Science.gov

Sample records for magnetic critical scattering

  1. MAGNETIC NEUTRON SCATTERING

    SciTech Connect

    ZALIZNYAK,I.A.; LEE,S.H.

    2004-07-30

    Much of our understanding of the atomic-scale magnetic structure and the dynamical properties of solids and liquids was gained from neutron-scattering studies. Elastic and inelastic neutron spectroscopy provided physicists with an unprecedented, detailed access to spin structures, magnetic-excitation spectra, soft-modes and critical dynamics at magnetic-phase transitions, which is unrivaled by other experimental techniques. Because the neutron has no electric charge, it is an ideal weakly interacting and highly penetrating probe of matter's inner structure and dynamics. Unlike techniques using photon electric fields or charged particles (e.g., electrons, muons) that significantly modify the local electronic environment, neutron spectroscopy allows determination of a material's intrinsic, unperturbed physical properties. The method is not sensitive to extraneous charges, electric fields, and the imperfection of surface layers. Because the neutron is a highly penetrating and non-destructive probe, neutron spectroscopy can probe the microscopic properties of bulk materials (not just their surface layers) and study samples embedded in complex environments, such as cryostats, magnets, and pressure cells, which are essential for understanding the physical origins of magnetic phenomena. Neutron scattering is arguably the most powerful and versatile experimental tool for studying the microscopic properties of the magnetic materials. The magnitude of the cross-section of the neutron magnetic scattering is similar to the cross-section of nuclear scattering by short-range nuclear forces, and is large enough to provide measurable scattering by the ordered magnetic structures and electron spin fluctuations. In the half-a-century or so that has passed since neutron beams with sufficient intensity for scattering applications became available with the advent of the nuclear reactors, they have became indispensable tools for studying a variety of important areas of modern science

  2. Magnetic diffuse scattering

    SciTech Connect

    Cable, J.W.

    1987-01-01

    The diffuse scattering of neutrons from magnetic materials provides unique and important information regarding the spatial correlations of the atoms and the spins. Such measurements have been extensively applied to magnetically ordered systems, such as the ferromagnetic binary alloys, for which the observed correlations describe the magnetic moment fluctuations associated with local environment effects. With the advent of polarization analysis, these techniques are increasingly being applied to study disordered paramagnetic systems such as the spin-glasses and the diluted magnetic semiconductors. The spin-pair correlations obtained are essential in understanding the exchange interactions of such systems. In this paper, we describe recent neutron diffuse scattering results on the atom-pair and spin-pair correlations in some of these disordered magnetic systems. 56 refs.

  3. Zeno: Critical Fluid Light Scattering Experiment

    NASA Technical Reports Server (NTRS)

    Gammon, Robert W.; Shaumeyer, J. N.; Briggs, Matthew E.; Boukari, Hacene; Gent, David A.; Wilkinson, R. Allen

    1996-01-01

    The Zeno (Critical Fluid Light Scattering) experiment is the culmination of a long history of critical fluid light scattering in liquid-vapor systems. The major limitation to making accurate measurements closer to the critical point was the density stratification which occurs in these extremely compressible fluids. Zeno was to determine the critical density fluctuation decay rates at a pair of supplementary angles in the temperature range 100 mK to 100 (mu)K from T(sub c) in a sample of xenon accurately loaded to the critical density. This paper gives some highlights from operating the instrument on two flights March, 1994 on STS-62 and February, 1996 on STS-75. More detail of the experiment Science Requirements, the personnel, apparatus, and results are displayed on the Web homepage at http://www.zeno.umd.edu.

  4. Multiple magnetic scattering in small-angle neutron scattering of Nd–Fe–B nanocrystalline magnet

    PubMed Central

    Ueno, Tetsuro; Saito, Kotaro; Yano, Masao; Ito, Masaaki; Shoji, Tetsuya; Sakuma, Noritsugu; Kato, Akira; Manabe, Akira; Hashimoto, Ai; Gilbert, Elliot P.; Keiderling, Uwe; Ono, Kanta

    2016-01-01

    We have investigated the influence of multiple scattering on the magnetic small-angle neutron scattering (SANS) from a Nd–Fe–B nanocrystalline magnet. We performed sample-thickness- and neutron-wavelength-dependent SANS measurements, and observed the scattering vector dependence of the multiple magnetic scattering. It is revealed that significant multiple scattering exists in the magnetic scattering rather than the nuclear scattering of Nd–Fe–B nanocrystalline magnet. It is considered that the mean free path of the neutrons for magnetic scattering is rather short in Nd–Fe–B magnets. We analysed the SANS data by the phenomenological magnetic correlation model considering the magnetic microstructures and obtained the microstructural parameters. PMID:27321149

  5. Multiple magnetic scattering in small-angle neutron scattering of Nd-Fe-B nanocrystalline magnet

    NASA Astrophysics Data System (ADS)

    Ueno, Tetsuro; Saito, Kotaro; Yano, Masao; Ito, Masaaki; Shoji, Tetsuya; Sakuma, Noritsugu; Kato, Akira; Manabe, Akira; Hashimoto, Ai; Gilbert, Elliot P.; Keiderling, Uwe; Ono, Kanta

    2016-06-01

    We have investigated the influence of multiple scattering on the magnetic small-angle neutron scattering (SANS) from a Nd-Fe-B nanocrystalline magnet. We performed sample-thickness- and neutron-wavelength-dependent SANS measurements, and observed the scattering vector dependence of the multiple magnetic scattering. It is revealed that significant multiple scattering exists in the magnetic scattering rather than the nuclear scattering of Nd-Fe-B nanocrystalline magnet. It is considered that the mean free path of the neutrons for magnetic scattering is rather short in Nd-Fe-B magnets. We analysed the SANS data by the phenomenological magnetic correlation model considering the magnetic microstructures and obtained the microstructural parameters.

  6. Multiple magnetic scattering in small-angle neutron scattering of Nd-Fe-B nanocrystalline magnet.

    PubMed

    Ueno, Tetsuro; Saito, Kotaro; Yano, Masao; Ito, Masaaki; Shoji, Tetsuya; Sakuma, Noritsugu; Kato, Akira; Manabe, Akira; Hashimoto, Ai; Gilbert, Elliot P; Keiderling, Uwe; Ono, Kanta

    2016-06-20

    We have investigated the influence of multiple scattering on the magnetic small-angle neutron scattering (SANS) from a Nd-Fe-B nanocrystalline magnet. We performed sample-thickness- and neutron-wavelength-dependent SANS measurements, and observed the scattering vector dependence of the multiple magnetic scattering. It is revealed that significant multiple scattering exists in the magnetic scattering rather than the nuclear scattering of Nd-Fe-B nanocrystalline magnet. It is considered that the mean free path of the neutrons for magnetic scattering is rather short in Nd-Fe-B magnets. We analysed the SANS data by the phenomenological magnetic correlation model considering the magnetic microstructures and obtained the microstructural parameters.

  7. Scattering in a magnetic field

    SciTech Connect

    David C. Carey

    2002-08-19

    The fixed target program at Fermilab has come to an end. New projects are in the planning stage. Among them is a muon storage ring. Up to the present, all storage rings in high-energy physics have carried stable particles, namely the electron and proton and their antiparticles. The muon is unstable and decays with a mean lifetime of 2.0 x 10{sup -6} sec. Two types of cooling have been used in the past. One is stochastic cooling where an electrode is used to detect the positions of the particles and send a signal to another position across the ring. Through successive applications of this technique, the phase space is ultimately greatly reduced and beams can be made to collide with a useful event rate. The second type of cooling is electron cooling. Here protons and electrons are made to travel together for a short distance. Equipartition causes transfer of transverse energy of the protons to that of the electrons. Neither of these methods is fast enough to allow acceleration of a sufficient number of muons up to maximum energy before they decay. A new method known as ionization cooling has been proposed.[1] The muons are cooled by passing them through a container of liquid hydrogen. The energy loss reduces both transverse and longitudinal momentum. The longitudinal momentum is restored with RF cavities. The net result is to maintain the longitudinal momentum while cooling the transverse momentum. To minimize the total travel distance of the muons the liquid hydrogen is placed inside the focusing solenoids. The question arises as to whether the presence of the solenoids influences the phase space occupied by the muons. After the muon scatters it has transverse momentum. In a constant longitudinal magnetic field the trajectory wraps around the field lines and coincides in momentum and position with a particle which scatters one cycle later. Here we calculate the change in emittance for both a drift space and a solenoid. We find that the presence of the solenoid does

  8. Quantum Criticality in an Organic Magnet

    SciTech Connect

    Stone, Matthew B; Broholm, C. L.; Reich, D. H.; Tchemyshyov, O.; Vorderwisch, P.; Harrison, N.

    2006-01-01

    Exchange interactions between S=1/2 sites in piperazinium hexachlorodicuprate produce a frustrated bilayer magnet with a singlet ground state. We have determined the field-temperature phase diagram by high field magnetization and neutron scattering experiments. There are two quantum critical points: H{sub c1}=7.5 T separates a quantum paramagnet phase from a three dimensional, antiferromagnetically ordered state while H{sub c2}=37 T marks the onset of a fully polarized state. The ordered phase, which we describe as a magnon Bose-Einstein condensate (BEC), is embedded in a quantum critical regime with short range correlations. A low temperature anomaly in the BEC phase boundary indicates that additional low energy features of the material become important near H{sub c1}.

  9. Probing fine magnetic particles with neutron scattering

    SciTech Connect

    Pynn, R.

    1991-12-31

    Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and colloidal suspensions of magnetic particles, known as ferrofluids. Diffraction, surface reflection, and small angle neutron scattering (SANS) are the techniques used. With the exception of surface reflection, these methods are described in this article. The combination of SANS with refractive-index matching and neutron polarisation analysis is particularly powerful because it allows the magnetic and atomic structures to be determined independently. This technique has been used to study both dilute and concentrated ferrofluid suspensions of relatively monodisperse cobalt particles, subjected to a series of applied magnetic fields. The size of the cobalt particle core and the surrounding surfactant layer were determined. The measured interparticle structure factor agrees well with a recent theory that allows correlations in binary mixtures of magnetic particles to be calculated in the case of complete magnetic alignment. When one of the species in such a binary mixture is a nonmagnetic, cyclindrical macromolecule, application of a magnetic field leads to some degree of alignment of the nonmagnetic species. This result has been demonstrated with tobacco mosaic virus suspended in a water-based ferrofluid.

  10. Probing fine magnetic particles with neutron scattering

    SciTech Connect

    Pynn, R.

    1991-01-01

    Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and colloidal suspensions of magnetic particles, known as ferrofluids. Diffraction, surface reflection, and small angle neutron scattering (SANS) are the techniques used. With the exception of surface reflection, these methods are described in this article. The combination of SANS with refractive-index matching and neutron polarisation analysis is particularly powerful because it allows the magnetic and atomic structures to be determined independently. This technique has been used to study both dilute and concentrated ferrofluid suspensions of relatively monodisperse cobalt particles, subjected to a series of applied magnetic fields. The size of the cobalt particle core and the surrounding surfactant layer were determined. The measured interparticle structure factor agrees well with a recent theory that allows correlations in binary mixtures of magnetic particles to be calculated in the case of complete magnetic alignment. When one of the species in such a binary mixture is a nonmagnetic, cyclindrical macromolecule, application of a magnetic field leads to some degree of alignment of the nonmagnetic species. This result has been demonstrated with tobacco mosaic virus suspended in a water-based ferrofluid.

  11. Neutron scattering investigations of frustated magnets

    NASA Astrophysics Data System (ADS)

    Fennell, Tom

    This thesis describes the experimental investigation of frustrated magnetic systems based on the pyrochlore lattice of corner-sharing tetrahedra. Ho2Ti207 and Dy2Ti207 are examples of spin ices, in which the manifold of disordered magnetic groundstates maps onto that of the proton positions in ice. Using single crystal neutron scattering to measure Bragg and diffuse scattering, the effect of applying magnetic fields along different directions in the crystal was investigated. Different schemes of degeneracy removal were observed for different directions. Long and short range order, and the coexistence of both could be observed by this technique.The field and temperature dependence of magnetic ordering was studied in Ho2Ti207 and Dy2Ti207. Ho2Ti2()7 has been more extensively investigated. The field was applied on [00l], [hh0], [hhh] and [hh2h]. Dy2Ti207 was studied with the field applied on [00l] and [hho] but more detailed information about the evolution of the scattering pattern across a large area of reciprocal space was obtained.With the field applied on [00l] both materials showed complete degeneracy removal. A long range ordered structure was formed. Any magnetic diffuse scattering vanished and was entirely replaced by strong magnetic Bragg scattering. At T =0.05 K both materials show unusual magnetization curves, with a prominent step and hysteresis. This was attributed to the extremely slow dynamics of spin ice materials at this temperature.Both materials were studied in greatest detail with the field applied on [hh0]. The coexistence of long and short range order was observed when the field was raised at T = 0.05 K. The application of a field in this direction separated the spin system into two populations. One could be ordered by the field, and one remained disordered. However, via spin-spin interactions, the field restricted the degeneracy of the disordered spin population. The neutron scattering pattern of Dy2Ti207 shows that the spin system was separated

  12. Inverse scattering problem in turbulent magnetic fluctuations

    NASA Astrophysics Data System (ADS)

    Treumann, Rudolf A.; Baumjohann, Wolfgang; Narita, Yasuhito

    2016-08-01

    We apply a particular form of the inverse scattering theory to turbulent magnetic fluctuations in a plasma. In the present note we develop the theory, formulate the magnetic fluctuation problem in terms of its electrodynamic turbulent response function, and reduce it to the solution of a special form of the famous Gelfand-Levitan-Marchenko equation of quantum mechanical scattering theory. The last of these applies to transmission and reflection in an active medium. The theory of turbulent magnetic fluctuations does not refer to such quantities. It requires a somewhat different formulation. We reduce the theory to the measurement of the low-frequency electromagnetic fluctuation spectrum, which is not the turbulent spectral energy density. The inverse theory in this form enables obtaining information about the turbulent response function of the medium. The dynamic causes of the electromagnetic fluctuations are implicit to it. Thus, it is of vital interest in low-frequency magnetic turbulence. The theory is developed until presentation of the equations in applicable form to observations of turbulent electromagnetic fluctuations as input from measurements. Solution of the final integral equation should be done by standard numerical methods based on iteration. We point to the possibility of treating power law fluctuation spectra as an example. Formulation of the problem to include observations of spectral power densities in turbulence is not attempted. This leads to severe mathematical problems and requires a reformulation of inverse scattering theory. One particular aspect of the present inverse theory of turbulent fluctuations is that its structure naturally leads to spatial information which is obtained from the temporal information that is inherent to the observation of time series. The Taylor assumption is not needed here. This is a consequence of Maxwell's equations, which couple space and time evolution. The inversion procedure takes advantage of a particular

  13. Critical Magnetic Field Determination of Superconducting Materials

    SciTech Connect

    Canabal, A.; Tajima, T.; Dolgashev, V.A.; Tantawi, S.G.; Yamamoto, T.; /Tsukuba, Natl. Res. Lab. Metrol.

    2011-11-04

    Superconducting RF technology is becoming more and more important. With some recent cavity test results showing close to or even higher than the critical magnetic field of 170-180 mT that had been considered a limit, it is very important to develop a way to correctly measure the critical magnetic field (H{sup RF}{sub c}) of superconductors in the RF regime. Using a 11.4 GHz, 50-MW, <1 {mu}s, pulsed power source and a TE013-like mode copper cavity, we have been measuring critical magnetic fields of superconductors for accelerator cavity applications. This device can eliminate both thermal and field emission effects due to a short pulse and no electric field at the sample surface. A model of the system is presented in this paper along with a discussion of preliminary experimental data.

  14. Magnetic-field induced critical endpoint

    NASA Astrophysics Data System (ADS)

    Rechenberger, Stefan

    2017-03-01

    The phase diagram of strong interaction matter is analyzed utilizing the Nambu-Jona-Lasinio model. Special emphasis is placed on its dependence on an external magnetic field and isospin chemical potential. Using flavor mixing induced by instanton effects the influence of isospin breaking due to the magnetic field and the isospin chemical potential is compared. It is found that at low temperatures and large quark chemical potential the magnetic field, depending on its strength, induces a new critical endpoint or a triple point.

  15. Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn5

    DOE PAGES

    Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; ...

    2016-06-27

    The thermal conductivity κ of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc2, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ/T with fieldmore » reveals that the electron-electron scattering (or transport mass m*) of those unpaired electrons diverges as H→Hc2 from below, in the same way that it does in the normal state as H→Hc2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn5 at H*=Hc2 even from inside the superconducting state. In conclusion, the fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.« less

  16. Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn5

    NASA Astrophysics Data System (ADS)

    Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; Shakeripour, H.; Petrovic, C.; Taillefer, Louis

    2016-07-01

    The thermal conductivity κ of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H , for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc 2, κ /T is found to increase as T →0 , just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ /T with field reveals that the electron-electron scattering (or transport mass m⋆) of those unpaired electrons diverges as H →Hc 2 from below, in the same way that it does in the normal state as H →Hc 2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn5 at H⋆=Hc 2 even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k -space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.

  17. Absolute cross-section normalization of magnetic neutron scattering data.

    PubMed

    Xu, Guangyong; Xu, Zhijun; Tranquada, J M

    2013-08-01

    We discuss various methods to obtain the resolution volume for neutron scattering experiments, in order to perform absolute normalization on inelastic magnetic neutron scattering data. Examples from previous experiments are given. We also try to provide clear definitions of a number of physical quantities which are commonly used to describe neutron magnetic scattering results, including the dynamic spin correlation function and the imaginary part of the dynamic susceptibility. Formulas that can be used for general purposes are provided and the advantages of the different normalization processes are discussed.

  18. Absolute cross-section normalization of magnetic neutron scattering data

    NASA Astrophysics Data System (ADS)

    Xu, Guangyong; Xu, Zhijun; Tranquada, J. M.

    2013-08-01

    We discuss various methods to obtain the resolution volume for neutron scattering experiments, in order to perform absolute normalization on inelastic magnetic neutron scattering data. Examples from previous experiments are given. We also try to provide clear definitions of a number of physical quantities which are commonly used to describe neutron magnetic scattering results, including the dynamic spin correlation function and the imaginary part of the dynamic susceptibility. Formulas that can be used for general purposes are provided and the advantages of the different normalization processes are discussed.

  19. Thomson scattering in a magnetic field. II - Arbitrary field orientation

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara A.

    1991-01-01

    This paper presents solutions to the equation of transfer for Thomson scattering in a constant magnetic field of arbitrary orientation. Results from several atmospheres are combined to give the flux from a dipole star. The results are compared to the polarization data of the magnetic white dwarf Grw + 70 deg 8247. The fit is good, though it implies a very large polarization in the ultraviolet. Thomson scattering is not thought to be an important opacity source in white dwarfs, so the good fit is either fortuitous or is perhaps explained by assuming the magnetic field affects the polarization processes in all opacities similarly.

  20. Magnetic field contribution to the last electron-photon scattering

    NASA Astrophysics Data System (ADS)

    Giovannini, Massimo

    2010-11-01

    When the cosmic microwave photons scatter electrons just prior to the decoupling of matter and radiation, magnetic fields do contribute to the Stokes matrix as well as to the scalar, vector and tensor components of the transport equations for the brightness perturbations. The magnetized electron-photon scattering is hereby discussed in general terms by including, for the first time, the contribution of magnetic fields with arbitrary direction and in the presence of the scalar, vector and tensor modes of the geometry. The propagation of relic vectors and relic gravitons is discussed for a varying magnetic field orientation and for different photon directions. The source terms of the transport equations in the presence of the relativistic fluctuations of the geometry are also explicitly averaged over the magnetic field orientations and the problem of a consistent account of the small-scale and large-scale magnetic field is briefly outlined.

  1. Electron Scattering on a Magnetic Skyrmion in the Nonadiabatic Approximation.

    PubMed

    Denisov, K S; Rozhansky, I V; Averkiev, N S; Lähderanta, E

    2016-07-08

    We present a theory of electron scattering on a magnetic Skyrmion for the case when the exchange interaction is moderate so that the adiabatic approximation and the Berry phase approach are not applicable. The theory explains the appearance of a topological Hall current in the systems with magnetic Skyrmions, the special importance of which is its applicability to dilute magnetic semiconductors with a weak exchange interaction.

  2. Diffraction as a critical element in soft scattering

    NASA Astrophysics Data System (ADS)

    Maor, Uri

    2016-10-01

    Gribov’s partonic Pomeron provides the foundations of updated models which incorporate soft and hard scattering, so as to reproduce the recent LHC p-p cross sections. Explicitly, total, elastic, inelastic and diffrative data. Leading models are: GLM (Gotsman, Levin, Maor), KMR (Khoze, Martin, Ryskin), Kaidalov-Poghosyan and Ostapchenco. None of these models in their pre-LHC versions reproduced the TOTEM, ALICE, ATLAS and CMS soft LHC data, needing considerable reconstructions, either in the fitting procedures (GLM), or in the details of the theoretical models. In the following, I shall relate mostly to the GLM model, emphasizing the critical role of the diffractive channels.

  3. Diffraction as a Critical Element in Soft Scattering

    NASA Astrophysics Data System (ADS)

    Maor, Uri

    Gribov's partonic Pomeron provides the foundations of updated models which incorporate soft and hard scattering, so as to reproduce the recent LHC p-p cross sections. Explicitly, total, elastic, inelastic and diffrative data. Leading models are: GLM (Gotsman, Levin, Maor), KMR (Khoze, Martin, Ryskin), Kaidalov-Poghosyan and Ostapchenco. None of these models in their pre-LHC versions reproduced the TOTEM, ALICE, ATLAS and CMS soft LHC data, needing considerable reconstructions, either in the fitting procedures (GLM), or in the details of the theoretical models. In the following, I shall relate mostly to the GLM model, emphasizing the critical role of the diffractive channels.

  4. Soft x-ray resonant magnetic scattering from an imprinted magnetic domain pattern

    SciTech Connect

    Kinane,C.; Suszka, A.; Marrows, C.; Hickey, B.; Arena, D.; Dvorak, J.; Charlton, T.; Langridge, S.

    2006-01-01

    The authors report on the use of a Co/Pt multilayer, which exhibits strong perpendicular magnetic anisotropy, to magnetostatically imprint a domain pattern onto a 50 Angstroms thick Permalloy layer. Element specific soft x-ray magnetic scattering experiments were then performed so as to be sensitive to the magnetic structure of the Permalloy only. Off-specular magnetic satellite peaks, corresponding to a periodic domain stripe width of 270 nm, were observed, confirmed by magnetic force microscopy and micromagnetic modeling. Thus the authors have exploited the element specificity of soft x-ray scattering to discern the purely magnetic correlations in a structurally flat Permalloy film.

  5. Resonant Compton Scattering in Highly-Magnetized Pulsars

    NASA Astrophysics Data System (ADS)

    Wadiasingh, Zorawar

    Soft gamma repeaters and anomalous X-ray pulsars are subset of slow-rotating neutron stars, known as magnetars, that have extremely high inferred surface magnetic fields, of the order 100-1000 TeraGauss. Hard, non-thermal and pulsed persistent X-ray emission extending between 10 keV and 230 keV has been seen in a number of magnetars by RXTE, INTEGRAL, and Suzaku. In this thesis, the author considers inner magnetospheric models of such persistent hard X-ray emission where resonant Compton upscattering of soft thermal photons is anticipated to be the most efficient radiative process. This high efficiency is due to the relative proximity of the surface thermal photons, and also because the scattering becomes resonant at the cyclotron frequency. At the cyclotron resonance, the effective cross section exceeds the classical Thomson one by over two orders of magnitude, thereby enhancing the efficiency of continuum production and cooling of relativistic electrons. In this thesis, a new Sokolov and Ternov formulation of the QED Compton scattering cross section for strong magnetic fields is employed in electron cooling and emission spectra calculations. This formalism is formally correct for treating spin-dependent effects and decay rates that are important at the cyclotron resonance. The author presents electron cooling rates at arbitrary interaction points in a magnetosphere using the QED cross sections. The QED effects reduce the rates below high-field extrapolations of older magnetic Thomson results. The author also computes angle-dependent upscattering model spectra, formed using collisional integrals, for uncooled monoenergetic relativistic electrons injected in inner regions of pulsar magnetospheres. These spectra are integrated over closed field lines and obtained for different observing perspectives. The spectral cut-off energies are critically dependent on the observer viewing angles and electron Lorentz factor. It is found that electrons with energies less than

  6. Theory of neutron scattering by electrons in magnetic materials

    NASA Astrophysics Data System (ADS)

    Lovesey, S. W.

    2015-10-01

    A theory of neutron scattering by magnetic materials is reviewed with emphasis on the use of electronic multipoles that have universal appeal, because they are amenable to calculation and appear in theories of many other experimental techniques. The conventional theory of magnetic neutron scattering, which dates back to Schwinger (1937 Phys. Rev. 51 544) and Trammell (1953 Phys. Rev. 92 1387), yields an approximation for the scattering amplitude in terms of magnetic dipoles formed with the spin (S) and orbital angular momentum (L) of valence electrons. The so-called dipole-approximation has been widely adopted by researchers during the past few decades that has seen neutron scattering develop to its present status as the method of choice for investigations of magnetic structure and excitations. Looking beyond the dipole-approximation, however, reveals a wealth of additional information about electronic degrees of freedom conveniently encapsulated in magnetic multipoles. In this language, the dipole-approximation retains electronic axial dipoles, S and L. At the same level of approximation are polar dipoles—called anapoles or toroidal dipoles—allowed in the absence of a centre of inversion symmetry. Anapoles are examples of magneto-electric multipoles, time-odd and parity-odd irreducible tensors, that have come to the fore as signatures of electronic complexity in materials.

  7. Stimulated Brillouin scatter in a magnetized ionospheric plasma.

    PubMed

    Bernhardt, P A; Selcher, C A; Lehmberg, R H; Rodriguez, S P; Thomason, J F; Groves, K M; McCarrick, M J; Frazer, G J

    2010-04-23

    High power electromagnetic waves transmitted from the HAARP facility in Alaska can excite low-frequency electrostatic waves by magnetized stimulated Brillouin scatter. Either an ion-acoustic wave with a frequency less than the ion cyclotron frequency (f(CI)) or an electrostatic ion cyclotron (EIC) wave just above f(CI) can be produced. The coupled equations describing the magnetized stimulated Brillouin scatter instability show that the production of both ion-acoustic and EIC waves is strongly influenced by the wave propagation relative to the background magnetic field. Experimental observations of stimulated electromagnetic emissions using the HAARP transmitter have confirmed that only ion-acoustic waves are excited for propagation along the magnetic zenith and that EIC waves can only be detected with oblique propagation angles. The ion composition can be obtained from the measured EIC frequency.

  8. Stimulated Brillouin Scatter in a Magnetized Ionospheric Plasma

    SciTech Connect

    Bernhardt, P. A.; Selcher, C. A.; Lehmberg, R. H.; Rodriguez, S. P.; Thomason, J. F.; Groves, K. M.; McCarrick, M. J.; Frazer, G. J.

    2010-04-23

    High power electromagnetic waves transmitted from the HAARP facility in Alaska can excite low-frequency electrostatic waves by magnetized stimulated Brillouin scatter. Either an ion-acoustic wave with a frequency less than the ion cyclotron frequency (f{sub CI}) or an electrostatic ion cyclotron (EIC) wave just above f{sub CI} can be produced. The coupled equations describing the magnetized stimulated Brillouin scatter instability show that the production of both ion-acoustic and EIC waves is strongly influenced by the wave propagation relative to the background magnetic field. Experimental observations of stimulated electromagnetic emissions using the HAARP transmitter have confirmed that only ion-acoustic waves are excited for propagation along the magnetic zenith and that EIC waves can only be detected with oblique propagation angles. The ion composition can be obtained from the measured EIC frequency.

  9. REACT: Alternatives to Critical Materials in Magnets

    SciTech Connect

    2012-01-01

    REACT Project: The 14 projects that comprise ARPA-E’s REACT Project, short for “Rare Earth Alternatives in Critical Technologies”, are developing cost-effective alternatives to rare earths, the naturally occurring minerals with unique magnetic properties that are used in electric vehicle (EV) motors and wind generators. The REACT projects will identify low-cost and abundant replacement materials for rare earths while encouraging existing technologies to use them more efficiently. These alternatives would facilitate the widespread use of EVs and wind power, drastically reducing the amount of greenhouse gases released into the atmosphere.

  10. Magnetic neutron scattering by magnetic vortices in thin submicron-sized soft ferromagnetic cylinders

    PubMed Central

    Metlov, Konstantin L.; Michels, Andreas

    2016-01-01

    Using analytical expressions for the magnetization textures of thin submicron-sized magnetic cylinders in vortex state, we derive closed-form algebraic expressions for the ensuing small-angle neutron scattering (SANS) cross sections. Specifically, for the perpendicular and parallel scattering geometries, we have computed the cross sections for the case of small vortex-center displacements without formation of magnetic charges on the side faces of the cylinder. The results represent a significant qualitative and quantitative step forward in SANS-data analysis on isolated magnetic nanoparticle systems, which are commonly assumed to be homogeneously or stepwise-homogeneously magnetized. We suggest a way to extract the fine details of the magnetic vortex structure during the magnetization process from the SANS measurements in order to help resolving the long-standing question of the magnetic vortex displacement mode. PMID:27112640

  11. Magnetic neutron scattering by magnetic vortices in thin submicron-sized soft ferromagnetic cylinders

    NASA Astrophysics Data System (ADS)

    Metlov, Konstantin L.; Michels, Andreas

    2016-04-01

    Using analytical expressions for the magnetization textures of thin submicron-sized magnetic cylinders in vortex state, we derive closed-form algebraic expressions for the ensuing small-angle neutron scattering (SANS) cross sections. Specifically, for the perpendicular and parallel scattering geometries, we have computed the cross sections for the case of small vortex-center displacements without formation of magnetic charges on the side faces of the cylinder. The results represent a significant qualitative and quantitative step forward in SANS-data analysis on isolated magnetic nanoparticle systems, which are commonly assumed to be homogeneously or stepwise-homogeneously magnetized. We suggest a way to extract the fine details of the magnetic vortex structure during the magnetization process from the SANS measurements in order to help resolving the long-standing question of the magnetic vortex displacement mode.

  12. Thomson scattering in magnetic fields. [of white dwarf stars

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara

    1989-01-01

    The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.

  13. The FN method for anisotropic scattering in neutron transport theory: the critical slab problem.

    NASA Astrophysics Data System (ADS)

    Gülecyüz, M. C.; Tezcan, C.

    1996-08-01

    The FN method which has been applied to many physical problems for isotropic and anisotropic scattering in neutron transport theory is extended for problems for extremely anisotropic scattering. This method depends on the Placzek lemma and the use of the infinite medium Green's function. Here the Green's function for extremely anisotropic scattering which was expressed as a combination of the Green's functions for isotropic scattering is used to solve the critical slab problem. It is shown that the criticality condition is in agreement with the one obtained previously by reducing the transport equation for anisotropic scattering to isotropic scattering and solving using the FN method.

  14. Spin-flip scattering of critical quasiparticles and the phase diagram of YbRh2Si2

    NASA Astrophysics Data System (ADS)

    Wölfle, Peter; Abrahams, Elihu

    2015-10-01

    Several observed transport and thermodynamic properties of the heavy-fermion compound YbRh2Si2 in the quantum critical regime are unusual and suggest that the fermionic quasiparticles are critical, characterized by a scale-dependent diverging effective mass. A theory based on the concept of critical quasiparticles scattering off antiferromagnetic spin fluctuations in a strong-coupling regime has been shown to successfully explain the unusual existing data and to predict a number of so far unobserved properties. In this paper, we point out a new feature of a magnetic field-tuned quantum critical point of a heavy-fermion metal: anomalies in the transport and thermodynamic properties caused by the freezing out of spin-flip scattering of critical quasiparticles and the scattering off collective spin excitations. We show a steplike behavior as a function of magnetic field of, e.g., the Hall coefficient and magnetoresistivity results, which accounts quantitatively for the observed behavior of these quantities. That behavior has been described as a crossover line T*(H ) in the T -H phase diagram of YbRh2Si2 . Whereas some authors have interpreted this observation as signaling the breakdown of Kondo screening and an associated abrupt change of the Fermi surface, our results suggest that the T* line may be quantitatively understood within the picture of robust critical quasiparticles.

  15. Surface Raman scattering from effervescent magnetic peroxyborates

    NASA Astrophysics Data System (ADS)

    Walrafen, G. E.; Krishnan, P. N.; Hokmabadi, M.; Griscom, D. L.; Munro, R. G.

    1982-10-01

    Surface Raman scattering using a spinning technique was investigated for solid NaBO3ṡ4H2O and NaBO3ṡH2O, as well as for electron bombarded peroxyborates, for peroxyborates heated for various times and at temperatures for 110-180 °C, and for solid Na2O2 and BaO2. The Raman spectra indicate that the breakdown of peroxy groups is accompanied by the formation of trapped molecular O2. Quantitative Raman intensity data were also obtained as functions of heating time at 115 °C for the 1556 cm-1 line from O2 and for the 890 and 705 cm-1 lines whose intensities scale with the peroxy concentration. These intensity data were treated by logistics theory, and they were found to be consistent with a second-order autocatalyzed forward reaction dependent on the product of the peroxy and O2 concentrations, plus a first-order reverse reaction dependent only on the O2 concentration.

  16. Surface Raman scattering from effervescent magnetic peroxyborates

    NASA Astrophysics Data System (ADS)

    Walrafen, G. E.; Krishnan, P. N.; Griscom, D. L.; Munro, R.

    1982-06-01

    Surface Raman scattering using a spinning technique was investigated for solid NaBO3.4H2O and NaBO3.H2O as well as for electron bombarded peroxyborates heated for various times and at temperatures form 110-180 deg C, and for solid Na2O2 and BaO2. The Raman spectra indicate that the breakdown of peroxy groups is accompanied by the formation of trapped molecular O2. Quantitative Raman intensity data were also obtained as functions of heating time at 115 deg C for the 1556 cm-1 line from O2 and for the 890 and 705 cm-1 lines whose intensities scale with the peroxy concentration. These intensity data were treated by logistics theory, and they were found to be consistent with a second-order auto-catalyzed forward reaction dependent on the product of the peroxy and O2 concentrations, plus a first-order reverse reaction dependent only on the O2 concentration.

  17. Resonant magnetic scattering of polarized soft x rays

    SciTech Connect

    Sacchi, M.; Hague, C.F.; Gullikson, E.M.; Underwood, J.

    1997-04-01

    Magnetic effects on X-ray scattering (Bragg diffraction, specular reflectivity or diffuse scattering) are a well known phenomenon, and they also represent a powerful tool for investigating magnetic materials since it was shown that they are strongly enhanced when the photon energy is tuned across an absorption edge (resonant process). The resonant enhancement of the magnetic scattering has mainly been investigated at high photon energies, in order to match the Bragg law for the typical lattice spacings of crystals. In the soft X-ray range, even larger effects are expected, working for instance at the 2p edges of transition metals of the first row or at the 3d edges of rare earths (300-1500 eV), but the corresponding long wavelengths prevent the use of single crystals. Two approaches have been recently adopted in this energy range: (i) the study of the Bragg diffraction from artificial structures of appropriate 2d spacing; (ii) the analysis of the specular reflectivity, which contains analogous information but has no constraints related to the lattice spacing. Both approaches have their own specific advantages: for instance, working under Bragg conditions provides information about the (magnetic) periodicity in ordered structures, while resonant reflectivity can easily be related to electronic properties and absorption spectra. An important aspect common to all the resonant X-ray scattering techniques is the element selectivity inherent to the fact of working at a specific absorption edge: under these conditions, X-ray scattering becomes in fact a spectroscopy. Results are presented for films of iron and cobalt.

  18. Magnetic relaxations in a Tb-based single molecule magnet studied by quasielastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Kofu, Maiko; Kajiwara, Takashi; Gardner, Jason S.; Simeoni, Giovanna G.; Tyagi, Madhusudan; Faraone, Antonio; Nakajima, Kenji; Ohira-Kawamura, Seiko; Nakano, Motohiro; Yamamuro, Osamu

    2013-12-01

    By using ac magnetic susceptibility and quasielatic neutron scattering (QENS) techniques, we have investigated a magnetization relaxation phenomenon of a rare-earth based single molecule magnet, TbCuC19H20N3O16. We clearly identified and characterized two magnetic relaxations. The slower relaxation observed in the ac susceptibility is at the ms timescale around T=2 K and its activation energy is 16 K. On the other hand, the faster relaxation in the QENS measurements occurs on the timescale between ns and ps with activation energy of 174 K. The slower relaxation may occur through thermally activated tunneling among magnetic substates. We discuss two possible origins for the faster relaxation; one is a thermally activated tunneling between the higher excited states, the other is the magnetic relaxation coupled with the motion of ligands around the magnetic ions. This is the first clear observation of magnetic relaxation on the single molecule magnet revealed by QENS.

  19. Thomson scattering in a magnetic field. I - Field along z

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara A.

    1991-01-01

    The Monte Carlo method is used here to solve the radiative transfer equation for Thomson scattering in a constant magnetic field perpendicular to the atmosphere. Emergent radiation and polarization are presented for various atmospheric thicknesses. The circular polarization peaks at frequencies near the cyclotron, omega(c), and for propagation direction along the field. At low field strengths, the circular polarization is roughly proportional to omega(c)/omega; the linear polarization is proportional to the square of omega(c)/omega and the amount of circular polarization present at each scatter and is therefore much smaller than the circular polarization. The linear polarization is large for propagation direction perpendicular to the magnetic field and at frequencies near the cyclotron and in the strong-field limit. The position angle of the linear polarization undergoes a rotation of 90 deg at a value of omega(c)/omega near the square root of three.

  20. Back Compton Scattering in Strong Uniform Magnetic Field

    SciTech Connect

    Xu, W.; Huang Wei; Yan Mulin

    2006-11-02

    In this paper, we show that there is a Non-Commutative Plane (NCP) in the perpendicular magnetic fields in the accelerator, and the QED with NCP (QED-NCP) has been formulated. Being similar to the theory of quantum Hall effects, an effective filling factor f(B) is introduced, which characters the possibility occupied the LLL state by the electrons living on NCP. The back Compton scattering amplitudes of QED-NCP are derived, and the differential cross sections for the process with fixed initial polarizing electrons and photons are calculated. We propose to precisely measure the polarization dependent differential cross sections of the back Compton scattering in the perpendicular magnetic fields experimentally, which may lead to reveal the effects of QED with NCP. This should be interesting and remarkable. The existing Spring-8's data have been analyzed primitively, and some hints for QED-NCP effects are seen.

  1. Micromagnetic modeling of critical current oscillations in magnetic Josephson junctions

    NASA Astrophysics Data System (ADS)

    Golovchanskiy, I. A.; Bol'ginov, V. V.; Stolyarov, V. S.; Abramov, N. N.; Ben Hamida, A.; Emelyanova, O. V.; Stolyarov, B. S.; Kupriyanov, M. Yu.; Golubov, A. A.; Ryazanov, V. V.

    2016-12-01

    In this work we propose and explore an effective numerical approach for investigation of critical current dependence on applied magnetic field for magnetic Josephson junctions with in-plane magnetization orientation. This approach is based on micromagnetic simulation of the magnetization reversal process in the ferromagnetic layer with introduced internal magnetic stiffness and subsequent reconstruction of the critical current value using total flux or reconstructed actual phase difference distribution. The approach is flexible and shows good agreement with experimental data obtained on Josephson junctions with ferromagnetic barriers. Based on this approach we have obtained a critical current dependence on applied magnetic field for rectangular magnetic Josephson junctions with high size aspect ratio. We have shown that the rectangular magnetic Josephson junctions can be considered for application as an effective Josephson magnetic memory element with the value of critical current defined by the orientation of magnetic moment at zero magnetic field. An impact of shape magnetic anisotropy on critical current is revealed and discussed. Finally, we have considered a curling magnetic state in the ferromagnetic layer and demonstrated its impact on critical current.

  2. Crystals for neutron scattering studies of quantum magnetism

    SciTech Connect

    Yankova, Tantiana; Hüvonen, Dan; Mühlbauer, Sebastian; Schmidiger, David; Wulf, Erik; Hong, Tao; Garlea, Vasile O; Custelcean, Radu; Ehlers, Georg

    2012-01-01

    We review a strategy for targeted synthesis of large single crystal samples of prototype quantum magnets for inelastic neutron scattering experiments. Four case studies of organic copper halogenide S = 1/2 systems are presented. They are meant to illustrate that exciting experimental results pertaining to the forefront of many-body quantum physics can be obtained on samples grown using very simple techniques, standard laboratory equipment, and almost no experience in advanced crystal growth techniques.

  3. Magnetic-Polaron-Induced Enhancement of Surface Raman Scattering

    PubMed Central

    Shao, Qi; Liao, Fan; Ruotolo, Antonio

    2016-01-01

    The studies of the effects of magnetic field on surface enhanced Raman scattering (SERS) have been so far limited to the case of ferromagnetic/noble-metal, core/shell nano-particles, where the influence was always found to be negative. In this work, we investigate the influence of magnetic field on a diluted magnetic semiconductor/metal SERS system. Guided by three dimensional finite-difference time-domain simulations, a high efficient SERS substrate was obtained by diluting Mn into Au-capped ZnO, which results in an increase of the dielectric constant and, therefore, an enhancement of Raman signals. More remarkably, an increase of intensities as well as a reduction of the relative standard deviation (RSD) of Raman signals have been observed as a function of the external magnetic strength. We ascribe these positive influences to magnetic-field induced nucleation of bound magnetic polarons in the Mn doped ZnO. The combination of diluted magnetic semiconductors and SERS may open a new avenue for future magneto-optical applications. PMID:26754049

  4. Study of Magnetic Alloys: Critical Phenomena.

    DTIC Science & Technology

    MAGNETIC ALLOYS, TRANSPORT PROPERTIES), ELECTRICAL RESISTANCE, SEEBECK EFFECT , MAGNETIC PROPERTIES, ALUMINUM ALLOYS, COBALT ALLOYS, GADOLINIUM ALLOYS, GOLD ALLOYS, IRON ALLOYS, NICKEL ALLOYS, PALLADIUM ALLOYS, PLATINUM ALLOYS, RHODIUM ALLOYS

  5. Critical phenomena of emergent magnetic monopoles in a chiral magnet

    NASA Astrophysics Data System (ADS)

    Kanazawa, N.; Nii, Y.; Zhang, X.-X.; Mishchenko, A. S.; de Filippis, G.; Kagawa, F.; Iwasa, Y.; Nagaosa, N.; Tokura, Y.

    2016-05-01

    Second-order continuous phase transitions are characterized by symmetry breaking with order parameters. Topological orders of electrons, characterized by the topological index defined in momentum space, provide a distinct perspective for phase transitions, which are categorized as quantum phase transitions not being accompanied by symmetry breaking. However, there are still limited observations of counterparts in real space. Here we show a real-space topological phase transition in a chiral magnet MnGe, hosting a periodic array of hedgehog and antihedgehog topological spin singularities. This transition is driven by the pair annihilation of the hedgehogs and antihedgehogs acting as monopoles and antimonopoles of the emergent electromagnetic field. Observed anomalies in the magnetoresistivity and phonon softening are consistent with the theoretical prediction of critical phenomena associated with enhanced fluctuations of emergent field near the transition. This finding reveals a vital role of topology of the spins in strongly correlated systems.

  6. Critical phenomena of emergent magnetic monopoles in a chiral magnet

    PubMed Central

    Kanazawa, N.; Nii, Y.; Zhang, X. -X.; Mishchenko, A. S.; De Filippis, G.; Kagawa, F.; Iwasa, Y.; Nagaosa, N.; Tokura, Y.

    2016-01-01

    Second-order continuous phase transitions are characterized by symmetry breaking with order parameters. Topological orders of electrons, characterized by the topological index defined in momentum space, provide a distinct perspective for phase transitions, which are categorized as quantum phase transitions not being accompanied by symmetry breaking. However, there are still limited observations of counterparts in real space. Here we show a real-space topological phase transition in a chiral magnet MnGe, hosting a periodic array of hedgehog and antihedgehog topological spin singularities. This transition is driven by the pair annihilation of the hedgehogs and antihedgehogs acting as monopoles and antimonopoles of the emergent electromagnetic field. Observed anomalies in the magnetoresistivity and phonon softening are consistent with the theoretical prediction of critical phenomena associated with enhanced fluctuations of emergent field near the transition. This finding reveals a vital role of topology of the spins in strongly correlated systems. PMID:27181484

  7. Charge-magnetic interference resonant scattering studies of ferromagnetic crystals and thin films

    SciTech Connect

    Haskel, D.; Kravtsov, E.; Choi, Y.; Lang, J.C.; Islam, Z.; Srajer, G.; Jiang, J.S.; Bader, S.D.; Canfield, Paul C.

    2012-06-15

    The element- and site-specificity of X-ray resonant magnetic scattering (XRMS) makes it an ideal tool for furthering our understanding of complex magnetic systems. In the hard X-rays, XRMS is readily applied to most antiferromagnets where the relatively weak resonant magnetic scattering (10 −2–10 −6Ic) is separated in reciprocal space from the stronger, Bragg charge scattered intensity, Ic. In ferro(ferri)magnetic materials, however, such separation does not occur and measurements of resonant magnetic scattering in the presence of strong charge scattering are quite challenging. We discuss the use of charge-magnetic interference resonant scattering for studies of ferromagnetic (FM) crystals and layered films. We review the challenges and opportunities afforded by this approach, particularly when using circularly polarized X-rays.We illustrate current capabilities at the Advanced Photon Source with studies aimed at probing site-specific magnetism in ferromagnetic crystals, and interfacial magnetism in films.

  8. Effect of diffusive scattering on giant magnetoresistance in magnetic multilayers

    NASA Astrophysics Data System (ADS)

    Stewart, Derek Alan

    2001-07-01

    Dramatic changes in resistance due to external magnetic fields or giant magnetoresistance (GMR) have provided revolutionary advances in disciplines ranging from computer memory to land mine detection. This thesis explores the crucial role of interfaces in producing GMR in systems such as magnetic multilayers and spin valves where magnetic layers (Co or Fe) are separated by simple metal layers of Cu or Cr. A semi-classical Boltzmann transport model is used to model GMR in Co|Cu magnetic multilayers. Parameters required to fit experimental results indicate minority carriers in Co have a very small mean free path and experience enhanced diffusive scattering at layer interfaces. Parameters fitted for magnetic multilayers (>100 layers) are used to calculate the GMR in corresponding spin valve systems. The model provides GMR and resistivity values in good agreement with current experimental results for spin valves. Scattering at a single interface is examined using two techniques to provide a better theoretical basis for treatment of interfaces in semi-classical calculations. An analytical Green's function approach is developed that treats the interface as a sheet of randomly placed point scatterers. This formalism provides closed forms for interface specularity parameters that depend on electron momentum and interface roughness. The specularity parameters for transmission and reflection differ in functional form, a fact neglected in current Boltzmann models. The layered Korringa Kohn Rostoker method (LKKR) is also used to examine transport across free electron and Co|Cu interfaces. The interdiffused region is treated as an alloy layer under the Coherent Potential Approximation (CPA). Specularity parameters found using this technique for free electrons agree well with analytical Green's function results. The LKKR also provides the first energy dependent specularity parameters for a real material interface. The electronic properties of FeCr alloys are examined using the

  9. Light scattering in colloidal solution of magnetite in electric and magnetic fields.

    PubMed

    Yerin, Constantine V

    2007-04-15

    Light scattering by magnetite particles in kerosene under the simultaneous action of crossed electric and magnetic fields was studied. Decreasing of variation of light scattering intensity at some values of electric and magnetic fields have been found. Values of fields at which a minimum of light scattering intensity occur depend on the angle between laser beam and the plane of crossed fields.

  10. CPP magnetoresistance of magnetic multilayers: A critical review

    NASA Astrophysics Data System (ADS)

    Bass, Jack

    2016-06-01

    We present a comprehensive, critical review of data and analysis of Giant (G) Magnetoresistance (MR) with Current-flow Perpendicular-to-the-layer-Planes (CPP-MR) of magnetic multilayers [F/N]n (n=number of repeats) composed of alternating nanoscale layers of ferromagnetic (F) and non-magnetic (N) metals, or of spin-valves that allow control of anti-parallel (AP) and parallel (P) orientations of the magnetic moments of adjacent F-layers. GMR, a large change in resistance when an applied magnetic field changes the moment ordering of adjacent F-layers from AP to P, was discovered in 1988 in the geometry with Current flow in the layer-Planes (CIP). The CPP-MR has two advantages over the CIP-MR: (1) relatively simple two-current series-resistor (2CSR) and more general Valet-Fert (VF) models allow more direct access to the underlying physics; and (2) it is usually larger, which should be advantageous for devices. When the first CPP-MR data were published in 1991, it was not clear whether electronic transport in GMR multilayers is completely diffusive or at least partly ballistic. It was not known whether the properties of layers and interfaces would vary with layer thickness or number. It was not known whether the CPP-MR would be dominated by scattering within the F-metals or at the F/N interfaces. Nothing was known about: (1) spin-flipping within F-metals, characterized by a spin-diffusion length, lsfF; (2) interface specific resistances (AR=area A times resistance R) for N1/N2 interfaces; (3) interface specific resistances and interface spin-dependent scattering asymmetry at F/N and F1/F2 interfaces; and (4) spin-flipping at F/N, F1/F2 and N1/N2 interfaces. Knowledge of spin-dependent scattering asymmetries in F-metals and F-alloys, and of spin-flipping in N-metals and N-alloys, was limited. Since 1991, CPP-MR measurements have quantified the scattering and spin-flipping parameters that determine GMR for a wide range of F- and N-metals and alloys and of F/N pairs. This

  11. Magnetic scattering in the simultaneous measurement of small-angle neutron scattering and Bragg edge transmission from steel.

    PubMed

    Oba, Yojiro; Morooka, Satoshi; Ohishi, Kazuki; Sato, Nobuhiro; Inoue, Rintaro; Adachi, Nozomu; Suzuki, Jun-Ichi; Tsuchiyama, Toshihiro; Gilbert, Elliot Paul; Sugiyama, Masaaki

    2016-10-01

    Pulsed neutron sources enable the simultaneous measurement of small-angle neutron scattering (SANS) and Bragg edge transmission. This simultaneous measurement is useful for microstructural characterization in steel. Since most steels are ferromagnetic, magnetic scattering contributions should be considered in both SANS and Bragg edge transmission analyses. An expression for the magnetic scattering contribution to Bragg edge transmission analysis has been derived. The analysis using this expression was applied to Cu steel. The ferrite crystallite size estimated from this Bragg edge transmission analysis with the magnetic scattering contribution was larger than that estimated using conventional expressions. This result indicates that magnetic scattering has to be taken into account for quantitative Bragg edge transmission analysis. In the SANS analysis, the ratio of magnetic to nuclear scattering contributions revealed that the precipitates consist of body-centered cubic Cu0.7Fe0.3 and pure Cu, which probably has 9R structure including elastic strain and vacancies. These results show that effective use of the magnetic scattering contribution allows detailed analyses of steel microstructure.

  12. Magnetic scattering in the simultaneous measurement of small-angle neutron scattering and Bragg edge transmission from steel1

    PubMed Central

    Oba, Yojiro; Morooka, Satoshi; Ohishi, Kazuki; Sato, Nobuhiro; Inoue, Rintaro; Adachi, Nozomu; Suzuki, Jun-ichi; Tsuchiyama, Toshihiro; Gilbert, Elliot Paul; Sugiyama, Masaaki

    2016-01-01

    Pulsed neutron sources enable the simultaneous measurement of small-angle neutron scattering (SANS) and Bragg edge transmission. This simultaneous measurement is useful for microstructural characterization in steel. Since most steels are ferromagnetic, magnetic scattering contributions should be considered in both SANS and Bragg edge transmission analyses. An expression for the magnetic scattering contribution to Bragg edge transmission analysis has been derived. The analysis using this expression was applied to Cu steel. The ferrite crystallite size estimated from this Bragg edge transmission analysis with the magnetic scattering contribution was larger than that estimated using conventional expressions. This result indicates that magnetic scattering has to be taken into account for quantitative Bragg edge transmission analysis. In the SANS analysis, the ratio of magnetic to nuclear scattering contributions revealed that the precipitates consist of body-centered cubic Cu0.7Fe0.3 and pure Cu, which probably has 9R structure including elastic strain and vacancies. These results show that effective use of the magnetic scattering contribution allows detailed analyses of steel microstructure. PMID:27738416

  13. Magnetic properties of Ga doped cobalt ferrite: Compton scattering study

    SciTech Connect

    Sharma, Arvind Mund, H. S.; Ahuja, B. L.; Sahariya, Jagrati; Itou, M.; Sakurai, Y.

    2014-04-24

    We present the spin momentum density of Ga doped CoFe{sub 2}O{sub 4} at 100 K using magnetic Compton scattering. The measurement has been performed using circularly polarized synchrotron radiations of 182.65 keV at SPring8, Japan. The experimental profile is decomposed into its constituent profile to determine the spin moment at individual sites. Co atom has the maximum contribution (about 58%) in the total spin moment of the doped CoFe{sub 2}O{sub 4}.

  14. Understanding spin structure in metallacrown single-molecule magnets using magnetic compton scattering.

    PubMed

    Deb, Aniruddha; Boron, Thaddeus T; Itou, Masayoshi; Sakurai, Yoshiharu; Mallah, Talal; Pecoraro, Vincent L; Penner-Hahn, James E

    2014-04-02

    The 3d-4f mixed metallacrowns frequently show single-molecule magnetic behavior. We have used magnetic Compton scattering to characterize the spin structure and orbital interactions in three isostructural metallacrowns: Gd2Mn4, Dy2Mn4, and Y2Mn4. These data allow the direct determination of the spin only contribution to the overall magnetic moment. We find that the lanthanide 4f spin in Gd2Mn4 and Dy2Mn4 is aligned parallel to the Mn 3d spin. For Y2Mn4 (manganese-only spin) we find evidence for spin delocalization into the O 2p orbitals. Comparing the magnetic Compton scattering data with SQUID studies that measure the total magnetic moment suggests that Gd2Mn4 and Y2Mn4 have only a small orbital contribution to the moment. In contrast, the total magnetic moment for Dy2Mn4 MCs is much larger than the spin-only moment, demonstrating a significant orbital contribution to the overall magnetic moment. Overall, these data provide direct insight into the correlation of molecular design with molecular magnetic properties.

  15. Neutron and synchrotron radiation scattering by nonpolar magnetic fluids

    SciTech Connect

    Aksenov, V. L.; Avdeev, M. V.; Shulenina, A. V.; Zubavichus, Y. V.; Veligzhanin, A. A.; Rosta, L.; Garamus, V. M.; Vekas, L.

    2011-09-15

    The complex approach (which comprises different physical methods, including neutron and synchrotron radiation scattering) is justified in the structural analysis of magnetic fluids (MFs). Investigations of MFs based on nonpolar organic solvents with magnetite nanoparticles (2-20 nm in size) coated by various monocarboxylic acids have been performed. It is shown that the use of saturated linear acids with various alkyl chain (C12-C18) lengths instead of unsaturated oleic acid (alkyl chain C18 with a kink in the middle due to the double bond in the cis-configuration) in the classical stabilization procedure for the given type of magnetic fluids leads to a decrease in the mean size and polydispersity of nanoparticles in the final systems.

  16. Characterization of magnetic nanoparticle by dynamic light scattering

    PubMed Central

    2013-01-01

    Here we provide a complete review on the use of dynamic light scattering (DLS) to study the size distribution and colloidal stability of magnetic nanoparticles (MNPs). The mathematical analysis involved in obtaining size information from the correlation function and the calculation of Z-average are introduced. Contributions from various variables, such as surface coating, size differences, and concentration of particles, are elaborated within the context of measurement data. Comparison with other sizing techniques, such as transmission electron microscopy and dark-field microscopy, revealed both the advantages and disadvantages of DLS in measuring the size of magnetic nanoparticles. The self-assembly process of MNP with anisotropic structure can also be monitored effectively by DLS. PMID:24011350

  17. Attraction, merger, reflection, and annihilation in magnetic droplet soliton scattering

    NASA Astrophysics Data System (ADS)

    Maiden, M. D.; Bookman, L. D.; Hoefer, M. A.

    2014-05-01

    The interaction behaviors of solitons are defining characteristics of these nonlinear, coherent structures. Due to recent experimental observations, thin ferromagnetic films offer a promising medium in which to study the scattering properties of two-dimensional magnetic droplet solitons, particle-like, precessing dipoles. Here, a rich set of two-droplet interaction behaviors are classified through micromagnetic simulations. Repulsive and attractive interaction dynamics are generically determined by the relative phase and speeds of the two droplets and can be classified into four types: (1) merger into a breather bound state, (2) counterpropagation trapped along the axis of symmetry, (3) reflection, and (4) violent droplet annihilation into spin wave radiation and a breather. Utilizing a nonlinear method of images, it is demonstrated that these dynamics describe repulsive/attractive scattering of a single droplet off of a magnetic boundary with pinned/free spin boundary conditions, respectively. These results explain the mechanism by which propagating and stationary droplets can be stabilized in a confined ferromagnet.

  18. Diffusion and Criticality in Undoped Graphene with Resonant Scatterers

    NASA Astrophysics Data System (ADS)

    Ostrovsky, P. M.; Titov, M.; Bera, S.; Gornyi, I. V.; Mirlin, A. D.

    2010-12-01

    A general theory is developed to describe graphene with an arbitrary number of isolated impurities. The theory provides a basis for an efficient numerical analysis of the charge transport and is applied to calculate the Dirac-point conductivity σ of graphene with resonant scatterers. In the case of smooth resonant impurities the symmetry class is identified as DIII and σ grows logarithmically with increasing impurity concentration. For vacancies (or strong on-site potential impurities, class BDI) σ saturates at a constant value that depends on the vacancy distribution among two sublattices.

  19. Transient magnetic birefringence for determining magnetic nanoparticle diameters in dense, highly light scattering media

    NASA Astrophysics Data System (ADS)

    Köber, Mariana; Moros, Maria; Grazú, Valeria; de la Fuente, Jesus M.; Luna, Mónica; Briones, Fernando

    2012-04-01

    The increasing use of biofunctionalized magnetic nanoparticles in biomedical applications calls for further development of characterization tools that allow for determining the interactions of the nanoparticles with the biological medium in situ. In cell-incubating conditions, for example, nanoparticles may aggregate and serum proteins adsorb on the particles, altering the nanoparticles’ performance and their interaction with cell membranes. In this work we show that the aggregation of spherical magnetite nanoparticles can be detected with high sensitivity in dense, highly light scattering media by making use of magnetically induced birefringence. Moreover, the hydrodynamic particle diameter distribution of anisometric nanoparticle aggregates can be determined directly in these media by monitoring the relaxation time of the magnetically induced birefringence. As a proof of concept, we performed measurements on nanoparticles included in an agarose gel, which scatters light in a similar way as a more complex biological medium but where particle-matrix interactions are weak. Magnetite nanoparticles were separated by agarose gel electrophoresis and the hydrodynamic diameter distribution was determined in situ. For the different particle functionalizations and agarose concentrations tested, we could show that gel electrophoresis did not yield a complete separation of monomers and small aggregates, and that the electrophoretic mobility of the aggregates decreased linearly with the hydrodynamic diameter. Furthermore, the rotational particle diffusion was not clearly affected by nanoparticle-gel interactions. The possibility to detect nanoparticle aggregates and their hydrodynamic diameters in complex scattering media like cell tissue makes transient magnetic birefringence an interesting technique for biological applications.

  20. Critical scattering of synchrotron radiation in lead zirconate-titanate with low titanium concentrations

    NASA Astrophysics Data System (ADS)

    Andronikova, D. A.; Bosak, A. A.; Bronwald, Iu. A.; Burkovsky, R. G.; Vakhrushev, S. B.; Leontiev, N. G.; Leontiev, I. N.; Tagantsev, A. K.; Filimonov, A. V.; Chernyshov, D. Yu.

    2015-12-01

    Diffuse scattering in the lead zirconate-titanate single crystal with a titanium concentration of 0.7 at % has been studied by the synchrotron radiation scattering method. Measurements have been performed both in the vicinity of the Brillouin zone center and at the M-point. Highly anisotropic diffuse scattering has been revealed in the paraelectric phase near the Brillouin zone center; diffuse scattering anisotropy is similar to that previously observed in pure lead zirconate. The temperature dependence of this diffuse scattering obeys a critical law with T c ≈ 480 K. Diffuse scattering in the vicinity of the M-point weakly depends on temperature; this dependence behaves differently at M-points with various indices.

  1. Critical damping constant of microwave-assisted magnetization switching

    NASA Astrophysics Data System (ADS)

    Yamaji, Toshiki; Arai, Hiroko; Matsumoto, Rie; Imamura, Hiroshi

    2016-02-01

    Microwave-assisted switching of magnetization in a perpendicularly magnetized disk was theoretically studied and special attention was paid to the effect of a damping constant on the switching field. We found that there exists a critical damping constant above which the switching field suddenly increases. We derived an analytical expression of the critical damping constant and showed that it decreases with increasing frequency of the microwave field, while it increases with increasing amplitude of the microwave field and the effective anisotropy field.

  2. Compton scattering in strong magnetic fields: Spin-dependent influences at the cyclotron resonance

    NASA Astrophysics Data System (ADS)

    Gonthier, Peter L.; Baring, Matthew G.; Eiles, Matthew T.; Wadiasingh, Zorawar; Taylor, Caitlin A.; Fitch, Catherine J.

    2014-08-01

    The quantum electrodynamical (QED) process of Compton scattering in strong magnetic fields is commonly invoked in atmospheric and inner magnetospheric models of x-ray and soft gamma-ray emission in high-field pulsars and magnetars. A major influence of the field is to introduce resonances at the cyclotron frequency and its harmonics, where the incoming photon accesses thresholds for the creation of virtual electrons or positrons in intermediate states with excited Landau levels. At these resonances, the effective cross section typically exceeds the classical Thomson value by over 2 orders of magnitude. Near and above the quantum critical magnetic field of 44.13 TeraGauss, relativistic corrections must be incorporated when computing this cross section. This profound enhancement underpins the anticipation that resonant Compton scattering is a very efficient process in the environs of highly magnetized neutron stars. This paper presents formalism for the QED magnetic Compton differential cross section valid for both subcritical and supercritical fields, yet restricted to scattered photons that are below pair creation threshold. Calculations are developed for the particular case of photons initially propagating along the field, and in the limit of zero vacuum dispersion, mathematically simple specializations that are germane to interactions involving relativistic electrons frequently found in neutron star magnetospheres. This exposition of relativistic, quantum, magnetic Compton cross sections treats electron spin dependence fully, since this is a critical feature for describing the finite decay lifetimes of the intermediate states. Such lifetimes are introduced to truncate the resonant cyclotronic divergences via standard Lorentz profiles. The formalism employs both the traditional Johnson and Lippmann (JL) wave functions and the Sokolov and Ternov (ST) electron eigenfunctions of the magnetic Dirac equation. The ST states are formally correct for self

  3. Determination of liquid-liquid critical point composition using 90∘ laser light scattering

    NASA Astrophysics Data System (ADS)

    Williamson, J. Charles; Brown, Allison M.; Helvie, Elise N.; Dean, Kevin M.

    2016-04-01

    Despite over a century of characterization efforts, liquid-liquid critical point compositions are difficult to identify with good accuracy. Reported values vary up to 10% for even well-studied systems. Here, a technique is presented for high-precision determination of the critical composition of a partially miscible binary liquid system. Ninety-degree laser light-scattering intensities from single-phase samples are analyzed using an equation derived from nonclassical power laws and the pseudospinodal approximation. Results are reported for four liquid-liquid systems (aniline + hexane, isobutyric acid + water, methanol + cyclohexane, and methanol + carbon disulfide). Compared to other methods, the 90∘ light-scattering approach has a strong dependence on composition near the critical point, is less affected by temperature fluctuations, and is insensitive to the presence of trace impurities in the samples. Critical compositions found with 90∘ light scattering are precise to the parts-per-thousand level and show long-term reproducibility.

  4. Determination of liquid-liquid critical point composition using 90^{∘} laser light scattering.

    PubMed

    Williamson, J Charles; Brown, Allison M; Helvie, Elise N; Dean, Kevin M

    2016-04-01

    Despite over a century of characterization efforts, liquid-liquid critical point compositions are difficult to identify with good accuracy. Reported values vary up to 10% for even well-studied systems. Here, a technique is presented for high-precision determination of the critical composition of a partially miscible binary liquid system. Ninety-degree laser light-scattering intensities from single-phase samples are analyzed using an equation derived from nonclassical power laws and the pseudospinodal approximation. Results are reported for four liquid-liquid systems (aniline + hexane, isobutyric acid + water, methanol + cyclohexane, and methanol + carbon disulfide). Compared to other methods, the 90^{∘} light-scattering approach has a strong dependence on composition near the critical point, is less affected by temperature fluctuations, and is insensitive to the presence of trace impurities in the samples. Critical compositions found with 90^{∘} light scattering are precise to the parts-per-thousand level and show long-term reproducibility.

  5. Analytical expression for critical frequency of microwave assisted magnetization switching

    NASA Astrophysics Data System (ADS)

    Arai, Hiroko; Imamura, Hiroshi

    2016-02-01

    The microwave-assisted switching (MAS) of magnetization in a perpendicularly magnetized circular disk is studied based on the macrospin model in a rotating frame. The analytical expression for the critical frequency of MAS is derived by analyzing the presence of a quasiperiodic mode. The critical frequency is expressed as a function of the radio frequency (rf) field Hrf and the effective anisotropy field H\\text{k}\\text{eff}. For a small rf field such that H\\text{rf} \\ll H\\text{k}\\text{eff}, the critical frequency is approximately equal to (γ /π )\\root 3 \\of{\\smash{H\\text{k}\\text{eff}H\\text{rf}2}\\mathstrut}.

  6. Mitigating Stimulated Raman Scattering in Hohlraum Plasmas Using Magnetic Insulation

    NASA Astrophysics Data System (ADS)

    Montgomery, D. S.; Albright, B. J.; Kline, J. L.; Yin, L.; Chang, P. Y.; Davies, J. R.; Fiksel, G.; Froula, D. H.; Betti, R.; MacDonald, M. J.

    2013-10-01

    Controlling stimulated Raman scattering (SRS) in hohlraum plasmas is important for achieving high-gain inertial fusion using indirect drive. Experiments at the National Ignition Facility (NIF) suggest that coronal electron temperatures in NIF hohlraums may be cooler than initially thought due to efficient thermal conduction from the under dense low-Z plasma to the dense high-Z hohlraum wall. This leads to weaker Landau damping and stronger growth of SRS. Magnetic insulation of the heat conducting electrons can occur when the Hall parameter ωceτei >> 1, where ωce is the electron-cyclotron frequency, and τei is the electron-ion collision time. For NIF laser-plasma conditions, it is shown that a 10-T external magnetic field may substantially reduce cross-field transport and may increase coronal plasma temperatures, thus increasing linear Landau damping and mitigating SRS. We will present calculations and simulations supporting this concept, and will present initial results from Omega experiments using gas-filled hohlraums with external B-fields up to 10-T. Work performed under the auspices of DOE by LANL under contract DE-AC52-06NA25396.

