.50 mole fraction of H2O.

  18. Rational extended thermodynamics of a rarefied polyatomic gas with molecular relaxation processes

    Science.gov (United States)

    Arima, Takashi; Ruggeri, Tommaso; Sugiyama, Masaru

    2017-10-01

    We present a more refined version of rational extended thermodynamics of rarefied polyatomic gases in which molecular rotational and vibrational relaxation processes are treated individually. In this case, we need a triple hierarchy of the moment system and the system of balance equations is closed via the maximum entropy principle. Three different types of the production terms in the system, which are suggested by a generalized BGK-type collision term in the Boltzmann equation, are adopted. In particular, the rational extended thermodynamic theory with seven independent fields (ET7) is analyzed in detail. Finally, the dispersion relation of ultrasonic wave derived from the ET7 theory is confirmed by the experimental data for CO2, Cl2, and Br2 gases.

  19. Investigations of effect of phase change mass transfer rate on cavitation process with homogeneous relaxation model

    Energy Technology Data Exchange (ETDEWEB)

    He, Zhixia; Zhang, Liang; Saha, Kaushik; Som, Sibendu; Duan, Lian; Wang, Qian

    2017-12-01

    The super high fuel injection pressure and micro size of nozzle orifice has been an important development trend for the fuel injection system. Accordingly, cavitation transient process, fuel compressibility, amount of noncondensable gas in the fuel and cavitation erosion have attracted more attention. Based on the fact of cavitation in itself is a kind of thermodynamic phase change process, this paper takes the perspective of the cavitation phase change mass transfer process to analyze above mentioned phenomenon. The two-phase cavitating turbulent flow simulations with VOF approach coupled with HRM cavitation model and U-RANS of standard k-ε turbulence model were performed for investigations of cavitation phase change mass transfer process. It is concluded the mass transfer time scale coefficient in the Homogenous Relaxation Model (HRM) representing mass transfer rate should tend to be as small as possible in a condition that ensured the solver stable. At very fast mass transfer rate, the phase change occurs at very thin interface between liquid and vapor phase and condensation occurs more focused and then will contribute predictably to a more serious cavitation erosion. Both the initial non-condensable gas in fuel and the fuel compressibility can accelerate the cavitation mass transfer process.

  20. Anomalous relaxation and self-organization in non-equilibrium processes

    OpenAIRE

    Fatkullin, Ibrahim; Kladko, Konstantin; Mitkov, Igor; Bishop, A. R.

    2000-01-01

    We study thermal relaxation in ordered arrays of coupled nonlinear elements with external driving. We find, that our model exhibits dynamic self-organization manifested in a universal stretched-exponential form of relaxation. We identify two types of self-organization, cooperative and anti-cooperative, which lead to fast and slow relaxation, respectively. We give a qualitative explanation for the behavior of the stretched exponent in different parameter ranges. We emphasize that this is a sys...

  1. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results.

    Science.gov (United States)

    Kanaya, Toshiji; Ogawa, Hiroki; Kishimoto, Mizuki; Inoue, Rintaro; Suter, Andreas; Prokscha, Thomas

    2015-08-01

    In a previous paper [Phys. Rev. E 83, 021801 (2011)] we performed neutron reflectivity (NR) measurements on a five-layer polystyrene (PS) thin film consisting of alternatively stacked deuterated polystyrene (dPS) and hydrogenated polystyrene (hPS) layers (dPS/hPS/dPS/hPS/dPS, ∼100 nm thick) on a Si substrate to reveal the distribution of Tg along the depth direction. Information on the Tg distribution is very useful to understand the interesting but unusual properties of polymer thin films. However, one problem that we have to clarify is if there are effects of deuterium labeling on Tg or not. To tackle the problem we performed low-energy muon spin relaxation (μSR) measurements on the above-mentioned deuterium-labeled five-layer PS thin film as well as dPS and hPS single-layer thin films ∼100 nm thick as a function of muon implantation energy. It was found that the deuterium labeling had no significant effects on the Tg distribution, guaranteeing that we can safely discuss the unusual thin film properties based on the Tg distribution revealed by NR on the deuterium-labeled thin films. In addition, the μSR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings.

  2. Spin torque nanooscillators: new applications in information processing

    Science.gov (United States)

    Macia, Ferran; Kent, Andrew D.; Hoppensteadt, Frank C.

    2013-03-01

    Nanonometer scale electrical contacts to ferromagnetic thin films (STNOs) can provide sufficient current densities to excite magnetic-moment dynamics resulting in emission of short wave-length spin waves. We discuss several applications of spin-wave patterns created from STNOs and their interaction with background oscillations. We review how to encode information in STNOs signals -modulating their amplitude, frequency or phase - and stability against noise. We first model arrays of STNOs in extended ferromagnetic thin films and define conditions to control spin-waves emission directions. We also study arrays of oscillators in patterned ferromagnetic thin films and we put forward a method to build an STNO lookup tables or an STNO based network analyzer. Using spin waves complements digital semiconductor technologies and offers new possibilities for increased memory capacity and computation performance. This work was supported by Marie Curie IOF 253214 and by ARO MURI Grant No. W911NF-08-1-0317 and NSF Grant No. ECS 07- 25280.

  3. Nuclear Spin Lattice Relaxation and Conductivity Studies of the Non-Arrhenius Conductivity Behavior in Lithium Fast Ion Conducting Sulfide Glasses

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, Benjamin Michael [Iowa State Univ., Ames, IA (United States)

    2003-01-01

    As time progresses, the world is using up more of the planet's natural resources. Without technological advances, the day will eventually arrive when these natural resources will no longer be sufficient to supply all of the energy needs. As a result, society is seeing a push for the development of alternative fuel sources such as wind power, solar power, fuel cells, and etc. These pursuits are even occurring in the state of Iowa with increasing social pressure to incorporate larger percentages of ethanol in gasoline. Consumers are increasingly demanding that energy sources be more powerful, more durable, and, ultimately, more cost efficient. Fast Ionic Conducting (FIC) glasses are a material that offers great potential for the development of new batteries and/or fuel cells to help inspire the energy density of battery power supplies. This dissertation probes the mechanisms by which ions conduct in these glasses. A variety of different experimental techniques give a better understanding of the interesting materials science taking place within these systems. This dissertation discusses Nuclear Magnetic Resonance (NMR) techniques performed on FIC glasses over the past few years. These NMR results have been complimented with other measurement techniques, primarily impedance spectroscopy, to develop models that describe the mechanisms by which ionic conduction takes place and the dependence of the ion dynamics on the local structure of the glass. The aim of these measurements was to probe the cause of a non-Arrhenius behavior of the conductivity which has been seen at high temperatures in the silver thio-borosilicate glasses. One aspect that will be addressed is if this behavior is unique to silver containing fast ion conducting glasses. more specifically, this study will determine if a non-Arrhenius correlation time, τ, can be observed in the Nuclear Spin Lattice Relaxation (NSLR) measurements. If so, then can this behavior be modeled with a new single

  4. Evaluation of an air spinning process to produce tailored biosynthetic nanofibre scaffolds

    International Nuclear Information System (INIS)

    Sabbatier, Gad

    2014-01-01

    We optimised the working parameters of an innovative air spinning device to produce nanofibrous polymer scaffolds for tissue engineering applications. Scanning electron microscopy was performed on the fibre scaffolds which were then used to identify various scaffold morphologies based on the ratio of surface occupied by the polymer fibres on that covered by the entire polymer scaffold assembly. Scaffolds were then produced with the spinning experimental parameters, resulting in 90% of fibres in the overall polymer construct, and were subsequently used to perform a multiple linear regression analysis to highlight the relationship between nanofibre diameter and the air spinning parameters. Polymer solution concentration was deemed as the most significant parameter to control fibre diameter during the spinning process, despite interactions between experimental parameters. Based on these findings, viscosity measurements were performed to clarify the effect of the polymer solution property on scaffold morphology. - Highlights: • An air spinning device for nanofibre scaffold production was optimised. • Relationships between fibre diameter and spinning parameters were established. • Polymer solution concentration was the most significant parameter. • Interactions between experimental parameters also influence the spinning process. • Nanofibres were formed due to polymer chain entanglements

  5. Microscopic understanding of spin current probed by shot noise

    Science.gov (United States)

    Arakawa, Tomonori

    The spin currents is one of key issue in the spintronics field and the generation and detection of those have been intensively studied by using various materials. The analysis of experiments, however, relies on phenomenological parameters such as spin relaxation length and spin flip time. The microscopic nature of the spin current such as energy distribution and energy relaxation mechanism, has not yet well understood. To establish a better microscopic understanding of spin currents, I focused on the shot noise measurement which is well established technique in the field of mesoscopic physics [Y. M. Blanter and M. B üttiker, Phys. Rep. 336, 1 (2000).]. Although there are many theoretically works about shot noise in the presence of spin currents, for example detection of spin accumulation [J. Meair, P. Stano, and P. Jacquod, Phys. Rev. B 84 (2011).], estimation of spin flip currents, and so on, these predictions have never been experimentally confirmed. In this context, we reported the first experimental detention of shot noise in the presence of the spin accumulation in a (Ga,Mn)As/tunnel barrier/n-GaAs based lateral spin valve device [T. Arakawa et al., Phys. Rev. Lett. 114, 016601 (2015).]. Together with this result, we found however that the effective temperature of the spin current drastically increases due to the spin injection process. This heating of electron system could be a big problem to realize future spin current devices by using quantum coherence, because the effective temperature rise directly related to the destruction of the coherence of the spin current. Therefore, then we focused on the mechanism of this heating and the energy relaxation in a diffusive channel. By measuring current noise and the DC offset voltage in the usual non-local spin valve signal as a function of the spin diffusion channel length, we clarified that the electron-electron interaction length, which is the characteristic length for the relaxation of the electron system, is

  6. Dynamic relaxation processes in compressible multiphase flows. Application to evaporation phenomena

    Directory of Open Access Journals (Sweden)

    Le Métayer O.

    2013-07-01

    Full Text Available Phase changes and heat exchanges are examples of physical processes appearing in many industrial applications involving multiphase compressible flows. Their knowledge is of fundamental importance to reproduce correctly the resulting effects in simulation tools. A fine description of the flow topology is thus required to obtain the interfacial area between phases. This one is responsible for the dynamics and the kinetics of heat and mass transfer when evaporation or condensation occurs. Unfortunately this exchange area cannot be obtained easily and accurately especially when complex mixtures (drops, bubbles, pockets of very different sizes appear inside the transient medium. The natural way to solve this specific trouble consists in using a thin grid to capture interfaces at all spatial scales. But this possibility needs huge computing resources and can be hardly used when considering physical systems of large dimensions. A realistic method is to consider instantaneous exchanges between phases by the way of additional source terms in a full non-equilibrium multiphase flow model [2,15,17]. In this one each phase obeys its own equation of state and has its own set of equations and variables (pressure, temperature, velocity, energy, entropy,.... When enabling the relaxation source terms the multiphase mixture instantaneously tends towards a mechanical or thermodynamic equilibrium state at each point of the flow. This strategy allows to mark the boundaries of the real flow behavior and to magnify the dominant physical effects (heat exchanges, evaporation, drag,... inside the medium. A description of the various relaxation processes is given in the paper. Les changements de phase et les transferts de chaleur sont des exemples de phénomènes physiques présents dans de nombreuses applications industrielles faisant intervenir des écoulements compressibles multiphasiques. La connaissance des mécanismes associés est primordiale afin de reproduire

  7. Anisotropy and relaxation processes of uniaxially oriented CoFe{sub 2}O{sub 4} nanoparticles dispersed in PDMS

    Energy Technology Data Exchange (ETDEWEB)

    Antonel, P.S.; Negri, R.M. [Instituto de Quimica Fisica de Materiales, Ambiente y Energia (INQUIMAE), Departamento de Quimica Inorganica, Analitica y Quimica Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellon II, Av. Cantilo s/n (1428), Buenos Aires (Argentina); Leyva, A.G. [Grupo de Materia Condensada, Gerencia de Investigacion y Aplicaciones, Centro Atomico Constituyentes, Comision Nacional de Energia Atomica, Avda. Gral. Paz 1499 (1650) San Martin, Pcia. de Buenos Aires, Argentina - Escuela de Ciencia y Tecnologia, UNSAM (Argentina); Jorge, G.A., E-mail: gjorge@df.uba.ar [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellon I, Av. Cantilo s/n (1428), Buenos Aires (Argentina)

    2012-08-15

    When a uniaxial magnetic field is applied to a non-magnetic dispersive medium filled with magnetic nanoparticles, they auto-assemble into thin needles parallel to the field direction, due to the strong dipolar interaction among them. We have prepared in this way magnetically oriented nanocomposites of nanometer-size CoFe{sub 2}O{sub 4} particles in a polydimethylsiloxane polymer matrix, with 10% w/w of magnetic particles. We present the characteristic magnetic relaxation curves measured after the application of a magnetic field forming an angle {alpha} with respect to the needle direction. We show that the magnetic viscosity (calculated from the logarithmic relaxation curves) as a function of {alpha} presents a minimum at {alpha}=0, indicating slower relaxation processes associated with this configuration of fields. The results seems to point out that the local magnetic anisotropy of the nanoparticles is oriented along the needles, resulting in the macroscopic magnetic anisotropy observed in our measurements.

  8. Anisotropy and relaxation processes of uniaxially oriented CoFe2O4 nanoparticles dispersed in PDMS

    International Nuclear Information System (INIS)

    Antonel, P.S.; Negri, R.M.; Leyva, A.G.; Jorge, G.A.

    2012-01-01

    When a uniaxial magnetic field is applied to a non-magnetic dispersive medium filled with magnetic nanoparticles, they auto-assemble into thin needles parallel to the field direction, due to the strong dipolar interaction among them. We have prepared in this way magnetically oriented nanocomposites of nanometer-size CoFe 2 O 4 particles in a polydimethylsiloxane polymer matrix, with 10% w/w of magnetic particles. We present the characteristic magnetic relaxation curves measured after the application of a magnetic field forming an angle α with respect to the needle direction. We show that the magnetic viscosity (calculated from the logarithmic relaxation curves) as a function of α presents a minimum at α=0, indicating slower relaxation processes associated with this configuration of fields. The results seems to point out that the local magnetic anisotropy of the nanoparticles is oriented along the needles, resulting in the macroscopic magnetic anisotropy observed in our measurements.

  9. Muon spin relaxation study on itinerant ferromagnet CeCrGe₃ and the effect of Ti substitution on magnetism of CeCrGe₃.

    Science.gov (United States)

    Das, Debarchan; Bhattacharyya, A; Anand, V K; Hillier, A D; Taylor, J W; Gruner, T; Geibel, C; Adroja, D T; Hossain, Z

    2015-01-14

    A Muon spin relaxation (µSR) study has been performed on the Kondo lattice heavy fermion itinerant ferromagnet CeCrGe3. Recent investigations of bulk properties have revealed a long-range ordering of Cr moments at Tc = 70 K in this compound. Our µSR investigation between 1.2 K and 125 K confirm the bulk magnetic order which is marked by a loss in initial asymmetry below 70 K accompanied with a sharp increase in the muon depolarization rate. Field dependent µSR spectra show that the internal field at the muon site is higher than 0.25 T apparently due to the ferromagnetic nature of ordering. The effect of Ti substitution on the magnetism in CeCrGe3 is presented. A systematic study has been made on polycrystalline CeCr(1-x)Ti(x)Ge3 (0 ⩽ x ⩽ 1) using magnetic susceptibility χ(T), isothermal magnetization M(H), specific heat C(T) and electrical resistivity ρ(T) measurements which clearly reveal that the substitution of Ti for Cr in CeCrGe3 strongly influences the exchange interaction and ferromagnetic ordering of Cr moments. The Cr moment ordering temperature is suppressed gradually with increasing Ti concentration up to x = 0.50 showing Tc = 7 K beyond which Ce moment ordering starts to dominate and a crossover between Cr and Ce moment ordering is observed with a Ce moment ordering Tc = 14 K for x = 1.0. The Kondo lattice behavior is evident from temperature dependence of ρ(T) in all CeCr(1-x)Ti(x)Ge3 samples.

  10. Proton NMR relaxation of hydrated insulin powder

    International Nuclear Information System (INIS)

    Sanches, R.; Donoso, J.P.; Mascarenhas, S.; Panepucci, H.C.

    1985-01-01

    Water proton nuclear magnetic relaxation measurements were obtained for hydrated insulin powder as a function of the water content. For samples containing enough water to complete the hydration shell, the data for the spin-lattice and spin-spin relaxation times are consistent with a model in which water molecules exist in two phases, one exhibiting restricted motion and identified with water of hydration and another identified as free water with motions similar to ordinary water. For samples containing only water of hydration, a model for the spin-spin relaxation time is discussed, in which the water molecules relaxation is described in terms for four relaxation times. Estimates are obtained for these relaxation times, in good agreement with the experimental data. (Author) [pt

  11. Vib--rotational energy distributions and relaxation processes in pulsed HF chemical lasers

    International Nuclear Information System (INIS)

    Ben-Shaul, A.; Kompa, K.L.; Schmailzl, U.

    1976-01-01

    The rate equations governing the temporal evolution of photon densities and level populations in pulsed F+H 2 →HF+H chemical lasers are solved for different initial conditions. The rate equations are solved simultaneously for all relevant vibrational--rotational levels and vibrational--rotational P-branch transitions. Rotational equilibrium is not assumed. Approximate expressions for the detailed state-to-state rate constants corresponding to the various energy transfer processes (V--V, V--R,T, R--R,T) coupling the vib--rotational levels are formulated on the basis of experimental data, approximate theories, and qualitative considerations. The main findings are as follows: At low pressures, R--T transfer cannot compete with the stimulated emission, and the laser output largely reflects the nonequilibrium energy distribution in the pumping reaction. The various transitions reach threshold and decay almost independently and simultaneous lasing on several lines takes place. When a buffer gas is added in excess to the reacting mixture, the enhanced rotational relaxation leads to nearly single-line operation and to the J shift in lasing. Laser efficiency is higher at high inert gas pressures owing to a better extraction of the internal energy from partially inverted populations. V--V exchange enhances lasing from upper vibrational levels but reduces the total pulse intensity. V--R,T processes reduce the efficiency but do not substantially modify the spectral output distribution. The photon yield ranges between 0.4 and 1.4 photons/HF molecule depending on the initial conditions. Comparison with experimental data, when available, is fair

  12. Electronic relaxation processes in polyatomic molecules. Progress report, October 1, 1975--September 30, 1976

    International Nuclear Information System (INIS)

    Lim, E.C.

    1976-09-01

    Excitation energy dependence of radiationless decay rate under collision-free conditions was utilized as a probe of intramolecular vibrational relaxation in tetracene and pentacene. The results give evidence of vibrational relaxation which competes with electronic relaxation. The substitution dependence of T 1 (nπ*) → S 0 radiationless transition in monocyclic diazines and the temperature dependence of S 1 non-radiative decay rate in alcoholic solutions of polycyclic monoazines indicate that the vibronic interaction between the lowest energy nπ* and ππ* states leads to a rapid radiationless deactivation of the lower of the two electronic states. Finally, a photon-counting spectrofluorometer of very high sensitivity was constructed, and it was used to record T 2 → T 1 fluorescence in bromoanthracenes and S 2 → S 1 fluorescence in azulene. These spectra represent the first bona-fide, or the most convincing, observation of fluorescence between excited electronic states

  13. Meniscal tears: comparison of the conventional spin-echo and fast spin-echo techniques through image processing.

    Science.gov (United States)

    Nogueira, Ibevan A; Frère, Annie F; Silva, Alessandro P; de Oliveira, Heverton C

    2014-03-27

    Conventional spin-echo (PD-CSE) and fast spin-echo (PD-FSE) techniques are frequently used to detect meniscal tears. However, the time delay for imaging with PD-CSE has resulted in its replacement with faster techniques, such as proton density fast spin-echo (PD-FSE), which has become a frequent tool at most diagnostic centres.Qualitative analysis shows that the PD-CSE technique is more sensitive, but other authors have not found significant differences between the aforementioned techniques. Therefore, we performed a quantitative analysis in this study that aims to measure differences in the quality of the images obtained with both techniques. We compared the PD-CSE and PD-FSE techniques by quantitatively analysing the obtained proton density images: the area shown, as well as the brightness and lesion contrast of the obtained image.A set of 100 images from 50 patients thought to contain meniscal tears of the knee were selected. These 100 images were obtained from all individuals using both the PD-CSE and PD-FSE techniques. The images were processed using software developed in Delphi. In addition to these quantifications, three physicians, who are specialists in radiology and capable of analysing magnetic resonance (MR) images of the musculoskeletal system, qualitatively analysed the diagnostic sensitivity of both techniques. On average, samples obtained via the PD-CSE technique contained 22% more pixels in the lesion area. The contrast differed by 28%, and the brightness differed by 31%. The two techniques were correlated using Student's t-test, which showed a statistically significant difference. The specialists detected meniscal tears in 30 of the images obtained via the PD-CSE technique, while only 72% of these cases were detected via the PD-FSE technique. The PD-CSE technique was shown to be superior to PD-FSE for all of the evaluated properties, making its selection preferable.

  14. Electronic phase diagrams and competing ground states of complex iron pnictides and chalcogenides. A Moessbauer spectroscopy and muon spin rotation/relaxation study

    Energy Technology Data Exchange (ETDEWEB)

    Kamusella, Sirko

    2017-03-01

    In this thesis the superconducting and magnetic phases of LiOH(Fe,Co)(Se,S), CuFeAs/CuFeSb, and LaFeP{sub 1-x}As{sub x}O - belonging to the 11, 111 and 1111 structural classes of iron-based arsenides and chalcogenides - are investigated by means of {sup 57}Fe Moessbauer spectroscopy and muon spin rotation/relaxation (μSR). Of major importance in this study is the application of high magnetic fields in Moessbauer spectroscopy to distinguish and characterize ferro- (FM) and antiferromagnetic (AFM) order. A user-friendly Moessbauer data analysis program was developed to provide suitable model functions not only for high field spectra, but relaxation spectra or parameter distributions in general. In LaFeP{sub 1-x}As{sub x}O the reconstruction of the Fermi surface is described by the vanishing of the Γ hole pocket with decreasing x. The continuous change of the orbital character and the covalency of the d-electrons is shown by Moessbauer spectroscopy. A novel antiferromagnetic phase with small magnetic moments of ∼ 0.1 μ{sub B} state is characterized. The superconducting order parameter is proven to continuously change from a nodal to a fully gapped s-wave like Fermi surface in the superconducting regime as a function of x, partially investigated on (O,F) substituted samples. LiOHFeSe is one of the novel intercalated FeSe compounds, showing strongly increased T{sub C} = 43 K mainly due to increased interlayer spacing and resulting two-dimensionality of the Fermi surface. The primary interest of the samples of this thesis is the simultaneously observed ferromagnetism and superconductivity. The local probe techniques prove that superconducting sample volume gets replaced by ferromagnetic volume. Ferromagnetism arises from magnetic order with T{sub C} = 10 K of secondary iron in the interlayer. The tendency of this system to show (Li,Fe) disorder is preserved upon (Se,S) substitution. However, superconductivity gets suppressed. The results of Moessbauer spectroscopy

  15. Thermal mixing in multiple-pulse nuclear quadrupole resonance spin-locking

    International Nuclear Information System (INIS)

    Beltjukov, P A; Kibrik, G E; Furman, G B; Goren, S D

    2007-01-01

    We report on an experimental and theoretical nuclear quadrupole resonance (NQR) multiple-pulse spin-locking study of the thermal mixing process in solids containing nuclei of two different sorts, I>1/2 and S = 1/2, coupled by dipole-dipole interactions and influenced by an external magnetic field. Two coupled equations for the inverse spin temperatures of both the spin systems describing the mutual spin-lattice relaxation and the thermal mixing were obtained using the method of the nonequilibrium state operator. It is shown that the relaxation process is realized with non-exponential time dependence described by a sum of two exponents. The calculated relaxation time versus the multiple-pulse field parameters agrees well with the obtained experimental data in 1,4-dichloro-2-nitrobenzene. The calculated magnetization relaxation time versus the strength of the applied magnetic field agrees well with the obtained experimental data

  16. A study of nuclear relaxation to the electron non-Zeeman system

    International Nuclear Information System (INIS)

    Honten, J. van.

    1979-01-01

    An examination of the nuclear spin-lattice relaxation mechanism in a series of diluted copper-caesium Tutton salt crystals, containing different percentages of D 2 O in the waters of hydration, is described. Results of relaxation measurements are presented and a strong angular dependence is observed. It is proved, however, that under most experimental conditions applied, the bottleneck in the relaxation path is not the cross-relaxation but the thermal contact between the proton Zeeman system and the electron dipole-dipole interaction system. Hence the proton spin-lattice relaxation measurements have enabled determination of the time constant of this thermal contact. The microscopic coupling process which provides thermal contact, is a simultaneous transition of two electron spins and one proton spin. This so-called three-spin transition is described and calculations presented. Double resonance experiments are performed, where the resonance signal of deuterium or caesium spins is saturated and the effect on the proton resonance signal observed. (C.F.)

  17. Ultrafast Physics Behind the Nonradiative Relaxation Process of Chromium Ions in Forsterite Crystals.

    Science.gov (United States)

    Demos, Stavros Gregorios

    The nonradiative relaxation following photoexcitation has been studied in Cr^{4+} -doped forsterite (Mg_2SiO _4) using picosecond laser excitation and ultrasensitive photon counting detection. The experimental techniques utilized were time resolved antiStokes Raman scattering and up-converted hot and ordinary luminescence. The up-converted hot luminescence technique allowed the investigation of the upper state nonradiative relaxation of the excited state manifold of Cr^{4+ }-doped forsterite. The excitation involves the absorption of two photons per photoexcited ion in a two-step absorption. Discrete peaks are observed in the hot up-converted luminescence spectrum and are attributed to the population of nonequilibrium vibronic levels during the deexcitation of the ions by phonon emission. This work reveals that the phonon modes participating in the initial steps of the nonradiative relaxation of the photoexcited ions have energies 218 +/- 20, 325 +/- 20, 365 +/- 20 and 513 +/- 12 cm^ {-1}. The shape of the luminescence spectral envelope suggests two electronic bottlenecks at ~2.1 and ~2.45 eV associated with slower rates of vibrational relaxation at different parts of the excited state manifold. Time resolved measurements indicated that the average time for phonon emission is of the order of hundreds of fs. Information on the nonequilibrium phonon dynamics of the 225, 335 and 370 cm^{-1} modes of forsterite has been obtained using time resolved Raman scattering. Laser pulses of 450 fs in duration and 590 nm in wavelength were used to excite the Cr ions 2.1 eV above the ground state. The probe pulses (obtained from the same laser) are monitoring the nonequilibrium phonon population through the intensity of the antiStokes Raman lines at various pump-probe delay times. Experiments were performed at room and liquid nitrogen temperatures. The observed nonequilibrium phonon populations are associated with the overall complex nonradiative decay following the excitation of

  18. Evaluation of biexponential relaxation processes by magnetic resonance imaging. A phantom study

    DEFF Research Database (Denmark)

    Kjaer, L; Thomsen, C; Larsson, H B

    1988-01-01

    .5 tesla (T). Measurements were performed on a phantom of bicompartmental perspex boxes with combinations of different CuSO4 concentrations. T1 determination was based on a 12-points partial saturation inversion recovery pulse sequence. T2 determination was provided by a multiple spin echo sequence with 32...

  19. Study of conduction mechanisms and relaxation processes in NiCl2-PVA composites

    International Nuclear Information System (INIS)

    Basha, A.F.; Amin, M.; Abdel Samad, H.A.

    1985-07-01

    Electric conduction measurements were made at different temperatures and fields on thin films NiCl 2 -PVA composites prepared by casting. The conduction is assumed to be generally ionic in nature and polarization contribution is suggested to operate mainly at higher temperatures. Space-charge limited conduction and relaxation phenomena have been observed. The obtained results made it possible to determine a complete set of conduction parameters including carrier mobility, carrier concentration, traps density, Fermi energy, activation energy, etc. (author)

  20. Magnetic cellular nonlinear network with spin wave bus for image processing

    Science.gov (United States)

    Khitun, Alexander; Bao, Mingqiang; Wang, Kang L.

    2010-03-01

    We describe and analyze a cellular nonlinear network based on magnetic nanostructures for image processing. The network consists of magneto-electric cells integrated onto a common ferromagnetic film-spin wave bus. The magneto-electric cell is an artificial two-phase multiferroic structure comprising piezoelectric and ferromagnetic materials. A bit of information is assigned to the cell's magnetic polarization, which can be controlled by the applied voltage. The information exchange among the cells is via the spin waves propagating in the spin wave bus. Each cell changes its state as a combined effect: magneto-electric coupling and the interaction with the spin waves. The distinct feature of a network with a spin wave bus is the ability to control the inter-cell communication by an external global parameter — magnetic field. The latter makes it possible to realize different image processing functions on the same template without rewiring or reconfiguration. We present the results of numerical simulations illustrating image filtering, erosion, dilation, horizontal and vertical line detection, inversion and edge detection accomplished on one template by the proper choice of the strength and direction of the external magnetic field. We also present numerical assets on the major network parameters such as cell density, power dissipation and functional throughput, and compare them with the parameters projected for other nano-architectures such as CMOL-CrossNet, Quantum-Dot Cellular Automata, and Quantum Dot-Image Processor. Potentially, the utilization of spin wave phenomena at the nanometer scale may provide a route to low-power consumption and functional logic circuits for special task data processing.

  1. Generalized approach to non-exponential relaxation

    Indian Academy of Sciences (India)

    Abstract. Non-exponential relaxation is a universal feature of systems as diverse as glasses, spin glasses, earthquakes, financial markets and the universe. Complex relaxation results from hierarchically constrained dynamics with the strength of the constraints being directly related to the form of the relaxation, which ...

  2. Effect of preheating on fatigue resistance of gears in spin induction coil hardening process

    Science.gov (United States)

    Kumar, Pawan; Aggarwal, M. L.

    2018-02-01

    Spin hardening inductors are typically used for fine-sized teeth gear geometry. With the proper selection of several design parameters, only the gear teeth can be case surface hardened without affecting the other surface of gear. Preheating may be done to reach an adapted high austenitizing temperature in the root circle to avoid overheating of the tooth tip during final heating. The effect of preheating of gear on control of compressive residual stresses and case hardening has been experimentally discussed in this paper. Present work is about analysing single frequency mode, preheat hardening treatment and compressive residual stresses field for hardening process of spur gear using spin hardening inductors.

  3. Electric-field effects in optically generated spin transport

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M. Idrish [Nanoscale Science and Technology Centre and School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)], E-mail: m.miah@griffith.edu.au

    2009-05-25

    Transport of spin-polarized electrons in semiconductors is studied experimentally. Spins are generated by optical excitation because of the selection rules governing optical transitions from heavy-hole and light-hole states to conduction-band states. Experiments designed for the control of spins in semiconductors investigate the bias-dependent spin transport process and detect the spin-polarized electrons during transport. A strong bias dependence is observed. The electric-field effects on the spin-polarized electron transport are also found to be depended on the excitation photon energy and temperature. Based on a field-dependent spin relaxation mechanism, the electric-field effects in the transport process are discussed.

  4. Process of optical excitation and relaxation of color center in synthetic diamond and its application to optoelectronics

    International Nuclear Information System (INIS)

    Nishida, Yoshio

    1989-01-01

    Irradiation of high-pressure synthesized diamond is carried out by using a nuclear reactor or a linac. Then, the effect of annealing on the color centers is observed. A study is made to identify different color centers and to provide techniques to control their introduction. Investigations cover the relation of color center formation with annealing temperature, dependence of color center formation on radiation dose, migration of H3 center and hydrogen, and applicability of five different color centers to optoelectronics. Next, a study is made of the formation and relaxation of the nitrogen vacancy (NV) center in a metastable excited state produced by optical excitation. An optical gain is essential to provide laser. Optical amplification is measured at the vibronic emission band of the NV center. An increase in absorption is detected, indicating that the NV center will not provide laser. In the optical excitation-relaxation process, the relaxation proceeds via a metastable state. Finally, hole burning of ZPL of the NV center is observed in the temperature range from 20K to 80K, and some of its features are described. (N.K.)

  5. Influence of Na doping on the magnetic relaxation processes of magnetite

    International Nuclear Information System (INIS)

    Torres, C.; Arias, A. Gonzalez; Hisatake, K.; Francisco, C. de; Hernandez-Gomez, P.; Kim, C.O.; Kim, D.J.

    2007-01-01

    The relaxation of the initial magnetic permeability was measured in polycrystalline Na-doped magnetite samples, with nominal composition Na x Fe 3- x O 4 (x ranging from 0 to 0.05), by means of the magnetic disaccommodation (DA) technique. We found that the increasing amount of Na ions modifies the DA spectra and a very different behaviour depending on the sintering atmosphere. These results were discussed in terms of the presence of Na ions in the magnetite lattice, giving rise to certain modifications in their neighbourhood

  6. Relaxation processes and conduction mechanism in bismuth ferrite lead titanate composites

    Science.gov (United States)

    Sahu, Truptimayee; Behera, Banarji

    2018-02-01

    In this study, samarium (Sm)-doped multiferroic composites of 0.8BiSmxFe1-xO3-0.2PbTiO3 where x = 0.05, 0.10, 0.15, and 0.20 were prepared via the conventional solid state reaction route. The electrical properties of these composites were analyzed using an impedance analyzer over a wide range of temperatures and frequencies (102-106 Hz). The impedance and modulus analyses confirmed the presence of both bulk and grain boundary effects in the materials. The temperature dependence of impedance and modulus spectrum indicated the negative temperature coefficient of resistance behavior. The dielectric relaxation exhibited non-Debye type behavior and it was temperature dependent. The relaxation time (τ) and DC conductivity followed an Arrhenius type behavior. The frequency-dependent AC conductivity obeyed Jonscher's power law. The correlated barrier hopping model was appropriate to understand the conduction mechanism in the composites considered.

  7. Photon drag investigations of current relaxation processes in a two-dimensional electron gas

    CERN Document Server

    Graf, S; Kohler, K U; Bachtold, W

    2000-01-01

    We have investigated the photon drag current that is excited by an infrared laser beam in the plane of the two-dimensional electron gas of GaAs/Al/sub 0.35/Ga/sub 0.65/As multiple-quantum-well systems. An analysis of the spectral response, measured with the picosecond infrared pulses of the wavelength-tunable free electron laser source FELIX, is presented for different doping schemes and examined as a function of temperature and intensity. The influence of the subband- selective scattering by a delta doping is explored, which demonstrates that the photon drag spectral response allows the determination of the momentum relaxation time ratio, R= tau /sub 1// tau /sub 2/, of the electrons in the ground and excited subbands. The relaxation time ratio is found to be surprisingly constant over a large temperature range. The variation of the ratio with intensity can be attributed to heating of the electron gas, whose temperature exceeds 1000 K at saturation intensity. (41 refs).

  8. Self-similarly evolving and minimally dissipated stable states of plasmas realized after relaxation and self-organization processes

    International Nuclear Information System (INIS)

    Kondoh, Yoshiomi; Hakoiwa, Toru; Okada, Akihito; Kobayashi, Naohiro; Takahashi, Toshiki

    2006-01-01

    A novel set of simultaneous eigenvalue equations having dissipative terms are derived to find self-similarly evolving and minimally dissipated stable states of plasmas realized after relaxation and self-organization processes. By numerically solving the set of eigenvalue equations in a cylindrical model, typical spatial profiles of plasma parameters, electric and magnetic fields and diffusion factors are presented, all of which determine self-consistently with each other by physical laws and mutual relations among them, just as in experimental plasmas. (author)

  9. Quantum cognition: The possibility of processing with nuclear spins in the brain

    Science.gov (United States)

    Fisher, Matthew P. A.

    2015-11-01

    The possibility that quantum processing with nuclear spins might be operative in the brain is explored. Phosphorus is identified as the unique biological element with a nuclear spin that can serve as a qubit for such putative quantum processing-a neural qubit-while the phosphate ion is the only possible qubit-transporter. We identify the "Posner molecule", Ca9(PO4)6, as the unique molecule that can protect the neural qubits on very long times and thereby serve as a (working) quantum-memory. A central requirement for quantum-processing is quantum entanglement. It is argued that the enzyme catalyzed chemical reaction which breaks a pyrophosphate ion into two phosphate ions can quantum entangle pairs of qubits. Posner molecules, formed by binding such phosphate pairs with extracellular calcium ions, will inherit the nuclear spin entanglement. A mechanism for transporting Posner molecules into presynaptic neurons during vesicle endocytosis is proposed. Quantum measurements can occur when a pair of Posner molecules chemically bind and subsequently melt, releasing a shower of intra-cellular calcium ions that can trigger further neurotransmitter release and enhance the probability of post-synaptic neuron firing. Multiple entangled Posner molecules, triggering non-local quantum correlations of neuron firing rates, would provide the key mechanism for neural quantum processing. Implications, both in vitro and in vivo, are briefly mentioned.

  10. The influence of the extraction process and spinning conditions on morphology and ultimate properties of gel-spun polyethylene fibres

    NARCIS (Netherlands)

    Hoogsteen, W.; Brinke, G. ten; Pennings, A.J.

    1987-01-01

    The morphology of gel-spun polyethylene fibres prior to hot-drawing, depends on the spinning conditions and the extraction process. Paraffin oil containing fibres spun at relatively low spin temperatures and high take-up speeds show a c-axis orientation parallel to the fibre axis due to shish-kebab

  11. Multiscale approach to mechanical behavior of polymeric nanocomposites: an application of T1.rho.(13C) relaxation experiments at variable spin-locking fields

    Czech Academy of Sciences Publication Activity Database

    Kotek, Jiří; Brus, Jiří

    2014-01-01

    Roč. 59, č. 9 (2014), s. 662-666 ISSN 0032-2725 R&D Projects: GA ČR(CZ) GA13-29009S Institutional support: RVO:61389013 Keywords : polyamide 6 * nanocomposite * T1ρ(13C) relaxation Subject RIV: JI - Composite Materials Impact factor: 0.633, year: 2014

  12. Exploring catalyst passivation with NMR relaxation.

    Science.gov (United States)

    Robinson, Neil; Gladden, Lynn F; D'Agostino, Carmine

    2017-10-26

    NMR relaxation has recently emerged as a novel and non-invasive tool for probing the surface dynamics of adsorbate molecules within liquid-saturated mesoporous catalysts. The elucidation of such dynamics is of particular relevance to the study and development of solvated green catalytic processes, such as the production of chemicals and fuels from bio-resources. In this paper we develop and implement a protocol using high field 1 H NMR spin-lattice relaxation as a probe of the reorientational dynamics of liquids imbibed within mesoporous oxide materials. The observed relaxation of liquids within mesoporous materials is highly sensitive to the adsorbed surface layer, giving insight into tumbling behaviour of spin-bearing chemical environments at the pore surface. As a prototypical example of relevance to liquid-phase catalytic systems, we examine the mobility of liquid methanol within a range of common catalyst supports. In particular, through the calculation and comparison of a suitable interaction parameter, we assess and quantify changes to these surface dynamics upon replacing surface hydroxyl groups with hydrophobic alkyl chains. Our results indicate that the molecular tumbling of adsorbed methanol is enhanced upon surface passivation due to the suppression of surface-adsorbate hydrogen bonding interactions, and tends towards that of the unrestricted bulk liquid. A complex analysis in which we account for the influence of changing pore structure and surface chemistry upon passivation is discussed. The results presented highlight the use of NMR spin-lattice relaxation measurements as a non-invasive probe of molecular dynamics at surfaces of interest to liquid-phase heterogeneous catalysis.

  13. Numerical study on physical mechanism of vortex breakdown occurrence in spin-up process

    OpenAIRE

    "小出, 輝明"; Teruaki", "Koide

    2008-01-01

    "A Numerical study presented on a vortex breakdown in spin-up process in an enclosed cylindrical container. In a transitional state, momentary vortex breakdowns can occur for particular parameter values ofthe Reynolds number and aspect ratio where no vortex breakdown appears in a steady state. This transient vortex breakdown flow is convenient to consider a mechanism for the occurrence of a vortex breakdown. It isdiscussed that periodical increase and decrease of angular momentum in upstream ...

  14. Highly efficient polymer solar cells with printed photoactive layer: rational process transfer from spin-coating

    KAUST Repository

    Zhao, Kui

    2016-09-05

    Scalable and continuous roll-to-roll manufacturing is at the heart of the promise of low-cost and high throughput manufacturing of solution-processed photovoltaics. Yet, to date the vast majority of champion organic solar cells reported in the literature rely on spin-coating of the photoactive bulk heterojunction (BHJ) layer, with the performance of printed solar cells lagging behind in most instances. Here, we investigate the performance gap between polymer solar cells prepared by spin-coating and blade-coating the BHJ layer for the important class of modern polymers exhibiting no long range crystalline order. We find that thickness parity does not always yield performance parity even when using identical formulations. Significant differences in the drying kinetics between the processes are found to be responsible for BHJ nanomorphology differences. We propose an approach which benchmarks the film drying kinetics and associated BHJ nanomorphology development against those of the champion laboratory devices prepared by spin-coating the BHJ layer by adjusting the process temperature. If the optimization requires the solution concentration to be changed, then it is crucial to maintain the additive-to-solute volume ratio. Emulating the drying kinetics of spin-coating is also shown to help achieve morphological and performance parities. We put this approach to the test and demonstrate printed PTB7:PC71BM polymer solar cells with efficiency of 9% and 6.5% PCEs on glass and flexible PET substrates, respectively. We further demonstrate performance parity for two other popular donor polymer systems exhibiting rigid backbones and absence of a long range crystalline order, achieving a PCE of 9.7%, the highest efficiency reported to date for a blade coated organic solar cell. The rational process transfer illustrated in this study should help the broader and successful adoption of scalable printing methods for these material systems.

  15. Studies of diluted antiferromagnets MnxMg1-xTiO3 with x=0.55 and 0.70 by muon spin relaxation method

    International Nuclear Information System (INIS)

    Fukaya, A.; Ito, A.; Torikai, E.; Nishiyama, K.; Nagamine, K.

    1997-01-01

    Longitudinal fields μSR measurements have been performed in order to probe the spin dynamics in the diluted antiferromagnets Mn x Mg 1-x TiO 3 with x=0.70 and 0.55. In the x=0.70 sample which forms the antiferromagnetic long-range order, the static and fluctuating fields coexist at the muon stopping site below T N . On the other hand, in the x=0.55 sample which shows the spin-glass behavior, the local fields fluctuate rather fast even below T SG . We infer that this drastic change occurs when Mn x Mg 1-x TiO 3 transforms from an antiferromagnetic system to a spin-glass system by dilution

  16. Guinea-pig interpubic joint (symphysis pubica relaxation at parturition: Underlying cellular processes that resemble an inflammatory response

    Directory of Open Access Journals (Sweden)

    Muñoz-de-Toro Mónica

    2003-11-01

    Full Text Available Abstract Background At term, cervical ripening in coordination with uterine contractions becomes a prerequisite for a normal vaginal delivery. Currently, cervical ripening is considered to occur independently from uterine contractions. Many evidences suggest that cervical ripening resembles an inflammatory process. Comparatively little attention has been paid to the increased flexibility of the pelvic symphysis that occurs in many species to enable safe delivery. The aim of this study was to investigate whether the guinea-pig interpubic joint relaxation process observed during late pregnancy and parturition resembles an inflammatory process. Methods Samples of pubic symphysis were taken from pregnant guinea-pigs sacrificed along gestation, parturition and postpartum. Serial sections of paraffin-embedded tissues were used to measure the interpubic distance on digitalized images, stained with Giemsa to quantify leukocyte infiltration and to describe the vascular area changes, or studied by the picrosirius-polarization method to evaluate collagen remodeling. P4 and E2 serum levels were measured by a sequential immunometric assay. Results Data showed that the pubic relaxation is associated with an increase in collagen remodeling. In addition, a positive correlation between E2 serum levels and the increase in the interpubic distance was found. On the other hand, a leukocyte infiltration in the interpubic tissue around parturition was described, with the presence of almost all inflammatory cells types. At the same time, histological images show an increase in vascular area (angiogenesis. Eosinophils reached their highest level immediately before parturition; whereas for the neutrophilic and mononuclear infiltration higher values were recorded one day after parturition. Correlation analysis showed that eosinophils and mononuclear cells were positively correlated with E2 levels, but only eosinophilic infiltration was associated with collagen remodeling

  17. Behavior of cesium and thallium cations inside a calixarene cavity as probed by nuclear spin relaxation. Evidence of cation-pi interactions in water.

    Science.gov (United States)

    Cuc, Diana; Bouguet-Bonnet, Sabine; Morel-Desrosiers, Nicole; Morel, Jean-Pierre; Mutzenhardt, Pierre; Canet, Daniel

    2009-08-06

    We have studied the complexes formed between the p-sulfonatocalix[4]arene and cesium or thallium metal cation, first by carbon-13 longitudinal relaxation of the calixarene molecule at two values of the magnetic field B(0). From the longitudinal relaxation times of an aromatic carbon directly bonded to a proton, thus subjected essentially to the dipolar interaction with that proton, we could obtain the correlation time describing the reorientation of the CH bond. The rest of this study has demonstrated that it is also the correlation time describing the tumbling of the whole calixarene assembly. From three non-proton-bearing carbons of the aromatic cycles (thus subjected to the chemical shift anisotropy and dipolar mechanisms), we have been able to determine the variation of the chemical shift anisotropy when going from the free to the complex form of the calixarene. These variations not only provide the location of the cation inside the calixarene cavity but also constitute a direct experimental proof of the cation-pi interactions. These results are complemented by cesium and thallium relaxation measurements performed again at two values of the magnetic field B(0). An estimation of the mean distance between the cation and the calixarene protons could be obtained. These measurements have also revealed an important chemical shift anisotropy of thallium upon complexation.

  18. Limiting factor of defect-engineered spin-filtering effect at room temperature

    Science.gov (United States)

    Puttisong, Y.; Buyanova, I. A.; Chen, W. M.

    2014-05-01

    We identify hyperfine-induced electron and nuclear spin cross-relaxation as the dominant physical mechanism for the longitudinal electron spin relaxation time 1 of the spin-filtering Gai2+ defects in GaNAs alloys. This conclusion is based on our experimental findings that T1 is insensitive to temperature over 4-300 K, and its exact value is directly correlated with the hyperfine coupling strength of the defects that varies between different configurations of the Gai2+ defects present in the alloys. These results thus provide a guideline for further improvements of the spin-filtering efficiency by optimizing growth and processing conditions to preferably incorporate the Gai2+ defects with a weak hyperfine interaction and by searching for new spin-filtering defects with zero nuclear spin.

  19. Kawasaki Dynamics on Bidimensional Spin Systems

    Science.gov (United States)

    Resende, Denilson C.; Cacüador, Felipe C.; Dantas, Sócrates O.

    Under the influence of an external field many systems exhibit slow relaxations processes. In that sense, we study the Physics of this behavior/process in the early stages of its evolution on bidimensional Ising systems using Monte Carlo simulations at a broad range of temperature and spins up concentration. The Monte Carlo simulations were done up to second neighbors interactions shown a more stable dynamic regime than first neighbors interactions, when the systems energy is considered. The behavior of relative energy/spin and the relative perimeter (the line between spin up and spin down regions) are monitored against Monte Carlo steps. Also, our findings show that the stretching index (a2) exhibit values below the borderline (1) in a broad range of concentration below 50% and temperature from 0.5 ≤T ≤ 4.5 (in units of J/kB , where J is the ferromagnetic constant and kB is the Boltzmann constant).

  20. Magnetism of the chromium thio-spinels Fe1-xCuxCr2S4 studied using muon spin rotation and relaxation.

    Science.gov (United States)

    Kalvius, G M; Krimmel, A; Wäppling, R; Hartmann, O; Litterst, F J; Wagner, F E; Tsurkan, V; Loidl, A

    2013-05-08

    Powder samples of Fe1-xCuxCr2S4 with x = 0,0.2,0.5,0.8 were studied, between 5 and 300 K. The results reveal that for x < 1, the magnetic order in the series is more varied than the simple collinear ferrimagnetic structure traditionally assumed to exist everywhere from the Curie point to T → 0. In FeCr2S4 several ordered magnetic phases are present, with the ground state likely to have an incommensurate cone-like helical structure. Fe0.8Cu0.2Cr2S4 is the compound for which simple collinear ferrimagnetism is best developed. In Fe0.5Cu0.5Cr2S4 the ferrimagnetic spin structure is not stable, causing spin reorientation around 90 K. In Fe0.2Cu0.8Cr2S4 the ferrimagnetic structure is at low temperatures considerably distorted locally, but with rising temperature this disorder shows a rapid reduction, coupled to increased spin fluctuation rates. In summary, the present data show that the changes induced by the replacement of Fe by Cu have more profound influences on the magnetic properties of the Fe1-xCuxCr2S4 compounds than merely a shift of Curie temperature, saturation magnetization and internal field magnitude.

  1. New evidence for the idea of timescale invariance of relaxation processes in simple liquids: the case of molten sodium

    CERN Document Server

    Yulmetyev, R M; Scopigno, T; Hänggi, P

    2003-01-01

    The idea of the timescale invariance of relaxation processes in liquids (Yulmetyev et al 2001 Phys. Rev. E 64 057101; 2002 JETP Lett. 76 147) is used to analyse the short-wave collective excitation in liquid sodium, as recently measured by means of very-high-energy-resolution inelastic x-ray scattering (Scopigno et al 2002 Phys. Rev. E 65 031205). The dynamic structure factor, S(Q, omega), calculated on the basis of this idea is in very good agreement with the experimental data in the wavevector range from 1.5 to 14.6 nm sup - sup 1 , where pronounced collective excitations exist. The frequency dependence of the non-Markovity parameter epsilon sub i (Q, omega) (i = 1, 2, 3, 4) allows us to reveal the alternation of the amplification and the decay of non-Markovity effects for the observed region of wavevector Q.

  2. Effect of radiation and non-Maxwellian electron distribution on relaxation processes in an atmospheric cesium seeded argon plasma

    International Nuclear Information System (INIS)

    Borghi, C.A.; Veefkind, A.; Wetzer, J.M.

    1982-03-01

    A model, describing the time dependent behaviour of a noble gas MHD generator plasma, has been set up. With this model it is possible to calculate the relaxation for ionization or recombination as a response to a stepwise temperature development, once the initial and final conditions are given. In model radiative transitions and a deviation from Maxwellian electron distribution are included. Radiation causes an enhancement of both the ionization relaxation time and the recombination relaxation time. A non-Maxwellian electron distribution results in an increase of the relaxation time for an ionizing plasma because of an underpopulation of the high energy electrons. A decrease of the relaxation time for a recombining plasma is caused by an overpopulation of high energy electrons. The relaxation time is strongly dependent on the seed ratio and the temperature step. (Auth.)