  7. Scattered radiation doses to some critical organs during pediatric radiotherapy.

    PubMed

    Agard, E T; Ehlers, G; Kirchberg, S

    1985-04-01

    The levels of scattered radiation doses imparted to the eyes, thyroid and gonads of pediatric patients treated with orthovoltage radiation (300 kVp, 2.0 mmCu HVL) and with a 4-MV linear accelerator, were determined by making thermoluminescent dosimeter (TLD) measurements in three paraffin phantoms of different sizes. These phantoms were made from molds of mannequins used for store display, of approximate heights 30", 40" and 50", representing children of ages 1-2, 4-5 and 8-10 yr, respectively. The sites chosen for irradiation were (1) the whole brain, (2) the chest, (3) the kidney bed, (4) the whole abdomen and (5) the spinal column. These sites are normally treated in such pediatric malignancies as medulloblastoma, neuroblastoma and Wilms' tumor. Some of the doses measured are less than 10 rad for an entire treatment regimen, and would therefore be categorized as low-level doses. Where radiation was the only mode of treatment for long-term survivors of such malignancies, especially those treated 20-30 yr ago with orthovoltage radiation, useful data may be extracted for contributing to our knowledge about the long-term effects of low levels of radiation.

  8. Critical Current Measurements in Commercial Tapes, Coils, and Magnets.

    NASA Astrophysics Data System (ADS)

    Gubser, D. U.; Soulen, R. J., Jr.; Fuller-Mora, W. W.; Francavilla, T. L.

    1996-03-01

    We have measured a number of tapes, coils, and magnets produced by commercial vendors and determined their properties as functions of magnetic field and temperature. The tapes were measured at the National High Magnetic Field Laboratory in magnetic fields to 20 tesla and at temperatures of 4.2 K, 27 K, 65 K, and 77 K. For the tapes we report critical currents and current-voltage characteristics. Six inch diameter coils were measured at NRL in zero magnetic field. Critical currents, current-voltage characteristics, and reliability studies are reported for the coils. Larger 10 inch diameter coils, which are to be used in a 200 hp superconducting motor, were also measured and results will be presented. The talk will also review the status of the most recent tests of the superconducting motor.

  9. Excitation spectra of disordered dimer magnets near quantum criticality.

    PubMed

    Vojta, Matthias

    2013-08-30

    For coupled-dimer magnets with quenched disorder, we introduce a generalization of the bond-operator method, appropriate to describe both singlet and magnetically ordered phases. This allows for a numerical calculation of the magnetic excitations at all energies across the phase diagram, including the strongly inhomogeneous Griffiths regime near quantum criticality. We apply the method to the bilayer Heisenberg model with bond randomness and characterize both the broadening of excitations and the transfer of spectral weight induced by disorder. Inside the antiferromagnetic phase this model features the remarkable combination of sharp magnetic Bragg peaks and broad magnons, the latter arising from the tendency to localization of low-energy excitations.

  10. Transport signatures of Kondo physics and quantum criticality in graphene with magnetic impurities

    NASA Astrophysics Data System (ADS)

    Ruiz-Tijerina, David A.; Dias da Silva, Luis G. G. V.

    2017-03-01

    Localized magnetic moments have been predicted to develop in graphene samples with vacancies or adsorbates. The interplay between such magnetic impurities and graphene's Dirac quasiparticles leads to remarkable many-body phenomena, which have, so far, proved elusive to experimental efforts. In this article we study the thermodynamic, spectral, and transport signatures of quantum criticality and Kondo physics of a dilute ensemble of atomic impurities in graphene. We consider vacancies and adatoms that either break or preserve graphene's C3 v and inversion symmetries. In a neutral graphene sample, all cases display symmetry-dependent quantum criticality, leading to enhanced impurity scattering for asymmetric impurities, in a manner analogous to bound-state formation by nonmagnetic resonant scatterers. Kondo correlations emerge only in the presence of a back gate, with estimated Kondo temperatures well within the experimentally accessible domain for all impurity types. For symmetry-breaking impurities at charge neutrality, quantum criticality is signaled by T-2 resistivity scaling, leading to full insulating behavior at low temperatures, while low-temperature resistivity plateaus appear both in the noncritical and Kondo regimes. By contrast, the resistivity contribution from symmetric vacancies and hollow-site adsorbates vanishes at charge neutrality and for arbitrary back-gate voltages, respectively. This implies that local probing methods are required for the detection of both Kondo and quantum critical signatures in these symmetry-preserving cases.

  11. Nuclear forward scattering of synchrotron radiation in pulsed high magnetic fields.

    PubMed

    Strohm, C; Van der Linden, P; Rüffer, R

    2010-02-26

    We report the demonstration of nuclear forward scattering of synchrotron radiation from 57Fe in ferromagnetic alpha iron in pulsed high magnetic fields up to 30 T. The observed magnetic hyperfine field follows the calculated high field bulk magnetization within 1%, establishing the technique as a precise tool for the study of magnetic solids in very high magnetic fields. To perform these experiments in pulsed fields, we have developed a detection scheme for fully time resolved nuclear forward scattering applicable to other pump probe experiments.

  12. Magnetic Modes in Rare Earth Perovskites: A Magnetic-Field-Dependent Inelastic Light Scattering study.

    PubMed

    Saha, Surajit; Cao, Bing-Chen; Motapothula, M; Cong, Chun-Xiao; Sarkar, Tarapada; Srivastava, Amar; Sarkar, Soumya; Patra, Abhijeet; Ghosh, Siddhartha; Ariando; Coey, J M D; Yu, Ting; Venkatesan, T

    2016-11-15

    Here, we report the presence of defect-related states with magnetic degrees of freedom in crystals of LaAlO3 and several other rare-earth based perovskite oxides using inelastic light scattering (Raman spectroscopy) at low temperatures in applied magnetic fields of up to 9 T. Some of these states are at about 140 meV above the valence band maximum while others are mid-gap states at about 2.3 eV. No magnetic impurity could be detected in LaAlO3 by Proton-Induced X-ray Emission Spectroscopy. We, therefore, attribute the angular momentum-like states in LaAlO3 to cationic/anionic vacancies or anti-site defects. Comparison with the other rare earth perovskites leads to the empirical rule that the magnetic-field-sensitive transitions require planes of heavy elements (e.g. lanthanum) and oxygen without any other light cations in the same plane. These magnetic degrees of freedom in rare earth perovskites with useful dielectric properties may be tunable by appropriate defect engineering for magneto-optic applications.

  13. Magnetic Modes in Rare Earth Perovskites: A Magnetic-Field-Dependent Inelastic Light Scattering study

    NASA Astrophysics Data System (ADS)

    Saha, Surajit; Cao, Bing-Chen; Motapothula, M.; Cong, Chun-Xiao; Sarkar, Tarapada; Srivastava, Amar; Sarkar, Soumya; Patra, Abhijeet; Ghosh, Siddhartha; Ariando; Coey, J. M. D.; Yu, Ting; Venkatesan, T.

    2016-11-01

    Here, we report the presence of defect-related states with magnetic degrees of freedom in crystals of LaAlO3 and several other rare-earth based perovskite oxides using inelastic light scattering (Raman spectroscopy) at low temperatures in applied magnetic fields of up to 9 T. Some of these states are at about 140 meV above the valence band maximum while others are mid-gap states at about 2.3 eV. No magnetic impurity could be detected in LaAlO3 by Proton-Induced X-ray Emission Spectroscopy. We, therefore, attribute the angular momentum-like states in LaAlO3 to cationic/anionic vacancies or anti-site defects. Comparison with the other rare earth perovskites leads to the empirical rule that the magnetic-field-sensitive transitions require planes of heavy elements (e.g. lanthanum) and oxygen without any other light cations in the same plane. These magnetic degrees of freedom in rare earth perovskites with useful dielectric properties may be tunable by appropriate defect engineering for magneto-optic applications.

  14. Magnetic Modes in Rare Earth Perovskites: A Magnetic-Field-Dependent Inelastic Light Scattering study

    PubMed Central

    Saha, Surajit; Cao, Bing-Chen; Motapothula, M.; Cong, Chun-Xiao; Sarkar, Tarapada; Srivastava, Amar; Sarkar, Soumya; Patra, Abhijeet; Ghosh, Siddhartha; Ariando; Coey, J. M. D.; Yu, Ting; Venkatesan, T.

    2016-01-01

    Here, we report the presence of defect-related states with magnetic degrees of freedom in crystals of LaAlO3 and several other rare-earth based perovskite oxides using inelastic light scattering (Raman spectroscopy) at low temperatures in applied magnetic fields of up to 9 T. Some of these states are at about 140 meV above the valence band maximum while others are mid-gap states at about 2.3 eV. No magnetic impurity could be detected in LaAlO3 by Proton-Induced X-ray Emission Spectroscopy. We, therefore, attribute the angular momentum-like states in LaAlO3 to cationic/anionic vacancies or anti-site defects. Comparison with the other rare earth perovskites leads to the empirical rule that the magnetic-field-sensitive transitions require planes of heavy elements (e.g. lanthanum) and oxygen without any other light cations in the same plane. These magnetic degrees of freedom in rare earth perovskites with useful dielectric properties may be tunable by appropriate defect engineering for magneto-optic applications. PMID:27845368

  15. Small-Angle Neutron Scattering by the Magnetic Microstructure of Nanocrystalline Ferromagnets Near Saturation

    PubMed Central

    Weissmüller, J.; McMichael, R. D.; Michels, A.; Shull, R. D.

    1999-01-01

    The paper presents a theoretical analysis of elastic magnetic small-angle neutron scattering (SANS) due to the nonuniform magnetic microstructure in nanocrystalline ferromagnets. The reaction of the magnetization to the magnetocrystalline and magnetoelastic anisotropy fields is derived using the theory of micromagnetics. In the limit where the scattering volume is a single magnetic domain, and the magnetization is nearly aligned with the direction of the magnetic field, closed form solutions are given for the differential scattering cross-section as a function of the scattering vector and of the magnetic field. These expressions involve an anisotropy field scattering function, that depends only on the Fourier components of the anisotropy field microstructure, not on the applied field, and a micromagnetic response function for SANS, that can be computed from tabulated values of the materials parameters saturation magnetization and exchange stiffness constant or spin wave stiffness constant. Based on these results, it is suggested that the anisotropy field scattering function SH can be extracted from experimental SANS data. A sum rule for SH suggests measurement of the volumetric mean square anisotropy field. When magnetocrystalline anisotropy is dominant, then a mean grain size or the grain size distribution may be determined by analysis of SH.

  16. Light Scattering Tests of Fundamental Theories of Transport Properties in the Critical Region

    NASA Technical Reports Server (NTRS)

    Gammon, R. W.; Moldover, M. R.

    1985-01-01

    The objective of this program is to measure the decay rates of critical density fluctuations in a simple fluid (xenon) very near its liquid-vapor critical point using laser light scattering and photon correlation spectroscopy. Such experiments have been severely limited on Earth by the presence of gravity which causes large density gradients in the sample when the compressibility diverges approaching the critical point. The goal is to measure decay rates deep in the critical region where the scaled wavevector is the order of 1000. This will require loading the sample to 0.01% of the critical density and taking data as close as 3 microKelvin to the critical temperature (Tc = 289.72 K). Other technical problems have to be addressed such as multiple scattering and the effect of wetting layers. The ability to avoid multiple scattering by using a thin sample (100 microns) was demonstrated, as well as a temperature history which can avoid wetting layers satisfactory temperature control and measurement, and accurate sample loading. Thus the questions of experimental art are solved leaving the important engineering tasks of mounting the experiment to maintain alignment during flight and automating the state-of-the-art temperature bridges for microcomputer control of the experiment.

  17. Magnetic Field Dependence of Excitations Near Spin-Orbital Quantum Criticality

    NASA Astrophysics Data System (ADS)

    Biffin, A.; Rüegg, Ch.; Embs, J.; Guidi, T.; Cheptiakov, D.; Loidl, A.; Tsurkan, V.; Coldea, R.

    2017-02-01

    The spinel FeSc2 S4 has been proposed to realize a near-critical spin-orbital singlet (SOS) state, where entangled spin and orbital moments fluctuate in a global singlet state on the verge of spin and orbital order. Here we report powder inelastic neutron scattering measurements that observe the full bandwidth of magnetic excitations and we find that spin-orbital triplon excitations of an SOS state can capture well key aspects of the spectrum in both zero and applied magnetic fields up to 8.5 T. The observed shift of low-energy spectral weight to higher energies upon increasing applied field is naturally explained by the entangled spin-orbital character of the magnetic states, a behavior that is in strong contrast to spin-only singlet ground state systems, where the spin gap decreases upon increasing applied field.

  18. Ultrahigh thermoelectric performance by electron and phonon critical scattering in Cu2 Se1-x Ix.

    PubMed

    Liu, Huili; Yuan, Xun; Lu, Ping; Shi, Xun; Xu, Fangfang; He, Ying; Tang, Yunshan; Bai, Shengqiang; Zhang, Wenqing; Chen, Lidong; Lin, Yue; Shi, Lei; Lin, He; Gao, Xingyu; Zhang, Xingmin; Chi, Hang; Uher, Ctirad

    2013-12-03

    Iodine-doped Cu2 Se shows a significantly improved thermoelectric performance during phase transitions by electron and phonon critical scattering, leading to a dramatic increase in zT by a factor of 3-7 times culminating in zT values of 2.3 at 400 K.

  19. Nonlinear Raman forward scattering driven by a short laser pulse in a collisional transversely magnetized plasma with nonextensive distribution

    SciTech Connect

    Qiu, Hui-Bin; Song, Hai-Ying; Liu, Shi-Bing

    2015-09-15

    Nonlinear Raman forward scattering of an intense short laser pulse with a duration shorter than the plasma period propagating through a homogenous collisional nonextensive distributed plasma in the presence of a uniform magnetic field perpendicular to both the direction of propagation and electric vector of the radiation field is investigated theoretically when ponderomotive, relativistic, and collisional nonlinearities are taken into account. The governing equations for nonlinear wave in the context of nonextensive statistics are given, the nonextensive coupled equations describing the nonlinear Raman forward scattering instability are solved by the Fourier transformation method, and the growth rate of the nonlinear Raman forward scattering instability is obtained. The results in the case q → 1 are consistent with those in the framework of the Maxwellian distribution. It is found that the instability growth rate first decreases on increasing electron thermal velocity, minimizes at a critical thermal velocity, and then increases steeply; the critical temperature dependents on the nonextensive parameter, and the greater nonextensive parameter, correspond to the greater critical temperature; when the thermal velocity of electron is less than the critical speed, the instability growth rate is found to be enhanced as the nonextensive parameter increases; but when the thermal velocity is greater than the critical speed, the instability growth rate decreases on increasing the nonextensive parameter.

  20. Perpendicular Magnetic Anisotropy and Induced Magnetic Structures of Pt Layers in the Fe/Pt Multilayers Investigated by Resonant X-ray Magnetic Scattering

    NASA Astrophysics Data System (ADS)

    Lee, Mihee; Takechi, Ryota; Hosoito, Nobuyoshi

    2017-02-01

    Depth distribution of the magnetization induced in the paramagnetic Pt layers of Fe/Pt multilayers was investigated by resonant X-ray magnetic scattering (RXMS) near the Pt L3 absorption edge. Two samples with different perpendicular magnetic anisotropy (PMA) were chosen for RXMS measurements. The magnetic depth profile of the Pt layer was determined in the magnetic saturation state of the Fe magnetization with the sample of weak PMA. The magnetization process of the Pt layer was investigated with the sample of moderate PMA. It is found that the Pt atoms near the interface region have a perpendicular component of the induced magnetization even in the saturation state of the Fe magnetization, suggesting that the PMA of Fe/Pt multilayers originates from the Pt atoms near the interface region. Concerning the magnetization process, the induced Pt magnetization is not proportional to the Fe magnetization. This implies a complicated magnetizing mechanism of the Pt layer by the Fe magnetization.

  1. Magnetic two-photon scattering and two-photon emission - Cross sections and redistribution functions

    NASA Technical Reports Server (NTRS)

    Alexander, S. G.; Meszaros, P.

    1991-01-01

    The magnetic two-photon scattering cross section is discussed within the framework of QED, and the corresponding scattering redistribution function for this process and its inverse, as well as the scattering source function are calculated explicitly. In a similar way, the magnetic two-photon emission process which follows the radiative excitation of Landau levels above ground is calculated. The two-photon scattering and two-photon emission are of the same order as the single-photon magnetic scattering. All three of these processes, and in optically thick cases also their inverses, are included in radiative transport calculations modeling accreting pulsars and gamma-ray bursters. These processes play a prominent role in determining the relative strength of the first two cyclotron harmonics, and their effects extend also to the higher harmonics.

  2. Aharonov-Bohm scattering of relativistic Dirac particles with an anomalous magnetic moment

    SciTech Connect

    Lin Qionggui

    2005-10-15

    The Aharonov-Bohm scattering of relativistic spin-1/2 particles with an anomalous magnetic moment are studied. The scattering cross sections for unpolarized and polarized particles are obtained by solving the Dirac-Pauli equation. It is somewhat unexpected that the results are in general the same as those for particles without an anomalous magnetic moment. However, when the incident energy takes some special values, the cross section for polarized particles is dramatically changed. In these cases the helicity of scattered particles is not conserved. In particular, the helicity of particles scattered in the backward direction is all reversed. In the nonrelativistic limit, a very simple relation between the polarized directions of the incident and scattered particles is found, for both general and special incident energies. For particles without an anomalous magnetic moment this relation can be drawn from previous results but it appears to be unnoticed.

  3. A theoretical study on critical phenomena of magnetic soft modes

    NASA Astrophysics Data System (ADS)

    Zeng, Xiaoyan; Yang, Guohong; Yan, Ming

    2017-02-01

    Below a threshold magnetic field, domain structures in ferromagnetic samples may start to nucleate from the initially saturated state via either continuous or discontinuous phase transitions. Such processes are usually accompanied by the occurrence of soft spin-wave modes at the critical point. In this paper, we present a theoretical study on the critical phenomena of uniform soft modes in a macrospin model and spatially non-uniform ones in ferromagnetic thin films. The critical exponents of the mode frequency and its polarization are derived. The value is found to be equal to one half, which is directly related to the breaking of a reflection-symmetry in the phase transition. At the critical point, the soft mode becomes linearly polarized, which provides an additional measurable effect of the critical phenomena.

  4. Mitigating stimulated scattering processes in gas-filled Hohlraums via external magnetic fields

    SciTech Connect

    Gong, Tao; Zheng, Jian; Li, Zhichao; Ding, Yongkun; Yang, Dong; Hu, Guangyue; Zhao, Bin

    2015-09-15

    A simple model, based on energy and pressure equilibrium, is proposed to deal with the effect of external magnetic fields on the plasma parameters inside the laser path, which shows that the electron temperature can be significantly enhanced as the intensity of the external magnetic fields increases. With the combination of this model and a 1D three-wave coupling code, the effect of external magnetic fields on the reflectivities of stimulated scattering processes is studied. The results indicate that a magnetic field with an intensity of tens of Tesla can decrease the reflectivities of stimulated scattering processes by several orders of magnitude.

  5. Neutron Scattering Study of Low Energy Magnetic Excitation in FeTeSe System

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Wen, Jinsheng; Schneeloch, John; Matsuda, Masaaki; Christianson, A. D.; Gu, Genda; Zaliznyak, I. A.; Xu, Guangyong; Tranquada, J. M.; Birgeneau, R. J.

    2014-03-01

    We have performed neutron scattering and magnetization/transport measurements on a series of FeTe1-xSex system single crystals to study the interplay between magnetism and superconductivity. Comparing to pure FeTe1-xSex compounds, extra Fe and Ni/Cu doping on Fe-site can change physics properties of these samples, including resistivity, magnetization and superconducting properties. Our neutron scattering studies also show the Fe-site doping change low energy magnetic spectrum, including the magnetic excitations intensity, position and magnetic correlation length in these samples. On the other hand, the temperature dependence of the low energy magnetic fluctuations are also found to be different depending on the composition. This work is supported by the Office of Basic Energy Sciences, DOE.

  6. Critical spin-flip scattering at the helimagnetic transition of MnSi

    NASA Astrophysics Data System (ADS)

    Kindervater, J.; Häußler, W.; Janoschek, M.; Pfleiderer, C.; Böni, P.; Garst, M.

    2014-05-01

    We report spherical neutron polarimetry (SNP) and discuss the spin-flip scattering cross sections as well as the chiral fraction η close to the helimagnetic transition in MnSi. For our study we have developed a miniaturized SNP device that allows fast data collection when used in small angle scattering geometry with an area detector. Critical spin-flip scattering is found to be governed by chiral paramagnons that soften on a sphere in momentum space. Carefully accounting for the incoherent spin-flip background, we find that the resulting chiral fraction η decreases gradually above the helimagnetic transition reflecting a strongly renormalized chiral correlation length with a temperature dependence in excellent quantitative agreement with the Brazovskii theory for a fluctuation-induced first order transition.

  7. Critical and supercritical current measurements by a magnetic induction method

    NASA Astrophysics Data System (ADS)

    Harris, E. A.; Bishop, J. E. L.; Havill, R. L.; Ward, P. J.

    1988-10-01

    The temperature dependence of the critical current and current-voltage characteristics at supercritical currents have been measured in the low field limit on toroidal samples of the ceramic high Tc superconductor YBa 2Cu 3O 7- δ by a contactless magnetic induction technique that is sensitive to the transport supercurrent but not to any intragrain current loops. The sample constitutes a tertiary winding on a small ferrite transformer core. The secondary voltage provides a very sensitive indication of when the critical current is exceeded, and when it is integrated it yields the supercritical current-voltage characteristic.

  8. Inverse near-critical-angle scattering as a tool to characterize bubble clouds

    NASA Astrophysics Data System (ADS)

    Onofri, Fabrice R. A.; Krzysiek, Mariusz; Barbosa, Séverine; Wozniak, Mariusz; Mroczka, Janusz; Yuan, Yijia; Ren, Kuan-Fang

    2010-02-01

    Under real flow conditions, the critical-angle scattering of a spherical bubble is too noisy to obtain directly the bubble diameter and refractive index. To solve this problem and to limit the drawback of any counting technique, the critical angle refractometry and sizing (CARS) technique has been extended as a collective ensemble technique. As an inverse method it allows to get the size distribution and composition of a cloud of bubbles. In this paper we review the principle, the advantages and limits of this new optical particle characterization method.

  9. Magnet nursing services recognition: transforming the critical care environment.

    PubMed

    Robinson, C A

    2001-08-01

    History repeats itself despite the best intentions of those in the nursing profession. Once again there is an emerging shortage of nurses, and critical care units are particularly affected. The work environment in critical care and medical/surgical units is demanding and stressful, but little effort has been made to mitigate the working conditions that cause nurses to leave. It is possible to apply lessons from magnet hospital research spanning the past 18 years to alter the pattern of repeated nursing shortages. The process of receiving the magnet nursing services designation has transformed the work environment for all nurses at the University of California Davis Medical Center. This broadly focused article describes the transformation process and the culture of an institution that values and consequently retains the best nurses to provide outstanding patient care despite the nursing shortage.

  10. Comparison between magnetic force microscopy and electron back-scatter diffraction for ferrite quantification in type 321 stainless steel.

    PubMed

    Warren, A D; Harniman, R L; Collins, A M; Davis, S A; Younes, C M; Flewitt, P E J; Scott, T B

    2015-01-01

    Several analytical techniques that are currently available can be used to determine the spatial distribution and amount of austenite, ferrite and precipitate phases in steels. The application of magnetic force microscopy, in particular, to study the local microstructure of stainless steels is beneficial due to the selectivity of this technique for detection of ferromagnetic phases. In the comparison of Magnetic Force Microscopy and Electron Back-Scatter Diffraction for the morphological mapping and quantification of ferrite, the degree of sub-surface measurement has been found to be critical. Through the use of surface shielding, it has been possible to show that Magnetic Force Microscopy has a measurement depth of 105-140 nm. A comparison of the two techniques together with the depth of measurement capabilities are discussed.

  11. Using scattered-light modeling for semiconductor critical dimension metrology and calibration

    NASA Astrophysics Data System (ADS)

    Krukar, Richard H.; Prins, Steven L.; Krukar, D. M.; Peterson, Gary A., Jr.; Gaspar, Steve; McNeil, John R.; Naqvi, S. Sohail H.; Hush, Donald R.

    1993-08-01

    Quantitative methods are developed to use optical scatter to measure the critical dimensions of gratings etched into bulk Si and developed photoresist patterns on silicon substrates. Previous work either classified microstructures qualitatively or employed a 'chi-by-eye' method to find that structures were similar or dissimilar. A single detector scanning scatterometer is used to measure large 32 micrometers pitch structures while another instrument that varies the angle of incidence and tracks diffracted orders via the grating equation is used to measure 2 micrometers pitch structures. A rigorous coupled wave light scatter model is used to simulate diffraction from a set of test wafers. Partial least squares and neural network analysis techniques are then employed to use correlations between the simulated diffraction and the critical dimensions of the modeled structures to produce a capability to measure the critical dimensions from scattered light measurements. The marriage of rigorous coupled wave diffraction modeling and optical scatterometry directly addresses the needs of the industry for a rapid and nondestructive metrology tool.

  12. Critical suppression of spin Seebeck effect by magnetic fields

    NASA Astrophysics Data System (ADS)

    Kikkawa, Takashi; Uchida, Ken-ichi; Daimon, Shunsuke; Qiu, Zhiyong; Shiomi, Yuki; Saitoh, Eiji

    2015-08-01

    The longitudinal spin Seebeck effect (LSSE) in Pt /Y3Fe5O12(YIG ) junction systems has been investigated at various magnetic fields and temperatures. We found that the LSSE voltage in a Pt/YIG-slab system is suppressed by applying high magnetic fields and this suppression is critically enhanced at low temperatures. The field-induced suppression of the LSSE in the Pt/YIG-slab system is too large at around room temperature to be explained simply by considering the effect of the Zeeman gap in magnon excitation. This result requires us to introduce a magnon-frequency-dependent mechanism into the scenario of LSSE; low-frequency magnons dominantly contribute to the LSSE. The magnetic field dependence of the LSSE voltage was observed to change by changing the thickness of YIG, suggesting that the thermospin conversion by the low-frequency magnons is suppressed in thin YIG films due to the long characteristic lengths of such magnons.

  13. Measurement of time series variation of thermal diffusivity of magnetic fluid under magnetic field by forced Rayleigh scattering method

    NASA Astrophysics Data System (ADS)

    Motozawa, Masaaki; Muraoka, Takashi; Motosuke, Masahiro; Fukuta, Mitsuhiro

    2017-04-01

    It can be expected that the thermal diffusivity of a magnetic fluid varies from time to time after applying a magnetic field because of the growth of the inner structure of a magnetic fluid such as chain-like clusters. In this study, time series variation of the thermal diffusivity of a magnetic fluid caused by applying a magnetic field was investigated experimentally. For the measurement of time series variation of thermal diffusivity, we attempted to apply the forced Rayleigh scattering method (FRSM), which has high temporal and high spatial resolution. We set up an optical system for the FRSM and measured the thermal diffusivity. A magnetic field was applied to a magnetic fluid in parallel and perpendicular to the heat flux direction, and the magnetic field intensity was 70 mT. The FRSM was successfully applied to measurement of the time series variation of the magnetic fluid from applying a magnetic field. The results show that a characteristic configuration in the time series variation of the thermal diffusivity of magnetic fluid was obtained in the case of applying a magnetic field parallel to the heat flux direction. In contrast, in the case of applying a magnetic field perpendicular to the heat flux, the thermal diffusivity of the magnetic fluid hardly changed during measurement.

  14. Light-scattering study of the effect of salt and polyelectrolyte on magnetic latex particles

    SciTech Connect

    Sohn, D.; Russo, P.S.

    1993-12-31

    Dynamic and static light scattering methods have been used to study the interaction between magnetic latex and polyelectrolytes (polystyrene sulfonate sodium salt, NaPSS) in solution. The light scattering signal from magnetic latex particles was far stronger than that of the polyelectrolyte, especially during depolarized measurements where the polyelectrolyte was essentially invisible. Rotational and translational diffusion of the magnetic latex is investigated as a function of the NaPSS concentration and added salt (NaCl). The diffusion coefficient of magnetic latex decreases abruptly with increasing salt concentration when NaPSS is absent, but it recovers upon addition of NaPSS to the system. Static light scattering results also give evidence of particle aggregation at high salt.

  15. Probing Spin Frustration in High-symmetry Magnetic Nanomolecules by Inelastic Neutron Scattering

    SciTech Connect

    Garlea, Vasile O; Nagler, Stephen E; Zarestky, Jerel L; Stassis, C.; Vaknin, D.; Kogerler, P.; McMorrow, D. F.; Niedermayer, C.; Tennant, D. A.; Lake, B.; Qiu, Y.; Exler, M.; Schnack, J.; Luban, M.

    2006-01-01

    Low temperature inelastic neutron scattering studies have been performed to characterize the low energy magnetic excitation spectrum of the magnetic nanomolecule {l_brace}Mo{sub 72}Fe{sub 30}{r_brace}. This unique highly symmetric cluster features spin frustration and is one of the largest discrete magnetic molecules studied to date by inelastic neutron scattering. The 30 s=5/2 Fe{sup III} ions, embedded in a spherical polyoxomolybdate molecule, occupy the vertices of an icosidodecahedron and are coupled via nearest-neighbor antiferromagnetic interactions. The overall energy scale of the excitation and the gross features of the temperature dependence of the observed neutron scattering are explained by a quantum model of the frustrated spin cluster. However, no satisfactory theoretical explanation is yet available for the observed magnetic field dependence.

  16. Element-specific characterization of the interface magnetism in [Co{sub 2}MnGe/Au]{sub n} multilayers by x-ray resonant magnetic scattering

    SciTech Connect

    Grabis, J.; Bergmann, A.; Nefedov, A.; Westerholt, K.; Zabel, H.

    2005-07-01

    The magnetism of the ferromagnetic half-metallic Heusler compounds at the interface with other metals, insulators, and semiconductors is a critical issue when judging the prospects for these materials to be used in future spintronic devices. We study the interface magnetism of the ferromagnetic half metal Co{sub 2}MnGe in a high-quality [Co{sub 2}MnGe/Au]{sub 50} multilayer by x-ray resonant magnetic reflectivity using circularly polarized x-ray radiation in the energy range of the Co and Mn L{sub 2,3} edges. An analysis of the magnetic part of the reflectivity at the superlattice Bragg peaks allows a precise determination of the magnetization profile within the Co{sub 2}MnGe layers. We find that the profile is definitely different for Mn and Co spins and asymmetric with respect to the growth direction. At room temperature nonferromagnetic interface layers exist with a thickness of about 0.45 nm at the bottom and 0.3 nm at the top of the Co{sub 2}MnGe layers. Additionally, the comparison of the nonresonant and resonant magnetic diffuse scattering reveals that the correlated structural and magnetic roughness are almost identical, the corresponding length scale being the in-plane crystallite size.

  17. Magnetic design evolution in perpendicular magnetic recording media as revealed by resonant small angle x-ray scattering

    NASA Astrophysics Data System (ADS)

    Wang, Tianhan; Mehta, Virat; Ikeda, Yoshihiro; Do, Hoa; Takano, Kentaro; Florez, Sylvia; Terris, Bruce D.; Wu, Benny; Graves, Catherine; Shu, Michael; Rick, Ramon; Scherz, Andreas; Stöhr, Joachim; Hellwig, Olav

    2013-09-01

    We analyze the magnetic design for different generations of perpendicular magnetic recording (PMR) media using resonant soft x-ray small angle x-ray scattering. This technique allows us to simultaneously extract in a single experiment the key structural and magnetic parameters, i.e., lateral structural grain and magnetic cluster sizes as well as their distributions. We find that earlier PMR media generations relied on an initial reduction in the magnetic cluster size down to the grain level of the high anisotropy granular base layer, while very recent media designs introduce more exchange decoupling also within the softer laterally continuous cap layer. We highlight that this recent development allows optimizing magnetic cluster size and magnetic cluster size distribution within the composite media system for maximum achievable area density, while keeping the structural grain size roughly constant.

  18. Static Magnetic Field Therapy: A Critical Review of Treatment Parameters

    PubMed Central

    Wahbeh, Helané; Harling, Noelle; Connelly, Erin; Schiffke, Heather C.; Forsten, Cora; Gregory, William L.; Markov, Marko S.; Souder, James J.; Elmer, Patricia; King, Valerie

    2009-01-01

    Static magnetic field (SMF) therapy, applied via a permanent magnet attached to the skin, is used by people worldwide for self-care. Despite a lack of established SMF dosage and treatment regimens, multiple studies are conducted to evaluate SMF therapy effectiveness. Our objectives in conducting this review are to:(i) summarize SMF research conducted in humans; (ii) critically evaluate reporting quality of SMF dosages and treatment parameters and (iii) propose a set of criteria for reporting SMF treatment parameters in future clinical trials. We searched 27 electronic databases and reference lists. Only English language human studies were included. Excluded were studies of electromagnetic fields, transcranial magnetic stimulation, magnets placed on acupuncture points, animal studies, abstracts, posters and editorials. Data were extracted on clinical indication, study design and 10 essential SMF parameters. Three reviewers assessed quality of reporting and calculated a quality assessment score for each of the 10 treatment parameters. Fifty-six studies were reviewed, 42 conducted in patient populations and 14 in healthy volunteers. The SMF treatment parameters most often and most completely described were site of application, magnet support device and frequency and duration of application. Least often and least completely described were characteristics of the SMF: magnet dimensions, measured field strength and estimated distance of the magnet from the target tissue. Thirty-four (61%) of studies failed to provide enough detail about SMF dosage to permit protocol replication by other investigators. Our findings highlight the need to optimize SMF dosing parameters for individual clinical conditions before proceeding to a full-scale clinical trial. PMID:18955243

  19. Second-order magnetic critical points at finite magnetic fields: Revisiting Arrott plots

    NASA Astrophysics Data System (ADS)

    Bustingorry, S.; Pomiro, F.; Aurelio, G.; Curiale, J.

    2016-06-01

    The so-called Arrott plot, which consists in plotting H /M against M2, with H the applied magnetic field and M the magnetization, is used to extract valuable information in second-order magnetic phase transitions. Besides, it is widely accepted that a negative slope in the Arrott plot is indicative of a first-order magnetic transition. This is known as the Banerjee criterion. In consequence, the zero-field transition temperature T* is reported as the characteristic first-order transition temperature. By carefully analyzing the mean-field Landau model used for studying first-order magnetic transitions, we show in this work that T* corresponds in fact to a triple point where three first-order lines meet. More importantly, this analysis reveals the existence of two symmetrical second-order critical points at finite magnetic field (Tc,±Hc) . We then show that a modified Arrott plot can be used to obtain information about these second-order critical points. To support this idea we analyze experimental data on La2 /3Ca1 /3MnO3 and discuss an estimate for the location of the triple point and the second-order critical points.

  20. Light-scattering signal may indicate critical time zone to rescue brain tissue after hypoxia.

    PubMed

    Kawauchi, Satoko; Sato, Shunichi; Uozumi, Yoichi; Nawashiro, Hiroshi; Ishihara, Miya; Kikuchi, Makoto

    2011-02-01

    A light-scattering signal, which is sensitive to cellular/subcellular structural integrity, is a potential indicator of brain tissue viability because metabolic energy is used in part to maintain the structure of cells. We previously observed a unique triphasic scattering change (TSC) at a certain time after oxygen/glucose deprivation for blood-free rat brains; TSC almost coincided with the cerebral adenosine triphosphate (ATP) depletion. We examine whether such TSC can be observed in the presence of blood in vivo, for which transcranial diffuse reflectance measurement is performed for rat brains during hypoxia induced by nitrogen gas inhalation. At a certain time after hypoxia, diffuse reflectance intensity in the near-infrared region changes in three phases, which is shown by spectroscopic analysis to be due to scattering change in the tissue. During hypoxia, rats are reoxygenated at various time points. When the oxygen supply is started before TSC, all rats survive, whereas no rats survive when the oxygen supply is started after TSC. Survival is probabilistic when the oxygen supply is started during TSC, indicating that the period of TSC can be regarded as a critical time zone for rescuing the brain. The results demonstrate that light scattering signal can be an indicator of brain tissue reversibility.

  1. Light-scattering signal may indicate critical time zone to rescue brain tissue after hypoxia

    NASA Astrophysics Data System (ADS)

    Kawauchi, Satoko; Sato, Shunichi; Uozumi, Yoichi; Nawashiro, Hiroshi; Ishihara, Miya; Kikuchi, Makoto

    2011-02-01

    A light-scattering signal, which is sensitive to cellular/subcellular structural integrity, is a potential indicator of brain tissue viability because metabolic energy is used in part to maintain the structure of cells. We previously observed a unique triphasic scattering change (TSC) at a certain time after oxygen/glucose deprivation for blood-free rat brains; TSC almost coincided with the cerebral adenosine triphosphate (ATP) depletion. We examine whether such TSC can be observed in the presence of blood in vivo, for which transcranial diffuse reflectance measurement is performed for rat brains during hypoxia induced by nitrogen gas inhalation. At a certain time after hypoxia, diffuse reflectance intensity in the near-infrared region changes in three phases, which is shown by spectroscopic analysis to be due to scattering change in the tissue. During hypoxia, rats are reoxygenated at various time points. When the oxygen supply is started before TSC, all rats survive, whereas no rats survive when the oxygen supply is started after TSC. Survival is probabilistic when the oxygen supply is started during TSC, indicating that the period of TSC can be regarded as a critical time zone for rescuing the brain. The results demonstrate that light scattering signal can be an indicator of brain tissue reversibility.

  2. Development of Metallic Magnetic Calorimeters with a Critical Temperature Switch

    NASA Astrophysics Data System (ADS)

    Kim, S. R.; Choi, J.; Jo, H. S.; Kang, C. S.; Kim, G. B.; Kim, H. L.; Kim, I. W.; Lee, H. J.; Lee, J. H.; Lee, M. K.; Oh, S. Y.; Sala, E.; So, J. H.; Yoon, W. S.; Kim, Y. H.

    2016-07-01

    We report on the progress in the development of meander-shaped metallic magnetic calorimeters (MMCs) with a critical temperature switch. A niobium meander-shaped coil in an MMC is arranged to form a superconducting loop. It is to measure the change in magnetization and to apply a persistent current that magnetizes the MMC sensor material. In this work, part of the superconducting loop is fabricated with another superconducting material with its transition temperature (T_C) lower than that of niobium. A persistent current can be injected in the loop while reducing the temperature from above to below the T_C of the switch. Aluminum (Al) wires and an alloy of molybdenum and germanium (MoGe) were tested as critical temperature switch. The test with the Al switch demonstrated the temperature switch concept for meander-shaped MMCs that require a large field current. Microfabricated MoGe switches showed a T_C near 4.3 K, but only 7 mA of persistent current could be charged due to MoGe film discontinuity. This issue requires further improvement in the fabrication procedure.

  3. The magnetization processes and critical transition in a nanogranular magnetic film with perpendicular anisotropy.

    PubMed

    Kalita, V M; Lozenko, A F; Ryabchenko, S M; Los, A V; Sitnikov, A V; Stognei, O V

    2013-02-13

    The mechanisms and properties of the equilibrium magnetization process for nanogranular films with perpendicular anisotropy placed in a tilted magnetic field are considered. The contributions of the effects of canting and flipping of the granules' magnetic moments to the process of film magnetization are studied. A critical behavior of the film magnetization at the transition, induced by a tilted magnetic field, from a state with non-uniform orientation of the granules' magnetic moments to one with a similar orientation is revealed. The results obtained within the two-level model of the orientation of the particles' magnetic moments are in good agreement with the experimental data for Co-Al(2)O(3) (61 at.% Co) granular film. The perpendicular anisotropy of the granules in this film originates mainly from their elongated shape. It is shown that in the non-uniform state the magnetostatic energy of a granular film with similarly oriented elongated granules can be described by the sum of contributions of two types: quasi-single-granular and quasi-film. The effective constant of the single-particle anisotropy of the granules in this case turns out to be dependent on the factor of volume filling of the film by granules, but not on its magnetization.

  4. Determination of the critical premicelle concentration, first critical micelle concentration and second critical micelle concentration of surfactants by resonance Rayleigh scattering method without any probe

    NASA Astrophysics Data System (ADS)

    Shi, Yan; Luo, Hong Qun; Li, Nian Bing

    2011-05-01

    The purpose of this work is to determine the values of critical premicelle concentration (CPMC), first critical micelle concentration (FCMC) and second critical micelle concentration (SCMC) of surfactants using a common spectrofluorophotometer by recording resonance Rayleigh scattering (RRS) signal without any probe. The plot of the RRS intensities at the maximum scattering wavelength ( IRRSmax) versus surfactant concentrations ( c) was constructed to obtain the IRRSmax-c curve. From the inflexions in IRRSmax-c curve, the CPMC, FCMC and SCMC values of a surfactant can be obtained sensitively. The FCMC of some anionic, cationic and nonionic surfactants such as sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), cetyltrimethylammonium bromide (CTAB), cetylpyridinium chloride (CPC), Tween-20, and Tween-80 were determined by RRS method and the values are in good agreement with those obtained from conductivity and surface tension measurements and literature values. The CPMC and SCMC of SDS and CTAB were also determined by RRS method respectively and the values conform to literature values too. Furthermore, RRS method can also be used to determine the FCMC of an amphiphilic macromolecule-hemoglobin, whose structure resembles a surfactant. From the experimental results, it is concluded that RRS method can be applied to the simultaneous determination of the CPMC, FCMC and SCMC values in a sensitive, accurate and no probe way.

  5. Josephson critical current of long SNS junctions in the presence of a magnetic field

    NASA Astrophysics Data System (ADS)

    Meier, Hendrik; Fal'Ko, Vladimir I.; Glazman, Leonid I.

    We evaluate the Josephson critical current of a long and wide two-dimensional superconductor-normal metal-superconductor (SNS) junction, taking into account the effect of electron reflection off the side edges of the junction. Considering clean junctions, we find that the effect of edges alters the usual Fraunhofer-like dependence of the Josephson critical current Ic on the magnetic flux Φ. At relatively weak fields, B <~Φ0 /W2 , the edge effect lifts zeros of the Ic (Φ) dependence and gradually shifts the maxima of that function by Φ0 / 2 . (Here W is the width of the junction and Φ0 the magnetic flux quantum.) At higher fields, B >~Φ0 /W2 , the edge effect leads to an accelerated decay of the critical current Ic (Φ) with increasing Φ. Our results are robust with respect to the roughness of realistic boundaries. Finally, we discuss the role of mesoscopic fluctuations of Ic (Φ) originating from the scattering off the edges, and compare our findings to recent experiments.

  6. Magnetism of CaRu{sub 1-x}Mn{sub x}O{sub 3}: Magnetic Compton scattering study

    SciTech Connect

    Mizusaki, S.; Taniguchi, T.; Okada, N.; Nagata, Y.; Itou, M.; Sakurai, Y.; Ozawa, T. C.; Noro, Y.; Samata, H.

    2008-04-01

    The magnetism of CaRu{sub 1-x}Mn{sub x}O{sub 3} was studied using magnetic Compton scattering measurements for polycrystalline specimens at 10 K under 2.5 T using a synchrotron-radiation x ray. The spin moment deduced from the magnetic Compton profiles has a maximum at x=0.7 and the value agrees with the result of the magnetization measurement. The magnetic Compton profiles indicate that the Mn spin moment is dominant in magnetization and that Ru moment, which is induced with Mn doping, couples with Mn spin moment antiferromagnetically. The results suggest that a sort of ferrimagnetism is established in the CaRu{sub 1-x}Mn{sub x}O{sub 3} system.

  7. Spin transport and spin-flip scattering in magnetic multilayer structures

    NASA Astrophysics Data System (ADS)

    Garzon, Samir

    2006-03-01

    The existence of spin-flip scattering at the interface between ferromagnetic (F) and nonmagnetic (N) layers of magnetoresistive F/N/F structures can significantly reduce the size of the magnetoresistance, limiting the sensitivity and increasing the power consumption of F/N/F devices such as GMR magnetic field sensors, magnetic read heads, and MRAM's [1]. Detecting and measuring the degree of spin flip scattering in F/N/F structures can allow further optimization in such devices as well as increase the understanding of interfacial spin transport. Our nonlocal spin injection and detection experiments on mesoscopic Co-Al2O3-Cu-Al2O3-Co spin valves provide evidence for the existence of interfacial spin-flip scattering in magnetoresistive devices [2]. By extending the conventional picture of spin-dependent interfacial resistances (R, R) to include two additional spin-flip scattering channels (R,R) [3] we have shown that the nonlocal resistance contains information about both the degree of spin polarization and the degree of spin-flip scattering at the F/N interface. The magnitudes of R and R depend on the relative orientation of the detector magnetization and the nonequilibrium magnetization in the normal metal. We have observed that the difference in spin-flip scattering between up and down channels vanishes at low temperatures, but for T>100K it increases nonlinearly with temperature. Further evidence for the presence of interfacial spin-flip scattering can be obtained from noise measurements, which are extremely sensitive to the microscopic transport details. [1] Spin Dependent Transport in Magnetic Nanostructures, edited by S. Maekawa and T. Shinjo (Taylor & Francis, New York, 2002). [2] S. Garzon, I. Zuti'c, and R. A. Webb, Phys. Rev. Lett. 94, 176601 (2005). [3] E. I. Rashba, Eur. Phys. J. B 29, 513 (2002).

  8. Magnetic reversals in basal Ediacaran cap carbonates: A critical review

    NASA Astrophysics Data System (ADS)

    Raub, T. D.; Evans, D. A.

    2006-05-01

    At least one paleomagnetic reversal has been reported from each of three "Snowball Earth" postglacial cap cabonate units: Walsh cap of Kimberley, northern Australia; Mirassol d'Oeste in Amazonia; and Hadash in Oman. Our data from Nuccaleena cap dolostone of South Australia add a fourth to that list. We critically review all four studies and note that: a) Strict stratigraphic control on position of reversals is only documented for Mirassol d'Oeste and Nuccaleena caps. The Walsh cap sites are not stratigraphically constrained, and the Hadash reversal stratigraphy is only apparent after site data are combined from sections separated by 10's to 100's of km. b) Although Walsh, Hadash, and Nuccaleena remanences pass regional fold tests, the folding events could be substantially younger than cap deposition. Dual-polarity remagnetizations are well-documented in other carbonates. Despite satisfactory rock-magnetic results from Mirassol d'Oeste, critical field stability tests on the age of magnetization are lacking. c) Indirect syn-sedimentary tests of magnetization are only documented and passed for Nuccaleena dolostone. Mean Nuccaleena magnetization directions are similar to those of the paraconformably underlying glacial Elatina Formation, which passes a synsedimentary fold test; and two postglacial reversal levels are correlatable across three sections and ~50 km of nearly continuous on-strike exposure. d) Reversals from Mirassol d'Oeste and Nuccaleena cap carbonates cannot correlate directly with each other if post-Snowball paleooceanographic carbon isotope trends or values are assumed to be globally synchronous. Allowing for complex ocean chemistry, the two units could be broadly coeval, but if both paleomagnetic signals are primary then they must be diachronous on polarity-zone timescales. e) Given the pattern of observed reversal profiles established with confidence for at least the Nuccaleena cap, we contend that only magnetostratigraphic studies of high spatial

  9. Critical binding and electron scattering by symmetric-top polar molecules.

    PubMed

    Garrett, W R

    2014-10-28

    Quantum treatments of electron interactions with polar symmetric-top rotor molecules show features not present in the treatment of the linear-polar-rotor model. For symmetric tops possessing non-zero angular momentum about the symmetry axis, a new critical dipole can be defined that guarantees an infinite set of dipole-bound states independent of the values of the components of the inertial tensor. Additionally, for this same class, the scattering cross section diverges for all nonzero values of dipole moments and inertial moments, similar to solutions for the fixed linear dipole. Additional predictions are presented for electron affinities and rotational resonances of these systems.

  10. Critical binding and electron scattering by symmetric-top polar molecules

    SciTech Connect

    Garrett, W. R.

    2014-10-28

    Quantum treatments of electron interactions with polar symmetric-top rotor molecules show features not present in the treatment of the linear-polar-rotor model. For symmetric tops possessing non-zero angular momentum about the symmetry axis, a new critical dipole can be defined that guarantees an infinite set of dipole-bound states independent of the values of the components of the inertial tensor. Additionally, for this same class, the scattering cross section diverges for all nonzero values of dipole moments and inertial moments, similar to solutions for the fixed linear dipole. Additional predictions are presented for electron affinities and rotational resonances of these systems.

  11. Direct observation of the magnetic spin component of samarium iron-based laves compound by magnetic Compton scattering

    NASA Astrophysics Data System (ADS)

    Mizusaki, S.; Kawamura, N.; Taniguchi, T.; Itou, M.; Samata, H.; Noro, Y.; Sakurai, Y.; Nagata, Y.

    2007-03-01

    The spin-polarized electron momentum distributions (magnetic Compton profiles: MCP's) of SmFe 1.86Al 0.14 along the [1 1 1] direction have been measured at 10 and 300 K using the magnetic Compton scattering technique. It is found that the orbital moment dominates the magnetization in this compound. A comparison with a theoretical profile support that the shape of the experimental MCP's is reproduced by a sum of positive Fe and negative Sm 4f spin components. A slight difference is observed in the shape of MCP between 10 and 300 K.

  12. SCATTERING OF THE f-MODE BY SMALL MAGNETIC FLUX ELEMENTS FROM OBSERVATIONS AND NUMERICAL SIMULATIONS

    SciTech Connect

    Felipe, T.; Braun, D.; Crouch, A.; Birch, A.

    2012-10-01

    The scattering of f-modes by magnetic tubes is analyzed using three-dimensional numerical simulations. An f-mode wave packet is propagated through a solar atmosphere embedded with three different flux tube models that differ in radius and total magnetic flux. A quiet-Sun simulation without a tube present is also performed as a reference. Waves are excited inside the flux tube and propagate along the field lines, and jacket modes are generated in the surroundings of the flux tube, carrying 40% as much energy as the tube modes. The resulting scattered wave is mainly an f-mode composed of a mixture of m = 0 and m = {+-}1 modes. The amplitude of the scattered wave approximately scales with the magnetic flux. A small amount of power is scattered into the p{sub 1}-mode. We have evaluated the absorption and phase shift from a Fourier-Hankel decomposition of the photospheric vertical velocities. They are compared with the results obtained from the ensemble average of 3400 small magnetic elements observed in high-resolution MDI Doppler datacubes. The comparison shows that the observed dependence of the phase shift with wavenumber can be matched reasonably well with the simulated flux tube model. The observed variation of the phase shifts with the azimuthal order m appears to depend on details of the ensemble averaging, including possible motions of the magnetic elements and asymmetrically shaped elements.

  13. A portable high-field pulsed magnet system for x-ray scattering studies.

    SciTech Connect

    Islam, Z.; Ruff, J.P.C.; Nojiri, H.; Matsuda, Y. H.; Ross, K. A.; Gaulin, B. D.; Qu, Z.; Lang, J. C.

    2009-01-01

    We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields (- 1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.

  14. Electromagnetic energy within a magnetic infinite cylinder and scattering properties for oblique incidence.

    PubMed

    Arruda, Tiago José; Martinez, Alexandre Souto

    2010-07-01

    We analytically calculate the time-averaged electromagnetic energy stored inside a nondispersive magnetic isotropic cylinder that is obliquely irradiated by an electromagnetic plane wave. An expression for the optical-absorption efficiency in terms of the magnetic internal coefficients is also obtained. In the low absorption limit, we derive a relation between the normalized internal energy and the optical-absorption efficiency that is not affected by the magnetism and the incidence angle. This relation, indeed, seems to be independent of the shape of the scatterer. This universal aspect of the internal energy is connected to the transport velocity and consequently to the diffusion coefficient in the multiple scattering regime. Magnetism favors high internal energy for low size parameter cylinders, which leads to a low diffusion coefficient for electromagnetic propagation in 2D random media.

  15. Vibration effect on magnetization and critical current density of superconductors

    NASA Astrophysics Data System (ADS)

    Golovchanskiy, Igor A.; Pan, Alexey V.; George, Jonathan; Wells, Frederick S.; Fedoseev, Sergey A.; Rozenfeld, Anatoly

    2016-07-01

    In this work the effect of vibrations on critical current density (J c ) of superconductors has been studied. The vibrations are shown to affect J c of all types of superconductors during their measurements, employing a vibrating sample magnetometer (VSM). Increasing vibration frequency (f) and/or amplitude (A) leads to progressive reduction of J c as a function of magnetic field (B a ). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on {J}c({B}a) curves. Analysis of magnetization loops and relaxation of magnetization in YBCO films revealed that the vibration effect can be treated as the effective reduction of pinning potential. The asymmetry of the vibration effect in ascending and descending B a is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A are shown to have rather insignificant influence, while the vibrational vortex dynamics exhibit a strong impact. The irreversibility field ({B}{{irr}}) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of {B}{{irr}} for J c modeling is demonstrated.

  16. Magnetic field dependence of critical currents in superconducting polycrystals

    SciTech Connect

    Kugel, K.I.; Lisovskaya, T.Y. ); Mints, R.G. )

    1992-02-10

    The authors study the dependence of critical current j{sub c} on magnetic field H in superconducting polycrystals which are considered as system of superconducting crystallites (isotropic or anisotropic) with Josephson contacts between them. Isotropy or anisotropy of contacts depends on the orientation of their crystallographic axes relatively to edges of contact planes. In this paper it is shown that for a system of randomly oriented isotropic contacts, the dependence j{sub c}(H) in a relatively wide field range has the asymptotic form j{sub c} {approximately} (InH)/H{sup 2}. This differs drastically from j{sub c}(H) for single contacts. Anisotropy effects due to large differences in London penetration depth {lambda} values corresponding to external magnetic field directed along different axes are analyzed in detail. It is shown that for uniaxal crystals with {lambda}{sub 1} = {lambda}{sub 2} {lt} {lambda}{sub 3}, this anisotropy leads to the relation j{sub c} {approximately} {radical}{lambda}{sub 3}/{lambda}{sub 1} for chaotic orientation of crystallites. The form of j{sub c}(H) curves for two different orientations of the magnetic field relatively to the transport current through the sample is found.

  17. A Laboratory Scale Critical-Dimension Small-Angle X-ray Scattering Instrument

    SciTech Connect

    Ho, Derek L.; Wang Chengqing; Lin, Eric K.; Jones, Ronald L.; Wu Wenli

    2007-09-26

    New methods for critical dimension (CD) measurements may be needed to enable the detailed characterization of nanoscale structures produced in the semiconductor industry and for nanotechnology applications. In earlier work, small angle x-ray scattering (SAXS) measurements with synchrotron sources have shown promise in meeting several grand challenges for CD metrology. However, it is not practical to depend upon x-ray synchrotron sources, which are large national facilities with limitations in the number of available instruments. To address this problem, a laboratory scale SAXS instrument for critical dimension measurements on periodic nanoscale patterns has been designed, installed, and tested. The system possesses two configurations, SAXS and ultra-small-angle x-ray scattering (USAXS), with a radiation target of either copper or molybdenum. With these configurations, the instrument is capable of accessing scattering angles that probe length scales ranging from ca. 0.5 nm to 2 {mu}m. In this work, we compare CD-SAXS measurements taken from a synchrotron-based SAXS at the Advanced Photon Source of the Argonne National Laboratory with those from the National Institute of Standards and Technology laboratory-scale SAXS instrument. The results from standard line/space gratings possessing periodic line-space patterns with CDs of tens to hundreds of nanometers show that the laboratory-scale system can quantitatively measure parameters, such as the pitch, line width, height, line-width roughness and sidewall angle. These results show that laboratory-scale measurements are feasible and can be used for research and development purposes or to assist calibration of optical scatterometry and CD-scanning electron microscopy instruments. The primary limitation of the measurement is that the data collection rate is unacceptably slow for production metrology because of the significantly lower x-ray beam fluxes currently available.

  18. Small-angle neutron scattering correlation functions of bulk magnetic materials

    PubMed Central

    Mettus, Denis; Michels, Andreas

    2015-01-01

    On the basis of the continuum theory of micromagnetics, the correlation function of the spin-misalignment small-angle neutron scattering cross section of bulk ferromagnets (e.g. elemental polycrystalline ferromagnets, soft and hard magnetic nanocomposites, nanoporous ferromagnets, or magnetic steels) is computed. For such materials, the spin disorder which is related to spatial variations in the saturation magnetization and magnetic anisotropy field results in strong spin-misalignment scattering dΣM/dΩ along the forward direction. When the applied magnetic field is perpendicular to the incoming neutron beam, the characteristics of dΣM/dΩ (e.g. the angular anisotropy on a two-dimensional detector or the asymptotic power-law exponent) are determined by the ratio of magnetic anisotropy field strength H p to the jump ΔM in the saturation magnetization at internal interfaces. Here, the corresponding one- and two-dimensional real-space correlations are analyzed as a function of applied magnetic field, the ratio H p/ΔM, the single-particle form factor and the particle volume fraction. Finally, the theoretical results for the correlation function are compared with experimental data on nanocrystalline cobalt and nickel. PMID:26500464

  19. Stimulated Raman back scattering of extraordinary electromagnetic waves from periodically magnetized nanoparticle lattice

    SciTech Connect

    Chakhmachi, A.

    2013-06-15

    Stimulated Raman back scattering of extraordinary electromagnetic waves from the nanoparticle lattice is investigated in the presence of the static magnetic field. In the context of macroscopic theory, dispersion relation and growth rate of extraordinary mode for different values of static magnetic field and lattice parameters are derived and analyzed. It is found that when the static magnetic field is off, dispersion relation has two branches. These branches are related to the plasmonic and body wave branches of the plane polarized wave. Low frequency branch of the pump wave is not involved in the instability while the other branch is not stable, and the growth rate of Raman back scattered wave has one peak. If the electrons have cyclotron frequency by static magnetic field, dispersion has three branches. These branches are related to the plasmonic and body wave branches of left and right hand circularly polarized waves. In this situation, it is found that low frequency lower branch of the pump wave is stable while other branches are not stable, and the growth rate of Raman back scattered wave has three peaks. Numerical study of growth rate in various cyclotron frequencies shows that the growth rate increases and the instability band width decreases with increasing static magnetic field.

  20. Spin-dependent scattering in multilayered magnetic rings.

    PubMed

    Castaño, F J; Morecroft, D; Jung, W; Ross, C A

    2005-09-23

    Narrow mesoscopic NiFe/Cu/Co elliptical rings exhibit room-temperature giant magnetoresistance with distinct resistance levels corresponding to three different micromagnetic states. The highest and lowest resistance states of the multilayer rings correspond to the Co layer being in a bidomain state, antiparallel or parallel, respectively, to the NiFe, while the intermediate resistance corresponds to the Co layer being in a vortex state. Micromagnetic simulations suggest that the behavior of these rings is dominated by magnetostatic interactions between the domain walls in the Co and NiFe layers. Additional magnetization states in the NiFe at low applied fields can account for the minor loop behavior.

  1. The effects of pseudo magnetic fields in molecular spectra and scattering

    SciTech Connect

    Kendrick, B.

    1996-12-31

    Pseudo magnetic fields appear in the Born-Oppenheimer method for molecules when conical intersections or electronic angular momenta are taken into account. These fields are not real magnetic fields but they have the same mathematical properties and can lead to real observable effects in the dynamics of molecules. A general vector potential (gauge theory) approach for including these field effects in the Born-Oppenheimer method is introduced and applied to H + O{sub 2} scattering and the vibrational spectrum of Na{sub 3}(X) for zero total angular momentum (J = 0). The scattering results for HO{sub 2} show significant shifts in the resonance energies and lifetimes due to a magnetic solenoid type field originating from the C{sub 2v} conical intersection in HO{sub 2}. Significant changes in the state-to-state transition probabilities are also observed. The non-degenerate A{sub 1} and A{sub 2} vibrational spectra of Na{sub 3}(X) show significant shifts in the energy levels due to a magnetic solenoid type field originating from the D{sub 3h} conical intersection in Na{sub 3}. These two examples show that the effects of pseudo magnetic fields can be significant and in many cases they must be included in order to obtain agreement between theory and experiment. The newly developed gauge theory techniques for treating pseudo magnetic fields are also relevant for including the effects of real magnetic fields.

  2. A single-solenoid pulsed-magnet system for single-crystal scattering studies.

    PubMed

    Islam, Zahirul; Capatina, Dana; Ruff, Jacob P C; Das, Ritesh K; Trakhtenberg, Emil; Nojiri, Hiroyuki; Narumi, Yasuo; Welp, Ulrich; Canfield, Paul C

    2012-03-01

    We present a pulsed-magnet system that enables x-ray single-crystal diffraction in addition to powder and spectroscopic studies with the magnetic field applied on or close to the scattering plane. The apparatus consists of a single large-bore solenoid, cooled by liquid nitrogen. A second independent closed-cycle cryostat is used for cooling samples near liquid helium temperatures. Pulsed magnetic fields close to ~30 T with a zero-to-peak-field rise time of ~2.9 ms are generated by discharging a 40 kJ capacitor bank into the magnet coil. The unique characteristic of this instrument is the preservation of maximum scattering angle (~23.6°) on the entrance and exit sides of the magnet bore by virtue of a novel double-funnel insert. This instrument will facilitate x-ray diffraction and spectroscopic studies that are impractical, if not impossible, to perform using split-pair and narrow-opening solenoid magnets. Furthermore, it offers a practical solution for preserving optical access in future higher-field pulsed magnets.

  3. New generation of cryogen free advanced superconducting magnets for neutron scattering experiments

    NASA Astrophysics Data System (ADS)

    Kirichek, O.; Brown, J.; Adroja, D. T.; Manuel, P.; Kouzmenko, G.; Bewley, R. I.; Wotherspoon, R.

    2012-12-01

    Recent advances in superconducting technology and cryocooler refrigeration have resulted in a new generation of advanced superconducting magnets for neutron beam applications. These magnets have outstanding parameters such as high homogeneity and stability at highest magnetic fields possible, a reasonably small stray field, low neutron scattering background and larger exposure to neutron detectors. At the same time the pulse tube refrigeration technology provides a complete re-condensing regime which allows to minimise the requirements for cryogens without introducing additional noise and mechanical vibrations. The magnets can be used with dilution refrigerator insert which expands the temperature range from 20mK to 300K. Here we are going to present design, test results and the operational data of the 14T magnet for neutron diffraction and the 9T wide angle chopper magnet for neutron spectroscopy developed by Oxford Instruments in collaboration with ISIS neutron source. First scientific results obtained from the neutron scattering experiments with these magnets are also going to be discussed.

  4. Exact scattering matrix of graphs in magnetic field and quantum noise

    SciTech Connect

    Caudrelier, Vincent; Mintchev, Mihail; Ragoucy, Eric

    2014-08-15

    We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear Johnson-Nyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.

  5. Spin, orbital ordering, and magnetic dynamics of LaVO{sub 3}: Magnetization, heat capacity, and neutron scattering studies

    SciTech Connect

    Tung, L. D.; Ivanov, A.; Schefer, J.; Lees, M. R.; Balakrishnan, G.; Paul, D. McK.

    2008-08-01

    We report the results of magnetization, heat capacity, and neutron scattering studies of LaVO{sub 3} single crystals. From the neutron-diffraction studies, it was found that the compound is magnetically ordered with a C-type antiferromagnetic spin structure at about 136 K. In the vicinity of the ordering temperature, we also observed hysteresis in the neutron-diffraction data measured on cooling and heating which indicates the first-order nature of the phase transition. In the antiferromagnetically ordered phase, the inelastic neutron scattering studies reveal the presence of a temperature independent c-axis spin-wave gap of about 6 meV which is similar to that previously reported for the sister compound YVO{sub 3}.

  6. Scattering-induced quantum correlation in electronic waveguides with static magnetic impurities

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, E.; Soltani, M.; Alami, Z.; Sheikhali, M.

    2016-10-01

    Entanglement generation due to low-energy scattering of the transporting electrons in an electronic waveguide by a quantum dot magnetic impurity is theoretically investigated. The transverse confining potential of the waveguide is considered as a two-dimensional harmonic potential, and the interaction of the electron with the impurity is described by a zero-range pseudopotential modulated by an Ising or a Heisenberg spin interaction. Our calculation shows that the scattering process leads to creation of a considerable amount of entanglement in the state of the reflected and transmitted electrons. The situation is extended to the scattering of the electrons by two well-separated magnetic impurities localized on the nanowire axis. It is shown that the scattering process causes the magnetic impurities embedded in the nanowire to share their quantum information; subsequently, they can be entangled by spin interaction with the injected electron. The created entanglement between the impurities is calculated and discussed. It is shown that the exact three-dimensional problem can be approximated as a one-dimensional problem under certain circumstances. The approximate results are compared to exact calculations and discussed.

  7. Stimulated Raman scattering in the relativistic regime in near-critical plasmas

    NASA Astrophysics Data System (ADS)

    Moreau, J. G.; d'Humières, E.; Nuter, R.; Tikhonchuk, V. T.

    2017-01-01

    Interaction of a high-intensity short laser pulse with near-critical plasmas allows us to achieve extremely high coupling efficiency and transfer laser energy to energetic ions. One-dimensional particle-in-cell simulations are considered to detail the processes involved in the energy transfer. A confrontation of the numerical results with the theory highlights a key role played by the process of stimulated Raman scattering in the relativistic regime. The interaction of a 1 ps laser pulse (I ˜6 ×1018W cm-2 with an undercritical (0.5 nc ) homogeneous plasma leads to a very high plasma absorption reaching 68% of the laser pulse energy. This permits a homogeneous electron heating all along the plasma and an efficient ion acceleration at the plasma edges and in cavities.

  8. STUDY MAGNETIC EXCITATIONS IN DOPED TRANSITION METAL OXIDES USING INELASTIC NEUTRON SCATTERING

    SciTech Connect

    Dai, Pengcheng

    2014-02-18

    Understanding the interplay between magnetism and superconductivity continues to be a “hot” topic in modern condensed matter physics. The discovery of high-temperature superconductivity in iron-based materials in 2008 provided an unique opportunity to compare and contrast these materials with traditional high-Tc copper oxide superconductors. Neutron scattering plays an important role in determining the dynamical spin properties in these materials. This proposal is a continuation of previous DOE supported proposal. This report summarizes the final progress we have made over from May 2005 till Aug. 2013. Overall, we continue to carry out extensive neutron scattering experiments on Fe-based materials, focusing on understanding their magnetic properties. In addition, we have established a materials laboratory at UT that has allowed us to grow these superconductors. Because neutron scattering typically demands a large amount of samples, by growing these materials in our own laboratory, we can now pursuit neutron scattering experiments over the entire electronic phase diagram, focusing on regions of interests. The material synthesis laboratory at UT was established entirely with the support of DOE funding. This not only allowed us to carry out neutron scattering experiments, but also permit us to provide samples to other US/International collaborators for studying these materials.

  9. Diffuse magnetic neutron scattering in the highly frustrated double perovskite Ba2YRuO6

    DOE PAGES

    Nilsen, Gøran. J.; Thompson, Corey M.; Ehlers, Georg; ...