  3. Spin-dependent recombination involving oxygen-vacancy complexes in silicon

    OpenAIRE

    Franke, David P.; Hoehne, Felix; Vlasenko, Leonid S.; Itoh, Kohei M.; Brandt, Martin S.

    2014-01-01

    Spin-dependent relaxation and recombination processes in $\\gamma$-irradiated $n$-type Czochralski-grown silicon are studied using continuous wave (cw) and pulsed electrically detected magnetic resonance (EDMR). Two processes involving the SL1 center, the neutral excited triplet state of the oxygen-vacancy complex, are observed which can be separated by their different dynamics. One of the processes is the relaxation of the excited SL1 state to the ground state of the oxygen-vacancy complex, t...

  4. Complex methyl groups dynamics in [(CH3)4P]3Sb2Br9 (PBA) from low to high temperatures by proton spin-lattice relaxation and narrowing of proton NMR spectrum.

    Science.gov (United States)

    Latanowicz, L; Medycki, W; Jakubas, R

    2009-11-01

    Molecular dynamics of a polycrystalline sample of [(CH(3))(4)P](3)Sb(2)Br(9) (PBA) has been studied on the basis of the T(1) (24.7 MHz) relaxation time measurement, the proton second moment of NMR and the earlier published T(1) (90 MHz) relaxation times. The study was performed in a wide range of temperatures (30-337 K). The tunnel splitting omega(T) of the methyl groups was estimated as of low frequency (from kHz to few MHz). The proton spin pairs of the methyl group are known to perform a complex internal motion being a resultant of four components. Three of them involve mass transportation over and through the potential barrier and are characterized by the correlation times tau(3) and tau(T)of the jumps over the barrier and tunnel jumps in the threefold potential of the methyl group and tau(iso) the correlation time of isotropic rotation of the whole TMP cation. For tau(3) and tau(iso) the Arrhenius temperature dependence was assumed, while for tau(T)--the Schrödinger one. The fourth motion causes fluctuations of the tunnel splitting frequency, omega(T), and it is related to the lifetime of the methyl spin at the energy level. The correlation function for this fourth motion (tau(omega) correlation time) has been proposed by Müller-Warmuth et al. In this paper a formula for the correlation function and spectral density of the complex motion made of the above-mentioned four components was derived and used in interpretation of the T(1) relaxation time. The second moment of proton NMR line at temperatures below 50K is four times lower than its value for the rigid structure. The three components of the internal motion characterized by tau(T), tau(H), and tau(iso) were proved to reduce the second moment of the NMR line. The tunnel jumps of the methyl group reduce M(2) at almost 0K, the classical jumps over the barrier reduce M(2) in the vicinity of 50K, while the isotropic motion near 150K. Results of the study on the dynamics of CH(3) groups of TMP cation based on

  5. Spin interactions in Graphene-Single Molecule Magnets Hybrids

    Science.gov (United States)

    Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Aña; Luis, Fernando; Rauschenbach, Stephan; Dressel, Martin; Kern, Klaus; Burghard, Marko; Bogani, Lapo

    2014-03-01

    Graphene is a potential component of novel spintronics devices owing to its long spin diffusion length. Besides its use as spin-transport channel, graphene can be employed for the detection and manipulation of molecular spins. This requires an appropriate coupling between the sheets and the single molecular magnets (SMM). Here, we present a comprehensive characterization of graphene-Fe4 SMM hybrids. The Fe4 clusters are anchored non-covalently to the graphene following a diffusion-limited assembly and can reorganize into random networks when subjected to slightly elevated temperature. Molecules anchored on graphene sheets show unaltered static magnetic properties, whilst the quantum dynamics is profoundly modulated. Interaction with Dirac fermions becomes the dominant spin-relaxation channel, with observable effects produced by graphene phonons and reduced dipolar interactions. Coupling to graphene drives the spins over Villain's threshold, allowing the first observation of strongly-perturbative tunneling processes. Preliminary spin-transport experiments at low-temperature are further presented.

  6. Spin transport in graphene nanostructures

    NARCIS (Netherlands)

    Guimaraes, M. H. D.; van den Berg, J. J.; Vera-Marun, I. J.; Zomer, P. J.; van Wees, B. J.

    2014-01-01

    Graphene is an interesting material for spintronics, showing long spin relaxation lengths even at room temperature. For future spintronic devices it is important to understand the behavior of the spins and the limitations for spin transport in structures where the dimensions are smaller than the

  7. Critical quench dynamics of random quantum spin chains: ultra-slow relaxation from initial order and delayed ordering from initial disorder

    Science.gov (United States)

    Roósz, Gergö; Lin, Yu-Cheng; Iglói, Ferenc

    2017-02-01

    By means of free fermionic techniques combined with multiple precision arithmetic we study the time evolution of the average magnetization, \\overline{m}(t), of the random transverse-field Ising chain after global quenches. We observe different relaxation behaviors for quenches starting from different initial states to the critical point. Starting from a fully ordered initial state, the relaxation is logarithmically slow described by \\overline{m}(t)∼ {{ln}}at, and in a finite sample of length L the average magnetization saturates at a size-dependent plateau {\\overline{m}}p(L)∼ {L}-b; here the two exponents satisfy the relation b/a=\\psi =1/2. Starting from a fully disordered initial state, the magnetization stays at zero for a period of time until t={t}{{d}} with {ln}{t}{{d}}∼ {L}\\psi and then starts to increase until it saturates to an asymptotic value {\\overline{m}}p(L)∼ {L}-b^{\\prime }, with b\\prime ≈ 1.5. For both quenching protocols, finite-size scaling is satisfied in terms of the scaled variable {ln}t/{L}\\psi . Furthermore, the distribution of long-time limiting values of the magnetization shows that the typical and the average values scale differently and the average is governed by rare events. The non-equilibrium dynamical behavior of the magnetization is explained through semi-classical theory.

  8. Spin Transport in High-Quality Suspended Graphene Devices

    NARCIS (Netherlands)

    Guimaraes, Marcos H. D.; Veligura, A.; Zomer, P. J.; Maassen, T.; Vera-Marun, I. J.; Tombros, N.; van Arees, B. J.; Wees, B.J. van

    We measure spin transport in high mobility suspended graphene (mu approximate to 10(5)cm(2)/(V s)), obtaining a (spin) diffusion coefficient of 0.1 m(2)/s and giving a lower bound on the spin relaxation time (tau(s) approximate to 150 ps) and spin relaxation length (lambda(s) = 4.7 mu m) for

  9. The role of non-equilibrium fluxes in the relaxation processes of the linear chemical master equation.

    Science.gov (United States)

    de Oliveira, Luciana Renata; Bazzani, Armando; Giampieri, Enrico; Castellani, Gastone C

    2014-08-14

    We propose a non-equilibrium thermodynamical description in terms of the Chemical Master Equation (CME) to characterize the dynamics of a chemical cycle chain reaction among m different species. These systems can be closed or open for energy and molecules exchange with the environment, which determines how they relax to the stationary state. Closed systems reach an equilibrium state (characterized by the detailed balance condition (D.B.)), while open systems will reach a non-equilibrium steady state (NESS). The principal difference between D.B. and NESS is due to the presence of chemical fluxes. In the D.B. condition the fluxes are absent while for the NESS case, the chemical fluxes are necessary for the state maintaining. All the biological systems are characterized by their "far from equilibrium behavior," hence the NESS is a good candidate for a realistic description of the dynamical and thermodynamical properties of living organisms. In this work we consider a CME written in terms of a discrete Kolmogorov forward equation, which lead us to write explicitly the non-equilibrium chemical fluxes. For systems in NESS, we show that there is a non-conservative "external vector field" whose is linearly proportional to the chemical fluxes. We also demonstrate that the modulation of these external fields does not change their stationary distributions, which ensure us to study the same system and outline the differences in the system's behavior when it switches from the D.B. regime to NESS. We were interested to see how the non-equilibrium fluxes influence the relaxation process during the reaching of the stationary distribution. By performing analytical and numerical analysis, our central result is that the presence of the non-equilibrium chemical fluxes reduces the characteristic relaxation time with respect to the D.B. condition. Within a biochemical and biological perspective, this result can be related to the "plasticity property" of biological systems and to their

  10. The role of non-equilibrium fluxes in the relaxation processes of the linear chemical master equation

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Luciana Renata de; Bazzani, Armando; Giampieri, Enrico; Castellani, Gastone C., E-mail: Gastone.Castellani@unibo.it [Physics and Astronomy Department, Bologna University and INFN Sezione di Bologna (Italy)

    2014-08-14

    We propose a non-equilibrium thermodynamical description in terms of the Chemical Master Equation (CME) to characterize the dynamics of a chemical cycle chain reaction among m different species. These systems can be closed or open for energy and molecules exchange with the environment, which determines how they relax to the stationary state. Closed systems reach an equilibrium state (characterized by the detailed balance condition (D.B.)), while open systems will reach a non-equilibrium steady state (NESS). The principal difference between D.B. and NESS is due to the presence of chemical fluxes. In the D.B. condition the fluxes are absent while for the NESS case, the chemical fluxes are necessary for the state maintaining. All the biological systems are characterized by their “far from equilibrium behavior,” hence the NESS is a good candidate for a realistic description of the dynamical and thermodynamical properties of living organisms. In this work we consider a CME written in terms of a discrete Kolmogorov forward equation, which lead us to write explicitly the non-equilibrium chemical fluxes. For systems in NESS, we show that there is a non-conservative “external vector field” whose is linearly proportional to the chemical fluxes. We also demonstrate that the modulation of these external fields does not change their stationary distributions, which ensure us to study the same system and outline the differences in the system's behavior when it switches from the D.B. regime to NESS. We were interested to see how the non-equilibrium fluxes influence the relaxation process during the reaching of the stationary distribution. By performing analytical and numerical analysis, our central result is that the presence of the non-equilibrium chemical fluxes reduces the characteristic relaxation time with respect to the D.B. condition. Within a biochemical and biological perspective, this result can be related to the “plasticity property” of biological

  11. Grain morphology of YBCO coated superconductors prepared by spin process on Ni substrate

    Energy Technology Data Exchange (ETDEWEB)

    Liu, C.F.; Du, S.J.; Yan, G.; Xi, W.; Wu, X.; Pang, Y.; Wang, F.Y.; Liu, X.H.; Feng, Y.; Zhang, P.X.; Wu, X.Z.; Zhou, L

    2003-04-15

    The YBCO thick films with c-axis preferred orientation were prepared by spin and printing processes on Ni substrates (including cold rolling Ni, cube textured Ni, and cube textured Ni+self-oxided NiO). The results show that the chrysanthemum (or spherulite) and polygon morphology grains dominate the microstructure of YBCO films. The chrysanthemum size is about 0.2-0.5 mm range, some reaches 1 mm, and polygon grains normally are placed in the center of the chrysanthemum grains. No chrysanthemum grains appear in the thick films prepared on the substrate with Ag or YBCO intermediate layers.

  12. Magnetization process in the exactly solved spin-1/2 Ising-Heisenberg model on decorated Bethe lattices

    Directory of Open Access Journals (Sweden)

    J. Strečka

    2012-12-01

    Full Text Available The spin-1/2 Ising-Heisenberg model on diamond-like decorated Bethe lattices is exactly solved in the presence of the longitudinal magnetic field by combining the decoration-iteration mapping transformation with the method of exact recursion relations. In particular, the ground state and low-temperature magnetization process of the ferrimagnetic version of the considered model is investigated in detail. Three different magnetization scenarios with up to two consecutive fractional magnetization plateaus were found, whereas the intermediate magnetization plateau may either correspond to the classical ferrimagnetic spin arrangement and/or the field-induced quantum ferrimagnetic spin ordering without any classical counterpart.

  13. Solvent dynamical effects in electron transfer: Predicted consequences of non-Debye relaxation processes and some comparisons with experimental kinetics

    Science.gov (United States)

    McManis, George E.; Weaver, Michael J.

    1989-01-01

    The consequences of non-Debye solvent relaxation upon the barrier-crossing dynamics of adiabatic electron-transfer processes have been explored numerically using a rate formulation due to Hynes for several common forms of the dielectric response function Ê(s), with the objective of assessing the likely experimental importance of such effects. For the ``multiple Debye'' form of Ê(s), analytic expressions for the required time-correlation function can be obtained, whereas for the Davidson-Cole and Cole-Cole forms numerical solutions to the inverse Laplace transform were required. Illustrative numerical results are presented of the increases in the adiabatic barrier-crossing frequency, νn, predicted to be engendered by the presence of higher-frequency relaxation components for dielectric conditions of likely experimental relevance. Substantial (five- to ten fold) rate enhancements are often obtained, resulting from the disproportionately large influence upon νn predicted to arise from the higher-frequency components of Ê(s). Neither νn, nor the non-Debye influence upon νn, are found to be affected greatly by alterations in the shape of the barrier top caused by variations in the electronic coupling matrix element. Comparisons between these numerical predictions and corresponding experimental solvent-dependent νn values extracted from metallocene self-exchange kinetics indicate that the former can account for a substantial fraction of the νn accelerations observed in alcohols and other non-Debye solvents. Roughly concordant non-Debye effects are also predicted from some other, but not all, recent rate formulations. The desirability of utilizing subpicosecond dynamical solvation information from fluorescence Stokes shifts to predict non-Debye effects upon electron-transfer barrier-crossing frequencies is pointed out.

  14. Process of advective diffusive enrichment using differential gradients and the effects of variations in relaxation times

    International Nuclear Information System (INIS)

    Suarez Antola R.; Bernasconi, G.; Bertolotti, Angel

    1995-01-01

    A multicomponent solution is considered in advective diffusion chambers between two half-permeable barriers. A mathematical model is developed to calculate the concentration fields in the chamber. A new enrichment process is proposed and assessed using a digital simulation of space-time dynamics, based on the analytical solution of the model

  15. Relaxation and excitation electronic processes in dielectrics irradiated by ultrafast IR and VUV pulses; Processus electroniques d'excitation et de relaxation dans les solides dielectriques excites par des impulsions IR et XUV ultracourtes

    Energy Technology Data Exchange (ETDEWEB)

    Gaudin, J

    2005-11-15

    We studied excitation and relaxation of electrons involved during interaction of visible and VUV femtosecond pulses with dielectrics. The generated population of hot electrons, having energy of few eV to few tens of eV above the bottom of the conduction band, is responsible of phenomena ranging to defect creation to optical breakdown. Owing to two techniques: photoemission and transient photoconductivity we improve the understanding of the The first photoemission experiments deal with dielectrics irradiated by 30 fs IR pulses. The photoemission spectra measured show a large population of electrons which energy rise up to 40 eV. We interpret this result in terms of a new absorption process: direct multi-photons inter-branch transitions. The 2. type of photoemission experiments are time resolved 'pump/probe' investigation. We study the relaxation of electrons excited by a VUV pulses. We used the high order harmonics (HOH) as light sources. We found surprisingly long decay time in the range of ps timescale. Last type of experiments is photoconductivity studies of diamond samples. Using HOH as light source we measure the displacement current induced by excited electrons in the conduction band. Those electrons relax mainly by impact ionisation creating secondary electrons. Hence by probing the number of electrons we were able to measure the efficiency of these relaxation processes. We observe a diminution of this efficiency when the energy of exciting photons is above 20 eV. Owing to Monte-Carlo simulation we interpret this result in terms of band structure effect. (author)

  16. Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine)2(CN)2

    DEFF Research Database (Denmark)

    Kjær, Kasper Skov; Zhang, Wenkai; Alonso-Mori, Roberto

    2017-01-01

    -visible spectra, associated with the 2,2′-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state...... of [Fe(bpy)2(CN)2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy)2(CN)2] complement prior measurement performed on [Fe(bpy)3]2+ and [Fe(bpy)(CN)4]2− in dimethylsulfoxide solution......We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy)2(CN)2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV...

  17. A general model to calculate the spin-lattice (T1) relaxation time of blood, accounting for haematocrit, oxygen saturation and magnetic field strength.

    Science.gov (United States)

    Hales, Patrick W; Kirkham, Fenella J; Clark, Christopher A

    2016-02-01

    Many MRI techniques require prior knowledge of the T1-relaxation time of blood (T1bl). An assumed/fixed value is often used; however, T1bl is sensitive to magnetic field (B0), haematocrit (Hct), and oxygen saturation (Y). We aimed to combine data from previous in vitro measurements into a mathematical model, to estimate T1bl as a function of B0, Hct, and Y. The model was shown to predict T1bl from in vivo studies with a good accuracy (± 87 ms). This model allows for improved estimation of T1bl between 1.5-7.0 T while accounting for variations in Hct and Y, leading to improved accuracy of MRI-derived perfusion measurements. © The Author(s) 2015.

  18. Influence of SnO2 nanoparticles on the relaxation dynamics of the conductive processes in polyaniline

    Science.gov (United States)

    Biswas, Swarup; Bhattacharya, Subhratanu

    2017-10-01

    The effect of stannic oxide (SnO2) nanoparticles on the electrical conductivity relaxation and distribution of relaxation times within the 4-Dodecylbenzenesulfonic acid (DBSA) doped polyaniline (Pani) was investigated using electrical impedance spectroscopy. A temperature dependent Kohlrausch-Williams-Watts (KWW) type temporal relaxation function in the time domain was generated from the analysis of the frequency dependence of the dielectric modulus (imaginary component). The thermal evolution of the characteristics parameters of the KWW function was evaluated and using these parameters the temperature dependent average conductivity relaxation time and associated macroscopic conductivity of different samples were estimated. The study revealed that SnO2 nanoparticles within the polyaniline matrix induced faster relaxation of charge carriers that essentially enhanced the conductivity of the nanocomposite. The observed phenomena were well supported by the observed improvement of the localization length of the charge carriers within the nanocomposite.

  19. Polarons induced electronic transport, dielectric relaxation and magnetodielectric coupling in spin frustrated Ba{sub 2}FeWO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Pezhumkattil Palakkal, Jasnamol [Academy of Scientific and Innovative Research (AcSIR), CSIR—National Institute for Interdisciplinary Science and Technology (CSIR-NIIST) Campus, Trivandrum 695 019 (India); Materials Science and Technology Division, National Institute for Interdisciplinary Science and Technology, CSIR, Trivandrum 695 019 (India); Lekshmi, P. Neenu; Thomas, Senoy [Materials Science and Technology Division, National Institute for Interdisciplinary Science and Technology, CSIR, Trivandrum 695 019 (India); Valant, Matjaz [Materials Research Laboratory, University of Nova Gorica, Nova Gorica 5000 (Slovenia); Suresh, K.G. [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400 076 (India); Varma, Manoj Raama, E-mail: manoj@niist.res.in [Academy of Scientific and Innovative Research (AcSIR), CSIR—National Institute for Interdisciplinary Science and Technology (CSIR-NIIST) Campus, Trivandrum 695 019 (India); Materials Science and Technology Division, National Institute for Interdisciplinary Science and Technology, CSIR, Trivandrum 695 019 (India)

    2016-04-15

    Highlights: • Ordered double perovskite Ba{sub 2}FeWO{sub 6} synthesized in reducing atmosphere possess a tetragonal I4/m crystal structure with mixed valent Fe/W cations. • Ba{sub 2}FeWO{sub 6} has an antiferromagnetic structure with T{sub N} at 19 K. • Insulating Ba{sub 2}FeWO{sub 6} shows different conducting mechanisms at different temperature regions and dielectric relaxation. • The polarons invoked by the mixed valence state of cations and their disordered arrangements are solely responsible for the various physical phenomena observed in Ba{sub 2}FeWO{sub 6}. - Abstract: Mixed valent double perovskite Ba{sub 2}FeWO{sub 6}, with tetragonal crystal structure, synthesized in a highly controlled reducing atmosphere, shows antiferromagnetic transition at T{sub N} = 19 K. A cluster glass-like transition is observed around 30 K arising from the competing interactions between inhomogeneous magnetic states. The structural distortion leads to the formation of polarons that are not contributing to DC conduction below charge ordering temperature, T{sub CO} = 279 K. Above T{sub CO}, small polarons will start to hop by exploiting thermal energy and participate in the conduction mechanism. The polarons are also responsible for the dielectric relaxor behavior, in which the dielectric relaxation time follows non-linearity in temperature as proposed by Fulcher. The material also exhibits a small room temperature magnetoresistance of 1.7% at 90 kOe. An intrinsic magnetodielectric coupling of ∼4% near room temperature and at lower temperatures, as well as an extrinsic magnetodielectric coupling change from +4% to −6% at around 210 K are reported.

  20. An Effective and Practical Method for Solving Hydro-Thermal Unit Commitment Problems Based on Lagrangian Relaxation Method

    Science.gov (United States)

    Sakurai, Takayoshi; Kusano, Takashi; Saito, Yutaka; Hirato, Kota; Kato, Masakazu; Murai, Masahiko; Nagata, Junichi

    This paper presents an effective and practical method based on the Lagrangian relaxation method for solving hydro-thermal unit commitment problem in which operational constraints involve spinning reserve requirements for thermal units and prohibition of simultaneous unit start-up/shut-down at the same plant. This method is processed in each iteration step of LRM that enables a direct solution. To improve convergence, this method applies an augmented Lagrangian relaxation method. Its effectiveness demonstrated for a real power system.

  1. Nanostructural Biochemical Modification Of Flax Fiber In The Processes Of Its Preparation For Spinning

    Directory of Open Access Journals (Sweden)

    Koksharov Sergey

    2015-09-01

    Full Text Available The elaborated principles of nanoengineering of linen textile materials implement the techniques of spatially localized effects of protein catalysts on polymeric cellulose companions with selective splitting of impurity compounds without damaging technologically necessary nano-sized formations of binders in the fiber structure. The ranges of optimal values of the residual content in flax fiber prepared for spinning are identified on the basis of the analysis of the successive stages of enzymatic and peroxide treatments contribution to the breakdown of polymers and the differentiation of the influence of impurities on the yarn technological properties. The recommended level of residual pectin, lignin and hemicellulose (wt. % is: after enzymatic treatment P1 = 1,0±0,1; L1 = 3,9±0,3; Hc1 = 11,0±1,0; after peroxide bleaching P2 = 0,4±0,05; L2 = 2,3±0,3; Hc2 = 7,5±0,5. The required level of fiber structural modification at the stage of preparing roving for spinning can be achieved through use of protein catalysts whose globule size is 50...100 nm. The use of enzymes with these dimensional characteristics helps to ensure breaking of polymer adhesives on the surface of incrusts and in the areas of intercellular formations, which hinder fiber crushing, without damaging nano-sized binding fractions. The implementation of this method contributes to a significant improvement in the uniformity of structural and physical and mechanical properties of flax yarn. Increase in yarn fineness and strength properties of semi-finished products, as well as improvement of deformation properties and reduction of yarn breakages during the spinning processes are achieved.

  2. Influence of relaxation processes in polymers on energy transfer by triplet levels

    International Nuclear Information System (INIS)

    Ibraev, N.Kh.; Zhunusbekov, A.M.

    1996-01-01

    Temperature influence on triplet-triplet (T-T) energy transfer between molecules of eosin and 3,4-benzopyrene is studied. Polyvenylbuteryl films have been used in capacity of polymer matrix. Calculation has being carried out on spectral-kinetic unit. It is revealed, that 3,4-benzopyrene triplets have been formed in polymer matrix after end of T-T energy transfer. These triplets join in a reaction of mixed triplet-triplet annihilation with non-blow out triplets of eosin and its sensitize slowed fluorescence (SF) of donor. This explains non-exponent character of eosin's dumping kinetics. Non-linear dependence of SF output ration to eosin phosphorescence output under presence of 3,4-benzopyrene molecules in film indicates on process of mixed annihilation. Fractal character of SF donor and acceptor has been evidenced about microscopical distribution of phosphor in polymer. 13 refs., 5 figs

  3. Effects of electric paravertebral muscle relaxation processes in the athletes heart

    Directory of Open Access Journals (Sweden)

    D. V. Syshko

    2013-02-01

    Full Text Available Influence of paravertebrals miorelaxation on electric processes in a heart at sportsmen is studied. Paravertebrals miorelaxation was the complex of exercises in a water environment directed on the decline of tone of paravertebral muscles. Before and after it was used of paravertebrals miorelaxation registered the indexes of electrocardiography at the sportsmen engaged in the Greek-Roman fight (n=22 by football (n=24 and heavy athletics (n=25. It is got, that at the sportsmen of engaged in the Greek -Roman fight after paravertebrals miorelaxation QRS and QT were it was increased, and R-R and PQ went down. At the sportsmen of engaged in heavy athletics HR and PQ went down after paravertebrals miorelaxation, R-R, QRS and QT were it was increased. At the sportsmen of getting busy by football the PQ interval shortened, and QRS and QT has multiplied. Findings testify to the presence of different mechanisms of adaptation of the conducting system of heart in the conditions of influencing of paravertebrals miorelaxation. These distinctions are fated by two basic factors: by the functional being of the cardio-vessels system on the whole and functional being of sine knot and conducting system of heart in particular.

  4. Relaxation of polarized nuclei in superconducting rhodium

    DEFF Research Database (Denmark)

    Knuuttila, T.A.; Tuoriniemi, J.T.; Lefmann, K.

    2000-01-01

    Nuclear spin lattice relaxation rates were measured in normal and superconducting (sc) rhodium with nuclear polarizations up to p = 0.55. This was sufficient to influence the sc state of Rh, whose T, and B-c, are exceptionally low. Because B-c ... is unchanged, the nuclear spin entropy was fully sustained across the sc transition. The relaxation in the sc state was slower at all temperatures without the coherence enhancement close to T-c. Nonzero nuclear polarization strongly reduced the difference between the relaxation rates in the sc and normal...