    2015-02-23

    Here we investigated diffuse magnetic scattering in the highly frustrated double perovskite Ba2YRuO6 using polarized neutrons. Consistent with previous reports, the material shows two apparent transitions at 47 and 36 K to an eventual type I face-centered-cubic magnetic ground state. The (100) magnetic reflection shows different behavior from the five other observed reflections upon heating from 1.8 K, with the former broadening well beyond the resolution limit near 36 K. Closer examination of the latter group reveals a small, but clear, increase in peak widths between 36 and 47 K, indicating that this regime is dominated by short-range spin correlations.more » Diffuse magnetic scattering persists above 47 K near the position of (100) to at least 200 K, consistent with strong frustration. Reverse Monte Carlo (RMC) modeling of the diffuse scattering from 45 to 200 K finds that the spin-spin correlations between nearest and next-nearest neighbors are antiferromagnetic and ferromagnetic, respectively, at temperatures near the upper ordering temperature, but both become antiferromagnetic and of similar magnitude above 100 K. The significance of this unusual crossover is discussed in light of the super-superexchange interactions between nearest and next-nearest neighbors in this material and the demands of type I order. The dimensionality of the correlations is addressed by reconstructing the scattering in the (hk0) plane using the RMC spin configurations. This indicates that one-dimensional spin correlations dominate at temperatures close to the first transition. In addition, a comparison between mean-field calculations and (hk0) scattering implies that further neighbor couplings play a significant role in the selection of the ground state. Finally, the results and interpretation are compared with those recently published for monoclinic Sr2YRuO6, and similarities and differences are emphasized.« less

  10. Buffer influence on magnetic dead layer, critical current, and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Frankowski, Marek; Żywczak, Antoni; Czapkiewicz, Maciej; Zietek, Sławomir; Kanak, Jarosław; Banasik, Monika; Powroźnik, Wiesław; Skowroński, Witold; Checiński, Jakub; Wrona, Jerzy; Głowiński, Hubert; Dubowik, Janusz; Ansermet, Jean-Philippe; Stobiecki, Tomasz

    2015-06-01

    We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magnetic anisotropy fields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights.

  11. Determination of the magnetic spin direction from the nuclear forward-scattering line intensities.

    PubMed

    Callens, R; L'abbé, C; Meersschaut, J; Serdons, I; Sturhahn, W; Toellner, T S

    2007-07-01

    An expression is derived for the line intensities in a nuclear forward-scattering energy spectrum that is obtained via a Fourier transformation of the time dependence of the wavefield. The calculation takes into account the coherent properties of the nuclear forward-scattering process and the experimental limitations on the observable time window. It is shown that, for magnetic samples, the spin direction can be determined from the ratios between the different lines in the energy spectrum. The theory is complemented with experimental results on alpha-iron.

  12. Stimulated ionization scattering of a wave beam forming a discharge channel in a magnetic mirror trap

    SciTech Connect

    Belov, A. S.; Markov, G. A.

    2008-03-15

    The stimulated scattering of a whistler wave beam forming an extended discharge channel in a magnetic mirror trap is discovered and investigated experimentally. It is shown that the beam is scattered by relaxaction oscillations of the lattice of plasma inhomogeneities excited by the beam field. The spectrum of the pump field in the RF discharge plasma is found to broaden considerably and to contain individual modulation peaks corresponding to lattice oscillations. The peaks are observed at working gas pressures at which the electron mean free path is close to the wavelength of the standing wave forming the discharge channel. A physical model describing the phenomena observed is developed.

  13. Pitch angle scattering of relativistic electrons from stationary magnetic waves: Continuous Markov process and quasilinear theory

    SciTech Connect

    Lemons, Don S.

    2012-01-15

    We develop a Markov process theory of charged particle scattering from stationary, transverse, magnetic waves. We examine approximations that lead to quasilinear theory, in particular the resonant diffusion approximation. We find that, when appropriate, the resonant diffusion approximation simplifies the result of the weak turbulence approximation without significant further restricting the regime of applicability. We also explore a theory generated by expanding drift and diffusion rates in terms of a presumed small correlation time. This small correlation time expansion leads to results valid for relatively small pitch angle and large wave energy density - a regime that may govern pitch angle scattering of high-energy electrons into the geomagnetic loss cone.

  14. Static and dynamic light scattering in nonionic critical micellar solutions of water-pentaethylene glycol n-dodecylether

    NASA Astrophysics Data System (ADS)

    Hamano, K.; Fukuhara, K.; Kuwahara, N.; Ducros, E.; Benseddik, M.; Rouch, J.; Tartaglia, P.

    1995-07-01

    Extensive sets of measurements of the shear viscosity, the scattered light intensity, and the relaxation rate of the order-parameter fluctuations lead us to reexamine the static and dynamic critical behaviors of binary solutions of pentaethylene glycol n-dodecylether (C12E5) and water. The scattered intensity, the scattered field correlation function, and the relaxation rate of the order parameter show systematic deviations from the behavior usually observed for simple or molecular binary fluids. A modified version of the Sorensen et al. [Phys. Rev. A 13, 1593 (1976)] dynamical droplet model that assumes that close to the critical point the critical clusters can be treated much like percolating aggregates having a fractal dimension df=2.49 and an associated polydispersity exponent τ=2.21 and which includes the finite size of the micelles, very well accounts for all our experimental results.

  15. Aerosol single-scattering albedo retrieval over North Africa using critical reflectance

    NASA Astrophysics Data System (ADS)

    Wells, Kelley C.

    The sign and magnitude of the aerosol radiative forcing over bright surfaces is highly dependent on the absorbing properties of the aerosol. Thus, the determination of aerosol forcing over desert regions requires accurate information about the aerosol single-scattering albedo (SSA). However, the brightness of desert surfaces complicates the retrieval of aerosol optical properties using passive space-based measurements. The aerosol critical reflectance is one parameter that can be used to relate top-of-atmosphere (TOA) reflectance changes over land to the aerosol absorption properties, without knowledge of the underlying surface properties or aerosol loading. Physically, the parameter represents the TOA reflectance at which increased aerosol scattering due to increased aerosol loading is balanced by increased absorption of the surface contribution to the TOA reflectance. It can be derived by comparing two satellite images with different aerosol loading, assuming that the surface reflectance and background aerosol are similar between the two days. In this work, we explore the utility of the critical reflectance method for routine monitoring of spectral aerosol absorption from space over North Africa, a region that is predominantly impacted by absorbing dust and biomass burning aerosol. We derive the critical reflectance from Moderate Resolution Spectroradiometer (MODIS) Level 1B reflectances in the vicinity of two Aerosol Robotic Network (AERONET) stations: Tamanrasset, a site in the Algerian Sahara, and Banizoumbou, a Sahelian site in Niger. We examine the sensitivity of the critical reflectance parameter to aerosol physical and optical properties, as well as solar and viewing geometry, using the Santa Barbara DISORT Radiative Transfer (SBDART) model, and apply our findings to retrieve SSA from the MODIS critical reflectance values. We compare our results to AERONET-retrieved estimates, as well as to measurements of the TOA albedo and surface fluxes from the

  16. Dynamical process of skyrmion-helical magnetic transformation of the chiral-lattice magnet FeGe probed by small-angle resonant soft x-ray scattering

    NASA Astrophysics Data System (ADS)

    Yamasaki, Y.; Morikawa, D.; Honda, T.; Nakao, H.; Murakami, Y.; Kanazawa, N.; Kawasaki, M.; Arima, T.; Tokura, Y.

    2015-12-01

    Small-angle soft x-ray scattering in resonance with Fe L absorption edge has been investigated for helical magnetic order and magnetic skyrmion crystal (SkX) in B20-type cubic FeGe. Transformation of magnetic structures among helical, conical, SkX, and field-polarized spin-collinear forms is observed with the application of a magnetic field parallel to the incident soft x-ray. The resonant soft x-ray scattering with high q -resolution revealed a transient dynamics of SkX, such as rotation of SkX and variation of the SkX lattice constant, upon the change of magnetic field.

  17. Weak localization and conductance fluctuations in a quantum dot with parallel magnetic field and spin-orbit scattering

    NASA Astrophysics Data System (ADS)

    Cremers, Jan-Hein; Brouwer, Piet W.; Fal'Ko, Vladimir I.

    2003-09-01

    In the presence of both spin-orbit scattering and a magnetic field the conductance of a chaotic GaAs quantum dot displays quite a rich behavior. Using a Hamiltonian derived by Aleiner and Fal’ko [Phys. Rev. Lett. 87, 256801 (2001)] we calculate the weak localization correction and the covariance of the conductance, as a function of parallel and perpendicular magnetic field and spin-orbit coupling strength. We also show how the combination of an in-plane magnetic field and spin-orbit scattering gives rise to a component to the magnetoconductance that is antisymmetric with respect to reversal of the perpendicular component of the magnetic field and how spin-orbit scattering leads to a “magnetic-field echo” in the conductance autocorrelation function. Our results can be used for a measurement of the Dresselhaus and Bychkov-Rashba spin-orbit scattering lengths in a GaAs/GaAlAs heterostructure.

  18. Tunable Magnetic Anisotropy from Higher-Harmonics Exchange Scattering on the Surface of a Topological Insulator.

    PubMed

    Paaske, Jens; Gaidamauskas, Erikas

    2016-10-21

    We show that higher-harmonics exchange scattering from a magnetic adatom on the surface of a three dimensional topological insulator leads to a magnetic anisotropy whose magnitude and sign may be tuned by adjusting the chemical potential of the helical surface band. As the chemical potential moves from the Dirac point towards the surface band edge, the surface normal is found to change from a magnetic easy to a hard axis. Hexagonal warping is shown to diminish the region with easy axis anisotropy, and to suppress the anisotropy altogether. This indirect contribution can be comparable in magnitude to the intrinsic term arising from crystal field splitting and atomic spin-orbit coupling, and its tunability with the chemical potential makes the two contributions experimentally discernible, and endows this source of anisotropy with potentially interesting magnetic functionality.

  19. Scattering of electromagnetic waves from a magnetized plasma column at oblique incidence

    SciTech Connect

    Ghaffari-Oskooei, Sara S.; Aghamir, Farzin M.

    2015-07-14

    Scattering of electromagnetic waves from a magnetized plasma column is investigated using Maxwell's equations and applying boundary conditions. Backscattering cross section is evaluated by analytic solution of electric fields inside and outside of plasma column. Plots of backscattering cross section versus frequency, for the range up to J band, reveal two main peaks and two sidebands. Effects of plasma density and radius, as main parameters determining the characteristics of plasma column, on backscattering are discussed. Furthermore, the effect of electromagnetic wave incidence angle on backscattering of plasma column is included in the analysis. The influence of wave incidence angle and frequency, as well as, plasma density and radius on scattering pattern, which is an indicator of the distribution of scattered power in different azimuthal angles, is discussed.

  20. Perturbative Quantum Analysis and Classical Limit of the Electron Scattering by a Solenoidal Magnetic Field

    SciTech Connect

    Murguia, Gabriela; Moreno, Matias; Torres, Manuel

    2009-04-20

    A well known example in quantum electrodynamics (QED) shows that Coulomb scattering of unpolarized electrons, calculated to lowest order in perturbation theory, yields a results that exactly coincides (in the non-relativistic limit) with the Rutherford formula. We examine an analogous example, the classical and perturbative quantum scattering of an electron by a magnetic field confined in an infinite solenoid of finite radius. The results obtained for the classical and the quantum differential cross sections display marked differences. While this may not be a complete surprise, one should expect to recover the classical expression by applying the classical limit to the quantum result. This turn not to be the case. Surprisingly enough, it is shown that the classical result can not be recuperated even if higher order corrections are included. To recover the classic correspondence of the quantum scattering problem a suitable non-perturbative methodology should be applied.

  1. Magnetic fields with photon beams: dose calculation using electron multiple-scattering theory.

    PubMed

    Jette, D

    2000-08-01

    Strong transverse magnetic fields can produce large dose enhancements and reductions in localized regions of a patient under irradiation by a photon beam. We have developed a new equation of motion for the transport of charged particles in an arbitrary magnetic field, incorporating both energy loss and multiple scattering. Key to modeling the latter process is a new concept, that of "typical scattered particles." The formulas which we have arrived at are particularly applicable to the transport of, and deposition of energy by, Compton electrons and pair-production electrons and positrons generated within a medium by a photon beam, and we have shown qualitatively how large dose enhancements and reductions can occur. A companion article examines this dose modification effect through systematic Monte Carlo simulations.

  2. Stochastic analysis of pitch angle scattering of charged particles by transverse magnetic waves

    SciTech Connect

    Lemons, Don S.; Liu Kaijun; Winske, Dan; Gary, S. Peter

    2009-11-15

    This paper describes a theory of the velocity space scattering of charged particles in a static magnetic field composed of a uniform background field and a sum of transverse, circularly polarized, magnetic waves. When that sum has many terms the autocorrelation time required for particle orbits to become effectively randomized is small compared with the time required for the particle velocity distribution to change significantly. In this regime the deterministic equations of motion can be transformed into stochastic differential equations of motion. The resulting stochastic velocity space scattering is described, in part, by a pitch angle diffusion rate that is a function of initial pitch angle and properties of the wave spectrum. Numerical solutions of the deterministic equations of motion agree with the theory at all pitch angles, for wave energy densities up to and above the energy density of the uniform field, and for different wave spectral shapes.

  3. Resonant Scattering off Magnetic Impurities in Graphene: Mechanism for Ultrafast Spin Relaxation

    NASA Astrophysics Data System (ADS)

    Kochan, D.; Gmitra, M.; Fabian, J.

    We give a tutorial account of our recently proposed mechanism for spin relaxation based on spin-flip resonant scattering off local magnetic moments. The mechanism is rather general, working in any material with a resonant local moment, but we believe that its particular niche is graphene, whose measured spin relaxation time is 100-1000 ps. Conventional spin-orbit coupling based mechanisms (Elliott-Yafet or Dyakonov-Perel) would require large concentrations (1000 ppm) of impurities to explain this. Our mechanism needs only 1 ppm of resonant local moments, as these act as local spin hot spots: the resonant scatterers do not appear to substantially affect graphene's measured resistivity, but are dominating spin relaxation. In principle, the local moments can come from a variety of sources. Most likely would be organic molecule adsorbants or metallic adatoms. As the representative model, particularly suited for a tutorial, we consider hydrogen adatoms which are theoretically and experimentally demonstrated to yield local magnetic moments when chemisorbed on graphene. We introduce the scattering formalism and apply it to graphene, to obtain the T-matrix and spin-flip scattering rates using the generalized Fermi golden rule.

  4. Absence of localized-spin magnetic scattering in the narrow-gap semiconductor FeSb2

    SciTech Connect

    Zaliznyak, Igor; Savici, Andrei T; Garlea, Vasile O; Hu, Rongwei; Petrovic, C

    2011-01-01

    We report inelastic neutron scattering measurements aimed at investigating the origin of the temperature-induced paramagnetism in the narrow-gap semiconductor FeSb2. We find that inelastic response for energies up to 60 meV and at temperatures ~ 4.2 K, ~ 300 K and ~ 550 K is consistent with scattering by the lattice phonon excitations. Hence, we observe no evidence for a well-defined magnetic excitation corresponding to transitions between the non-magnetic ground state and states of magnetic multiplet in the localized spin picture. However, a broad magnetic scattering continuum in the 15 meV to 35 meV energy range is not ruled out by our data. Our findings make description in terms of the localized Fe magnetic states unlikely and suggest that paramagnetic susceptibility of itinerant electrons is at the origin of the temperature-induced magnetism in FeSb2.

  5. Magnetic excitations in the kondo liquid: superconductivity and hidden magnetic quantum critical fluctuations.

    PubMed

    Yang, Yi-Feng; Urbano, Ricardo; Curro, Nicholas J; Pines, David; Bauer, E D

    2009-11-06

    We report Knight-shift experiments on the superconducting heavy-electron material CeCoIn5 that allow one to track with some precision the behavior of the heavy-electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the 115In nuclear quadrupole resonance spin-lattice relaxation rate T1(-1) measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy-electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point located at slightly negative pressure in CeCoIn5 and provide additional evidence for significant similarities between the heavy-electron materials and the high-T(c) cuprates.

  6. Influence of nonmagnetic impurity scattering on spin dynamics in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Cygorek, M.; Ungar, F.; Tamborenea, P. I.; Axt, V. M.

    2017-01-01

    The doping of semiconductors with magnetic impurities gives rise not only to a spin-spin interaction between quasifree carriers and magnetic impurities but also to a local spin-independent disorder potential for the carriers. Based on a quantum kinetic theory for the carrier and impurity density matrices as well as the magnetic and nonmagnetic carrier-impurity correlations, the influence of the nonmagnetic scattering potential on the spin dynamics in DMS after optical excitation with circularly polarized light is investigated using the example of Mn-doped CdTe. It is shown that non-Markovian effects, which are predicted in calculations where only the magnetic carrier-impurity interaction is accounted for, can be strongly suppressed in the presence of nonmagnetic impurity scattering. This effect can be traced back to a significant redistribution of carriers in k -space which is enabled by the build-up of large carrier-impurity correlation energies. A comparison with the Markov limit of the quantum kinetic theory shows that, in the presence of an external magnetic field parallel to the initial carrier polarization, the asymptotic value of the spin polarization at long times is significantly different in the quantum kinetic and the Markovian calculations. This effect can also be attributed to the formation of strong correlations, which invalidates the semiclassical Markovian picture and it is stronger when the nonmagnetic carrier-impurity interaction is accounted for. In an external magnetic field perpendicular to the initial carrier spin, the correlations are also responsible for a renormalization of the carrier spin precession frequency. Considering only the magnetic carrier-impurity interaction, a significant renormalization is predicted for a very limited set of material parameters and excitation conditions. Accounting also for the nonmagnetic interaction, a relevant renormalization of the precession frequency is found to be more ubiquitous.

  7. Mirroring within the Fokker-Planck formulation of cosmic ray pitch angle scattering in homogeneous magnetic turbulence

    NASA Technical Reports Server (NTRS)

    Goldstein, M. L.; Klimas, A. J.; Sandri, G.

    1974-01-01

    The Fokker-Planck coefficient for pitch angle scattering, appropriate for cosmic rays in homogeneous, stationary, magnetic turbulence, is computed from first principles. No assumptions are made concerning any special statistical symmetries the random field may have. This result can be used to compute the parallel diffusion coefficient for high energy cosmic rays moving in strong turbulence, or low energy cosmic rays moving in weak turbulence. Becuase of the generality of the magnetic turbulence which is allowed in this calculation, special interplanetary magnetic field features such as discontinuities, or particular wave modes, can be included rigorously. The reduction of this results to previously available expressions for the pitch angle scattering coefficient in random field models with special symmetries is discussed. The general existance of a Dirac delta function in the pitch angle scattering coefficient is demonstrated. It is proved that this delta function is the Fokker-Planck prediction for pitch angle scattering due to mirroring in the magnetic field.

  8. Observation of Laser Induced Magnetization Dynamics in Co/Pd Multilayers with Coherent X-ray Scattering

    SciTech Connect

    Wu, Benny

    2012-04-05

    We report on time-resolved coherent x-ray scattering experiments of laser induced magnetization dynamics in Co/Pd multilayers with a high repetition rate optical pump x-ray probe setup. Starting from a multi-domain ground state, the magnetization is uniformly reduced after excitation by an intense 50 fs laser pulse. Using the normalized time correlation, we study the magnetization recovery on a picosecond timescale. The dynamic scattering intensity is separated into an elastic portion at length scales above 65 nm which retains memory of the initial domain magnetization, and a fluctuating portion at smaller length scales corresponding to domain boundary motion during recovery.

  9. Stable superconducting magnet. [high current levels below critical temperature

    NASA Technical Reports Server (NTRS)

    Boom, R. W. (Inventor)

    1967-01-01

    Operation of a superconducting magnet is considered. A method is described for; (1) obtaining a relatively high current in a superconducting magnet positioned in a bath of a gas refrigerant; (2) operating a superconducting magnet at a relatively high current level without training; and (3) operating a superconducting magnet containing a plurality of turns of a niobium zirconium wire at a relatively high current level without training.

  10. Magnetic-field-dependent small-angle neutron scattering on random anisotropy ferromagnets

    NASA Astrophysics Data System (ADS)

    Michels, Andreas; Weissmüller, Jörg

    2008-06-01

    We report on the recently developed technique of magnetic-field-dependent small-angle neutron scattering (SANS), with attention to bulk ferromagnets exhibiting random magnetic anisotropy. In these materials, the various magnetic anisotropy fields (magnetocrystalline, magnetoelastic, and/or magnetostatic in origin) perturb the perfectly parallel spin alignment of the idealized ferromagnetic state. By varying the applied magnetic field, one can control one of the ordering terms which competes with the above-mentioned perturbing fields. Experiments which explore the ensuing reaction of the magnetization will therefore provide information not only on the field-dependent spin structure but, importantly, on the underlying magnetic interaction terms. This strategy, which underlies conventional studies of hysteresis loops in magnetometry, is here combined with magnetic SANS. While magnetometry generally records only a single scalar quantity, the integral magnetization, SANS provides access to a vastly richer data set, the Fourier spectrum of the response of the spin system as a function of the magnitude and orientation of the wave vector. The required data-analysis procedures have recently been established, and experiments on a number of magnetic materials, mostly nanocrystalline or nanocomposite metals, have been reported. Here, we summarize the theory of magnetic-field-dependent SANS along with the underlying description of random anisotropy magnets by micromagnetic theory. We review experiments which have explored the magnetic interaction parameters, the value of the exchange-stiffness constant as well as the Fourier components of the magnetic anisotropy field and of the magnetostatic stray field. A model-independent approach, based on the experimental autocorrelation function of the spin misalignment, provides access to the characteristic length of the spin misalignment. The field dependence of this quantity is in quantitative agreement with the predictions of

  11. Levitation force on a permanent magnet over a superconducting plane: Modified critical-state model

    SciTech Connect

    Yang, Z.J.

    1997-08-01

    The authors consider a model system of a permanent magnet above a semi-infinite superconductor. They introduce a modified critical-state model, and carry out derivations of the levitation force acting on the magnet. A key feature of the modification allows the current density to be less than the critical value. The theoretical results show an exponential relationship between the force and the distance. Analytical expressions are developed for permanent magnets in the form of a point dipole, a tip of a magnetic force microscope, and a cylindrical magnet. In the latter case, the exponential relationship has been observed in numerous experiments but without previous interpretation.

  12. An Assessment of Critical Dimension Small Angle X-ray Scattering Metrology for Advanced Semiconductor Manufacturing

    SciTech Connect

    Settens, Charles M.

    2015-01-01

    Simultaneous migration of planar transistors to FinFET architectures, the introduction of a plurality of materials to ensure suitable electrical characteristics, and the establishment of reliable multiple patterning lithography schemes to pattern sub-10 nm feature sizes imposes formidable challenges to current in-line dimensional metrologies. Because the shape of a FinFET channel cross-section immediately influences the electrical characteristics, the evaluation of 3D device structures requires measurement of parameters beyond traditional critical dimension (CD), including their sidewall angles, top corner rounding and footing, roughness, recesses and undercuts at single nanometer dimensions; thus, metrologies require sub-nm and approaching atomic level measurement uncertainty. Synchrotron critical dimension small angle X-ray scattering (CD-SAXS) has unique capabilities to non-destructively monitor the cross-section shape of surface structures with single nanometer uncertainty and can perform overlay metrology to sub-nm uncertainty. In this dissertation, we perform a systematic experimental investigation using CD-SAXS metrology on a hierarchy of semiconductor 3D device architectures including, high-aspect-ratio contact holes, H2 annealed Si fins, and a series of grating type samples at multiple points along a FinFET fabrication process increasing in structural intricacy and ending with fully fabricated FinFET. Comparative studies between CD-SAXS metrology and other relevant semiconductor dimensional metrologies, particularly CDSEM, CD-AFM and TEM are used to determine physical limits of CD-SAXS approach for advanced semiconductor samples. CD-SAXS experimental tradeoffs, advice for model-dependent analysis and thoughts on the compatibility with a semiconductor manufacturing environment are discussed.

  13. High Field Pulsed Magnets for Neutron Scattering at the Spallation Neutron Source

    NASA Astrophysics Data System (ADS)

    Granroth, G. E.; Lee, J.; Fogh, E.; Christensen, N. B.; Toft-Petersen, R.; Nojiri, H.

    2015-03-01

    A High Field Pulsed Magnet (HFPM) setup, is in use at the Spallation Nuetron Source(SNS), Oak Ridge National Laboratory. With this device, we recently measured the high field magnetic spin structure of LiNiPO4. The results of this study will be highlighted as an example of possible measurements that can be performed with this device. To further extend the HFPM capabilities at SNS, we have learned to design and wind these coils in house. This contribution will summarize the magnet coil design optimization procedure. Specifically by varying the geometry of the multi-layer coil, we arrive at a design that balances the maximum field strength, neutron scattering angle, and the field homogeneity for a specific set of parameters. We will show that a 6.3kJ capacitor bank, can provide a magnetic field as high as 30T for a maximum scattering angle around 40° with homogeneity of +/- 4 % in a 2mm diameter spherical volume. We will also compare the calculations to measurements from a recently wound test coil. This work was supported in part by the Lab Directors' Research and Development Fund of ORNL.

  14. Magnetic Excitations in Transition-metal Oxides Studied by Inelastic Neutron Scattering

    NASA Astrophysics Data System (ADS)

    Braden, M.

    2008-03-01

    Inelastic neutron scattering using a triple axis spectrometer is a very efficient tool to analyze magnetic excitations. We will discuss several recent experiments on transition-metal oxides where orbital degrees of freedom play an important role. Different kinds of experimental techniques including longitudinal and spherical polarization analysis were used in order to determine not only magnon frequencies but also polarization vectors. In layered ruthenates bands of different orbital character contribute to the magnetic excitations which are of both, ferromagnetic and antiferromagnetic, character. The orbital dependent magnetic excitations seem to play different roles in the superconducting pairing as well as in the metamagnetism . In manganates the analysis of the magnon dispersion in the charge and orbital ordered phase yields direct insight into the microscopic coupling of orbital and magnetic degrees of freedom and helps understanding, how the switching between metallic and insulating phases in manganates may occur. In multiferroic TbMnO3 the combination of our polarized neutron scattering results with the infrared measurements identifies a soft collective excitation of hybridized magnon-phonon character.

  15. IRMA-2 at SOLEIL: a set-up for magnetic and coherent scattering of polarized soft x-rays

    NASA Astrophysics Data System (ADS)

    Sacchi, M.; Popescu, H.; Gaudemer, R.; Jaouen, N.; Avila, A.; Delaunay, R.; Fortuna, F.; Maier, U.; Spezzani, C.

    2013-03-01

    We have designed, built and tested a new instrument for soft x-ray scattering experiments. IRMA-2 is a UHV set-up for elastic and coherent scattering experiments developed at the SEXTANTS beamline of the SOLEIL synchrotron. Applications will be in the field of solid state physics, with emphasis on the investigation of the magnetic properties of artificially structured materials.

  16. Double criticality in the magnetic field driven transition of a high-TC superconductor

    NASA Astrophysics Data System (ADS)

    Leridon, Brigitte; Vanacken, Johan; Moshchalkov, V. V.; Vignolle, Baptiste; Porwal, Rajni; Budhani, R. C.

    2015-03-01

    The magnetic-field driven transition of a set of high critical temperature La2 - x Srx CuO4 superconducting thin films has been investigated using high pulsed magnetic fields. For the underdoped samples, the existence of two distinct critical regions in the superconductor/insulator transition has been evidenced for the first time. The first quantum critical region is observed at intermediate magnetic fields (~= 19 T)and temperatures and gives way at lower temperature to a quantum critical point at about twice critical magnetic field and resistance per square. The critical exponents inferred from scaling behaviour are markedly different for the two regions. We attribute this behaviour to the existence of a clean/dirty crossover due to the presence of electronic inhomogeneities. This work has been supported by a SESAME grant from Region Ile-de-France. Part of the experiments at KULeuven have been founded by EuroMagNET II under the EU Contract Number 228043.

  17. Fiber optic quench detection via optimized Rayleigh Scattering in high-field YBCO accelerator magnets

    SciTech Connect

    Flanagan, Gene

    2016-02-17

    Yttrium barium copper oxide (YBCO) coated conductors are known for their ability to operate in the superconducting state at relatively high temperatures, even above the boiling point of liquid nitrogen (77 K). When these same conductors are operated at lower temperatures, they are able to operate in much higher magnetic fields than traditional superconductors like NiTi or Nb3Sn. Thus, YBCO superconducting magnets are one of the primary options for generating the high magnetic fields needed for future high energy physics devices. Due to slow quench propagation, quench detection remains one of the primary limitations to YBCO magnets. Fiber optic sensing, based upon Rayleigh scattering, has the potential for spatial resolution approaching the wavelength of light, or very fast temporal resolution at low spatial resolution, and a continuum of combinations in between. This project has studied, theoretically and experimentally, YBCO magnets and Rayleigh scattering quench detection systems to demonstrate feasibility of the systems for YBCO quench protection systems. Under this grant an experimentally validated 3D quench propagation model was used to accurately define the acceptable range of spatial and temporal resolutions for effective quench detection in YBCO magnets and to evaluate present-day and potentially improved YBCO conductors. The data volume and speed requirements for quench detection via Rayleigh scattering required the development of a high performance fiber optic based quench detection/data acquisition system and its integration with an existing voltage tap/thermo-couple based system. In this project, optical fibers are tightly co-wound into YBCO magnet coils, with the fiber on top of the conductor as turn-to-turn insulation. Local changes in the temperature or strain of the conductor are sensed by the optical fiber, which is in close thermal and mechanical contact with the conductor. Intrinsic imperfections in the fiber reflect Rayleigh

  18. Stimulated Raman Scattering of a Laser in a Magnetic Plasma Channel

    NASA Astrophysics Data System (ADS)

    Parashar, J.

    A depressed density plasma channel, in the presence of a strong azimuthal magnetic field, supports localized lower hybrid modes of finite azimuthal mode number. A high amplitude laser propagating through the channel undergoes stimulated Raman scattering off a lower hybrid mode producing a back propagating electromagnetic sideband wave. The pump beats with the sideband to exert a ponderomotive force on the electrons driving the lower hybrid wave. The density perturbations associated with the lower hybrid wave couple with the oscillatory velocity due to the pump, producing a nonlinear current, driving the sideband. The radial profile of the sideband and the frequency shift have signatures of magnetic field and can be used as a diagnostics for azimuthal magnetic field.

  19. Light scattering of rectangular slot antennas: parallel magnetic vector vs perpendicular electric vector

    PubMed Central

    Lee, Dukhyung; Kim, Dai-Sik

    2016-01-01

    We study light scattering off rectangular slot nano antennas on a metal film varying incident polarization and incident angle, to examine which field vector of light is more important: electric vector perpendicular to, versus magnetic vector parallel to the long axis of the rectangle. While vector Babinet’s principle would prefer magnetic field along the long axis for optimizing slot antenna function, convention and intuition most often refer to the electric field perpendicular to it. Here, we demonstrate experimentally that in accordance with vector Babinet’s principle, the incident magnetic vector parallel to the long axis is the dominant component, with the perpendicular incident electric field making a small contribution of the factor of 1/|ε|, the reciprocal of the absolute value of the dielectric constant of the metal, owing to the non-perfectness of metals at optical frequencies. PMID:26740335

  20. Magnetic assistance highly sensitive protein assay based on surface-enhanced resonance Raman scattering.

    PubMed

    Chen, Lei; Hong, Wonjin; Guo, Zhinan; Sa, Youngjo; Wang, Xu; Jung, Young Mee; Zhao, Bing

    2012-02-15

    A simple and effective surface-enhanced Raman scattering (SERS)-based protocol for the detection of protein-small molecule interactions has been developed. We employed silver-coated magnetic particles (AgMNPs), which can provide high SERS activity as a protein carrier to capture a small molecule. Combining magnetic separation and the SERS method for protein detection, highly reproducible SERS spectra of a protein-small molecule complex can be obtained with high sensitivity. This time-saving method employs an external magnetic field to induce the AgMNPs to aggregate to increase the amount of atto610-biotin/avidin complex in a unit area with the SERS enhancement. Because of the contribution of the AgMNP aggregation to the SERS, this protocol has great potential for practical high-throughput detection of the protein-small molecule complex and the antigen-antibody immunocomplex.

  1. Investigation of coercivity mechanism in hot deformed Nd-Fe-B permanent magnets by small-angle neutron scattering

    SciTech Connect

    Yano, M. Manabe, A.; Shoji, T.; Kato, A.; Ono, K.; Harada, M.; Kohlbrecher, J.

    2014-05-07

    The magnetic reversal behaviors of single domain sized Nd-Fe-B permanent magnets, with and without isolation between the Nd{sub 2}Fe{sub 14}B grains, was clarified using small-angle neutron scattering (SANS). The SANS patterns obtained arose from changes in the magnetic domains and were analyzed using the Teubner–Stray model, a phenomenological correlation length model, to quantify the periodicity and morphology of the magnetic domains. The results indicated that the magnetic reversal evolved with the magnetic domains that had similar sized grains. The grain isolation enabled us to realize the reversals of single domains.

  2. Small-angle neutron scattering study of magnetic ordering and inhomogeneity across the martensitic phase transformation in Ni50–xCoxMn₄₀Sn₁₀ alloys

    DOE PAGES

    Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; ...

    2012-04-27

    The Heusler-derived multiferroic alloy Ni50–xCoxMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390 K. Themore » static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.« less

  3. Magnetic scattering and spin-orbit coupling induced magnetoresistance in nonmagnetic heavy metal and magnetic insulator bilayer systems

    NASA Astrophysics Data System (ADS)

    Miao, B. F.; Sun, L.; Wu, D.; Chien, C. L.; Ding, H. F.

    2016-11-01

    We report on the experimental study of the angular dependent magnetoresistance (MR) of heavy metal/ferromagnetic insulator bilayer structures. Through altering the relative composition in heavy metal P tδT a1 -δ alloy, we continuously tune its spin Hall angle from positive, crossing zero, and to negative and study its impact on the MR. Most notably, both spin Hall effect and MR disappear simultaneously in P t0.32T a0.68 (3 nm)/YIG when the effective spin Hall angle vanishes, evidencing the essential role of spin-orbit coupling in heavy metal for the MR. By introducing Fe impurities, we further identify that magnetic scattering is also essential to induce the MR in Pt/Fe-doped Si O2 at large magnetic field, where the MR ratio increases monotonically with doping level.

  4. Hidden magnetism and quantum criticality in the heavy fermion superconductor CeRhIn5.

    PubMed

    Park, Tuson; Ronning, F; Yuan, H Q; Salamon, M B; Movshovich, R; Sarrao, J L; Thompson, J D

    2006-03-02

    With only a few exceptions that are well understood, conventional superconductivity does not coexist with long-range magnetic order (for example, ref. 1). Unconventional superconductivity, on the other hand, develops near a phase boundary separating magnetically ordered and magnetically disordered phases. A maximum in the superconducting transition temperature T(c) develops where this boundary extrapolates to zero Kelvin, suggesting that fluctuations associated with this magnetic quantum-critical point are essential for unconventional superconductivity. Invariably, though, unconventional superconductivity masks the magnetic phase boundary when T < T(c), preventing proof of a magnetic quantum-critical point. Here we report specific-heat measurements of the pressure-tuned unconventional superconductor CeRhIn5 in which we find a line of quantum-phase transitions induced inside the superconducting state by an applied magnetic field. This quantum-critical line separates a phase of coexisting antiferromagnetism and superconductivity from a purely unconventional superconducting phase, and terminates at a quantum tetracritical point where the magnetic field completely suppresses superconductivity. The T --> 0 K magnetic field-pressure phase diagram of CeRhIn5 is well described with a theoretical model developed to explain field-induced magnetism in the high-T(c) copper oxides, but in which a clear delineation of quantum-phase boundaries has not been possible. These experiments establish a common relationship among hidden magnetism, quantum criticality and unconventional superconductivity in copper oxides and heavy-electron systems such as CeRhIn5.

  5. Effect of spin-orbit scattering on the magnetic and superconducting properties of nearly ferromagnetic metals: application to granular Pt.

    PubMed

    Fay, D; Appel, J

    2002-09-16

    We calculate the effect of scattering on the static, exchange enhanced, spin susceptibility and show that, in particular, spin-orbit scattering leads to a reduction of the giant moments and spin glass freezing temperature due to dilute magnetic impurities. The harmful spin fluctuation contribution to the intragrain pairing interaction is strongly reduced opening the way for BCS superconductivity. We are thus able to explain the superconducting and magnetic properties recently observed in granular Pt as being due to scattering effects in single small grains.

  6. Effect of Spin-Orbit Scattering on the Magnetic and Superconducting Properties of Nearly Ferromagnetic Metals: Application to Granular Pt

    NASA Astrophysics Data System (ADS)

    Fay, D.; Appel, J.

    2002-08-01

    We calculate the effect of scattering on the static, exchange enhanced, spin susceptibility and show that, in particular, spin-orbit scattering leads to a reduction of the giant moments and spin glass freezing temperature due to dilute magnetic impurities. The harmful spin fluctuation contribution to the intragrain pairing interaction is strongly reduced opening the way for BCS superconductivity. We are thus able to explain the superconducting and magnetic properties recently observed in granular Pt as being due to scattering effects in single small grains.

  7. Impurity screening and stability of Fermi arcs against Coulomb and magnetic scattering in a Weyl monopnictide

    NASA Astrophysics Data System (ADS)

    Sessi, Paolo; Sun, Yan; Bathon, Thomas; Glott, Florian; Li, Zhilin; Chen, Hongxiang; Guo, Liwei; Chen, Xiaolong; Schmidt, Marcus; Felser, Claudia; Yan, Binghai; Bode, Matthias

    2017-01-01

    We present a quasiparticle interference study of clean and Mn surface-doped TaAs, a prototypical Weyl semimetal, to test the screening properties as well as the stability of Fermi arcs against Coulomb and magnetic scattering. Contrary to topological insulators, the impurities are effectively screened in Weyl semimetals. The adatoms significantly enhance the strength of the signal such that theoretical predictions on the potential impact of Fermi arcs can be unambiguously scrutinized. Our analysis reveals the existence of three extremely short, previously unknown scattering vectors. Comparison with theory traces them back to scattering events between large parallel segments of spin-split trivial states, strongly limiting their coherence. In sharp contrast to previous work [R. Batabyal et al., Sci. Adv. 2, e1600709 (2016), 10.1126/sciadv.1600709], where similar but weaker subtle modulations were interpreted as evidence of quasiparticle interference originating from Femi arcs, we can safely exclude this being the case. Overall, our results indicate that intra- as well as inter-Fermi arc scattering are strongly suppressed and may explain why—in spite of their complex multiband structure—transport measurements show signatures of topological states in Weyl monopnictides.

  8. Magnetic Field Dependence of the Critical Current in S-N Bilayer Thin Films

    NASA Technical Reports Server (NTRS)

    Sadleir, John E.; Lee, Sang-Jun; Smith, Stephen James; Bandler, Simon; Chervenak, James; Kilbourne, Caroline A.; Finkbeiner, Fred M.; Porter, Frederick S.; Kelley, Richard L.; Adams, Joseph S.; Eckart, Megan E.; Busch, Sarah; Porst, Jan-Patrick

    2013-01-01

    Here we investigate the effects a non-uniform applied magnetic field has on superconducting transition-edge sensors (TESs) critical current. This has implications on TES optimization. It has been shown that TESs resistive transition can be altered by magnetic fields. We have observed critical current rectification effects and explained these effects in terms of a magnetic self-field arising from asymmetric current injection into the sensor. Our TES physical model shows that this magnetic self-field can result in significantly degraded or improved TES performance. In order for this magnetically tuned TES strategy to reach its full potential we are investigating the effect a non-uniform applied magnetic field has on the critical current.

  9. Vagus nerve stimulation magnet activation for seizures: a critical review.

    PubMed

    Fisher, R S; Eggleston, K S; Wright, C W

    2015-01-01

    Some patients receiving VNS Therapy report benefit from manually activating the generator with a handheld magnet at the time of a seizure. A review of 20 studies comprising 859 subjects identified patients who reported on-demand magnet mode stimulation to be beneficial. Benefit was reported in a weighted average of 45% of patients (range 0-89%) using the magnet, with seizure cessation claimed in a weighted average of 28% (range 15-67%). In addition to seizure termination, patients sometimes reported decreased intensity or duration of seizures or the post-ictal period. One study reported an isolated instance of worsening with magnet stimulation (Arch Pediatr Adolesc Med, 157, 2003 and 560). All of the reviewed studies assessed adjunctive magnet use. No studies were designed to provide Level I evidence of efficacy of magnet-induced stimulation. Retrospective analysis of one pivotal randomized trial of VNS therapy showed significantly more seizures terminated or improved in the active stimulation group vs the control group. Prospective, controlled studies would be required to isolate the effect and benefit of magnet mode stimulation and to document that the magnet-induced stimulation is the proximate cause of seizure reduction. Manual application of the magnet to initiate stimulation is not always practical because many patients are immobilized or unaware of their seizures, asleep or not in reach of the magnet. Algorithms based on changes in heart rate at or near the onset of the seizure provide a methodology for automated responsive stimulation. Because literature indicates additional benefits from on-demand magnet mode stimulation, a potential role exists for automatic activation of stimulation.

  10. Magnetization dynamics and its scattering mechanism in thin CoFeB films with interfacial anisotropy.

    PubMed

    Okada, Atsushi; He, Shikun; Gu, Bo; Kanai, Shun; Soumyanarayanan, Anjan; Lim, Sze Ter; Tran, Michael; Mori, Michiyasu; Maekawa, Sadamichi; Matsukura, Fumihiro; Ohno, Hideo; Panagopoulos, Christos

    2017-04-11

    Studies of magnetization dynamics have incessantly facilitated the discovery of fundamentally novel physical phenomena, making steady headway in the development of magnetic and spintronics devices. The dynamics can be induced and detected electrically, offering new functionalities in advanced electronics at the nanoscale. However, its scattering mechanism is still disputed. Understanding the mechanism in thin films is especially important, because most spintronics devices are made from stacks of multilayers with nanometer thickness. The stacks are known to possess interfacial magnetic anisotropy, a central property for applications, whose influence on the dynamics remains unknown. Here, we investigate the impact of interfacial anisotropy by adopting CoFeB/MgO as a model system. Through systematic and complementary measurements of ferromagnetic resonance (FMR) on a series of thin films, we identify narrower FMR linewidths at higher temperatures. We explicitly rule out the temperature dependence of intrinsic damping as a possible cause, and it is also not expected from existing extrinsic scattering mechanisms for ferromagnets. We ascribe this observation to motional narrowing, an old concept so far neglected in the analyses of FMR spectra. The effect is confirmed to originate from interfacial anisotropy, impacting the practical technology of spin-based nanodevices up to room temperature.

  11. Brillouin light scattering from quantized spin waves in micron-size magnetic wires

    NASA Astrophysics Data System (ADS)

    Jorzick, J.; Demokritov, S. O.; Mathieu, C.; Hillebrands, B.; Bartenlian, B.; Chappert, C.; Rousseaux, F.; Slavin, A. N.

    1999-12-01

    An experimental study of spin-wave quantization in arrays of micron-size magnetic Ni80Fe20 wires by means of Brillouin light-scattering spectroscopy is reported. Dipolar-dominated Damon-Eshbach spin-wave modes laterally quantized in a single wire with quantized wave vector values determined by the width of the wire are studied. The frequency splitting between quantized modes, which decreases with increasing mode number, depends on the wire sizes and is up to 1.5 GHz. The transferred wave vector interval, where each mode is observed, is calculated using a light-scattering theory for confined geometries. The frequencies of the modes are calculated, taking into account finite-size effects. The results of the calculations are in a good agreement with the experimental data.

  12. Pitch angle scattering of an energetic magnetized particle by a circularly polarized electromagnetic wave

    SciTech Connect

    Bellan, P. M.

    2013-04-15

    The interaction between a circularly polarized wave and an energetic gyrating particle is described using a relativistic pseudo-potential that is a function of the frequency mismatch. Analysis of the pseudo-potential provides a means for interpreting numerical results. The pseudo-potential profile depends on the initial mismatch, the normalized wave amplitude, and the initial angle between the wave magnetic field and the particle perpendicular velocity. For zero initial mismatch, the pseudo-potential consists of only one valley, but for finite mismatch, there can be two valleys separated by a hill. A large pitch angle scattering of the energetic electron can occur in the two-valley situation but fast scattering can also occur in a single valley. Examples relevant to magnetospheric whistler waves show that the energetic electron pitch angle can be deflected 5 Degree-Sign towards the loss cone when transiting a 10 ms long coherent wave packet having realistic parameters.

  13. Magnetic-field-induced criticality in superconducting two-leg ladders

    NASA Astrophysics Data System (ADS)

    Vekua, Temo

    2017-03-01

    We study magnetic-field-induced critical singularities in the superconducting phase of the hole-doped Hubbard model of repulsively interacting electrons, defined on a two-leg ladder. We argue that, provided the low-energy spin excitations in doped ladders carry electric charge, the low-temperature thermodynamic quantities, such as the specific-heat coefficient and magnetic susceptibility, will show logarithmic singularities in the quantum critical regime. This behavior is in drastic contrast to the magnetic-field-induced criticality in undoped Mott insulator ladders, which is governed by the zero-scale-factor universality with its hallmark square-root singularities.

  14. Spin reorientation transition in Fe/CeH2 multilayers probed by soft X-ray resonant magnetic scattering

    NASA Astrophysics Data System (ADS)

    Dürr, H. A.; Münzenberg, M.; Felsch, W.; Dhesi, S. S.

    The magnetic domain configurations of Fe 3d spins in Fe/CeH2 multilayers were measured by soft X-ray resonant magnetic scattering. The interface region could be probed by setting up X-ray standing waves due to the multilayer periodicity. By resolving first- and second-order magnetic scattering contributions, we show that the latter probe directly the magneto-crystalline anisotropy which is dominated by the Fe interface layers causing a spin reorientation transition when the temperature is lowered.

  15. Magnetic Order and Crystal Field Excitations in Er2Ru2O7: A Neutron Scattering Study

    SciTech Connect

    Ehlers, Georg; Gardner, Jason

    2009-01-01

    The magnetic pyrochlore Er{sub 2}Ru{sub 2}O{sub 7} has been studied with neutron scattering and susceptibility measurements down to a base temperature of 270 mK. For the low temperature phase in which the Er sublattice orders, new magnetic Bragg peaks are reported which can be indexed with integer (hkl) for a face centered cubic cell. Inelastic measurements reveal a wealth of crystal field levels of the Er ion and a copious amount of magnetic scattering below 15 meV. The three lowest groups of crystal field levels are at 6.7, 9.1 and 18.5 meV.

  16. Observation of spin-wave dispersion in Nd-Fe-B magnets using neutron Brillouin scattering

    SciTech Connect

    Ono, K. Inami, N.; Saito, K.; Takeichi, Y.; Kawana, D.; Yokoo, T.; Itoh, S.; Yano, M.; Shoji, T.; Manabe, A.; Kato, A.; Kaneko, Y.

    2014-05-07

    The low-energy spin-wave dispersion in polycrystalline Nd-Fe-B magnets was observed using neutron Brillouin scattering (NBS). Low-energy spin-wave excitations for the lowest acoustic spin-wave mode were clearly observed. From the spin-wave dispersion, we were able to determine the spin-wave stiffness constant D{sub sw} (100.0 ± 4.9 meV.Å{sup 2}) and the exchange stiffness constant A (6.6 ± 0.3 pJ/m)

  17. Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment from lattice QCD

    DOE PAGES

    Blum, Thomas; Chowdhury, Saumitra; Hayakawa, Masashi; ...

    2015-01-07

    The form factor that yields the light-by-light scattering contribution to the muon anomalous magnetic moment is computed in lattice QCD+QED and QED. A non-perturbative treatment of QED is used and is checked against perturbation theory. The hadronic contribution is calculated for unphysical quark and muon masses, and only the diagram with a single quark loop is computed. Statistically significant signals are obtained. Initial results appear promising, and the prospect for a complete calculation with physical masses and controlled errors is discussed.

  18. Neutron Scattering Studies of Structural and Magnetic Excitations in Lamellar Copper Oxides — a Review

    NASA Astrophysics Data System (ADS)

    Birgeneau, Robert J.; Shirane, Gen

    The following sections are included: * INTRODUCTION * La2-xSrxCuO4 STRUCTURE AND LATTICE DYNAMICS * MAGNETIC ORDERING IN La2CuO4 * Stoichiometric Material * Lightly Doped La2CuO4 * 2D STATIC AND DYNAMIC SPIN CORRELATIONS IN La2CuO4 * SPIN CORRELATIONS IN INSULATING, METALLIC AND SUPERCONDUCTING La2-xSrxCuO4 * NEUTRON SCATTERING STUDIES OF La2NiO4 and La2CoO4 * ANTIFERROMAGNETISM IN YBa2Cu3O6+x * CONCLUSIONS * ACKNOWLEDGEMENTS * References

  19. Magnetic excitations in (SiO 2)Co nano-composite films: Brillouin light scattering study

    NASA Astrophysics Data System (ADS)

    Stashkevich, A. A.; Roussigné, Y.; Stognij, A. I.; Novitskii, N. I.; Wurtz, G.; Zayats, A. V.; Viau, G.; Chaboussant, G.; Ott, F.; Lutsev, L. V.; Djemia, P.; Kostylev, M. P.; Belotelov, V.

    2009-04-01

    Behaviour of magnetic excitations in the Damon-Eshbach (DE) and backward volume (BV) geometries in nano-composite (SiO 2) 100-xCo x (50% at< x<80% at) films has been studied by Brillouin light scattering (BLS). It has been shown that it is the structure of Stokes/anti-Stokes BLS lines in the DE geometry that allows reliable identification of dipole-exchange spin waves (SW) and numerical estimation of the value of the effective exchange constant A eff of a super-ferromagnetic nano-granular sample ( x=80% at).

  20. Endstation for ultrafast magnetic scattering experiments at the free-electron laser in Hamburg

    NASA Astrophysics Data System (ADS)

    Müller, L.; Gutt, C.; Streit-Nierobisch, S.; Walther, M.; Schaffert, S.; Pfau, B.; Geilhufe, J.; Büttner, F.; Flewett, S.; Günther, C. M.; Eisebitt, S.; Kobs, A.; Hille, M.; Stickler, D.; Frömter, R.; Oepen, H. P.; Lüning, J.; Grübel, G.

    2013-01-01

    An endstation for pump-probe small-angle X-ray scattering (SAXS) experiments at the free-electron laser in Hamburg (FLASH) is presented. The endstation houses a solid-state absorber, optical incoupling for pump-probe experiments, time zero measurement, sample chamber, and detection unit. It can be used at all FLASH beamlines in the whole photon energy range offered by FLASH. The capabilities of the setup are demonstrated by showing the results of resonant magnetic SAXS measurements on cobalt-platinum multilayer samples grown on freestanding Si_3N_4 membranes and pump-laser-induced grid structures in multilayer samples.

  1. Endstation for ultrafast magnetic scattering experiments at the free-electron laser in Hamburg

    SciTech Connect

    Mueller, L.; Gutt, C.; Streit-Nierobisch, S.; Walther, M.; Gruebel, G.; Schaffert, S.; Pfau, B.; Flewett, S.; Geilhufe, J.; Eisebitt, S.; Buettner, F.; Guenther, C. M.; Kobs, A.; Hille, M.; Stickler, D.; Froemter, R.; Oepen, H. P.; Luening, J.

    2013-01-15

    An endstation for pump-probe small-angle X-ray scattering (SAXS) experiments at the free-electron laser in Hamburg (FLASH) is presented. The endstation houses a solid-state absorber, optical incoupling for pump-probe experiments, time zero measurement, sample chamber, and detection unit. It can be used at all FLASH beamlines in the whole photon energy range offered by FLASH. The capabilities of the setup are demonstrated by showing the results of resonant magnetic SAXS measurements on cobalt-platinum multilayer samples grown on freestanding Si{sub 3}N{sub 4} membranes and pump-laser-induced grid structures in multilayer samples.

  2. Development and application of setup for ac magnetic field in neutron scattering experiments.

    PubMed

    Klimko, Sergey; Zhernenkov, Kirill; Toperverg, Boris P; Zabel, Hartmut

    2010-10-01

    We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm(3) and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed.

  3. Neutrino scattering on atomic electrons in searches for the neutrino magnetic moment.

    PubMed

    Voloshin, M B

    2010-11-12

    The scattering of a neutrino on atomic electrons is considered in the situation where the energy transferred to the electrons is comparable to the characteristic atomic energies, as relevant to the current experimental search for the neutrino magnetic moment. The process is induced by the standard electroweak interaction as well as by the possible neutrino magnetic moment. Quantum-mechanical sum rules are derived for the inclusive cross section at a fixed energy deposited in the atomic system, and it is shown that the differential over the energy transfer cross section is given, modulo very small corrections, by the same expression as for free electrons, once all possible final states of the electronic system are taken into account. Thus, the atomic effects effectively cancel in the inclusive process.

  4. Magnetization and Raman scattering studies of (Co,Mn) codoped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Duan, L. B.; Rao, G. H.; Wang, Y. C.; Yu, J.; Wang, T.

    2008-07-01

    Single-phase (Co,Mn) codoped ZnO nanoparticles were synthesized by an autocombustion method. Hysteresis loop was observed at 300 K for the sample Zn0.98Co0.01Mn0.01O with a low coercivity (40±5 Oe). Temperature dependence of magnetization rules out the possibility of superparamagnetism or spin-glass behavior. Raman scattering studies manifested that there might exist a defect annihilation arising from the (Co,Mn) codoped into ZnO host lattice. As the ferromagnetism of diluted magnetic semiconductors is closely related to the dopant-defect hybridization, the ferromagnetic ordering was significantly enhanced in the sample Zn0.98Co0.01Mn0.01O by the (Co,Mn) codoping, in comparison to the Zn0.99Co0.01O and Zn0.99Mn0.01O fabricated by the same method.

  5. Magnetic field and temperature dependence of the critical vortex velocity in type-II superconducting films.

    PubMed

    Grimaldi, G; Leo, A; Cirillo, C; Attanasio, C; Nigro, A; Pace, S

    2009-06-24

    We study the vortex dynamics in the instability regime induced by high dissipative states well above the critical current in Nb superconducting strips. The magnetic field and temperature behavior of the critical vortex velocity corresponding to the observed dynamic instability is ascribed to intrinsic non-equilibrium phenomena. The Larkin-Ovchinnikov (LO) theory of electronic instability in high velocity vortex motion has been applied to interpret the temperature dependence of the critical vortex velocity. The magnetic field dependence of the vortex critical velocity shows new features in the low-field regime not predicted by LO.

  6. X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

    SciTech Connect

    Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.; Tian, Di; Kim, J.; Upton, M. H.; Casa, D.; Gog, T.; Islam, Z.; Jeon, Byung -Gu; Kim, Kee Hoon; Desgreniers, S.; Kim, Yong Baek; Julian, S. J.; Kim, Young -June

    2016-07-06

    We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu2Ir2O7 and Pr2Ir2O7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu2Ir2O7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (~6 to 300 K) and pressures (~0.1 to 17 GPa) studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of Eu2Ir2O7 and Pr2Ir2O7 using high-resolution Ir L-3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ~3-5 eV, spin-orbit excitations at ~ 0.5-1 eV, and broad low-lying excitations below ~0.15 eV. In single-crystal samples of "Eu-rich" Eu2Ir2O7 (found to possess an actual stoichiometry of Eu2.18Ir1.82O7.06) we observe highly damped magnetic excitations at ~45 meV, which display significant momentum dependence. Here, we compare these results with recent dynamical structure factor calculations

  7. Application of small-angle neutron scattering to the study of forces between magnetically chained monodisperse ferrofluid emulsion droplets

    SciTech Connect

    Jain, Dr Nirmesh; Liu, Dr C K; Hawkett, Dr B. S.; Warr, G. G.; Hamilton, William A

    2014-01-01

    The optical magnetic chaining technique (MCT) developed by Leal-Calderon, Bibette and co-workers in the 1990 s allows precise measurements of force profiles between droplets in monodisperse ferrofluid emulsions. However, the method lacks an in-situ determination of droplet size and therefore requires the combination of separately acquired measurements of droplet chain periodicity versus an applied magnetic field from optical Bragg scattering and droplet diameter inferred from dynamic light scattering (DLS) to recover surface force-distance profiles between the colloidal particles. Compound refractive lens (CRL) focussed small-angle scattering (SANS) MCT should result in more consistent measurements of droplet size (form factor measurements in the absence of field) and droplet chaining period (from structure factor peaks when the magnetic field is applied); and, with access to shorter length scales, extend force measurements to closer approaches than possible by optical measurements. We report on CRL-SANS measurements of monodisperse ferrofluid emulsion droplets aligned in straight chains by an applied field perpendicular to the incident beam direction. Analysis of the scattering from the closely spaced droplets required algorithms that carefully treated resolution and its effect on mean scattering vector magnitudes in order to determine droplet size and chain periods to sufficient accuracy. At lower applied fields scattering patterns indicate structural correlations transverse to the magnetic field direction due to the formation of intermediate structures in early chain growth.

  8. Critical behavior of the order-disorder phase transition in β -brass investigated by x-ray scattering

    NASA Astrophysics Data System (ADS)

    Madsen, A.; Als-Nielsen, J.; Hallmann, J.; Roth, T.; Lu, W.

    2016-07-01

    β -brass exhibits an archetypical example of an order-disorder transition with a critical behavior that was previously investigated by neutron scattering. The data were well described by the three-dimensional (3d) Ising model but the relatively crude experimental resolution prevented an in-depth examination of the single-length scaling hypothesis, a cornerstone in the theory of critical phenomena. With the development of synchrotron x-ray experiments, high-resolution data could be recorded and surprisingly it was found that the single-length scaling did not hold in most critical systems, possibly due to strain originating from surface defects and/or impurities. In this paper we demonstrate single-length critical behavior using high-resolution x-ray scattering in β -brass. The investigations confirm that β -brass behaves like a 3d Ising system over a wide range of length scales comprising correlated clusters of millions of atoms. To vary the surface sensitivity, experiments have been performed both in Bragg reflection and Laue transmission geometries but without any substantial differences observed in the scaling and critical behavior.

  9. Magnetic Compton scattering study of the Co2FeGa Heusler alloy: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Deb, Aniruddha; Itou, M.; Sakurai, Y.; Hiraoka, N.; Sakai, N.

    2001-02-01

    The spin density in Co2FeGa Heusler alloy has been measured in a magnetic Compton scattering experiment using 274-keV circularly polarized synchrotron radiation at the high energy inelastic scattering beamline (BL08W) at SPring-8, Japan. A detailed band-structure calculation including hyperfine field study was performed utilizing the generalized gradient corrected full-potential linear augmented plane-wave (FLAPW-GGA) method. The magnetic Compton profiles for the [100], [110], and [111] principal directions, reported here, show anisotropy in the momentum density which is in good agreement with the FLAPW-GGA results based on ferromagnetic ground state. The conduction electrons were found to have a negative spin polarization of 0.60μB, which is at variance with the prediction of a positive moment from the recent neutron data. In the calculation, 3d spin moment at the Co and Fe site was found to be 1.20μB and 2.66μB, and their respective contribution in the eg and t2g sub-bands are in excellent agreement with the earlier reported neutron-diffraction measurements. It is also seen from our calculated results that the Co and Fe moment are mainly eg in character.

  10. Magnetic Rotation and Chirality and X(5) Critical Symmetry in Nucleus

    SciTech Connect

    Zhu, L. H.; Wu, X. G.; He, C. Y.; Hao, X.; Wang, L. L.; Zheng, Y.; Li, G. S.

    2010-05-12

    The magnetic and chiral rotation, the critical symmetry are fundamental problems in the study of nuclear structure. Here we report the recent results from the experiments on the magnetic and electric rotations in {sup 106}Ag, the chiral rotation in {sup 130}Cs and the evolution of X(5) symmetry in {sup 176}Os.

  11. Electronic and magnetic properties of manganite thin films with different compositions and its correlation with transport properties: An X-ray resonant magnetic scattering study

    DOE PAGES

    Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; ...

    2014-12-08

    Here, we present x-ray resonant magnetic dichroism and x-ray resonant magnetic scattering measurements of the temperature dependence of magnetism in Pr-doped La-Ca-Mn-O films grown on (110) NdGaO3 substrates. We observed thermal hysteresis of the ferromagnetism in one film that also showed large thermal hysteresis of ~18K in transport measurements. While in a second film of a different nominal chemistry, which showed very small thermal hysteresis ~3K in transport measurements, no thermal hysteresis of the ferromagnetism was observed. As a result, these macroscopic properties are correlated with evolution of surface magnetization across metal insulator transition for these films as observed bymore » soft x-ray resonant magnetic scattering measurements.« less

  12. Electronic and magnetic properties of manganite thin films with different compositions and its correlation with transport properties: An X-ray resonant magnetic scattering study

    SciTech Connect

    Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.

    2014-12-08

    Here, we present x-ray resonant magnetic dichroism and x-ray resonant magnetic scattering measurements of the temperature dependence of magnetism in Pr-doped La-Ca-Mn-O films grown on (110) NdGaO3 substrates. We observed thermal hysteresis of the ferromagnetism in one film that also showed large thermal hysteresis of ~18K in transport measurements. While in a second film of a different nominal chemistry, which showed very small thermal hysteresis ~3K in transport measurements, no thermal hysteresis of the ferromagnetism was observed. As a result, these macroscopic properties are correlated with evolution of surface magnetization across metal insulator transition for these films as observed by soft x-ray resonant magnetic scattering measurements.

  13. Electronic and magnetic properties of manganite thin films with different compositions and its correlation with transport properties: An X-ray resonant magnetic scattering study

    SciTech Connect

    Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.

    2014-12-14

    Here, we present x-ray resonant magnetic dichroism and x-ray resonant magnetic scattering measurements of the temperature dependence of magnetism in Pr-doped La-Ca-Mn-O films grown on (110) NdGaO{sub 3} substrates. We observed thermal hysteresis of the ferromagnetism in one film that also showed large thermal hysteresis of ∼18 K in transport measurements. While in a second film of a different nominal chemistry, which showed very small thermal hysteresis ∼3 K in transport measurements, no thermal hysteresis of the ferromagnetism was observed. These macroscopic properties are correlated with evolution of surface magnetization across metal insulator transition for these films as observed by soft x-ray resonant magnetic scattering measurements.

  14. Feasibility of alpha particle measurement in a magnetically confined plasma by CO/sub 2/ laser Thomson scattering

    SciTech Connect

    Richards, R.K.; Vander Sluis, K.L.; Hutchinson, D.P.

    1987-08-01

    Fusion-product alpha particles will dominate the behavior of the next generation of ignited D-T fusion reactors. Advanced diagnostics will be required to characterize the energy deposition of these fast alpha particles in the magnetically confined plasma. For small-angle coherent Thomson scattering of a CO/sub 2/ laser beam from such a plasma, a resonance in the scattered power occurs near 90/sup 0/ with respect to the magnetic field direction. This spatial concentration permits a simplified detection of the scattered laser power from the plasma using a heterodyne system. The signal produced by the presence of fusion-product alpha particles in an ignited plasma is calculated to be well above the noise level, which results from statistical variations of the background signal produced by scattering from free electrons. 7 refs.

  15. X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

    DOE PAGES

    Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.; ...

    2016-07-06

    We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu2Ir2O7 and Pr2Ir2O7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu2Ir2O7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (~6 to 300 K) and pressures (~0.1 to 17 GPa) studied. We have also investigated the electronic and magneticmore » excitations in single-crystal samples of Eu2Ir2O7 and Pr2Ir2O7 using high-resolution Ir L-3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ~3-5 eV, spin-orbit excitations at ~ 0.5-1 eV, and broad low-lying excitations below ~0.15 eV. In single-crystal samples of "Eu-rich" Eu2Ir2O7 (found to possess an actual stoichiometry of Eu2.18Ir1.82O7.06) we observe highly damped magnetic excitations at ~45 meV, which display significant momentum dependence. Here, we compare these results with recent dynamical structure factor calculations« less

  16. Depth dependence of strain, mosaicity and sharp component in the critical scattering of SrTiO3

    NASA Astrophysics Data System (ADS)

    Rütt, U.; Diederichs, A.; Schneider, J. R.; Shirane, G.

    1997-08-01

    The sharp component observed in the critical scattering above the cubic-to-tetragonal phase transition in SrTiO3 is now generally considered as a surface-related phenomenon. In the present paper, for the first time, the structural difference between the bulk and a skin layer of a highly perfect crystal has been shown quantitatively by diffraction methods. High-resolution measurements have been performed with highly penetrating 121 keV synchrotron radiation X-rays. The lattice parameter d, its fluctuations Δd/d, the crystal mosaicity and the critical scattering were found to be depth dependent. The two-length-scale behaviour in the critical fluctuations is confined to a skin layer approximately 100 μm thick and related to an increase in strain. Approaching the crystal surface the lattice parameter decreases by 6.2·10-5 Å, Δd/d increases from the bulk value of 5.2·10-5 to 13·10-5, the mosaicity increases from 1.0 to 8.2 seconds of arc. In addition the critical temperature determined from the temperature dependence of the 1/2(511) reflection at the surface and 150 μm below, is smaller than the bulk value by 1.7 and 2.4 K, respectively.

  17. An Enhanced Nonlinear Critical Gradient for Electron Turbulent Transport due to Reversed Magnetic Shear

    SciTech Connect

    Peterson, J. L.; Hammet, G. W.; Mikkelsen, D. R.; Yuh, H. Y.; Candy, J.; Guttenfelder, W.; Kaye, S. M.; LeBlanc, B.

    2011-05-11

    The first nonlinear gyrokinetic simulations of electron internal transport barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed magnetic shear can suppress thermal transport by increasing the nonlinear critical gradient for electron-temperature-gradient-driven turbulence to three times its linear critical value. An interesting feature of this turbulence is non- linearly driven off-midplane radial streamers. This work reinforces the experimental observation that magnetic shear is likely an effective way of triggering and sustaining e-ITBs in magnetic fusion devices.

  18. Magnetic structure determination of Ca3LiOsO6 using neutron and x-ray scattering

    SciTech Connect

    Calder, Stuart A; Lumsden, Mark D; Garlea, Vasile O; Kim, Jong-Woo; Shi, Y. G.; Yamaura, K.; Christianson, Andrew D

    2012-01-01

    We present a neutron and x-ray scattering investigation of Ca3LiOsO6, a material that has been predicted to host magnetic ordering through an extended superexchange pathway involving two anions. Despite the apparent 1D nature and triangular units of magnetic osmium ions the onset of magnetic correlations has been observed at a high temperature of 117 K in bulk measurements. We experimentally determine the magnetically ordered structure and show it to be long range and three dimensional. Our results support the model of extended superexchange interaction.

  19. Interface effects on the magnetic properties of exchange coupled Co/Fe multilayers studied by Brillouin light scattering

    NASA Astrophysics Data System (ADS)

    D'Orazio, F.; Lucari, F.; Carlotti, G.; Gubbiotti, G.; Carbucicchio, M.; Ruggiero, G.

    2001-05-01

    Exchange-coupled 5[Co ( x) /Fe (3 x) ]/Co ( x) with x=5, 10, 15 nm multilayers were grown by UHV electron-beam evaporation. The influence of the interface magnetic anisotropy and interlayer exchange interaction on the magnetic properties was studied by means of Brillouin light scattering from thermally excited spin waves. Both the Damon-Eshbach surface mode of the total multilayer and bulk standing modes are present in the BLS spectra. A careful study of spin waves frequency dependence on the applied magnetic field allowed the determination of the magnetic parameters of the Co/Fe multilayers.

  20. Brillouin light scattering study of magnetic-element normal modes in a square artificial spin ice geometry

    NASA Astrophysics Data System (ADS)

    Li, Y.; Gubbiotti, G.; Casoli, F.; Gonçalves, F. J. T.; Morley, S. A.; Rosamond, M. C.; Linfield, E. H.; Marrows, C. H.; McVitie, S.; Stamps, R. L.

    2017-01-01

    We report the results, from experimental and micromagnetic studies, of the magnetic normal modes in artificial square spin ice systems consisting of ferromagnetic-monodomain islands. Spin-wave properties are measured by Brillouin light scattering. The mode spectra contain several branches whose frequencies are sensitive to the magnitude and in-plane orientation of an applied magnetic field. We also identify soft modes that exhibit different behaviours depending on the direction of the applied magnetic field. The obtained results are well described with micromagnetic simulations of independent magnetic elements arranged along two sublattices.

  1. Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn5

    SciTech Connect

    Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; Shakeripour, H.; Petrovic, C.; Taillefer, Louis

    2016-06-27

    The thermal conductivity κ of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc2, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ/T with field reveals that the electron-electron scattering (or transport mass m*) of those unpaired electrons diverges as H→Hc2 from below, in the same way that it does in the normal state as H→Hc2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn5 at H*=Hc2 even from inside the superconducting state. In conclusion, the fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.

  2. Magnetocaloric effect and critical behavior in Mn2-imidazole-[Nb(CN)8] molecular magnetic sponge

    NASA Astrophysics Data System (ADS)

    Fitta, Magdalena; Pełka, Robert; Gajewski, Marcin; Mihalik, Marian; Zentkova, Maria; Pinkowicz, Dawid; Sieklucka, Barbara; Bałanda, Maria

    2015-12-01

    A comprehensive study of magnetocaloric effect (MCE) and critical behavior in the {Mn2(imH)2(H2O)4[Nb(CN)8]·4H2O}n molecular magnet is reported. The compound is an example of a magnetic sponge, where structural changes provoked by dehydration process lead to the increase of Tc critical temperature from 25 K for the as-synthesized sample (1) up to 60 K for the anhydrous one (2). MCE and critical behavior were investigated by magnetization measurements. The maximum value of magnetic entropy change ΔS, determined by the magnetization measurements for 1 is 6.70 J mol-1 K-1 (8.95 J kg-1 K-1) at μ0ΔH=5 T, while for 2 it is equal to 4.02 J mol-1 K-1 (7.73 J kg-1 K-1) at the same magnetic field change. The field dependence of MCE at Tc for 1 and 2 was consistent with critical exponents, which allowed to classify both phases to 3D Heisenberg universality class. The Tc-2/3 dependence of the maximum entropy change has been tested using data of 1 and 2 together with MCE data previously reported for other members of the ferrimagnetic Mn2-L-[Nb(CN)8] (L=imidazole, pyridazine and pyrazole) series. Experimental MCE results have been compared with the spin contribution to the magnetic entropy change estimated using a molecular field approximation.

  3. Magnetization reversal of a Nd-Cu-infiltrated Nd-Fe-B nanocrystalline magnet observed with small-angle neutron scattering

    SciTech Connect

    Saito, Kotaro Ono, Kanta; Ueno, Tetsuro; Yano, Masao; Shoji, Tetsuya; Sakuma, Noritsugu; Manabe, Akira; Kato, Akira; Harada, Masashi; Keiderling, Uwe

    2015-05-07

    The magnetization reversal process of Nd-Fe-B nanocrystalline magnets infiltrated with Nd-Cu alloy was examined using small-angle neutron scattering (SANS). The magnetic-field dependence of SANS intensity revealed a qualitative difference between Nd-Cu-infiltrated samples and as-deformed samples. Insufficient magnetic isolation along the direction perpendicular to the nominal c-axis is expected from comparable SANS intensities for different ranges of q values along this direction. For small q values near the coercivity field, Nd-Cu-infiltrated samples show a noticeable reduction in SANS intensity along the nominal c-axis, which is parallel to the external magnetic field. This indicates less spatial fluctuation of magnetic moments in Nd-Cu-infiltrated samples, owing to magnetically isolated Nd{sub 2}Fe{sub 14}B grains.

  4. Electron back scattered diffraction characterization of Sm(CoFeCuZr)z magnets

    NASA Astrophysics Data System (ADS)

    Yonamine, T.; Fukuhara, M.; Archanjo, B. S.; Missell, F. P.

    2011-04-01

    In permanent magnets based on the Sm2Co17 phase, the high coercivity depends on the presence of a complex microstructure, consisting of a Sm2(Co,Fe)17 cell phase, a cell boundary phase Sm(Co,Cu)5, and a Zr-rich platelet or lamellae phase. The aim of this work is to use electron back scatter diffraction (EBSD) in order to identify the different phases present in the isotropic magnets produced from cast alloys with the composition of Sm(CobalFe0.2Cu0.1Zrx)8, where x = 0, 0.02, or 0.06, and correlate them with the different phases observed in scanning electron microscopy (SEM) images. Due to the combination of careful surface preparation and high resolution microscopy, it was possible to observe the cellular structure characteristic of the 2:17 magnets in the SEM images. Until now, only transmission electron microscopy (TEM) had been used. Composition maps, energy dispersive spectroscopy (EDS), and EBSD measurements were used for doing the phase identification.

  5. Electron back scattered diffraction characterization of Sm(CoFeCuZr){sub z} magnets

    SciTech Connect

    Yonamine, T.; Fukuhara, M.; Archanjo, B. S.; Missell, F. P.

    2011-04-01

    In permanent magnets based on the Sm{sub 2}Co{sub 17} phase, the high coercivity depends on the presence of a complex microstructure, consisting of a Sm{sub 2}(Co,Fe){sub 17} cell phase, a cell boundary phase Sm(Co,Cu){sub 5}, and a Zr-rich platelet or lamellae phase. The aim of this work is to use electron back scatter diffraction (EBSD) in order to identify the different phases present in the isotropic magnets produced from cast alloys with the composition of Sm(Co{sub bal}Fe{sub 0.2}Cu{sub 0.1}Zr{sub x}){sub 8}, where x = 0, 0.02, or 0.06, and correlate them with the different phases observed in scanning electron microscopy (SEM) images. Due to the combination of careful surface preparation and high resolution microscopy, it was possible to observe the cellular structure characteristic of the 2:17 magnets in the SEM images. Until now, only transmission electron microscopy (TEM) had been used. Composition maps, energy dispersive spectroscopy (EDS), and EBSD measurements were used for doing the phase identification.

  6. Measurement of local, internal magnetic fluctuations via cross-polarization scattering in the DIII-D tokamak (invited).

    PubMed

    Barada, K; Rhodes, T L; Crocker, N A; Peebles, W A

    2016-11-01

    We present new measurements of internal magnetic fluctuations obtained with a novel eight channel cross polarization scattering (CPS) system installed on the DIII-D tokamak. Measurements of internal, localized magnetic fluctuations provide a window on an important physics quantity that we heretofore have had little information on. Importantly, these measurements provide a new ability to challenge and test linear and nonlinear simulations and basic theory. The CPS method, based upon the scattering of an incident microwave beam into the opposite polarization by magnetic fluctuations, has been significantly extended and improved over the method as originally developed on the Tore Supra tokamak. A new scattering geometry, provided by a unique probe beam, is utilized to improve the spatial localization and wavenumber range. Remotely controllable polarizer and mirror angles allow polarization matching and wavenumber selection for a range of plasma conditions. The quasi-optical system design, its advantages and challenges, as well as important physics validation tests are presented and discussed. Effect of plasma beta (ratio of kinetic to magnetic pressure) on both density and magnetic fluctuations is studied and it is observed that internal magnetic fluctuations increase with beta. During certain quiescent high confinement operational regimes, coherent low frequency modes not detected by magnetic probes are detected locally by CPS diagnostics.

  7. Measurement of local, internal magnetic fluctuations via cross-polarization scattering in the DIII-D tokamak (invited)

    NASA Astrophysics Data System (ADS)

    Barada, K.; Rhodes, T. L.; Crocker, N. A.; Peebles, W. A.

    2016-11-01

    We present new measurements of internal magnetic fluctuations obtained with a novel eight channel cross polarization scattering (CPS) system installed on the DIII-D tokamak. Measurements of internal, localized magnetic fluctuations provide a window on an important physics quantity that we heretofore have had little information on. Importantly, these measurements provide a new ability to challenge and test linear and nonlinear simulations and basic theory. The CPS method, based upon the scattering of an incident microwave beam into the opposite polarization by magnetic fluctuations, has been significantly extended and improved over the method as originally developed on the Tore Supra tokamak. A new scattering geometry, provided by a unique probe beam, is utilized to improve the spatial localization and wavenumber range. Remotely controllable polarizer and mirror angles allow polarization matching and wavenumber selection for a range of plasma conditions. The quasi-optical system design, its advantages and challenges, as well as important physics validation tests are presented and discussed. Effect of plasma beta (ratio of kinetic to magnetic pressure) on both density and magnetic fluctuations is studied and it is observed that internal magnetic fluctuations increase with beta. During certain quiescent high confinement operational regimes, coherent low frequency modes not detected by magnetic probes are detected locally by CPS diagnostics.

  8. A portable high-field pulsed-magnet system for single-crystal x-ray scattering studies

    SciTech Connect

    Islam, Zahirul; Lang, Jonathan C.; Ruff, Jacob P. C.; Ross, Kathryn A.; Gaulin, Bruce D.; Nojiri, Hiroyuki; Matsuda, Yasuhiro H.; Qu Zhe

    2009-11-15

    We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields ({approx}1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.

  9. A portable high-field pulsed-magnet system for single-crystal x-ray scattering studies.

    PubMed

    Islam, Zahirul; Ruff, Jacob P C; Nojiri, Hiroyuki; Matsuda, Yasuhiro H; Ross, Kathryn A; Gaulin, Bruce D; Qu, Zhe; Lang, Jonathan C

    2009-11-01

    We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields (approximately 1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.

  10. Study of the in-plane magnetic structure of a layered system using polarized neutron scattering under grazing incidence geometry

    NASA Astrophysics Data System (ADS)

    Maruyama, R.; Bigault, T.; Wildes, A. R.; Dewhurst, C. D.; Soyama, K.; Courtois, P.

    2016-05-01

    The in-plane magnetic structure of a layered system with a polycrystalline grain size less than the ferromagnetic exchange length was investigated using polarized neutron off-specular scattering and grazing incidence small angle scattering measurements to gain insight into the mechanism that controls the magnetic properties which are different from the bulk. These complementary measurements with different length scales and the data analysis based on the distorted wave Born approximation revealed the lateral correlation on a length scale of sub- μm due to the fluctuating orientation of the magnetization in the layer. The obtained in-plane magnetic structure is consistent with the random anisotropy model, i.e. competition between the exchange interactions between neighboring spins and the local magnetocrystalline anisotropy.

  11. Mn L{sub 2,3} edge resonant x-ray scattering in manganites: Influence of the magnetic state

    SciTech Connect

    Stojic, N.; Binggeli, N.; Altarelli, M.

    2005-09-01

    We present an analysis of the dependence of the resonant orbital-order and magnetic scattering spectra on the spin configuration. We consider an arbitrary spin direction with respect to the local crystal field axis, thus lowering significantly the local symmetry. To evaluate the atomic scattering in this case, we generalized the Hannon-Trammel formula and implemented it inside the framework of atomic multiplet calculations in a crystal field. For an illustration, we calculate the magnetic and orbital scattering in the CE phase of La{sub 0.5}Sr{sub 1.5}MnO{sub 4} in the cases when the spins are aligned with the crystal lattice vector a (or equivalently b) and when they are rotated in the ab-plane by 45 deg. with respect to this axis. Magnetic spectra differ for the two cases. For the orbital scattering, we show that for the former configuration there is a non-negligible {sigma}{yields}{sigma}{sup '} ({pi}{yields}{pi}{sup '}) scattering component, which vanishes in the 45 deg. case, while the {sigma}{yields}{pi}{sup '} ({pi}{yields}{sigma}{sup '}) components are similar in the two cases. From the consideration of two 90 deg. spin canted structures, we conclude there is a significant dependence of the orbital scattering spectra on the spin arrangement. Recent experiments detected a sudden decrease of the orbital scattering intensity upon increasing the temperature above the Neel temperature in La{sub 0.5}Sr{sub 1.5}MnO{sub 4}. We discuss this behavior considering the effect of different types of misorientations of the spins on the orbital scattering spectrum.

  12. Tunneling study of cavity grade Nb : possible magnetic scattering at the surface.

    SciTech Connect

    Prolier, T.; Zasadzinski, J. F.; Cooley, L.; Antoine, C.; Moore, J.; Pellin, M.; Norem, J.; Gray, K. E.; Materials Science Division; Illinois Inst. Tech.; FNAL; Centre d'etude de Saclay

    2008-01-01

    Tunneling spectroscopy was performed on Nb pieces prepared by the same processes used to etch and clean superconducting radio frequency (SRF) cavities. Air exposed, electropolished Nb exhibited a surface superconducting gap {Delta} = 1.55 meV, which is characteristic of a clean, bulk Nb. However, the tunneling density of states (DOS) was significantly broadened. The Nb pieces, which were treated with the same mild baking used to improve the Q slope in SRF cavities, reveal a sharper DOS. Good fits to the DOS were obtained by using the Shiba theory, suggesting that magnetic scattering of quasiparticles is the origin of the gapless surface superconductivity and a heretofore unrecognized contributor to the Q-slope problem of Nb SRF cavities.

  13. Raman scattering under structural and magnetic phase transitions in terbium ferroborate

    NASA Astrophysics Data System (ADS)

    Peschanskii, A. V.; Yeremenko, A. V.; Fomin, V. I.; Bezmaternykh, L. N.; Gudim, I. A.

    2014-02-01

    The Raman scattering spectrum of single crystal TbFe3(BO3)4 was studied in the frequency range 3-500 cm-1 at temperatures from 2 to 300 K. It was found that in high- and low-temperature phases there exist additional phonon lines which were not known before. In the high-temperature phase, these lines originate from LO-TO splitting of polar phonons. Appearance of the additional lines in the low temperature phase is due to both a reduction of the crystal symmetry under the phase transition and an increase of the primitive cell volume. It was established that the frequencies of some phonon lines in the magneto-ordered phase are shifted towards the high-energy region upon applying an external magnetic field along the third-order axis. The spectrum of two-magnon Raman scattering was investigated. It was shown that at low temperatures the two-magnon band has a complex shape that reflects specific features in the density of state of the magnon branches. The magnon energy at the Brillouin zone boundary was determined.

  14. Stimulated X-ray Raman scattering - a critical assessment of the building block of nonlinear X-ray spectroscopy.

    PubMed

    Kimberg, Victor; Sanchez-Gonzalez, Alvaro; Mercadier, Laurent; Weninger, Clemens; Lutman, Alberto; Ratner, Daniel; Coffee, Ryan; Bucher, Maximilian; Mucke, Melanie; Agåker, Marcus; Såthe, Conny; Bostedt, Christoph; Nordgren, Joseph; Rubensson, Jan Erik; Rohringer, Nina

    2016-12-16

    With the invention of femtosecond X-ray free-electron lasers (XFELs), studies of light-induced chemical reaction dynamics and structural dynamics reach a new era, allowing for time-resolved X-ray diffraction and spectroscopy. To ultimately probe coherent electron and nuclear dynamics on their natural time and length scales, coherent nonlinear X-ray spectroscopy schemes have been proposed. In this contribution, we want to critically assess the experimental realisation of nonlinear X-ray spectroscopy at current-day XFEL sources, by presenting first experimental attempts to demonstrate stimulated resonant X-ray Raman scattering in molecular gas targets.

  15. Measurement of plasma wave frequency from absolute stimulated Raman scattering near the quarter-critical surface in a laser plasma

    NASA Astrophysics Data System (ADS)

    Villeneuve, D. M.; Bernard, J. E.; Baldis, H. A.

    1987-12-01

    Thomson scattering techniques were used to measure the frequency of plasma waves near the quarter-critical surface in a well-diagnosed plasma irradiated by a nanosecond CO2 laser with intensity ˜1014 W/cm2. The frequency ωp was shown to be less than ω0/2, in disagreement with the commonly used estimate ωp=ω0/2+ (9)/(8) (ve/c)2ω0. The theory of Afeyan and Williams [Phys. Fluids 28, 3397 (1985)] gives better agreement, and shows that the density scale length is more important than the temperature in determining the frequency shift.

  16. Spin-flop transition on Gd5Ge4 observed by x-ray resonant magnetic scattering and first-principles calculations of magnetic anisotropy

    SciTech Connect

    Tan, L.; Kreyssig, A.; Nandi, S.; Jia, S.; Lee, Y. B.; Lang, J. C.; Islam, Z.; Lograsso, T.; Schlagel, D.; Pecharsky, V.; Gschneidner, K.; Canfield, P.; Harmon, B.; McQueeney, R.; Goldman, A.

    2008-02-21

    X-ray resonant magnetic scattering was employed to study a fully reversible spin-flop transition in orthorhombic Gd{sub 5}Ge{sub 4} and to elucidate details of the magnetic structure in the spin-flop phase. The orientation of the moments at the three Gd sites flop 90{sup o} from the c axis to the a axis when a magnetic field, H{sub sf} = 9 kOe, is applied along the c axis at T = 9 K. The magnetic space group changes from Pnm'a to Pn'm'a' for all three Gd sublattices. The magnetic anisotropy energy determined from experimental measurements is in good agreement with the calculations of the magnetic anisotropy based on the spin-orbit coupling of the conduction electrons and an estimation of the dipolar interactions anisotropy. No significant magnetostriction effects were observed at the spin-flop transition.

  17. Magnetic and superconducting quantum critical behavior of itinerant electronic systems

    NASA Astrophysics Data System (ADS)

    Sknepnek, Rastko

    Quantum phase transitions occur at zero temperature as a function of some non-thermal parameter, e.g., pressure or chemical composition. In addition to being of fundamental interest, quantum phase transitions are important because they are believed to underlie a number of interesting low temperature phenomena. Quantum phase transitions differ from the classical phase transitions in many important aspects, two of them being (i) the mode-coupling effects and (ii) the behavior in the presence of disorder. We devote two projects of this dissertation to each of the two. First, we investigate the quantum phase transition of itinerant electrons from a paramagnet to a state which displays long-period helical structures due to a Dzyaloshinskii instability of the ferromagnetic state. In particular, we study how the self generated effective long-range interaction recently identified in itinerant quantum ferromagnets is cut-off by the helical ordering. Second, we discuss a quantum phase transition between a disordered metal and an exotic (non-s-wave) superconductor. Like in the case of ferromagnetic quantum phase transition mode coupling effects lead to an effective long-range interaction between the anomalous density fluctuations. We find that the asymptotic critical region is characterized by run-away flow to large disorder. However, for weak coupling, this region is very narrow, and it is preempted by a wide crossover regime with mean-field critical behavior. Then, we present results of large-scale Monte Carlo simulations for a 3d Ising model with short range interactions and planar defects. We show that the phase transition in this system is smeared, i.e., there is no single critical temperature, but different parts of the system order at different temperatures. Our Monte-Carlo results are in good agreement with a recent theory. Finally, we present large-scale Monte-Carlo simulations of a 2d bilayer quantum Heisenberg antiferromagnet with random dimer dilution. In contrast

  18. The design of the inelastic neutron scattering mode for the Extreme Environment Diffractometer with the 26 T High Field Magnet

    NASA Astrophysics Data System (ADS)

    Bartkowiak, Maciej; Stüßer, Norbert; Prokhnenko, Oleksandr

    2015-10-01

    The Extreme Environment Diffractometer is a neutron time-of-flight instrument, designed to work with a constant-field hybrid magnet capable of reaching fields over 26 T, unprecedented in neutron science; however, the presence of the magnet imposes both spatial and technical limitations on the surrounding instrument components. In addition to the existing diffraction and small-angle neutron scattering modes, the instrument will operate also in an inelastic scattering mode, as a direct time-of-flight spectrometer. In this paper we present the Monte Carlo ray-tracing simulations, the results of which illustrate the performance of the instrument in the inelastic-scattering mode. We describe the focussing neutron guide and the chopper system of the existing instrument and the planned design for the instrument upgrade. The neutron flux, neutron spatial distribution, divergence distribution and energy resolution are calculated for standard instrument configurations.

  19. Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment from lattice QCD.

    PubMed

    Blum, Thomas; Chowdhury, Saumitra; Hayakawa, Masashi; Izubuchi, Taku

    2015-01-09

    The most compelling possibility for a new law of nature beyond the four fundamental forces comprising the standard model of high-energy physics is the discrepancy between measurements and calculations of the muon anomalous magnetic moment. Until now a key part of the calculation, the hadronic light-by-light contribution, has only been accessible from models of QCD, the quantum description of the strong force, whose accuracy at the required level may be questioned. A first principles calculation with systematically improvable errors is needed, along with the upcoming experiments, to decisively settle the matter. For the first time, the form factor that yields the light-by-light scattering contribution to the muon anomalous magnetic moment is computed in such a framework, lattice QCD+QED and QED. A nonperturbative treatment of QED is used and checked against perturbation theory. The hadronic contribution is calculated for unphysical quark and muon masses, and only the diagram with a single quark loop is computed for which statistically significant signals are obtained. Initial results are promising, and the prospect for a complete calculation with physical masses and controlled errors is discussed.

  20. Hadronic Light-by-Light Scattering Contribution to the Muon Anomalous Magnetic Moment from Lattice QCD

    NASA Astrophysics Data System (ADS)

    Blum, Thomas; Chowdhury, Saumitra; Hayakawa, Masashi; Izubuchi, Taku

    2015-01-01

    The most compelling possibility for a new law of nature beyond the four fundamental forces comprising the standard model of high-energy physics is the discrepancy between measurements and calculations of the muon anomalous magnetic moment. Until now a key part of the calculation, the hadronic light-by-light contribution, has only been accessible from models of QCD, the quantum description of the strong force, whose accuracy at the required level may be questioned. A first principles calculation with systematically improvable errors is needed, along with the upcoming experiments, to decisively settle the matter. For the first time, the form factor that yields the light-by-light scattering contribution to the muon anomalous magnetic moment is computed in such a framework, lattice QCD +QED and QED. A nonperturbative treatment of QED is used and checked against perturbation theory. The hadronic contribution is calculated for unphysical quark and muon masses, and only the diagram with a single quark loop is computed for which statistically significant signals are obtained. Initial results are promising, and the prospect for a complete calculation with physical masses and controlled errors is discussed.

  1. Lattice dynamics in magnetic superelastic Ni-Mn-In alloys. Neutron scattering and ultrasonic experiments

    SciTech Connect

    Moya, Xavier; Gonzalez-Alonso, David; Manosa, Lluis; Planes, A.; Lograsso, Tom; Schlagel, D. L.; Zarestky, Jerel L.; Acet, Mehmet; Garlea, Vasile O

    2009-01-01

    Neutron scattering and ultrasonic methods have been used to study the lattice dynamics of two single crystals of Ni-Mn-In Heusler alloys close to Ni50Mn34In16 magnetic superelastic composition. The paper reports the experimental determination of the low-lying phonon dispersion curves and the elastic constants for this alloy system. We found that the frequencies of the TA2 branch are relatively low and it exhibits a small dip anomaly at a wave number n= 1/3, which softens with decreasing temperature. Associated with the softening of this phonon, we also observed the softening of the shear elastic constant C0 = (C11 C12)=2. Both temperature softenings are typical for bcc based solids which undergo martensitic transformations and re ect the dynamical instability of the cubic lattice against shearing of f110g planes along h1 10i directions. Additionally, we measured low-lying phonon dispersion branches and elastic constants in applied magnetic fields aimed to characterize the magnetoelastic coupling.

  2. Relative Significance of the Stimulated Raman Scattering and Two-Plasmon-Decay Instabilities at Quarter-Critical Density

    NASA Astrophysics Data System (ADS)

    Short, R. W.; Wen, H.; Maximov, A. V.; Myatt, J. F.; Seka, W.

    2016-10-01

    In direct-drive experiments on OMEGA, correlated signals of half-harmonic light and hot-electron production have usually been ascribed to two-plasmon decay (TPD). However, as scale lengths and temperatures increase, absolute stimulated Raman scattering (SRS) is expected to play a larger role in generating hot electrons and half-harmonic light. This may already be occurring in more-recent OMEGA experiments. Both instabilities occur at quarter-critical density, and for obliquely incident light, they can merge into a ``hybrid'' instability with a threshold differing from SRS and TPD thresholds considered separately. This talk analyzes how the thresholds of the quarter-critical instabilities vary with the incidence angle and polarization of the incident light, as well as the plasma parameters, and the expected significance for direct-drive experiments. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

  3. Cerium-Based Magnets: Novel High Energy Permanent Magnet Without Critical Elements

    SciTech Connect

    2012-01-01

    REACT Project: Ames Laboratory will develop a new class of permanent magnets based on the more commonly available element cerium for use in both EVs and renewable power generators. Cerium is 4 times more abundant and significantly less expensive than the rare earth element neodymium, which is frequently used in today’s most powerful magnets. Ames Laboratory will combine other metal elements with cerium to create a new magnet that can remain stable at the high temperatures typically found in electric motors. This new magnetic material will ultimately be demonstrated in a prototype electric motor, representing a cost-effective and efficient alternative to neodymium-based motors.

  4. The Scattering of f- and p-modes from Ensembles of Thin Magnetic Flux Tubes: An Analytical Approach

    NASA Astrophysics Data System (ADS)

    Hanson, Chris S.; Cally, Paul S.

    2014-08-01

    Motivated by the observational results of Braun, we extend the model of Hanson & Cally to address the effect of multiple scattering of f and p modes by an ensemble of thin vertical magnetic flux tubes in the surface layers of the Sun. As in the observational Hankel analysis, we measure the scatter and phase shift from an incident cylindrical wave in a coordinate system roughly centered in the core of the ensemble. It is demonstrated that although thin flux tubes are unable to interact with high-order fluting modes individually, they can indirectly absorb energy from these waves through the scatters of kink and sausage components. It is also shown how the distribution of absorption and phase shift across the azimuthal order m depends strongly on the tube position as well as on the individual tube characteristics. This is the first analytical study into an ensembles multiple-scattering regime that is embedded within a stratified atmosphere.

  5. Small-Angle Neutron Scattering Studies of Magnetic Correlation Lengths in Nanoparticle Assemblies

    NASA Astrophysics Data System (ADS)

    Majetich, Sara

    2009-03-01

    Small-angle neutron scattering (SANS) measurements of ordered arrays of surfactant-coated magnetic nanoparticle reveal characteristic length scales associated with interparticle and intraparticle magnetic ordering. The high degree of uniformity in the monodisperse nanoparticle size and spacing leads to a pronounced diffraction peak and allows for a straightforward determination of these length scales [1]. There are notable differences in these length scales depending on the particle moment, which depends on the material (Fe, Co, Fe3O4) and diameter, and also on whether the metal particle core is surrounded by an oxide shell. For 8.5 nm particles containing an Fe core and thick Fe3O4 shell, evidence of a spin flop phase is seen in the magnetite shell when a field is applied , but not when the shell thickness is ˜0.5 nm [2]. 8.0 nm particles with an e-Co core and 0.75 nm CoO shell show no exchange bias effects while similar particles with a 2 nm thick shell so significant training effects below 90 K. Polarized SANS studied of 7 nm Fe3O4 nanoparticle assemblies show the ability to resolve the magnetization components in 3D. [4pt] [1] M. Sachan, C. Bonnoit, S. A. Majetich, Y. Ijiri, P. O. Mensah-Bonsu, J. A. Borchers, and J. J. Rhyne, Appl. Phys. Lett. 92, 152503 (2008). [0pt] [2] Yumi Ijiri, Christopher V. Kelly, Julie A. Borchers, James J. Rhyne, Dorothy F. Farrell, Sara A. Majetich, Appl. Phys. Lett. 86, 243102-243104 (2005). [0pt] [3] K. L. Krycka, R. Booth, J. A. Borchers, W. C. Chen, C. Conlon, T. Gentile, C. Hogg, Y. Ijiri, M. Laver, B. B. Maranville, S. A. Majetich, J. Rhyne, and S. M. Watson, Physica B (submitted).

  6. High-field magnets using high-critical-temperature superconducting thin films

    DOEpatents

    Mitlitsky, F.; Hoard, R.W.

    1994-05-10

    High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla are disclosed. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field. 4 figures.

  7. High-field magnets using high-critical-temperature superconducting thin films

    DOEpatents

    Mitlitsky, Fred; Hoard, Ronald W.

    1994-01-01

    High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field.

  8. Reactivity impact of {sup 16}O thermal elastic-scattering nuclear data for some numerical and critical benchmark systems

    SciTech Connect

    Kozier, K. S.; Roubtsov, D.; Plompen, A. J. M.; Kopecky, S.

    2012-07-01

    The thermal neutron-elastic-scattering cross-section data for {sup 16}O used in various modern evaluated-nuclear-data libraries were reviewed and found to be generally too high compared with the best available experimental measurements. Some of the proposed revisions to the ENDF/B-VII.0 {sup 16}O data library and recent results from the TENDL system increase this discrepancy further. The reactivity impact of revising the {sup 16}O data downward to be consistent with the best measurements was tested using the JENDL-3.3 {sup 16}O cross-section values and was found to be very small in MCNP5 simulations of the UO{sub 2} and reactor-recycle MOX-fuel cases of the ANS Doppler-defect numerical benchmark. However, large reactivity differences of up to about 14 mk (1400 pcm) were observed using {sup 16}O data files from several evaluated-nuclear-data libraries in MCNP5 simulations of the Los Alamos National Laboratory HEU heavy-water solution thermal critical experiments, which were performed in the 1950's. The latter result suggests that new measurements using HEU in a heavy-water-moderated critical facility, such as the ZED-2 zero-power reactor at the Chalk River Laboratories, might help to resolve the discrepancy between the {sup 16}O thermal elastic-scattering cross-section values and thereby reduce or better define its uncertainty, although additional assessment work would be needed to confirm this. (authors)

  9. Ultraviolet Thomson Scattering from Two-Plasmon-Decay Driven Electron Plasma Waves at Quarter-Critical Densities

    NASA Astrophysics Data System (ADS)

    Follett, R. K.; Michel, D. T.; Hu, S. X.; Myatt, J. F.; Henchen, R. J.; Katz, J.; Froula, D. H.

    2013-10-01

    Thomson scattering (TS) was used to probe electron plasma waves (EPW's) driven by the two-plasmon-decay (TPD) instability near quarter-critical density. TPD-driven EPW's were observed at densities consistent with the common-wave TPD model. Five laser beams (λ3ω = 351nm) produced 400- μm-diam (FWHM) laser spots with overlapped intensities up to 3 ×1014W/cm2 . A 263-nm TS beam was used to probe densities ranging from 0.18 to 0.26 nc, where nc is the critical density for 351-nm light. The experimental geometry was chosen to match the five-beam TPD common wave k vector. The TS spectrum shows a large amplitude, narrow (~1.6-nm FHWM) feature centered around 423.4 nm. This wavelength corresponds to scattering from EPW's with a normalized wave vector k / k3 ω = 1 . 3 , a density of ne/nc = 0.243, and a temperature of Te = 2 keV. This is consistent with the predicted values given by the dispersion relations and TPD maximum growth hyperbola. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

  10. Self-Magnetic Field Effects on Electron Emission as the Critical Current is Approached

    SciTech Connect

    Ottinger, P. F.; Cooperstein, G.; Schumer, J. W.; Swanekamp, S. B.

    2001-09-28

    The self-magnetic field associated with the current in a planar diode is shown to reduce electron emission below the Child-Langmuir current density. As the magnetic field increases, the diode current is limited to the critical current. Here, a ID analysis is carried out to calculate the suppressed current density in the presence of a transverse magnetic field. The problem is shown to be similar to that of the limiting current (i.e., Hull current) calculated in a crossed field gap, in which a constant transverse magnetic field is applied across the gap to insulate the electron flow. In the case considered here, the magnetic field is produced by the diode current itself and this self-magnetic field decreases with distance along the gap. It is shown that the emitted current density is only modestly reduced from the Child-Langmuir current density. The 1-D analysis remains valid until critical current is approached, at which point orbit crossing occurs and a 2-D kinetic analysis is required. The minimum diode length required to reach critical current is also derived.

  11. Magnetic entropy change and critical exponents in double perovskite Y2NiMnO6

    NASA Astrophysics Data System (ADS)

    Sharma, G.; Tripathi, T. S.; Saha, J.; Patnaik, S.

    2014-11-01

    We report the magnetic entropy change (ΔSM) and the critical exponents in the double perovskite manganite Y2NiMnO6 with a ferromagnetic to paramagnetic transition TC~85 K. For a magnetic field change ΔH=80 kOe, a maximum magnetic entropy change ΔSM=-6.57 J/kg K is recorded around TC. The critical exponents β=0.363±0.05 and γ=1.331±0.09 obtained from power law fitting to spontaneous magnetization MS(T) and the inverse initial susceptibility χ0-1(T) satisfy well to values derived for a 3D-Heisenberg ferromagnet. The critical exponent δ=4.761±0.129 is determined from the isothermal magnetization at TC. The scaling exponents corresponding to second order phase transition are consistent with the exponents from Kouvel-Fisher analysis and satisfy Widom's scaling relation δ=1+(γ/β). Additionally, they also satisfy the single scaling equation M(H,ɛ)=ɛβf±(H/ɛ) according to which the magnetization-field-temperature data around TC should collapse into two curves for temperatures below and above TC.

  12. The Physical Origin and Magnetic Sensitivity of the Scattering Polarization Observed in the O i IR Triplet at 777 nm

    NASA Astrophysics Data System (ADS)

    del Pino Alemán, T.; Trujillo Bueno, J.

    2017-04-01

    The linearly polarized solar limb spectrum caused by the absorption and scattering of anisotropic radiation has a very rich diagnostic potential, given its sensitivity to the thermal, dynamic, and magnetic structure of the solar atmosphere. A crucial first step toward its scientific exploitation is understanding the physical origin of the observed spectral line polarization and its magnetic sensitivity via the Hanle and Zeeman effects. Here, we study the linear polarization signals observed in the IR triplet of O i at 777 nm, describing in detail the multilevel radiative transfer calculations that allowed us to decipher their physical origin. We investigate the sensitivity of the calculated scattering polarization signals to various modeling parameters, finding that the observed fractional linear polarization pattern originates mainly in the solar chromosphere, although the intensity profiles of the O i IR triplet come mainly from the lower photosphere. We find that the three lines are sensitive, via the Hanle effect, to magnetic fields with strengths between 0.01 and 30 G, in a extended region of the solar atmosphere. We show this through calculations of the response function to magnetic field perturbations in a semi-empirical model of the quiet Sun atmosphere. The dominant response of the linear polarization signals occurs at heights ∼ 1000 km above the visible model’s surface, which demonstrates that the scattering linear polarization signals of the oxygen IR triplet encode information on the magnetism of the solar chromosphere.

  13. Ground state of the quasi-1D compound BaVS3 resolved by resonant magnetic x-ray scattering.

    PubMed

    Leininger, Ph; Ilakovac, V; Joly, Y; Schierle, E; Weschke, E; Bunau, O; Berger, H; Pouget, J-P; Foury-Leylekian, P

    2011-04-22

    Resonant magnetic x-ray scattering near the vanadium L2,3-absorption edges has been used to investigate the low temperature magnetic structure of high quality BaVS3 single crystals. Below T(N)=31  K, the strong resonance revealed a triple-incommensurate magnetic ordering at the wave vector (0.226   0.226   ξ) in hexagonal notation, with ξ=0.033. The azimuthal-angle dependence of the scattering signal and time-dependent density functional theory simulations indicate an antiferromagnetic order within the ab plane with the spins polarized along a in the monoclinic structure.

  14. Loading and testing a light scattering cell with a binary fluid mixture near its critical composition

    NASA Astrophysics Data System (ADS)

    Jacobs, Donald T.; Becker, James S.

    1993-06-01

    Critical phenomena has been the subject of physics research for many years. However, only in recent years has the research effort become intense. The current intensity has caused the study of critical phenomena to be grouped into a previous older era and a present contemporary era. Turbidity cell filling with methanol cyclohexane is one of the first steps toward a further understanding of critical phenomena. Work performed during the research period is outlined. During this period, research was spent developing apparatus and techniques that will make it possible to study critical phenomena through turbidity measurements on methanol cyclohexane. Topics covered range from the orientation of turbidity cell parts for assembly to the filling apparatus and procedure used when th cell is built. The last section will briefly cover some of the observations made when viewing the cell in a controlled water bath. However, before mention is made of the specifics of the summer research, a short introduction to critical phenomena and turbidity and how they relate to this experiment is provided.

  15. Loading and testing a light scattering cell with a binary fluid mixture near its critical composition

    NASA Technical Reports Server (NTRS)

    Jacobs, Donald T.; Becker, James S.

    1993-01-01

    Critical phenomena has been the subject of physics research for many years. However, only in recent years has the research effort become intense. The current intensity has caused the study of critical phenomena to be grouped into a previous older era and a present contemporary era. Turbidity cell filling with methanol cyclohexane is one of the first steps toward a further understanding of critical phenomena. Work performed during the research period is outlined. During this period, research was spent developing apparatus and techniques that will make it possible to study critical phenomena through turbidity measurements on methanol cyclohexane. Topics covered range from the orientation of turbidity cell parts for assembly to the filling apparatus and procedure used when th cell is built. The last section will briefly cover some of the observations made when viewing the cell in a controlled water bath. However, before mention is made of the specifics of the summer research, a short introduction to critical phenomena and turbidity and how they relate to this experiment is provided.

  16. Magnetic relaxation and lower critical field in MgB2 wires

    NASA Astrophysics Data System (ADS)

    Y, Feng; G, Yan; Y, Zhao; Pradhan, A. K.; F, Liu C.; X, Zhang P.; L, Zhou

    2003-09-01

    Magnetic relaxation behaviour, critical current density Jc and lower critical field Hc1 have been investigated in MgB2/Ta/Cu wires. It is found that Jc and Hc1 decrease linearly with temperature in the whole temperature region below Tc. The relaxation rate is very small and has a weak temperature dependence compared to high-Tc superconductors. Also, the pinning potential is much larger and the temperature and field dependences of the pinning potential are briefly discussed.

  17. Critical scattering and incommensurate phase transition in antiferroelectric PbZrO3 under pressure

    PubMed Central

    Burkovsky, R. G.; Bronwald, I.; Andronikova, D.; Wehinger, B.; Krisch, M.; Jacobs, J.; Gambetti, D.; Roleder, K.; Majchrowski, A.; Filimonov, A. V.; Rudskoy, A. I.; Vakhrushev, S. B.; Tagantsev, A. K.

    2017-01-01

    Antiferroelectric lead zirconate is the key ingredient in modern ferroelectric and piezoelectric functional solid solutions. By itself it offers opportunities in new-type non-volatile memory and energy storage applications. A highly useful and scientifically puzzling feature of this material is the competition between the ferro- and antiferroelectric phases due to their energetic proximity, which leads to a challenge in understanding of the critical phenomena driving the formation of the antiferroelectric structure. We show that application of hydrostatic pressure drastically changes the character of critical lattice dynamics and enables the soft-mode-driven incommensurate phase transition sequence in lead zirconate. In addition to the long known cubic and antiferroelectric phases we identify the new non-modulated phase serving as a bridge between the cubic and the incommensurate phases. The pressure effect on ferroelectric and incommensurate critical dynamics shows that lead zirconate is not a single-instability-driven system. PMID:28134296

  18. Critical scattering and incommensurate phase transition in antiferroelectric PbZrO3 under pressure

    NASA Astrophysics Data System (ADS)

    Burkovsky, R. G.; Bronwald, I.; Andronikova, D.; Wehinger, B.; Krisch, M.; Jacobs, J.; Gambetti, D.; Roleder, K.; Majchrowski, A.; Filimonov, A. V.; Rudskoy, A. I.; Vakhrushev, S. B.; Tagantsev, A. K.

    2017-01-01

    Antiferroelectric lead zirconate is the key ingredient in modern ferroelectric and piezoelectric functional solid solutions. By itself it offers opportunities in new-type non-volatile memory and energy storage applications. A highly useful and scientifically puzzling feature of this material is the competition between the ferro- and antiferroelectric phases due to their energetic proximity, which leads to a challenge in understanding of the critical phenomena driving the formation of the antiferroelectric structure. We show that application of hydrostatic pressure drastically changes the character of critical lattice dynamics and enables the soft-mode-driven incommensurate phase transition sequence in lead zirconate. In addition to the long known cubic and antiferroelectric phases we identify the new non-modulated phase serving as a bridge between the cubic and the incommensurate phases. The pressure effect on ferroelectric and incommensurate critical dynamics shows that lead zirconate is not a single-instability-driven system.

  19. Dipolar structures in magnetite ferrofluids studied with small-angle neutron scattering with and without applied magnetic field

    SciTech Connect

    Klokkenburg, M.; Erne, B. H.; Petukhov, A. V.; Philipse, A. P.; Wiedenmann, A.

    2007-05-15

    Field-induced structure formation in a ferrofluid with well-defined magnetite nanoparticles with a permanent magnetic dipole moment was studied with small-angle neutron scattering (SANS) as a function of the magnetic interactions. The interactions were tuned by adjusting the size of the well-defined, single-magnetic-domain magnetite (Fe{sub 3}O{sub 4}) particles and by applying an external magnetic field. For decreasing particle dipole moments, the data show a progressive distortion of the hexagonal symmetry, resulting from the formation of magnetic sheets. The SANS data show qualitative agreement with recent cryogenic transmission electron microscopy results obtained in 2D [Klokkenburg et al., Phys. Rev. Lett. 97, 185702 (2006)] on the same ferrofluids.

  20. Continuous critical current measurement of high-temperature superconductor tapes with magnetic substrates using magnetic-circuit method.

    PubMed

    Zou, S N; Gu, C; Qu, T M; Han, Z

    2013-10-01

    The critical current (I(c)) of high-temperature superconductor (HTS) tapes has to be examined not only for short samples, but also for the entire tape, because local weak points can possibly lead to the quenching of the whole HTS device. Some methods were reported for continuous I(c) measurement along the length of a HTS tape, but few of them were applicable to tapes with magnetic substrates represented by YBa2Cu3O(7-δ)(YBCO)-coated conductors based on Ni5W alloy substrate by rolling assisted bi-axially textured substrate process. We previously presented a contact-free method using magnetic circuits to measure I(c) continuously of long HTS tapes, namely the magnetic-circuit (MC) method. This method has been previously applied with high speed and resolution to measure I(c) of HTS tapes with non-magnetic substrates, due to its resistance to noise aroused by mechanical vibration. In this work, its ability to measure HTS tapes with magnetic substrates is demonstrated both theoretically and experimentally. A 100 m long commercial YBCO tape based on Ni5W alloy substrate was measured and regular I(c) fluctuations were discovered. The MC method can be a powerful tool for quality control of HTS tapes, especially for tapes with magnetic substrates.

  1. Magnetic field orientation dependence of critical current in industrial Nb 3Sn strands

    NASA Astrophysics Data System (ADS)

    Schild, T.; Cloez, H.

    In usual superconducting devices such as magnets for NMR, the magnetic field is perpendicular to the superconducting strand axis. But in some special devices, such as magnets for the toroidal field system of fusion machines, the strands can experience any field orientation. For NbTi strands, the pinning force is dependent on the field orientation because of the drawing process (Takacs, S., Polak, M. and Krempasky, L., Critical currents of NbTi tapes with differently oriented anisotropic defects, Cryogenics, 1983, 23, 153-159). In the case of Nb 3Sn strands, the draw and react process suggests that the pinning force is isotropic. In fact, preliminary experiments have shown the contrary, which is why the magnetic field orientation dependence of the critical current for two types of industrial Nb 3Sn strands has been measured. These measurements have been performed for seven field orientations at field strengths up to 20 T. A clear anisotropic effect has been observed, which cannot be explained by Kramer's pinning law. The results are in very good agreement with an empirical law proposed in a recent study by Takayasu et al. (Takayasu, M., Montgomery, D.B. and Minervini, J.V., Effect of magnetic field direction on the critical current of twisted multifilamentary superconducting wires, Inst. of Phys. Conf. Ser., 1997, 158, 917-920). The parameters to be used in this law could be specific to the manufacturing process.

  2. Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake

    PubMed Central

    HAYAKAWA, Masashi; SCHEKOTOV, Alexander; POTIRAKIS, Stelios; EFTAXIAS, Kostas

    2015-01-01

    The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) Fh (horizontal magnetic field), (2) Fz (vertical magnetic field), and (3) Dh (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03–0.05 Hz was averaged for nighttime hours. The analysis results indicate that Fh fulfilled all criticality conditions on March 3–5, 2011, and that the additional parameter, Dh reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ. PMID:25743063

  3. Magnetic Compton scattering study of Ni2+xMn1-xGa ferromagnetic shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Ahuja, B. L.; Sharma, B. K.; Mathur, S.; Heda, N. L.; Itou, M.; Andrejczuk, A.; Sakurai, Y.; Chakrabarti, Aparna; Banik, S.; Awasthi, A. M.; Barman, S. R.

    2007-04-01

    In this paper, we report the spin-polarized momentum densities of Ni2+xMn1-xGa ( x=0.03 , 0.26, and 0.35) Heusler alloys at various temperatures and magnetic fields using magnetic Compton scattering technique. Magnetization studies are also performed for comparison. It is seen that the variation of magnetic effect (ratio of magnetic to charge intensities) is consistent with the martensitic transition, as shown by the differential scanning calorimetry data. The magnetic Compton profiles have been analyzed mainly in terms of the contributions from the 3d electrons of Mn to determine their role in the formation of total spin moment. The full potential linearized augmented plane-wave method has been used to calculate the spin-polarized energy bands and the spin moments of Ni2MnGa and Ni2.25Mn0.75Ga . Ni2MnGa exhibits half metallicity along certain high-symmetry directions of the Brillouin zone. For Ni2MnGa , the total and Mn local moments obtained from Compton scattering are in excellent agreement with theory.

  4. First in situ evidence of electron pitch angle scattering due to magnetic field line curvature in the Ion diffusion region

    NASA Astrophysics Data System (ADS)

    Zhang, Y. C.; Shen, C.; Marchaudon, A.; Rong, Z. J.; Lavraud, B.; Fazakerley, A.; Yao, Z.; Mihaljcic, B.; Ji, Y.; Ma, Y. H.; Liu, Z. X.

    2016-05-01

    Theory predicts that the first adiabatic invariant of a charged particle may be violated in a region of highly curved field lines, leading to significant pitch angle scattering for particles whose gyroradius are comparable to the radius of the magnetic field line curvature. This scattering generates more isotropic particle distribution functions, with important impacts on the presence or absence of plasma instabilities. Using magnetic curvature analysis based on multipoint Cluster spacecraft observations, we present the first investigation of magnetic curvature in the vicinity of an ion diffusion region where reconnected field lines are highly curved. Electrons at energies > 8 keV show a clear pitch angle ordering between bidirectional and trapped distribution in surrounding regions, while we show that in the more central part of the ion diffusion region electrons above such energies become isotropic. By contrast, colder electrons (~1 keV) retain their bidirectional character throughout the diffusion regions. The calculated adiabatic parameter K2 for these electrons is in agreement with theory. This study provides the first observational evidence for particle pitch angle scattering due to magnetic field lines with well characterized curvature in a space plasma.

  5. Critical care nurses' perceptions of workplace empowerment, magnet hospital traits and mental health.

    PubMed

    Tigert, Judy A; Laschinger, Heather K Spence

    2004-01-01

    The purpose of this study was to test Kanter's Theory (1977, 1993) of Structural Power in Organizations in a sample of Canadian critical care nurses. A secondary analysis of data from a larger descriptive correlational survey design was used to examine the relationships between perceived empowerment, perceived magnet hospital traits and critical care nurses' mental health (n = 75). The instruments in this study included the Conditions for Work Effectiveness Questionnaire II, the Job Activities Scale II, the Organizational Relationship Scale II, the Nurses Work Index-Revised, the Emotional Exhaustion Subscale, and the State of Mind Subscale. Empowerment was significantly and positively related to perceptions of magnet hospital traits (r = .49, p = 0.001). The combination of empowerment and magnet hospital traits explained a significant amount of the variance in mental health indicators: burn-out (19%) and state of mind (12%).

  6. Critical entropies for magnetic ordering in bosonic mixtures on a lattice

    SciTech Connect

    Capogrosso-Sansone, B.; Soeyler, S. G.; Prokof'ev, N. V.; Svistunov, B. V.

    2010-05-15

    We perform a numeric study (Worm algorithm Monte Carlo simulations) of ultracold two-component bosons in two- and three-dimensional optical lattices. At strong enough interactions and low enough temperatures the system features magnetic ordering. We compute critical temperatures and entropies for the disappearance of the Ising antiferromagnetic and the xy-ferromagnetic order and find that the largest possible entropies per particle are {approx} 0.5k{sub B}. We also estimate (optimistically) the experimental hold times required to reach equilibrium magnetic states to be on a scale of seconds. Low critical entropies and long hold times render the experimental observations of magnetic phases challenging and call for increased control over heating sources.

  7. Small angle neutron scattering studies of critical phenomena in a three-component microemulsion

    SciTech Connect

    Seto, H.; Komura, S.; Wignall, G.D.; Triolo, R.; Chillura-Martino, D.

    1996-12-31

    Critical density fluctuations of a ``water-in-oil`` microemulsion consisting of water, benzene, and BHDC (benzyldimethyl-n-hexadecyl ammonium chloride) were observed near the phase boundary by SANS. Observed profiles were well described by product of a form factor of spherical droplets and a structure factor, consisting of a term describing the inter-droplet correlations and also an Ornstein- Zernike component describing the droplet density fluctuations. Allowance was also made fro droplet polydispersity,though the width of the distribution turned out to be very small (1-2%). Observed temperature dependence of osmotic compressibility was fitted using the crossover function proposed by Belyakov et al., and the Ginzburg numbers were obtained on the order of 10{sup -2}. This indicates that long range interdroplet forces are not significant in this system, which displays upper critical solution temperature behavior. In contrast, previous studies of systems displaying lower critical solution temperature behavior (e.g., water, n-decane, and dioctyl sulfosuccinate sodium salt) indicate that long range interactions appear to dominate the phase separation behavior.

  8. Scattering of massless scalar waves by magnetically charged black holes in Einstein–Yang–Mills–Higgs theory

    NASA Astrophysics Data System (ADS)

    Gußmann, Alexander

    2017-03-01

    The existence of the classical black hole solutions of the Einstein–Yang–Mills–Higgs equations with non-Abelian Yang–Mills–Higgs hair implies that not all classical stationary magnetically charged black holes can be uniquely described by their asymptotic characteristics. In fact, in a certain domain of parameters, there exist different spherically-symmetric, non-rotating and asymptotically-flat classical black hole solutions of the Einstein–Yang–Mills–Higgs equations which have the same ADM mass and the same magnetic charge but significantly different geometries in the near-horizon regions. (These are black hole solutions which are described by a Reissner–Nordström metric on the one hand and the black hole solutions with non-Abelian Yang–Mills–Higgs hair which are described by a metric which is not of Reissner–Nordström form on the other hand). One can experimentally distinguish such black holes with the same asymptotic characteristics but different near-horizon geometries classically by probing the near-horizon regions of the black holes. We argue that one way to probe the near-horizon region of a black hole which allows one to distinguish magnetically charged black holes with the same asymptotic characteristics but different near-horizon geometries is by classical scattering of waves. Using the example of a minimally-coupled massless probe scalar field scattered by magnetically charged black holes which can be obtained as solutions of the Einstein–Yang–Mills–Higgs equations with a Higgs triplet and gauge group SU(2) in the limit of an infinite Higgs self-coupling constant we show how, in this case, the scattering cross sections differ for the magnetically charged black holes with different near-horizon geometries but the same asymptotic characteristics. We find in particular that the characteristic glory peaks in the cross sections are located at different scattering angles.

  9. Inelastic electron and Raman scattering from the collective excitations in quantum wires: Zero magnetic field

    NASA Astrophysics Data System (ADS)

    Kushwaha, Manvir S.

    2013-04-01

    The nanofabrication technology has taught us that an m-dimensional confining potential imposed upon an n-dimensional electron gas paves the way to a quasi-(n-m)-dimensional electron gas, with m ⩽ n and 1 ⩽ n, m ⩽ 3. This is the road to the (semiconducting) quasi-n dimensional electron gas systems we have been happily traversing on now for almost two decades. Achieving quasi-one dimensional electron gas (Q-1DEG) [or quantum wire(s) for more practical purposes] led us to some mixed moments in this journey: while the reduced phase space for the scattering led us believe in the route to the faster electron devices, the proximity to the 1D systems left us in the dilemma of describing it as a Fermi liquid or as a Luttinger liquid. No one had ever suspected the potential of the former, but it took quite a while for some to convince the others on the latter. A realistic Q-1DEG system at the low temperatures is best describable as a Fermi liquid rather than as a Luttinger liquid. In the language of condensed matter physics, a critical scrutiny of Q-1DEG systems has provided us with a host of exotic (electronic, optical, and transport) phenomena unseen in their higher- or lower-dimensional counterparts. This has motivated us to undertake a systematic investigation of the inelastic electron scattering (IES) and the inelastic light scattering (ILS) from the elementary electronic excitations in quantum wires. We begin with the Kubo's correlation functions to derive the generalized dielectric function, the inverse dielectric function, and the Dyson equation for the dynamic screened potential in the framework of Bohm-Pines' random-phase approximation. These fundamental tools then lead us to develop methodically the theory of IES and ILS for the Q-1DEG systems. As an application of the general formal results, which know no bounds regarding the subband occupancy, we compute the density of states, the Fermi energy, the full excitation spectrum [comprised of intrasubband and

  10. Covariant Spectator Theory of np scattering: Deuteron magnetic moment and form factors

    SciTech Connect

    Gross, Franz L.

    2014-06-01

    The deuteron magnetic moment is calculated using two model wave functions obtained from 2007 high precision fits to $np$ scattering data. Included in the calculation are a new class of isoscalar $np$ interaction currents which are automatically generated by the nuclear force model used in these fits. After normalizing the wave functions, nearly identical predictions are obtained: model WJC-1, with larger relativistic P-state components, gives 0.863(2), while model WJC-2 with very small $P$-state components gives 0.864(2) These are about 1\\% larger than the measured value of the moment, 0.857 n.m., giving a new prediction for the size of the $\\rho\\pi\\gamma$ exchange, and other purely transverse interaction currents that are largely unconstrained by the nuclear dynamics. The physical significance of these results is discussed, and general formulae for the deuteron form factors, expressed in terms of deuteron wave functions and a new class of interaction current wave functions, are given.

  11. Observation of the dynamic modes of a magnetic antivortex using Brillouin light scattering

    NASA Astrophysics Data System (ADS)

    Riley, Grant A.; Liu, H. J. Jason; Asmat-Uceda, Martin A.; Haldar, Arabinda; Buchanan, Kristen S.

    2015-08-01

    The dynamic behavior of magnetic antivortices stabilized in patterned pound-key-like microstructures was studied using microfocus Brillouin light scattering (micro-BLS) at frequencies above the gyrotropic mode (>1 GHz ). Micro-BLS spectra obtained as a function of the frequency of a driving microwave field show an intricate spectrum for the antivortex state for an in-plane driving field. Spatial mode profiles for the strongest antivortex resonance frequencies, obtained for samples in the antivortex as well as the single domain states, show that while the symmetry of one of the observed resonances is relatively insensitive to the spin configuration, the antivortex exhibits a unique mode profile for the other. A comparison with micromagnetic simulations shows that the frequency and symmetry of the latter are consistent with one of the antivortex azimuthal modes. Furthermore, the simulations show that this mode involves coupling between the antivortex spin excitations and propagating spin waves in the structure legs, which may be useful for high-wave-number spin-wave generation.

  12. Neutron Scattering Study of Magnetic Field Effect on the Stripe Order in LBCO

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Wen, Jinsheng; Xu, Guangyong; Hücker, Markus; Tranquada, John; Gu, Genda

    2009-03-01

    We have been investigating the relationship of stripe order to high-temperature superconductivity in cuprates. In particular, our neutron scattering results indicate that spin-stripe order is present in La2-xBaxCuO4 (LBCO) over a substantial range of doping about x = 1/8, where the bulk superconductivity is anomalously suppressed. Focusing on the x = 1/8 composition, we have recently studied the impact on stripe order of a magnetic field applied along the c-axis [1]. Applying a field up to 7 T, we observed a small enhancement of the intensity of the incommensurate antiferromagnetic superlattice peaks and a slight increase in the ordering temperature. In measurements of the spin dynamics, the field had no significant impact on the small spin gap (˜ 0.5 meV) found in the ordered phase [2]. [1] Jinsheng Wen et al., arXiv:0810.4085. [2] J.M. Tranquada et al., arXiv:0809.0711. Work supported by Office of Science, U.S. DOE, under Contract No. DEAC02-98CH10886

  13. How external magnetic fields alter the parameter dependence of reflectivity in stimulated Raman scattering

    NASA Astrophysics Data System (ADS)

    Winjum, B. J.; Tableman, A.; Tsung, F. S.; Mori, W. B.

    2016-10-01

    We show the parameter dependence of stimulated Raman scattering (SRS) reflectivity over a range of electron temperatures and densities, laser intensities, and external magnetic field (B0) amplitudes and orientations in particle-in-cell simulations with kλD = 0.2 - 0.4 for the backscatter plasma wave. B0 can modify kinetic SRS by altering the phasespace dynamics of trapped particles. We show how B0 (both in amplitude and in orientation relative to the incident laser wavevector) affects the onset intensity and threshold values for reflectivity. Without an external field, and for constant kλD , lower electron densities have lower reflectivities, since SRS saturates at amplitudes for which the detuning rate due to the nonlinear frequency shift is on the order of the growth rate. Lower reflectivities are also seen for shorter speckle lengths in multi-speckle ensembles. The sensitivity of SRS reflectivity to B0 depends on the underlying kinetic physics, though we comment on generalities and the parameter regimes for which B0 eliminates kinetic SRS reflectivity. Supported under Grant DE-NA0001833; simulations were carried out on the Dawson2 cluster, Edison, Mira, and BlueWaters.

  14. Modifying the Kinetic Behavior of Stimulated Raman Scattering with External Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Winjum, B. J.; Tableman, A.; Tsung, F. S.; Mori, W. B.

    2015-11-01

    We show the effect of an external magnetic field (B0) on stimulated Raman scattering (SRS) in the kinetic regime using particle-in-cell simulations. 1D simulations (with three velocity components for particle motion) are sufficient to show that orienting B0 perpendicular to the laser propagation direction can reduce SRS reflectivity. We show the effect of B0 on trapped particle motion and on local heating. In 2D simulations of single- and multi-speckled laser beams, trapped particles can be restricted to, or freed from, speckles and local bursts of SRS activity by B0. B0 collinear with the laser propagation direction acts to align trapped particles with the daughter electron plasma wave (EPW) in SRS, which can both limit collective speckle interactions and make 2D SRS more 1D-like. On the other hand, B0 perpendicular to the laser propagation direction acts to deflect trapped particles transversely across the daughter EPW and to dynamically change the population of particles that are resonant with the EPW, disrupting the nonlinear wave-particle effects on EPWs. This acts to decrease SRS reflectivity. Hot electron motion is restricted for either orientation, but to different effect with regard to local heating, SRS recurrence, and speckle interactivity. Supported by DOE, Grant No. DE-NA0001833.

  15. Fe K-edge X-ray resonant magnetic scattering from Ba(Fe1−xCox)2As2 superconductors

    SciTech Connect

    Kim, Min Gyu; Kreyssig, Andreas; Lee, Yongbin; McQueeney, Robert J.; Harmon, Bruce N.; Goldman, Alan I.

    2012-06-15

    We present an X-ray resonant magnetic scattering study at the Fe-K absorption edge of the BaFe2As2 compound. The energy spectrum of the resonant scattering, together with our calculation using the full-potential linear-augmented plane wave method with a local density functional suggests that the observed resonant scattering arises from electric dipole (E1) transitions. We discuss the role of Fe K-edge X-ray resonant magnetic scattering in understanding the relationship between the structure and the antiferromagnetic transition in the doped Ba(Fe1−xCox)2As2 superconductors.

  16. Effects of the scatter in sunspot group tilt angles on the large-scale magnetic field at the solar surface

    SciTech Connect

    Jiang, J.; Cameron, R. H.; Schüssler, M.

    2014-08-10

    The tilt angles of sunspot groups represent the poloidal field source in Babcock-Leighton-type models of the solar dynamo and are crucial for the build-up and reversals of the polar fields in surface flux transport (SFT) simulations. The evolution of the polar field is a consequence of Hale's polarity rules, together with the tilt angle distribution which has a systematic component (Joy's law) and a random component (tilt-angle scatter). We determine the scatter using the observed tilt angle data and study the effects of this scatter on the evolution of the solar surface field using SFT simulations with flux input based upon the recorded sunspot groups. The tilt angle scatter is described in our simulations by a random component according to the observed distributions for different ranges of sunspot group size (total umbral area). By performing simulations with a number of different realizations of the scatter we study the effect of the tilt angle scatter on the global magnetic field, especially on the evolution of the axial dipole moment. The average axial dipole moment at the end of cycle 17 (a medium-amplitude cycle) from our simulations was 2.73 G. The tilt angle scatter leads to an uncertainty of 0.78 G (standard deviation). We also considered cycle 14 (a weak cycle) and cycle 19 (a strong cycle) and show that the standard deviation of the axial dipole moment is similar for all three cycles. The uncertainty mainly results from the big sunspot groups which emerge near the equator. In the framework of Babcock-Leighton dynamo models, the tilt angle scatter therefore constitutes a significant random factor in the cycle-to-cycle amplitude variability, which strongly limits the predictability of solar activity.

  17. X-ray magnetic circular dichroism and small angle neutron scattering study of thiol capped gold nanoparticles.

    SciTech Connect

    de la Venta, J.; Bouzas, V.; Pucci, A.; Laguna-Marco, M. A.; Haskel, D.; Pinel, E. F.; te Velthuis, S. G. E.; Hoffmann, A.; Lal, J.; Bleuel, M.; Ruggeri, G.; de Julian, C.; Garcia, M. A.; Univ. Complutense de Madrid; Inst. de Magnetismo Aplicado UCM; Univ. Pisa; Univ. di Padova

    2009-11-01

    X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 {center_dot} 10{sup -4} was found at the Au L{sub 3} edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M{sub s}, of 0.06 emu/g{sub Au}. SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences.

  18. Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study.

    PubMed

    Zighem, F; Roussigné, Y; Chérif, S-M; Moch, P; Ben Youssef, J; Paumier, F

    2010-10-13

    Microstrip ferromagnetic resonance and Brillouin scattering are used to provide a comparative determination of the magnetic parameters of thin permalloy layers interfaced with a non-magnetic (Al(2)O(3)) or with an antiferromagnetic oxide (NiO). It results from our microstructural study that no preferential texture is favoured in the observed polycrystalline sublayers. It is shown that the perpendicular anisotropy can be monitored using an interfacial surface energy term which is practically independent of the nature of the interface. In the interval of thicknesses investigated (5-25 nm) the saturation magnetization does not significantly differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy and exchange bias anisotropy are also derived from the study of the dynamic magnetic excitations and compared with our independent evaluations using conventional magnetometry.

  19. Ab initio calculations as a quantitative tool in the inelastic neutron scattering study of a single-molecule magnet analogue.

    PubMed

    Vonci, Michele; Giansiracusa, Marcus J; Gable, Robert W; Van den Heuvel, Willem; Latham, Kay; Moubaraki, Boujemaa; Murray, Keith S; Yu, Dehong; Mole, Richard A; Soncini, Alessandro; Boskovic, Colette

    2016-02-04

    Ab initio calculations carried out on the Tb analogue of the single-molecule magnet family Na9[Ln(W5O18)2] (Ln = Nd, Gd, Ho and Er) have allowed interpretation of the inelastic neutron scattering spectra. The combined experimental and theoretical approach sheds new light on the sensitivity of the electronic structure of the Tb(III) ground and excited states to small structural distortions from axial symmetry, thus revealing the subtle relationship between molecular geometry and magnetic properties of the two isostructural species that comprise the sample.

  20. Influence of magnetism on phonons in CaFe2As2 as seen via inelastic x-ray scattering

    SciTech Connect

    Hahn, S.E.; Lee, Y.; Ni, N.; Canfield, P.C.; Goldman, A.I.; McQueeney, R.J.; Harmon, B.N.; Alatas, A.; Leu, B.M.; Alp, E.E.; Chung, D.Y.; Todorov, I.S.; Kanatzidis, M.G.

    2009-06-19

    In the iron pnictides, the strong sensitivity of the iron magnetic moment to the arsenic position suggests a significant relationship between phonons and magnetism. We measured the phonon dispersion of several branches in the high-temperature tetragonal phase of CaFe{sub 2}As{sub 2} using inelastic x-ray scattering on single-crystal samples. These measurements were compared to ab initio calculations of the phonons. Spin-polarized calculations imposing the antiferromagnetic order present in the low-temperature orthorhombic phase dramatically improve agreement between theory and experiment. This is discussed in terms of the strong antiferromagnetic correlations that are known to persist in the tetragonal phase.

  1. Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions

    NASA Astrophysics Data System (ADS)

    Rakyta, Péter; Kormányos, Andor; Cserti, József

    2016-06-01

    We study the Josephson current in long ballistic superconductor-monolayer graphene-superconductor junctions. As a first step, we have developed an efficient computational approach to calculate the Josephson current in tight-binding systems. This approach can be particularly useful in the long-junction limit, which has hitherto attracted less theoretical interest but has recently become experimentally relevant. We use this computational approach to study the dependence of the critical current on the junction geometry, doping level, and an applied perpendicular magnetic field B . In zero magnetic field we find a good qualitative agreement with the recent experiment of M. Ben Shalom et al. [Nat. Phys. 12, 318 (2016), 10.1038/nphys3592] for the length dependence of the critical current. For highly doped samples our numerical calculations show a broad agreement with the results of the quasiclassical formalism. In this case the critical current exhibits Fraunhofer-like oscillations as a function of B . However, for lower doping levels, where the cyclotron orbit becomes comparable to the characteristic geometrical length scales of the system, deviations from the results of the quasiclassical formalism appear. We argue that due to the exceptional tunability and long mean free path of graphene systems a new regime can be explored where geometrical and dynamical effects are equally important to understand the magnetic field dependence of the critical current.

  2. Magnetic-field-tuned quantum criticality of the heavy-fermion system YbPtBi

    SciTech Connect

    Mun, E. D.; Budko, Serguei L.; Martin, Catalin; Kim, Hyong June; Tanatar, Makariy A.; Park, J.-H.; Murphy, T.; Schmiedeshoff, G. M.; Dilley, N.; Prozorov, Ruslan; Canfield, Paul C.

    2013-02-15

    In this paper, we present systematic measurements of the temperature and magnetic field dependencies of the thermodynamic and transport properties of the Yb-based heavy fermion YbPtBi for temperatures down to 0.02 K with magnetic fields up to 140 kOe to address the possible existence of a field-tuned quantum critical point. Measurements of magnetic-field- and temperature-dependent resistivity, specific heat, thermal expansion, Hall effect, and thermoelectric power indicate that the AFM order can be suppressed by an applied magnetic field of Hc~4 kOe. In the H-T phase diagram of YbPtBi, three regimes of its low-temperature states emerge: (I) AFM state, characterized by a spin density wave-like feature, which can be suppressed to T=0 by the relatively small magnetic field of Hc~4 kOe; (II) field-induced anomalous state in which the electrical resistivity follows Δρ(T)∝T1.5 between Hc and ~8 kOe; and (III) Fermi liquid (FL) state in which Δρ(T)∝T2 for H≥8 kOe. Regions I and II are separated at T=0 by what appears to be a quantum critical point. Whereas region III appears to be a FL associated with the hybridized 4f states of Yb, region II may be a manifestation of a spin liquid state.

  3. Dynamics of quantum spin liquid and spin solid phases in IPA-CuCl3 under an applied magnetic field studied with neutron scattering

    NASA Astrophysics Data System (ADS)

    Zheludev, A.; Garlea, V. O.; Masuda, T.; Manaka, H.; Regnault, L.-P.; Ressouche, E.; Grenier, B.; Chung, J.-H.; Qiu, Y.; Habicht, K.; Kiefer, K.; Boehm, M.