  5. Processes of Molecular Relaxation in Binary Crystalline Systems KNO3-KClO4, KNO3-KNO2, and K2CO3-K2SO4

    Science.gov (United States)

    Aliev, A. R.; Akhmedov, I. R.; Kakagasanov, M. G.; Aliev, Z. A.; Gafurov, M. M.; Rabadanov, K. Sh.; Amirov, A. M.

    2018-03-01

    The processes of molecular relaxation in binary crystalline systems KNO3-KClO4, KNO3-KNO2, and K2CO3-K2SO4 are studied via differential thermal analysis and Raman spectroscopy. It is found that the relaxation time of the vibrations ν1( A) of anions NO- 3 and CO2- 3 in systems KNO3-KClO4, KNO3-KNO2, and K2CO3-K2SO4 is less than that in KNO3 and K2CO3, respectively. It is shown that the increased rate of relaxation is explained by an additional relaxation mechanism presented in the system. This mechanism is associated with the excitation of vibrations of anions ClO- 4, NO- 2, and SO2- 4 and the lattice phonons that emerge. It is found that this relaxation mechanism requires correspondence of the frequency difference of these vibrations to the region of sufficiently high density of states of the phonon spectrum.

  6. Optimal process parameters for phosphorus spin-on-doping of germanium

    Energy Technology Data Exchange (ETDEWEB)

    Boldrini, Virginia [Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Via Marzolo 8, I-35131 Padova (Italy); INFN-LNL, Viale dell’Università 2, I-35020 Legnaro, Padova (Italy); Carturan, Sara Maria, E-mail: sara.carturan@lnl.infn.it [Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Via Marzolo 8, I-35131 Padova (Italy); INFN-LNL, Viale dell’Università 2, I-35020 Legnaro, Padova (Italy); Maggioni, Gianluigi; Napolitani, Enrico [Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Via Marzolo 8, I-35131 Padova (Italy); INFN-LNL, Viale dell’Università 2, I-35020 Legnaro, Padova (Italy); Napoli, Daniel Ricardo [INFN-LNL, Viale dell’Università 2, I-35020 Legnaro, Padova (Italy); Camattari, Riccardo [INFN Sezione di Ferrara, Dipartimento di Fisica, Università di Ferrara, Via Saragat 1, 44122, Ferrara (Italy); De Salvador, Davide [Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Via Marzolo 8, I-35131 Padova (Italy); INFN-LNL, Viale dell’Università 2, I-35020 Legnaro, Padova (Italy)

    2017-01-15

    Highlights: • Optimized protocol for the application of phosphorus spin-on-doping to Ge surface. • Homogeneous n-type Ge layers, fully electrically active, are obtained. • Crucial parameters for SOD curing are relative humidity, time and temperature. • Characterization of Ge loss from the surface into the SOD film by diffusion. • Spike annealing in standard tube chamber furnace are performed. - Abstract: The fabrication of homogeneously doped germanium layers characterized by total electrical activation is currently a hot topic in many fields, such as microelectronics, photovoltaics, optics and radiation detectors. Phosphorus spin-on-doping technique has been implemented on Ge wafers, by developing a protocol for the curing process and subsequent diffusion annealing for optimal doping. Parameters such as relative humidity and curing time turned out to affect the surface morphology, the degree of reticulation reached by the dopant source and the amount of dopant available for diffusion. After spike annealing in a conventional furnace, diffusion profiles and electrical properties have been measured. Ge loss from the surface during high-temperature annealing, due to diffusion into the source film, has been observed and quantified.

  7. Nonequilibrium Dynamics of Anisotropic Large Spins in the Kondo Regime: Time-Dependent Numerical Renormalization Group Analysis

    Science.gov (United States)

    Roosen, David; Wegewijs, Maarten R.; Hofstetter, Walter

    2008-02-01

    We investigate the time-dependent Kondo effect in a single-molecule magnet (SMM) strongly coupled to metallic electrodes. Describing the SMM by a Kondo model with large spin S>1/2, we analyze the underscreening of the local moment and the effect of anisotropy terms on the relaxation dynamics of the magnetization. Underscreening by single-channel Kondo processes leads to a logarithmically slow relaxation, while finite uniaxial anisotropy causes a saturation of the SMM’s magnetization. Additional transverse anisotropy terms induce quantum spin tunneling and a pseudospin-1/2 Kondo effect sensitive to the spin parity.

  8. Changes in T1 relaxation processes in the bone marrow following treatment in children with acute lymphoblastic leukemia

    International Nuclear Information System (INIS)

    Jensen, K.E.; Thomsen, C.; Henriksen, O.; Hertz, H.; Johansen, H.K.; Yssing, M.

    1990-01-01

    Magnetic resonance imaging (MRI) and T 1 relaxation time measurements of the vertebral bone marrow were performed in 11 children with acute lymphoblastic leukemia (ALL) at diagnosis. Nine of the children were re-examined after chemotherapeutic treatment. The results were compared with histological data from bone marrow biopsies obtained in close association to the MR examinations. Ten age matched children were examined as a control group. A 1.5 Tesla whole body scanner was used for the measurements. The pretreatment T 1 relaxation times of the bone marrow were significantly prolonged, compared to the age matched controls. After chemotherapy the T 1 relaxation times of the children with ALL decreased significantly towards or into the normal range. A significant correlation was found between the T 1 relaxation time and the content of malignant blast cells in the bone marrow. (orig.)

  9. Optical spin generation/detection and spin transport lifetimes

    International Nuclear Information System (INIS)

    Miah, M. Idrish

    2011-01-01

    We generate electron spins in semiconductors by optical pumping. The detection of them is also performed by optical technique using time-resolved pump-probe photoluminescence polarization measurements in the presence of an external magnetic field perpendicular to the generated spin. The spin polarization in dependences of the pulse length, pump-probe delay and external magnetic field is studied. From the dependence of spin-polarization on the delay of the probe, the electronic spin transport lifetimes and the spin relaxation frequencies as a function of the strength of the magnetic field are estimated. The results are discussed based on hyperfine effects for interacting electrons.

  10. Optical spin generation/detection and spin transport lifetimes

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M. Idrish, E-mail: m.miah@griffith.edu.au [Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)

    2011-02-25

    We generate electron spins in semiconductors by optical pumping. The detection of them is also performed by optical technique using time-resolved pump-probe photoluminescence polarization measurements in the presence of an external magnetic field perpendicular to the generated spin. The spin polarization in dependences of the pulse length, pump-probe delay and external magnetic field is studied. From the dependence of spin-polarization on the delay of the probe, the electronic spin transport lifetimes and the spin relaxation frequencies as a function of the strength of the magnetic field are estimated. The results are discussed based on hyperfine effects for interacting electrons.

  11. Relationship between the catalytic activity of Pt/alumina and the relaxation process of the photoexcited electrons

    International Nuclear Information System (INIS)

    Ito, Junji; Hanaki, Yasunari; Shen, Qing; Toyoda, Taro

    2012-01-01

    Highlights: ► We determined the decay time of photoexcited electrons of Pt/Al 2 O 3 . ► Faster decay of excited electrons in Pt/Al 2 O 3 leads to its faster oxidation rate. ► Decreasing excited electron lifetime in Pt/Al 2 O 3 may decrease Pt consumption in catalytic convertors. - Abstract: In order to decrease the consumption of precious metals used in the catalytic converters used in automobiles, we studied the relationship between the catalytic activity of Pt/alumina (Pt/Al 2 O 3 ) and the relaxation process of photoexcited electrons. Firstly, we studied the relationship between the size of the Pt particles in Pt/Al 2 O 3 and catalytic performance. Secondly, the relationship between the size of the Pt particles in Pt/Al 2 O 3 and the decay time of the excited electrons was studied using an improved transient grating (TG) technique. The results showed that faster decay of the excited electrons leads to greater oxidation rates. The decay time obtained with the improved TG technique gives an indication of the time that the exited electrons take to return to the ground state. According to studies utilizing FT-IR, one of the processes necessary for quickly generating CO 2 with Pt is that the electron in the Pt-O bond moves to the Pt side and that the Pt + becomes Pt metal. Thus, the decay time obtained with the improved TG technique corresponds to the process whereby Pt + returns to Pt metal. Thus, we found that the consumption of precious metals can be reduced by increasing the speed of the decay of the excited electrons.

  12. Coherent and correlated spin transport in nanoscale superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Morten, Jan Petter

    2008-03-15

    Motivated by the desire for better understanding of nano electronic systems, we theoretically study the conductance and noise characteristics of current flow between superconductors, ferromagnets, and normal-metals. Such nano structures can reveal information about superconductor proximity effects, spin-relaxation processes, and spintronic effects with potential applications for different areas of mesoscopic physics. We employ the quasiclassical theory of superconductivity in the Keldysh formalism, and calculate the nonequilibrium transport of spin and charge using various approaches like the circuit theory of quantum transport and full counting statistics. For two of the studied structures, we have been able to compare our theory to experimental data and obtain good agreement. Transport and relaxation of spin polarized current in superconductors is governed by energy-dependent transport coefficients and spin-flip rates which are determined by quantum interference effects. We calculate the resulting temperature-dependent spin flow in ferromagnet-superconductor devices. Experimental data for spin accumulation and spin relaxation in a superconducting nano wire is in agreement with the theory, and allows for a spin-flip spectroscopy that determines the dominant mechanism for spin-flip relaxation in the studied samples. A ferromagnet precessing under resonance conditions can give rise to pure spin current injection into superconductors. We find that the absorbed spin current is measurable as a temperature dependent Gilbert damping, which we calculate and compare to experimental data. Crossed Andreev reflection denotes superconducting pairing of electrons flowing from different normal-metal or ferromagnet terminals into a superconductor. We calculate the nonlocal currents resulting from this process in competition with direct electron transport between the normal-metal terminals. We take dephasing into account, and study the nonlocal current when the types of contact in

  13. Multi-Quanta Spin-Locking Nuclear Magnetic Resonance Relaxation Measurements: An Analysis of the Long-Time Dynamical Properties of Ions and Water Molecules Confined within Dense Clay Sediments

    Directory of Open Access Journals (Sweden)

    Patrice Porion

    2017-11-01

    Full Text Available Solid/liquid interfaces are exploited in various industrial applications because confinement strongly modifies the physico-chemical properties of bulk fluids. In that context, investigating the dynamical properties of confined fluids is crucial to identify and better understand the key factors responsible for their behavior and to optimize their structural and dynamical properties. For that purpose, we have developed multi-quanta spin-locking nuclear magnetic resonance relaxometry of quadrupolar nuclei in order to fill the gap between the time-scales accessible by classical procedures (like dielectric relaxation, inelastic and quasi-elastic neutron scattering and obtain otherwise unattainable dynamical information. This work focuses on the use of quadrupolar nuclei (like 2H, 7Li and 133Cs, because quadrupolar isotopes are the most abundant NMR probes in the periodic table. Clay sediments are the confining media selected for this study because they are ubiquitous materials implied in numerous industrial applications (ionic exchange, pollutant absorption, drilling, waste storing, cracking and heterogeneous catalysis.

  14. Probing the superconducting ground state of the rare-earth ternary boride superconductors R RuB2 (R = Lu,Y) using muon-spin rotation and relaxation

    Science.gov (United States)

    Barker, J. A. T.; Singh, R. P.; Hillier, A. D.; Paul, D. McK.

    2018-03-01

    The superconductivity in the rare-earth transition-metal ternary borides R RuB2 (where R =Lu and Y) has been investigated using muon-spin rotation and relaxation. Measurements made in zero field suggest that time-reversal symmetry is preserved upon entering the superconducting state in both materials; a small difference in depolarization is observed above and below the superconducting transition in both compounds, however, this has been attributed to quasistatic magnetic fluctuations. Transverse-field measurements of the flux-line lattice indicate that the superconductivity in both materials is fully gapped, with a conventional s -wave pairing symmetry and BCS-like magnitudes for the zero-temperature gap energies. The electronic properties of the charge carriers in the superconducting state have been calculated, with effective masses m*/me=9.8 ±0.1 and 15.0 ±0.1 in the Lu and Y compounds, respectively, with superconducting carrier densities ns=(2.73 ±0.04 ) ×1028m-3 and (2.17 ±0.02 ) ×1028m-3 . The materials have been classified according to the Uemura scheme for superconductivity, with values for Tc/TF of 1 /(414 ±6 ) and 1 /(304 ±3 ) , implying that the superconductivity may not be entirely conventional in nature.

  15. Nuclear relaxation in semiconductors doped with magnetic impurities

    International Nuclear Information System (INIS)

    Mel'nichuk, S.V.; Tovstyuk, N.K.

    1984-01-01

    The temperature and concentration dependences are investigated of the nuclear spin-lattice relaxation time with account of spin diffusion for degenerated and non-degenerated semicon- ductors doped with magnetic impurities. In case of the non-degenerated semiconductor the time is shown to grow with temperature, while in case of degenerated semiconductor it is practically independent of temperature. The impurity concentration growth results in decreasing the spin-lattice relaxation time

  16. Tunable room-temperature spin-selective optical Stark effect in solution-processed layered halide perovskites.

    Science.gov (United States)

    Giovanni, David; Chong, Wee Kiang; Dewi, Herlina Arianita; Thirumal, Krishnamoorthy; Neogi, Ishita; Ramesh, Ramamoorthy; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

    2016-06-01

    Ultrafast spin manipulation for opto-spin logic applications requires material systems that have strong spin-selective light-matter interaction. Conventional inorganic semiconductor nanostructures [for example, epitaxial II to VI quantum dots and III to V multiple quantum wells (MQWs)] are considered forerunners but encounter challenges such as lattice matching and cryogenic cooling requirements. Two-dimensional halide perovskite semiconductors, combining intrinsic tunable MQW structures and large oscillator strengths with facile solution processability, can offer breakthroughs in this area. We demonstrate novel room-temperature, strong ultrafast spin-selective optical Stark effect in solution-processed (C6H4FC2H4NH3)2PbI4 perovskite thin films. Exciton spin states are selectively tuned by ~6.3 meV using circularly polarized optical pulses without any external photonic cavity (that is, corresponding to a Rabi energy of ~55 meV and equivalent to applying a 70 T magnetic field), which is much larger than any conventional system. The facile halide and organic replacement in these perovskites affords control of the dielectric confinement and thus presents a straightforward strategy for tuning light-matter coupling strength.

  17. Probing quantum coherence in single-atom electron spin resonance

    Science.gov (United States)

    Willke, Philip; Paul, William; Natterer, Fabian D.; Yang, Kai; Bae, Yujeong; Choi, Taeyoung; Fernández-Rossier, Joaquin; Heinrich, Andreas J.; Lutz, Christoper P.

    2018-01-01

    Spin resonance of individual spin centers allows applications ranging from quantum information technology to atomic-scale magnetometry. To protect the quantum properties of a spin, control over its local environment, including energy relaxation and decoherence processes, is crucial. However, in most existing architectures, the environment remains fixed by the crystal structure and electrical contacts. Recently, spin-polarized scanning tunneling microscopy (STM), in combination with electron spin resonance (ESR), allowed the study of single adatoms and inter-atomic coupling with an unprecedented combination of spatial and energy resolution. We elucidate and control the interplay of an Fe single spin with its atomic-scale environment by precisely tuning the phase coherence time T2 using the STM tip as a variable electrode. We find that the decoherence rate is the sum of two main contributions. The first scales linearly with tunnel current and shows that, on average, every tunneling electron causes one dephasing event. The second, effective even without current, arises from thermally activated spin-flip processes of tip spins. Understanding these interactions allows us to maximize T2 and improve the energy resolution. It also allows us to maximize the amplitude of the ESR signal, which supports measurements even at elevated temperatures as high as 4 K. Thus, ESR-STM allows control of quantum coherence in individual, electrically accessible spins. PMID:29464211

  18. Probing quantum coherence in single-atom electron spin resonance.

    Science.gov (United States)

    Willke, Philip; Paul, William; Natterer, Fabian D; Yang, Kai; Bae, Yujeong; Choi, Taeyoung; Fernández-Rossier, Joaquin; Heinrich, Andreas J; Lutz, Christoper P

    2018-02-01

    Spin resonance of individual spin centers allows applications ranging from quantum information technology to atomic-scale magnetometry. To protect the quantum properties of a spin, control over its local environment, including energy relaxation and decoherence processes, is crucial. However, in most existing architectures, the environment remains fixed by the crystal structure and electrical contacts. Recently, spin-polarized scanning tunneling microscopy (STM), in combination with electron spin resonance (ESR), allowed the study of single adatoms and inter-atomic coupling with an unprecedented combination of spatial and energy resolution. We elucidate and control the interplay of an Fe single spin with its atomic-scale environment by precisely tuning the phase coherence time T 2 using the STM tip as a variable electrode. We find that the decoherence rate is the sum of two main contributions. The first scales linearly with tunnel current and shows that, on average, every tunneling electron causes one dephasing event. The second, effective even without current, arises from thermally activated spin-flip processes of tip spins. Understanding these interactions allows us to maximize T 2 and improve the energy resolution. It also allows us to maximize the amplitude of the ESR signal, which supports measurements even at elevated temperatures as high as 4 K. Thus, ESR-STM allows control of quantum coherence in individual, electrically accessible spins.

  19. Sealed magic angle spinning nuclear magnetic resonance probe and process for spectroscopy of hazardous samples

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Herman M.; Washton, Nancy M.; Mueller, Karl T.; Sears, Jr., Jesse A.; Townsend, Mark R.; Ewing, James R.

    2016-06-14

    A magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) probe is described that includes double containment enclosures configured to seal and contain hazardous samples for analysis. The probe is of a modular design that ensures containment of hazardous samples during sample analysis while preserving spin speeds for superior NMR performance and convenience of operation.

  20. Application of an automatic yarn dismantler to track changes in cotton fibre properties during processing on a miniature spinning line

    CSIR Research Space (South Africa)

    Fassihi, A

    2014-11-01

    Full Text Available This paper reports on the application of a newly developed automatic yarn dismantler for dismantling short staple ring-spun yarns, to track changes in cotton fibre properties from lint to yarn, during processing on a miniature spinning line...

  1. Electronic spin transport in graphene field-effect transistors

    NARCIS (Netherlands)

    Popinciuc, M.; Jozsa, C.; Zomer, P. J.; Tombros, N.; Veligura, A.; Jonkman, H. T.; van Wees, B. J.

    2009-01-01

    Spin transport experiments in graphene, a single layer of carbon atoms ordered in a honeycomb lattice, indicate spin-relaxation times that are significantly shorter than the theoretical predictions. We investigate experimentally whether these short spin-relaxation times are due to extrinsic factors,

  2. Stretched exponential relaxation in molecular and electronic glasses

    International Nuclear Information System (INIS)

    Phillips, J.C.

    1996-01-01

    Stretched exponential relaxation, exp[-(t/τ) β ], fits many relaxation processes in disordered and quenched electronic and molecular systems, but it is widely believed that this function has no microscopic basis, especially in the case of molecular relaxation. For electronic relaxation the appearance of the stretched exponential is often described in the context of dispersive transport, where β is treated as an adjustable parameter, but in almost all cases it is generally assumed that no microscopic meaning can be assigned to 0 g , a glass transition temperature. We show that for molecular relaxation β(T g ) can be understood, providing that one separates extrinsic and intrinsic effects, and that the intrinsic effects are dominated by two magic numbers, β SR =3/5 for short-range forces, and β K =3/7 for long-range Coulomb forces, as originally observed by Kohlrausch for the decay of residual charge on a Leyden jar. Our mathematical model treats relaxation kinetics using the Lifshitz-Kac-Luttinger diffusion to traps depletion model in a configuration space of effective dimensionality, the latter being determined using axiomatic set theory and Phillips-Thorpe constraint theory. The experiments discussed include ns neutron scattering experiments, particularly those based on neutron spin echoes which measure S(Q, t) directly, and the traditional linear response measurements which span the range from μs to s, as collected and analysed phenomenologically by Angell, Ngai, Boehmer and others. The electronic materials discussed include a-Si:H, granular C 60 , semiconductor nanocrystallites, charge density waves in TaS 3 , spin glasses, and vortex glasses in high-temperature semiconductors. The molecular materials discussed include polymers, network glasses, electrolytes and alcohols, Van der Waals supercooled liquids and glasses, orientational glasses, water, fused salts, and heme proteins. In the intrinsic cases the theory of β(T g ) is often accurate to 2%, which

  3. Spin Structures in Magnetic Nanoparticles

    DEFF Research Database (Denmark)

    Mørup, Steen; Brok, Erik; Frandsen, Cathrine

    2013-01-01

    Spin structures in nanoparticles of ferrimagnetic materials may deviate locally in a nontrivial way from ideal collinear spin structures. For instance, magnetic frustration due to the reduced numbers of magnetic neighbors at the particle surface or around defects in the interior can lead to spin...... canting and hence a reduced magnetization. Moreover, relaxation between almost degenerate canted spin states can lead to anomalous temperature dependences of the magnetization at low temperatures. In ensembles of nanoparticles, interparticle exchange interactions can also result in spin reorientation...

  4. Development of a Novel Melt Spinning-Based Processing Route for Oxide Dispersion-Strengthened Steels

    Science.gov (United States)

    Hong, Zuliang; Morrison, Alasdair P. C.; Zhang, Hongtao; Roberts, Steve G.; Grant, Patrick S.

    2018-02-01

    Melt spinning of an Fe-5Y and Fe-1Y-1Ti (wt pct) alloy produced a relatively uniform spatial distribution of Y and Ti in solid solution and ribbons with consistent yield (> 60 pct by weight), fast processing time ( 100 g feedstock material), and repeatability. Heat treatment in the presence of Fe2O3 as an oxygen source (Rhines pack method) at 973 K validated the potential of forming consolidated to bulk using the field-assisted sintering technique (FAST) incorporating nano-sized Fe3O4 powder as the oxygen source. After FAST at 1273 K, 50 MPa, and 30 minutes, a comparatively high number density of sub-micron Y and/or Ti-rich oxides were developed. Further formation of fine-scale oxides took place during post-FAST annealing, resulting in an approximate 20 pct increase in hardness at temperatures below 573 K, but with a reduced hardening effect above 673 K due to a small fraction of persistent porosity and mechanically weak prior ribbon boundaries that were decorated with Ti-rich oxides.

  5. Effect of spin-orbit scattering on transport properties of low-dimensional dilute alloys

    Energy Technology Data Exchange (ETDEWEB)

    Heers, Swantje

    2011-09-21

    The scope of this thesis is to gain insight, by means of ab initio-calculations, into the physics of momentum and spin relaxation phenomena induced by electron scattering at impurities and defects in the noble metals copper, silver and gold. The main results are subdivided in three parts. In the first part, momentum- and spinrelaxation times due to scattering at 3d, 4sp, 4d, 5sp, 5d and 6sp impurities in copper and gold fcc bulk are investigated. The inversion symmetry of the crystals leads to a two-fold degeneracy of all states on the Fermi surface, and therefore spin relaxation is dominated by the Elliott-Yafet mechanism as well as the spin-orbit coupling of the impurity. For impurities in gold, we calculate much shorter spin-relaxation times than in copper because of the stronger spin-orbit coupling of the gold host. Furthermore, we have found important qualitative differences between the relaxation times obtained for the d- and the sp- impurities. As scattering at d-impurities is resonant, the electrons spend much more time at the impurity sites than in the case of the sp-impurities; therefore, they are much longer exhibited to the spin-orbit coupling of the impurity. This results in considerably shorter spin-relaxation times, even if the momentum scattering rates are in the same order of magnitude. Finally, the investigation of interference of scattering processes at impurity dimers reveals that relevant differences to the independent-impurity approximation appear only for strong d-scatterer, placed at nearest neighboring sites. In the second part we investigate the reduction of spin-conserving surface-state lifetimes induced by adatom- and impurity-scattering on the (111) surfaces of copper, silver and gold films with different thicknesses. We have found strong qualitative differences in the lifetimes when comparing the results for adatoms to those of impurities in the first and second layer. The trends for the latter ones are similar to those calculated in

  6. Modulation bandwidth of a spin laser

    Science.gov (United States)

    Banerjee, D.; Adari, R.; Murthy, M.; Suggisetti, P.; Ganguly, S.; Saha, D.

    2011-04-01

    We have studied small signal frequency response of a spin laser. We have shown that the response is characterized by two distinct resonant peaks corresponding to the two polarization modes of the spin laser. It is observed that the modulation bandwidth of a spin laser can be smaller or larger than that of a conventional laser depending upon the current bias and spin relaxation time constant. A small value for spin relaxation constant may not be detrimental for modulation bandwidth. This anomalous observation is explained by considering both the amplitude and phase response of the two polarization modes. A spin laser can act as a combination of low-pass and bandpass filters. The passband frequency range is tunable by external bias. We have also studied the evolution of resonant peaks and modulation bandwidth as a function of spin relaxation time constant.

  7. Spin diffusion length of Permalloy using spin absorption in lateral spin valves

    Science.gov (United States)

    Sagasta, Edurne; Omori, Yasutomo; Isasa, Miren; Otani, YoshiChika; Hueso, Luis E.; Casanova, Fèlix

    2017-08-01

    We employ the spin absorption technique in lateral spin valves to extract the spin diffusion length of Permalloy (Py) as a function of temperature and resistivity. A linear dependence of the spin diffusion length with the conductivity of Py is observed, evidencing that the Elliott-Yafet mechanism is the dominant spin relaxation mechanism in Permalloy. Completing the dataset with additional data found in the literature, we obtain λPy = (0.91 ± 0.04) (fΩm2)/ρPy.