    2007-08-01

    Inelastic and elastic neutron scattering is used to study spin correlations in the quasi-one-dimensional quantum antiferromagnet IPA-CuCl3 in strong applied magnetic fields. A condensation of magnons and commensurate transverse long-range ordering is observe at a critical field Hc=9.5T . The field dependencies of the energies and polarizations of all magnon branches are investigated both below and above the transition point. Their dispersion is measured across the entire one-dimensional Brillouin zone in magnetic fields up to 14T . The critical wave vector of magnon spectrum truncation [Masuda , Phys. Rev. Lett. 96, 047210 (2006)] is found to shift from hc≈0.35 at HHc . A drastic reduction of magnon bandwidths in the ordered phase [Garlea , Phys. Rev. Lett. 98, 167202 (2007)] is observed and studied in detail. New features of the spectrum, presumably related to this bandwidth collapse, are observed just above the transition field.

  4. Dynamics of quantum spin liquid and spin solid phases in IPA-CuCl3 under an applied magnetic field studied with neutron scattering

    SciTech Connect

    Zheludev, Andrey I; Garlea, Vasile O; Masuda, T.; Manaka, H.; Regnault, L.-P.; Ressouche, E.; Grenier, B.; Chung, J.-H.; Qiu, Y.; Habicht, Klaus; Kiefer, K.; Boehm, Martin

    2007-01-01

    Inelastic and elastic neutron scattering is used to study spin correlations in the quasi-one-dimensional quantum antiferromagnet IPA-CuCl3 in strong applied magnetic fields. A condensation of magnons and commensurate transverse long-range ordering is observe at a critical field Hc=9.5 T. The field dependencies of the energies and polarizations of all magnon branches are investigated both below and above the transition point. Their dispersion is measured across the entire one-dimensional Brillouin zone in magnetic fields up to 14 T. The critical wave vector of magnon spectrum truncation Masuda et al., Phys. Rev. Lett. 96, 047210 2006 is found to shift from hc0,35 at HHC to hc=0.25 for HHC. A drastic reduction of magnon bandwidths in the ordered phase Garlea et al., Phys. Rev. Lett. 98, 167202 2007 is observed and studied in detail. New features of the spectrum, presumably related to this bandwidth collapse, are observed just above the transition field.

  5. Magnetic and electric coherence in forward- and back-scattered electromagnetic waves by a single dielectric subwavelength sphere

    NASA Astrophysics Data System (ADS)

    Geffrin, J. M.; García-Cámara, B.; Gómez-Medina, R.; Albella, P.; Froufe-Pérez, L. S.; Eyraud, C.; Litman, A.; Vaillon, R.; González, F.; Nieto-Vesperinas, M.; Sáenz, J. J.; Moreno, F.

    2012-11-01

    Magnetodielectric small spheres present unusual electromagnetic scattering features, theoretically predicted a few decades ago. However, achieving such behaviour has remained elusive, due to the non-magnetic character of natural optical materials or the difficulty in obtaining low-loss highly permeable magnetic materials in the gigahertz regime. Here we present unambiguous experimental evidence that a single low-loss dielectric subwavelength sphere of moderate refractive index (n=4 like some semiconductors at near-infrared) radiates fields identical to those from equal amplitude crossed electric and magnetic dipoles, and indistinguishable from those of ideal magnetodielectric spheres. The measured scattering radiation patterns and degree of linear polarization (3-9 GHz/33-100 mm range) show that, by appropriately tuning the a/λ ratio, zero-backward (‘Huygens’ source) or almost zero-forward (‘Huygens’ reflector) radiated power can be obtained. These Kerker scattering conditions only depend on a/λ. Our results open new technological challenges from nano- and micro-photonics to science and engineering of antennas, metamaterials and electromagnetic devices.

  6. Influence of Magnetic Molecules on Electron Spin Scattering in InAs as Seen in Its Low Temperature Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Gilpin, Joseph; Soghomonian, Victoria; Heremans, Jean; Kallaher, Raymond

    2009-04-01

    Quantum interference between different scattering trajectories of electrons in solid-state systems leads to corrections to the classically predicted electrical resistivity. InAs films were studied, focusing on the influence of a monolayer of the magnetic molecule, Mn12, on the spin scattering of the electrons in the InAs accumulation layer. The weak localization and anti localization phenomena were examined via comparison of the magneto-resistance, as predicted by Bergman.ootnotetextBergmann, G. (1984). Weak Localization In Thin Films: a time-of-flight experiment with conduction electrons. Physics Reports (Review Section of Physics Letters) (107), 1-58. The localization effects were measured at temperatures of 0.4 K. Through the study of the characteristic localization effects it is possible to determine the existence and effect of the quantum scatterings. In initial experiments clear anti-localization is observed, but the trends have not yet yielded systematic and consistent answers correlating the effect of the Mn12 monolayer to the spin scattering in the InAs layer. Future refinement of our system of Mn12 application better suited to the delicate InAs surface is expected to produce clearer evidence of the localization phenomena, and subsequently insight into scattering effects.

  7. Shell thickness and dynamic magnetic field effects on the critical phenomena of magnetic core-shell nanoparticles with spherical geometry

    NASA Astrophysics Data System (ADS)

    Yüksel, Yusuf

    2017-03-01

    By using Monte Carlo simulations for classical Heisenberg spins, we study the critical phenomena and ferrimagnetic properties of spherical nanoparticles with core-shell geometry. The particle core is composed of ferromagnetic spins, and it is coated by a ferromagnetic shell. Total size of the particle is fixed but the thickness of the shell is varied in such a way that the shell layer is grown at the expense of the core. Effects of the shell thickness, as well as dynamic magnetic field parameters such as oscillation period and field amplitude on the magnetization profiles, dynamic hysteresis loops and phase diagrams have been investigated for the present system. It has been found that as the shell thickness varies then the easy axis magnetization of the overall system may exhibit Q-, P-, L- and N- type behaviors based on the Neél terminology. We also found that three distinct anomalies originate in the thermal variation of specific heat with increasing field period. Dynamic hysteresis loops corresponding to off-axial magnetization components exhibit unconventional behavior such as double rings with symmetric shapes around the vertical axis over the h (t) = 0 line which may originate due to the stochastic resonance behavior of these components.

  8. Magnetic-field-induced quantum criticality in a planar ferromagnet with single-ion anisotropy

    NASA Astrophysics Data System (ADS)

    Mercaldo, M. T.; Rabuffo, I.; De Cesare, L.; Caramico D'Auria, A.

    2014-08-01

    We analyze the effects induced by single-ion anisotropy on quantum criticality in a d-dimensional spin-3/2 planar ferromagnet. To tackle this problem we employ the two-time Green's function method, using the Tyablikov decoupling for exchange interactions and the Anderson-Callen decoupling for single-ion anisotropy. In our analysis the role of non-thermal control parameter which drives the quantum phase transition is played by a longitudinal external magnetic field. We find that the single-ion anisotropy has substantial effects on the structure of the phase diagram close to the quantum critical point.

  9. Application of Fermi scattering theory to a magnetically scanned electron linear accelerator.

    PubMed

    Sandison, G A; Huda, W

    1988-01-01

    This paper uses a solution to the Fermi electron transport equation for an isotropic point source to characterize the magnetically scanned broad electron beams from the Sagittaire Therac 40 accelerator in the air space above patients. Thick lead collimation is shown to be adequately modeled by an infinitely thin absorbing plate when used to predict penumbra shape. A relationship between broad beam penumbra width and the value of the root-mean-square spatial Gaussian spread sigma (z) of an elementary pencil beam is derived. This relationship is applicable for any rectangular field size. Measurement of the variation in broad beam penumbra width with source-surface distance (SSD) for a 7-MeV beam locates the isotropic source to be coincident with the exit window of the accelerator and indicates that the scattering effect of the monitor chamber may be considered negligibly small. Using this source location accurate predictions of beam profile shape for any clinically used beam energy, SSD, or field size are made in the presence of lead trimmer collimation. Field penumbra beyond the photon collimation system is formed in each lateral direction by two lead blocks whose faces are aligned along a diverging ray emanating from the source. The photon collimator closest to the source restricts the field size causing a variation of both fluence and the mean square angle spread of the electrons across the plane at the level of the lower collimator. This variation is accounted for by introducing an empirical perturbation factor into the mathematical formalism. An interesting feature of this perturbation factor is that it is field size dependent and its effect on penumbra width may be scaled for both beam energy and SSD to accurately predict beam profile shape.

  10. Application of Fermi scattering theory to a magnetically scanned electron linear accelerator

    SciTech Connect

    Sandison, G.A.; Huda, W.

    1988-07-01

    This paper uses a solution to the Fermi electron transport equation for an isotropic point source to characterize the magnetically scanned broad electron beams from the Sagittaire Therac 40 accelerator in the air space above patients. Thick lead collimation is shown to be adequately modeled by an infinitely thin absorbing plate when used to predict penumbra shape. A relationship between broad beam penumbra width and the value of the root-mean-square spatial Gaussian spread sigma (z) of an elementary pencil beam is derived. This relationship is applicable for any rectangular field size. Measurement of the variation in broad beam penumbra width with source-surface distance (SSD) for a 7-MeV beam locates the isotropic source to be coincident with the exit window of the accelerator and indicates that the scattering effect of the monitor chamber may be considered negligibly small. Using this source location accurate predictions of beam profile shape for any clinically used beam energy, SSD, or field size are made in the presence of lead trimmer collimation. Field penumbra beyond the photon collimation system is formed in each lateral direction by two lead blocks whose faces are aligned along a diverging ray emanating from the source. The photon collimator closest to the source restricts the field size causing a variation of both fluence and the mean square angle spread of the electrons across the plane at the level of the lower collimator. This variation is accounted for by introducing an empirical perturbation factor into the mathematical formalism. An interesting feature of this perturbation factor is that it is field size dependent and its effect on penumbra width may be scaled for both beam energy and SSD to accurately predict beam profile shape.

  11. Behavior of the critical temperature of Ising thin films with variable surface magnetic moments.

    PubMed

    Monroe, James L

    2005-01-01

    Properties of magnetic thin films are of considerable interest both for applied as well as theoretical reasons. I study the behavior of Ising thin films through the use of layered Bethe lattices and Husimi trees. In particular the behavior of the critical temperature both as a function of the number of layers and as a function of variable magnetic moments of surface spins is presented. The later is motivated by that fact that such variation has been found to occur in physical systems such as Ni and Fe free surfaces and Ni/Co interfaces. The approach used is more accurate than many previously used and most importantly shows a different qualitative behavior of the critical temperature from previous studies.

  12. Scaling laws for the critical current density of NbN films in high magnetic fields

    SciTech Connect

    Hampshire, D.P. . Dept. of Physics); Gray, K.E.; Kampwirth, R.T. )

    1992-08-01

    We have measured the critical current density (Jc) of two NbN films (500 {Angstrom} and 1550 {Angstrom} thick) as a function of temperature in magnetic fields up to 25 Tesla using transport measurements. In both films, the functional form of the volume pinning force F{sub p} obeys the Fietz - Webb scaling law throughout the entire magnetic field and temperature range such that: F{sub p}=J{sub c} {times} B= {alpha}B{sub c2}{sup m}(T)b{sup {1/2}} (1-b){sup 2} = {alpha}*(1-T/T{sub c}){sup m}b{sup {1/2}}(1-b){sup 2} where {alpha} and {alpha}* are constants dependent on the film, B{sub c2}(T) is the upper critical field, b = B/B{sub c2}(T) is the reduced magnetic field, {Tc} is the critical temperature and we find m = 2.7 {plus minus} 0.1. Over a limited range of magnetic fields close to B{sub c2}(T), we can approximate this functional form by: F{sub p} = {Beta}B{sub c2}{sup M}(T)b(1-b){sup 2}={Beta}*(1-T/{Tc}){sup M}b(1-b){sup 2} where {Beta} and {Beta}* are constants and we find M = 2.6{plus minus}0.2. Values of J{sub c} derived from D.C. magnetisation data obtained using Bean's model show qualitative agreement with the transport measurements throughout the superconducting phase. Despite the marked granularity in the microstructure of these films, we interpret our results as evidence that a flux pinning mechanism determines the transport current density in NbN films in high magnetic fields.

  13. Scaling laws for the critical current density of NbN films in high magnetic fields

    SciTech Connect

    Hampshire, D.P.; Gray, K.E.; Kampwirth, R.T.

    1992-08-01

    We have measured the critical current density (Jc) of two NbN films (500 {Angstrom} and 1550 {Angstrom} thick) as a function of temperature in magnetic fields up to 25 Tesla using transport measurements. In both films, the functional form of the volume pinning force F{sub p} obeys the Fietz - Webb scaling law throughout the entire magnetic field and temperature range such that: F{sub p}=J{sub c} {times} B= {alpha}B{sub c2}{sup m}(T)b{sup {1/2}} (1-b){sup 2} = {alpha}*(1-T/T{sub c}){sup m}b{sup {1/2}}(1-b){sup 2} where {alpha} and {alpha}* are constants dependent on the film, B{sub c2}(T) is the upper critical field, b = B/B{sub c2}(T) is the reduced magnetic field, {Tc} is the critical temperature and we find m = 2.7 {plus_minus} 0.1. Over a limited range of magnetic fields close to B{sub c2}(T), we can approximate this functional form by: F{sub p} = {Beta}B{sub c2}{sup M}(T)b(1-b){sup 2}={Beta}*(1-T/{Tc}){sup M}b(1-b){sup 2} where {Beta} and {Beta}* are constants and we find M = 2.6{plus_minus}0.2. Values of J{sub c} derived from D.C. magnetisation data obtained using Bean`s model show qualitative agreement with the transport measurements throughout the superconducting phase. Despite the marked granularity in the microstructure of these films, we interpret our results as evidence that a flux pinning mechanism determines the transport current density in NbN films in high magnetic fields.

  14. Intergrain magnetic properties and critical currents of T1-1223 bulk and tape superconductors

    NASA Astrophysics Data System (ADS)

    Zalecki, R.; Kolodziejczyk, A.; Chmist, J.; König, W.; Gritzner, G.

    2000-11-01

    The magnetic field and the temperature dependencies of the dispersive and the absorption components of the low frequency ac magnetic susceptibility for Pb and Bi single doped bulk superconductors as well as for Pb and Bi co-doped Ag-sheathed superconducting T1-1223 tapes have been measured and analyzed. The studies were accompanied by optical and electron microscopic observations of the microstructure. The ac susceptibility measured at various ac magnetic field amplitudes showed both intergrain and intragrain features. The temperature dependencies of the intergrain critical current densities were extracted from the absorption susceptibility via a modified Bean model. They were at relevant temperatures one order of magnitude larger for the tape than for the bulk specimens.

  15. The frustrated fcc antiferromagnet Ba2 YOsO6: Structural characterization, magnetic properties and neutron scattering studies

    DOE PAGES

    Kermarrec, E.; Marjerrison, Casey A.; Thompson, C. M.; ...

    2015-02-26

    Here we report the crystal structure, magnetization, and neutron scattering measurements on the double perovskite Ba2 YOsO6. The Fmmore » $$\\bar{3}$$m space group is found both at 290 K and 3.5 K with cell constants a0=8.3541(4) Å and 8.3435(4) Å, respectively. Os5+ (5d3) ions occupy a nondistorted, geometrically frustrated face-centered-cubic (fcc) lattice. A Curie-Weiss temperature θ ~₋700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long-range antiferromagnetic order, consistent with a type-I fcc state below TN~69 K, is revealed by magnetization, Fisher heat capacity, and elastic neutron scattering, with an ordered moment of 1.65(6) μB on Os5+. The ordered moment is much reduced from either the expected spin-only value of ~3 μB or the value appropriate to 4d3 Ru5+ in isostructural Ba2 YRuO6 of 2.2(1) μB, suggesting a role for spin-orbit coupling (SOC). Triple-axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T=67.45 K, and the existence of a second-ordered state. We find time-of-flight inelastic neutron results reveal a large spin gap Δ~17 meV, unexpected for an orbitally quenched, d3 electronic configuration. In conclusion, we discuss this in the context of the ~5 meV spin gap observed in the related Ru5+,4d3 cubic double perovskite Ba2YRuO6, and attribute the ~3 times larger gap to stronger SOC present in this heavier, 5d, osmate system.« less

  16. Small-angle neutron scattering study of magnetic ordering and inhomogeneity across the martensitic phase transformation in Ni50–xCoxMn₄₀Sn₁₀ alloys

    SciTech Connect

    Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; James, R. D.; Leighton, C.

    2012-04-27

    The Heusler-derived multiferroic alloy Ni50–xCoxMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390 K. The static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.

  17. Risk Management in Magnetic Resonance: Failure Mode, Effects, and Criticality Analysis

    PubMed Central

    Granata, Vincenza; Filice, Salvatore; Raiano, Nicola; Amato, Daniela Maria; Zirpoli, Maria; di Finizio, Alessandro; Sansone, Mario; Russo, Anna; Covelli, Eugenio Maria; Pedicini, Tonino; Triassi, Maria

    2013-01-01

    The aim of the study was to perform a risk management procedure in “Magnetic Resonance Examination” process in order to identify the critical phases and sources of radiological errors and to identify potential improvement projects including procedures, tests, and checks to reduce the error occurrence risk. In this study we used the proactive analysis “Failure Mode Effects Criticality Analysis,” a qualitative and quantitative risk management procedure; has calculated Priority Risk Index (PRI) for each activity of the process; have identified, on the PRI basis, the most critical activities and, for them, have defined improvement projects; and have recalculated the PRI after implementation of improvement projects for each activity. Time stop and audits are performed in order to control the new procedures. The results showed that the most critical tasks of “Magnetic Resonance Examination” process were the reception of the patient, the patient schedule drafting, the closing examination, and the organization of activities. Four improvement projects have been defined and executed. PRI evaluation after improvement projects implementation has shown that the risk decreased significantly following the implementation of procedures and controls defined in improvement projects, resulting in a reduction of the PRI between 43% and 100%. PMID:24171173

  18. Study on the critical properties of thin magnetic films using the clock model

    NASA Astrophysics Data System (ADS)

    Nguyen, T.-L. H.; Thanh Ngo, V.

    2017-03-01

    We study the critical behaviour of very thin magnetic films. This system can be described by the q-state clock model. In order to determine the critical exponents of the system when there exists the Berezinskii–Kosterlitz–Thouless phase between the two phase transitions, we introduce a new technique for calculating the order parameter. The simulation is performed by very high-resolution Monte Carlo method with including the Wang–Landau algorithm. The results showed that the Berezinskii–Kosterlitz–Thouless phase starts to occur when q≥slant 3 with a small symmetry breaking field. We obtained not only the critical exponents of a common transition at high temperature but also the ones of unclear transition at low temperature.

  19. Thomson Scattering Measurements of Temperature and Density in a Low-Density, Laser-Driven Magnetized Plasma

    NASA Astrophysics Data System (ADS)

    Schaeffer, D. B.; Montgomery, D. S.; Bondarenko, A. S.; Morton, L. A.; Johnson, R. P.; Shimada, T.; Constantin, C. G.; Everson, E. T.; Letzring, S. A.; Gaillard, S. A.; Flippo, K. A.; Glenzer, S. H.; Niemann, C.

    2012-02-01

    We present electron temperature and density measurements from Thomson scattering on recent collisionless shock experiments on the Trident laser at Los Alamos National Laboratory. A graphite target placed inside a static magnetic field (lesssim1 kG) created by a 50 cm-diameter Helmholtz coil was ablated by a 1053 nm beam, which created a low-density, magnetized plasma. A separate 527 nm beam was used for Thomson scattering to characterize the plasma 3 cm radially from the target and 0.5-8.5 μs after ablation. The electron temperature was found to be relatively constant over 8 μs at 11-13 eV and, combined with Rayleigh scattering, the electron density was found to be 2 × 1014-4 × 1014 cm-3 over the same timescale. Several carbon emission lines were also observed in the Thomson spectrum and were utilized to independently measure the electron temperature and density and to characterize the plasma charge state.

  20. Field-induced magnetization jumps and quantum criticality in the 2D J-Q model

    NASA Astrophysics Data System (ADS)

    Iaizzi, Adam; Sandvik, Anders

    The J-Q model is a `designer hamiltonian' formed by adding a four spin `Q' term to the standard antiferromagnetic S = 1 / 2 Heisenberg model. The Q term drives a quantum phase transition to a valence-bond solid (VBS) state: a non-magnetic state with a pattern of local singlets which breaks lattice symmetries. The elementary excitations of the VBS are triplons, i.e. gapped S=1 quasiparticles. There is considerable interest in the quantum phase transition between the Néel and VBS states as an example of deconfined quantum criticality. Near the phase boundary, triplons deconfine into pairs of bosonic spin-1/2 excitations known as spinons. Using exact diagonalization and the stochastic series expansion quantum monte carlo method, we study the 2D J-Q model in the presence of an external magnetic field. We use the field to force a nonzero density of magnetic excitations at T=0 and look for signatures of Bose-Einstein condensation of spinons. At higher magnetic fields, there is a jump in the induced magnetization caused by the onset of an effective attractive interaction between magnons on a ferromagnetic background. We characterize the first order quantum phase transition and determine the minimum value of the coupling ratio q ≡ Q / J required to produce this jump. Funded by NSF DMR-1410126.

  1. Modeling the nuclear magnetic resonance behavior of lung: from electrical engineering to critical care medicine.

    PubMed

    Cutillo, A G; Ailion, D C

    1999-01-01

    The present article reviews the basic principles of a new approach to the characterization of pulmonary disease. This approach is based on the unique nuclear magnetic resonance (NMR) properties of the lung and combines experimental measurements (using specially developed NMR techniques) with theoretical simulations. The NMR signal from inflated lungs decays very rapidly compared with the signal from completely collapsed (airless) lungs. This phenomenon is due to the presence of internal magnetic field inhomogeneity produced by the alveolar air-tissue interface (because air and water have different magnetic susceptibilities). The air-tissue interface effects can be detected and quantified by magnetic resonance imaging (MRI) techniques using temporally symmetric and asymmetric spin-echo sequences. Theoretical models developed to explain the internal (tissue-induced) magnetic field inhomogeneity in aerated lungs predict the NMR lung behavior as a function of various technical and physiological factors (e.g., the level of lung inflation) and simulate the effects of various lung disorders (in particular, pulmonary edema) on this behavior. Good agreement has been observed between the predictions obtained from the mathematical models and the results of experimental NMR measurements in normal and diseased lungs. Our theoretical and experimental data have important pathophysiological and clinical implications, especially with respect to the characterization of acute lung disease (e.g., pulmonary edema) and the management of critically ill patients.

  2. Development of a cross-polarization scattering system for the measurement of internal magnetic fluctuations in the DIII-D tokamak

    SciTech Connect

    Rhodes, T. L. Peebles, W. A.; Crocker, N. A.; Nguyen, X.

    2014-11-15

    The design and performance of a new cross-polarization scattering (CPS) system for the localized measurement of internal magnetic fluctuations is presented. CPS is a process whereby magnetic fluctuations scatter incident electromagnetic radiation into a perpendicular polarization which is subsequently detected. A new CPS design that incorporates a unique scattering geometry was laboratory tested, optimized, and installed on the DIII-D tokamak. Plasma tests of signal-to-noise, polarization purity, and frequency response indicate proper functioning of the system. CPS data show interesting features related to internal MHD perturbations known as sawteeth that are not observed on density fluctuations.

  3. Slow Magnetic Relaxations in Cobalt(II) Tetranitrate Complexes. Studies of Magnetic Anisotropy by Inelastic Neutron Scattering and High-Frequency and High-Field EPR Spectroscopy

    DOE PAGES

    Chen, Lei; Cui, Hui-Hui; Stavretis, Shelby E.; ...

    2016-12-07

    We synthesized and studied three mononuclear cobalt(II) tetranitrate complexes (A)2[Co(NO3)4] with different countercations, Ph4P+ (1), MePh3P+ (2), and Ph4As+ (3), using X-ray single-crystal diffraction, magnetic measurements, inelastic neutron scattering (INS), high-frequency and high-field EPR (HF-EPR) spectroscopy, and theoretical calculations. Furthermore, the X-ray diffraction studies reveal that the structure of the tetranitrate cobalt anion varies with the countercation. 1 and 2 exhibit highly irregular seven-coordinate geometries, while the central Co(II) ion of 3 is in a distorted-dodecahedral configuration. The sole magnetic transition observed in the INS spectroscopy of 1–3 corresponds to the zero-field splitting (2(D2 + 3E2)1/2) from 22.5(2) cm–1 inmore » 1 to 26.6(3) cm–1 in 2 and 11.1(5) cm–1 in 3. The positive sign of the D value, and hence the easy-plane magnetic anisotropy, was demonstrated for 1 by INS studies under magnetic fields and HF-EPR spectroscopy. The combined analyses of INS and HF-EPR data yield the D values as +10.90(3), +12.74(3), and +4.50(3) cm–1 for 1–3, respectively. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements reveal the slow magnetization relaxation in 1 and 2 at an applied dc field of 600 Oe, which is a characteristic of field-induced single-molecule magnets (SMMs). Finally, the electronic structures and the origin of magnetic anisotropy of 1–3 were revealed by calculations at the CASPT2/NEVPT2 level.« less

  4. Perpendicular Giant Magnetoresistance Studies of Spin-Dependent Scattering in Magnetic Multilayers.

    NASA Astrophysics Data System (ADS)

    Yang, Qing

    1995-01-01

    We present new measurements of Giant (negative) Magnetoresistance (GMR) in Ferromagnetic/Non-magnetic (F/N) metal multilayers in the Current Perpendicular to the layer Plane (CPP) geometry. At low temperature, when the spin diffusion lengths l_sp{sf} {N} and l_sp{sf }{F} in the N and F metals are longer than the layer thicknesses, t_{N } and t_{F}, and the elastic mean-free-paths lambda _sp{el}{N} and lambda_sp{el}{F}, a simple two current, series resistor model should describe CPP data. Prior work in our group showed that this model describes well data on Co/Ag, Co/Cu, and Permalloy (Py)/Cu. The present thesis both tests this model further, and first tests an extension of the model by Valet and Fert to shorter spin-diffusion lengths. The intrinsic CPP quantity is the area A times total resistance R_{t} of the multilayer. The first study in this thesis extends work by Lee in testing the model's prediction that a plot of a certain square root quantity sqrt {[ AR_{T}(H_{o })-AR_{T}(H_{s}) ] AR_{T}(H_{o}) } versus the bilayer number N should give the same straight line for a given F/N pair and for the same pair upon alloying the N-metal with impurities (e.g., Sn) that don't flip spins. Importantly, the prediction is independent of the specific values of the parameters of the multilayer. We show that samples of Co/Ag and Co/AgSn with fixed t_{Co}=t_ {N} obey the prediction. In the previous test, the experimental quantities AR_{t}(H_{o }) and AR_{t}(H_ {s})--H_{rm o} is the state of the sample as initially prepared and H_{rm s} is the state after taking the sample to above the saturation field H_{rm s} where the resistance stops decreasing--were taken to closely represent, respectively, AR_sp{t} {AP} and AR_sp{t} {P}, the states of anti-parallel (AP) and parallel (P) alignment of the magnetizations of adjacent F layers that are assumed in the models. In our second study, we test this assumption quantitatively. We made a set of (Co/Cu/Py/Cu) _{N } quadrilayers, measured

  5. Simplified Formulae System for Resonant Inverse Compton Scattering of a Fast Electron in an Intense Magnetic Field

    NASA Technical Reports Server (NTRS)

    You, J. H.; Chen, W. P.; Zhang, S. N.; Chen, L.; Liu, D.; Chou, C. K.

    2003-01-01

    We present simple analytical formulae for the emission spectrum and total power of a special kind of resonant inverse Compton scattering (RICS) of a relativistic electron in an intense magnetic field. In contrast with the available formulae system, we obtain a markedly simplified one based on the semiclassical quantum theory, which is more understandable for people who are unfamiliar with quantum electrodynamics. We show that the RICS process, under an appropriate 'accommodation condition' derived in this paper, is predominantly much more efficient than the coexistent ordinary inverse Compton scattering, and produces highly beamed high-frequency radiation with moderately good monochromaticity. Our formulae are simple to use - thus offering a lucid physical intuition for the theory - and may find wide applications in hard X-ray and gamma-ray astrophysics.

  6. Ce 5d magnetic profile in Fe/Ce multilayers for the α and γ-like Ce phases by x-ray resonant magnetic scattering

    NASA Astrophysics Data System (ADS)

    Jaouen, N.; Tonnerre, J. M.; Raoux, D.; Bontempi, E.; Ortega, L.; Müenzenberg, M.; Felsch, W.; Rogalev, A.; Dürr, H. A.; Dudzik, E.; van der Laan, G.; Maruyama, H.; Suzuki, M.

    2002-10-01

    The in-depth distribution of the induced 5d magnetic moments across the Ce layers in Fe/Ce/La/Ce, Fe/La/Ce/La and Fe/CeH2-δ multilayers has been investigated by x-ray resonant magnetic scattering (XRMS) at the Ce L2 edge. The determination of the composition profile across the period of the multilayer is required for a quantitative analysis of XRMS and has been derived from x-ray resonant reflectivity measurements. In Fe/Ce/La/Ce and Fe/La/Ce/La multilayers, Ce adopts an α-like electronic configuration and the local magnetization, across the Ce layer, is found to be highly nonuniform. The Ce 5d magnetic profile shows an oscillating behavior with an amplitude decreasing from the Fe interface in Fe/Ce/La/Ce. Conversely, in Fe/La/Ce/La, where the Ce atoms are not in direct contact with Fe atoms, it presents an oscillatory profile with, however, a nearly constant amplitude. In Fe/CeH2-δ multilayers, where hydrogen leads to a strain relaxation and to a 4f relocalization (Ce γ-like configuration), a nonoscillating decreasing profile has been observed. These experiments allow one to evidence an antiferromagnetic component in a α Ce ultrathin layer and a sharply decreasing induced magnetization due to 5d-3d hybridization at the interface.

  7. Multifunctional superparamagnetic nanoshells: combining two-photon luminescence imaging, surface-enhanced Raman scattering and magnetic separation.

    PubMed

    Jin, Xiulong; Li, Haiyan; Wang, Shanshan; Kong, Ni; Xu, Hong; Fu, Qihua; Gu, Hongchen; Ye, Jian

    2014-11-06

    With the increasing need for multi-purpose analysis in the biomedical field, traditional single diagnosis methods cannot meet the requirements. Therefore new multifunctional technologies and materials for the integration of sample collection, sensing and imaging are in great demand. Core-shell nanoparticles offer a unique platform to combine multifunctions in a single particle. In this work, we have constructed a novel type of core-shell superparamagnetic nanoshell (Fe₃O₄@SiO₂@Au), composed of a Fe₃O₄ cluster core, a thin Au shell and a SiO₂ layer in between. The obtained multifunctional nanoparticles combine the magnetic properties and plasmonic optical properties effectively, which were well investigated by a number of experimental characterization methods and theoretical simulations. We have demonstrated that Fe₃O₄@SiO₂@Au nanoparticles can be utilized for two-photon luminescence (TPL) imaging, near-infrared surface-enhanced Raman scattering (NIR SERS) and cell collection by magnetic separation. The TPL intensity could be further greatly enhanced through the plasmon coupling effect in the self-assembled nanoparticle chains, which were triggered by an external magnetic field. In addition, Fe₃O₄@SiO₂@Au nanoparticles may have great potential applications such as enhanced magnetic resonance imaging (MRI) and photo-thermotherapy. Successful combination of multifunctions including magnetic response, biosensing and bioimaging in single nanoparticles allows further manipulation, real-time tracking, and intracellular molecule analysis of live cells at a single-cell level.

  8. Tailoring of SmCo5 for optimal structure, magnetic anisotropy, and reduced criticality

    NASA Astrophysics Data System (ADS)

    Paudyal, Durga; Chouhan, R.; Gschneidner, K. A., Jr.

    SmCo5 orms hexagonal CaCu5-type structure with three non-equivalent sites: Sm (1a), Co (2c), and Co (3g). Sm lies in the middle of the Co (2c) hexagonal layers. Advanced density functional theory calculations employing Hubbard model show crystal field split localized Sm 4f states, which are responsible for the large part of the magnetic anisotropy exhibited by this system. In addition, the hexagonal Co (2c) layers help enhancing the anisotropy. Due to the partially quenched Sm 4f orbital moment, there is a net Sm 4f moment, which also helps enhancing magnetic moment. The substitution of some of the Sm sites by Nd adds Nd 4f multiplet thereby enhancing crystal field split 4f states and overall magnetic moment. The substitution of Co (2c) by Fe is preferred over Co (3g) but the compound becomes chemically unstable. The criticality issues could be addressed by substituting abundant Ce. This work is supported by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office.

  9. High magnetic-field scales and critical currents in SmFeAs(O, F) crystals

    NASA Astrophysics Data System (ADS)

    Moll, Philip J. W.; Puzniak, Roman; Balakirev, Fedor; Rogacki, Krzysztof; Karpinski, Janusz; Zhigadlo, Nikolai D.; Batlogg, Bertram

    2010-08-01

    With the discovery of new superconducting materials, such as the iron pnictides, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature Tc is high, intrinsic electronic properties might render applications difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates. Although many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed and estimates point to a very high upper critical field, their application potential is less clear. Thus, we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65T. Our detailed study of the transport properties of SmFeAsO0.7F0.25 single crystals reveals a promising combination of high (>2×106Acm-2) and nearly isotropic critical current densities along all crystal directions. This favourable intragrain current transport in SmFeAs(O, F), which shows the highest Tc of 54K at ambient pressure, is a crucial requirement for possible applications. Essential in these experiments are four-probe measurements on focused-ion-beam-cut single crystals with a sub-square-micrometre cross-section, with current along and perpendicular to the crystallographic c axis.

  10. Structural and magnetic properties of transition metal substituted BaFe2As2 compounds studied by x-ray and neutron scattering

    SciTech Connect

    Kim, Min Gyu

    2012-01-01

    The purpose of my dissertation is to understand the structural and magnetic properties of the newly discovered FeAs-based superconductors and the interconnection between superconductivity, antiferromagnetism, and structure. X-ray and neutron scattering techniques are powerful tools to directly observe the structure and magnetism in this system. I used both x-ray and neutron scattering techniques on different transition substituted BaFe2As2 compounds in order to investigate the substitution dependence of structural and magnetic transitions and try to understand the connections between them.

  11. Inelastic neutron scattering of the itinerant magnets Cr2Te3 and tr-Cr5Te8

    NASA Astrophysics Data System (ADS)

    Aczel, Adam; Granroth, Garrett; Ghimire, Nirmal; McGuire, Michael; Mandrus, David; Nagler, Steve

    2012-02-01

    Itinerant magnets based on transition metal chalcogenide compounds are of current interest, in part due to their relationship to the parent compounds of Fe-based superconductors. Two particularly interesting systems in this family are the chromium tellurides Cr2Te3 and trigonal (tr) Cr5Te8. These materials crystallize in layered structures with alternating partially and fully-occupied planes of Cr atoms stacked along the c-axis. Magnetization measurements along different crystallographic directions show a net ferromagnetic response and large magnetic anisotropy. In addition, the saturation moments are smaller than predicted by an ionic model; consistent with itinerant behavior. Previous neutron diffraction results for Cr2Te3 revealed an ordered moment of < 0.2 μB in the partially-occupied planes. We examined the magnetic excitations in these materials by powder neutron spectroscopy measurements using the SEQUOIA instrument at the SNS. We find similar moment sizes for the magnetic Cr atoms of both systems. However, despite their similar crystal structures, ordered moment sizes, and chemical compositions, their magnetic excitation spectra are strikingly different. We compare our data to the predictions of various models in an effort to determine the relevant exchange parameters, put constraints on their magnitudes, and understand the differences between the inelastic magnetic spectra. We find that exchange along the c-direction is critical to explain our data.

  12. A critical review of the genotoxic potential of electric and magnetic fields. Final report

    SciTech Connect

    McCann, J.; Dietrich, F.M.; Martin, A.

    1993-12-01

    Fifty five published articles were identified which reported results of tests of ELF (extremely low frequency) or static electric or magnetic fields for genotoxic effects. An additional 35 articles involving microwave or radiofrequency exposures were also identified. Primary emphasis was given to the electric and magnetic field studies. The analysis of microwave and radio frequency studies is presented in Appendix A. The biological assays used spanned a wide range, including microbial systems, plants, Drosophila, mammalian and human cells in vitro and in vivo. Experimental results were grouped into four exposure categories: ELF Electric; ELF Magnetic; Static Electric; and Static Magnetic. The internal electric fields present in media (for in vitro experiments) and in the torso and extremities (for in vivo experiments) were estimated, providing an index of comparison. All experiments were critically analyzed with respect to basic data quality criteria. Experiments within each exposure category were then compared to determine if results reinforced or contradicted one another. The preponderance of evidence suggests that neither ELF or static electric or magnetic fields have a clearly demonstrated potential to cause genotoxic effects. However, there may be weak genotoxic activity from exposure under conditions where phenomena auxiliary to an electric field, such as spark discharges, electrical shocks, or corona can occur. In addition, two unconfirmed reports suggest the genotoxic potential of certain chemical mutagens or ionizing radiation may be weakly affected by co-exposure to electric or magnetic fields. Certain exposure categories are not represented or are under-represented by tests in some genotoxicity test systems that are usually included in minimal test batteries as specified by EPA for chemicals. It is suggested that consideration be given to whether additional genotoxicity testing is warranted to fill these gaps.

  13. X-ray magnetic circular dichroism of CeFe2 by resonant inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Jaouen, N.; Chiuzbăian, S. G.; Hague, C. F.; Delaunay, R.; Baumier, C.; Lüning, J.; Rogalev, A.; Schmerber, G.; Kappler, J.-P.

    2010-05-01

    We have measured the CeL x-ray magnetic circular dichroism (XMCD) in ferromagnetic CeFe2 using the partial fluorescence yield given by the Ce2p3d resonant inelastic x-ray scattering (RIXS) spectrum. The lifetime broadening of the 3d core hole is four times smaller than that of the Ce2p core hole providing improved resolution over earlier experiments. Clear evidence for a 4f2 , 4f1 , 4f0 strongly mixed-valent ground state is observed confirming, by and large, impurity Anderson model predictions which take into account the RIXS XMCD geometrical dependence.

  14. Experimental magnetic form factors in Co3V2O8 : A combined study of ab initio calculations, magnetic Compton scattering, and polarized neutron diffraction

    NASA Astrophysics Data System (ADS)

    Qureshi, N.; Zbiri, M.; Rodríguez-Carvajal, J.; Stunault, A.; Ressouche, E.; Hansen, T. C.; Fernández-Díaz, M. T.; Johnson, M. R.; Fuess, H.; Ehrenberg, H.; Sakurai, Y.; Itou, M.; Gillon, B.; Wolf, Th.; Rodríguez-Velamazan, J. A.; Sánchez-Montero, J.

    2009-03-01

    We present a combination of ab initio calculations, magnetic Compton scattering, and polarized neutron experiments, which elucidate the density distribution of unpaired electrons in the kagome staircase system Co3V2O8 . Ab initio wave functions were used to calculate the spin densities in real and momentum spaces, which show good agreement with the respective experiments. It has been found that the spin polarized orbitals are equally distributed between the t2g and the eg levels for the spine (s) Co ions while the eg orbitals of the cross-tie (c) Co ions only represent 30% of the atomic spin density. Furthermore, the results reveal that the magnetic moments of the cross-tie Co ions, which are significantly smaller than those of the spine Co ions in the zero-field ferromagnetic structure, do not saturate by applying an external magnetic field of 2 T along the easy axis a . In turn, the increasing bulk magnetization, which can be observed by field dependent macroscopic measurements, originates from induced magnetic moments on the O and V sites. The refined individual magnetic moments are μ(Coc)=1.54(4)μB , μ(Cos)=2.87(3)μB , μ(V)=0.41(4)μB , μ(O1)=0.05(5)μB , μ(O2)=0.35(5)μB , and μ(O3)=0.36(5)μB combining to the same macroscopic magnetization value, which was previously only attributed to the Co ions.

  15. Critical Current Test of Liquid Hydrogen Cooled HTC Superconductors under External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Shirai, Yasuyuki; Shiotsu, Masahiro; Tatsumoto, Hideki; Kobayashi, Hiroaki; Naruo, Yoshihiro; Nonaka, Satoshi; Inatani, Yoshifumi

    High-Tc (HTC) superconductors including MgB2 will show excellent properties under temperature of Liquid Hydrogen (LH2:20K), which has large latent heat and low viscosity coefficient. In order to design and fabricate the LH2 cooled superconducting energy devices, we must clear the cooling property of LH2 for superconductors, the cooling system and safety design of LH2 cooled superconducting devices and electro-magnetic property evaluation of superconductors (BSCCO, REBCO and MgB2) and their magnets cooled by LH2. As the first step of the study, an experimental setup which can be used for investigating heat transfer characteristics of LH2 in a pool and also in forced flow (circulation loop with a pump), and also for evaluation of electro-magnetic properties of LH2 cooled superconductors under external magnetic field (up to 7 T). In this paper, we will show a short sketch of the experimental set-up, practical experiences in safety operation of liquid hydrogen cooling system and example test results of critical current evaluation of HTC superconductors cooled by LH2.

  16. Contactless measurement of critical current of high temperature superconductor tape by magnetic circuit.

    PubMed

    Gu, C; Qu, T-M; Zou, S-N; Han, Z

    2010-08-01

    A method based on the principle of the magnetic circuit is proposed and realized for contactless measurement of critical current (I(c)) of high temperature superconductor tapes. This method has two unique features: first, it eliminates noises caused by mechanical fluctuations and thus makes high speed and high stability measurement possible and second, adapts for both Bi(2)Si(2)Ca(2)Cu(3)O(x) (Bi2223) and YBa(2)Cu(3)O(7-x) (YBCO) tape, which even has a magnetic substrate. Theoretical analysis is given and an apparatus for the reel-to-reel measurement has been constructed, by which continuous inspection of I(c) uniformity of YBCO and Bi2223 tapes measured at different speeds is reported.

  17. Critical behavior and spontaneous magnetization estimation in La0.5Sr0.5MnO3 compound

    NASA Astrophysics Data System (ADS)

    Hazzez, M.; Ihzaz, N.; Boudard, M.; Oumezzine, M.

    2015-07-01

    We report the critical behavior in La0.5Sr0.5MnO3 perovskite oxide manganite using methods including modified Arrott plot, Kouvel-Fisher plot, and critical isotherm analysis. By means of the above techniques around the ferromagnetic-paramagnetic (FM-PM) transition, the magnetic data analyzed shows the sample attending the second-order magnetic phase transition with the critical parameters β = 0.553±0.020 with TC=352.02±0.63 K (from the spontaneous magnetization MS(T) below TC) and γ =1.169±0.058 with TC=352.49±0.85 K (from the inverse initial susceptibility χ 0 - 1 (T) above TC). The exponent δ =3,216 independently obtained from the critical magnetization isotherm satisfies the Widom scaling relation δ = 1 + β / γ . Moreover, the critical exponents are in the theoretically expected values for mean-field interaction model rather than the other universal theory and also follow the single scaling equation of M (H , ε)ε-β =f± (H /ε β + γ) . Furthermore, to estimate the spontaneous magnetization of La0.5Sr0.5MnO3 perovskite, we used the magnetic entropy change (-ΔSM), obtained from isothermal magnetization. The results of this approach are compared to results obtained from classical analysis using Arrott curves.

  18. Neutrons Scattering Study of Magnetic Correlations in Y0.7La0.3VO3

    NASA Astrophysics Data System (ADS)

    Chang, Sung; Yan, Jiaqiang; McQueeney, Robert

    2009-03-01

    RVO3 (R = rare earth) perovskite vanadites exhibit multiple orbital and spin orderings and provide a unique opportunity to study the spin-orbital-lattice coupling of π-bonding t electrons. The nature of the orbital order in these vanadites has been a matter of significant controversy, particularly with respect to whether the different orbital-ordered phases of YVO3 and LaVO3 are best described by a novel orbital-Peierls model or more traditional Jahn-Teller interactions. Here we report on a neutron scattering study of the magnetic correlations in Y0.7La0.3VO3, which may be expected to depend sensitively on the orbital degrees of freedom. The results are discussed in terms of the interplay between magnetism and orbital order.

  19. Investigations of surface structural, dynamical, and magnetic properties of systems exhibiting multiferroicity, and topological phases by helium scattering spectroscopies

    SciTech Connect

    El-Batanouny, Maged

    2015-08-03

    We propose to investigate the surface structural, dynamics and magnetic properties of the novel class of topological insulator crystals, as well as crystals that exhibit multiferroicity, magnetoelectricity and thermoelectricity. Topological insulators (TIs) are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin-orbit coupling inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. These exotic metallic states are formed by topological conditions that also render the electrons travelling on such surfaces insensitive to scattering by impurities. The electronic quasi-particles populating the topological surface state are Dirac fermions; they have a linear dispersion and thus are massless just like photons. We propose to investigate the interaction of these massless Dirac fermions with the massive lattice in the newly discovered crystals, Bi2Se3, Bi2Te3 and Sb2Te3. We shall use inelastic helium beam scattering from surfaces to search for related signatures in surface phonon dispersions mappings that cover the entire surface Brillouin zone of these materials. Our recent investigations of the (001) surface of the multiferroic crystals (Li/Na)Cu2O2 revealed an anomalous surface structural behavior where surface Cu$^{2+}$ row rise above the surface plane as the crystal was cooled. Subsequent worming revealed the onset of a thermally activated incommensurate surface phase, driven by the elevated rows. We are currently investigating the structure of the magnetic phases in these quasi-one-dimensional magnetic rows. Multiferroics are excellent candidates for large magnetoelectric response. We propose to extend this investigation to the class of delafossites which are also multiferroics and have been investigated as good candidates for

  20. Magnetic Neutron Scattering of Thermally Quenched K-Co-Fe Prussian Blue

    SciTech Connect

    Pajerowski, Daniel M.; Garlea, Vasile O; Knowles, E. S.; Andrus, Matthew; Dumont, Matthieu; Calm, Yitzi; Nagler, Stephen E; Tong, Xin Tony; Talham, Daniel R.; Meisel, Mark W.

    2012-01-01

    Magnetic order in the thermally quenched photomagnetic Prussian blue analogue coordination polymer K0.27Co[Fe(CN)6]0.73[D2O6]0.27-1.42D2O has been studied down to 4 K with unpolarized and polarized neutron powder diraction as a function of applied magnetic eld. Analysis of the data allows the onsite coherent magnetization of the Co and Fe spins to be established. Specically, magnetic elds of 1 T and 4 T induce moments parallel to the applied eld, and the sample behaves as a ferromagnet with a wandering axis.

  1. Critical behavior and magnetic entropy change at magnetic phase transitions in Ni50Mn35In14Si1 ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Das, R.; Alagarsamy, P.; Srinivasan, A.

    2014-12-01

    We have investigated critical behaviour and magnetocaloric effect in polycrystalline Ni50Mn35In14Si1 alloy near the second-order ferromagnetic phase transitions (SOPT) at austenite Curie temperature (TC,A) and at martensite Curie temperature (TC,M) by determining the critical exponents, β, γ and δ corresponding to the temperature dependence of spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively. The field dependence of the maximum value of the magnetic entropy change (Δ SM) at the two TC's was estimated using the Maxwell relation as well as from the values of the critical exponents. Values of Δ SM obtained by these two methods at both the SOPT are in remarkable agreement with each other. The critical exponents have been determined by analysing isothermal magnetization data using two different methods, viz., the modified Arrott plot method and the Widom scaling relation. The scaling plots depicted on linear as well as logarithmic scales confirm the reliability of the values of critical exponents obtained. The values of the critical exponents of polycrystalline Ni50Mn35In14Si1 alloy at both the TC's are close to those predicted by mean-field theory confirming the presence of long-range magnetic ordering in the investigated alloy.

  2. Quasiperiodic superconducting V/Zr multilayers: critical magnetic fields and crossover

    NASA Astrophysics Data System (ADS)

    Fogel, N. Ya.; Cherkasova, V. G.; Mikhailov, M. Yu.; Bomze, Yu. V.; Yuzephovich, O. I.; Dmitrenko, I. M.; Stetsenko, A. N.

    1998-08-01

    Critical magnetic fields parallel and perpendicular to the planes of quasiperiodic superconducting Fibonacci multilayers (ML) consisting of vanadium and zirconium are measured. The temperature dependence of the parallel critical field Hc∥ displays two crossovers. The Hc∥(T) dependence is of square-root type in the vicinity of the transition temperature Tc and linear at low temperatures. Between these temperature intervals, the dependence follows a power law: Hc∥˜(1-T/Tc)α, α=0,78±0,02. The complex nature of this dependence can be explained in the framework of the Ginzburg-Landau theory for a quasiperiodic ML, as well as by the scaling theory for fractal multilayers which takes into account the different structure length scales in the case of ML with a complex sequence of layers.

  3. Quantum critical dynamics of a magnetic impurity in a semiconducting host

    NASA Astrophysics Data System (ADS)

    Dasari, Nagamalleswararao; Acharya, Swagata; Taraphder, A.; Moreno, Juana; Jarrell, Mark; Vidhyadhiraja, N. S.; N. S. Vidhyadhiraja Collaboration, Prof.; Mark Jarrell Collaboration, Prof.; A. Taraphder Collaboration, Prof.

    We have investigated the finite temperature dynamics of the singlet to doublet continuous quantum phase transition in the gapped Anderson impurity model using hybridization expansion continuous time quantum Monte Carlo. Using the self-energy and the longitudinal static susceptibility, we obtain a phase diagram in the temperature-gap plane. The separatrix between the low-temperature local moment phase and the high temperature generalized Fermi liquid phase is shown to be the lower bound of the critical scaling region of the zero gap interacting quantum critical point. We have computed the nuclear magnetic spin-lattice relaxation rate, the Knight shift, and the Korringa ratio, which show strong deviations for any non-zero gap from the corresponding quantities in the gapless Kondo screened impurity case. This work is supported by NSF DMR-1237565 and NSF EPSCoR Cooperative Agreement EPS-1003897 with additional support from the Louisiana Board of Regents, and by CSIR and DST, India.

  4. Carbonate-Bridged Lanthanoid Triangles: Single-Molecule Magnet Behavior, Inelastic Neutron Scattering, and Ab Initio Studies.

    PubMed

    Giansiracusa, Marcus J; Vonci, Michele; Van den Heuvel, Willem; Gable, Robert W; Moubaraki, Boujemaa; Murray, Keith S; Yu, Dehong; Mole, Richard A; Soncini, Alessandro; Boskovic, Colette

    2016-06-06

    Optimization of literature synthetic procedures has afforded, in moderate yield, homogeneous and crystalline samples of the five analogues Na11[{RE(OH2)}3CO3(PW9O34)2] (1-RE; RE = Y, Tb, Dy, Ho, and Er). Phase-transfer methods have allowed isolation of the mixed salts (Et4N)9Na2[{RE(OH2)}3CO3(PW9O34)2] (2-RE; RE = Y and Er). The isostructural polyanions in these compounds are comprised of a triangular arrangement of trivalent rare-earth ions bridged by a μ3-carbonate ligand and sandwiched between two trilacunary Keggin {PW9O34} polyoxometalate ligands. Alternating-current (ac) magnetic susceptibility studies of 1-Dy, 1-Er, and 2-Er reveal the onset of frequency dependence for the out-of-phase susceptibility in the presence of an applied magnetic field at the lowest measured temperatures. Inelastic neutron scattering (INS) spectra of 1-Ho and 1-Er exhibit transitions between the lowest-lying crystal-field (CF) split states of the respective J = 8 and (15)/2 ground-state spin-orbit multiplets of the Ho(III) and Er(III) ions. Complementary ab initio calculations performed for these two analogues allow excellent reproduction of the experimental magnetic susceptibility and low-temperature magnetization data and are in reasonable agreement with the experimental INS data. The ab initio calculations reveal that the slight difference in coordination environments of the three Ln(III) ions in each complex gives rise to differences in the CF splitting that are not insignificant. This theoretical result is consistent with the observation of multiple relaxation processes by ac magnetic susceptibility and the broadness of the measured INS peaks. The ab initio calculations also indicate substantial mixing of the MJ contributions to the CF split energy levels of each Ln(III) ion. Calculations indicate that the CF ground states of the Ho(III) centers in 1-Ho are predominantly comprised of contributions from small MJ, while those of the Er(III) centers in 1-Er are predominantly

  5. Critical dimension small angle X-ray scattering measurements of FinFET and 3D memory structures

    NASA Astrophysics Data System (ADS)

    Settens, Charles; Bunday, Benjamin; Thiel, Brad; Kline, R. Joseph; Sunday, Daniel; Wang, Chengqing; Wu, Wen-li; Matyi, Richard

    2013-04-01

    We have demonstrated that transmission critical dimension small angle X-ray scattering (CD-SAXS) provides high accuracy and precision CD measurements on advanced 3D microelectronic architectures. The competitive advantage of CD-SAXS over current 3D metrology methods such as optical scatterometry is that CD-SAXS is able to decouple and fit cross-section parameters without any significant parameter cross-correlations. As the industry aggressively scales beyond the 22 nm node, CD-SAXS can be used to quantitatively measure nanoscale deviations in the average crosssections of FinFETs and high-aspect ratio (HAR) memory devices. Fitting the average cross-section of 18:1 isolated HAR contact holes with an effective trapezoid model yielded an average pitch of 796.9 +/- 0.4 nm, top diameter of 70.3 +/- 0.9 nm, height of 1088 +/- 4 nm, and sidewall angle below 0.1°. Simulations of dense 40:1 HAR contact holes and FinFET fin-gate crossbar structures have been analyzed using CD-SAXS to inquire the theoretical precision of the technique to measure important process parameters such as fin CD, height, and sidewall angle; BOX etch recess, thickness of hafnium oxide and titanium nitride layers; gate CD, height, and sidewall angle; and hafnium oxide and titanium nitride etch recess. The simulations of HAR and FinFET structures mimic the characteristics of experimental data collected at a synchrotron x-ray source. Using the CD-SAXS simulator, we estimate the measurement capabilities for smaller similar structures expected at future nodes to predict the applicability of this technique to fulfill important CD metrology needs.

  6. Magnetic ordering of the antiferromagnet Cu2MnSnS4 from magnetization and neutron-scattering measurements

    NASA Astrophysics Data System (ADS)

    Fries, T.; Shapira, Y.; Palacio, Fernando; Morón, M. Carmen; McIntyre, Garry J.; Kershaw, R.; Wold, A.; McNiff, E. J., Jr.

    1997-09-01

    Magnetization and neutron-diffraction measurements were performed on a single crystal of Cu2MnSnS4. This quartenary magnetic semiconductor has the stannite structure (derived from the zinc-blende structure which is common to many II-VI dilute magnetic semiconductors), and it orders antiferromagnetically at low temperature. The neutron data for the nuclear structure confirm that the space group is I4¯2m. Both the neutron and magnetization data give TN=8.8 K for the Néel temperature. The neutron data show a collinear antiferromagnetic (AF) structure with a propagation vector k=[1/2,0,1/2], in agreement with earlier neutron data on a powder. However, the deduced angle θ between the spin axis and the crystallographic c direction is between 6° and 16°, in contrast to the earlier value of 40°. The magnetization curve at T<magnetic anisotropy gives an anisotropy field HA≅2 kOe. At high magnetic fields the magnetization curve at T<magnetic semiconductors (DMS's). The much weaker antiferromagnetic interactions are expected from the difference in the crystal structures (stannite versus zinc-blende). A more surprising result is that the exchange constant which controls the AF order below TN is not between Mn ions with the smallest separation. This result contrasts with a prediction made for the related II-VI DMS, according to which the exchange constants decrease rapidly with distance.

  7. AFM nano-plough planar YBCO micro-bridges: critical currents and magnetic field effects.

    PubMed

    Elkaseh, A A O; Perold, W J; Srinivasu, V V

    2010-10-01

    The critical current (Ic) of YBa2Cu3O7-x (YBCO) AFM plough micro-constrictions is measured as a function of temperature, width and the magnetic flux density (B), which was applied perpendicular to the YBCO ab-plane and surface of the bridges. C-axis oriented thin films of YBa2Cu3O7-x were deposited on MgO substrates using an inverted cylindrical magnetron (ICM) sputtering technique. The films were then patterned into 8-10 micron size strips, using standard photolithography and dry etching processes. Micro-bridges with widths between 1.9 microm to 4.1 microm were fabricated by using atomic force microscope (AFM) nanolithography techniques. Critical current versus temperature data shows a straight-line behavior, which is typical of constriction type Josephson junctions. The Ic versus B characteristics exhibited a modulation, and a suppression of the critical current of up to 84%. It was also found that the critical current increases with increasing constriction width.

  8. Critical properties of a two-dimensional Ising magnet with quasiperiodic interactions

    NASA Astrophysics Data System (ADS)

    Alves, G. A.; Vasconcelos, M. S.; Alves, T. F. A.

    2016-04-01

    We address the study of quasiperiodic interactions on a square lattice by using an Ising model with ferromagnetic and antiferromagnetic exchange interactions following a quasiperiodic Fibonacci sequence in both directions of a square lattice. We applied the Monte Carlo method, together with the Metropolis algorithm, to calculate the thermodynamic quantities of the system. We obtained the Edwards-Anderson order parameter qEA, the magnetic susceptibility χ , and the specific heat c in order to characterize the universality class of the phase transition. We also use the finite size scaling method to obtain the critical temperature of the system and the critical exponents β ,γ , and ν . In the low-temperature limit we obtained a spin-glass phase with critical temperature around Tc≈2.274 , and the critical exponents β ,γ , and ν , indicating that the quasiperiodic order induces a change in the universality class of the system. Also, we discovered a spin-glass ordering in a two-dimensional system which is rare and, as far as we know, the unique example is an under-frustrated Ising model.

  9. Critical properties of a two-dimensional Ising magnet with quasiperiodic interactions.

    PubMed

    Alves, G A; Vasconcelos, M S; Alves, T F A

    2016-04-01

    We address the study of quasiperiodic interactions on a square lattice by using an Ising model with ferromagnetic and antiferromagnetic exchange interactions following a quasiperiodic Fibonacci sequence in both directions of a square lattice. We applied the Monte Carlo method, together with the Metropolis algorithm, to calculate the thermodynamic quantities of the system. We obtained the Edwards-Anderson order parameter q_{EA}, the magnetic susceptibility χ, and the specific heat c in order to characterize the universality class of the phase transition. We also use the finite size scaling method to obtain the critical temperature of the system and the critical exponents β,γ, and ν. In the low-temperature limit we obtained a spin-glass phase with critical temperature around T_{c}≈2.274, and the critical exponents β,γ, and ν, indicating that the quasiperiodic order induces a change in the universality class of the system. Also, we discovered a spin-glass ordering in a two-dimensional system which is rare and, as far as we know, the unique example is an under-frustrated Ising model.

  10. Employing soft x-ray resonant magnetic scattering to study domain sizes and anisotropy in Co/Pd multilayers

    NASA Astrophysics Data System (ADS)

    Bagschik, Kai; Frömter, Robert; Bach, Judith; Beyersdorff, Björn; Müller, Leonard; Schleitzer, Stefan; Berntsen, Magnus Hârdensson; Weier, Christian; Adam, Roman; Viefhaus, Jens; Schneider, Claus Michael; Grübel, Gerhard; Oepen, Hans Peter

    2016-10-01

    It is demonstrated that the magnetic diffraction pattern of the isotropic disordered maze pattern is well described utilizing a gamma distribution of domain sizes in a one-dimensional model. From the analysis, the mean domain size and the shape parameter of the distribution are obtained. The model reveals an average domain size that is significantly different from the value that is determined from the peak position of the structure factor in reciprocal space. As a proof of principle, a wedge-shaped (Cot Å/Pd10 Å)8 multilayer film, that covers the thickness range of the spin-reorientation transition, has been used. By means of soft x-ray resonant magnetic scattering (XRMS) and imaging techniques the thickness-driven evolution of the magnetic properties of the cobalt layers is explored. It is shown that minute changes of the domain pattern concerning domain size and geometry can be investigated and analyzed due to the high sensitivity and lateral resolution of the XRMS technique. The latter allows for the determination of the magnetic anisotropies of the cobalt layers within a thickness range of a few angstroms.

  11. Critical current density of a spin-torque oscillator with an in-plane magnetized free layer and an out-of-plane magnetized polarizer

    NASA Astrophysics Data System (ADS)

    Matsumoto, R.; Imamura, H.

    2016-12-01

    Spin-torque induced magnetization dynamics in a spin-torque oscillator with an in-plane (IP) magnetized free layer and an out-of-plane (OP) magnetized polarizer under IP shape-anisotropy field (Hk) and applied IP magnetic field (Ha) was theoretically studied based on the macrospin model. The rigorous analytical expression of the critical current density (Jc1) for the OP precession was obtained. The obtained expression successfully reproduces the experimentally obtained Ha-dependence of Jc1 reported in [D. Houssameddine et al., Nat. Mater. 6, 447 (2007)].

  12. Magnetic and Structural Characterization of Fe-Ga Using Kerr Microscopy and Neutron Scattering

    DTIC Science & Technology

    2010-01-01

    4 1.1.3 Paramagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1.4 Ferromagnetism...field. This is called diamagnetism. Elememts like Cu, Ag, Au, Pb with no unpaired electrons demonstrate diamagnetism. 5 1.1.3 Paramagnetism ... Paramagnetism appears only in elements with unpaired electrons. As in dia- magnetism, the negative magnetic moment is induced even in paramagnetic ma- terials

  13. Investigation of an 18 Å Al 2O 3 layer in a magnetic multilayer system by Rutherford and resonant scattering

    NASA Astrophysics Data System (ADS)

    Kling, A.; da Silva, M. F.; Soares, J. C.; Freitas, P. P.; Baptista, D. L.; Zawislak, F. C.

    2000-03-01

    Spin tunnel junctions, consisting of a metallic multilayer with a thin insulating buffer layer, in most cases Al 2O 3, show a large tunneling magnetoresistance (TMR) and are therefore of high interest for future magnetic read heads and non-volatile memories. The properties of these junctions are strongly influenced by the quality of the insulating buffer layer and its behavior during thermal treatment. Measurements with conventional RBS using devices in the as-deposited state and after different heat treatments at temperatures up to 200°C revealed changes in the stoichiometry and O distribution in the buffer layer that can be correlated with changes in the respective magnetic properties. The application of the 16O( 4He, 4He) 16O resonant scattering resonance with incident energies ranging from 3.01 to 3.35 MeV enabled the separate profiling of O in all parts of the sample: the partly oxidized sample surface, the aluminum oxide layer and the silicon dioxide layer covering the Si substrate. Simulations of the energy dependence of the O scattering yield showed that the oxygen is fully retained in the aluminum oxide buffer layer and no diffusion into adjacent metallic layers has occurred. The results indicate also that even Al 2O 3 layers with significantly lower thicknesses can be profiled with this method.

  14. Quasinormal modes, scattering, and Hawking radiation of Kerr-Newman black holes in a magnetic field

    SciTech Connect

    Kokkotas, K. D.; Konoplya, R. A.; Zhidenko, A.

    2011-01-15

    We perform a comprehensive analysis of the spectrum of proper oscillations (quasinormal modes), transmission/reflection coefficients, and Hawking radiation for a massive charged scalar field in the background of the Kerr-Newman black hole immersed in an asymptotically homogeneous magnetic field. There are two main effects: the Zeeman shift of the particle energy in the magnetic field and the difference of values of an electromagnetic potential between the horizon and infinity, i.e. the Faraday induction. We have shown that 'turning on' the magnetic field induces a stronger energy-emission rate and leads to 'recharging' of the black hole. Thus, a black hole immersed in a magnetic field evaporates much quicker, achieving thereby an extremal state in a shorter period of time. Quasinormal modes are moderately affected by the presence of a magnetic field which is assumed to be relatively small compared to the gravitational field of the black hole.

  15. Influence of Critical Current Density on Magnetic Force of Htsc Bulk above Pmr with 3D-MODELING Numerical Solutions

    NASA Astrophysics Data System (ADS)

    Lu, Yiyun; Lu, Bingjuan; Ge, Yunwang; Chen, Wenqing

    Numerical electromagnetic field simulations of high-temperature superconductors (HTSC) bulk were carried out to calculate the magnetic force between the HTSC bulk and the permanent magnet railway (PMR). A 3D-modeling numerical calculation method is proposed using the finite element method. The model is formulated with the magnetic field vector (H-method). The resulting code was written with FORTRAN language. The electric field intensity E and the current density J constitutive relation of HTSC were described with E-J power law. The Kim macro-model is used to describe critical current density Jc of HTSC bulk. Two virtual HTSC bulks were used to solve the critical current density Jc anisotropic properties of HTSC materials. A superconducting levitation system composed of one HTSC bulk and PMR is successfully investigated using the proposed method. By this method, the influence of critical current density on magnetic levitation force of the superconducting levitation system is mathematically studied.

  16. Magnetic Signatures of Quantum Critical Points of the Ferrimagnetic Mixed Spin-(1/2, S) Heisenberg Chains at Finite Temperatures

    NASA Astrophysics Data System (ADS)

    Strečka, Jozef; Verkholyak, Taras

    2016-10-01

    Magnetic properties of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains are examined using quantum Monte Carlo simulations for two different quantum spin numbers S=1 and 3/2. The calculated magnetization curves at finite temperatures are confronted with zero-temperature magnetization data obtained within the density matrix renormalization group method, which imply an existence of two quantum critical points determining a breakdown of the gapped Lieb-Mattis ferrimagnetic phase and Tomonaga-Luttinger spin-liquid phase, respectively. While a square root behavior of the magnetization accompanying each quantum critical point is gradually smoothed upon rising temperature, the susceptibility and isothermal entropy change data at low temperatures provide a stronger evidence of the zero-temperature quantum critical points through marked local maxima and minima, respectively.

  17. Recent development of collective Thomson scattering for magnetically confined fusion plasmas

    NASA Astrophysics Data System (ADS)

    Nielsen, S. K.; Michelsen, P. K.; Hansen, S. K.; Korsholm, S. B.; Leipold, F.; Rasmussen, J.; Salewski, M.; Schubert, M.; Stejner, M.; Stober, J.; Wagner, D.; The ASDEX Upgrade Team

    2017-02-01

    Here we review recent experimental developments within the field of collective Thomson scattering with a focus on the progress made on the devices TEXTOR and ASDEX Upgrade. We discuss recently discovered possibilities and limitations of the diagnostic technique. Diagnostic applications with respect to ion measurements are demonstrated. Examples include measurements of the ion temperature, energetic ion distribution function, and the ion composition.

  18. Small angle X-ray scattering study of the effect of pressure on the aggregation of asphaltene fractions in petroleum fluids under near-critical solvent conditions

    SciTech Connect

    Carnahan, N.F.; Quintero, L. ); Pfund, D.M.; Fulton, J.L.; Smith, R.D. ); Capel, M. ); Leontaritis, K. )

    1993-08-01

    Small angle X-ray scattering was used to determine the effect of pressure on the extent of asphaltene aggregation for a system under near-critical conditions. A mixture containing 60 vol% Crude Oil A in n-pentane was studied at 110[degree]C, at pressures ranging from 25 to 400 bar. As the pressure of the near-critical solution is isothermally decreased, these results indicate (1) an increase in the extent of asphaltene aggregation and/or; (2) increased attractive interactions among aggregates. Information derived from different regions of the X-ray scattering curve indicate increasing aggregation with decreasing pressure. From these experimental results, together with theoretical interpretation, we infer that as the pressure is reduced, increased aggregation of asphaltenes results which may contribute to formation damage in hydrocarbon reservoirs, and to fouling in hydrotreatment and cracking catalysts. 71 refs., 10 figs., 2 tabs.

  19. Polarized-neutron-scattering studies on the chiral magnetism in multiferroic MnWO4

    NASA Astrophysics Data System (ADS)

    Finger, T.; Senff, D.; Schmalzl, K.; Schmidt, W.; Regnault, L. P.; Becker, P.; Bohatý, L.; Braden, M.

    2010-02-01

    Neutron diffraction with spherical polarization analysis is a powerful tool for studying the multiferroic materials where the ferroelectric polarization arises from a complex magnetic structure. Analyzing the off-diagonal terms in the polarization matrix one may directly detect the chiral contributions even in a multidomain arrangement. In MnWO4 one can control the chiral magnetism by varying an electric field at constant temperature. The analysis of multiferroic hysteresis cycles at four equivalent magnetic Bragg peaks fully agrees with a nearly monodomain chiral arrangement controlled by the electric field. A pronounced asymmetry of the hysteresis cycles and memory effects point to strong pinning of the chiral magnetism in MnWO4. We find a second-order harmonic modulation which exhibits both magnetic and structural character and which may be related with the domain pinning. The observed interference between the nuclear and the magnetic modulation is another manifestation of the coupling between the crystal structure and the magnetism in the multiferroic oxides.

  20. Critical speeds and forced response solutions for active magnetic bearing turbomachinery, part 2

    NASA Technical Reports Server (NTRS)

    Rawal, D.; Keesee, J.; Kirk, R. Gordon

    1991-01-01

    The need for better performance of turbomachinery with active magnetic bearings has necessitated a study of such systems for accurate prediction of their vibrational characteristics. A modification of existing transfer matrix methods for rotor analysis is presented to predict the response of rotor systems with active magnetic bearings. The position of the magnetic bearing sensors is taken into account and the effect of changing sensor position on the vibrational characteristics of the rotor system is studied. The modified algorithm is validated using a simpler Jeffcott model described previously. The effect of changing from a rotating unbalance excitation to a constant excitation in a single plane is also studied. A typical eight stage centrifugal compressor rotor is analyzed using the modified transfer matrix code. The results for a two mass Jeffcott model were presented previously. The results obtained by running this model with the transfer matrix method were compared with the results of the Jeffcott analysis for the purposes of verification. Also included are plots of amplitude versus frequency for the eight stage centrifugal compressor rotor. These plots demonstrate the significant influence that sensor location has on the amplitude and critical frequencies of the rotor system.

  1. In-situ neutron scattering studies of magnetic shape memory alloys under stress, temperature, and magnetic fields

    SciTech Connect

    Brown, Donald W; Sisneros, Thomas A; Kabra, Saurabh; Schlagel, Deborah

    2010-01-01

    We have utilized the SMARTS engineering neutron diffractometer to study the crystallographic orientation and phase transformations in the ferromagnetic shape memory alloy Ni 2MnGa under conditions of temperature (200-600K), stress (500MPa), and magnetic field (2T). Neutrons are uniquely suited to probe the crystallographic response of materials to external stimuli because of their high penetration, which allows them to sample the bulk of the material (as opposed to the surface) as well as pass through environmental chambers. A single crystal of Ni{sub 5}MnGa was repeatedly thermally cycled through the Austenitic-Martensitic phase transformation under varying conditions of applied stress, magnetic field or both. In-situ neutron diffraction was used to quantitatively monitor the population of the crystallographic variants in the martensitic phase as a function of the external stimuli during cooling. Neutron diffraction was used to monitor variant selection in the Ferromagnetic Shape Memory Alloy Ni{sub 2}Mn Ga during austenitic to martensitic transformation under varying conditions of externally applied stress and magnetic field. Qualitatively, the results were to be expected in this simple example. The shorter and magnetically soft c-axis of the tetragonal martensitic phase aligned with the compressive stress or magnetic field. However, neutron diffraction proved useful in directly quantifying the selection of the preferred variant by external influence. For instance, by quantifying the variant selection, the neutron diffraction results made apparent that the sample 'remembered' a loading cycle following a 'reset' cycle with no external applied stress. Moreover, the power of in-situ neutron diffraction will become more apparent when applied to more complex, less understood, samples such as polycrystalline samples or composite samples.

  2. Electron in a Two Dimensional System with Point Scatterers Amd Magnetic Field

    NASA Astrophysics Data System (ADS)

    Gredeskul, S. A.; Avishai, Y.; Azbel, M. Ya.; Zusman, M.

    We consider non-interacting electrons in two dimensions subject to a perpendicular magnetic field and interacting with point impurities with random strength located on the sites of a square lattice. For very strong magnetic field (such that there are more than n+1 flux quanta per plaque), we obtain (in closed analytic form) extended solutions, which are independent on the strength of disorder, for each Landau level with a number smaller or equal to n. If the rational magnetic flux per plaque is less than one unit, we construct dispersion laws and Hofstadter-like butterfly for all denominators less than ten.

  3. A summary of the low angle x-ray atomic scattering factors which have been measured by the critical voltage effect in High Energy Electron Diffraction (HEED)

    SciTech Connect

    Fox, A.G.; Fisher, R.M.

    1987-08-01

    A tabulated summary of all the accurate (/approximately/0.1%) low-angle x-ray atomic scattering (form) factors which have been determined by the systematic critical voltage technique in HEED is presented. For low atomic number elements (Z/approx lt/40) the low angle form factors can be significantly different to best free atom values, and so the best band structure calculated and/or x-ray measured form factors consistent with the critical voltage measurements are also indicated. At intermediate atomic numbers Zapprox. =40..-->..50 only the very low-angle form factors appear to be different to the best free atom values, and even then only by a small amount. For heavy elements (Z/approx lt/70) the best free atom form factors appear to agree very closely with the critical voltage measured values and so, in this case, critical voltage measurements give very accurate measurements of Debye-Waller factors. 48 refs.

  4. Multifunctional superparamagnetic nanoshells: combining two-photon luminescence imaging, surface-enhanced Raman scattering and magnetic separation

    NASA Astrophysics Data System (ADS)

    Jin, Xiulong; Li, Haiyan; Wang, Shanshan; Kong, Ni; Xu, Hong; Fu, Qihua; Gu, Hongchen; Ye, Jian

    2014-11-01

    With the increasing need for multi-purpose analysis in the biomedical field, traditional single diagnosis methods cannot meet the requirements. Therefore new multifunctional technologies and materials for the integration of sample collection, sensing and imaging are in great demand. Core-shell nanoparticles offer a unique platform to combine multifunctions in a single particle. In this work, we have constructed a novel type of core-shell superparamagnetic nanoshell (Fe3O4@SiO2@Au), composed of a Fe3O4 cluster core, a thin Au shell and a SiO2 layer in between. The obtained multifunctional nanoparticles combine the magnetic properties and plasmonic optical properties effectively, which were well investigated by a number of experimental characterization methods and theoretical simulations. We have demonstrated that Fe3O4@SiO2@Au nanoparticles can be utilized for two-photon luminescence (TPL) imaging, near-infrared surface-enhanced Raman scattering (NIR SERS) and cell collection by magnetic separation. The TPL intensity could be further greatly enhanced through the plasmon coupling effect in the self-assembled nanoparticle chains, which were triggered by an external magnetic field. In addition, Fe3O4@SiO2@Au nanoparticles may have great potential applications such as enhanced magnetic resonance imaging (MRI) and photo-thermotherapy. Successful combination of multifunctions including magnetic response, biosensing and bioimaging in single nanoparticles allows further manipulation, real-time tracking, and intracellular molecule analysis of live cells at a single-cell level.With the increasing need for multi-purpose analysis in the biomedical field, traditional single diagnosis methods cannot meet the requirements. Therefore new multifunctional technologies and materials for the integration of sample collection, sensing and imaging are in great demand. Core-shell nanoparticles offer a unique platform to combine multifunctions in a single particle. In this work, we have

  5. Slow Magnetic Relaxations in Cobalt(II) Tetranitrate Complexes. Studies of Magnetic Anisotropy by Inelastic Neutron Scattering and High-Frequency and High-Field EPR Spectroscopy

    SciTech Connect

    Chen, Lei; Cui, Hui-Hui; Stavretis, Shelby E.; Hunter, Seth C.; Zhang, Yi-Quan; Chen, Xue-Tai; Sun, Yi-Chen; Wang, Zhenxing; Song, You; Podlesnyak, Andrey A.; Ouyang, Zhong-Wen; Xue, Zi-Ling

    2016-12-07

    We synthesized and studied three mononuclear cobalt(II) tetranitrate complexes (A)2[Co(NO3)4] with different countercations, Ph4P+ (1), MePh3P+ (2), and Ph4As+ (3), using X-ray single-crystal diffraction, magnetic measurements, inelastic neutron scattering (INS), high-frequency and high-field EPR (HF-EPR) spectroscopy, and theoretical calculations. Furthermore, the X-ray diffraction studies reveal that the structure of the tetranitrate cobalt anion varies with the countercation. 1 and 2 exhibit highly irregular seven-coordinate geometries, while the central Co(II) ion of 3 is in a distorted-dodecahedral configuration. The sole magnetic transition observed in the INS spectroscopy of 1–3 corresponds to the zero-field splitting (2(D2 + 3E2)1/2) from 22.5(2) cm–1 in 1 to 26.6(3) cm–1 in 2 and 11.1(5) cm–1 in 3. The positive sign of the D value, and hence the easy-plane magnetic anisotropy, was demonstrated for 1 by INS studies under magnetic fields and HF-EPR spectroscopy. The combined analyses of INS and HF-EPR data yield the D values as +10.90(3), +12.74(3), and +4.50(3) cm–1 for 1–3, respectively. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements reveal the slow magnetization relaxation in 1 and 2 at an applied dc field of 600 Oe, which is a characteristic of field-induced single-molecule magnets (SMMs). Finally, the electronic structures and the origin of magnetic anisotropy of 1–3 were revealed by calculations at the CASPT2/NEVPT2 level.

  6. Perpendicular Giant Magnetoresistance: Study and Application of Spin Dependent Scattering in Magnetic Multilayers of Cobalt/copper and NICKEL(84) IRON(16)/COPPER

    NASA Astrophysics Data System (ADS)

    Holody, Paul Robert Joseph

    Perpendicular transport through magnetic multilayers has been successfully described by the two spin channel model. In the limit where spin flip scattering can be neglected, the transport current is carried by parallel channels of spin up and spin down electrons. Large negative magnetoresistances arise from spin dependent scattering occurring in these channels. Electrons with spins parallel to the local magnetization undergo a different amount of scattering from those with spins antiparallel to the local magnetization. Consequently the multilayer's resistance can be controlled by the relative orientation of the ferromagnetic layers' magnetizations. Usually with the relative orientation antiparallel (parallel) the multilayer has a high (low) resistance. In this dissertation, an analysis of perpendicular transport measurements in the context of the two spin channel model provides quantitative information about the amounts of spin dependent scattering at the Ferromagnetic/Normal metal interfaces and in the bulk Ferromagnet metal for the Co/Cu and Ni_{84}Fe _{16}/Cu systems (Ni_{84}Fe_{16}=Py). This is essential to the understanding of the scattering mechanisms involved in Giant Magnetoresistance. Our results show a significant bulk contribution to the spin dependent scattering; but, it is the interfaces which make the larger contribution to spin dependent scattering in these systems. A larger bulk spin dependent scattering asymmetry was determined for the Py/Cu multilayers, but not as large as expected from data derived previously from ternary alloys. Measurements were made on several Co/CuX series (where X = Pt, Mn, Ge and Ni) to study the transport properties of magnetic multilayers when significant spin flip scattering is present in the system. Analysis was done using the Valet-Fert theory which generalizes the two spin channel model to include finite spin diffusion lengths. A sharp drop in the magnetoresistance is observed when the spin diffusion length ~ layer

  7. Magnetically stabilized nematic order. II. Critical states and algebraically ordered nematic spin liquids in one-dimensional optical lattices

    SciTech Connect

    Zhai Hui; Zhou Fei

    2005-07-01

    We investigate the Zeeman-field-driven quantum phase transitions between singlet spin liquids and algebraically ordered O(2) nematic spin liquids of spin-one bosons in one-dimensional optical lattices. We find that the critical behavior is characterized by condensation of hardcore bosons instead of ideal magnons in high-dimensional lattices. Critical exponents are strongly renormalized by hardcore interactions and critical states are equivalent to the free Fermion model up to the Friedel oscillations. We also find that the algebraically ordered nematic spin liquids close to critical points are fully characterized by the Luttinger-liquid dynamics with Luttinger-liquid parameters magnetically tunable. The Bethe ansatz solution has been applied to determine the critical magnetization and nematic correlations.

  8. Complex Scattered Radiation Fields And Multiple Magnetic Fields In The Protostellar Cluster In NGC 2264

    NASA Astrophysics Data System (ADS)

    KWON, Jungmi; Tamura, M.; Kandori, R.; Kusakabe, N.; Hashimoto, J.; Nakajima, Y.; Nakamura, F.; Nagayama, T.; Nagata, T.; Hough, J. H.; Werner, M. W.; Teixeira, P. S.

    2012-05-01

    Near-infrared imaging polarimetry in the J, H, and Ks bands has been carried out for the protostellar cluster region around NGC 2264 IRS 2 in the Monoceros OB1 molecular cloud. Various infrared reflection nebula clusters (IRNCs) associated with NGC 2264 IRS 2 and the IRAS 12 S1 core, as well as local infrared reflection nebulae (IRNe), were detected. The illuminating sources of the IRNe were identified with known or new near- and mid-infrared sources. In addition, 314 point-like sources were detected in all three bands and their aperture polarimetry was studied. Using a color-color diagram, reddened field stars and diskless pre-main-sequence stars were selected to trace the magnetic field structure of the molecular cloud. The mean polarization position angle of the point-like sources is 80 degrees in the cluster core, and 60 degrees in the perimeter of the cluster core, which is interpreted as the projected direction on the sky of the magnetic field in the observed region of the cloud. The Chandrasekhar-Fermi method gives a rough estimate of the magnetic field strength to be about 100 micro-Gauss. A comparison with recent numerical simulations of the cluster formation implies that the cloud dynamics is controlled by the relatively strong magnetic field. The local magnetic field direction is well associated with that of CO outflow for IRAS 12 S1 and consistent with that inferred from submillimeter polarimetry. In contrast, the local magnetic field direction runs roughly perpendicular to the Galactic magnetic field direction.

  9. Superconducting-magnetic heterostructures: a method of decreasing AC losses and improving critical current density in multifilamentary conductors.

    PubMed

    Glowacki, B A; Majoros, M

    2009-06-24

    Magnetic materials can help to improve the performance of practical superconductors on the macroscale/microscale as magnetic diverters and also on the nanoscale as effective pinning centres. It has been established by numerical modelling that magnetic shielding of the filaments reduces AC losses in self-field conditions due to decoupling of the filaments and, at the same time, it increases the critical current of the composite. This effect is especially beneficial for coated conductors, in which the anisotropic properties of the superconductor are amplified by the conductor architecture. However, ferromagnetic coatings are often chemically incompatible with YBa(2)Cu(3)O(7) and (Pb,Bi)(2)Sr(2)Ca(2)Cu(3)O(9) conductors, and buffer layers have to be used. In contrast, in MgB(2) conductors an iron matrix may remain in direct contact with the superconducting core. The application of superconducting-magnetic heterostructures requires consideration of the thermal and electromagnetic stability of the superconducting materials used. On one hand, magnetic materials reduce the critical current gradient across the individual filaments but, on the other hand, they often reduce the thermal conductivity between the superconducting core and the cryogen, which may cause destruction of the conductor in the event of thermal instability. A possible nanoscale method of improving the critical current density of superconducting conductors is the introduction of sub-micron magnetic pinning centres. However, the volumetric density and chemical compatibility of magnetic inclusions has to be controlled to avoid suppression of the superconducting properties.

  10. Pitch-angle Scattering of Energetic Charged Particles in Nearly Constant Magnitude Magnetic Turbulence

    NASA Astrophysics Data System (ADS)

    Sun, P.; Jokipii, J. R.; Giacalone, J.

    2016-08-01

    We use a method developed by Roberts that optimizes the phase angles of an ensemble of plane waves with amplitudes determined from a Kolmogorov-like power spectrum, to construct magnetic field vector fluctuations having nearly constant magnitude and large variances in its components. This is a representation of the turbulent magnetic field consistent with that observed in the solar wind. Charged-particle pitch-angle diffusion coefficients are determined by integrating the equations of motion for a large number of charged particles moving under the influence of forces from our predefined magnetic field. We tested different cases by varying the kinetic energy of the particles (E p) and the turbulent magnetic field variance ({σ }B2). For each combination of E p and {σ }B2, we tested three different models: (1) the so-called “slab” model, where the turbulent magnetic field depends on only one spatial coordinate and has significant fluctuations in its magnitude (b=\\sqrt{δ {B}x2(z)+δ {B}y2(z)+{B}02}) (2) the slab model optimized with nearly constant magnitude b; and (3) the slab model turbulent magnetic field with nearly constant magnitude plus a “variance-conserving” adjustment. In the last case, this model attempts to conserve the variance of the turbulent components ({σ }{Bx}2+{σ }{By}2), which is found to decrease during the optimization with nearly constant magnitude. We found that there is little or no effect on the pitch-angle diffusion coefficient {D}μ μ between models 1 and 2. However, the result from model 3 is significantly different. We also introduce a new method to accurately determine the pitch-angle diffusion coefficients as a function of μ.

  11. The Effect of Planar Magnetic Inhomogeneities on the Critical Temperature of Ferromagnet-Superconductor Systems

    NASA Astrophysics Data System (ADS)

    Tumanov, V. A.; Proshin, Yu. N.

    2016-12-01

    We study superconducting systems with the inhomogeneous effective exchange field background. A model of magnetic superconductor which takes into account the collectivized electrons interaction with the inhomogeneous effective exchange field is used. With local unitary rotation in spinor space we rewrite the Hamiltonian in a new basis where this interaction is diagonal. The problem is reduced to the one with a uniform exchange field but the effective tensor field appears. This method allows us to simplify the Gor'kov, Eilenberger, and Usadel equations in many symmetric cases. We calculate the critical temperature of the superconductor/ferromagnet proximity system in the dirty limit where the ferromagnet has periodic domain structure with planar domain walls.

  12. Flux Pinning and Enhanced Critical Current in Magnetic Field by Artificial Pinning Centers.#

    NASA Astrophysics Data System (ADS)

    Wang, J.-Q.; Rizzo, N. D.; McCambridge, J. D.; Prober, D. E.; Motowidlo, L. R.; Zeitlin, B. A.

    1996-03-01

    Flux pinning to enhance critical currents (Jc) in type II superconductors (NbTi) in a magnetic field was studied, using nanometer sized artificial pins. From consideration of free energy and proximity effects, we compare pinning by various materials, ranging from weak superconductors (Nb), normal metals (Ti, Cu), to ferromagnets (Ni, Fe). A trade-off is found between induced superconductivity in the pin and a reduction of superconductivity in the NbTi. Thus, a normal metal can have stronger pinning than a similar-sized void. This idea is supported by our finding that Ti provides the strongest pinning in multilayer film systems. Pinning mechanisms by ferromagnetic (FM) pins are also discussed, along with results of Jc for NbTiTa wires with FM artificial pinning centers. #Support by CT Dept. Econ. Dev. Grant 94G014 and IGC-AS. *present address: Westinghouse STC, Pittsburgh, PA

  13. Small-angle Neutron Scattering Study of Magnetic Ordering and Inhomogeneity Across the Martensitic Phase Transformation in Ni50-xCoxMn40Sn10 Alloys

    DTIC Science & Technology

    2012-04-27

    dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered 1. REPORT DATE...observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin...magnetometry and small- angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions

  14. Widely tunable two-colour seeded free-electron laser source for resonant-pump resonant-probe magnetic scattering

    PubMed Central

    Ferrari, Eugenio; Spezzani, Carlo; Fortuna, Franck; Delaunay, Renaud; Vidal, Franck; Nikolov, Ivaylo; Cinquegrana, Paolo; Diviacco, Bruno; Gauthier, David; Penco, Giuseppe; Ribič, Primož Rebernik; Roussel, Eleonore; Trovò, Marco; Moussy, Jean-Baptiste; Pincelli, Tommaso; Lounis, Lounès; Manfredda, Michele; Pedersoli, Emanuele; Capotondi, Flavio; Svetina, Cristian; Mahne, Nicola; Zangrando, Marco; Raimondi, Lorenzo; Demidovich, Alexander; Giannessi, Luca; De Ninno, Giovanni; Danailov, Miltcho Boyanov; Allaria, Enrico; Sacchi, Maurizio

    2016-01-01

    The advent of free-electron laser (FEL) sources delivering two synchronized pulses of different wavelengths (or colours) has made available a whole range of novel pump–probe experiments. This communication describes a major step forward using a new configuration of the FERMI FEL-seeded source to deliver two pulses with different wavelengths, each tunable independently over a broad spectral range with adjustable time delay. The FEL scheme makes use of two seed laser beams of different wavelengths and of a split radiator section to generate two extreme ultraviolet pulses from distinct portions of the same electron bunch. The tunability range of this new two-colour source meets the requirements of double-resonant FEL pump/FEL probe time-resolved studies. We demonstrate its performance in a proof-of-principle magnetic scattering experiment in Fe–Ni compounds, by tuning the FEL wavelengths to the Fe and Ni 3p resonances. PMID:26757813

  15. Size-dependent magnetization dynamics in individual Ni80Fe20 disk using micro-focused Brillouin Light Scattering spectroscopy

    NASA Astrophysics Data System (ADS)

    Shimon, G.; Adeyeye, A. O.

    2015-09-01

    A direct and systematic investigation of the magnetization dynamics in individual circular Ni80Fe20 disk of diameter (D) in the range from 300 nm to 1 μm measured using micro-focused Brillouin Light Scattering (μ-BLS) spectroscopy is presented. At high field, when the disks are in a single domain state, the resonance frequency of the uniform center mode is observed to reduce with reducing disk's diameter. For D = 300 nm, additional edge and end-domains resonant modes are observed due to size effects. At low field, when the disks are in a vortex state, a systematic increase of resonant frequency of magnetostatic modes in a vortex state with the square root of the disks' aspect ratio (thickness divided by radius) is observed. Such dependence diminishes for disks with larger aspect ratio due to an increasing exchange energy contribution. Micromagnetic simulations are in excellent agreement with the experiments.

  16. Asymptotic Behavior of the Magnetization Near Critical and Tricritical Points via Ginzburg Landau Polynomials

    NASA Astrophysics Data System (ADS)

    Ellis, Richard S.; Machta, Jonathan; Otto, Peter Tak-Hun

    2008-10-01

    The purpose of this paper is to prove connections among the asymptotic behavior of the magnetization, the structure of the phase transitions, and a class of polynomials that we call the Ginzburg-Landau polynomials. The model under study is a mean-field version of a lattice spin model due to Blume and Capel. It is defined by a probability distribution that depends on the parameters β and K, which represent, respectively, the inverse temperature and the interaction strength. Our main focus is on the asymptotic behavior of the magnetization m( β n , K n ) for appropriate sequences ( β n , K n ) that converge to a second-order point or to the tricritical point of the model and that lie inside various subsets of the phase-coexistence region. The main result states that as ( β n , K n ) converges to one of these points ( β, K), m(βn,Kn)˜ bar{x}|β -βn|^{γ}→ 0 . In this formula γ is a positive constant, and bar{x} is the unique positive, global minimum point of a certain polynomial g. We call g the Ginzburg-Landau polynomial because of its close connection with the Ginzburg-Landau phenomenology of critical phenomena. For each sequence the structure of the set of global minimum points of the associated Ginzburg-Landau polynomial mirrors the structure of the set of global minimum points of the free-energy functional in the region through which ( β n , K n ) passes and thus reflects the phase-transition structure of the model in that region. This paper makes rigorous the predictions of the Ginzburg-Landau phenomenology of critical phenomena and the tricritical scaling theory for the mean-field Blume-Capel model.

  17. Quenching of the nonlocal electron heat transport by large external magnetic fields in a laser produced plasma measured with imaging Thomson scattering

    SciTech Connect

    Froula, D H; Davis, P; Pollock, B B; Divol, L; Ross, J S; Edwards, J; Town, R; Price, D; Glenzer, S H; Offenberger, A A; Tynan, G R; James, A N

    2006-04-14

    We present a direct measurement of the quenching of nonlocal heat transport in a laser produced plasma by high external magnetic fields. Temporally resolved measurements of the electron temperature profile transverse to a high power laser beam were obtained using imaging Thomson scattering. The results are simulated with the 2D hydrodynamic code LASNEX with a recently included magnetic field model that self-consistently evolves the fields in the plasma.

  18. Ferromagnetic Quantum Critical Point Avoided by the Appearance of Another Magnetic Phase in LaCrGe3 under Pressure

    NASA Astrophysics Data System (ADS)

    Taufour, Valentin; Kaluarachchi, Udhara S.; Khasanov, Rustem; Nguyen, Manh Cuong; Guguchia, Zurab; Biswas, Pabitra Kumar; Bonfà, Pietro; De Renzi, Roberto; Lin, Xiao; Kim, Stella K.; Mun, Eun Deok; Kim, Hyunsoo; Furukawa, Yuji; Wang, Cai-Zhuang; Ho, Kai-Ming; Bud'ko, Sergey L.; Canfield, Paul C.

    2016-07-01

    The temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ . Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q =0 to finite Q , as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 is a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets.

  19. Ferromagnetic quantum critical point avoided by the appearance of another magnetic phase in LaCrGe3 under pressure

    DOE PAGES

    Taufour, Valentin; Kaluarachchi, Udhara S.; Khasanov, Rustem; ...

    2016-07-13

    Here, the temperature-pressure phase diagram of the ferromagnet LaCrGe3 is determined for the first time from a combination of magnetization, muon-spin-rotation, and electrical resistivity measurements. The ferromagnetic phase is suppressed near 2.1 GPa, but quantum criticality is avoided by the appearance of a magnetic phase, likely modulated, AFMQ. Our density functional theory total energy calculations suggest a near degeneracy of antiferromagnetic states with small magnetic wave vectors Q allowing for the potential of an ordering wave vector evolving from Q=0 to finite Q, as expected from the most recent theories on ferromagnetic quantum criticality. Our findings show that LaCrGe3 ismore » a very simple example to study this scenario of avoided ferromagnetic quantum criticality and will inspire further study on this material and other itinerant ferromagnets.« less

  20. Parity-Violating Electron Scattering and the Electric and Magnetic Strange Form Factors of the Nucleon

    SciTech Connect

    Armstrong, David S.; McKeown, Robert

    2012-11-01

    Measurement of the neutral weak vector form factors of the nucleon provides unique access to the strange quark content of the nucleon. These form factors can be studied using parity-violating electron scattering. A comprehensive program of experiments has been performed at three accelerator laboratories to determine the role of strange quarks in the electromagnetic form factors of the nucleon. This article reviews the remarkable technical progress associated with this program, describes the various methods used in the different experiments, and summarizes the physics results along with recent theoretical calculations.

  1. Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2.

    PubMed

    Liu, Yi; Xie, Donghua; Wang, Xiaoying; Zhu, Kangwei; Yang, Ruilong

    2016-01-13

    The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems.

  2. Magnetically induced forward scattering at visible wavelengths in silicon nanosphere oligomers

    PubMed Central

    Yan, J. H.; Liu, P.; Lin, Z. Y.; Wang, H.; Chen, H. J.; Wang, C. X.; Yang, G. W.

    2015-01-01

    Electromagnetically induced transparency is a type of quantum interference that induces near-zero reflection and near-perfect transmission. As a classical analogy, metal nanostructure plasmonic ‘molecules' produce plasmon-induced transparency conventionally. Herein, an electromagnetically induced transparency interaction is demonstrated in silicon nanosphere oligomers, wherein the strong magnetic resonance couples with the electric gap mode effectively to markedly suppress reflection. As a result, a narrow-band transparency window created at visible wavelengths, called magnetically induced transparency, is easily realized in nearly touching silicon nanospheres, exhibiting low dependence on the number of spheres and aggregate states compared with plasmon induced transparency. A hybridization mechanism between magnetic and electric modes is proposed to pursue the physical origin, which is crucial to build all-dielectric metamaterials. Remarkably, magnetic induced transparency effect exhibiting near-zero reflection and near-perfect transmission causes light to propagate with no extra phase change. This makes silicon nanosphere oligomers promising as a unit cell in epsilon-near-zero metamaterials. PMID:25940445

  3. Development of a Thomson scattering system and its use in a rotating magnetic field driven field-reversed configurations plasma

    NASA Astrophysics Data System (ADS)

    Lee, Kiyong

    The Thomson scattering system has been utilized on the Translation Confinement & Sustainment Upgrade (TCSU) experiment to measure the electron temperature and density. The system uses five polychromators from General Atomics attached with three pre-amplifier modules from Princeton Plasma Physics Laboratory to measure five spatial points during a single plasma discharge. The diagnostic consisting of various mechanical and optical components is introduced, followed by the calibration procedure of the system. For validating measurements, the electron temperature and the relative density obtained from Thomson scattering are compared with measurements from the Langmuir probe. Both measurements are in good agreement. A power scan was conducted by applying different voltages to the rotating magnetic field (RMF) current drive to observe the scaling properties of temperature and density for even-parity and odd-parity RMF operations. Also, a discrepancy is observed when comparing the density based on pressure-balance with localized measurements. Further analysis indicates a possibility of an ion-temperature-gradient, presumably due to ion cyclotron heating, present during steady-state operation.

  4. The Ising Model on the Random Planar Causal Triangulation: Bounds on the Critical Line and Magnetization Properties

    NASA Astrophysics Data System (ADS)

    Napolitano, George M.; Turova, Tatyana S.

    2016-02-01

    We investigate a Gibbs (annealed) probability measure defined on Ising spin configurations on causal triangulations of the plane. We study the region where such measure can be defined and provide bounds on the boundary of this region (critical line). We prove that for any finite random triangulation the magnetization of the central spin is sensitive to the boundary conditions. Furthermore, we show that in the infinite volume limit, the magnetization of the central spin vanishes for values of the temperature high enough.

  5. Spectral properties and localization of an electron in a two-dimensional system with point scatterers in a magnetic field

    NASA Astrophysics Data System (ADS)

    Gredeskul, S. A.; Zusman, M.; Avishai, Y.; Azbel', M. Ya.

    1997-09-01

    Electron spectral properties and localization in a two-dimensional system with point potentials subject to a perpendicular magnetic field are studied. A brief review of the known results concerning electron dynamics in such systems is presented. For a set of periodic point potentials, exact dispersion laws and energy-flux diagram (Hofstadter-type butterfly) are obtained. It is shown that, in the case of one-dimensional disorder, the electron localization in a strong magnetic field is described by the random Harper equation. Energy-flux diagram for the localization length is presented and the fractal structure of the localization length is demonstrated. Near the Landau levels an exact formula for the localization length as a function of energy and disorder is obtained. The corresponding critical exponent is equal to unity which is reminiscent of one-dimensional characteristics.

  6. Neutron scattering and nuclear magnetic resonance spectroscopy structural studies of protein-DNA complexes

    SciTech Connect

    Bradbury, E.M.; Catasti, P.; Chen, X.; Gupta, G.; Imai, B.; Moyzis, R.; Ratliff, R.; Velupillai, S.

    1996-03-01

    This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project sought to employ advanced biophysical measurements to study the structure of nucleosomes and the structure of origins of DNA replication. The fundamental repeating unit of human chromosomes is the nucleosome, which contains about 200 base pairs of DNA and 9 histone proteins. Genome replication is strictly associated with the reversible acetylations of histones that unfold chromatin to allow access of factors to origins of DNA replications. The authors have studied two major structural problems: (1) the effects of histone acetylation on nucleosome structure, and (2) the structure of DNA origins of replication. They have recently completed preliminary X-ray scattering experiments at Stanford on positioned nucleosomes with defined DNA sequence and length, histone composition and level of acetylation. These experiments have shown that lengths of the DNA and acetylations of the histone H4 result in nucleosome structural changes. To understand internucleosomal interactions and the roles of histone H1 the authors have made preliminary x-ray scatter studies on native dinucleosomes that have demonstrated the feasibility of these experiments. The DNA sequence of the yeast replication origin has been synthesized for structure determination by multi-dimensional NMR spectroscopy.

  7. Quantum critical scaling at a Bose-glass/superfluid transition: Theory and experiment for a model quantum magnet

    NASA Astrophysics Data System (ADS)

    Yu, Rong; Miclea, Corneliu F.; Weickert, Franziska; Movshovich, Roman; Paduan-Filho, Armando; Zapf, Vivien S.; Roscilde, Tommaso

    2012-10-01

    In this paper we investigate the quantum phase transition from magnetic Bose Glass to magnetic Bose-Einstein condensation induced by a magnetic field in NiCl2·4SC(NH2)2 (dichloro-tetrakis-thiourea-nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z=d; moreover the correlation length exponent is found to be ν=0.75(10), and the order parameter exponent to be β=0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.40.546 40, 546 (1989)]. However they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator.

  8. Self-organized criticality in a two-dimensional cellular automaton model of a magnetic flux tube with background flow

    NASA Astrophysics Data System (ADS)

    Dănilă, B.; Harko, T.; Mocanu, G.

    2015-11-01

    We investigate the transition to self-organized criticality in a two-dimensional model of a flux tube with a background flow. The magnetic induction equation, represented by a partial differential equation with a stochastic source term, is discretized and implemented on a two-dimensional cellular automaton. The energy released by the automaton during one relaxation event is the magnetic energy. As a result of the simulations, we obtain the time evolution of the energy release, of the system control parameter, of the event lifetime distribution and of the event size distribution, respectively, and we establish that a self-organized critical state is indeed reached by the system. Moreover, energetic initial impulses in the magnetohydrodynamic flow can lead to one-dimensional signatures in the magnetic two-dimensional system, once the self-organized critical regime is established. The applications of the model for the study of gamma-ray bursts (GRBs) is briefly considered, and it is shown that some astrophysical parameters of the bursts, like the light curves, the maximum released energy and the number of peaks in the light curve can be reproduced and explained, at least on a qualitative level, by working in a framework in which the systems settles in a self-organized critical state via magnetic reconnection processes in the magnetized GRB fireball.

  9. Level crossings and zero-field splitting in the {Cr8}-cubane spin-cluster studied using inelastic neutron scattering and magnetization

    SciTech Connect

    Vaknin, D.; Garlea, Vasile O; Demmel, F.; Mamontov, Eugene; Nojiri, H; Martin, Catalin; Chiorescu, Irinel; Qiu, Y.; Luban, M.; Kogerler, P.; Fielden, J.; Engelhardt, L; Rainey, C

    2010-01-01

    Inelastic neutron scattering (INS) in variable magnetic field and high-field magnetization measurements in the millikelvin temperature range were performed to gain insight into the low-energy magnetic excitation spectrum and the field-induced level crossings in the molecular spin cluster {Cr8}-cubane. These complementary techniques provide consistent estimates of the lowest level-crossing field. The overall features of the experimental data are explained using an isotropic Heisenberg model, based on three distinct exchange interactions linking the eight CrIII paramagnetic centers (spins s = 3/2), that is supplemented with a relatively large molecular magnetic anisotropy term for the lowest S = 1 multiplet. It is noted that the existence of the anisotropy is clearly evident from the magnetic field dependence of the excitations in the INS measurements, while the magnetization measurements are not sensitive to its effects.

  10. Level crossings and zero-field splitting in the {Cr8}-cubane spin cluster studied using inelastic neutron scattering and magnetization.

    PubMed

    Vaknin, D; Garlea, V O; Demmel, F; Mamontov, E; Nojiri, H; Martin, C; Chiorescu, I; Qiu, Y; Kögerler, P; Fielden, J; Engelhardt, L; Rainey, C; Luban, M

    2010-11-24

    Inelastic neutron scattering (INS) in variable magnetic field and high-field magnetization measurements in the millikelvin temperature range were performed to gain insight into the low-energy magnetic excitation spectrum and the field-induced level crossings in the molecular spin cluster {Cr(8)}-cubane. These complementary techniques provide consistent estimates of the lowest level-crossing field. The overall features of the experimental data are explained using an isotropic Heisenberg model, based on three distinct exchange interactions linking the eight Cr(III) paramagnetic centers (spins s = 3/2), that is supplemented with a relatively large molecular magnetic anisotropy term for the lowest S = 1 multiplet. It is noted that the existence of the anisotropy is clearly evident from the magnetic field dependence of the excitations in the INS measurements, while the magnetization measurements are not sensitive to its effects.

  11. Magnetic-field-induced quantum criticality in a spin- S planar ferromagnet with single-ion anisotropy

    NASA Astrophysics Data System (ADS)

    Mercaldo, M. T.; Rabuffo, I.; De Cesare, L.; Caramico D'Auria, A.

    2013-08-01

    The effects of single-ion anisotropy on quantum criticality in a d-dimensional spin- S planar ferromagnet is explored by means of the two-time Green's function method. We work at the Tyablikov decoupling level for exchange interactions and the Anderson-Callen decoupling level for single-ion anisotropy. In our analysis a longitudinal external magnetic field is used as the non-thermal control parameter and the phase diagram and the quantum critical properties are established for suitable values of the single-ion anisotropy parameter D. We find that the single-ion anisotropy has sensible effects on the structure of the phase diagram close to the quantum critical point. However, for values of the uniaxial crystal-field parameter below a positive threshold, the conventional magnetic-field-induced quantum critical scenario remains unchanged.

  12. Comparison between the magnetic and transport critical current densities in high critical current density melt-textured yttrium barium copper-oxide

    NASA Technical Reports Server (NTRS)

    Gao, L.; Meng, R. L.; Xue, Y. Y.; Hor, P. H.; Chu, C. W.

    1991-01-01

    Using a recently developed pulsed critical current density (Jc) measuring system, the Jc of the high-Jc melt-textured YBa2Cu3O(7-delta) (Y123) bulk samples has been determined. I-V curves with a voltage resolution of 0.5 microV were obtained, and transport Jc's along the a-b plane as high as 7.2 x 10 to the 4th A/sq cm were extracted. These results are comparable to the values obtained magnetically. On the other hand, transport Jc along the c axis were found to be two orders of magnitude smaller, even though the magnetic Jc along the c axis is only about five times smaller than Jc along the a-b plane. It is suggested that for the high-temperature superconducting materials which are highly anisotropic, caution should be taken when using the nontransport magnetic methods to determine Jc.

  13. Raman Scattering Studies in Dilute Magnetic Semiconductor Zn(1-x)Co(x)O

    NASA Technical Reports Server (NTRS)

    Samanta, K.; Bhattacharya, P.; Katiyar, R. S.; Iwamoto, W.; Pagiluso, P. G.; Rettori, C.

    2006-01-01

    Raman spectra of ZnO and Co substituted Zn1-xCoxO (ZCO) were carried out using the Raman microprobe system with an p.,+ ion laser source of 514.5 nm wavelength. The shift towards the lower frequency side of the nonpolar E210w mode and the broadening due to Co substitution in ZnO were analyzed using the phonon confinement model. The magnetic measurements showed ferromagnetic behavior with the maximum saturation magnetization (1.2micron Beta/ErCo) for 10% Co substitution, which decreased wi th at further increase in Co concentrations. The intensities of E1(LO) at 584 cm-1 and multiphonon modes at 540 cm-1 were increased with an increase in Co substitution. The additional Raman modes in ceramic targets of ZCO spectra for higher concentration of Co substitution (x=15%-20%) were identified to be due to the spinel ZnCo2O4 secondary phase.

  14. Brillouin backward scattering in the nonlinear interaction of a short-pulse laser with an underdense transversely magnetized plasma with nonextensive distribution

    NASA Astrophysics Data System (ADS)

    Qiu, Hui-Bin; Song, Hai-Ying; Liu, Shi-Bing

    2017-03-01

    Nonlinear Brillouin backward scattering of a linearly polarized short laser pulse propagating through a homogenous nonextensive distributed plasma in the presence of a uniform magnetic field perpendicular to both the direction of propagation and electric vector of the radiation field is investigated theoretically when ponderomotive relativistic and nonlinearity effects up to third order are taken into account. The governing equations for nonlinear wave in the context of nonextensive statistics are given, and the nonextensive coupled equations describing the nonlinear Brillouin backward scattering instability are solved by the Fourier transformation method, and the growth rate of the nonlinear Brillouin backward scattering instability is obtained. The results in the case q → 1 are consistent with those in the framework of the Maxwellian distribution. It is found that the instability growth rate increases on increasing plasma density, radiation field amplitude, and nonextensive parameter, while the instability growth rate shows a decrease due to the presence of external magnetic field.

  15. The loss rates of O{sup +} in the inner magnetosphere caused by both magnetic field line curvature scattering and charge exchange reactions

    SciTech Connect

    Ji, Y.; Shen, C.

    2014-03-15

    With consideration of magnetic field line curvature (FLC) pitch angle scattering and charge exchange reactions, the O{sup +} (>300 keV) in the inner magnetosphere loss rates are investigated by using an eigenfunction analysis. The FLC scattering provides a mechanism for the ring current O{sup +} to enter the loss cone and influence the loss rates caused by charge exchange reactions. Assuming that the pitch angle change is small for each scattering event, the diffusion equation including a charge exchange term is constructed and solved; the eigenvalues of the equation are identified. The resultant loss rates of O{sup +} are approximately equal to the linear superposition of the loss rate without considering the charge exchange reactions and the loss rate associated with charge exchange reactions alone. The loss time is consistent with the observations from the early recovery phases of magnetic storms.

  16. A rapid method for detection of genetically modified organisms based on magnetic separation and surface-enhanced Raman scattering.

    PubMed

    Guven, Burcu; Boyacı, İsmail Hakkı; Tamer, Ugur; Çalık, Pınar

    2012-01-07

    In this study, a new method combining magnetic separation (MS) and surface-enhanced Raman scattering (SERS) was developed to detect genetically modified organisms (GMOs). An oligonucleotide probe which is specific for 35 S DNA target was immobilized onto gold coated magnetic nanospheres to form oligonucleotide-coated nanoparticles. A self assembled monolayer was formed on gold nanorods using 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) and the second probe of the 35 S DNA target was immobilized on the activated nanorod surfaces. Probes on the nanoparticles were hybridized with the target oligonucleotide. Optimization parameters for hybridization were investigated by high performance liquid chromatography. Optimum hybridization parameters were determined as: 4 μM probe concentration, 20 min immobilization time, 30 min hybridization time, 55 °C hybridization temperature, 750 mM buffer salt concentration and pH: 7.4. Quantification of the target concentration was performed via SERS spectra of DTNB on the nanorods. The correlation between the target concentration and the SERS signal was found to be linear within the range of 25-100 nM. The analyses were performed with only one hybridization step in 40 min. Real sample analysis was conducted using Bt-176 maize sample. The results showed that the developed MS-SERS assay is capable of detecting GMOs in a rapid and selective manner.

  17. Magneto-optical biosensing platform based on light scattering from self-assembled chains of functionalized rotating magnetic beads.

    PubMed

    Park, Sang Yoon; Handa, Hiroshi; Sandhu, Adarsh

    2010-02-10

    We describe a simple protocol for the rapid, highly sensitive, and quantitative measurement of the concentration of biomolecules in a solution by monitoring light scattered by self-assembled chains of functionalized superparamagnetic beads (SBs) rotating in the solution. A rotating external field (H(ex)) applied to an aqueous solution containing 250 nm diameter biotinylated SBs produced linear chains of SBs rotating in phase with Hex due to magnetically induced self-assembly. At constant Hex, the addition of avidin to the solution led to the formation of longer SB-chains than without the presence of avidin. The generation of longer SB-chains was revealed by increases in the amplitude of the oscillating optical transmittance signal of the magnetic colloid solution. Monitoring changes in the amplitude of the optical transmittance of the solution enabled quantitative determination of the concentration of avidin added to the solution with a sensitivity of 100 pM (6.7 ng/mL) and a dynamic range of at least 3 orders of magnitude. The rotating chains acted as biomolecule probes and micromagnetic mixers, enabling detection of biomolecular recognition in less than 30 s. This approach offers a rapid, highly sensitive, inexpensive, and homogeneous means for detecting biorecognition processes.

  18. Progesterone and testosterone studies by neutron scattering and nuclear magnetic resonance methods and quantum chemistry calculations

    NASA Astrophysics Data System (ADS)

    Szyczewski, A.; Hołderna-Natkaniec, K.; Natkaniec, I.

    2004-05-01

    Inelastic incoherent neutron scattering spectra of progesterone and testosterone measured at 20 and 290 K were compared with the IR spectra measured at 290 K. The Phonon Density of States spectra display well resolved peaks of low frequency internal vibration modes up to 1200 cm -1. The quantum chemistry calculations were performed by semiempirical PM3 method and by the density functional theory method with different basic sets for isolated molecule, as well as for the dimer system of testosterone. The proposed assignment of internal vibrations of normal modes enable us to conclude about the sequence of the onset of the torsion movements of the CH 3 groups. These conclusions were correlated with the results of proton molecular dynamics studies performed by NMR method. The GAUSSIAN program had been used for calculations.

  19. Temperature and field dependent magnetization in a sub-μm patterned Co/FeRh film studied by resonant x-ray scattering

    NASA Astrophysics Data System (ADS)

    Lounis, Lounès; Spezzani, Carlo; Delaunay, Renaud; Fortuna, Franck; Obstbaum, Martin; Günther, Stefan; Back, Christian H.; Popescu, Horia; Vidal, Franck; Sacchi, Maurizio

    2016-05-01

    We studied the temperature and field dependence of the magnetization in a Co/FeRh/MgO(0 0 1) film patterned into a matrix of sub-μm sized rectangles, using element selective resonant scattering of polarized soft x-rays. We show that it is possible to reverse partially the magnetization of the Co layer in a thermal cycle that crosses the FeRh antiferromagnetic to ferromagnetic transition. Our results support interest in patterned Co/FeRh films and their potential for achieving temperature induced magnetization switching.

  20. Simultaneous measurement of magnetic and density fluctuations via cross-polarization scattering and Doppler backscattering on the DIII-D tokamak

    NASA Astrophysics Data System (ADS)

    Rhodes, T. L.; Barada, K.; Peebles, W. A.; Crocker, N. A.

    2016-11-01

    An upgraded cross-polarization scattering (CPS) system for the simultaneous measurement of internal magnetic fluctuations B ˜ and density fluctuations ñ is presented. The system has eight radial quadrature channels acquired simultaneously with an eight-channel Doppler backscattering system (measures density fluctuations ñ and flows). 3-D ray tracing calculations based on the GENRAY ray tracing code are used to illustrate the scattering and geometric considerations involved in the CPS implementation on DIII-D. A unique quasi-optical design and IF electronics system allow direct comparison of B ˜ and ñ during dynamic or transient plasma events (e.g., Edge Localized Modes or ELMs, L to H-mode transitions, etc.). The system design allows the interesting possibility of both magnetic-density ( B ˜ -ñ) fluctuation and magnetic-temperature ( B ˜ - T ˜ ) fluctuation cross-phase measurements suitable for detailed tests of turbulence simulations.

  1. Neutron Scattering Study of Low Energy Magnetic Excitation in superconducting Te-vapor annealed under-doped FeTeSe

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Yi, Ming; Xu, Guangyong; Shneeloch, J. A.; Matsuda, Masaaki; Chi, Songxue; Gu, Genda; Tranquada, J. M.; Birgeneau, R. J.

    To study the interplay between magnetism and superconductivity, we have performed neutron scattering and magnetization measurements on a Te vapor annealed single crystal Fe1 +yTe0.8Se0.2 (Tc~13K) sample. Te vapor annealed process is found to reduce/remove the excess Fe in the as-grown sample and make the under-doped originally non-superconducting sample become good superconducting sample. Our neutron scattering studies show both spin gap and spin resonance found in the Te vapor annealed superconducting sample. Comparing to commensurate spin resonance in as-grown optimal-doped sample, the spin resonance of Te annealed sample only shows up at the clearly incommensurate positions. The temperature and energy dependence of low energy magnetic excitations are also measured in the sample. This work is supported by the Office of Basic Energy Sciences, DOE.

  2. Unconventional critical magnetic behavior in the Griffiths ferromagnet La₀.₄Ca₀.₆MnO₂.₈□₀.₂ oxide

    SciTech Connect

    Triki, M.; Dhahri, E.; Hlil, E.K.

    2013-05-01

    The effects of oxygen vacancy on the critical magnetic behavior in La₀.₄Ca₀.₆MnO₂.₈□₀.₂ around the paramagnetic-ferromagnetic (PM-FM) phase transition were investigated through various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis via dc magnetization measurements recorded around the Curie temperature TC. The obtained critical exponents values are β~0.8, γ~0.7 and δ~1.882 with TC~164.5 K. Thus the scaling law γ+β=δβ is fulfilled. The critical exponents obey the single scaling-equation of state M(H,ε)|ε|{sup -β}=f{sub ±}(H|ε|{sup -(β+γ)}) where, f₊ for T>TC and f⁻ for T>TC. The found exponents are inconsistent with any known universality class. These results attributed to the existence of Griffiths Phase (Triki et al. (2012) [1]) seem to actually reflect the unconventional critical scaling of the magnetic susceptibility. - Graphical abstract: Modified Arrott plots: M{sup 1/β} vs. (μ₀H){sup 1/γ} with (a) mean-field model (β=0.5, γ=1), (b) 3D-Heisenberg model (β=0.365, γ=1.336), (c) 3D-Ising model (β=0.325, γ=1.24), (d) tricritical mean-field model (β=0.25, γ=1) and (e) (β=0.79, γ=0.71). Highlights: • Study of the critical behavior for La₀.₄Ca₀.₆MnO₂.₈□₀.₂ compound. • A typical second-order magnetic transition near TC. • Unconventional critical exponents were found.

  3. On the magnon interaction in Haematite. 2: Magnon energy of the acoustical mode and magnetic critical fields

    NASA Technical Reports Server (NTRS)

    Bonavito, N. L.; Nagai, O.; Tanaka, T.

    1975-01-01

    Previous spin wave theories of the antiferromagnet hematite were extended. The behavior of thermodynamic quantities around the Morin transition temperature was studied, and the latent heat of the Morin transition was calculated. The temperature dependence of the antiferromagnetic resonance frequency and the parallel and perpendicular critical spin-flop magnetic fields were calculated. It was found that the theory agrees well with experiment.

  4. Order-by-disorder near criticality in X Y pyrochlore magnets

    NASA Astrophysics Data System (ADS)

    Javanparast, Behnam; Day, Alexandre G. R.; Hao, Zhihao; Gingras, Michel J. P.

    2015-05-01

    We consider a system of spins on the sites of a three-dimensional pyrochlore lattice of corner-sharing tetrahedra interacting with a predominant effective x y exchange. In particular, we investigate the selection of a long-range ordered state with broken discrete symmetry induced by thermal fluctuations near the critical region. At the standard mean-field theory (s-MFT) level, in a region of the parameter space of this Hamiltonian that we refer to as Γ5 region, the ordered state possesses an accidental U(1) degeneracy. In this paper, we show that fluctuations beyond s-MFT lift this degeneracy by selecting one of two states (so-called ψ2 and ψ3) from the degenerate manifold, thus exposing a certain form of order-by-disorder (ObD). We analytically explore this selection at the microscopic level and close to criticality by elaborating upon and using an extension of the so-called TAP method, originally developed by Thouless, Anderson, and Palmer to study the effect of fluctuations in spin glasses. We also use a single-tetrahedron cluster-mean-field theory (c-MFT) to explore over what minimal length scale fluctuations can lift the degeneracy. We find the phase diagrams obtained by these two methods to be somewhat different since c-MFT only includes the shortest-range fluctuations. General symmetry arguments used to construct a Ginzburg-Landau theory to lowest order in the order parameters predict that a weak magnetic moment mz along the local <111 > (z ̂) direction is generically induced for a system ordering into a ψ2 state, but not so for ψ3 ordering. Both E-TAP and c-MFT calculations confirm this weak fluctuation-induced mz moment. Using a Ginzburg-Landau theory, we discuss the phenomenology of multiple phase transitions below the paramagnetic phase transition and within the Γ5 long-range ordered phase.

  5. Measuring Critical Thinking in Physics: Development and Validation of a Critical Thinking Test in Electricity and Magnetism

    ERIC Educational Resources Information Center

    Tiruneh, Dawit Tibebu; De Cock, Mieke; Weldeslassie, Ataklti G.; Elen, Jan; Janssen, Rianne

    2017-01-01

    Although the development of critical thinking (CT) is a major goal of science education, adequate emphasis has not been given to the measurement of CT skills in specific science domains such as physics. Recognizing that adequately assessing CT implies the assessment of both domain-specific and domain-general CT skills, this study reports on the…

  6. Observation of a critical pressure gradient for the stabilization of interchange modes in simple magnetized toroidal plasmas

    SciTech Connect

    Federspiel, L.; Labit, B.; Ricci, P.; Fasoli, A.; Furno, I.; Theiler, C.

    2009-09-15

    The existence of a critical pressure gradient needed to drive the interchange instability is experimentally demonstrated in the simple magnetized torus TORoidal Plasma EXperiment [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)]. This gradient is reached during a scan in the neutral gas pressure p{sub n}. Around a critical value for p{sub n}, depending on the magnetic configuration and on the injected rf power, a small increase in the neutral gas pressure triggers a transition in the plasma behavior. The pressure profile is locally flattened, stabilizing the interchange mode observed at lower neutral gas densities. The measured value for the critical gradient is close to the linear theory estimate.

  7. POLARIZED SCATTERING OF LIGHT FOR ARBITRARY MAGNETIC FIELDS WITH LEVEL-CROSSINGS FROM THE COMBINATION OF HYPERFINE AND FINE STRUCTURE SPLITTINGS

    SciTech Connect

    Sowmya, K.; Nagendra, K. N.; Sampoorna, M.; Stenflo, J. O. E-mail: knn@iiap.res.in E-mail: stenflo@astro.phys.ethz.ch

    2015-12-01

    Interference between magnetic substates of the hyperfine structure states belonging to different fine structure states of the same term influences the polarization for some of the diagnostically important lines of the Sun's spectrum, like the sodium and lithium doublets. The polarization signatures of this combined interference contain information on the properties of the solar magnetic fields. Motivated by this, in the present paper, we study the problem of polarized scattering on a two-term atom with hyperfine structure by accounting for the partial redistribution in the photon frequencies arising due to the Doppler motions of the atoms. We consider the scattering atoms to be under the influence of a magnetic field of arbitrary strength and develop a formalism based on the Kramers–Heisenberg approach to calculate the scattering cross section for this process. We explore the rich polarization effects that arise from various level-crossings in the Paschen–Back regime in a single scattering case using the lithium atomic system as a concrete example that is relevant to the Sun.

  8. Magnetic Field Dependence of the Critical Current of Planar Geometry Josephson Junctions

    NASA Astrophysics Data System (ADS)

    Ma, Meng; Cho, Ethan; Huynh, Chuong; Cybart, Shane; Dynes, Robert

    2015-03-01

    We report a study on the magnetic field dependence of the critical current of planar geometry Josephson junctions. We have fabricated Josephson junctions by using a focused helium ion beam to irradiate a narrow barrier in the plane of a 25 nm thick Y-Ba-Cu-O film. The London penetration depth λL is large (~1 μm) because of the ultra-thin thickness of the film. As a result, calculations of the Josephson penetration depth λJ are not realistic nor physical. Therefore in this work, we measure λJ experimentally. We tested devices with bridge widths ranging from 4 to 50 μm, and present measurements of the Fraunhofer quantum diffraction pattern (IC (B)). We observe a crossover from short to long junction behavior, which gives an experimentally measured λJ that ranges between 3 μm to 5 μm. The shape of the IC (B) pattern is strongly affected by the width of the bridge because of self-field effects. As the bridge width increases, Josephson vortices enter the junction and skew the patterns. This work shows that the electronic properties of the planar junctions are very different than those classical ``sandwich'' junctions due to the differences in geometry.

  9. Measurements of the generalized electric and magnetic polarizabilities of the proton at low Q2 using the virtual Compton scattering reaction

    NASA Astrophysics Data System (ADS)

    Bourgeois, P.; Sato, Y.; Shaw, J.; Alarcon, R.; Bernstein, A. M.; Bertozzi, W.; Botto, T.; Calarco, J.; Casagrande, F.; Distler, M. O.; Dow, K.; Farkondeh, M.; Georgakopoulos, S.; Gilad, S.; Hicks, R.; Holtrop, M.; Hotta, A.; Jiang, X.; Karabarbounis, A.; Kirkpatrick, J.; Kowalski, S.; Milner, R.; Miskimen, R.; Nakagawa, I.; Papanicolas, C. N.; Sarty, A. J.; Sirca, S.; Six, E.; Sparveris, N. F.; Stave, S.; Stiliaris, E.; Tamae, T.; Tsentalovich, G.; Tschalaer, C.; Turchinetz, W.; Zhou, Z.-L.; Zwart, T.

    2011-09-01

    Experimental details of a virtual Compton scattering (VCS) experiment performed on the proton at the MIT-Bates out-of-plane scattering facility are presented. The VCS response functions PLL-PTT/PTTɛɛ and PLT have been measured at Q2=0.057GeV2/c2. The generalized electric and magnetic polarizabilities, α(Q2) and β(Q2), and the mean-square electric polarizability radius are obtained from a dispersion analysis of the data. The results are in good agreement with O(p3) heavy baryon chiral perturbation and indicate the dominance of mesonic effects in the polarizabilities.

  10. Quantum Mechanical Simulation and X-Ray Scattering Applied to Pressure-Induced Invar Anomaly in Magnetic Iron Alloy

    NASA Astrophysics Data System (ADS)

    Winterrose, Michael L.

    The Invar effect has remained at the forefront of materials research since Charles-Edouard Guillaume discovered the vanishing thermal expansion of Fe-Ni alloys in 1897. More recently, a pressure-induced Invar effect was discovered in Fe-Ni alloys, and the relationship between classical and pressure-induced Invar phenomena has added complexity to the century-old struggle to comprehend the microscopic origins of Invar behavior. In this thesis I present our recent discovery of pressure-induced Invar behavior in Pd3Fe with the ordered L12 structure. Nuclear forward scattering measurements show that the ferromagnetic ground state in Pd3Fe is destabilized with pressure, collapsing around 10GPa (V/V 0=0.96) to a low-spin magnetic state. From high-pressure synchrotron x-ray diffraction measurements we find a large volume collapse at ambient temperature to accompany the collapse of ferromagnetism. After the volume collapse there is a significant increase in the bulk modulus. Using nuclear resonant inelastic x-ray scattering to study the 57Fe phonon partial density of states (PDOS) at high pressures, we find the pressure-induced magnetic transition to cause an anomalous relative softening of the average phonon frequency. Heating our sample to 650K in a furnace at a pressure of 7GPa, synchrotron x-ray diffraction measurements reveal negligible thermal expansion from 300 to 523 K, demonstrating pressure-induced Invar behavior in Pd3Fe. Density functional theory calculations identify a ferromagnetic ground state in Pd3Fe with large moments at the Fe sites. These calculations show that the application of pressure counteracts the band-filling effect of Pd. By tuning the position of the top of the 3d band with respect to the Fermi level, pressure-induced Invar behavior resembles classical Invar behavior that is controlled by chemical composition. This insight marks the first step towards a unification of our understanding of classical and pressure-induced Invar behavior. Pressure

  11. OH MASER SOURCES IN W49N: PROBING MAGNETIC FIELD AND DIFFERENTIAL ANISOTROPIC SCATTERING WITH ZEEMAN PAIRS USING THE VERY LONG BASELINE ARRAY

    SciTech Connect

    Deshpande, Avinash A.; Goss, W. M.; Mendoza-Torres, J. E. E-mail: mgoss@aoc.nrao.edu

    2013-09-20

    Our analysis of a Very Long Baseline Array 12 hr synthesis observation of the OH masers in the well-known star-forming region W49N has yielded valuable data that enable us to probe distributions of magnetic fields in both the maser columns and the intervening interstellar medium (ISM). The data, consisting of detailed high angular resolution images (with beam width ∼20 mas) of several dozen OH maser sources, or spots, at 1612, 1665, and 1667 MHz, reveal anisotropic scatter broadening with typical sizes of a few tens of milliarcseconds and axial ratios between 1.5 and 3. Such anisotropies have been reported previously by Desai et al. and have been interpreted as being induced by the local magnetic field parallel to the Galactic plane. However, we find (1) apparent angular sizes of, on average, a factor of about 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred previously, and (2) a significant deviation in the average orientation of the scatter-broadened images (by ∼10°) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, significant differences (up to 6σ) are apparent in the scatter-broadened images for the two hands of circular polarization, even when the apparent velocity separation is less than 0.1 km s{sup –1}. This may possibly be the first example of a Faraday rotation contribution to the diffractive effects in the ISM. Using the Zeeman pairs, we also study the distribution of the magnetic field in the W49N complex, finding no significant trend in the spatial structure function. In this paper, we present the details of our observations and analysis leading to these findings, discuss implications of our results for the intervening anisotropic magneto-ionic medium, and suggest possible implications for the structure of magnetic fields within this star-forming region.

  12. Effect of a pinning field on the critical current density for current-induced domain wall motion in perpendicular magnetic anisotropy nanowires.

    PubMed

    Ooba, Ayaka; Fujimura, Yuma; Takahashi, Kota; Komine, Takashi; Sugita, Ryuji

    2012-09-01

    In this study, the effect of a pinning field on the critical current density for current-induced domain wall motion in nanowires with perpendicular magnetic anisotropy was investigated using micromagnetic simulations. In order to estimate the pinning field in notched nanowires, we conducted wall energy calculations for nanowires with various saturation magnetizations. The pinning field increased as the notch size increased. The pinning field decreased as the saturation magnetization decreased. As a result, the decreased in the pinning field causes the reduction of the critical current density. Therefore, a significant reduction of the critical current density can be obtained by decreasing the saturation magnetization, even if wall pinning occurs.

  13. Evaluation of the intragrain critical current density in a multidomain FeSe crystal by means of dc magnetic measurements

    NASA Astrophysics Data System (ADS)

    Galluzzi, A.; Polichetti, M.; Buchkov, K.; Nazarova, E.; Mancusi, D.; Pace, S.

    2015-11-01

    The magnetic behavior of an iron-based FeSe crystal sample has been studied by means of dc magnetization measurements as a function of the temperature (T), the dc magnetic field (H) and the time (t). The M(T) curves show a discrepancy in the determination of the onset of the critical temperature T C with respect to what is observed in the superconducting M(H) measurements obtained by subtracting the ferromagnetic background from the curves measured at various temperatures. By using magnetic relaxation measurements M(t), the correct value of T C has been obtained. Moreover, the superconducting M(H) loops show the presence of a noisy signal up to an anomalous ‘peak effect’ only found for positive and negative increasing fields. These features have been analyzed by fitting the temperature dependence of the critical current density J c(T), extracted from the M(H) loops, with the help of the J c(T) dependencies governing an S-N-S junction network. This analysis has allowed us to interpret the behavior found in the M(H) loops and to obtain the value of the intrinsic critical current density J 0 which is not influenced by the presence of the junctions.

  14. Micro-focused Brillouin light scattering study of the magnetization dynamics driven by Spin Hall effect in a transversely magnetized NiFe nanowire

    SciTech Connect

    Madami, M. Carlotti, G.; Gubbiotti, G.; Tacchi, S.; Siracusano, G.; Finocchio, G.; Carpentieri, M.

    2015-05-07

    We employed micro-focused Brillouin light scattering to study the amplification of the thermal spin wave eigenmodes by means of a pure spin current, generated by the spin-Hall effect, in a transversely magnetized Pt(4 nm)/NiFe(4 nm)/SiO{sub 2}(5 nm) layered nanowire with lateral dimensions 500 × 2750 nm{sup 2}. The frequency and the cross section of both the center (fundamental) and the edge spin wave modes have been measured as a function of the intensity of the injected dc electric current. The frequency of both modes exhibits a clear redshift while their cross section is greatly enhanced on increasing the intensity of the injected dc. A threshold-like behavior is observed for a value of the injected dc of 2.8 mA. Interestingly, an additional mode, localized in the central part of the nanowire, appears at higher frequency on increasing the intensity of the injected dc above the threshold value. Micromagnetic simulations were used to quantitatively reproduce the experimental results and to investigate the complex non-linear dynamics induced by the spin-Hall effect, including the modification of the spatial profile of the spin wave modes and the appearance of the extra mode above the threshold.

  15. Complex Scattered Radiation Fields and Multiple Magnetic Fields in the Protostellar Cluster in NGC 2264

    NASA Astrophysics Data System (ADS)

    Kwon, Jungmi; Tamura, Motohide; Kandori, Ryo; Kusakabe, Nobuhiko; Hashimoto, Jun; Nakajima, Yasushi; Nakamura, Fumitaka; Nagayama, Takahiro; Nagata, Tetsuya; Hough, James H.; Werner, Michael W.; Teixeira, Paula S.

    2011-11-01

    Near-infrared imaging polarimetry in the J, H, and Ks bands has been carried out for the protostellar cluster region around NGC 2264 IRS 2 in the Monoceros OB1 molecular cloud. Various infrared reflection nebula clusters (IRNCs) associated with NGC 2264 IRS 2 and the IRAS 12 S1 core, as well as local infrared reflection nebulae (IRNe), were detected. The illuminating sources of the IRNe were identified with known or new near- and mid-infrared sources. In addition, 314 point-like sources were detected in all three bands and their aperture polarimetry was studied. Using a color-color diagram, reddened field stars and diskless pre-main-sequence stars were selected to trace the magnetic field (MF) structure of the molecular cloud. The mean polarization position angle of the point-like sources is 81° ± 29° in the cluster core, and 58° ± 24° in the perimeter of the cluster core, which is interpreted as the projected direction on the sky of the MF in the observed region of the cloud. The Chandrasekhar-Fermi method gives a rough estimate of the MF strength to be about 100 μG. A comparison with recent numerical simulations of the cluster formation implies that the cloud dynamics is controlled by the relatively strong MF. The local MF direction is well associated with that of CO outflow for IRAS 12 S1 and consistent with that inferred from submillimeter polarimetry. In contrast, the local MF direction runs roughly perpendicular to the Galactic MF direction.

  16. Comparison of temporal and spectral scattering methods using acoustically large breast models derived from magnetic resonance images

    PubMed Central

    Hesford, Andrew J.; Tillett, Jason C.; Astheimer, Jeffrey P.; Waag, Robert C.

    2014-01-01

    Accurate and efficient modeling of ultrasound propagation through realistic tissue models is important to many aspects of clinical ultrasound imaging. Simplified problems with known solutions are often used to study and validate numerical methods. Greater confidence in a time-domain k-space method and a frequency-domain fast multipole method is established in this paper by analyzing results for realistic models of the human breast. Models of breast tissue were produced by segmenting magnetic resonance images of ex vivo specimens into seven distinct tissue types. After confirming with histologic analysis by pathologists that the model structures mimicked in vivo breast, the tissue types were mapped to variations in sound speed and acoustic absorption. Calculations of acoustic scattering by the resulting model were performed on massively parallel supercomputer clusters using parallel implementations of the k-space method and the fast multipole method. The efficient use of these resources was confirmed by parallel efficiency and scalability studies using large-scale, realistic tissue models. Comparisons between the temporal and spectral results were performed in representative planes by Fourier transforming the temporal results. An RMS field error less than 3% throughout the model volume confirms the accuracy of the methods for modeling ultrasound propagation through human breast. PMID:25096103

  17. Magnetic immunoassay for cancer biomarker detection based on surface-enhanced resonance Raman scattering from coupled plasmonic nanostructures.