  8. Reworkable spin-on trilayer materials: optimization of rework process and solutions for manufacturability

    Science.gov (United States)

    Zhang, Ruzhi; Timko, Allen G.; Zook, John; Wei, Yayi; Pylneva, Lyudmila; Yi, Yi; Li, Chenghong; Wu, Hengpeng; Rahman, Dalil; McKenzie, Douglas S.; Anyadiegwu, Clement; Lu, Ping-Hung; Neisser, Mark; Dammel, Ralph R.; Bradbury, Ron; Lee, Timothy

    2009-03-01

    Trilayer stacks with alternating etch selectivity were developed and extensively investigated for high NA immersion lithography at 32nm node and beyond. The conveyance of pattern transfer function from photoresist to Si-containing bottom anti-reflective coating (Si-BARC) and carbonrich underlayer hard-mask (UL) elegantly solved the small etch budget issue for ultra-thin photoresists in immersion lithography. However, due to the hybrid nature of Si-BARC, many different behaviors were observed in comparison to conventional BARC. Lithographic performance, stability, and reworkability were among the most challenging issues for trilayer scheme. Despite of the rapid improvement in lithographic performance and stability of trilayer materials reported by several papers, the rework and cleaning of trilayer materials by wet chemistry remained a challenging problem for manufacturability. The dual function requirement of reflection control and pattern transfer (i.e. hard-masking) for spin-on Si-BARC mandates hybrid materials. Si-BARC containing both organic moiety and inorganic backbone were extensively studied and demonstrated excellent performance. However, the hybrid nature of Si-BARC necessitates the revisit of different wet chemistries and process adjustment is essential to achieve desirable results. In addition, the similarity in chemical structures between Si-BARC and low-κ dielectrics demands subtle rework differentiation by wet chemistry from a chemistry point of view. In our development, we strived to identify rework solutions for trilayer materials in both front-end-of-line (FEOL) and back-end-of-line (BEOL) applications. Rework solutions including diluted HF, Piranha, and low-κ compatible strippers were extensively investigated. The optimization of solution mixture ratios and processing conditions was systematically studied. Thorough defect inspection after rework was performed to ensure the readiness for manufacturability. Extensive Piranha rework study on stack

  9. Spin-dependent recombination involving oxygen-vacancy complexes in silicon

    Science.gov (United States)

    Franke, David P.; Hoehne, Felix; Vlasenko, Leonid S.; Itoh, Kohei M.; Brandt, Martin S.

    2014-05-01

    Spin-dependent relaxation and recombination processes in γ-irradiated n-type Czochralski-grown silicon are studied using continuous wave (cw) and pulsed electrically detected magnetic resonance (EDMR). Two processes involving the SL1 center, the neutral excited triplet state of the oxygen-vacancy complex, are observed which can be separated by their different dynamics. One of the processes is the relaxation of the excited SL1 state to the ground state of the oxygen-vacancy complex, the other a charge transfer between 31P donors and SL1 centers forming close pairs, as indicated by electrically detected electron double resonance. For both processes, the recombination dynamics is studied with pulsed EDMR techniques. We demonstrate the feasibility of true zero-field cw and pulsed EDMR for spin-1 systems and use this to measure the lifetimes of the different spin states of SL1 also at vanishing external magnetic field.

  10. Relaxation in the glass former acetylsalicylic acid studied by deuteron magnetic resonance and dielectric spectroscopy

    Science.gov (United States)

    Nath, R.; El Goresy, T.; Geil, B.; Zimmermann, H.; Böhmer, R.

    2006-08-01

    Supercooled liquid and glassy acetylsalicylic acid was studied using dielectric spectroscopy and deuteron relaxometry in a wide temperature range. The supercooled liquid is characterized by major deviations from thermally activated behavior. In the glass the secondary relaxation exhibits the typical features of a Johari-Goldstein process. Via measurements of spin-lattice relaxation times the selectively deuterated methyl group was used as a sensitive probe of its local environments. There is a large difference in the mean activation energy in the glass with respect to that in crystalline acetylsalicylic acid. This can be understood by taking into account the broad energy barrier distribution in the glass.

  11. Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes

    Science.gov (United States)

    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.

  12. Entanglement, decoherence and thermal relaxation in exactly solvable models

    International Nuclear Information System (INIS)

    Lychkovskiy, Oleg

    2011-01-01

    Exactly solvable models provide an opportunity to study different aspects of reduced quantum dynamics in detail. We consider the reduced dynamics of a single spin in finite XX and XY spin 1/2 chains. First we introduce a general expression describing the evolution of the reduced density matrix. This expression proves to be tractable when the combined closed system (i.e. open system plus environment) is integrable. Then we focus on comparing decoherence and thermalization timescales in the XX chain. We find that for a single spin these timescales are comparable, in contrast to what should be expected for a macroscopic body. This indicates that the process of quantum relaxation of a system with few accessible states can not be separated in two distinct stages - decoherence and thermalization. Finally, we turn to finite-size effects in the time evolution of a single spin in the XY chain. We observe three consecutive stages of the evolution: regular evolution, partial revivals, irregular (apparently chaotic) evolution. The duration of the regular stage is proportional to the number of spins in the chain. We observe a 'quiet and cold period' in the end of the regular stage, which breaks up abruptly at some threshold time.

  13. Diffusional mechanisms augment the fluorine MR relaxation in paramagnetic perfluorocarbon nanoparticles that provides a "relaxation switch" for detecting cellular endosomal activation.

    Science.gov (United States)

    Hu, Lingzhi; Zhang, Lei; Chen, Junjie; Lanza, Gregory M; Wickline, Samuel A

    2011-09-01

    To develop a physical model for the (19)F relaxation enhancement in paramagnetic perfluorocarbon nanoparticles (PFC NP) and demonstrate its application in monitoring cellular endosomal functionality through a "(19)F relaxation switch" phenomenon. An explicit expression for (19)F longitudinal relaxation enhancement was derived analytically. Monte-Carlo simulation was performed to confirm the gadolinium-induced magnetic field inhomogeneity inside the PFC NP. Field-dependent T(1) measurements for three types of paramagnetic PFC NPs were carried out to validate the theoretical prediction. Based on the physical model, (19)F and (1)H relaxation properties of macrophage internalized paramagnetic PFC NPs were measured to evaluate the intracellular process of NPs by macrophages in vitro. The theoretical description was confirmed experimentally by field-dependent T(1) measurements. The shortening of (19)F T(1) was found to be attributed to the Brownian motion of PFC molecules inside the NP in conjunction with their ability to permeate into the lipid surfactant coating. A dramatic change of (19)F T(1) was observed upon endocytosis, revealing the transition from intact bound PFC NP to processed constituents. The proposed first-principle analysis of (19)F spins in paramagnetic PFC NP relates their structural parameters to the special MR relaxation features. The demonstrated "(19)F relaxation switch" phenomenon is potentially useful for monitoring cellular endosomal functionality. Copyright © 2011 Wiley-Liss, Inc.

  14. Reduction process of nitroxyl spin probes used in Overhauser-enhanced magnetic resonance imaging: An ESR study

    Energy Technology Data Exchange (ETDEWEB)

    Meenakumari, V.; Premkumar, S.; Benial, A. Milton Franklin, E-mail: miltonfranklin@yahoo.com [Department of Physics, NMSSVN College, Nagamalai, Madurai-625 019, Tamilnadu (India); Jawahar, A. [Department of Chemistry, NMSSVN College, Nagamalai, Madurai-625 019, Tamilnadu (India)

    2016-05-23

    The Electron spin resonance studies on the reduction process of nitroxyl spin probes were carried out for 1mM {sup 14}N- labeled nitroxyl radicals in pure water and 1 mM concentration of ascorbic acid as a function of time. The electron spin resonance parameters, such as line width, hyperfine coupling constant, g-factor, signal intensity ratio and rotational correlation time were estimated. The 3-carbamoyl-PROXYL radical has narrowest line width and fast tumbling motion compared with 3-carboxy-PROXYL, 4-methoxy-TEMPO, and 4-acetamido-TEMPO radicals. The half life time and decay rate were estimated for 1mM concentration of {sup 14}N- labeled nitroxyl radicals in 1 mM concentration of ascorbic acid. From the results, the 3-carbamoyl-PROXYL has long half life time and high stability compared with 3-carboxy-PROXYL, 4-methoxy-TEMPO and 4-acetamido-TEMPO radicals. Therefore, this study reveals that the 3-carbamoyl-PROXYL radical can act as a good redox sensitive spin probe for Overhauser-enhanced Magnetic Resonance Imaging.

  15. Natural relaxation

    Science.gov (United States)

    Marzola, Luca; Raidal, Martti

    2016-11-01

    Motivated by natural inflation, we propose a relaxation mechanism consistent with inflationary cosmology that explains the hierarchy between the electroweak scale and Planck scale. This scenario is based on a selection mechanism that identifies the low-scale dynamics as the one that is screened from UV physics. The scenario also predicts the near-criticality and metastability of the Standard Model (SM) vacuum state, explaining the Higgs boson mass observed at the Large Hadron Collider (LHC). Once Majorana right-handed neutrinos are introduced to provide a viable reheating channel, our framework yields a corresponding mass scale that allows for the seesaw mechanism as well as for standard thermal leptogenesis. We argue that considering singlet scalar dark matter extensions of the proposed scenario could solve the vacuum stability problem and discuss how the cosmological constant problem is possibly addressed.

  16. Elastic oscillation damping and magnetic susceptibility in Y19Fe81 spin glass in the temperature range 70-300 K

    International Nuclear Information System (INIS)

    Zolotukhin, I.V.; Balalaev, S.Yu.

    1990-01-01

    Relaxation properties of Y 19 Fe 81 spin glass (SG) were investigated by means of internal friction(IF). Relaxation process resulting from transition to SG state was determined at sound range frequencies in amorphous alloy. On the basis of the obtained results concerning IF and magnetic susceptibility it follows, that relaxation of certain part of cluster magnetic moments lies within 10 -5 -10 -3 s limits with 0.11±0.06 eV activation energy. IF technique is shown to be used for investigation into relaxation properties, in particular, for acquisition of data on temperature of transition to SG' state

  17. Actuality the process of relaxation on the lessons of physical training on the current stage of higher education

    Directory of Open Access Journals (Sweden)

    Vankova A.U.

    2010-04-01

    Full Text Available Facilities are considered of making healthy for the improvement of ability to resist stress situations of students. Engaged in a physical culture in the net of educational clock must be conducted in the institute of higher before and after the special disciplines. Application of method of relaxation together with musical accompaniment promote claim of higher type of pedagogical organization of employments. A chronic mental overstrain without the sufficient physical discharging results in a nervous overstrain, negative emotions, deficit of time, violation of the mode of labour and rest, reduction of possibility of physical activity.

  18. Transverse spin observables in hard-scattering hadronic processes within collinear factorization

    Science.gov (United States)

    Pitonyak, Daniel

    2016-10-01

    We review what is currently known about the transverse spin structure of hadrons, in particular from observables that can be analyzed within a collinear framework. These effects have been around for 40 years and represent a critical test of perturbative QCD. We look at both proton-proton and lepton-nucleon collisions for various final states. While the main focus is on transverse single-spin asymmetries, we also discuss how longitudinal-transverse double-spin asymmetries offer a complimentary, yet equally important, source of information on the quark-gluon content of hadrons. We also summarize some recent progress in solidifying the theoretical formalism behind these observables and give an outlook on future directions of research.

  19. Surface spin tunneling and heat dissipation in magnetic nanoparticles

    Science.gov (United States)

    Palakkal, Jasnamol P.; Obula Reddy, Chinna; Paulose, Ajeesh P.; Sankar, Cheriyedath Raj

    2018-03-01

    Quantum superparamagnetic state is observed in ultra-fine magnetic particles, which is often experimentally identified by a significant hike in magnetization towards low temperatures much below the superparamagnetic blocking temperature. Here, we report experimentally observed surface spin relaxation at low temperatures in hydrated magnesium ferrite nanoparticles of size range of about 5 nm. We observed time dependent oscillatory magnetization of the sample below 2.5 K, which is attributed to surface spin tunneling. Interestingly, we observed heat dissipation during the process by using an external thermometer.

  20. Spin dynamics in the single molecule magnet Ni4 under microwave irradiation

    Science.gov (United States)

    de Loubens, Gregoire

    2009-03-01

    Quantum mechanical effects such as quantum tunneling of magnetization (QTM) and quantum phase interference have been intensively studied in single molecule magnets (SMMs). These materials have also been suggested as candidates for qubits and are promising for molecular spintronics. Understanding decoherence and energy relaxation mechanisms in SMMs is then both of fundamental interest and important for the use of SMMs in applications. Interestingly, the single-spin relaxation rate due to direct process of a SMM embedded in an elastic medium can be derived without any unknown coupling constant [1]. Moreover, nontrivial relaxation mechanisms are expected from collective effects in SMM single crystals, such as phonon superradiance or phonon bottleneck. In order to investigate the spin relaxation between the two lowest lying spin-states of the S=4 single molecule magnet Ni4, we have developed an integrated sensor that combines a microstrip resonator and micro-Hall effect magnetometer on a chip [2]. This sensor enables both real time studies of magnetization dynamics under pulse irradiation as well as simultaneous measurements of the absorbed power and magnetization changes under continuous microwave irradiation. The latter technique permits the study of small deviations from equilibrium under steady state conditions, i.e. small amplitude cw microwave irradiation. This has been used to determine the energy relaxation rate of a Ni4 single crystal as a function of temperature at two frequencies, 10 and 27.8 GHz. A strong temperature dependence is observed below 1.5 K, which is not consistent with a direct spin-phonon relaxation process. The data instead suggest that the spin relaxation is dominated by a phonon bottleneck at low temperatures and occurs by an Orbach process involving excited spin-levels at higher temperatures [3]. Experimental results will be compared with detailed calculations of the relaxation rate using the density matrix equation with the relaxation

  1. Devices and process for high-pressure magic angle spinning nuclear magnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Hoyt, David W.; Sears, Jesse A.; Turcu, Romulus V. F.; Rosso, Kevin M.; Hu, Jian Zhi

    2017-12-05

    A high-pressure magic angle spinning (MAS) rotor is detailed that includes a high-pressure sample cell that maintains high pressures exceeding 150 bar. The sample cell design minimizes pressure losses due to penetration over an extended period of time.

  2. The Proton Spin, Semi-Inclusive processes, and measurements at a future Electron Ion Collider

    Energy Technology Data Exchange (ETDEWEB)

    Abhay, Deshpande

    2018-01-12

    We discuss spin physics, Guido’s contribution to it, and what we still have to learn. We set out in particular a programme for incorporating constraints from semi-inclusive data into global fits of polarized PDFs, and discuss the need for the EIC to increase the precision and kinematic coverage of current measurements.

  3. Phonon-magnon resonant processes with relevance to acoustic spin pumping

    KAUST Repository

    Deymier, P. A.

    2014-12-23

    The recently described phenomenon of resonant acoustic spin pumping is due to resonant coupling between an incident elastic wave and spin waves in a ferromagnetic medium. A classical one-dimensional discrete model of a ferromagnet with two forms of magnetoelastic coupling is treated to shed light on the conditions for resonance between phonons and magnons. Nonlinear phonon-magnon interactions in the case of a coupling restricted to diagonal terms in the components of the spin degrees of freedom are analyzed within the framework of the multiple timescale perturbation theory. In that case, one-phonon-two-magnon resonances are the dominant mechanism for pumping. The effect of coupling on the dispersion relations depends on the square of the amplitude of the phonon and magnon excitations. A straightforward analysis of a linear phonon-magnon interaction in the case of a magnetoelastic coupling restricted to off-diagonal terms in the components of the spins shows a one-phonon to one-magnon resonance as the pumping mechanism. The resonant dispersion relations are independent of the amplitude of the waves. In both cases, when an elastic wave with a fixed frequency is used to stimulate magnons, application of an external magnetic field can be used to approach resonant conditions. Both resonance conditions exhibit the same type of dependency on the strength of an applied magnetic field.

  4. (DARPA) Topologically Protected Quantum Information Processing In Spin-Orbit Compled Semiconductors

    Science.gov (United States)

    2013-12-17

    tunneling peak experiments performed in our proposed semiconductor heterostructures in detail, explaining the absence of the gap closing signatures...true smoking-gun signature of MFs in spin-orbit coupled semiconductor nanowires in terms of a charge tunneling quantum interference experiment...5) Unambiguous determination of Majorana fermions: Charge tunneling interference in semiconductor nanowires : Using the fractionalization property

  5. Enacted identities in the university spin-off process - bridging an imaginative gap

    DEFF Research Database (Denmark)

    Hannibal, Martin

    2017-01-01

    This paper employs a case study to explore the interdependencies between enacted role identities and behavioural logics of eight inventor-founders embedded in university spin-off venturing. The major tendencies in the findings suggest that the inventor-founders enact their academic role identity...

  6. An order-by-disorder process in the cyclic phase of spin-2 condensate with a weak magnetic field

    International Nuclear Information System (INIS)

    Zheng, Gong-Ping; Xu, Lei-Kuan; Qin, Shuai-Feng; Jian, Wen-Tian; Liang, J.-Q.

    2013-01-01

    We present in this paper a model study on the “order-by-disorder” process in the cyclic phase of spin-2 condensate, which forms a family of incommensurable, spiral degenerate ground states. On the basis of the ordering mechanism of entropic splitting, it is demonstrated that the energy corrections resulting from quantum fluctuations of disorder lift the accidental degeneracy of the cyclic configurations and thus lead to an eventual spiral order called the cyclic order. The order-by-disorder phenomenon is then realized even if the magnetic field exists. Finally, we show that our theoretic observations can be verified experimentally by direct detection of the cyclic order in the 87 Rb condensate of a spin-2 manifold with a weak magnetic field. -- Highlights: •A model for the order-by-disorder process in the cyclic phase of spin-2 condensate is presented. •The second-order quantum fluctuations of the mean-field states are studied. •The energy corrections lift the accidental degeneracy of the cyclic configurations. •The order-by-disorder phenomenon is realized even if a magnetic field exists. •The theoretic observations can be verified experimentally for 87 Rb condensate

  7. Dynamics of spin-flip photon-assisted tunneling

    NARCIS (Netherlands)

    Braakman, F.R.; Danon, J.; Schreiber, L.R.; Wegscheider, W.; Vandersypen, L.M.K.

    2014-01-01

    We present time-resolved measurements of spin-flip photon-assisted tunneling and spin-flip relaxation in a doubly occupied double quantum dot. The photon-assisted excitation rate as a function of magnetic field indicates that spin-orbit coupling is the dominant mechanism behind the spin-flip under

  8. Quantum one dimensional spin systems. Disorder and impurities; Systemes de spins quantiques unidimensionnels. Desordre et impuretes

    Energy Technology Data Exchange (ETDEWEB)

    Brunel, V

    1999-06-29

    This thesis presents three studies that are respectively the spin-1 disordered chain, the non magnetic impurities in the spin-1/2 chain and the reaction-diffusion process. The spin-1 chain of weak disorder is performed by the Abelian bosonization and the renormalization group. This allows to take into account the competition between the disorder and the interactions and predicts the effects of various spin-1 anisotropy chain phases under many different disorders. A second work uses the non magnetic impurities as local probes of the correlations in the spin-1/2 chain. When the impurities are connected to the chain boundary, the author predicts a temperature dependence of the relaxation rate (1/T) of the nuclear spin impurities, different from the case of these impurities connected to the whole chain. The last work deals with one dimensional reaction-diffusion problem. The Jordan-Wigner transformation allows to consider a fermionic field theory that critical exponents follow from the renormalization group. (A.L.B.)

  9. Direct Observation on Spin-Coating Process of PS- b -P2VP Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Ogawa, Hiroki; Takenaka, Mikihito; Miyazaki, Tsukasa; Fujiwara, Akihiko; Lee, Byeongdu; Shimokita, Keisuke; Nishibori, Eiji; Takata, Masaki

    2016-05-10

    We studied the structural development of symmetric poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) block copolymers during spin-coating using in situ grazing incidence small angle X-ray scattering (GISAXS) measurements. During the spin-coating process, after the formation of the micelles in dilute solution, the selective solvent induced two kinds of the morphological transition. Firstly, the disordered spherical micelles were transformed into a BCC lattice of spheres of which the (110) plane was oriented perpendicularly to the substrate surface. Secondly, further evaporation induced a transition from spheres on the BCC lattice into cylindrical structures. The orientation of the cylinders perpendicular to the substrate surface was induced by solvent convection perpendicular to the substrate, which occurs during rapid solvent evaporation. After this transition, vitrification of PS and P2VP prevented any further transition from cylinders to the more thermodynamically stable lamellar structures, as are generally observed as the bulk equilibrium state.

  10. Breathing and Relaxation

    Science.gov (United States)

    ... Home Health Insights Stress & Relaxation Breathing and Relaxation Breathing and Relaxation Make an Appointment Ask a Question ... level is often dependent on his or her breathing pattern. Therefore, people with chronic lung conditions may ...

  11. Relaxation to Negative Temperatures in Double Domain Systems

    Science.gov (United States)

    Hama, Yusuke; Munro, William J.; Nemoto, Kae

    2018-02-01

    The engineering of quantum systems and their environments has led to our ability now to design composite or complex systems with the properties one desires. In fact, this allows us to couple two or more distinct systems to the same environment where potentially unusual behavior and dynamics can be exhibited. In this Letter we investigate the relaxation of two giant spins or collective spin ensembles individually coupled to the same reservoir. We find that, depending on the configuration of the two individual spin ensembles, the steady state of the composite system does not necessarily reach the ground state of the individual systems, unlike what one would expect for independent environments. Further, when the size of one individual spin ensemble is much larger than the second, collective relaxation can drive the second system to an excited steady state even when it starts in the ground state; that is, the second spin ensemble relaxes towards a negative-temperature steady state.

  12. Electron Spin Dynamics in Semiconductor Quantum Dots

    International Nuclear Information System (INIS)

    Marie, X.; Belhadj, T.; Urbaszek, B.; Amand, T.; Krebs, O.; Lemaitre, A.; Voisin, P.

    2011-01-01

    An electron spin confined to a semiconductor quantum dot is not subject to the classical spin relaxation mechanisms known for free carriers but it strongly interacts with the nuclear spin system via the hyperfine interaction. We show in time resolved photoluminescence spectroscopy experiments on ensembles of self assembled InAs quantum dots in GaAs that this interaction leads to strong electron spin dephasing.

  13. Predicting acoustic relaxation absorption in gas mixtures for extraction of composition relaxation contributions.

    Science.gov (United States)

    Liu, Tingting; Wang, Shu; Zhu, Ming

    2017-12-01

    The existing molecular relaxation models based on both parallel relaxation theory and series relaxation theory cannot extract the contributions of gas compositions to acoustic relaxation absorption in mixtures. In this paper, we propose an analytical model to predict acoustic relaxation absorption and clarify composition relaxation contributions based on the rate-determining energy transfer processes in molecular relaxation in excitable gases. By combining parallel and series relaxation theory, the proposed model suggests that the vibration-translation process of the lowest vibrational mode in each composition provides the primary deexcitation path of the relaxation energy, and the rate-determining vibration-vibration processes between the lowest mode and others dominate the coupling energy transfer between different modes. Thus, each gas composition contributes directly one single relaxation process to the molecular relaxation in mixture, which can be illustrated by the decomposed acoustic relaxation absorption spectrum of the single relaxation process. The proposed model is validated by simulation results in good agreement with experimental data such as N 2 , O 2 , CO 2 , CH 4 and their mixtures.

  14. Spin excitation in granular structures with ferromagnetic nanoparticles

    CERN Document Server

    Lutsev, L V

    2002-01-01

    In terms of s-d-exchange model one studied spin excitations and relaxation in granular structures with metallic ferromagnetic nanoparticles in an insulating amorphous matrix. One studies spins of granule as a d-system; s-system represents a multitude of localized electrons of amorphous matrix. In terms of single-ring approximation on the basis of s-d-exchange interaction for the Green spin function expansion one determined spectrum of spin excitations composed of spin-wave excitations of granules and spin-polarization excitations. One studied spin-polarization relaxation occurring by way of spin-polarization excitations. Spin-polarization relaxation was determined to be efficient one within wide range of frequencies. Evaluations made for structures containing cobalt granules show that one should observe it in the centimeter, the millimeter and the submillimeter ranges of wavelength

  15. Spin diffusion in Fermi gases

    DEFF Research Database (Denmark)

    Bruun, Georg

    2011-01-01

    We examine spin diffusion in a two-component homogeneous Fermi gas in the normal phase. Using a variational approach, analytical results are presented for the spin diffusion coefficient and the related spin relaxation time as a function of temperature and interaction strength. For low temperatures......, strong correlation effects are included through the Landau parameters which we extract from Monte Carlo results. We show that the spin diffusion coefficient has a minimum for a temperature somewhat below the Fermi temperature with a value that approaches the quantum limit ~/m in the unitarity regime...

  16. Mechanisms of optical orientation of an individual Mn2+ ion spin in a II–VI quantum dot

    Science.gov (United States)

    Smoleński, T.; Cywiński, Ł.; Kossacki, P.

    2018-02-01

    We provide a theoretical description of the optical orientation of a single Mn2+ ion spin under quasi-resonant excitation demonstrated experimentally by Goryca et al (2009 Phys. Rev. Lett. 103 087401). We build and analyze a hierarchy of models by starting with the simplest assumptions (transfer of perfectly spin-polarized excitons from Mn-free dot to the other dot containing a single Mn2+ spin, followed by radiative recombination) and subsequently adding more features, such as spin relaxation of electrons and holes. Particular attention is paid to the role of the influx of the dark excitons and the process of biexciton formation, which are shown to contribute significantly to the orientation process in the quasi-resonant excitation case. Analyzed scenarios show how multiple features of the excitonic complexes in magnetically-doped quantum dots, such as the values of exchange integrals, spin relaxation times, etc, lead to a plethora of optical orientation processes, characterized by distinct dependencies on light polarization and laser intensity, and occurring on distinct timescales. Comparison with experimental data shows that the correct description of the optical orientation mechanism requires taking into account Mn2+ spin-flip processes occurring not only when the exciton is already in the orbital ground state of the light-emitting dot, but also those that happen during the exciton transfer from high-energy states to the ground state. Inspired by the experimental results on energy relaxation of electrons and holes in nonmagnetic dots, we focus on the process of biexciton creation allowed by mutual spin-flip of an electron and the Mn2+ spin, and we show that by including it in the model, we obtain good qualitative and quantitative agreement with the experimental data on quasi-resonantly driven Mn2+ spin orientation.

  17. Steepest-entropy-ascent quantum thermodynamic modeling of the relaxation process of isolated chemically reactive systems using density of states and the concept of hypoequilibrium state.

    Science.gov (United States)

    Li, Guanchen; von Spakovsky, Michael R

    2016-01-01

    This paper presents a study of the nonequilibrium relaxation process of chemically reactive systems using steepest-entropy-ascent quantum thermodynamics (SEAQT). The trajectory of the chemical reaction, i.e., the accessible intermediate states, is predicted and discussed. The prediction is made using a thermodynamic-ensemble approach, which does not require detailed information about the particle mechanics involved (e.g., the collision of particles). Instead, modeling the kinetics and dynamics of the relaxation process is based on the principle of steepest-entropy ascent (SEA) or maximum-entropy production, which suggests a constrained gradient dynamics in state space. The SEAQT framework is based on general definitions for energy and entropy and at least theoretically enables the prediction of the nonequilibrium relaxation of system state at all temporal and spatial scales. However, to make this not just theoretically but computationally possible, the concept of density of states is introduced to simplify the application of the relaxation model, which in effect extends the application of the SEAQT framework even to infinite energy eigenlevel systems. The energy eigenstructure of the reactive system considered here consists of an extremely large number of such levels (on the order of 10^{130}) and yields to the quasicontinuous assumption. The principle of SEA results in a unique trajectory of system thermodynamic state evolution in Hilbert space in the nonequilibrium realm, even far from equilibrium. To describe this trajectory, the concepts of subsystem hypoequilibrium state and temperature are introduced and used to characterize each system-level, nonequilibrium state. This definition of temperature is fundamental rather than phenomenological and is a generalization of the temperature defined at stable equilibrium. In addition, to deal with the large number of energy eigenlevels, the equation of motion is formulated on the basis of the density of states and a set

  18. Spinning-out university technologies: a role for students in the commercialization process

    DEFF Research Database (Denmark)

    Murdock, Karen; Johnsen, Lasse Emil; Ølund, Michael

    2015-01-01

    in developing knoweldege about markets to supplement the knowledge–gap among academics, which as far as we know have not been widely explored. The analysis is based in the context of a technical university which provides a unique opportunity to explore how students working to fulfil academic requirements can...... a singular formula to increase university spin-outs. A common theme in much of the empirical evidence is that academics/university researchers lack knowledge related to market development which must be supplemented for successful commercialization. This study analyses the role of non-research students...... create momentum around a technology to increase its spinout potential. The results show that students working with potential spin-out technologies as class projects are seen as nonthreatening which allow them to gather useful market information. This early information can stimulate interest leading...

  19. Spin-polarized spin excitation spectroscopy

    International Nuclear Information System (INIS)

    Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J

    2010-01-01

    We report on the spin dependence of elastic and inelastic electron tunneling through transition metal atoms. Mn, Fe and Cu atoms were deposited onto a monolayer of Cu 2 N on Cu(100) and individually addressed with the probe tip of a scanning tunneling microscope. Electrons tunneling between the tip and the substrate exchange energy and spin angular momentum with the surface-bound magnetic atoms. The conservation of energy during the tunneling process results in a distinct onset threshold voltage above which the tunneling electrons create spin excitations in the Mn and Fe atoms. Here we show that the additional conservation of spin angular momentum leads to different cross-sections for spin excitations depending on the relative alignment of the surface spin and the spin of the tunneling electron. For this purpose, we developed a technique for measuring the same local spin with a spin-polarized and a non-spin-polarized tip by exchanging the last apex atom of the probe tip between different transition metal atoms. We derive a quantitative model describing the observed excitation cross-sections on the basis of an exchange scattering process.

  20. Turbulent Magnetic Relaxation in Pulsar Wind Nebulae

    Science.gov (United States)

    Zrake, Jonathan; Arons, Jonathan

    2017-09-01

    We present a model for magnetic energy dissipation in a pulsar wind nebula. A better understanding of this process is required to assess the likelihood that certain astrophysical transients may be powered by the spin-down of a “millisecond magnetar.” Examples include superluminous supernovae, gamma-ray bursts, and anticipated electromagnetic counterparts to gravitational wave detections of binary neutron star coalescence. Our model leverages recent progress in the theory of turbulent magnetic relaxation to specify a dissipative closure of the stationary magnetohydrodynamic (MHD) wind equations, yielding predictions of the magnetic energy dissipation rate throughout the nebula. Synchrotron losses are self-consistently treated. To demonstrate the model’s efficacy, we show that it can reproduce many features of the Crab Nebula, including its expansion speed, radiative efficiency, peak photon energy, and mean magnetic field strength. Unlike ideal MHD models of the Crab (which lead to the so-called σ-problem), our model accounts for the transition from ultra to weakly magnetized plasma flow and for the associated heating of relativistic electrons. We discuss how the predicted heating rates may be utilized to improve upon models of particle transport and acceleration in pulsar wind nebulae. We also discuss implications for the Crab Nebula’s γ-ray flares, and point out potential modifications to models of astrophysical transients invoking the spin-down of a millisecond magnetar.

  1. Tunneling spin injection into single layer graphene.

    Science.gov (United States)

    Han, Wei; Pi, K; McCreary, K M; Li, Yan; Wong, Jared J I; Swartz, A G; Kawakami, R K

    2010-10-15

    We achieve tunneling spin injection from Co into single layer graphene (SLG) using TiO₂ seeded MgO barriers. A nonlocal magnetoresistance (ΔR(NL)) of 130  Ω is observed at room temperature, which is the largest value observed in any material. Investigating ΔR(NL) vs SLG conductivity from the transparent to the tunneling contact regimes demonstrates the contrasting behaviors predicted by the drift-diffusion theory of spin transport. Furthermore, tunnel barriers reduce the contact-induced spin relaxation and are therefore important for future investigations of spin relaxation in graphene.

  2. Relaxation of the magnetization in magnetic molecules

    Science.gov (United States)

    Carretta, S.; Bianchi, A.; Liviotti, E.; Santini, P.; Amoretti, G.

    2006-04-01

    Several mechanisms characterize the relaxation dynamics in magnetic molecules. We investigate two of them, spin-lattice coupling and incoherent quantum tunneling. The effect of the phonon heat bath is studied by analyzing the exponential time decay of the autocorrelation of the magnetization. We show that in ferromagnetic (Cu6) and antiferromagnetic (Fe6) molecular rings this decay is characterized by a single characteristic time. At very low temperature, relaxation through incoherent quantum tunneling may occur in nanomagnets such as Fe8 or Ni4. The mixing between levels with different values of the total spin (S mixing) greatly influences this mechanism. In particular, we demonstrate that a fourth-order anisotropy term O44, required to interpret experimental electron paramagnetic resonance and relaxation data in Ni4, naturally arises when S mixing is considered in calculations.

  3. Low frequency dielectric relaxation processes and ionic conductivity of montmorillonite clay nanoparticles colloidal suspension in poly(vinyl pyrrolidone−ethylene glycol blends

    Directory of Open Access Journals (Sweden)

    2008-11-01

    Full Text Available The dielectric dispersion behaviour of montmorillonite (MMT clay nanoparticles colloidal suspension in poly(vinyl pyrrolidone-ethylene glycol (PVP-EG blends were investigated over the frequency range 20 Hz to 1 MHz at 30°C. The 0, 1, 2, 3, 5 and 10 wt% MMT clay concentration of the weight of total solute (MMT+PVP were prepared in PVP-EG blends using EG as solvent. The complex relative dielectric function, alternating current (ac electrical conductivity, electric modulus and impedance spectra of these materials show the relaxation processes corresponding to the micro-Brownian motion of PVP chain, ion conduction and electrode polarization phenomena. The real part of ac conductivity spectra of these materials obeys Jonscher power law σ′(ω =σdc + Aωn in upper frequency end of the measurement, whereas dispersion in lower frequency end confirms the presence of electrode polarization effect. It was observed that the increase of clay concentration in the PVP-EG blends significantly increases the ac conductivity values, and simultaneously reduces the ionic conductivity relaxation time and electric double layer relaxation time, which suggests that PVP segmental dynamics and ionic motion are strongly coupled. The intercalation of EG structures in clay galleries and exfoliation of clay sheets by adsorption of PVP-EG structures on clay surfaces are discussed by considering the hydrogen bonding interactions between the hydroxyl group (–OH of EG molecules, carbonyl group (C=O of PVP monomer units, and the hydroxylated aluminate surfaces of the MMT clay particles. Results suggest that the colloidal suspension of MMT clay nano particles in the PVP-EG blends provide a convenient way to obtain an electrolyte solution with tailored electrical conduction properties.

  4. Scan Rate Dependent Spin Crossover Iron(II) Complex with Two Different Relaxations and Thermal Hysteresis fac-[Fe(II)(HL(n-Pr))3]Cl·PF6 (HL(n-Pr) = 2-Methylimidazol-4-yl-methylideneamino-n-propyl).

    Science.gov (United States)

    Fujinami, Takeshi; Nishi, Koshiro; Hamada, Daisuke; Murakami, Keishiro; Matsumoto, Naohide; Iijima, Seiichiro; Kojima, Masaaki; Sunatsuki, Yukinari

    2015-08-03

    Solvent-free spin crossover Fe(II) complex fac-[Fe(II)(HL(n-Pr))3]Cl·PF6 was prepared, where HL(n-Pr) denotes 2-methylimidazol-4-yl-methylideneamino-n-propyl. The magnetic susceptibility measurements at scan rate of 0.5 K min(-1) showed two successive spin transition processes consisting of the first spin transition T1 centered at 122 K (T1↑ = 127.1 K, T1↓ = 115.8 K) and the second spin transition T2 centered at ca. 105 K (T2↑ = 115.8 K, T2↓ = 97.2 K). The magnetic susceptibility measurements at the scan rate of 2.0, 1.0, 0.5, 0.25, and 0.1 K min(-1) showed two scan speed dependent spin transitions, while the Mössbauer spectra detected only the first spin transition T1. The crystal structures were determined at 160, 143, 120, 110, 95 K in the cooling mode, and 110, 120, and 130 K in the warming mode so as to follow the spin transition process of high-spin HS → HS(T1) → HS(T2) → low-spin LS → LS(T2) → LS(T1) → HS. The crystal structures at all temperatures have a triclinic space group P1̅ with Z = 2. The complex-cation has an octahedral N6 coordination geometry with three bidentate ligands and assume a facial-isomer with Δ- and Λ-enantimorphs. Three imidazole groups of fac-[Fe(II)(HL(n-Pr))3](2+) are hydrogen-bonded to three Cl(-) ions. The 3:3 NH(imidazole)···Cl(-) hydrogen-bonds form a stepwise ladder assembly structure, which is maintained during the spin transition process. The spin transition process is related to the structural changes of the FeN6 coordination environment, the order-disorder of PF6(-) anion, and the conformation change of n-propyl groups. The Fe-N bond distance in the HS state is longer by 0.2 Å than that in the LS state. Disorder of PF6(-) anion is not observed in the LS state but in the HS state. The conformational changes of n-propyl groups are found in the spin transition processes except for HS → HS(T1) → HS(T2).

  5. Sandpile model for relaxation in complex systems

    International Nuclear Information System (INIS)

    Vazquez, A.; Sotolongo-Costa, O.; Brouers, F.

    1997-10-01

    The relaxation in complex systems is, in general, nonexponential. After an initial rapid decay the system relaxes slowly following a long time tail. In the present paper a sandpile moderation of the relaxation in complex systems is analysed. Complexity is introduced by a process of avalanches in the Bethe lattice and a feedback mechanism which leads to slower decay with increasing time. In this way, some features of relaxation in complex systems: long time tails relaxation, aging, and fractal distribution of characteristic times, are obtained by simple computer simulations. (author)

  6. Magic angle spinning nuclear magnetic resonance apparatus and process for high-resolution in situ investigations

    Science.gov (United States)

    Hu, Jian Zhi; Sears, Jr., Jesse A.; Hoyt, David W.; Mehta, Hardeep S.; Peden, Charles H. F.

    2015-11-24

    A continuous-flow (CF) magic angle sample spinning (CF-MAS) NMR rotor and probe are described for investigating reaction dynamics, stable intermediates/transition states, and mechanisms of catalytic reactions in situ. The rotor includes a sample chamber of a flow-through design with a large sample volume that delivers a flow of reactants through a catalyst bed contained within the sample cell allowing in-situ investigations of reactants and products. Flow through the sample chamber improves diffusion of reactants and products through the catalyst. The large volume of the sample chamber enhances sensitivity permitting in situ .sup.13C CF-MAS studies at natural abundance.

  7. Relaxation Pathways in Metallic Glasses

    Science.gov (United States)

    Gallino, Isabella; Busch, Ralf

    2017-11-01

    At temperatures below the glass transition temperature, physical properties of metallic glasses, such as density, viscosity, electrical resistivity or enthalpy, slowly evolve with time. This is the process of physical aging that occurs among all types of glasses and leads to structural changes at the microscopic level. Even though the relaxation pathways are ruled by thermodynamics as the glass attempts to re-attain thermodynamic equilibrium, they are steered by sluggish kinetics at the microscopic level. Understanding the structural and dynamic pathways of the relaxing glassy state is still one of the grand challenges in materials physics. We review some of the recent experimental advances made in understanding the nature of the relaxation phenomenon in metallic glasses and its implications to the macroscopic and microscopic properties changes of the relaxing glass.

  8. Sprayed and Spin-Coated Multilayer Antireflection Coating Films for Nonvacuum Processed Crystalline Silicon Solar Cells

    Directory of Open Access Journals (Sweden)

    Abdullah Uzum

    2017-01-01

    Full Text Available Using the simple and cost-effective methods, spin-coated ZrO2-polymer composite/spray-deposited TiO2-compact multilayer antireflection coating film was introduced. With a single TiO2-compact film on the surface of a crystalline silicon wafer, 5.3% average reflectance (the reflectance average between the wavelengths of 300 nm and 1100 nm was observed. Reflectance decreased further down to 3.3% after forming spin-coated ZrO2 on the spray-deposited TiO2-compact film. Silicon solar cells were fabricated using CZ-Si p-type wafers in three sets: (1 without antireflection coating (ARC layer, (2 with TiO2-compact ARC film, and (3 with ZrO2-polymer composite/TiO2-compact multilayer ARC film. Conversion efficiency of the cells improved by a factor of 0.8% (from 15.19% to 15.88% owing to the multilayer ARC. Jsc was improved further by 2 mA cm−2 (from 35.3 mA cm−2 to 37.2 mA cm−2 when compared with a single TiO2-compact ARC.

  9. Zero field spin splitting in asymmetric quantum wells

    International Nuclear Information System (INIS)

    Hao Yafei

    2012-01-01

    Spin splitting of asymmetric quantum wells is theoretically investigated in the absence of any electric field, including the contribution of interface-related Rashba spin-orbit interaction as well as linear and cubic Dresselhaus spin-orbit interaction. The effect of interface asymmetry on three types of spin-orbit interaction is discussed. The results show that interface-related Rashba and linear Dresselhaus spin-orbit interaction can be increased and cubic Dresselhaus spin-orbit interaction can be decreased by well structure design. For wide quantum wells, the cubic Dresselhaus spin-orbit interaction dominates under certain conditions, resulting in decreased spin relaxation time.

  10. Spin drift and spin diffusion currents in semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Idrish Miah, M [Nanoscale Science and Technology Centre and School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia)], E-mail: m.miah@griffith.edu.au

    2008-09-15

    On the basis of a spin drift-diffusion model, we show how the spin current is composed and find that spin drift and spin diffusion contribute additively to the spin current, where the spin diffusion current decreases with electric field while the spin drift current increases, demonstrating that the extension of the spin diffusion length by a strong field does not result in a significant increase in spin current in semiconductors owing to the competing effect of the electric field on diffusion. We also find that there is a spin drift-diffusion crossover field for a process in which the drift and diffusion contribute equally to the spin current, which suggests a possible method of identifying whether the process for a given electric field is in the spin drift or spin diffusion regime. Spin drift-diffusion crossover fields for GaAs are calculated and are found to be quite small. We derive the relations between intrinsic spin diffusion length and the spin drift-diffusion crossover field of a semiconductor for different electron statistical regimes. The findings resulting from this investigation might be important for semiconductor spintronics.

  11. Spin drift and spin diffusion currents in semiconductors

    Directory of Open Access Journals (Sweden)

    M Idrish Miah

    2008-01-01

    Full Text Available On the basis of a spin drift-diffusion model, we show how the spin current is composed and find that spin drift and spin diffusion contribute additively to the spin current, where the spin diffusion current decreases with electric field while the spin drift current increases, demonstrating that the extension of the spin diffusion length by a strong field does not result in a significant increase in spin current in semiconductors owing to the competing effect of the electric field on diffusion. We also find that there is a spin drift-diffusion crossover field for a process in which the drift and diffusion contribute equally to the spin current, which suggests a possible method of identifying whether the process for a given electric field is in the spin drift or spin diffusion regime. Spin drift-diffusion crossover fields for GaAs are calculated and are found to be quite small. We derive the relations between intrinsic spin diffusion length and the spin drift-diffusion crossover field of a semiconductor for different electron statistical regimes. The findings resulting from this investigation might be important for semiconductor spintronics.

  12. Spin drift and spin diffusion currents in semiconductors

    International Nuclear Information System (INIS)

    Idrish Miah, M

    2008-01-01

    On the basis of a spin drift-diffusion model, we show how the spin current is composed and find that spin drift and spin diffusion contribute additively to the spin current, where the spin diffusion current decreases with electric field while the spin drift current increases, demonstrating that the extension of the spin diffusion length by a strong field does not result in a significant increase in spin current in semiconductors owing to the competing effect of the electric field on diffusion. We also find that there is a spin drift-diffusion crossover field for a process in which the drift and diffusion contribute equally to the spin current, which suggests a possible method of identifying whether the process for a given electric field is in the spin drift or spin diffusion regime. Spin drift-diffusion crossover fields for GaAs are calculated and are found to be quite small. We derive the relations between intrinsic spin diffusion length and the spin drift-diffusion crossover field of a semiconductor for different electron statistical regimes. The findings resulting from this investigation might be important for semiconductor spintronics.

  13. Effect of structural relaxation of glassy PET on crystallization process observed by the simultaneous DSC-XRD and DSC-FTIR

    International Nuclear Information System (INIS)

    Yoshii, Tomoko; Yoshida, Hirohisa; Kawai, Tadashi

    2005-01-01

    The effect of structural relaxation of the glassy poly(ethylene terephtalate) (PET) caused by annealing below its glass transition temperature (T g ) on the cold-crystallization observed was investigated by the simultaneous DSC-FTIR and DSC-XRD methods. The nucleation and the conformational ordering processes proceeded faster by annealing. From the relationship between the absorbance change and the exothermic heat during the cold-crystallization, the heat of cold-crystallization for the unannealed PET was caused mainly by the conformational ordering. For the annealed PET, the long range ordering contributed to the heat of crystallization in the late stage of cold-crystallization, which was also confirmed by the DSC-XRD method

  14. Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Sivers asymmetries

    CERN Document Server

    Adolph, C.; Alexakhin, V.Yu.; Alexandrov, Yu.; Alexeev, G.D.; Amoroso, A.; Antonov, A.A.; Austregesilo, A.; Badelek, B.; Balestra, F.; Barth, J.; Baum, G.; Bedfer, Y.; Bernhard, J.; Bertini, R.; Bettinelli, M.; Bicker, K.; Bieling, J.; Birsa, R.; Bisplinghoff, J.; Bordalo, P.; Bradamante, F.; Braun, C.; Bravar, A.; Bressan, A.; Burtin, E.; Capozza, L.; Chiosso, M.; Chung, S.U.; Cicuttin, A.; Crespo, M.L.; Dalla Torre, S.; Das, S.; Dasgupta, S.S.; Dasgupta, S.; Denisov, O.Yu.; Dhara, L.; Donskov, S.V.; Doshita, N.; Duic, V.; Dunnweber, W.; Dziewiecki, M.; Efremov, A.; Elia, C.; Eversheim, P.D.; Eyrich, W.; Faessler, M.; Ferrero, A.; Filin, A.; Finger, M.; Fischer, H.; Franco, C.; von Hohenesche, N.du Fresne; Friedrich, J.M.; Frolov, V.; Garfagnini, R.; Gautheron, F.; Gavrichtchouk, O.P.; Gerassimov, S.; Geyer, R.; Giorgi, M.; Gnesi, I.; Gobbo, B.; Goertz, S.; Grabmuller, S.; Grasso, A.; Grube, B.; Gushterski, R.; Guskov, A.; Guthorl, T.; Haas, F.; von Harrach, D.; Heinsius, F.H.; Herrmann, F.; Hess, C.; Hinterberger, F.; Horikawa, N.; Hoppner, Ch.; d'Hose, N.; Ishimoto, S.; Ivanov, O.; Ivanshin, Yu.; Iwata, T.; Jahn, R.; Jary, V.; Jasinski, P.; Joosten, R.; Kabuss, E.; Kang, D.; Ketzer, B.; Khaustov, G.V.; Khokhlov, Yu.A.; Kisselev, Yu.; Klein, F.; Klimaszewski, K.; Koblitz, S.; Koivuniemi, J.H.; Kolosov, V.N.; Kondo, K.; Konigsmann, K.; Konorov, I.; Konstantinov, V.F.; Korzenev, A.; Kotzinian, A.M.; Kouznetsov, O.; Kramer, M.; Kroumchtein, Z.V.; Kunne, F.; Kurek, K.; Lauser, L.; Lednev, A.A.; Lehmann, A.; Levorato, S.; Lichtenstadt, J.; Liska, T.; Maggiora, A.; Magnon, A.; Makke, N.; Mallot, G.K.; Mann, A.; Marchand, C.; Martin, A.; Marzec, J.; Matsuda, T.; Meshcheryakov, G.; Meyer, W.; Michigami, T.; Mikhailov, Yu.V.; Moinester, M.A.; Morreale, A.; Mutter, A.; Nagaytsev, A.; Nagel, T.; Negrini, T.; Nerling, F.; Neubert, S.; Neyret, D.; Nikolaenko, V.I.; Nowak, W.D.; Nunes, A.S.; Olshevsky, A.G.; Ostrick, M.; Padee, A.; Panknin, R.; Panzieri, D.; Parsamyan, B.; Paul, S.; Perevalova, E.; Pesaro, G.; Peshekhonov, D.V.; Piragino, G.; Platchkov, S.; Pochodzalla, J.; Polak, J.; Polyakov, V.A.; Pretz, J.; Quaresma, M.; Quintans, C.; Rajotte, J.F.; Ramos, S.; Rapatsky, V.; Reicherz, G.; Richter, A.; Rocco, E.; Rondio, E.; Rossiyskaya, N.S.; Ryabchikov, D.I.; Samoylenko, V.D.; Sandacz, A.; Sapozhnikov, M.G.; Sarkar, S.; Savin, I.A.; Sbrizzai, G.; Schiavon, P.; Schill, C.; Schluter, T.; Schmidt, K.; Schmitt, L.; Schonning, K.; Schopferer, S.; Schott, M.; Schroder, W.; Shevchenko, O.Yu.; Silva, L.; Sinha, L.; Sissakian, A.N.; Slunecka, M.; Smirnov, G.I.; Sosio, S.; Sozzi, F.; Srnka, A.; Steiger, L.; Stolarski, M.; Sulc, M.; Sulej, R.; Suzuki, H.; Sznajder, P.; Takekawa, S.; Wolbeek, J.Ter; Tessaro, S.; Tessarotto, F.; Tkatchev, L.G.; Uhl, S.; Uman, I.; Vandenbroucke, M.; Virius, M.; Vlassov, N.V.; Wang, L.; Wilfert, M.; Windmolders, R.; Wislicki, W.; Wollny, H.; Zaremba, K.; Zavertyaev, M.; Zemlyanichkina, E.; Ziembicki, M.; Zhuravlev, N.; Zvyagin, A.

    2012-10-31

    The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV positive muon beam and a transversely polarised NH_3 target. The Sivers asymmetry of the proton has been extracted in the Bjorken x range 0.003 0.03. The asymmetry is different from zero and positive also in the low x region, where sea-quarks dominate. The kinematic dependence of the asymmetry has also been investigated and results are given for various intervals of hadron and virtual photon fractional energy. In contrast to the case of the Collins asymmetry, the results on the Sivers asymmetry suggest a strong dependence on the four-momentum transfer to the nucleon, in agreement with the most recent calculations.