    PubMed

    Rong, Zhen; Wang, Chongwen; Wang, Junfeng; Wang, Donggen; Xiao, Rui; Wang, Shengqi

    2016-10-15

    A surface-enhanced resonance Raman scattering (SERRS) sensor was developed for the ultrasensitive detection of cancer biomarkers. Capture antibody-coated silver shell magnetic nanoparticles (Fe3O4@Ag MNPs) were utilized as the CEA enrichment platform and the SERRS signal amplification substrate. Gold nanorods (AuNRs) were coated with a thin silver shell to be in resonance with the resonant Raman dye diethylthiatricarbocyanine iodide (DTTC) and the excitation wavelength at 785nm. The silver-coated AuNRs (Au@Ag NRs) were then modified with detection antibody as the SERRS tags. Sandwich immune complexes formed in the presence of the target biomarker carcinoembryonic antigen (CEA), and this formation induced the plasmonic coupling between the Au@Ag NRs and Fe3O4@Ag MNPs. The SERRS signal of DTTC molecules located in the coupled plasmonic nanostructures was significantly enhanced. As a result, the proposed SERRS sensor was able to detect CEA with a low limit of detection of 4.75fg/mL and a wide dynamic linear range from 10fg/mL to 100ng/mL. The sensor provides a novel SERRS strategy for trace analyte detection and has a potential for clinical applications.

  18. Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe.

    PubMed

    Jung, Soon-Gil; Kang, Ji-Hoon; Park, Eunsung; Lee, Sangyun; Lin, Jiunn-Yuan; Chareev, Dmitriy A; Vasiliev, Alexander N; Park, Tuson

    2015-11-09

    We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors.

  19. Magnetization behavior and critical current density along the c-axis in melt-grown YBCO fiber crystal

    NASA Astrophysics Data System (ADS)

    Ishii, H.; Hara, T.; Hirano, S.; Figueredo, A. M.; Cima, M. J.

    1994-05-01

    The magnetic-hysteresis behavior of single-crystal YBCO fibers was investigated below 1 T and in the temperature range 40 to 88 K. The sample was prepared by the laser-heated floating zone method. The magnetization curves exhibited a fairly large asymmetry with respect to the field axis, especially at elevated temperatures. This behavior may be attributed to the surface Meissner current contribution. It was demonstrated for the temperature range examined that the magnetic hysteresis width, Δ M, versus external-field curves were well described by assuming that the critical current density in the c-axis direction Jcc obeys the critical-state model of the form Jc( B)= JcO[1+( B/ B0) n]-1. Then, in turn, the field dependence of the critical current density along the c-axis at field temperatures was deduced using parameters obtained by fitting the Δ M vs. field curves. It was shown that the critical current density in the direction of the c-axis in our sample was over 10 4 A/cm 2 at 77.3 K below 0.3 T. The field and temperature variations of Jcc were discussed in relation to the previous studies on some melt-processed YBCO.

  20. Finite-size scaling of the magnetization probability density for the critical Ising model in slab geometry.

    PubMed

    Cardozo, David Lopes; Holdsworth, Peter C W

    2016-04-27

    The magnetization probability density in d  =  2 and 3 dimensional Ising models in slab geometry of volume [Formula: see text] is computed through Monte-Carlo simulation at the critical temperature and zero magnetic field. The finite-size scaling of this distribution and its dependence on the system aspect-ratio [Formula: see text]and boundary conditions are discussed. In the limiting case [Formula: see text] of a macroscopically large slab ([Formula: see text]) the distribution is found to scale as a Gaussian function for all tested system sizes and boundary conditions.

  1. Finite-size scaling of the magnetization probability density for the critical Ising model in slab geometry

    NASA Astrophysics Data System (ADS)

    Lopes Cardozo, David; Holdsworth, Peter C. W.

    2016-04-01

    The magnetization probability density in d  =  2 and 3 dimensional Ising models in slab geometry of volume L\\paralleld-1× {{L}\\bot} is computed through Monte-Carlo simulation at the critical temperature and zero magnetic field. The finite-size scaling of this distribution and its dependence on the system aspect-ratio ρ =\\frac{{{L}\\bot}}{{{L}\\parallel}} and boundary conditions are discussed. In the limiting case ρ \\to 0 of a macroscopically large slab ({{L}\\parallel}\\gg {{L}\\bot} ) the distribution is found to scale as a Gaussian function for all tested system sizes and boundary conditions.

  2. Neutron scattering study of magnetic excitations in a 5d-based double-perovskite Ba2FeReO6

    SciTech Connect

    Plumb, K. W.; Cook, A. M.; Clancy, J.P.; Kolesnikov, Alexander I; Jeon, B. C.; Noh, Tae Won; Paramekanti, A.; Kim, Young-June

    2013-01-01

    Motivated by exploring spin-orbit-coupled magnetism in 5d-based transition metal oxides (TMOs) beyond the iridates, we present a powder inelastic neutron scattering study of magnetic excitations in Ba2FeReO6 - a member of the double-perovskite family of materials which exhibit half-metallic behavior and high Curie temperatures Tc. We find clear evidence of two well-defined dispersing magnetic modes in its low-temperature ferromagnetic state. We develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re and show that it captures our experimental observations. This allows us to extract moment sizes and exchange couplings, explain the magnitude of Tc, and infer that magnetostructural locking terms are weak. Our study further opens up Re-based compounds as model systems to explore the interplay of strong correlations and spin-orbit coupling in 5d TMOs.

  3. Identifying the critical point of the weakly first-order itinerant magnet DyCo2 with complementary magnetization and calorimetric measurements

    NASA Astrophysics Data System (ADS)

    Morrison, K.; Dupas, A.; Mudryk, Y.; Pecharsky, V. K.; Gschneidner, K. A.; Caplin, A. D.; Cohen, L. F.

    2013-04-01

    We examine the character of the itinerant magnetic transition of DyCo2 by different calorimetric methods, thereby separating the heat capacity and latent heat contributions to the entropy—allowing direct comparison to other itinerant electron metamagnetic systems. The heat capacity exhibits a large λ-like peak at the ferrimagnetic ordering phase transition, a signature that is remarkably similar to La(Fe,Si)13, where it is attributed to giant spin fluctuations. Using calorimetric measurements, we also determine the point at which the phase transition ceases to be first order: the critical magnetic field, μ0Hcrit = 0.4 ± 0.1 T and temperature Tcrit = 138.5 ± 0.5 K, and we compare these values to those obtained from analysis of magnetization by application of the Shimizu inequality for itinerant electron metamagnetism. Good agreement is found between these independent measurements, thus establishing the phase diagram and critical point with some confidence. In addition, we find that the often-used Banerjee criterion may not be suitable for determination of first order behavior in itinerant magnet systems.

  4. Influence of magnetism on phonons in CaFe{sub 2}As{sub 2} as seen via inelastic x-ray scattering.

    SciTech Connect

    Hahn, S. E.; Lee, Y.; Ni, N.; Canfield, P. C.; Goldman, A. I.; McQueeney, R. J.; Harmon, B. N.; Alatas, A.; Leu, B. M.; Alp, E. E.; Chung, D. Y.; Todorov, I. S.; Kanatzidis, M. G.; Iowa State Univ.; Northwestern Univ.

    2009-01-01

    In the iron pnictides, the strong sensitivity of the iron magnetic moment to the arsenic position suggests a significant relationship between phonons and magnetism. We measured the phonon dispersion of several branches in the high-temperature tetragonal phase of CaFe{sub 2}As{sub 2} using inelastic x-ray scattering on single-crystal samples. These measurements were compared to ab initio calculations of the phonons. Spin-polarized calculations imposing the antiferromagnetic order present in the low-temperature orthorhombic phase dramatically improve agreement between theory and experiment. This is discussed in terms of the strong antiferromagnetic correlations that are known to persist in the tetragonal phase.

  5. Magnetic-field-induced quantum criticality in a spin-1 planar ferromagnet with single-ion anisotropy

    NASA Astrophysics Data System (ADS)

    Mercaldo, Maria Teresa; Rabuffo, Ileana; Decesare, Luigi; Caramicod'Auria, Alvaro

    2014-03-01

    The effects of single-ion anisotropy on field-induced quantum criticality in spin-1 planar ferromagnet is explored by means of the two-time Green's function method. We work at the Tyablikov decoupling level for exchange interactions and the Anderson-Callen decoupling level for single-ion anisotropy. In our analysis a longitudinal external magnetic field is used as the non-thermal control parameter and the phase diagram and the quantum critical properties are established for suitable values of the single-ion anisotropy parameter. We find that the single-ion anisotropy has sensible effects on the structure of the phase diagram close to the quantum critical point. Indeed, for values of the uniaxial crystal-field parameter above a positive threshold a re-entrant behavior appears for the critical line, while above this value the conventional magnetic-field-induced quantum critical scenario remains unchanged. M. T. Mercaldo, I. Rabuffo, L. De Cesare, A. Caramico D'Auria, Eur. Phys. J. B 86, 340 (2013)

  6. Evidence of Magnetic Breakdown on the Defects With Thermally Suppressed Critical Field in High Gradient SRF Cavities

    SciTech Connect

    Eremeev, Grigory; Palczewski, Ari

    2013-09-01

    At SRF 2011 we presented the study of quenches in high gradient SRF cavities with dual mode excitation technique. The data differed from measurements done in 80's that indicated thermal breakdown nature of quenches in SRF cavities. In this contribution we present analysis of the data that indicates that our recent data for high gradient quenches is consistent with the magnetic breakdown on the defects with thermally suppressed critical field. From the parametric fits derived within the model we estimate the critical breakdown fields.

  7. Field-induced quantum criticality and universal temperature dependence of the magnetization of a spin-1/2 heisenberg chain.

    PubMed

    Kono, Y; Sakakibara, T; Aoyama, C P; Hotta, C; Turnbull, M M; Landee, C P; Takano, Y

    2015-01-23

    High-precision dc magnetization measurements have been made on Cu(C4H4N2) (NO3)2 in magnetic fields up to 14.7 T, slightly above the saturation field Hs=13.97  T, in the temperature range from 0.08 to 15 K. The magnetization curve and differential susceptibility at the lowest temperature show excellent agreement with exact theoretical results for the spin-1/2 Heisenberg antiferromagnet in one dimension. A broad peak is observed in magnetization measured as a function of temperature, signaling a crossover to a low-temperature Tomonaga-Luttinger-liquid regime. With an increasing field, the peak moves gradually to lower temperatures, compressing the regime, and, at Hs, the magnetization exhibits a strong upturn. This quantum critical behavior of the magnetization and that of the specific heat withstand quantitative tests against theory, demonstrating that the material is a practically perfect one-dimensional spin-1/2 Heisenberg antiferromagnet.

  8. Line Edge Roughness and Cross Sectional Characterization of Sub-50 nm Structures Using Critical Dimension Small Angle X-ray Scattering

    SciTech Connect

    Wang Chengqing; Jones, Ronald L.; Lin, Eric K.; Wu Wenli; Ho, Derek L.; Villarrubia, John S.; Choi, Kwang-Woo; Clarke, James S.; Roberts, Jeanette; Bristol, Robert; Bunday, Benjamin

    2007-09-26

    The need to characterize line edge and line width roughness in patterns with sub-50 nm critical dimensions challenges existing platforms based on electron microscopy and optical scatterometry. The development of x-ray based metrology platforms provides a potential route to characterize a variety of parameters related to line edge roughness by analyzing the diffracted intensity from a periodic array of test patterns. In this study, data from a series of photoresist line/space patterns featuring programmed line width roughness are measured by critical dimension small angle x-ray scattering (CD-SAXS). For samples with designed periodic roughness, CD-SAXS provides the wavelength and amplitude of the periodic roughness through satellite diffraction peaks. For real world applications, the rate of decay of intensity, termed an effective 'Debye-Waller' factor in CD-SAXS, provides an overall measure of the defects of the patterns. CD-SAXS data are compared to values obtained from critical dimension scanning electron microscopy (CD-SEM). Correlations between the techniques exist, however significant differences are observed for the current samples. A tapered cross sectional profile provides a likely explanation for the observed differences between CD-SEM and CD-SAXS measurements.

  9. Temperature and Magnetic Field Dependence of Critical Current Density of YBCO with Varying Flux Pinning Additions (POSTPRINT)

    DTIC Science & Technology

    2010-03-01

    coverage corresponding to M phase 1 nm thickness was found to be necessary to increase compared to YBCO . The op- timal layer thickness for each M phase was...kept constant in this experiment: , Y211 0.8 nm , and [17]. Using the optimal M phase thickness, the YBCO layer was also systematically varied for...AFRL-RZ-WP-TP-2010-2083 TEMPERATURE AND MAGNETIC FIELD DEPENDENCE OF CRITICAL CURRENT DENSITY OF YBCO WITH VARYING FLUX PINNING ADDITIONS

  10. Tracing engineered nanomaterials in biological tissues using coherent anti-Stokes Raman scattering (CARS) microscopy - A critical review.

    PubMed

    Goodhead, Rhys M; Moger, Julian; Galloway, Tamara S; Tyler, Charles R

    2015-01-01

    Nanomaterials (NMs) are used in an extremely diverse range of products and are increasingly entering the environment, driving a need to better understand their potential health effects in both humans and wildlife. A major challenge in nanoparticle (eco)toxicology is the ability to localise NMs post exposure, to enable more targeted biological effects analyses. A range of imaging techniques have been applied to do so, but they are limited, requiring either extensive processing of the material, staining or use of high intensity illumination that can lead to photo damage and/or have limited tissue penetration. Coherent anti-Stokes Raman scattering (CARS) microscopy is a label-free imaging technique, providing contrast based on the intrinsic molecular vibrations of a specimen, circumventing the need for chemical perturbation by exogenous labels. CARS uses near infra-red excitation wavelengths which allow microscopy at depths of several hundred microns in intact tissues and minimises photo-damage to live and delicate samples. Here we provide an overview of the CARS process and present a series of illustrative examples demonstrating its application for detecting NMs within biological tissues, ranging from isolated cells to whole organisms and including materials spanning metals to polymers. We highlight the advantages of this technique which include chemically selective live imaging and substantial depth penetration, but we also discuss its limitations when applied to nanotoxicology, which most notably include the lack of resolution for studies on single nanoparticles.

  11. Neutron Scattering Study of the Dependence of Magnetic Correlations on Se and Fe Content in the Fe(Te,Se) System

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Wen, Jinsheng; Xu, Guangyong; Gu, Genda; Tranquada, John

    2011-03-01

    We have performed a series of neutron scattering and magnetization measurements on Fe 1+y Te 1-x Se x with different Fe and Se compositions to study the interplay between magnetism and superconductivity. FeTeSe is rather unique for possessing two different types of spin configurations: one is a ``bicollinear'' or ``E-type'' structure that corresponds to the static order near (0.5,0), and the other is a ``collinear'' or ``C-type'' spin configuration that gives rise to spin excitations near (0.5,0.5). Short-range static magnetic order near the (0 . 5 , 0) in-plane wave-vector (using the two-Fe unit cell) is found in all non-superconducting samples. The static order disappears and bulk superconductivity emerges, as the spectral weight of the magnetic excitations shift to the region of reciprocal space near the in-plane wave-vector (0 . 5 , 0 . 5) with Se doping. Besides Se doping, Fe also plays an essential role in superconductivity and the magnetic correlations. Our results suggest that spin fluctuations associated with the collinear magnetic structure appear to be universal in all Fe-based superconductors, and there is a strong correlation between superconductivity and the character of the magnetic order/fluctuations in this system.

  12. Neutron, Electron and X-ray Scattering Investigation of Cr1-xVx Near Quantum Criticality

    SciTech Connect

    Sokolov, D A; Aronson, Meigan C.; Wu, Lijun; Zhu, Yimei; Nelson, C.; Mansfield, J. F.; Sun, K.; Erwin, R.; Lynn, J. W.; Lumsden, Mark D; Nagler, Stephen E

    2014-01-01

    The weakness of electron-electron correlations in the itinerant antiferromagnet Cr doped with V has long been considered the reason that neither new collective electronic states or even non Fermi liquid behaviour are observed when antiferromagnetism in Cr1 xVx is suppressed to zero temperature. We present the results of neutron and electron diffraction measurements of several lightly doped single crystals of Cr1 xVx in which the archtypal spin density wave instability is progressively suppressed as the V content increases, freeing the nesting-prone Fermi surface for a new striped charge instability that occurs at xc=0.037. This novel nesting driven instability relieves the entropy accumulation associated with the suppression of the spin density wave and avoids the formation of a quantum critical point by stabilising a new type of charge order at temperatures in excess of 400 K. Restructuring of the Fermi surface near quantum critical points is a feature found in materials as diverse as heavy fermions, high temperature copper oxide superconductors and now even elemental metals such as Cr.

  13. User's manual for three dimensional FDTD version D code for scattering from frequency-dependent dielectric and magnetic materials

    NASA Technical Reports Server (NTRS)

    Beggs, John H.; Luebbers, Raymond J.; Kunz, Karl S.

    1992-01-01

    The Penn State Finite Difference Time Domain Electromagnetic Scattering Code version D is a 3-D numerical electromagnetic scattering code based upon the finite difference time domain technique (FDTD). The manual provides a description of the code and corresponding results for several scattering problems. The manual is organized into 14 sections: introduction; description of the FDTD method; operation; resource requirements; version D code capabilities; a brief description of the default scattering geometry; a brief description of each subroutine; a description of the include file; a section briefly discussing Radar Cross Section computations; a section discussing some scattering results; a sample problem setup section; a new problem checklist; references and figure titles. The FDTD technique models transient electromagnetic scattering and interactions with objects of arbitrary shape and/or material composition. In the FDTD method, Maxwell's curl equations are discretized in time-space and all derivatives (temporal and spatial) are approximated by central differences.

  14. Purely bianisotropic scatterers

    NASA Astrophysics Data System (ADS)

    Albooyeh, M.; Asadchy, V. S.; Alaee, R.; Hashemi, S. M.; Yazdi, M.; Mirmoosa, M. S.; Rockstuhl, C.; Simovski, C. R.; Tretyakov, S. A.

    2016-12-01

    The polarization response of molecules or meta-atoms to external electric and magnetic fields, which defines the electromagnetic properties of materials, can either be direct (electric field induces electric moment and magnetic field induces magnetic moment) or indirect (magnetoelectric coupling in bianisotropic scatterers). Earlier studies suggest that there is a fundamental bound on the indirect response of all passive scatterers: It is believed to be always weaker than the direct one. In this paper, we prove that there exist scatterers which overcome this bound substantially. Moreover, we show that the amplitudes of electric and magnetic polarizabilities can be negligibly small as compared to the magnetoelectric coupling coefficients. However, we prove that if at least one of the direct-excitation coefficients vanishes, magnetoelectric coupling effects in passive scatterers cannot exist. Our findings open a way to a new class of electromagnetic scatterers and composite materials.

  15. Evidence of magnetic clusters in the disordered ferromagnet Ni-V close to the quantum critical concentration

    NASA Astrophysics Data System (ADS)

    Wang, Ruizhe; Ubaid-Kassis, S.; Schroeder, A.; Baker, P. J.; Pratt, F. L.; Blundell, S. J.; Lancaster, T.; Franke, I.; Moeller, J. S.; Vojta, T.

    2015-03-01

    We report the results of muon spin relaxation (μSR) experiments in zero field (ZF) and transverse field (TF) as well as magnetization (M) data of Ni1-xVx close to the critical vanadium concentration xc ~ 11 . 6 % where the onset of the ferromagnetic (FM) order is suppressed. This material features a prototypical disordered quantum phase transition (QPT) as seen in the temperature (T) and magnetic field (H) dependence of M (H , T) . In the paramagnetic phase (PM) above xc, M (H , T) is well described by non-universal power laws characterized by an exponent α (x -xc) , establishing a quantum Griffiths phase. Here, we focus on the FM side of the QPT below xc. After subtracting the spontaneous magnetization M0, we find that M (H , T) -M0 also follows a power law in H at low T with an analogous non-universal exponent α (xc - x) . This is the first evidence of a quantum Griffiths phase within the FM phase in this disordered alloy. μSR in ZF recognized a broad field distribution below xc as evidence of magnetic spatial inhomogeneities in the FM phase. Different muon depolarization rates in TF and ZF reveal magnetic clusters already in the PM regime. These observed clusters are important generic ingredients of a disordered QPT. Current: Durham University, U.K.

  16. Neutron Scattering Study of Magnetic Excitation Spectrum on Fe1-x(Ni/Cu)xTe0.5Se0.5

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Wen, Jinsheng; Xu, Guangyong; Gu, Genda; Tranquada, John

    2012-02-01

    We have performed a series of neutron scattering and magnetization measurements on Fe1-x(Ni/Cu)xTe0.5Se0.5 with different Ni/Cu compositions to study the interplay between magnetism and superconductivity. Substituting 2% and 4% of Ni for Fe reduces Tc from 15 K to 12 K and 8 K, while 10% of Cu results in lost of superconductivity. Spin resonance with lower energy are found in all superconducting samples. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T>>Tc to a distinctly different U-shaped dispersion at low temperature in superconducting samples. This spectral reconstruction is apparent for temperature up to 3Tc. On the other hand, no static order around (0.5,0,0.5) was found in any of these samples.

  17. User's manual for three dimensional FDTD version C code for scattering from frequency-independent dielectric and magnetic materials

    NASA Technical Reports Server (NTRS)

    Beggs, John H.; Luebbers, Raymond J.; Kunz, Karl S.

    1991-01-01

    The Penn State Finite Difference Time Domain Electromagnetic Scattering Code Version C is a three dimensional numerical electromagnetic scattering code based upon the Finite Difference Time Domain Technique (FDTD). The supplied version of the code is one version of our current three dimensional FDTD code set. This manual provides a description of the code and corresponding results for several scattering problems. The manual is organized into fourteen sections: introduction, description of the FDTD method, operation, resource requirements, Version C code capabilities, a brief description of the default scattering geometry, a brief description of each subroutine, a description of the include file (COMMONC.FOR), a section briefly discussing Radar Cross Section (RCS) computations, a section discussing some scattering results, a sample problem setup section, a new problem checklist, references and figure titles.

  18. User's manual for three dimensional FDTD version C code for scattering from frequency-independent dielectric and magnetic materials

    NASA Technical Reports Server (NTRS)

    Beggs, John H.; Luebbers, Raymond J.; Kunz, Karl S.

    1992-01-01

    The Penn State Finite Difference Time Domain Electromagnetic Scattering Code Version C is a three-dimensional numerical electromagnetic scattering code based on the Finite Difference Time Domain (FDTD) technique. The supplied version of the code is one version of our current three-dimensional FDTD code set. The manual given here provides a description of the code and corresponding results for several scattering problems. The manual is organized into 14 sections: introduction, description of the FDTD method, operation, resource requirements, Version C code capabilities, a brief description of the default scattering geometry, a brief description of each subroutine, a description of the include file (COMMONC.FOR), a section briefly discussing radar cross section computations, a section discussing some scattering results, a new problem checklist, references, and figure titles.

  19. User's manual for three dimensional FDTD version D code for scattering from frequency-dependent dielectric and magnetic materials

    NASA Technical Reports Server (NTRS)

    Beggs, John H.; Luebbers, Raymond J.; Kunz, Karl S.

    1991-01-01

    The Penn State Finite Difference Time Domain Electromagnetic Scattering Code Version D is a three dimensional numerical electromagnetic scattering code based upon the Finite Difference Time Domain Technique (FDTD). The supplied version of the code is one version of our current three dimensional FDTD code set. This manual provides a description of the code and corresponding results for several scattering problems. The manual is organized into fourteen sections: introduction, description of the FDTD method, operation, resource requirements, Version D code capabilities, a brief description of the default scattering geometry, a brief description of each subroutine, a description of the include file (COMMOND.FOR), a section briefly discussing Radar Cross Section (RCS) computations, a section discussing some scattering results, a sample problem setup section, a new problem checklist, references and figure titles.

  20. High-energy magnetic excitations in overdoped La2-xSrxCuO4 studied by neutron and resonant inelastic X-ray scattering

    DOE PAGES

    Wakimoto, S.; Ishii, K.; Kimura, H.; ...

    2015-05-21

    We have performed neutron inelastic scattering and resonant inelastic x-ray scattering (RIXS) at the Cu-L3 edge to study high-energy magnetic excitations at energy transfers of more than 100 meV for overdoped La2₋xSrxCuO4 with x=0.25 (Tc=15 K) and x=0.30 (nonsuperconducting) using identical single-crystal samples for the two techniques. From constant-energy slices of neutron-scattering cross sections, we have identified magnetic excitations up to ~250 meV for x=0.25. Although the width in the momentum direction is large, the peak positions along the (π,π) direction agree with the dispersion relation of the spin wave in the nondoped La2CuO4 (LCO), which is consistent with themore » previous RIXS results of cuprate superconductors. Using RIXS at the Cu-L3 edge, we have measured the dispersion relations of the so-called paramagnon mode along both (π,π) and (π,0) directions. Although in both directions the neutron and RIXS data connect with each other and the paramagnon along (π,0) agrees well with the LCO spin-wave dispersion, the paramagnon in the (π,π) direction probed by RIXS appears to be less dispersive and the excitation energy is lower than the spin wave of LCO near (π/2,π/2). Thus, our results indicate consistency between neutron inelastic scattering and RIXS, and elucidate the entire magnetic excitation in the (π,π) direction by the complementary use of two probes. The polarization dependence of the RIXS profiles indicates that appreciable charge excitations exist in the same energy range of magnetic excitations, reflecting the itinerant character of the overdoped sample. Lastly, we find a possible anisotropy in the charge excitation intensity might explain the apparent differences in the paramagnon dispersion in the (π,π) direction as detected by the x-ray scattering.« less

  1. X-ray resonant magnetic scattering investigations of hexagonal multiferroics RMnO3 (R = Dy, Ho, Er)

    SciTech Connect

    Nandi, Shibabrata

    2009-01-01

    Electricity and magnetism were unified into a common subject by James Clerk Maxwell in the nineteenth century yielding the electromagnetic theory. Four equations govern the dynamics of electric charges and magnetic fields, commonly known as Maxwell's equations. Maxwell's equations demonstrate that an accelerated charged particle can produce magnetic fields and a time varying magnetic field can induce a voltage - thereby linking the two phenomena. However, in solids, electric and magnetic ordering are most often considered separately and usually with good reason: the electric charges of electrons and ions are responsible for the charge effects, whereas the electron spin governs magnetic properties.

  2. Replacement and Original Magnet Engineering Options (ROMEOs): A European Seventh Framework Project to Develop Advanced Permanent Magnets Without, or with Reduced Use of, Critical Raw Materials

    NASA Astrophysics Data System (ADS)

    Mcguiness, P.; Akdogan, O.; Asali, A.; Bance, S.; Bittner, F.; Coey, J. M. D.; Dempsey, N. M.; Fidler, J.; Givord, D.; Gutfleisch, O.; Katter, M.; Le Roy, D.; Sanvito, S.; Schrefl, T.; Schultz, L.; Schwöbl, C.; Soderžnik, M.; Šturm, S.; Tozman, P.; Üstüner, K.; Venkatesan, M.; Woodcock, T. G.; Žagar, K.; Kobe, S.

    2015-06-01

    The rare-earth crisis, which peaked in the summer of 2011 with the prices of both light and heavy rare earths soaring to unprecedented levels, brought about the widespread realization that the long-term availability and price stability of rare earths could not be guaranteed. This triggered a rapid response from manufacturers involved in rare earths, as well as governments and national and international funding agencies. In the case of rare-earth-containing permanent magnets, three possibilities were given quick and serious consideration: (I) increased recycling of devices containing rare earths; (II) the search for new, mineable, rare-earth resources beyond those in China; and (III) the development of high-energy-product permanent magnets with little or no rare-earth content used in their manufacture. The Replacement and Original Magnet Engineering Options (ROMEO) project addresses the latter challenge using a two-pronged approach. With its basis on work packages that include materials modeling and advanced characterization, the ROMEO project is an attempt to develop a new class of novel permanent magnets that are free of rare earths. Furthermore, the project aims to minimize rare-earth content, particularly heavy-rare-earth (HRE) content, as much as possible in Nd-Fe-B-type magnets. Success has been achieved on both fronts. In terms of new, rare-earth-free magnets, a Heusler alloy database of 236,945 compounds has been narrowed down to approximately 20 new compounds. Of these compounds, Co2MnTi is expected to be a ferromagnet with a high Curie temperature and a high magnetic moment. Regarding the reduction in the amount of rare earths, and more specifically HREs, major progress is seen in electrophoretic deposition as a method for accurately positioning the HRE on the surface prior to its diffusion into the microstructure. This locally increases the coercivity of the rather small Nd-Fe-B-type magnet, thereby substantially reducing the dependence on the HREs Dy and

  3. Three-dimensional critical phase diagram of the Ising antiferromagnet CeRh2Si2 under intense magnetic field and pressure

    NASA Astrophysics Data System (ADS)

    Knafo, W.; Settai, R.; Braithwaite, D.; Kurahashi, S.; Aoki, D.; Flouquet, J.

    2017-01-01

    Using novel instrumentation to combine extreme conditions of intense pulsed magnetic field up to 60 T and high pressure up to 4 GPa, we have established the three-dimensional (3D) magnetic field-pressure-temperature phase diagram of a pure stoichiometric heavy-fermion antiferromagnet (CeRh2Si2 ). We find a temperature- and pressure-dependent decoupling of the critical and pseudometamagnetic fields at the borderlines of antiferromagnetism and strongly-correlated paramagnetism. This 3D phase diagram is representative of a class of heavy-fermion Ising antiferromagnets, where long-range magnetic ordering is decoupled from a maximum in the magnetic susceptibility. The combination of extreme conditions enabled us to characterize different quantum phase transitions, where peculiar quantum critical properties are revealed. The interest to couple the effects of magnetic field and pressure on quantum-critical correlated-electron systems is stressed.

  4. Chemically Inhomogeneous RE-Fe-B Permanent Magnets with High Figure of Merit: Solution to Global Rare Earth Criticality.

    PubMed

    Jin, Jiaying; Ma, Tianyu; Zhang, Yujing; Bai, Guohua; Yan, Mi

    2016-08-24

    The global rare earth (RE) criticality, especially for those closely-relied Nd/Pr/Dy/Tb in the 2:14:1-typed permanent magnets (PMs), has triggered tremendous attempts to develop new alternatives. Prospective candidates La/Ce with high abundance, however, cannot provide an equivalent performance due to inferior magnetic properties of (La/Ce)2Fe14B to Nd2Fe14B. Here we report high figure-of-merit La/Ce-rich RE-Fe-B PMs, where La/Ce are inhomogeneously distributed among the 2:14:1 phase. The resultant exchange coupling within an individual grain and magnetostatic interactions across grains ensure much superior performance to the La/Ce homogeneously distributed magnet. Maximum energy product (BH)max of 42.2 MGOe is achieved even with 36 wt. % La-Ce incorporation. The cost performance, (BH)max/cost, has been raised by 27.1% compared to a 48.9 MGOe La/Ce-free commercial magnet. The construction of chemical heterogeneity offers recipes to develop commercial-grade PMs using the less risky La/Ce, and also provides a promising solution to the REs availability constraints.

  5. Chemically Inhomogeneous RE-Fe-B Permanent Magnets with High Figure of Merit: Solution to Global Rare Earth Criticality

    PubMed Central

    Jin, Jiaying; Ma, Tianyu; Zhang, Yujing; Bai, Guohua; Yan, Mi

    2016-01-01

    The global rare earth (RE) criticality, especially for those closely-relied Nd/Pr/Dy/Tb in the 2:14:1-typed permanent magnets (PMs), has triggered tremendous attempts to develop new alternatives. Prospective candidates La/Ce with high abundance, however, cannot provide an equivalent performance due to inferior magnetic properties of (La/Ce)2Fe14B to Nd2Fe14B. Here we report high figure-of-merit La/Ce-rich RE-Fe-B PMs, where La/Ce are inhomogeneously distributed among the 2:14:1 phase. The resultant exchange coupling within an individual grain and magnetostatic interactions across grains ensure much superior performance to the La/Ce homogeneously distributed magnet. Maximum energy product (BH)max of 42.2 MGOe is achieved even with 36 wt. % La-Ce incorporation. The cost performance, (BH)max/cost, has been raised by 27.1% compared to a 48.9 MGOe La/Ce-free commercial magnet. The construction of chemical heterogeneity offers recipes to develop commercial-grade PMs using the less risky La/Ce, and also provides a promising solution to the REs availability constraints. PMID:27553789

  6. Chemically Inhomogeneous RE-Fe-B Permanent Magnets with High Figure of Merit: Solution to Global Rare Earth Criticality

    NASA Astrophysics Data System (ADS)

    Jin, Jiaying; Ma, Tianyu; Zhang, Yujing; Bai, Guohua; Yan, Mi

    2016-08-01

    The global rare earth (RE) criticality, especially for those closely-relied Nd/Pr/Dy/Tb in the 2:14:1-typed permanent magnets (PMs), has triggered tremendous attempts to develop new alternatives. Prospective candidates La/Ce with high abundance, however, cannot provide an equivalent performance due to inferior magnetic properties of (La/Ce)2Fe14B to Nd2Fe14B. Here we report high figure-of-merit La/Ce-rich RE-Fe-B PMs, where La/Ce are inhomogeneously distributed among the 2:14:1 phase. The resultant exchange coupling within an individual grain and magnetostatic interactions across grains ensure much superior performance to the La/Ce homogeneously distributed magnet. Maximum energy product (BH)max of 42.2 MGOe is achieved even with 36 wt. % La-Ce incorporation. The cost performance, (BH)max/cost, has been raised by 27.1% compared to a 48.9 MGOe La/Ce-free commercial magnet. The construction of chemical heterogeneity offers recipes to develop commercial-grade PMs using the less risky La/Ce, and also provides a promising solution to the REs availability constraints.

  7. Four-component relativistic theory for nuclear magnetic shielding constants: critical assessments of different approaches.

    PubMed

    Xiao, Yunlong; Liu, Wenjian; Cheng, Lan; Peng, Daoling

    2007-06-07

    Both formal and numerical analyses have been carried out on various exact and approximate variants of the four-component relativistic theory for nuclear magnetic shielding constants. These include the standard linear response theory (LRT), the full or external field-dependent unitary transformations of the Dirac operator, as well as the orbital decomposition approach. In contrast with LRT, the latter schemes take explicitly into account both the kinetic and magnetic balances between the large and small components of the Dirac spinors, and are therefore much less demanding on the basis sets. In addition, the diamagnetic contributions, which are otherwise "missing" in LRT, appear naturally in the latter schemes. Nevertheless, the definitions of paramagnetic and diamagnetic terms are not the same in the different schemes, but the difference is only of O(c(-2)) and thus vanishes in the nonrelativistic limit. It is shown that, as an operator theory, the full field-dependent unitary transformation approach cannot be applied to singular magnetic fields such as that due to the magnetic point dipole moment of a nucleus. However, the inherent singularities can be avoided by the corresponding matrix formulation (with a partial closed summation). All the schemes are combined with the Dirac-Kohn-Sham ansatz for ground state calculations, and by using virtually complete basis sets a new and more accurate set of absolute nuclear magnetic resonance shielding scales for the rare gases He-Rn have been established.

  8. Investigation of magnetic field enriched surface enhanced resonance Raman scattering performance using Fe3O4@Ag nanoparticles for malaria diagnosis

    NASA Astrophysics Data System (ADS)

    Yuen, Clement; Liu, Quan

    2014-03-01

    Recently, we have demonstrated the magnetic field-enriched surface-enhanced resonance Raman spectroscopy (SERRS) of β-hematin by using nanoparticles with iron oxide core and silver shell (Fe3O4@Ag) for the potential application in the early malaria diagnosis. In this study, we investigate the dependence of the magnetic field-enriched SERRS performance of β-hematin on the different core and shell sizes of the Fe3O4@Ag nanoparticles. We note that the core and shell parameters are critical in the realization of the optimal magnetic field-enrich SERRS β-hematin signal. These results are consistent with our simulations that will guide the optimization of the magnetic SERRS performance for the potential early diagnosis in the malaria disease.

  9. Extracting magnetic cluster size and its distributions in advanced perpendicular recording media with shrinking grain size using small angle x-ray scattering

    NASA Astrophysics Data System (ADS)

    Mehta, Virat; Wang, Tianhan; Ikeda, Yoshihiro; Takano, Ken; Terris, Bruce D.; Wu, Benny; Graves, Catherine; Dürr, Hermann A.; Scherz, Andreas; Stöhr, Jo; Hellwig, Olav

    2015-05-01

    We analyze the magnetic cluster size (MCS) and magnetic cluster size distribution (MCSD) in a variety of perpendicular magnetic recording (PMR) media designs using resonant small angle x-ray scattering at the Co L3 absorption edge. The different PMR media flavors considered here vary in grain size between 7.5 and 9.5 nm as well as in lateral inter-granular exchange strength, which is controlled via the segregant amount. While for high inter-granular exchange, the MCS increases rapidly for grain sizes below 8.5 nm, we show that for increased amount of segregant with less exchange the MCS remains relatively small, even for grain sizes of 7.5 and 8 nm. However, the MCSD still increases sharply when shrinking grains from 8 to 7.5 nm. We show evidence that recording performance such as signal-to-noise-ratio on the spin stand correlates well with the product of magnetic cluster size and magnetic cluster size distribution.

  10. Extracting magnetic cluster size and its distributions in advanced perpendicular recording media with shrinking grain size using small angle x-ray scattering

    SciTech Connect

    Mehta, Virat; Ikeda, Yoshihiro; Takano, Ken; Terris, Bruce D.; Hellwig, Olav; Wang, Tianhan; Wu, Benny; Graves, Catherine; Dürr, Hermann A.; Scherz, Andreas; Stöhr, Jo

    2015-05-18

    We analyze the magnetic cluster size (MCS) and magnetic cluster size distribution (MCSD) in a variety of perpendicular magnetic recording (PMR) media designs using resonant small angle x-ray scattering at the Co L{sub 3} absorption edge. The different PMR media flavors considered here vary in grain size between 7.5 and 9.5 nm as well as in lateral inter-granular exchange strength, which is controlled via the segregant amount. While for high inter-granular exchange, the MCS increases rapidly for grain sizes below 8.5 nm, we show that for increased amount of segregant with less exchange the MCS remains relatively small, even for grain sizes of 7.5 and 8 nm. However, the MCSD still increases sharply when shrinking grains from 8 to 7.5 nm. We show evidence that recording performance such as signal-to-noise-ratio on the spin stand correlates well with the product of magnetic cluster size and magnetic cluster size distribution.

  11. Reduction of critical current in magnetic tunnel junctions with CoFeB/Ru/CoFeB synthetic free layer

    NASA Astrophysics Data System (ADS)

    Zaleski, A.; Skowronski, W.; Czapkiewicz, M.; Kanak, J.; Stobiecki, T.; Macedo, R.; Cardoso, S.; Freitas, P. P.

    2010-01-01

    Reduction of the critical current density (Jc) in magnetic tunnel junctions (MTJs) can be achieved by replacing the standard Co40Fe40B20 free layer with a synthetic antiferromagnet. Patterned MTJs prepared by ion-beam assisted deposition (nanopillars, sizes down to 60 nm × 80 nm) with 2 nm CoFeB free layer and Co40Fe40B20/Ru (tRu)/ Co40Fe40B20 as a synthetic free layer (SyF) were studied. We have measured critical current density of CIMS in thermally activated switching regime (long current pulses). Values of switching current densities for standard MTJs with SyF were of the order 106 A/cm2, whilst MTJs with standard free layer demonstrated up to four times higher values of Jc.

  12. Neutron Scattering Studies of the S=1/2 Triangular Lattice Magnets NaNiO2 and LiNiO2

    NASA Astrophysics Data System (ADS)

    Clancy, J. Patrick

    2011-03-01

    NaNi O2 and LiNi O2 are isostructural quantum magnets based on a stacked triangular lattice in which magnetism arises from S=1/2 magnetic moments carried by Ni 3+ ions. Surprisingly, while these compounds are structurally and electronically very similar, the magnetic properties they exhibit are dramatically different. NaNi O2 undergoes a cooperative Jahn-Teller phase transition at 480K and magnetically orders below TN ~ 23 K, adopting a structure which consists of ferromagnetic sheets of S=1/2 moments stacked in an antiferromagnetic fashion. In contrast, LiNi O2 undergoes a spin glass transition at Tg ~ 9 K and remains disordered down to the lowest measured temperatures. Understanding the absence of long-range magnetic order in LiNi O2 is a problem which has attracted considerable interest for more than twenty five years. Among many potential explanations, the answer has most notably been attributed to geometric frustration caused by inherent mixing of the Li and Ni sublattices, or orbital degeneracy resulting from the lack of a coherent Jahn-Teller distortion. In this talk I will describe time-of-flight neutron scattering measurements performed on polycrystalline samples of NaNi O2 and LiNi O2 using the wide Angular-Range Chopper Spectrometer (ARCS) at ORNL and the Disk Chopper Spectrometer (DCS) at NIST. These measurements provide a thorough characterization of the excitation spectra for these two compounds, probing the inelastic scattering over energy scales ranging from ~ 0.1 meV to 1.5 eV. In NaNi O2 , our measurements reveal two sets of well-defined spin excitations, which we associate with ferromagnetic spin waves mediated by in-plane interactions and antiferromagnetic spin waves mediated by out-of-plane interactions. In LiNi O2 , we observe similar, albeit much broader, excitations consistent with short-range two-dimensional magnetic correlations. In the case of NaNi O2 , we have developed a simple linear spin wave theory model to describe these excitations

  13. Reconstruction from small-angle neutron scattering measurements of the real space magnetic field distribution in the mixed state of Sr2RuO4.

    PubMed

    Kealey, P G; Riseman, T M; Forgan, E M; Galvin, L M; Mackenzie, A P; Lee, S L; Paul, D M; Cubitt, R; Agterberg, D F; Heeb, R; Mao, Z Q; Maeno, Y

    2000-06-26

    We have measured the diffracted neutron scattering intensities from the square magnetic flux lattice in the perovskite superconductor Sr2RuO4, which is thought to exhibit p-wave pairing with a two-component order parameter. The relative intensities of different flux lattice Bragg reflections over a wide range of field and temperature have been shown to be inconsistent with a single component Ginzburg-Landau theory but qualitatively agree with a two-component p-wave Ginzburg-Landau theory.

  14. Aperiodic sequences and magnetic models: non-universal critical behavior within mean-field approximation

    NASA Astrophysics Data System (ADS)

    Branco, Nilton; Faria, Maicon; Tragtenberg, Marcelo

    2007-03-01

    We study the Ising model on a Bethe lattice, such that the exchange constant can assume two values, according to two-letter aperiodic sequences. Critical temperatures and exponents are calculated for three different sequences: Fibonacci, period-doubling and two-letter Rudin-Shapiro ones. These sequences are found to be irrelevant, marginal, and relevant, respectively, in the renormalization-group sense. The Fibonacci sequence presents the same critical behavior as for the uniform model and no log-periodic behavior is observed. For the marginal sequence, critical exponents depend on the ratio between the two possible exchange constants and a log-periodic behavior is clearly determined. Due to computational constraints, our results are not as precise for the Rudin-Shapiro sequence but we obtain evidence that the exponents are different from the classical ones and do not depend on the ratio between the exchange constants.

  15. Magnetorotational Turbulence Transports Angular Momentum in Stratified Disks with Low Magnetic Prandtl Number but Magnetic Reynolds Number above a Critical Value

    SciTech Connect

    Oishi, Jeffrey S.; Low, Mordecai-Mark Mac; /Amer. Museum Natural Hist.

    2012-02-14

    The magnetorotational instability (MRI) may dominate outward transport of angular momentum in accretion disks, allowing material to fall onto the central object. Previous work has established that the MRI can drive a mean-field dynamo, possibly leading to a self-sustaining accretion system. Recently, however, simulations of the scaling of the angular momentum transport parameter {alpha}{sub SS} with the magnetic Prandtl number Pm have cast doubt on the ability of the MRI to transport astrophysically relevant amounts of angular momentum in real disk systems. Here, we use simulations including explicit physical viscosity and resistivity to show that when vertical stratification is included, mean field dynamo action operates, driving the system to a configuration in which the magnetic field is not fully helical. This relaxes the constraints on the generated field provided by magnetic helicity conservation, allowing the generation of a mean field on timescales independent of the resistivity. Our models demonstrate the existence of a critical magnetic Reynolds number Rm{sub crit}, below which transport becomes strongly Pm-dependent and chaotic, but above which the transport is steady and Pm-independent. Prior simulations showing Pm-dependence had Rm < Rm{sub crit}. We conjecture that this steady regime is possible because the mean field dynamo is not helicity-limited and thus does not depend on the details of the helicity ejection process. Scaling to realistic astrophysical parameters suggests that disks around both protostars and stellar mass black holes have Rm >> Rm{sub crit}. Thus, we suggest that the strong Pm dependence seen in recent simulations does not occur in real systems.

  16. MAGNETOROTATIONAL TURBULENCE TRANSPORTS ANGULAR MOMENTUM IN STRATIFIED DISKS WITH LOW MAGNETIC PRANDTL NUMBER BUT MAGNETIC REYNOLDS NUMBER ABOVE A CRITICAL VALUE

    SciTech Connect

    Oishi, Jeffrey S.

    2011-10-10

    The magnetorotational instability (MRI) may dominate outward transport of angular momentum in accretion disks, allowing material to fall onto the central object. Previous work has established that the MRI can drive a mean-field dynamo, possibly leading to a self-sustaining accretion system. Recently, however, simulations of the scaling of the angular momentum transport parameter {alpha}{sub SS} with the magnetic Prandtl number Pm have cast doubt on the ability of the MRI to transport astrophysically relevant amounts of angular momentum in real disk systems. Here, we use simulations including explicit physical viscosity and resistivity to show that when vertical stratification is included, mean-field dynamo action operates, driving the system to a configuration in which the magnetic field is not fully helical. This relaxes the constraints on the generated field provided by magnetic helicity conservation, allowing the generation of a mean field on timescales independent of the resistivity. Our models demonstrate the existence of a critical magnetic Reynolds number Rm{sub crit}, below which transport becomes strongly Pm-dependent and chaotic, but above which the transport is steady and Pm-independent. Prior simulations showing Pm dependence had Rm < Rm{sub crit}. We conjecture that this steady regime is possible because the mean-field dynamo is not helicity-limited and thus does not depend on the details of the helicity ejection process. Scaling to realistic astrophysical parameters suggests that disks around both protostars and stellar mass black holes have Rm >> Rm{sub crit}. Thus, we suggest that the strong Pm dependence seen in recent simulations does not occur in real systems.

  17. Ammonium ionic liquid as modulator of the critical micelle concentration of ammonium surfactant at aqueous solution: conductimetric and dynamic light scattering (DLS) studies.

    PubMed

    Sifaoui, Hocine; Lugowska, Katarzyna; Domańska, Urszula; Modaressi, Ali; Rogalski, Marek

    2007-10-15

    We report measurements of self aggregation in aqueous solution of an ionic liquid (IL), didecyl-dimethylammonium nitrate ([DDA][NO(3)]) and a surfactant hexadecyl-trimethylammonium bromide (CTAB) and of mixtures of these two salts. The electrical conductivity and dynamic light scattering (DLS) measurements were used for the characterization of the aggregation process. The conductivity measurements were performed at three temperatures. The critical micelle concentration (CMC) was determined at different temperatures and at different ratio of two salts. The effect of IL on the micellization of CTAB has been discussed. Our results suggest that organized structures formed by CTAB and [DDA][NO(3)] self assembly in domains of several hundred nanometers size. The micellar solubility of the salicylic acid in mixed salt aqueous solutions was determined to probe the physical properties of these assemblies. We have observed, that the micellar solubility enhancement was only slightly influenced by the nature of micelles present in aqueous solution. This proves that salicylic acid solubilization is enthalpy driven.

  18. Local-moment magnetism in superconducting FeTe0.35Se0.65 as seen via inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Wen, Jinsheng; Xu, Guangyong; Chi, Songxue; Ku, Wei; Gu, Genda; Tranquada, J. M.

    2011-08-01

    The nature of the magnetic correlations in Fe-based superconductors remains a matter of controversy. To address this issue, we use inelastic neutron scattering to characterize the strength and temperature dependence of low-energy spin fluctuations in FeTe0.35Se0.65 (Tc˜14 K). Integrating magnetic spectral weight for energies up to 12 meV, we find a substantial moment (LE˜0.07μB2/Fe)that shows little change with temperature, from below Tc to 300 K. Such behavior cannot be explained by the response of conduction electrons alone; states much farther from the Fermi energy must have an instantaneous local spin polarization. It raises interesting questions regarding the formation of the spin gap and resonance peak in the superconducting state.

  19. High performance Nd-Fe-B permanent magnets without critical elements

    DOE PAGES

    Pathak, Arjun K.; Gschneidner, Jr., K. A.; Khan, M.; ...

    2016-01-28

    Scanning electron microscopy, and magnetization measurements reveal that as cast (Nd1–xCex)2Fe14B alloys contain significant amounts of α-Fe that can be dramatically reduced by annealing the alloys at 1000 °C for 3 days. The room temperature intrinsic coercivity, Hci, of (Nd0.8Ce0.2)2.2Fe14B melt spun ribbons was found to be 11 kOe, which is ~32 to ~10% higher in comparison to that of Nd2Fe14B (Hci = 8.3 kOe), and (Nd0.8Ce0.2)2.0Fe14B (Hci = 10 kOe), respectively. The substitution of Co for Fe in (Nd0.8Ce0.2)2Fe14–zCozB significantly increases both TC and the maximum energy product, (BH)max. Our study shows that both Co-containing and Co-free Ce-substituted Nd2Fe14Bmore » alloys have excellent magnetic properties at room temperature and above. As a result, the experimental results also demonstrate the potential of Nd-Ce-Fe-TM-B based alloys as alternative to expensive Dy-containing high performance rare earth magnets.« less

  20. Critical condition for the propeller effect in systems with magnetized neutron stars accreting from geometrically thin accretion disks

    NASA Astrophysics Data System (ADS)

    Ertan, Unal

    2016-07-01

    The inner disk radius around a magnetized neutron star in the spin-down phase is usually assumed to be close to the radius at which the viscous and magnetic stresses are balanced. With different assumptions, this radius is estimated to be very close the Alfven radius. Furthermore, it is commonly assumed that the propeller mechanism can expel the matter from the system when this radius is found to be greater than the co-rotation radius. In the present work, we have shown with simple analytical calculations from the first principles that a steady-state propeller mechanism cannot be established at the radius where the viscous and the magnetic torques are balanced. We have found that a steady-state propeller phase can be built up with an inner disk radius that is at least ~10 - 30 times smaller than the Alfven radius depending on the current mass-flow rate of the disk, the field strength and the rotational period of the source. This result also indicates that the critical accretion rate for the accretion-propeller transition is orders of magnitude smaller than the rate found by equating the Alfven and the co-rotation radii. Our results are consistent with the properties of recently discovered transitional millisecond pulsars which show transitions between the rotational powered radio pulsar and the accretion powered X-ray pulsar states.

  1. Forced flow He vapor cooled critical current testing facility for measurements of superconductors in a wide temperature and magnetic field range

    NASA Astrophysics Data System (ADS)

    Baskys, Algirdas; Hopkins, Simon C.; Bader, Jakob; Glowacki, Bartek A.

    2016-10-01

    As superconducting materials find their way into applications, there is increasing need to verify their performance at operating conditions. Testing of critical current with respect to temperature and magnetic field is of particular importance. However, testing facilities covering a range of temperatures and magnetic fields can be costly, especially when considering the cooling power required in the cryogenic system in the temperature range below 65 K (inaccessible for LN2). Critical currents in excess of 500 A are common for commercial samples, making the testing of such samples difficult in setups cooled via a cryocooler, moreover it often does not represent the actual cooling conditions that the sample will experience in service. This work reports the design and operation of a low-cost critical current testing facility, capable of testing samples in a temperature range of 10-65 K, with magnetic field up to 1.6 T and measuring critical currents up to 900 A with variable cooling power.

  2. 3D-xy critical properties of YBa2Cu4O8 and magnetic-field-induced 3D to 1D crossover

    NASA Astrophysics Data System (ADS)

    Weyeneth, S.; Schneider, T.; Bukowski, Z.; Karpinski, J.; Keller, H.

    2008-08-01

    We present reversible magnetization data of a YBa2Cu4O8 single crystal and analyze the evidence for 3D-xy critical behavior and a magnetic-field-induced 3D to 1D crossover. Remarkable consistency with these phenomena is observed in agreement with a magnetic-field-induced finite size effect, whereupon the correlation length transverse to the applied magnetic field cannot grow beyond the limiting magnetic length scale LH = (Φ0/(aH))1/2. By applying the appropriate scaling form we obtain the zero-field critical temperature, the 3D to 1D crossover, the vortex melting line and the universal ratios of the related scaling variables. Accordingly there is no continuous phase transition in the (H,T) plane along the Hc2 lines as predicted by the mean-field treatment.

  3. Novel ferroferric oxide/polystyrene/silver core-shell magnetic nanocomposite microspheres as regenerable substrates for surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Liu, Bo; Bai, Chong; Zhao, Dan; Liu, Wei-Liang; Ren, Man-Man; Liu, Qin-Ze; Yang, Zhi-Zhou; Wang, Xin-Qiang; Duan, Xiu-Lan

    2016-02-01

    A novel Ag-coated Fe3O4@Polystyrene core-shell microsphere has been designed via fabrication of Fe3O4@Polystyrene core-shell magnetic microsphere through a seed emulsion polymerization, followed by deposition of Ag nanoparticles using in-situ reduction method. Such magnetic microspheres can be utilized as sensitive surface-enhanced Raman scattering (SERS) substrates, using Rhodamine 6G (R6G) as a probe molecule, with both stable and reproducible performances. The SERS detection limit of R6G decreased to 1 × 10-10 M and the enhancement factor of this substrate on the order of 106 was obtained. In addition, owing to possessing excellent magnetic properties, the resultant microspheres could be separated rapidly by an external magnetic field and utilized repeatedly for three times at least. Therefore, the unique renewable property suggests a new route to eliminate the single-use problem of traditional SERS substrates and will be promising for the practical application.

  4. Comment on "Critical point scaling of Ising spin glasses in a magnetic field"

    NASA Astrophysics Data System (ADS)

    Temesvári, T.

    2016-11-01

    In a section of a recent paper [Phys. Rev. B 91, 104432 (2015), 10.1103/PhysRevB.91.104432], the authors discuss some of the arguments in the paper by Parisi and Temesvári [Nucl. Phys. B 858, 293 (2012), 10.1016/j.nuclphysb.2012.01.014]. In this Comment, it is shown how these arguments are misinterpreted and the existence of the Almeida-Thouless transition in the upper critical dimension six reasserted.

  5. High performance Nd-Fe-B permanent magnets without critical elements

    SciTech Connect

    Pathak, Arjun K.; Gschneidner, Jr., K. A.; Khan, M.; McCallum, R. W.; Pecharsky, V. K.

    2016-01-28

    Scanning electron microscopy, and magnetization measurements reveal that as cast (Nd1–xCex)2Fe14B alloys contain significant amounts of α-Fe that can be dramatically reduced by annealing the alloys at 1000 °C for 3 days. The room temperature intrinsic coercivity, Hci, of (Nd0.8Ce0.2)2.2Fe14B melt spun ribbons was found to be 11 kOe, which is ~32 to ~10% higher in comparison to that of Nd2Fe14B (Hci = 8.3 kOe), and (Nd0.8Ce0.2)2.0Fe14B (Hci = 10 kOe), respectively. The substitution of Co for Fe in (Nd0.8Ce0.2)2Fe14–zCozB significantly increases both TC and the maximum energy product, (BH)max. Our study shows that both Co-containing and Co-free Ce-substituted Nd2Fe14B alloys have excellent magnetic properties at room temperature and above. As a result, the experimental results also demonstrate the potential of Nd-Ce-Fe-TM-B based alloys as alternative to expensive Dy-containing high performance rare earth magnets.

  6. Resonant soft x-ray magnetic scattering from the 4f and 3d electrons in DyFe{sub 4}Al{sub 8}: Magnetic interactions in a cycloidal antiferromagnet

    SciTech Connect

    Beale, T. A. W.; Hatton, P. D.; Wilkins, S. B.; Abbamonte, P.; Stanescu, S.; Paixao, J. A.

    2007-05-01

    Soft x-ray resonant scattering has been used to examine the charge and magnetic interactions in the cycloidal antiferromagnetic compound DyFe{sub 4}Al{sub 8}. By tuning to the Dy M{sub 4} and M{sub 5} absorption edges and the Fe L{sub 2} and L{sub 3} absorption edges, we can directly observe the behavior of the Dy 4f and Fe 3d electron shells. Magnetic satellites surrounding the (110) Bragg peak were observed below 65 K. The diffraction peaks display complex spectra at the Dy M{sub 5} edge, indicative of a split 4f electron band. This is in contrast to the simple resonance observed at the Fe L{sub 3} absorption edge, which probes the Fe 3d electron shell. Temperature-dependent measurements detail the ordering of the magnetic moments on both the iron and the dysprosium antiferromagnetic cycloids. The ratio between the superlattice peak intensities of the Dy M{sub 4} and M{sub 5} absorption edges remained constant throughout the temperature range, in contrast to a previous study conducted at the Dy L{sub 2,3} edges. Our results demonstrate the ability of soft x-ray diffraction to separate the individual magnetic components in complicated multielement magnetic structures.

  7. Critical point scaling of Ising spin glasses in a magnetic field

    NASA Astrophysics Data System (ADS)

    Yeo, Joonhyun; Moore, M. A.

    2015-03-01

    Critical point scaling in a field H applies for the limits t →0 (where t =T /Tc-1 ) and H →0 but with the ratio R =t /H2 /Δ finite. Δ is a critical exponent of the zero-field transition. We study the replicon correlation length ξ and from it the crossover scaling function f (R ) defined via 1 /(ξ H4 /(d +2 -η )) ˜f (R ) . We have calculated analytically f (R ) for the mean-field limit of the Sherrington-Kirkpatrick model. In dimension d =3 , we have determined the exponents and the critical scaling function f (R ) within two versions of the Migdal-Kadanoff (MK) renormalization group procedure. One of the MK versions gives results for f (R ) in d =3 in reasonable agreement with those of the Monte Carlo simulations at the values of R for which they can be compared. If there were a de Almeida-Thouless (AT) line for d ≤6 , it would appear as a zero of the function f (R ) at some negative value of R , but there is no evidence for such behavior. This is consistent with the arguments that there should be no AT line for d ≤6 , which we review.

  8. Magnetic properties of the rivers feeding the South China Sea: a critical step for understanding the paleo-marine records.

    NASA Astrophysics Data System (ADS)

    Kissel, Catherine; Liu, Zhifei; Wandres, Camille; Liu, Qingsong

    2014-05-01

    In order to use the magnetic properties of marine sediments as a tracer for past changes in the precipitation rate and in oceanic water masses transport and exchanges, it is critical to identify and to characterize the different sources of the detrital fraction among which the magnetic particles. This is of peculiar importance in marginal seas such as the South China Sea extending from about 25°N to the equator. Thanks to the Westpac project, we had access to a number of sediments collected in the deltas of the main rivers feeding the South China Sea. This is represented on the Asian continent by the Pearl river, the Red River, the Mekong river, by Malaysia, Sumatra and Borneo regions with minor rivers but also contributing to the South China Sea, and finally by Luzon and Taiwan. The geological formations contributing to the river sediment discharges are different from one catchment basin to another as well as the present climatic conditions. The magnetic analyses conducted on the samples are the low-field magnetic susceptibility, the ARM acquisition and decay, the IRM acquisition and decay, the back-field acquisition, the thermal demagnetization of 3-axes IRM, the hysteresis parameters, the FORC diagrams. The obtained parameters all together allow us to define the nature of the magnetic grains and their grain size distribution when magnetite is dominant. Some degree of variability is observed at the river mouths, illustrating different geological sources at the local/regional scale. As an average, it appears that the Southern basin of the South China Sea is surrounded by regions richer in high coercivity magnetic minerals than the northern basin. This mineral is identified as hematite while magnetite is more abundant in the north. These results are complementary to the clay mineral assemblages previously determined on the same samples. We'll give some example of how this knowledge allows us to interpret the paleo-marine records from the South China Sea in terms

  9. Surface-enhanced Raman scattering (SERS) detection of multiple viral antigens using magnetic capture of SERS-active nanoparticles

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A highly sensitive immunoassay based on surface-enhanced Raman scattering (SERS) spectroscopy has been developed for multiplex detection of surface envelope and capsid antigens of the viral zoonotic pathogens West Nile virus (WNV) and Rift Valley fever virus (RVFV). Detection was mediated by antibo...

  10. The frustrated fcc antiferromagnet Ba2 YOsO6: Structural characterization, magnetic properties and neutron scattering studies

    SciTech Connect

    Kermarrec, E.; Marjerrison, Casey A.; Thompson, C. M.; Maharaj, Dalini D.; Levin, K.; Kroeker, S.; Granroth, Garrett E.; Flacau, Roxana; Yamani, Zahra; Greedan, John E.; Gaulin, Bruce D.

    2015-02-26

    Here we report the crystal structure, magnetization, and neutron scattering measurements on the double perovskite Ba2 YOsO6. The Fm$\\bar{3}$m space group is found both at 290 K and 3.5 K with cell constants a0=8.3541(4) Å and 8.3435(4) Å, respectively. Os5+ (5d3) ions occupy a nondistorted, geometrically frustrated face-centered-cubic (fcc) lattice. A Curie-Weiss temperature θ ~₋700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long-range antiferromagnetic order, consistent with a type-I fcc state below TN~69 K, is revealed by magnetization, Fisher heat capacity, and elastic neutron scattering, with an ordered moment of 1.65(6) μB on Os5+. The ordered moment is much reduced from either the expected spin-only value of ~3 μB or the value appropriate to 4d3 Ru5+ in isostructural Ba2 YRuO6 of 2.2(1) μB, suggesting a role for spin-orbit coupling (SOC). Triple-axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T=67.45 K, and the existence of a second-ordered state. We find time-of-flight inelastic neutron results reveal a large spin gap Δ~17 meV, unexpected for an orbitally quenched, d3 electronic configuration. In conclusion, we discuss this in the context of the ~5 meV spin gap observed in the related Ru5+,4d3 cubic double perovskite Ba2YRuO6, and attribute the ~3 times larger gap to stronger SOC present in this heavier, 5d, osmate system.

  11. Use of proton magnetic resonance spectroscopy in the treatment of psychiatric disorders: a critical update.

    PubMed

    Bustillo, Juan R

    2013-09-01

    Because of the wide availability of hardware as well as of standardized analytic quantification tools, proton magnetic resonance spectroscopy ((1)H-MRS) has become widely used to study psychiatric disorders. (1)H-MRS allows measurement of brain concentrations of more traditional singlet neurometabolites like N-acetylaspartate, choline, and creatine. More recently, quantification of the more complex multiplet spectra for glutamate, glutamine, inositol, and γ-aminobutyric acid have also been implemented. Here we review applications of (1)H-MRS in terms of informing treatment options in schizophrenia, bipolar disorder, and major depressive disorders. We first discuss recent meta-analytic studies reporting the most reliable findings. Then we evaluate the more sparse literature focused on 1H-MRS-detected neurometabolic effects of various treatment approaches in psychiatric populations. Finally we speculate on future developments that may result in translation of these tools to improve the treatment of psychiatric disorders.

  12. Critical aspects of ELM crash suppression by magnetic perturbations in KSTAR

    NASA Astrophysics Data System (ADS)

    Kim, Jayhyun; Jeon, Y. M.; Park, G. Y.; Choi, M. J.; in, Y.; Yoon, S. W.; Bae, C.; Lee, J.; Park, J.-K.; Ahn, J.; The Kstar Team Team

    2016-10-01

    ELM crash suppressions have been achieved by low n (n = 1, 2, and mixture of them) magnetic perturbations (MPs) with using various configurations of in-vessel perturbation coils in KSTAR. So far, the suppressed periods are extended longer than 10 seconds. In KSTAR, the complete suppression of ELM crashes almost always accompany with the increase of edge fluctuations which are likely to be excited by applied MPs. The excitation of edge fluctuation exhibited the bifurcation-like feature depending on the strength of MPs. The conditions to excite edge fluctuations were investigated with including well known q95 window. On the other hand, ELM mitigation does not come with the increase of edge fluctuations. Instead, it seems that applied MPs directly trigger small frequent ELMs since the mitigated ELMs suddenly disappear when turning MPs off. The results stress the importance of stability analysis with the use of perturbed equilibrium since most stability studies have assumed unperturbed/undistorted equilibrium.

  13. Light Scattering from Two Dimensional Electron Gases -- Gallium-Arsenide - ALUMINUM(X)GALLIUM(1-X)ARSENIDE Superlattices in High Magnetic Fields.

    NASA Astrophysics Data System (ADS)

    Tien, Zu-Jean

    1981-11-01

    Electronic transitions of 2 DEG in modulation doped semiconductor superlattices have been studied by resonant inelastic light scattering in strong magnetic field perpendicular to the two dimensional planes. Both the intersubband transition and unexpected cyclotron resonance have been observed in magnetic fields up to 19 Tesla for carrier concentration between 2.2 x 10('11)/cm('2) and 6.5 x 10('11)/cm('2). At modest magnetic field, B < 12 Tesla: The single particle intersubband excitation (E(,10)) and collective intersubband excitations (E(,-) and E(,+)) depend upon layer thickness and carrier concentration but are field independent. The energies of (DELTA)l = 1 and (DELTA)l = 2 inter-Landau level transitions ((H/2PI)(omega)(,c) and 2(H/2PI)(omega)(,c)) are linear in magnetic field, and yields an electron effective mass m* = (0.068 (+OR -) 0.003) m(,0), which is slightly higher than the accepted effective mass of the conduction band of GaAs 0.065 m(,0). In addition, collective cyclotron resonance ((H/2PI)(OMEGA)(,c)) was also observed. (OMEGA)(,c) is found greater than (omega)(,c), and (OMEGA)(,c)-(omega)(,c) is a function of magnetic field and carrier concentration. (OMEGA)(,c) is interpreted as the mixture of cyclotron resonance and plasma excitations. At higher fields, B < 19 Tesla: cyclotron resonance energy and cyclotron mass deviate from linear behavior by about 10%. E(,10) decreases while E(,-) increases in the quantum limit. The modest field spectra require a new theory, while the anomalous behavior of the high field spectra may require interpretation invoking electron ordering.

  14. Influence of critical current density on magnetic force of HTSC bulk above PMR with 3D-modeling numerical solutions

    NASA Astrophysics Data System (ADS)

    Lu, Yiyun; Qin, Yujie

    2015-09-01

    Numerical simulations of thermo-electromagnetic properties of a high temperature superconducting (HTS) bulk levitating over a permanent magnetic guideway (PMG) are performed by resorting to the quasistatic approximation of the H-method coupling with the classical description of the heat conduction equation. The numerical resolving codes are practiced with the help of the finite element program generation system (FEPG) platform using finite element method (FEM). The E-J power law is used to describe the electric current nonlinear characteristics of HTS bulk. The simulation results show that the heat conduction and the critical current density are tightly relative to the thermal effects of the HTS bulk over the PMG. The heat intensity which responds to the heat loss of the HTS bulk is mainly distributed at the two bottom-corners of the bulk sample.

  15. Self-organized criticality in a spherically closed cellular automaton: Modeling soft gamma repeater bursts driven by magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Nakazato, Ken'ichiro

    2014-08-01

    A new cellular automaton (CA) model is presented for the self-organized criticality (SOC) in recurrent bursts of soft gamma repeaters (SGRs), which are interpreted as avalanches of reconnection in the magnetosphere of neutron stars. The nodes of a regular dodecahedron and a truncated icosahedron are adopted as spherically closed grids enclosing a neutron star. It is found that the system enters the SOC state if there are sites where the expectation value of the added perturbation is nonzero. The energy distributions of SOC avalanches in CA simulations are described by a power law with a cutoff, which is consistent with the observations of SGR 1806-20 and SGR 1900+14. The power-law index is not universal and depends on the amplitude of the perturbation. This result shows that the SOC of SGRs can be illustrated not only by the crust quake model but also by the magnetic reconnection model.