  15. Fused-Ring Derivatives of Quinoxalines: Spectroscopic Characterization and Photoinduced Processes Investigated by EPR Spin Trapping Technique

    Directory of Open Access Journals (Sweden)

    Zuzana Barbieriková

    2014-08-01

    Full Text Available 10-Ethyl-7-oxo-7,10-dihydropyrido[2,3-f]quinoxaline derivatives, synthesized as promising biologically/photobiologically active compounds were characterized by UV/vis, FT-IR and fluorescent spectroscopy. Photoinduced processes of these derivatives were studied by EPR spectroscopy, monitoring in situ the generation of reactive intermediates upon UVA (λmax = 365 nm irradiation. The formation of reactive oxygen species and further oxygen- and carbon-centered radical intermediates was detected and possible reaction routes were suggested. To quantify the investigated processes, the quantum yields of the superoxide radical anion spin-adduct and 4-oxo-2,2,6,6-tetramethylpiperidine N-oxyl generation were determined, reflecting the activation of molecular oxygen by the excited state of the quinoxaline derivative.

  16. Multispin-assisted optical pumping of bulk 13C nuclear spin polarization in diamond

    Science.gov (United States)

    Pagliero, Daniela; Rao, K. R. Koteswara; Zangara, Pablo R.; Dhomkar, Siddharth; Wong, Henry H.; Abril, Andrea; Aslam, Nabeel; Parker, Anna; King, Jonathan; Avalos, Claudia E.; Ajoy, Ashok; Wrachtrup, Joerg; Pines, Alexander; Meriles, Carlos A.

    2018-01-01

    One of the most remarkable properties of the nitrogen-vacancy (NV) center in diamond is that optical illumination initializes its electronic spin almost completely, a feature that can be exploited to polarize other spin species in their proximity. Here we use field-cycled nuclear magnetic resonance to investigate the mechanisms of spin-polarization transfer from NVs to 13C spins in diamond at room temperature. We focus on the dynamics near 51 mT, where a fortuitous combination of energy-matching conditions between electron and nuclear spin levels gives rise to alternative polarization transfer channels. By monitoring the 13C spin polarization as a function of the applied magnetic field, we show 13C spin pumping takes place via a multispin cross-relaxation process involving the N V- spin and the electronic and nuclear spins of neighboring P1 centers. Further, we find that this mechanism is insensitive to the crystal orientation relative to the magnetic field, although the absolute level of 13C polarization—reaching up to ˜3 % under optimal conditions—can vary substantially depending on the interplay between optical pumping efficiency, photogenerated carriers, and laser-induced heating.

  17. Spin waves propagation and confinement in magnetic microstructures

    International Nuclear Information System (INIS)

    Bailleul, Matthieu

    2002-01-01

    In this thesis, ferromagnetic thin film elements have been studied on a small scale (μm) and at high frequencies (GHz). For those studies, a microwave spectrometer based on the use of micro-antennae has been developed. It had been applied to two different systems. In a first time, we have launched and detected spin waves in continuous films. This allowed us to describe both the transduction process and the relaxation law for long wavelength spin waves. In a second time, we have studied micrometer-wide stripe for which the magnetic ground state is inhomogeneous. The obtained microwave response has been interpreted in terms of micro-magnetic phase transitions and in terms of spin waves confinement. (author)

  18. Postseismic relaxation process and lithospheric rheology inferred from eight years of postseismic deformation after the 2008 Mw7.9 Wenchuan earthquake

    Science.gov (United States)

    Zhao, B.; Burgmann, R.; Rui, X.; Wang, D.; Yu, J.; He, K.

    2017-12-01

    Current inferences of postseismic deformation mechanisms and lithospheric rheology in the eastern Tibetan Plateau strongly depend on spatial and temporal observations of postseismic transients following the 2008 Mw=7.9 Wenchuan earthquake. We processed regional continuously operating and survey-mode GPS data from the Crustal Movement Observation Network of China and Sichuan Continuous Operation Reference System. These data cover a broad region and time intervals of up to eight years. The determined amplitude of postseismic displacements show clear contrast between the Sichuan Basin and eastern Tibet. In addition to significant amounts of deformation in the region between the Longmen Shan and Longriba fault, reliable deformation transients are also visible in the far field, such as regions to the west of the Longriba fault and along the left-lateral Xianshuihe fault. In contrast, no more than 10 mm of postseismic transients are observed in the Sichuan Basin. Guided by previous studies, we conducted multiple-mechanism models of afterslip and viscoelastic relaxation. We first explored a series of forward viscoelastic relaxation models using a heterogeneous rheological earth structure, and then inverted corresponding afterslip distributions on the shallowly dipping detachment to explain the remaining residuals. Our preliminary results indicate the viscoelastic relaxation in the lower crust and upper mantle dominantly contributed to the mid- and far-field observations, whereas afterslip below the coseismic asperities and on small patches near the surface can explain the near-field measurements. Time-dependent slip inversions illustrate that afterslip decays more rapidly on the shallow portions of the fault interface than on the shallowly dipping detachment. Relatively long-lived right-lateral afterslip is revealed in the north segment of the Beichuan fault, suggesting variations of frictional properties along strike of the fault zone. Our results also support previous

  19. Migration of additive molecules in a polymer filament obtained by melt spinning: Influence of the fiber processing steps

    Science.gov (United States)

    Gesta, E.; Skovmand, O.; Espuche, E.; Fulchiron, R.

    2015-12-01

    The purpose of this study is to understand the influence of the yarn processing on the migration of additives molecules, especially insecticide, within polyethylene (PE) yarns. Yarns were manufactured in the laboratory focusing on three key-steps (spinning, post-stretching and heat-setting). Influence of each step on yarn properties was investigated using tensile tests, differential scanning calorimetry and wide-angle X-ray diffraction. The post-stretching step was proved to be critical in defining yarn mechanical and structural properties. Although a first orientation of polyethylene crystals was induced during spinning, the optimal orientation was only reached by post-stretching. The results also showed that the heat-setting did not significantly change these properties. The presence of additives crystals at the yarn surface was evidenced by scanning-electron microscopy. These studies performed at each yarn production step allowed a detailed analysis of the additives' ability to migrate. It is concluded that while post-stretching decreased the migration rate, heat-setting seems to boost this migration.

  20. Migration of additive molecules in a polymer filament obtained by melt spinning: Influence of the fiber processing steps

    Energy Technology Data Exchange (ETDEWEB)

    Gesta, E. [Ingénierie des Matériaux Polymères - UMR CNRS 5223, Université de Lyon - Université Lyon 1, Bâtiment POLYTECH Lyon - 15 boulevard Latarjet, 69622, Villeurbanne (France); Intelligent Insect Control, 118 Chemin des Alouettes, Castelnau-le-Lez, 34170 (France); Skovmand, O., E-mail: osk@insectcontrol.net [Intelligent Insect Control, 118 Chemin des Alouettes, Castelnau-le-Lez, 34170 (France); Espuche, E., E-mail: eliane.espuche@univ-lyon1.fr; Fulchiron, R., E-mail: rene.fulchiron@univ-lyon1.fr [Ingénierie des Matériaux Polymères - UMR CNRS 5223, Université de Lyon - Université Lyon 1, Bâtiment POLYTECH Lyon - 15 boulevard Latarjet, 69622, Villeurbanne (France)

    2015-12-17

    The purpose of this study is to understand the influence of the yarn processing on the migration of additives molecules, especially insecticide, within polyethylene (PE) yarns. Yarns were manufactured in the laboratory focusing on three key-steps (spinning, post-stretching and heat-setting). Influence of each step on yarn properties was investigated using tensile tests, differential scanning calorimetry and wide-angle X-ray diffraction. The post-stretching step was proved to be critical in defining yarn mechanical and structural properties. Although a first orientation of polyethylene crystals was induced during spinning, the optimal orientation was only reached by post-stretching. The results also showed that the heat-setting did not significantly change these properties. The presence of additives crystals at the yarn surface was evidenced by scanning-electron microscopy. These studies performed at each yarn production step allowed a detailed analysis of the additives’ ability to migrate. It is concluded that while post-stretching decreased the migration rate, heat-setting seems to boost this migration.

  1. Migration of additive molecules in a polymer filament obtained by melt spinning: Influence of the fiber processing steps

    International Nuclear Information System (INIS)

    Gesta, E.; Skovmand, O.; Espuche, E.; Fulchiron, R.

    2015-01-01

    The purpose of this study is to understand the influence of the yarn processing on the migration of additives molecules, especially insecticide, within polyethylene (PE) yarns. Yarns were manufactured in the laboratory focusing on three key-steps (spinning, post-stretching and heat-setting). Influence of each step on yarn properties was investigated using tensile tests, differential scanning calorimetry and wide-angle X-ray diffraction. The post-stretching step was proved to be critical in defining yarn mechanical and structural properties. Although a first orientation of polyethylene crystals was induced during spinning, the optimal orientation was only reached by post-stretching. The results also showed that the heat-setting did not significantly change these properties. The presence of additives crystals at the yarn surface was evidenced by scanning-electron microscopy. These studies performed at each yarn production step allowed a detailed analysis of the additives’ ability to migrate. It is concluded that while post-stretching decreased the migration rate, heat-setting seems to boost this migration

  2. Investigation of thermalization in giant-spin models by different Lindblad schemes

    Energy Technology Data Exchange (ETDEWEB)

    Beckmann, Christian; Schnack, Jürgen, E-mail: jschnack@uni-bielefeld.de

    2017-09-01

    Highlights: • The non-equilibrium magnetization is investigated with quantum master equations that rest on Lindblad schemes. • It is studied how different couplings to the bath modify the magnetization. • Various field protocols are employed; relaxation times are deduced. • Result: the time evolution depends strongly on the details of the transition operator used in the Lindblad term. - Abstract: The theoretical understanding of time-dependence in magnetic quantum systems is of great importance in particular for cases where a unitary time evolution is accompanied by relaxation processes. A key example is given by the dynamics of single-molecule magnets where quantum tunneling of the magnetization competes with thermal relaxation over the anisotropy barrier. In this article we investigate how good a Lindblad approach describes the relaxation in giant spin models and how the result depends on the employed operator that transmits the action of the thermal bath.

  3. Exciton-relaxation dynamics in lead halides

    International Nuclear Information System (INIS)

    Iwanaga, Masanobu; Hayashi, Tetsusuke

    2003-01-01

    We survey recent comprehensive studies of exciton relaxation in the crystals of lead halides. The luminescence and electron-spin-resonance studies have revealed that excitons in lead bromide spontaneously dissociate and both electrons and holes get self-trapped individually. Similar relaxation has been also clarified in lead chloride. The electron-hole separation is ascribed to repulsive correlation via acoustic phonons. Besides, on the basis of the temperature profiles of self-trapped states, we discuss the origin of luminescence components which are mainly induced under one-photon excitation into the exciton band in lead fluoride, lead chloride, and lead bromide

  4. What is the surface specific area of porous cement-based material? A nuclear magnetic relaxation dispersion approach.

    Science.gov (United States)

    Barberon, F; Korb, J-P; Petit, D; Morin, V; Bermejo, E

    2003-01-01

    We propose a new NMR method to measure and follow the evolution of the surface specific area, Sp, of a porous cement-based material. This method, that does not require any preliminary drying process, uses nuclear magnetic relaxation dispersion (NMRD), the measurement of spin-lattice relaxation rate as a function of magnetic field strength or nuclear Larmor frequency. The method is applied for three different mortars samples prepared by mixing cement, sand, silica fume, water and superplasticizer with a water to cement ratio w/c=0.25, 0.38 and 0.65, respectively. The evolution of Sp grows linearly with the degree of advancement of chemical reactions measured by thermal heating and we evidence two relaxation processes independent of the w/c ratio.

  5. Magnetic excitations in CuMn spin-glass alloys

    International Nuclear Information System (INIS)

    Tsunoda, Y.; Kunitomi, N.; Cable, J.W.

    1985-01-01

    Recent neutron scattering measurements have helped to clarify two important features of CuMn spin glasses. Murani and co-workers have studied the dynamical behavior of spin-glass systems and have observed characteristic ferromagnetic spin correlations with a broad distribution of relaxation times and a dynamical freezing process. By means of the polarization analysis technique, Cable and co-workers have observed the coexistence of two types of magnetic short-range order (MSRO): one is a modulated-spin structure, and the other is a ferromagnetic cluster associated with the atomic short-range order (ASRO). These ordered regions produce diffraction maxima which are found at the (1 1/2 +/- delta 0) and the (1 1/2 0) reciprocal lattice points, respectively. Both of these observations seem to be essential for understanding the CuMn spin-glass system. However, the physical relationship of these properties is not yet understood. The authors have studied the inelastic scattering of neutrons around the magnetic diffuse peak positions of a Cu/sub 78.7/Mn/sub 21.3/ single crystal. The spin-glass freezing temperature of a CuMn alloy with this Mn concentration is estimated to be T/sub f/ approx. 90 K. Most of the data were taken by scanning along the [0 1 0] direction from the (1 0 0) to the (1 1 0) reciprocal lattice points

  6. Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Collins asymmetries

    CERN Document Server

    Adolph, C.; Alexakhin, V.Yu.; Alexandrov, Yu.; Alexeev, G.D.; Amoroso, A.; Antonov, A.A.; Austregesilo, A.; Badelek, B.; Balestra, F.; Barth, J.; Baum, G.; Bedfer, Y.; Bernhard, J.; Bertini, R.; Bettinelli, M.; Bicker, K.; Bieling, J.; Birsa, R.; Bisplinghoff, J.; Bordalo, P.; Bradamante, F.; Braun, C.; Bravar, A.; Bressan, A.; Burtin, E.; Capozza, L.; Chiosso, M.; Chung, S.U.; Cicuttin, A.; Crespo, M.L.; Dalla Torre, S.; Das, S.; Dasgupta, S.S.; Dasgupta, S.; Denisov, O.Yu.; Dhara, L.; Donskov, S.V.; Doshita, N.; Duic, V.; Dunnweber, W.; Dziewiecki, M.; Efremov, A.; Elia, C.; Eversheim, P.D.; Eyrich, W.; Faessler, M.; Ferrero, A.; Filin, A.; Finger, M.; Fischer, H.; Franco, C.; von Hohenesche, N.du Fresne; Friedrich, J.M.; Frolov, V.; Garfagnini, R.; Gautheron, F.; Gavrichtchouk, O.P.; Gerassimov, S.; Geyer, R.; Giorgi, M.; Gnesi, I.; Gobbo, B.; Goertz, S.; Grabmuller, S.; Grasso, A.; Grube, B.; Gushterski, R.; Guskov, A.; Guthorl, T.; Haas, F.; von Harrach, D.; Heinsius, F.H.; Herrmann, F.; Hess, C.; Hinterberger, F.; Horikawa, N.; Hoppner, Ch.; d'Hose, N.; Ishimoto, S.; Ivanov, O.; Ivanshin, Yu.; Iwata, T.; Jahn, R.; Jary, V.; Jasinski, P.; Joosten, R.; Kabuss, E.; Kang, D.; Ketzer, B.; Khaustov, G.V.; Khokhlov, Yu.A.; Kisselev, Yu.; Klein, F.; Klimaszewski, K.; Koblitz, S.; Koivuniemi, J.H.; Kolosov, V.N.; Kondo, K.; Konigsmann, K.; Konorov, I.; Konstantinov, V.F.; Korzenev, A.; Kotzinian, A.M.; Kouznetsov, O.; Kramer, M.; Kroumchtein, Z.V.; Kunne, F.; Kurek, K.; Lauser, L.; Lednev, A.A.; Lehmann, A.; Levorato, S.; Lichtenstadt, J.; Liska, T.; Maggiora, A.; Magnon, A.; Makke, N.; Mallot, G.K.; Mann, A.; Marchand, C.; Martin, A.; Marzec, J.; Matsuda, T.; Meshcheryakov, G.; Meyer, W.; Michigami, T.; Mikhailov, Yu.V.; Moinester, M.A.; Morreale, A.; Mutter, A.; Nagaytsev, A.; Nagel, T.; Negrini, T.; Nerling, F.; Neubert, S.; Neyret, D.; Nikolaenko, V.I.; Nowak, W.D.; Nunes, A.S.; Olshevsky, A.G.; Ostrick, M.; Padee, A.; Panknin, R.; Panzieri, D.; Parsamyan, B.; Paul, S.; Perevalova, E.; Pesaro, G.; Peshekhonov, D.V.; Piragino, G.; Platchkov, S.; Pochodzalla, J.; Polak, J.; Polyakov, V.A.; Pretz, J.; Quaresma, M.; Quintans, C.; Rajotte, J.F.; Ramos, S.; Rapatsky, V.; Reicherz, G.; Richter, A.; Rocco, E.; Rondio, E.; Rossiyskaya, N.S.; Ryabchikov, D.I.; Samoylenko, V.D.; Sandacz, A.; Sapozhnikov, M.G.; Sarkar, S.; Savin, I.A.; Sbrizzai, G.; Schiavon, P.; Schill, C.; Schluter, T.; Schmidt, K.; Schmitt, L.; Schonning, K.; Schopferer, S.; Schott, M.; Schroder, W.; Shevchenko, O.Yu.; Silva, L.; Sinha, L.; Sissakian, A.N.; Slunecka, M.; Smirnov, G.I.; Sosio, S.; Sozzi, F.; Srnka, A.; Steiger, L.; Stolarski, M.; Sulc, M.; Sulej, R.; Suzuki, H.; Sznajder, P.; Takekawa, S.; Wolbeek, J.Ter; Tessaro, S.; Tessarotto, F.; Tkatchev, L.G.; Uhl, S.; Uman, I.; Vandenbroucke, M.; Virius, M.; Vlassov, N.V.; Wang, L.; Wilfert, M.; Windmolders, R.; Wislicki, W.; Wollny, H.; Zaremba, K.; Zavertyaev, M.; Zemlyanichkina, E.; Ziembicki, M.; Zhuravlev, N.; Zvyagin, A.

    2012-10-31

    The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV positive muon beam and a transversely polarised NH_3 target. The Collins asymmetry of the proton was extracted in the Bjorken x range 0.003

  7. Spin coating apparatus

    Science.gov (United States)

    Torczynski, John R.

    2000-01-01

    A spin coating apparatus requires less cleanroom air flow than prior spin coating apparatus to minimize cleanroom contamination. A shaped exhaust duct from the spin coater maintains process quality while requiring reduced cleanroom air flow. The exhaust duct can decrease in cross section as it extends from the wafer, minimizing eddy formation. The exhaust duct can conform to entrainment streamlines to minimize eddy formation and reduce interprocess contamination at minimal cleanroom air flow rates.

  8. Spin Transport Measurements in Hydrogenated Graphene Devices

    Science.gov (United States)

    Koon, Gavin; Balakrishnan, Jayakumar; Oezyilmaz, Barbaros

    2013-03-01

    Graphene with all its extraordinary properties still fall short when it comes to manipulation of electron spins. Chemically modified Graphene has been explored by many to further enhance Graphene properties, tailoring it to suit desired application purposes. Here we study the effects of hydrogenation rate on graphene spin transport, spin relaxation time and length in this defected system. These findings are important for future theoretical and experimental studies on other adatoms modified Graphene.

  9. Spin-drift transport in semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M Idrish [Nanoscale Science and Technology Centre and School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong, Chittagong-4331 (Bangladesh)

    2008-02-07

    We present a study on spin transport in semiconductors under applied electric fields. Our experiments detect photoinjected electron spins and their relaxation during drift transport in intrinsic and moderately n-doped GaAs, based on the extraordinary Hall (eH) effect. For relatively low electric field (E), the optically spin-induced eH effect in n-doped GaAs is found to be enhanced with increasing doping density and not to depend much on E, indicating that a substantial amount of optical spin polarization is preserved during the drift transport in these extrinsic semiconductors. However, when the spin-oriented electrons are injected with a high E, a very significant decrease is observed in the eH voltage (V{sub eH}) due to an increase in the spin precession frequency of the hot electrons. Spin relaxation by the D'yakonov-Perel' mechanism is calculated, and is suggested to be the reason for such a rapid spin relaxation for hot electrons under a high E. However, in an intrinsic GaAs (i-GaAs), a much weaker V{sub eH} is observed and, as the electron spins scattered by holes due to the Coulomb interaction in i-GaAs, the spin relaxation by the Bir-Aronov-Pikus mechanism is considered. Skew scattering and side jump as possible mechanisms of the optically spin-induced transverse Hall currents are discussed. Based on a spin drift-diffusion model, drift and diffusion contributions to the V{sub eH} are examined. The results are also discussed in comparison with theoretical investigations.

  10. Spin injection from a normal metal into a mesoscopic superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Wolf, Michael J.; Kolenda, Stefan [Institut fuer Nanotechnologie, KIT, 76021 Karlsruhe (Germany); Huebler, Florian [Institut fuer Nanotechnologie, KIT, 76021 Karlsruhe (Germany); Center for Functional Nanostructures, KIT, 76131 Karlsruhe (Germany); Institut fuer Festkoerperphysik, KIT, 76021 Karlsruhe (Germany); Loehneysen, Hilbert v. [Center for Functional Nanostructures, KIT, 76131 Karlsruhe (Germany); Institut fuer Festkoerperphysik, KIT, 76021 Karlsruhe (Germany); Physikalisches Institut, KIT, 76128 Karlsruhe (Germany); Beckmann, Detlef [Institut fuer Nanotechnologie, KIT, 76021 Karlsruhe (Germany); Center for Functional Nanostructures, KIT, 76131 Karlsruhe (Germany)

    2013-07-01

    We report on nonlocal transport in superconductor hybrid structures, with ferromagnetic as well as normal-metal tunnel junctions attached to the superconductor. In the presence of a strong Zeeman splitting of the density of states, both charge and spin imbalance is injected into the superconductor. While previous experiments demonstrated spin injection from ferromagnetic electrodes, we show that spin imbalance is also created for normal-metal injector contacts. Using the combination of ferromagnetic and normal-metal detectors allows us to directly discriminate between charge and spin injection, and demonstrate a complete separation of charge and spin imbalance. The relaxation length of the spin imbalance is of the order of several μm and is found to increase with a magnetic field, but is independent of temperature. We further discuss possible relaxation mechanisms for the explanation of the spin relaxation length.

  11. Spin noise spectroscopy on donors in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Bernien, Hannes; Mueller, Georg; Roemer, Michael; Huebner, Jens; Oestreich, Michael [Institute for Solid State Physics, Gottfried Wilhelm Leibniz University Hannover (Germany)

    2009-07-01

    In recent experiments spin noise spectroscopy (SNS) has proven to be a very sensitive technique to study electron spin dynamics in semiconductors at thermal equilibrium. Here we present SNS-measurements on donor bound electrons in very low doped bulk GaAs. In this environment the donors do not interact with each other and form artificial atoms. We discuss the detection of single donor bound electron spins, which should have extremely long spin relaxation times compared to ensemble spin relaxation times. In further experiments the electron bound to the donor will be used to probe and study the local nuclear magnetic field at the donor site.

  12. Spin current

    CERN Document Server

    Valenzuela, Sergio O; Saitoh, Eiji; Kimura, Takashi

    2012-01-01

    In a new branch of physics and technology called spin-electronics or spintronics, the flow of electrical charge (usual current) as well as the flow of electron spin, the so-called 'spin current', are manipulated and controlled together. This book provides an introduction and guide to the new physics and application of spin current.

  13. Spinning process variables and polymer solution effects in the die-swell phenomenon during hollow fiber membranes formation

    Directory of Open Access Journals (Sweden)

    Pereira C.C.

    2000-01-01

    Full Text Available During hollow fiber spinning many variables are involved whose effects are still not completely clear. However, its understanding is of great interest because the control of these variables may originate membranes with the desired morphologies and physical properties. In this work, the phase inversion process induced by the immersion precipitation technique was applied to prepare hollow fibers membranes. It was verified that some of the variables involved, can promote a visco-elastic polymer solution expansion, called die-swell phenomenon, which is undesired since it may lead to low reproducibility of the permeation properties. The effects of the distance between spinneret and precipitation bath, the bore liquid composition, and the polymer solution composition were analyzed and discussed in order to avoid this phenomenon. According to the results, it was verified that the parameters investigated might promote a delay precipitation, which restrained the visco-elastic expansion.

  14. Microscopic studies of nonlocal spin dynamics and spin transport (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris, E-mail: hammel@physics.osu.edu [Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States)

    2015-05-07

    Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

  15. NV-NV electron-electron spin and NV-N S electron - electron and electron-nuclear spin interaction in diamond

    Science.gov (United States)

    Armstrong, Seiji; Rogers, Lachlan J.; McMurtrie, Roger L.; Manson, Neil B.

    2010-02-01

    Features associated with the cross relaxation between spin of the ground electric state of the nitrogen vacancy centre (NV) and other impurity spins, mainly substitutional nitrogen, NS, are observed as changes of the emission intensity as a function of external magnetic field. The features are attributed to NV-NV electron-electron spin interaction, NV- NS electron-nuclear spin interaction and NV electron spin interaction with simultaneous change of an NS electron and nuclear spin change.

  16. Location of a metallic cation complexed in a calixarene cavity as determined by calixarene 13C spin relaxation. application to cesium and thallium complexed by p-sulfonatocalix[4]arene in water.

    Science.gov (United States)

    Cuc, Diana; Bouguet-Bonnet, Sabine; Morel-Desrosiers, Nicole; Morel, Jean-Pierre; Mutzenhardt, Pierre; Canet, Daniel

    2009-03-19

    This study deals with the exact location of the monovalent metal cations Cs(+) and Tl(+) which are complexed by the p-sulfonatocalix[4]arene in water. This determination rests on the measurements of longitudinal relaxation times of carbon-13 not directly bonded to protons. The difference between the relaxation times of the free calixarene and of the complex definitely demonstrates that the monovalent metal cation is well inside the calixarene cavity. These features are in fact enhanced by the presence of paramagnetic species which act in a different way in the complexed form. Experimental results also show without any ambiguity that the calixarene cavity is essentially hydrophobic. Finally, it is observed that thallium is more mobile than cesium within the calixarene cavity.

  17. Chemical exchange effects during refocusing pulses in constant-time CPMG relaxation dispersion experiments

    International Nuclear Information System (INIS)

    Myint, Wazo; Ishima, Rieko

    2009-01-01

    In the analysis of the constant-time Carr-Purcell-Meiboom-Gill (CT-CPMG) relaxation dispersion experiment, chemical exchange parameters, such as rate of exchange and population of the exchanging species, are typically optimized using equations that predict experimental relaxation rates recorded as a function of effective field strength. In this process, the effect of chemical exchange during the CPMG pulses is typically assumed to be the same as during the free-precession. This approximation may introduce systematic errors into the analysis of data because the number of CPMG pulses is incremented during the constant-time relaxation period, and the total pulse duration therefore varies as a function of the effective field strength. In order to estimate the size of such errors, we simulate the time-dependence of magnetization during the entire constant time period, explicitly taking into account the effect of the CPMG pulses on the spin relaxation rate. We show that in general the difference in the relaxation dispersion profile calculated using a practical pulse width from that calculated using an extremely short pulse width is small, but under certain circumstances can exceed 1 s -1 . The difference increases significantly when CPMG pulses are miscalibrated

  18. Characterization of Oat (Avena nuda L.) β-Glucan Cryogelation Process by Low-Field NMR.

    Science.gov (United States)

    Wu, Jia; Li, Linlin; Wu, Xiaoyan; Dai, Qiaoling; Zhang, Ru; Zhang, Yi

    2016-01-13

    Low-field nuclear magnetic resonance (LF-NMR) is a useful method in studying the water distribution and mobility in heterogeneous systems. This technique was used to characterize water in an oat β-glucan aqueous system during cryogelation by repeated freeze-thaw treatments. The results indicated that microphase separation occurred during cryogelation, and three water components were determined in the cryostructure. The spin-spin relaxation time was analyzed on the basis of chemical exchange and diffusion exchange theory. The location of each water component was identified in the porous microstructure of the cryogel. The pore size measured from the SEM image is in accordance with that estimated from relaxation time. The formation of cryogel is confirmed by rheological method. The results suggested that the cryogelation process of the polysaccharide could be monitored by LF-NMR through the evolution of spin-spin relaxation characteristics.

  19. Delta Relaxation Enhanced Magnetic Resonance

    Science.gov (United States)

    Alford, Jamu K.

    synchronizes this waveform with the rest of the MRI pulse sequence. On two separate dreMR systems, images were obtained having contrast which was directly proportional to the magnetic field dependence of the sample's relaxation rates. This contrast unambiguously indicated the presence of the bound probe, and its imaging therefore yields a map of the targeted biological molecule. Keywords Magnetic Resonance Imaging; Field-Cycled MRI; MR Probe; Targeted Contrast Agent; Gadolinium; Insert Coil; Power Supply; Relaxation Rate; Relaxivity; Actively Shielded; dreMR; Delta Relaxation Enhanced MRI; MRI Hardware; Gradient Echo; Spin Echo; Spoiled Gradient; Echo iv

  20. Brief overview of the long-lived radionuclide separation processes developed in France in connection with the SPIN program

    Energy Technology Data Exchange (ETDEWEB)

    Madic, C.; Bourges, J. [DRDD, Fontenay-aux-Roses (France); Dozol, J.F. [DESD, Cadarache (France)

    1995-10-01

    To reduce the long-term potential hazards associated with the management of nuclear wastes generated by nuclear fuel reprocessing, one alternative is the transmutation of long-lived radionuclides into short-lived radionuclides by nuclear means (P & T strategy). In this context, according to the law passed by the French Parliament on 30 December 1991, the CEA launched the SPIN program for the design of long-lived radionuclide separation and nuclear incineration processes. The research in progress to define separation processes focused mainly on the minor actinides (neptunium, americium and curium) and some fission products, like cesium and technetium. To separate these long-lived radionuclides, two strategies were developed. The first involves research on new operating conditions for improving the PUREX fuel reprocessing technology. This approach concerns the elements neptunium and technetium (iodine and zirconium can also be considered). The second strategy involves the design of new processes; DIAMEX for the co-extraction of minor actinides from the high-level liquid waste leaving the PUREX process, An(III)/Ln(III) separation using tripyridyltriazine derivatives or picolinamide extracting agents; SESAME for the selective separation of americium after its oxidation to Am(IV) or Am(VI) in the presence of a heteropolytungstate ligand, and Cs extraction using a new class of extracting agents, calixarenes, which exhibit exceptional Cs separation properties, especially in the presence of sodium ion. This lecture focuses on the latest achievements in these research areas.

  1. Digital operation and eye diagrams in spin-lasers

    International Nuclear Information System (INIS)

    Wasner, Evan; Bearden, Sean; Žutić, Igor; Lee, Jeongsu

    2015-01-01

    Digital operation of lasers with injected spin-polarized carriers provides an improved operation over their conventional counterparts with spin-unpolarized carriers. Such spin-lasers can attain much higher bit rates, crucial for optical communication systems. The overall quality of a digital signal in these two types of lasers is compared using eye diagrams and quantified by improved Q-factors and bit-error-rates in spin-lasers. Surprisingly, an optimal performance of spin-lasers requires finite, not infinite, spin-relaxation times, giving a guidance for the design of future spin-lasers

  2. Quantum spin transport in semiconductor nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Schindler, Christoph

    2012-05-15

    In this work, we study and quantitatively predict the quantum spin Hall effect, the spin-orbit interaction induced intrinsic spin-Hall effect, spin-orbit induced magnetizations, and spin-polarized electric currents in nanostructured two-dimensional electron or hole gases with and without the presence of magnetic fields. We propose concrete device geometries for the generation, detection, and manipulation of spin polarization and spin-polarized currents. To this end a novel multi-band quantum transport theory, that we termed the multi-scattering Buettiker probe model, is developed. The method treats quantum interference and coherence in open quantum devices on the same footing as incoherent scattering and incorporates inhomogeneous magnetic fields in a gauge-invariant and nonperturbative manner. The spin-orbit interaction parameters that control effects such as band energy spin splittings, g-factors, and spin relaxations are calculated microscopically in terms of an atomistic relativistic tight-binding model. We calculate the transverse electron focusing in external magnetic and electric fields. We have performed detailed studies of the intrinsic spin-Hall effect and its inverse effect in various material systems and geometries. We find a geometry dependent threshold value for the spin-orbit interaction for the inverse intrinsic spin-Hall effect that cannot be met by n-type GaAs structures. We propose geometries that spin polarize electric current in zero magnetic field and analyze the out-of-plane spin polarization by all electrical means. We predict unexpectedly large spin-orbit induced spin-polarization effects in zero magnetic fields that are caused by resonant enhancements of the spin-orbit interaction in specially band engineered and geometrically designed p-type nanostructures. We propose a concrete realization of a spin transistor in HgTe quantum wells, that employs the helical edge channel in the quantum spin Hall effect.

  3. Quantum spin transport in semiconductor nanostructures

    International Nuclear Information System (INIS)

    Schindler, Christoph

    2012-01-01

    In this work, we study and quantitatively predict the quantum spin Hall effect, the spin-orbit interaction induced intrinsic spin-Hall effect, spin-orbit induced magnetizations, and spin-polarized electric currents in nanostructured two-dimensional electron or hole gases with and without the presence of magnetic fields. We propose concrete device geometries for the generation, detection, and manipulation of spin polarization and spin-polarized currents. To this end a novel multi-band quantum transport theory, that we termed the multi-scattering Buettiker probe model, is developed. The method treats quantum interference and coherence in open quantum devices on the same footing as incoherent scattering and incorporates inhomogeneous magnetic fields in a gauge-invariant and nonperturbative manner. The spin-orbit interaction parameters that control effects such as band energy spin splittings, g-factors, and spin relaxations are calculated microscopically in terms of an atomistic relativistic tight-binding model. We calculate the transverse electron focusing in external magnetic and electric fields. We have performed detailed studies of the intrinsic spin-Hall effect and its inverse effect in various material systems and geometries. We find a geometry dependent threshold value for the spin-orbit interaction for the inverse intrinsic spin-Hall effect that cannot be met by n-type GaAs structures. We propose geometries that spin polarize electric current in zero magnetic field and analyze the out-of-plane spin polarization by all electrical means. We predict unexpectedly large spin-orbit induced spin-polarization effects in zero magnetic fields that are caused by resonant enhancements of the spin-orbit interaction in specially band engineered and geometrically designed p-type nanostructures. We propose a concrete realization of a spin transistor in HgTe quantum wells, that employs the helical edge channel in the quantum spin Hall effect.

  4. Dynamics of polymers in elongational flow studied by the neutron spin-echo technique

    International Nuclear Information System (INIS)

    Rheinstaedter, Maikel C.; Sattler, Rainer; Haeussler, Wolfgang; Wagner, Christian

    2010-01-01

    The nanoscale fluctuation dynamics of semidilute high molecular weight polymer solutions of polyethylenoxide (PEO) in D 2 O under non-equilibrium flow conditions were studied by the neutron spin-echo technique. The sample cell was in contraction flow geometry and provided a pressure driven flow with a high elongational component that stretched the polymers most efficiently. Neutron scattering experiments in dilute polymer solutions are challenging because of the low polymer concentration and corresponding small quasi-elastic signals. A relaxation process with relaxation times of about 10 ps was observed, which shows anisotropic dynamics with applied flow.

  5. SPINning parallel systems software

    International Nuclear Information System (INIS)

    Matlin, O.S.; Lusk, E.; McCune, W.

    2002-01-01

    We describe our experiences in using Spin to verify parts of the Multi Purpose Daemon (MPD) parallel process management system. MPD is a distributed collection of processes connected by Unix network sockets. MPD is dynamic processes and connections among them are created and destroyed as MPD is initialized, runs user processes, recovers from faults, and terminates. This dynamic nature is easily expressible in the Spin/Promela framework but poses performance and scalability challenges. We present here the results of expressing some of the parallel algorithms of MPD and executing both simulation and verification runs with Spin

  6. Spin Transport in Nondegenerate Si with a Spin MOSFET Structure at Room Temperature

    Science.gov (United States)

    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.

  7. Sensitivity optimization of Bell-Bloom magnetometers by manipulation of atomic spin synchronization

    Science.gov (United States)

    Ranjbaran, M.; Tehranchi, M. M.; Hamidi, S. M.; Khalkhali, S. M. H.

    2018-05-01

    Many efforts have been devoted to the developments of atomic magnetometers for achieving the high sensitivity required in biomagnetic applications. To reach the high sensitivity, many types of atomic magnetometers have been introduced for optimization of the creation and relaxation rates of atomic spin polarization. In this paper, regards to sensitivity optimization techniques in the Mx configuration, we have proposed a novelty approach for synchronization of the spin precession in the Bell-Bloom magnetometers. We have utilized the phenomenological Bloch equations to simulate the spin dynamics when modulation of pumping light and radio frequency magnetic field were both used for atomic spin synchronization. Our results showed that the synchronization process, improved the magnetometer sensitivity respect to the classical configurations.

  8. Spin temperatures under dynamic polarization in a one-dimensional system, the TANOL

    International Nuclear Information System (INIS)

    Barjhoux, Yves.

    1974-01-01

    A quantitative model of Tanol submitted to dynamic polarization has been developed. The spin systems are described using a network of interconnected reservoirs. The model involves six (or ten) Zeeman nuclear reservoirs mutually coupled by nuclear-nuclear dipole interactions and coupled to electron spins by hyperfine interactions. When the electronic line is saturated, different nuclear temperatures appear in the molecule. These temperatures have been calculated as a function of the magnetic field orientation against the crystallographic axes. Experimental results are correctly reproduced. A quantitative agreement is obtained for the anisotropy of total polarization. The calculation also shows that, in certain directions, positive and negative spin temperatures simultaneously appear, that explains the complex shape of the signals observed. Nuclear relaxation processes involving two electron spins of the same exchange chain are taken into account for the calculation. The different possible chain directions (a, a+c, or c vectors) were envisaged. Only the c-vector hypothesis succeeded in interpreting experimental results [fr

  9. Distorted spin dependent spectral function of {sup 3}He and semi-inclusive deep inelastic scattering processes

    Energy Technology Data Exchange (ETDEWEB)

    Kaptari, Leonya P. [University of Perugia (Italy); INFN-Perugia (Italy); Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Joint Inst. for Nuclear Research, Dubna (Russia); Del Dotto, Alessio [University of Rome, Rome (Italy); INFN-Roma (Italy); Pace, Emanuele [University of Rome (Italy); INFN-Tor Vergata (Italy); Salme, Giovanni [INFN-Roma (Italy); Scopetta, Sergio [University of Perugia (Italy); INFN-Perugia (Italy)

    2014-03-01

    The spin dependent spectral function, relevant to describe polarized electron scattering off polarized {sup 3}He, is studied, within the Plane Wave Impulse Approximation and taking into account final state interaction effects (FSI). In particular, the case of semi-inclusive deep inelastic scattering (SiDIS) is considered, evaluating the FSI of the hadronizing quark with the nuclear remnants. It is shown that particular kinematical regions can be selected to minimize the latter effects, so that parton distributions in the neutron can be accessed. On the other side, in the regions where FSI dominates, the considered reactions can elucidate the mechanism of hadronization of quarks during the propagation in the nuclear medium. It is shown that the obtained spin dependent spectral function can be directly applied to investigate the SiDIS reaction e-vector + {sup 3}He-vector to h+X, where the hadron h originates from the current fragmentation. Experiments of this type are being performed at JLab to extract neutron transverse momentum dependent parton distributions. As a case study, a different SiDIS process, with detection of slow (A-1) systems in the final state, is considered in more details, in order to establish when nuclear structure effects and FSI can be distinguished from elementary reactions on quasi-free nucleons. It is argued that, by a proper choice of kinematics, the origin of nuclear effects in polarized DIS phenomena and the details of the interaction between the hadronizing quark and the nuclear medium can be investigated at a level which is not reachable in inclusive deep inelastic scattering.

  10. Proton NMR relaxation in hydrous melts

    International Nuclear Information System (INIS)

    Braunstein, J.; Bacarella, A.L.; Benjamin, B.M.; Brown, L.L.; Girard, C.

    1976-01-01

    Pulse and continuous wave NMR measurements are reported for protons in hydrous melts of calcium nitrate at temperatures between -4 and 120 0 C. Although measured in different temperature ranges, spin-lattice (T 1 ) and spin-spin (T 2 ) relaxation times appear to be nearly equal to each other and proportional to the self-diffusion coefficients of solute metal cations such as Cd 2+ . At temperatures near 50 0 C, mean Arrhenius coefficients Δ H/sub T 1 / (kcal/mol) are 7.9, 7.3, and 4.8, respectively, for melts containing 2.8, 4.0, and 8.0 moles of water per mole of calcium nitrate, compared to 4.6 kcal/mol for pure water. Temperature dependence of T 1 and T 2 in Ca(NO 3 ) 2 -2.8 H 2 O between -4 and 120 0 C are non-Arrhenius and can be represented by a Fulcher-type equation with a ''zero mobility temperature'' (T 0 ) of 225 0 K, close to the value of T 0 for solute diffusion, electrical conductance and viscosity. Resolution of the relaxation rates into correlation times for intramolecular (rotational) and intermolecular (translational) diffusional motion is discussed in terms of the Bloembergen-Purcell-Pound and more recent models for dipolar relaxation

  11. Analyzing the Effect of Spinning Process Variables on Draw Frame Blended Cotton Mélange Yarn Quality

    Science.gov (United States)

    Ray, Suchibrata; Ghosh, Anindya; Banerjee, Debamalya

    2017-12-01

    An investigation has been made to study the effect of important spinning process variables namely shade depth, ring frame spindle speed and yarn twist multiplier (TM) on various yarn quality parameters like unevenness, strength, imperfection, elongation at break and hairiness index of draw frame blended cotton mélange yarn. Three factors Box and Behnken design of experiment has been used to conduct the study. The quadratic regression model is used to device the statistical inferences about sensitivity of the yarn quality parameters to the different process variables. The response surfaces are constructed for depicting the geometric representation of yarn quality parameters plotted as a function of process variables. Analysis of the results show that yarn strength of draw frame blended cotton mélange yarn is significantly affected by shade depth and TM. Yarn unevenness is affected by shade depth and ring frame spindle speed. Yarn imperfection level is mainly influenced by the shade depth and spindle speed. The shade depth and yarn TM have shown significant impact on yarn hairiness index.

  12. Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation

    Directory of Open Access Journals (Sweden)

    Srinivasa Rao Singamaneni

    2014-04-01

    Full Text Available Electronic spin transport properties of graphene nanoribbons (GNRs are influenced by the presence of adatoms, adsorbates and edge functionalization. To improve the understanding of the factors that influence the spin properties of GNRs, local (element spin-sensitive techniques such as electron spin resonance (ESR spectroscopy are important for spintronics applications. Here, we present results of multi-frequency continuous wave (CW, pulse and hyperfine sublevel correlation (HYSCORE ESR spectroscopy measurements performed on oxidatively unzipped graphene nanoribbons (GNRs, which were subsequently chemically converted (CCGNRs with hydrazine. ESR spectra at 336 GHz reveal an isotropic ESR signal from the CCGNRs, of which the temperature dependence of its line width indicates the presence of localized unpaired electronic states. Upon functionalization of CCGNRs with 4-nitrobenzene diazonium tetrafluoroborate, the ESR signal is found to be 2 times narrower than that of pristine ribbons. NH3 adsorption/desorption on CCGNRs is shown to narrow the signal, while retaining the signal intensity and g value. The electron spin-spin relaxation process at 10 K is found to be characterized by slow (163 ns and fast (39 ns components. HYSCORE ESR data demonstrate the explicit presence of protons and 13C atoms. With the provided identification of intrinsic point magnetic defects such as proton and 13C has been reported, which are roadblocks to spin travel in graphene-based materials, this work could help in advancing the present fundamental understanding on the edge-spin (or magnetic-based transport properties of CCGNRs.

  13. A mixed relaxed clock model

    Science.gov (United States)

    2016-01-01

    Over recent years, several alternative relaxed clock models have been proposed in the context of Bayesian dating. These models fall in two distinct categories: uncorrelated and autocorrelated across branches. The choice between these two classes of relaxed clocks is still an open question. More fundamentally, the true process of rate variation may have both long-term trends and short-term fluctuations, suggesting that more sophisticated clock models unfolding over multiple time scales should ultimately be developed. Here, a mixed relaxed clock model is introduced, which can be mechanistically interpreted as a rate variation process undergoing short-term fluctuations on the top of Brownian long-term trends. Statistically, this mixed clock represents an alternative solution to the problem of choosing between autocorrelated and uncorrelated relaxed clocks, by proposing instead to combine their respective merits. Fitting this model on a dataset of 105 placental mammals, using both node-dating and tip-dating approaches, suggests that the two pure clocks, Brownian and white noise, are rejected in favour of a mixed model with approximately equal contributions for its uncorrelated and autocorrelated components. The tip-dating analysis is particularly sensitive to the choice of the relaxed clock model. In this context, the classical pure Brownian relaxed clock appears to be overly rigid, leading to biases in divergence time estimation. By contrast, the use of a mixed clock leads to more recent and more reasonable estimates for the crown ages of placental orders and superorders. Altogether, the mixed clock introduced here represents a first step towards empirically more adequate models of the patterns of rate variation across phylogenetic trees. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’. PMID:27325829

  14. Theoretical studies of nonadiabatic and spin-forbidden processes: Investigations of the reactions and spectroscopy of radical species relevant to combustion reactions and diagnostics

    Energy Technology Data Exchange (ETDEWEB)

    Yarkony, D.R. [Johns Hopkins Univ., Baltimore, MD (United States)

    1993-12-01

    This research program focusses on studies of spin-forbidden and electronically nonadiabatic processes involving radical species relevant to combustion reactions and combustion diagnostics. To study the electronic structure aspects of these processes a unique and powerful system of electronic structure programs, developed over the past nine years, the BROOKLYN codes, is employed. These programs enable the authors to address questions basic to the understanding of elementary combustion processes not tractable using more standard quantum chemistry codes.

  15. Crossover between spin swapping and Hall effect in disordered systems

    KAUST Repository

    Saidaoui, Hamed Ben Mohamed

    2015-07-16

    We theoretically study the crossover between spin Hall effect and spin swapping, a recently predicted phenomenon that consists of the interchange between the current flow and its spin polarization directions [M. B. Lifshits and M. I. Dyakonov, Phys. Rev. Lett. 103, 186601 (2009)]. Using a tight-binding model with spin-orbit coupled disorder, spin Hall effect, spin relaxation, and spin swapping are treated on equal footing. We demonstrate that spin swapping and spin Hall effect present very different dependencies as a function of the spin-orbit coupling and disorder strengths and confirm that the former exceeds the latter in the parameter range considered. Three setups are proposed for the experimental observation of the spin swapping effect.

  16. Spin dynamics in SiGe quantum dot lines and ring molecules

    Science.gov (United States)

    Zinovieva, A. F.; Nenashev, A. V.; Dvurechenskii, A. V.

    2016-04-01

    Semiconductor quantum dot (QD) structures can be used as a model for understanding the effect of the microscopic structure, symmetry of crystals, and molecules on their macroscopic properties. In this work, the results of two theoretical approaches demonstrate that the spin dynamics in ordered QD structures depends on the size, spatial configuration, and topology of the object built of QDs. It was shown that the spin dynamics in QD structures with the hopping regime of conductivity significantly differs from the spin dynamics in two-dimensional (2D) and three-dimensional (3D) structures being at the other side of the metal-insulator transition. The special character of the effective magnetic field δ H fluctuations appearing only during tunneling between quantum dots is responsible for the insensitivity of spin relaxation times to the magnitude of the external magnetic field in infinite QD structures (2D square lattice and 1D linear QD chain). In finite QD structures (QD rings and linear chains), an external magnetic field H0 is directly involved in the spin relaxation process and spin is lost due to interaction with a special combination of fields Δ H ˜[H0×δ H ]/δ H that leads to an unusual orientation dependence of ESR linewidth, recently observed for QD chains. It was shown that the ordering of QD structures can be used for the conservation of spin orientation. For 1D finite quantum dot chains, the ordering can provide the stabilization of all spin components Sx,Sy, and Sz, while for ringlike molecules only Sz polarization can be stabilized. The results obtained in this work can be useful for development of novel semiconductor devices and in quantum information processing.

  17. Zero-field NMR study on a spin glass: iron-doped 2H-niobium diselenide

    International Nuclear Information System (INIS)

    Chen, M.C.

    1982-01-01

    Spin echoes are used to study the 93 Nb NQR in 2H-NbSe 2 Fe/sub x/. Measured are (intensity) x (temperature), and T/sub 1P/ (spin-lattice relaxation parameter) and T 2 (spin-spin relaxation time) as a function of temperature. Data reveal dramatic differences between non-spin glass samples (x = 0, 0.25%, 1% and 5%) and spin glass samples (x = 8%, 10% and 12%). All of the NQR results and the model calculation of the correlation times of Fe spins are best described by the phase transition picture of spin glasses

  18. Mechanical relaxation in glasses

    International Nuclear Information System (INIS)

    Hiki, Y.

    2004-01-01

    The basic properties of glasses and the characteristics of mechanical relaxation in glasses were briefly reviewed, and then our studies concerned were presented. Experimental methods adopted were viscosity, internal friction, ultrasonic attenuation, and Brillouin scattering measurements. The specimens used were several kinds of inorganic, organic, and metallic glasses. The measurements were mainly carried out from the room temperature up to the glass transition temperature, and the relaxation time was determined as a function of temperature. The 'double relaxation' composed of two Arrhenius-type relaxations was observed in many materials. In both relaxations, the 'compensation effect' showing a correlation of the pre-exponential factor and the activation energy was observed. These results were explained by considering the 'complex relaxation' due to cooperative motions of atoms or group of atoms. Values of activation energy near the glass transition determined by the various experimental methods were compared with each other

  19. Spin injection, accumulation, and precession in a mesoscopic nonmagnetic metal island

    NARCIS (Netherlands)

    Zaffalon, M; van Wees, BJ

    We experimentally study spin accumulation in an aluminum island with all dimensions smaller than the spin-relaxation length, so that the spin imbalance throughout the island is uniform. Electrical injection and detection of the spin accumulation are carried out in a four-terminal geometry by means

  20. Nuclear magnetic relaxation in aqueous praseodymium and europium solutions

    International Nuclear Information System (INIS)

    Lopez, J.L.; Diaz, D.

    1991-01-01

    A general theory for the relaxation of the nuclear spin in paramagnetic complexes where the electronic spin is within a slow-movement regime was presented by Benetis et al. and applied to d-group elements (Ni 2+ , Co 2+ ). This paper show the possibility to apply such formalism to f-group elements and it was developed for S=3(Eu 3+ ). A group of magnitudes characterizing the microstructure and dynamics of these solutions is reported with the approximations used. The dispersion of the nuclear magnetic relaxation (NMRD) for the proton of the variable field was also assessed which had a similar behaviour to what was experimentally reported