  16. Status of intense permanent magnet proton source for China-accelerator driven sub-critical system Linac

    SciTech Connect

    Wu, Q. Ma, H. Y.; Yang, Y.; Sun, L. T.; Zhang, X. Z.; Zhang, Z. M.; Zhao, H. Y.; He, Y.; Zhao, H. W.

    2016-02-15

    Two compact intense 2.45 GHz permanent magnet proton sources and their corresponding low energy beam transport (LEBT) system were developed successfully for China accelerator driven sub-critical system in 2014. Both the proton sources operate at 35 kV potential. The beams extracted from the ion source are transported by the LEBT, which is composed of two identical solenoids, to the 2.1 MeV Radio-Frequency Quadrupole (RFQ). In order to ensure the safety of the superconducting cavities during commissioning, an electrostatic-chopper has been designed and installed in the LEBT line that can chop the continuous wave beam into a pulsed one. The minimum width of the pulse is less than 10 μs and the fall/rise time of the chopper is about 20 ns. The performance of the proton source and the LEBT, such as beam current, beam profile, emittance and the impact to RFQ injection will be presented.

  17. Quantum criticality in a magnetic chain with two- and four-spin interactions in a transverse field

    NASA Astrophysics Data System (ADS)

    de Alcantara Bonfim, O. F.; Saguia, A.; Boechat, B.; Florencio, J.

    2015-03-01

    We use entanglement entropy and finite-size scaling methods to investigate the ground-state properties of a spin - 1 / 2 Ising chain with two-spin (J2) and four-spin (J4) interactions in a transverse magnetic field (B). We concentrate our study on the unexplored critical region B = 1 and obtain the phase diagram of the model in the (J4-J2) plane. The phases found include ferromagnetic (F), antiferromagnetic (AF), as well as more complex phases involving spin configurations with multiple periodicity. The system presents both first and second order transitions separated by tricritical points. We find an unusual phase boundary on the semi-infinite segment (J4 < - 1 , J2 =0) separating the F and AF phases.

  18. FAST TRACK COMMUNICATION: Critical phenomena at the 140 and 200 K magnetic phase transitions in BiFeO3

    NASA Astrophysics Data System (ADS)

    Scott, J. F.; Singh, M. K.; Katiyar, R. S.

    2008-08-01

    We have measured the magnon Raman cross-sections for bismuth ferrite as a function of temperature near the newly discovered magnetic phase transitions near T2 = 140.3 ± 0.2 K and T1 = 201.0 ± 0.8 K (Singh et al 2008 J. Phys.: Condens. Matter 20 252203) and evaluate the critical exponents (α = 0.05 and α' = 0.09) characterizing that at 140.3 K and (α = 0.06 and α' = 0.13) that at 201.0 K. These are {\\ll } 1 , and hence the data fit a logarithmic divergence about as well. The occurrence of divergences in the electric susceptibility proportional to the specific heat anomaly in non-ferroelectric transitions due to piezoelectric coupling was first reported by Kizhaev et al (1986 JETP Lett. 43 445); in the present paper we apply an analogous theory to magnetoelastic coupling at magnetic transitions. This is an application of the basic Pippard relationship between susceptibilities and specific heat (Pippard 1956 Phil. Mag. 1 473) to a magnetoelastic system. The observations are related to the mechanical loss anomalies observed at the same temperatures (Redfern et al 2008 Preprint cond-mat). Our results support the distorted spin cycloid model of Zalesskii et al (2003 Phys. Solid State 45 141) and not the earlier model of Sosnowska et al (1982 J. Phys. C: Solid State Phys. 15 4835).

  19. PLANETESIMAL FORMATION IN MAGNETOROTATIONALLY DEAD ZONES: CRITICAL DEPENDENCE ON THE NET VERTICAL MAGNETIC FLUX

    SciTech Connect

    Okuzumi, Satoshi; Hirose, Shigenobu

    2012-07-01

    Turbulence driven by magnetorotational instability (MRI) affects planetesimal formation by inducing diffusion and collisional fragmentation of dust particles. We examine conditions preferred for planetesimal formation in MRI-inactive 'dead zones' using an analytic dead-zone model based on our recent resistive MHD simulations. We argue that successful planetesimal formation requires not only a sufficiently large dead zone (which can be produced by tiny dust grains) but also a sufficiently small net vertical magnetic flux (NVF). Although often ignored, the latter condition is indeed important since the NVF strength determines the saturation level of turbulence in MRI-active layers. We show that direct collisional formation of icy planetesimal across the fragmentation barrier is possible when the NVF strength is lower than 10 mG (for the minimum-mass solar nebula model). Formation of rocky planetesimals via the secular gravitational instability is also possible within a similar range of the NVF strength. Our results indicate that the fate of planet formation largely depends on how the NVF is radially transported in the initial disk formation and subsequent disk accretion processes.

  20. Critical Current of Superconducting Rutherford Cable in High Magnetic Fields with Transverse Pressure

    SciTech Connect

    Dietderich, D.R.; Scanlan, R.M.; Walsh, R.P.; Miller, J.R.

    1998-09-01

    For high energy physics applications superconducting cables are subjected to large stresses and high magnetic fields during service. It is essential to know how these cables perform in these operating conditions. A loading fixture capable of applying loads of up to 700 kN has been developed by NHMFL for LBNL. This fixture permits uniform loading of straight cables over a 122 mm length in a split-pair solenoid in fields up to 12 T at 4.2 K. The first results from this system for Rutherford cables of internal-tin and modified jelly roll strand of Nb{sub 3}Sn produced by IGC and TWC showed that little permanent degradation occurs up to 210 MPa. However, the cable made from internal-tin strand showed a 40% reduction in K{sub c} at 11T and 210 MPa while a dable made from modified jelly roll material showed only a 15% reduction in I{sub c} at 11T and 185 MPa.

  1. Temperature dependence of the upper critical field of type-II superconductors from isothermal magnetization data: Application to high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Landau, I. L.; Ott, H. R.

    2002-10-01

    Using the Ginzburg-Landau theory in very general terms, we develop a simple scaling procedure which allows to establish the temperature dependence of the upper critical field Hc2 and the value of the superconducting critical temperature Tc of type-II superconductors from measurements of the reversible isothermal magnetization. An analysis of existing experimental data shows that the normalized dependencies of Hc2 on T/Tc are practically identical for all families of high-Tc superconductors at all temperatures for which the magnetization data are available.

  2. Self-organized criticality and the dynamics of near-marginal turbulent transport in magnetically confined fusion plasmas

    NASA Astrophysics Data System (ADS)

    Sanchez, R.; Newman, D. E.

    2015-12-01

    The high plasma temperatures expected at reactor conditions in magnetic confinement fusion toroidal devices suggest that near-marginal operation could be a reality in future devices and reactors. By near-marginal it is meant that the plasma profiles might wander around the local critical thresholds for the onset of instabilities. Self-organized criticality (SOC) was suggested in the mid 1990s as a more proper paradigm to describe the dynamics of tokamak plasma transport in near-marginal conditions. It advocated that, near marginality, the evolution of mean profiles and fluctuations should be considered simultaneously, in contrast to the more common view of a large separation of scales existing between them. Otherwise, intrinsic features of near-marginal transport would be missed, that are of importance to understand the properties of energy confinement. In the intervening 20 years, the relevance of the idea of SOC for near-marginal transport in fusion plasmas has transitioned from an initial excessive hype to the much more realistic standing of today, which we will attempt to examine critically in this review paper. First, the main theoretical ideas behind SOC will be described. Secondly, how they might relate to the dynamics of near-marginal transport in real magnetically confined plasmas will be discussed. Next, we will review what has been learnt about SOC from various numerical studies and what it has meant for the way in which we do numerical simulation of fusion plasmas today. Then, we will discuss the experimental evidence available from the several experiments that have looked for SOC dynamics in fusion plasmas. Finally, we will conclude by identifying the various problems that still remain open to investigation in this area. Special attention will be given to the discussion of frequent misconceptions and ongoing controversies. The review also contains a description of ongoing efforts that seek effective transport models better suited than traditional

  3. Cancer risk assessment of extremely low frequency electric and magnetic fields: a critical review of methodology.

    PubMed Central

    McCann, J

    1998-01-01

    This review provides a discussion of cancer risk assessment methodology pertinent to developing a strategy for extremely low frequency electric and magnetic fields (EMF). Approaches taken for chemical agents or ionizing radiation in six key topic areas are briefly reviewed, and then those areas are examined from the perspective of EMF, identifying issues to be addressed in developing a risk assessment strategy. The following recommendations are offered: 1) risk assessment should be viewed as an iterative process that informs an overall judgment as to health risk and consists of a complex of related activities incorporating both positive and negative data, tumor and nontumor end points, and human and nonhuman sources of information; 2) a hazard identification resulting in a conclusion of weak or null effects, such as may be associated with EMF, will need to assign significant weight to animal cancer bioassays conducted under defined exposure conditions as well as to human epidemiologic studies; 3) a default factor to account for possible age differences in sensitivity to carcinogenesis should be included in an EMF risk assessment; 4) lack of evidence of dose response and the apparent lack of DNA reactivity of EMF suggest that a safety (or uncertainty) factor or margin of exposure type of risk characterization may be most appropriate; and 5) an EMF risk assessment should permit at least tentative conclusions to be reached as to the limits of carcinogenic risk from exposure to EMF, and should also define an efficient research agenda aimed at clarifying uncertainties appropriate to a more complete assessment. PMID:9799185

  4. Nematic quantum critical point without magnetism in FeSe1−xSx superconductors

    PubMed Central

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-01-01

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1−xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near x≈0.17, the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1−xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity. PMID:27382157

  5. Nematic quantum critical point without magnetism in FeSe1-xSx superconductors

    NASA Astrophysics Data System (ADS)

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-07-01

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near ≈0.17, the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.

  6. Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.

    PubMed

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-07-19

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.

  7. Temperature dependences of the upper critical field and the Ginzburg-Landau parameter of Li 2Pd 3B from magnetization measurements

    NASA Astrophysics Data System (ADS)

    Landau, I. L.; Khasanov, R.; Togano, K.; Keller, H.

    2007-01-01

    We present temperature dependences of the upper critical magnetic field Hc2 and the Ginzburg-Landau parameter κ for a ternary boride superconductor Li2Pd3B obtained from magnetization measurements. A specially developed scaling approach was used for the data analysis. The resulting Hc2(T) curve turns out to be surprisingly close to predictions of the BCS theory. The magnetic field penetration depth λ, evaluated in this work, is in excellent agreement with recent muon-spin-rotation experiments. We consider this agreement as an important proof of the validity of our approach.

  8. Analytical computation of process noise matrix in Kalman filter for fitting curved tracks in magnetic field within dense, thick scatterers

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Kolahal; Banerjee, Sudeshna; Mondal, Naba K.

    2016-07-01

    In the context of track fitting problems by a Kalman filter, the appropriate functional forms of the elements of the random process noise matrix are derived for tracking through thick layers of dense materials and magnetic field. This work complements the form of the process noise matrix obtained by Mankel [1].

  9. Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres. Numerical methods and application to the quiet, non-magnetic, surface of a solar-type star

    NASA Astrophysics Data System (ADS)

    Hayek, W.; Asplund, M.; Carlsson, M.; Trampedach, R.; Collet, R.; Gudiksen, B. V.; Hansteen, V. H.; Leenaarts, J.

    2010-07-01

    Aims: We present the implementation of a radiative transfer solver with coherent scattering in the new BIFROST code for radiative magneto-hydrodynamical (MHD) simulations of stellar surface convection. The code is fully parallelized using MPI domain decomposition, which allows for large grid sizes and improved resolution of hydrodynamical structures. We apply the code to simulate the surface granulation in a solar-type star, ignoring magnetic fields, and investigate the importance of coherent scattering for the atmospheric structure. Methods: A scattering term is added to the radiative transfer equation, requiring an iterative computation of the radiation field. We use a short-characteristics-based Gauss-Seidel acceleration scheme to compute radiative flux divergences for the energy equation. The effects of coherent scattering are tested by comparing the temperature stratification of three 3D time-dependent hydrodynamical atmosphere models of a solar-type star: without scattering, with continuum scattering only, and with both continuum and line scattering. Results: We show that continuum scattering does not have a significant impact on the photospheric temperature structure for a star like the Sun. Including scattering in line-blanketing, however, leads to a decrease of temperatures by about 350 K below log10 τ5000 ⪉ -4. The effect is opposite to that of 1D hydrostatic models in radiative equilibrium, where scattering reduces the cooling effect of strong LTE lines in the higher layers of the photosphere. Coherent line scattering also changes the temperature distribution in the high atmosphere, where we observe stronger fluctuations compared to a treatment of lines as true absorbers.

  10. Rayleigh Scattering.

    ERIC Educational Resources Information Center

    Young, Andrew T.

    1982-01-01

    The correct usage of such terminology as "Rayleigh scattering,""Rayleigh lines,""Raman lines," and "Tyndall scattering" is resolved during an historical excursion through the physics of light-scattering by gas molecules. (Author/JN)

  11. Scattering of High Energy Photons in Condensed Matter

    NASA Astrophysics Data System (ADS)

    Schneider, Jochen R.

    Modern synchrotron radiation facilities provide bright beams at photon energies higher than 80 keV which only weakly interact with matter; most diffraction experiments can be interpreted within 1. order Born approximation. The technique is considered a new probe in condensed matter research because it combines the high penetration power of thermal neutrons with the extreme momentum space resolution obtained in state of the art X-ray diffraction experiments. Identical samples can be studied with both probes and the information content is strongly enhanced by combining their results because of the difference in the intrinsic cross section, or in cases where high resolution inelastic neutron scattering experiments can be performed on the same crystal. After a short description of the experimental technique examples are presented including accurate structure factor measurements for charge density studies, defect induced diffuse scattering, structural phase transitions including critical scattering, and non-resonant bulk magnetic scattering.

  12. Stimulated Brillouin side-scattering of the beat wave excited by two counter-propagating X-mode lasers in magnetized plasma

    NASA Astrophysics Data System (ADS)

    Verma, Kanika; Sajal, Vivek; Baliyan, Sweta; Kumar, Ravindra; Sharma, Navneet K.

    2015-06-01

    The stimulated Brillouin scattering (SBS) of nonresonant beat mode in the presence of static magnetic field is investigated in a plasma. Two counter-propagating lasers of frequencies ( ω 1 and ω 2 ) and wave vectors ( k 1 and k 2 ) drive a nonresonant space charge beat mode at the phase matching condition of frequency ω 0 ≈ ω 1 ˜ ω 2 and wave number k → 0 ≈ k → 1 + k → 2 . The driver wave parametrically excites a pair of ion acoustic wave ( ω , k → ) and a sideband electromagnetic wave ( ω 3 , k → 3 ) . The beat wave couples with the sideband electromagnetic wave to exert a nonlinear ponderomotive force at the frequency of ion acoustic wave. Density perturbations due to ion acoustic wave and ponderomotive force couple with the oscillatory motion of plasma electron due to velocity of beat wave to give rise to a nonlinear current (by feedback mechanism) responsible for the growth of sideband wave at resonance. The growth rate of SBS was reduced (from ˜ 10 12 s - 1 to 10 10 s - 1 ) by applying a transverse static magnetic field ˜ 90 T. The present study can be useful for the excitation of fast plasma waves (for the purpose of electron acceleration) by two counter-propagating laser beams.

  13. Wide-angle x-ray scattering and solid-state nuclear magnetic resonance data combined to test models for cellulose microfibrils in mung bean cell walls.

    PubMed

    Newman, Roger H; Hill, Stefan J; Harris, Philip J

    2013-12-01

    A synchrotron wide-angle x-ray scattering study of mung bean (Vigna radiata) primary cell walls was combined with published solid-state nuclear magnetic resonance data to test models for packing of (1→4)-β-glucan chains in cellulose microfibrils. Computer-simulated peak shapes, calculated for 36-chain microfibrils with perfect order or uncorrelated disorder, were sharper than those in the experimental diffractogram. Introducing correlated disorder into the models broaden the simulated peaks but only when the disorder was increased to unrealistic magnitudes. Computer-simulated diffractograms, calculated for 24- and 18-chain models, showed good fits to experimental data. Particularly good fits to both x-ray and nuclear magnetic resonance data were obtained for collections of 18-chain models with mixed cross-sectional shapes and occasional twinning. Synthesis of 18-chain microfibrils is consistent with a model for cellulose-synthesizing complexes in which three cellulose synthase polypeptides form a particle and six particles form a rosette.

  14. Magnetic Raman Scattering in Two-Dimensional Spin-1/2 Heisenberg Antiferromagnets: Explanation of the Spectral Shape Anomaly

    NASA Astrophysics Data System (ADS)

    Nori, F.; Merlin, R.; Haas, S.; Sandvick, A.; Dagotto, E.

    1996-03-01

    We calculate(F. Nori, R.Merlin, S. Haas, A.W. Sandvik, and E. Dagotto, Physical Review Letters) 75, 553 (1995). the Raman spectrum of the two-dimensional (2D) spin-1/2 Heisenberg antiferromagnet by exact diagonalization and quantum Monte Carlo techniques on clusters of up to 144 sites. On a 16-site cluster, we consider the phonon-magnon interaction which leads to random fluctuations of the exchange integral. Results are in good agreement with experiments on various high-Tc precursors, such as La_2CuO4 and YBa_2Cu_3O_6.2. In particular, our calculations reproduce the broad lineshape of the two-magnon peak, the asymmetry about its maximum, the existence of spectral weight at high energies, and the observation of nominally forbidden A_1g scattering.

  15. Effects of vortex line shape on critical current density in high Tc superconducting film with nano-rod pinning centers under applied magnetic field of various orientations

    NASA Astrophysics Data System (ADS)

    Kwak, K.; Rhee, J.; Lee, W.; Lee, H.; Youm, D.; Yoo, J.

    2013-03-01

    We measured magneto-optical images (MOIs) on a coated conductor comprised of (Gd,Y)1Ba2Cu3O7-δ-BaZrO3 film under applied magnetic field of various orientations. MOIs showed systematic changes of asymmetric distribution of magnetic flux density and critical current density. TEM measurements showed that nano-rod pinning centers (RPCs) tilt by ∼13° from the c-axis. We were able to explain the results of MOI measurements using a simple model calculation about vortex line shapes, which change according to the magnitude and the orientation of applied magnetic field. In this model the critical current density, which is due to the vortex pinning, is determined by the geometrical relationship of the curved vortex lines and the tilted RPCs.

  16. Magnetic field induced enlargement of the regime of critical fluctuations in the classical superconductor V3Si from high-resolution specific heat experiments

    NASA Astrophysics Data System (ADS)

    Zheng, Y.; Liu, Y.; Toyota, N.; Lortz, R.

    2015-02-01

    We present high-resolution specific heat data from a high-purity single crystal of the classical superconductor V3Si, which reveal tiny lambda-shape anomalies at the superconducting transition superimposed onto the BCS specific heat jump in magnetic fields of 2 T and higher. The appearance of these anomalies is accompanied by a magnetic-field-induced broadening of the superconducting transition. We demonstrate, using scaling relations predicted by the fluctuation models of the 3d-XY and the 3d-lowest-Landau-level (3d-LLL) universality class that the effect of critical fluctuations becomes experimentally observable due to of a magnetic field-induced enlargement of the regime of critical fluctuations. The scaling indicates that a reduction of the effective dimensionality due to the confinement of quasiparticles into low Landau levels is responsible for this effect.

  17. Neutron spin echo scattering angle measurement (SESAME)

    SciTech Connect

    Pynn, R.; Fitzsimmons, M.R.; Fritzsche, H.; Gierlings, M.; Major, J.; Jason, A.

    2005-05-15

    We describe experiments in which the neutron spin echo technique is used to measure neutron scattering angles. We have implemented the technique, dubbed spin echo scattering angle measurement (SESAME), using thin films of Permalloy electrodeposited on silicon wafers as sources of the magnetic fields within which neutron spins precess. With 30-{mu}m-thick films we resolve neutron scattering angles to about 0.02 deg. with neutrons of 4.66 A wavelength. This allows us to probe correlation lengths up to 200 nm in an application to small angle neutron scattering. We also demonstrate that SESAME can be used to separate specular and diffuse neutron reflection from surfaces at grazing incidence. In both of these cases, SESAME can make measurements at higher neutron intensity than is available with conventional methods because the angular resolution achieved is independent of the divergence of the neutron beam. Finally, we discuss the conditions under which SESAME might be used to probe in-plane structure in thin films and show that the method has advantages for incident neutron angles close to the critical angle because multiple scattering is automatically accounted for.

  18. Improvements in Fabrication of Elastic Scattering Foils Used to Measure Neutron Yield by the Magnetic Recoil Spectrometer

    DOE PAGES

    Reynolds, H. G.; Schoff, M. E.; Farrell, M. P.; ...

    2016-08-01

    The magnetic recoil spectrometer uses a deuterated polyethylene polymer (CD2) foil to measure neutron yield in inertial confinement fusion experiments. Higher neutron yields in recent experiments have resulted in primary signal saturation in the detector CR-39 foils, necessitating the fabrication of thinner CD2 foils than established methods could provide. A novel method of fabricating deuterated polymer foils is described. The resulting foils are thinner, smoother, and more uniform in thickness than the foils produced by previous methods. Here, these new foils have successfully been deployed at the National Ignition Facility, enabling higher neutron yield measurements than previous foils, with nomore » primary signal saturation.« less

  19. Improvements in Fabrication of Elastic Scattering Foils Used to Measure Neutron Yield by the Magnetic Recoil Spectrometer

    SciTech Connect

    Reynolds, H. G.; Schoff, M. E.; Farrell, M. P.; Gatu Johnson, M.; Bionta, R. M.; Frenje, J. A.

    2016-08-01

    The magnetic recoil spectrometer uses a deuterated polyethylene polymer (CD2) foil to measure neutron yield in inertial confinement fusion experiments. Higher neutron yields in recent experiments have resulted in primary signal saturation in the detector CR-39 foils, necessitating the fabrication of thinner CD2 foils than established methods could provide. A novel method of fabricating deuterated polymer foils is described. The resulting foils are thinner, smoother, and more uniform in thickness than the foils produced by previous methods. Here, these new foils have successfully been deployed at the National Ignition Facility, enabling higher neutron yield measurements than previous foils, with no primary signal saturation.

  20. Stochastic macromodel of magnetic tunnel junction resistance variation and critical current dependence on resistance variation for SPICE simulation

    NASA Astrophysics Data System (ADS)

    Choi, Juntae; Song, Yunheub

    2017-04-01

    The resistance distribution of a magnetic tunnel junction (MTJ) shows nonuniformity according to various MTJ parameters. Moreover, this resistance variation leads to write-current density variation, which can cause serious problems when designing peripheral circuits for spin transfer torque magnetoresistance random access memory (STT-MRAM) and commercializing gigabit STT-MRAM. Therefore, a macromodel of MTJ including resistance, tunneling magnetoresistance ratio (TMR), and critical current variations is required for circuit designers to design MRAM peripheral circuits, that can overcome the various effects of the variations, such as write failure and read failure, and realize STT-MRAM. In this study, we investigated a stochastic behavior macromodel of the write current dependence on the MTJ resistance variation. The proposed model can possibly be used to analyze the write current density in relation to the resistance and TMR variations of MTJ with various parameter variations. It can be very helpful for designing STT-MRAM circuits and simulating the operation of STT-MRAM devices considering MTJ variations.

  1. Resonant soft x-ray scattering investigation of orbital and magnetic ordering in La{sub 0.5}Sr{sub 1.5}MnO{sub 4}

    SciTech Connect

    Wilkins, S.B.; Stojic, N.; Binggeli, N.; Beale, T.A.W.; Hatton, P.D.; Castleton, C.W.M.; Prabhakaran, D.; Boothroyd, A.T.; Altarelli, M.

    2005-06-15

    We report resonant x-ray scattering data of the orbital and magnetic ordering at low temperatures at the Mn L{sub 2,3} edges in La{sub 0.5}Sr{sub 1.5}MnO{sub 4}. The orderings display complex energy features close to the Mn absorption edges. Systematic modeling with atomic multiplet crystal field calculations was used to extract meaningful information regarding the interplay of spin, orbital, and Jahn-Teller order. These calculations provide a good general agreement with the observed energy dependence of the scattered intensity for a dominant orbital ordering of the d{sub x{sup 2}}{sub -z{sup 2}}/d{sub y{sup 2}}{sub -z{sup 2}} type. In addition, the origins of various spectral features are identified. The temperature dependence of the orbital and magnetic ordering was measured and suggests a strong interplay between the magnetic and orbital order parameters.

  2. Vibrations and reorientations of H2O molecules in [Sr(H2O)6]Cl2 studied by Raman light scattering, incoherent inelastic neutron scattering and proton magnetic resonance.

    PubMed

    Hetmańczyk, Joanna; Hetmańczyk, Lukasz; Migdał-Mikuli, Anna; Mikuli, Edward; Florek-Wojciechowska, Małgorzata; Harańczyk, Hubert

    2014-04-24

    Vibrational-reorientational dynamics of H2O ligands in the high- and low-temperature phases of [Sr(H2O)6]Cl2 was investigated by Raman Spectroscopy (RS), proton magnetic resonance ((1)H NMR), quasielastic and inelastic incoherent Neutron Scattering (QENS and IINS) methods. Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS, did not indicated a change of the crystal structure at the phase transition (detected earlier by differential scanning calorimetry (DSC) at TC(h)=252.9 K (on heating) and at TC(c)=226.5K (on cooling)). Temperature dependence of the full-width at half-maximum (FWHM) of νs(OH) band at ca. 3248 cm(-1) in the RS spectra indicated small discontinuity in the vicinity of phase transition temperature, what suggests that the observed phase transition may be associated with a change of the H2O reorientational dynamics. However, an activation energy value (Ea) for the reorientational motions of H2O ligands in both phases is nearly the same and equals to ca. 8 kJ mol(-1). The QENS peaks, registered for low temperature phase do not show any broadening. However, in the high temperature phase a small QENS broadening is clearly visible, what implies that the reorientational dynamics of H2O ligands undergoes a change at the phase transition. (1)H NMR line is a superposition of two powder Pake doublets, differentiated by a dipolar broadening, suggesting that there are two types of the water molecules in the crystal lattice of [Sr(H2O)6]Cl2 which are structurally not equivalent average distances between the interacting protons are: 1.39 and 1.18 Å. However, their reorientational dynamics is very similar (τc=3.3⋅10(-10) s). Activation energies for the reorientational motion of these both kinds of H2O ligands have nearly the same values in an experimental error limit: and equal to ca. 40 kJ mole(-1). The phase transition is not seen in the (1)H NMR spectra temperature dependencies. Infrared (IR), Raman (RS) and inelastic

  3. Magnetic Transitions in Iron Porphyrin Halides by Inelastic Neutron Scattering and Ab-initio Studies of Zero-Field Splittings

    DOE PAGES

    Stavretis, Shelby E.; Atanasov, Mihail; Podlesnyak, Andrey A.; ...

    2015-10-02

    Zero-field splitting (ZFS) parameters of nondeuterated metalloporphyrins [Fe(TPP)X] (X = F, Br, I; H2TPP = tetraphenylporphyrin) are determined by inelastic neutron scattering (INS). The ZFS values are D = 4.49(9) cm–1 for tetragonal polycrystalline [Fe(TPP)F], and D = 8.8(2) cm–1, E = 0.1(2) cm–1 and D = 13.4(6) cm–1, E = 0.3(6) cm–1 for monoclinic polycrystalline [Fe(TPP)Br] and [Fe(TPP)I], respectively. Along with our recent report of the ZFS value of D = 6.33(8) cm–1 for tetragonal polycrystalline [Fe(TPP)Cl], these data provide a rare, complete determination of ZFS parameters in a metalloporphyrin halide series. The electronic structure of [Fe(TPP)X] (X =more » F, Cl, Br, I) has been studied by multireference ab initio methods: the complete active space self-consistent field (CASSCF) and the N-electron valence perturbation theory (NEVPT2) with the aim of exploring the origin of the large and positive zero-field splitting D of the 6A1 ground state. D was calculated from wave functions of the electronic multiplets spanned by the d5 configuration of Fe(III) along with spin–orbit coupling accounted for by quasi degenerate perturbation theory. Results reproduce trends of D from inelastic neutron scattering data increasing in the order from F, Cl, Br, to I. A mapping of energy eigenvalues and eigenfunctions of the S = 3/2 excited states on ligand field theory was used to characterize the σ- and π-antibonding effects decreasing from F to I. This is in agreement with similar results deduced from ab initio calculations on CrX63- complexes and also with the spectrochemical series showing a decrease of the ligand field in the same directions. A correlation is found between the increase of D and decrease of the π- and σ-antibonding energies eλX (λ = σ, π) in the series from X = F to I. Analysis of this correlation using second-order perturbation theory expressions in terms of angular overlap parameters rationalizes the experimentally deduced trend

  4. Magnons Heat Transfer and Magnons Scattering in Magnetic Sandwich Lattices: Application to Fe/Gd(5)/Fe System

    NASA Astrophysics Data System (ADS)

    Bourahla, Boualem; Nafa, Ouahiba

    2016-07-01

    A model calculation is presented for the coherent magnon transmission and thermal transport at ferromagnetic nanojunction boundaries. The system consists of a Gd ultrathin film sandwiched between two Fe semi-infinite ferromagnetically ordered crystals. The dynamic of the system is analyzed using the equations of motion for the spin precession amplitudes on the lattice sites, valid for the range of temperatures of interest. The coherent transmission and reflection cross sections at the nanojunction boundary are calculated using the matching method. These calculations are presented for arbitrary directions on the boundary, for all accessible frequencies in the propagating bands, at variable temperatures and for a given thicknesses of the ultrathin nanojunction, with no externally applied magnetic field. The model is applied in particular to the Fe/Gd(5)/Fe system with a ferromagnetic Gd nanojunction. Our model yields the total integrated coherent thermal conductivity due to coherent magnons transmission via the sandwiched five Gd spin layers of the nanojunction. It elucidates, in particular, the dependence of the coherent magnons transmission and thermal transport in relation to the spatially inhomogeneous magnetic order of the atomic planes of the nanojunction for a given thickness.

  5. Inelastic light and electron scattering in parabolic quantum dots in magnetic field: Implications of generalized Kohn's theorem

    NASA Astrophysics Data System (ADS)

    Kushwaha, Manvir S.

    2016-03-01

    We investigate a one-component, quasi-zero-dimensional, quantum plasma exposed to a parabolic potential and an applied magnetic field in the symmetric gauge. If the size of such a system as can be realized in the semiconducting quantum dots is on the order of the de Broglie wavelength, the electronic and optical properties become highly tunable. Then the quantum size effects challenge the observation of many-particle phenomena such as the magneto-optical absorption, Raman intensity, and electron energy loss spectrum. An exact analytical solution of the problem leads us to infer that these many-particle phenomena are, in fact, dictated by the generalized Kohn's theorem in the long-wavelength limit. Maneuvering the confinement and/or the magnetic field furnishes the resonance energy capable of being explored with the FIR, Raman, or electron energy loss spectroscopy. This implies that either of these probes should be competent in observing the localized magnetoplasmons in the system. A deeper insight into the physics of quantum dots is paving the way for their implementation in diverse fields such as quantum computing and medical imaging.

  6. Deconvoluting Protein (Un)folding Structural Ensembles Using X-Ray Scattering, Nuclear Magnetic Resonance Spectroscopy and Molecular Dynamics Simulation.

    PubMed

    Nasedkin, Alexandr; Marcellini, Moreno; Religa, Tomasz L; Freund, Stefan M; Menzel, Andreas; Fersht, Alan R; Jemth, Per; van der Spoel, David; Davidsson, Jan

    2015-01-01

    The folding and unfolding of protein domains is an apparently cooperative process, but transient intermediates have been detected in some cases. Such (un)folding intermediates are challenging to investigate structurally as they are typically not long-lived and their role in the (un)folding reaction has often been questioned. One of the most well studied (un)folding pathways is that of Drosophila melanogaster Engrailed homeodomain (EnHD): this 61-residue protein forms a three helix bundle in the native state and folds via a helical intermediate. Here we used molecular dynamics simulations to derive sample conformations of EnHD in the native, intermediate, and unfolded states and selected the relevant structural clusters by comparing to small/wide angle X-ray scattering data at four different temperatures. The results are corroborated using residual dipolar couplings determined by NMR spectroscopy. Our results agree well with the previously proposed (un)folding pathway. However, they also suggest that the fully unfolded state is present at a low fraction throughout the investigated temperature interval, and that the (un)folding intermediate is highly populated at the thermal midpoint in line with the view that this intermediate can be regarded to be the denatured state under physiological conditions. Further, the combination of ensemble structural techniques with MD allows for determination of structures and populations of multiple interconverting structures in solution.

  7. Evolution of magnetic and superconducting fluctuations with doping of high-T{sub c} superconductors : an electronic Raman scattering study.

    SciTech Connect

    Blumberg, G.

    1998-01-14

    For YBa{sub 2}Cu{sub 3}O{sub 6+{delta}} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 3{+-}{delta}} superconductors, electronic Raman scattering from high- and low-energy excitations has been studied in relation to the hole doping level, temperature, and energy of the incident photons. For underdoped superconductors, it is concluded that short range antiferromagnetic (AF) correlations persist with hole doping and doped single holes are incoherent in the AF environment. Above the superconducting (SC) transition temperature T{sub c} the system exhibits a sharp Raman resonance of B{sub 1g} symmetry and about 75 meV energy and a pseudogap for electron-hole excitations below 75 meV, a manifestation of a partially coherent state forming from doped incoherent quasi-particles. The occupancy of the coherent state increases with cooling until phase ordering at T{sub c} produces a global SC state.

  8. The effect of anisotropic flux pinning microstructure on the sample length dependence of the magnetization critical current density in niobium-titanium superconductors

    NASA Astrophysics Data System (ADS)

    Nunes, C. Bormio; Heussner, R. W.; Larbalestier, D. C.

    1996-08-01

    Magnetization measurements of the critical current density Jc in Nb 47 wt % Ti with Nb artificial pinning centers revealed that the shape and magnitude of the field dependent magnetization hysteresis ΔM(H) was a strong function of the sample length and that ΔM(H) for short wire samples was up to six times smaller than for long wires. This is caused by the strong anisotropy of the critical current density Jc. The magnitude of Jc flowing perpendicular to the wire axis J⊥ was deduced to be 50-175 times smaller than the longitudinal current density J∥. The source of the anisotropy lies in the anisotropic flux pinning microstructure of the wires. When the magnetization current crosses perpendicular to the filament axis at each end of the wire, the Lorentz force is parallel to the pinning center axis. The pinning force is weak in this direction and J⊥ is correspondingly small. The technologically important critical current density is the longitudinal current density J∥. It can be extracted from magnetization measurements only in the case of large length to diameter filaments, as is quantitatively analyzed here.

  9. Temperature-dependent roles of inter- and intragrain current systems on the critical current and magnetization of BSCCO-2223/Ag tapes

    NASA Astrophysics Data System (ADS)

    Paasi, Jaakko; Kottman, Peter; Polák, Milan

    1995-02-01

    In this study we examine the role of inter- and intragrain current systems on the temperature-dependent critical current and magnetization of BSCCO-2223/Ag tapes. Experiments were done by measuring the sample magnetization field with movable miniature Hall sensors. We found that both systems have their own irreversible characteristics. The overall level of the intergrain (transport) critical current density, Jc, was limited at both lower (<30 K) and higher temperatures (30-95 K) by intergranular flux pinning, which seemed to be related to the maximum Josephson current of the weak links. Furthermore, we found that the irreversible intragranular magnetization has an influence on the magnetic field dependence of the intergrain Jc: when the intragrain pinning is strong (as at lower temperatures), the reduction of Jc in magnetic fields is moderate, and, when it is weaker (at higher temperatures), the decrease of Jc in fields is strong. This is a consequence of the field dependence of the maximum Josephson current density of the weak links, when the adjacent superconducting grains are in the mixed state.

  10. Magnetic Transitions in Iron Porphyrin Halides by Inelastic Neutron Scattering and Ab-initio Studies of Zero-Field Splittings

    SciTech Connect

    Stavretis, Shelby E.; Atanasov, Mihail; Podlesnyak, Andrey A.; Hunter, Seth C.; Neese, Frank; Xue, Zi-Ling

    2015-10-02

    Zero-field splitting (ZFS) parameters of nondeuterated metalloporphyrins [Fe(TPP)X] (X = F, Br, I; H2TPP = tetraphenylporphyrin) are determined by inelastic neutron scattering (INS). The ZFS values are D = 4.49(9) cm–1 for tetragonal polycrystalline [Fe(TPP)F], and D = 8.8(2) cm–1, E = 0.1(2) cm–1 and D = 13.4(6) cm–1, E = 0.3(6) cm–1 for monoclinic polycrystalline [Fe(TPP)Br] and [Fe(TPP)I], respectively. Along with our recent report of the ZFS value of D = 6.33(8) cm–1 for tetragonal polycrystalline [Fe(TPP)Cl], these data provide a rare, complete determination of ZFS parameters in a metalloporphyrin halide series. The electronic structure of [Fe(TPP)X] (X = F, Cl, Br, I) has been studied by multireference ab initio methods: the complete active space self-consistent field (CASSCF) and the N-electron valence perturbation theory (NEVPT2) with the aim of exploring the origin of the large and positive zero-field splitting D of the 6A1 ground state. D was calculated from wave functions of the electronic multiplets spanned by the d5 configuration of Fe(III) along with spin–orbit coupling accounted for by quasi degenerate perturbation theory. Results reproduce trends of D from inelastic neutron scattering data increasing in the order from F, Cl, Br, to I. A mapping of energy eigenvalues and eigenfunctions of the S = 3/2 excited states on ligand field theory was used to characterize the σ- and π-antibonding effects decreasing from F to I. This is in agreement with similar results deduced from ab initio calculations on CrX63- complexes and also with the spectrochemical series showing a decrease of the ligand field in the same directions. A correlation is found between the increase of D and decrease of the π- and σ-antibonding energies eλX (λ = σ, π) in the series from X = F to I. Analysis of this

  11. Diffuse magnetic neutron scattering in the highly frustrated double perovskite Ba2YRuO6

    SciTech Connect

    Nilsen, Gøran. J.; Thompson, Corey M.; Ehlers, Georg; Marjerrison, Casey A.; Greedan, John E.

    2015-02-23

    Here we investigated diffuse magnetic scattering in the highly frustrated double perovskite Ba2YRuO6 using polarized neutrons. Consistent with previous reports, the material shows two apparent transitions at 47 and 36 K to an eventual type I face-centered-cubic magnetic ground state. The (100) magnetic reflection shows different behavior from the five other observed reflections upon heating from 1.8 K, with the former broadening well beyond the resolution limit near 36 K. Closer examination of the latter group reveals a small, but clear, increase in peak widths between 36 and 47 K, indicating that this regime is dominated by short-range spin correlations. Diffuse magnetic scattering persists above 47 K near the position of (100) to at least 200 K, consistent with strong frustration. Reverse Monte Carlo (RMC) modeling of the diffuse scattering from 45 to 200 K finds that the spin-spin correlations between nearest and next-nearest neighbors are antiferromagnetic and ferromagnetic, respectively, at temperatures near the upper ordering temperature, but both become antiferromagnetic and of similar magnitude above 100 K. The significance of this unusual crossover is discussed in light of the super-superexchange interactions between nearest and next-nearest neighbors in this material and the demands of type I order. The dimensionality of the correlations is addressed by reconstructing the scattering in the (hk0) plane using the RMC spin configurations. This indicates that one-dimensional spin correlations dominate at temperatures close to the first transition. In addition, a comparison between mean-field calculations and (hk0) scattering implies that further neighbor couplings play a significant role in the selection of the ground state. Finally, the results and interpretation are compared with those recently published for monoclinic Sr2YRuO6, and similarities and differences are emphasized.

  12. Magnetic interactions in the multiferroic phase of CuFe1 xGaxO2 (x = 0.035) refined by inelastic neutron scattering with uniaxial-pressure control of domain structure

    SciTech Connect

    Nakajima, Taro; Mitsuda, Setsuo; Haraldsen, Jason T.; Fishman, Randy Scott; Hong, Tao; Terada, Noriki; Uwatoko, Yoshiya

    2012-01-01

    We have performed inelastic neutron scattering measurements in the ferroelectric noncollinear- magnetic phase of CuFe1 xGaxO2 (CFGO) with x = 0.035 under applied uniaxial pressure. This system has three types of magnetic domains with three different orientations reflecting the trigonal symmetry of the crystal structure. To identify the magnetic excitation spectrum corresponding to a magnetic domain, we have produced a nearly single-domain multiferroic phase by applying a uniaxial pressure of 10 MPa onto the [1 10] surfaces of a single crystal CFGO sample. As a result, we have successfully observed the single-domain spectrum in the multiferroic phase. Using the Hamiltonian employed in the previous inelastic neutron scattering study on the multi-domain multiferroic phase of CFGO (x = 0.035) [Haraldsen et al. Phys. Rev. B 82 020404R (2010)], we have refined the Hamiltonian parameters so as to simultaneously reproduce both of the observed single-domain and multi-domaim spectra. Comparing between the Hamiltonian parameters in the multiferroic phase of CFGO and in the collinear four-sublattice magnetic ground state of undoped CuFeO2 [Nakajima et al, Phys. Rev. B 84 184401 (2011)], we suggest that the nonmagnetic substitution weakens the spin-lattice coupling, which often favors a collinear magnetic ordering, as a consequence of the partial release of the spin frustration.

  13. Impact of a high magnetic field on the orientation of gravitactic unicellular organisms--a critical consideration about the application of magnetic fields to mimic functional weightlessness.

    PubMed

    Hemmersbach, Ruth; Simon, Anja; Waßer, Kai; Hauslage, Jens; Christianen, Peter C M; Albers, Peter W; Lebert, Michael; Richter, Peter; Alt, Wolfgang; Anken, Ralf

    2014-03-01

    The gravity-dependent behavior of Paramecium biaurelia and Euglena gracilis have previously been studied on ground and in real microgravity. To validate whether high magnetic field exposure indeed provides a ground-based facility to mimic functional weightlessness, as has been suggested earlier, both cell types were observed during exposure in a strong homogeneous magnetic field (up to 30 T) and a strong magnetic field gradient. While swimming, Paramecium cells were aligned along the magnetic field lines; orientation of Euglena was perpendicular, demonstrating that the magnetic field determines the orientation and thus prevents the organisms from the random swimming known to occur in real microgravity. Exposing Astasia longa, a flagellate that is closely related to Euglena but lacks chloroplasts and the photoreceptor, as well as the chloroplast-free mutant E. gracilis 1F, to a high magnetic field revealed no reorientation to the perpendicular direction as in the case of wild-type E. gracilis, indicating the existence of an anisotropic structure (chloroplasts) that determines the direction of passive orientation. Immobilized Euglena and Paramecium cells could not be levitated even in the highest available magnetic field gradient as sedimentation persisted with little impact of the field on the sedimentation velocities. We conclude that magnetic fields are not suited as a microgravity simulation for gravitactic unicellular organisms due to the strong effect of the magnetic field itself, which masks the effects known from experiments in real microgravity.

  14. Impact of a High Magnetic Field on the Orientation of Gravitactic Unicellular Organisms—A Critical Consideration about the Application of Magnetic Fields to Mimic Functional Weightlessness

    PubMed Central

    Simon, Anja; Waßer, Kai; Hauslage, Jens; Christianen, Peter C.M.; Albers, Peter W.; Lebert, Michael; Richter, Peter; Alt, Wolfgang; Anken, Ralf

    2014-01-01

    Abstract The gravity-dependent behavior of Paramecium biaurelia and Euglena gracilis have previously been studied on ground and in real microgravity. To validate whether high magnetic field exposure indeed provides a ground-based facility to mimic functional weightlessness, as has been suggested earlier, both cell types were observed during exposure in a strong homogeneous magnetic field (up to 30 T) and a strong magnetic field gradient. While swimming, Paramecium cells were aligned along the magnetic field lines; orientation of Euglena was perpendicular, demonstrating that the magnetic field determines the orientation and thus prevents the organisms from the random swimming known to occur in real microgravity. Exposing Astasia longa, a flagellate that is closely related to Euglena but lacks chloroplasts and the photoreceptor, as well as the chloroplast-free mutant E. gracilis 1F, to a high magnetic field revealed no reorientation to the perpendicular direction as in the case of wild-type E. gracilis, indicating the existence of an anisotropic structure (chloroplasts) that determines the direction of passive orientation. Immobilized Euglena and Paramecium cells could not be levitated even in the highest available magnetic field gradient as sedimentation persisted with little impact of the field on the sedimentation velocities. We conclude that magnetic fields are not suited as a microgravity simulation for gravitactic unicellular organisms due to the strong effect of the magnetic field itself, which masks the effects known from experiments in real microgravity. Key Words: Levitation—Microgravity—Gravitaxis—Gravikinesis—Gravity. Astrobiology 14, 205–215. PMID:24621307

  15. Development of a new plasma diagnostic of the critical surface and studies of the ion acoustic decay instability using collective Thomson scattering. Final report

    SciTech Connect

    Mizuno, K.; DeGroot, J.S.; Seka, W. l Drake, R.P.

    1991-12-31

    We have developed 5-channel collective Thomson scattering system to measure the ion acoustic wave excited by the ion acoustic wave decay instabilities. The multichannel collective Thomson scattering technique was established with 4{omega} probe laser beam using GDL laser system at LLE, Univ. of Rochester. We have obtained the ionic charge state Z by measuring the second harmonic emission from the ion acoustic decay instability. The LASNEX computer simulation calculations have been carried out. The experimental results agree very well with the LASNEX computer simulation results with the flux number f=0.1. In high power laser regime, the spectrum become broad, and the {alpha}{gamma} decreases indicating that the turbulent like spectrum is observed. In order to understand the experimental results, we have developed a theory to study absorption of laser and heat transport. This new theory includes the temporal evolution of the heat conduction region. The results agree with flux-limited hydrodynamic simulations. 20 refs.

  16. Development of a new plasma diagnostic of the critical surface and studies of the ion acoustic decay instability using collective Thomson scattering

    SciTech Connect

    Mizuno, K.; DeGroot, J.S. ); Seka, W. . Lab. for Laser Energetics)l Drake, R.P. )

    1991-01-01

    We have developed 5-channel collective Thomson scattering system to measure the ion acoustic wave excited by the ion acoustic wave decay instabilities. The multichannel collective Thomson scattering technique was established with 4{omega} probe laser beam using GDL laser system at LLE, Univ. of Rochester. We have obtained the ionic charge state Z by measuring the second harmonic emission from the ion acoustic decay instability. The LASNEX computer simulation calculations have been carried out. The experimental results agree very well with the LASNEX computer simulation results with the flux number f=0.1. In high power laser regime, the spectrum become broad, and the {alpha}{gamma} decreases indicating that the turbulent like spectrum is observed. In order to understand the experimental results, we have developed a theory to study absorption of laser and heat transport. This new theory includes the temporal evolution of the heat conduction region. The results agree with flux-limited hydrodynamic simulations. 20 refs.

  17. Stimulated Brillouin side-scattering of the beat wave excited by two counter-propagating X-mode lasers in magnetized plasma

    SciTech Connect

    Verma, Kanika; Sajal, Vivek Kumar, Ravindra; Sharma, Navneet K.; Baliyan, Sweta

    2015-06-15

    The stimulated Brillouin scattering (SBS) of nonresonant beat mode in the presence of static magnetic field is investigated in a plasma. Two counter-propagating lasers of frequencies (ω{sub 1} and ω{sub 2}) and wave vectors (k{sub 1} and k{sub 2}) drive a nonresonant space charge beat mode at the phase matching condition of frequency ω{sub 0}≈ω{sub 1}∼ω{sub 2} and wave number k{sup →}{sub 0}≈k{sup →}{sub 1}+k{sup →}{sub 2}. The driver wave parametrically excites a pair of ion acoustic wave (ω,k{sup →}) and a sideband electromagnetic wave (ω{sub 3},k{sup →}{sub 3}). The beat wave couples with the sideband electromagnetic wave to exert a nonlinear ponderomotive force at the frequency of ion acoustic wave. Density perturbations due to ion acoustic wave and ponderomotive force couple with the oscillatory motion of plasma electron due to velocity of beat wave to give rise to a nonlinear current (by feedback mechanism) responsible for the growth of sideband wave at resonance. The growth rate of SBS was reduced (from ∼10{sup 12}s{sup −1} to 10{sup 10}s{sup −1}) by applying a transverse static magnetic field ∼90 T. The present study can be useful for the excitation of fast plasma waves (for the purpose of electron acceleration) by two counter-propagating laser beams.

  18. Measurement of the parity violating asymmetry in the quasielastic electron-deuteron scattering and improved determination of the magnetic strange form factor and the isovector anapole radiative correction

    NASA Astrophysics Data System (ADS)

    Balaguer Ríos, D.; Aulenbacher, K.; Baunack, S.; Diefenbach, J.; Gläser, B.; von Harrach, D.; Imai, Y.; Kabuß, E.-M.; Kothe, R.; Lee, J. H.; Merkel, H.; Mora Espí, M. C.; Müller, U.; Schilling, E.; Weinrich, C.; Capozza, L.; Maas, F. E.; Arvieux, J.; El-Yakoubi, M. A.; Frascaria, R.; Kunne, R. A.; Ong, S.; van de Wiele, J.; Kowalski, S.; Prok, Y.

    2016-09-01

    A new measurement of the parity-violating asymmetry in the electron-deuteron quasielastic scattering for backward angles at ⟨Q2⟩ =0.224 (GeV/c ) 2 , obtained in the A4 experiment at the Mainz Microtron accelerator (MAMI) facility, is presented. The measured asymmetry is APV d=(-20.11 ±0.8 7stat±1.0 3sys)×10-6. A combination of these data with the proton measurements of the parity-violating asymmetry in the A4 experiment yields a value for the effective isovector axial-vector form factor of GAe ,(T =1 )=-0.19 ±0.43 and RA(T =1 ),anap=-0.41 ±0.35 for the anapole radiative correction. When combined with a reanalysis of measurements obtained in the G0 experiment at the Thomas Jefferson National Accelerator Facility, the uncertainties are further reduced to GMs=0.17 ±0.11 for the magnetic strange form factors, and RA(T =1 ),anap=-0.54 ±0.26 .

  19. Raman scattering of magnetic excitations in Y1-x Prx Ba2Cu3-yAlyO7-δ single crystals

    NASA Astrophysics Data System (ADS)

    Rübhausen, M.; Dieckmann, N.; Bock, A.; Merkt, U.; Widder, W.; Braun, H. F.

    1996-11-01

    Magnetic excitations and their role for the superconductivity in cuprate superconductors have been widely discussed in the literature. Here, we present a study of Y1-x Prx Ba2Cu3-yAlyO7-δ single crystals using Raman spectroscopy in an energy range of 50 10000 cm-1 Raman shift. The high energy range is dominated by a two-magnon scattering process at 3J, where J is the superexchange energy. In the Pr-123 single crystal, we find J = 720 cm-1, a damping of the one-magnon states Γ = 200 cm-1, and a resonance energy of 2.79eV for the two-magnon excitation. The two-magnon peak shows a continuous increase of the one-magnon damping with decreasing x and a nearly constant J across the phase transition to the superconductor. Especially, we find a weak two-magnon peak for a superconductor with a Tc = 86 K.

  20. Interaction of bovine serum albumin (BSA) with novel gemini surfactants studied by synchrotron radiation scattering (SR-SAXS), circular dichroism (CD), and nuclear magnetic resonance (NMR).

    PubMed

    Gospodarczyk, W; Szutkowski, K; Kozak, M

    2014-07-24

    The interaction of three dicationic (gemini) surfactants-3,3'-[1,6-(2,5-dioxahexane)]bis(1-dodecylimidazolium) chloride (oxyC2), 3,3'-[1,16-(2,15-dioxahexadecane)]bis(1-dodecylimidazolium) chloride (oxyC12), and 1,4-bis(butane)imidazole-1-yl-3-dodecylimidazolium chloride (C4)--with bovine serum albumin (BSA) has been studied by the use of small-angle X-ray scattering (SAXS), circular dichroism (CD), and (1)H nuclear magnetic resonance diffusometry. The results of CD studies show that the conformation of BSA was changed dramatically in the presence of all studied surfactants. The greater decrease (from 56 to 24%) in the α-helical structure of BSA was observed for oxyC2 surfactant. The radii of gyration estimated from SAXS data varied between 3 and 26 nm for the BSA/oxyC2 and BSA/oxyC12 systems. The hydrodynamic radius of the BSA/surfactant system estimated from NMR diffusometry varies between 5 and 11 nm for BSA/oxyC2 and 5 and 8 nm for BSA/oxyC12.

  1. Neutron scattering study of the interplay between structure and magnetism in Ba(Fe1-xCox)2As2

    NASA Astrophysics Data System (ADS)

    Lester, C.; Chu, Jiun-Haw; Analytis, J. G.; Capelli, S. C.; Erickson, A. S.; Condron, C. L.; Toney, M. F.; Fisher, I. R.; Hayden, S. M.

    2009-04-01

    Single-crystal neutron diffraction is used to investigate the magnetic and structural phase diagrams of the electron-doped superconductor Ba(Fe1-xCox)2As2 . Heat-capacity and resistivity measurements have demonstrated that Co doping this system splits the combined antiferromagnetic and structural transition present in BaFe2As2 into two distinct transitions. For x=0.025 , we find that the upper transition is between the high-temperature tetragonal and low-temperature orthorhombic structures with (TTO=99±0.5K) and the antiferromagnetic transition occurs at TAF=93±0.5K . We find that doping rapidly suppresses the antiferromagnetism, with antiferromagnetic order disappearing at x≈0.055 . However, there is a region of coexistence of antiferromagnetism and signatures of superconductivity obtained from thermodynamic and transport properties. For all the compositions studied, we find two anomalies in the temperature dependence of the structural Bragg peaks from both neutron scattering and x-ray diffraction at the same temperatures where anomalies in the heat capacity and resistivity have been previously identified. Thus for x=0.025 , where we have shown that the lower anomaly occurs at TAF , we infer that there is strong coupling between the antiferromagnetism and the crystal lattice which may persist to larger x .

  2. Brillouin Light Scattering study of the rotatable magnetic anisotropy in exchange biased bilayers of Ni81 Fe19 Ir20 Mn80

    NASA Astrophysics Data System (ADS)

    Rodríguez, Roberto; Oliveira, Alexandre; Estrada, Francisco; Santos, Obed; Azevedo, Antonio; Rezende, Sergio

    It is known that when a ferromagnet (FM) is in atomic contact with an antiferromagnet (AF) the exchange coupling between the FM and AF spins at the interface induces a unidirectional anisotropy in the ferromagnetic film. This effect is known as exchange bias (EB). Despite the large amount of research on this topic there are still several aspects of the EB mechanism that are not well understood. One of this aspects is the origin of the rotatable anisotropy in polycrystalline AFs. By means of Brillouin Light Scattering (BLS) measurements, we investigated the dependence of the rotatable anisotropy field HRA and exchange field HE with the magnitude of the external magnetic field (Ho) in FM/AM bilayers of Ni81Fe19(10nm)/Ir20Mn80(tAF) . We developed an algorithm to numerically fit the in-plane angular dependence of the magnon frequency, at a fixed value of Ho measured by BLS. From the fit parameters we were able to investigate HRA and HE dependency on Ho. The results reveal that HRA value depends on Ho, so we argue that AF grain distribution at the interface is partially modified by the applied field strength. Contrary to this, the relation between HE and Ho is not straightforward, remaining constant at high values of Ho.

  3. High-Pressure Single-Crystal Neutron Scattering Study of Magnetic and Fe Vacancy Orders in (Tl,Rb)2 Fe4 Se5 Superconductor

    DOE PAGES

    Ye, Feng; Bao, Wei; Chi, Song-Xue; ...

    2014-12-01

    We investigate the magnetic and iron vacancy orders in superconducting (Tl,Rb)2Fe4Se5 single-crystals by using a high-pressure neutron diffraction technique. Similar to the temperature effect, the block antiferromagnetic order gradually decreases upon increasing pressure while the Fe vacancy superstructural order remains intact before its precipitous disappearance at the critical pressure Pc = 8.3 GPa. Combined with previously determined Pc for superconductivity, our phase diagram under pressure reveals the concurrence of the block AFM order, the √5 × √5 iron vacancy order and superconductivity for the 245 superconductor. Lastly, a synthesis of current experimental data in a coherent physical picture is attempted.

  4. Transport and magnetization critical current densities in TlBa sub 2 Ca sub 2 Cu sub 3 O sub x tapes

    SciTech Connect

    Willis, J.O.; Maley, M.P.; Kung, P.J.; Coulter, J.Y.; Peterson, D.E.; Wahlbeck, P.G.; Bingert, J.F.; Phillips, D.S.

    1992-01-01

    The powder in tube process was used to produce silver-sheathed tapes of TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+x} (Tl-1223). The powder was produced by thalliating a precursor powder mixture to produce the Tl-2223 phase and then beating to drive off excess Tl and reach the Tl-1223 stoichiometry. The tapes were rolled and pressed, each step followed with a 3 h sintering. The 200 {mu}m thick tapes show little sign of texturing; however, the critical current shows a small ({approximately}50%) dependence on the direction of the applied magnetic field. Both transport and magnetization measurents indicate relatively strong pinning at high temperatures. The 75 K self field critical current density is 62 MA/m{sup 2}. Transport measurements reveal the presence of weak links at all temperatures, but with a relatively weak field dependence above {approx}0.1T.

  5. Magnetic moment distribution of magnetic cataclysmic variables

    NASA Technical Reports Server (NTRS)

    Wu, Kinwah; Wickramasinghe, Dayal T.

    1991-01-01

    A simulation study is made of the relative numbers of the AM Herculis binaries and the intermediate polars as a function of the orbital period using random variables subject to suitable constraints to describe the various parameters. It is shown that the observations can be matched by a single distribution in the magnetic moment equals 0.7 +/- 0.3. For such an ensemble, the intermediate polars are distributed in the log(Porb) - log(Ps) diagram about the critical disk line but with a larger scatter than observed.

  6. Critical fluctuations near the consolute point of n-pentanol-nitromethane. An ultrasonic spectrometry, dynamic light scattering, and shear viscosity study.

    PubMed

    Iwanowski, I; Behrends, R; Kaatze, U

    2004-05-15

    Ultrasonic attenuation spectra, the shear viscosity, and the mutual diffusion coefficient of the n-pentanol-nitromethane mixture of critical composition have been measured at different temperatures near the critical temperature. The noncritical background contribution, proportional to frequency, to the acoustical attenuation-per-wavelength spectra has been determined and subtracted from the total attenuation to yield the critical contribution. When plotted versus the reduced frequency, with the relaxation rate of order-parameter fluctuations from the shear viscosity and diffusion coefficient measurements, the critical part in the sonic attenuation coefficient displays a scaling function which nicely fits to the data for the critical system 3-methylpentane-nitromethane and also to the empirical scaling function of the Bhattacharjee-Ferrell dynamic scaling theory. The scaled half-attenuation frequency follows from the experimental data as Omega(1/2)emp= 1.8+/-0.1. The relaxation rate of order-parameter fluctuation shows power-law behavior with the theoretically predicted universal exponent and the extraordinary high amplitude Gammao= (187+/-2) x 10(9) s(-1). The amount of the adiabatic coupling constant /g/= 0.03, as estimated from the amplitude of the critical contribution to the acoustical spectra, is unusually small.

  7. Inelastic neutron scattering studies on the incommensurate-to-commensurate transformation of low energy magnetic excitations in Fe1 + δ - y(Ni / Cu) y Te1 - x Sex

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Wen, Jinsheng; Schneeloch, John; Zhao, Yang; Matsuda, Masaaki; Ku, Wei; Liu, Xuerong; Gu, Genda; Lee, D.-H.; Birgeneau, R. J.; Tranquada, J. M.; Xu, Guangyong

    2013-03-01

    We have performed a series of neutron scattering and magnetization measurements on Fe1 + δ - y(Ni / Cu) y Te1 - x Sex system to study the interplay between magnetism and superconductivity. Both non-superconducting and superconducting samples with Tc 8 ~15K are studied. The low energy magnetic excitations of all samples at T > >Tc consist of two incommensurate vertical columns. They change to a distinctly different U-shaped dispersion at T >Tc for the superconducting samples and the transition temperature depend on the composition. On the other hand, for all non-superconducting samples, there is no clear temperature dependence, and the low energy magnetic excitations remain two columns for temperatures down to 1.5 K. Work is supported by the Office of Basic Energy Sciences, DOE.

  8. Magnetic properties and critical behavior of the pure and diluted two-dimensional weak ferromagnet (CH3NH3)2Mn1-xCdxCl4

    NASA Astrophysics Data System (ADS)

    Paduan-Filho, A.; Becerra, C. C.

    2002-05-01

    The compound (CH3NH3)2MnCl4 had for a long time been considered a good example of a quasi-two-dimensional Heisenberg antiferromagnet, however, it is a weak ferromagnet with a nearly quadratic layer structure. In this work we measure the magnetization of (CH3NH3)2MnCl4 and the diluted with cadmium compound (CH3NH3)2Mn0.95Cd0.05Cl4. The Néel temperature for the pure sample was determined as TN=44.75 K and a weak-ferromagnetic moment was observed within the nearly quadratic layer (perpendicular to the easy axis). From the measured weak magnetic moment, we estimate a canting angle for the sublattices magnetizations θ˜0.07° from the easy axis. The overall temperature dependence of the weak magnetic moment is the same as that previously measured for the sublattice magnetization in neutron diffraction experiments (as expected). However, close to TN the critical exponent β of the magnetization changes from β1=0.17±0.02 [0.01<(1-T/TN)<0.1] to β2=0.23±0.02 [0.001<(1-T/TN)<0.01] in the immediate neighborhood of TN. In the diluted compound (TN=41.0±0.5 K) and below 0.9TN the magnetization due to the weak component follows the same behavior found for the pure system but closer to TN an almost linear dependence of the magnetization with temperature is observed.

  9. Critical magnetic fields of superconducting aluminum-substituted Ba{sub 8}Si{sub 42}Al{sub 4} clathrate

    SciTech Connect

    Li, Yang Garcia, Jose; Lu, Kejie; Shafiq, Basir; Franco, Giovanni; Lu, Junqiang; Rong, Bo; Chen, Ning; Liu, Yang; Liu, Lihua; Song, Bensheng; Wei, Yuping; Johnson, Shardai S.; Luo, Zhiping; Feng, Zhaosheng

    2015-06-07

    In recent years, efforts have been made to explore the superconductivity of clathrates containing crystalline frameworks of group-IV elements. The superconducting silicon clathrate is unusual in that the structure is dominated by strong sp{sup 3} covalent bonds between silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. This paper reports on critical magnetic fields of superconducting Al-substituted silicon clathrates, which were investigated by transport, ac susceptibility, and dc magnetization measurements in magnetic fields up to 90 kOe. For the sample Ba{sub 8}Si{sub 42}Al{sub 4}, the critical magnetic fields were measured to be H{sub C1} = 40.2 Oe and H{sub C2} = 66.4 kOe. The London penetration depth of 4360 Å and the coherence length 70 Å were obtained, whereas the estimated Ginzburg–Landau parameter of κ = 62 revealed that Ba{sub 8}Si{sub 42}Al{sub 4} is a strong type-II superconductor.

  10. The application of inelastic neutron scattering to explore the significance of a magnetic transition in an iron based Fischer-Tropsch catalyst that is active for the hydrogenation of CO.

    PubMed

    Warringham, Robbie; McFarlane, Andrew R; MacLaren, Donald A; Webb, Paul B; Tooze, Robert P; Taylor, Jon; Ewings, Russell A; Parker, Stewart F; Lennon, David

    2015-11-07

    An iron based Fischer-Tropsch synthesis catalyst is evaluated using CO hydrogenation at ambient pressure as a test reaction and is characterised by a combination of inelastic neutron scattering (INS), powder X-ray diffraction, temperature-programmed oxidation, Raman scattering, and transmission electron microscopy. The INS spectrum of the as-prepared bulk iron oxide pre-catalyst (hematite, α-Fe2O3) is distinguished by a relatively intense band at 810 cm(-1), which has previously been tentatively assigned as a magnon (spinon) feature. An analysis of the neutron scattering intensity of this band as a function of momentum transfer unambiguously confirms this assignment. Post-reaction, the spinon feature disappears and the INS spectrum is characterised by the presence of a hydrocarbonaceous overlayer. A role for the application of INS in magnetic characterisation of iron based FTS catalysts is briefly considered.

  11. The application of inelastic neutron scattering to explore the significance of a magnetic transition in an iron based Fischer-Tropsch catalyst that is active for the hydrogenation of CO

    SciTech Connect

    Warringham, Robbie; McFarlane, Andrew R.; Lennon, David; MacLaren, Donald A.; Webb, Paul B.; Tooze, Robert P.; Taylor, Jon; Ewings, Russell A.; Parker, Stewart F.

    2015-11-07

    An iron based Fischer-Tropsch synthesis catalyst is evaluated using CO hydrogenation at ambient pressure as a test reaction and is characterised by a combination of inelastic neutron scattering (INS), powder X-ray diffraction, temperature-programmed oxidation, Raman scattering, and transmission electron microscopy. The INS spectrum of the as-prepared bulk iron oxide pre-catalyst (hematite, α-Fe{sub 2}O{sub 3}) is distinguished by a relatively intense band at 810 cm{sup −1}, which has previously been tentatively assigned as a magnon (spinon) feature. An analysis of the neutron scattering intensity of this band as a function of momentum transfer unambiguously confirms this assignment. Post-reaction, the spinon feature disappears and the INS spectrum is characterised by the presence of a hydrocarbonaceous overlayer. A role for the application of INS in magnetic characterisation of iron based FTS catalysts is briefly considered.

  12. Neutron inelastic scattering investigation of the magnetic excitations in Cu{sub 2}Te{sub 2}O{sub 5}X{sub 2} (X=Br,Cl)

    SciTech Connect

    Crowe, S.J.; Majumdar, S.; Lees, M.R.; Paul, D. McK.; Bewley, R.I.; Levett, S.J.; Ritter, C.

    2005-06-01

    Neutron inelastic scattering investigations have been performed on the spin tetrahedral system Cu{sub 2}Te{sub 2}O{sub 5}X{sub 2} (X=Cl,Br). We report the observation of magnetic excitations with a dispersive component in both compounds, associated with the three-dimensional incommensurate magnetic order that develops below T{sub N}{sup Cl}=18.2 K and T{sub N}{sup Br}=11.4 K. The excitation in Cu{sub 2}Te{sub 2}O{sub 5}Cl{sub 2} softens as the temperature approaches T{sub N}{sup Cl}, leaving diffuse quasi-elastic scattering above the transition temperature. In the bromide, the excitations are present well above T{sub N}{sup Br}, which might be attributed to the presence of a degree of low dimensional correlations above T{sub N}{sup Br} in this compound.

  13. Magnetically induced Mie resonance in a magnetic sphere suspended in a ferrofluid.

    PubMed

    Bhatt, Hem; Patel, Rajesh; Mehta, R V

    2010-04-01

    Mie scattering functions for a magnetizable sphere whose relative refractive index is dependent on the externally applied magnetic field are computed for four different sizes of the sphere. It is found that Mie resonances are observed at certain critical fields when the incident light is polarized with its electric vector perpendicular to the applied field. The width of resonance as well as the critical fields shifts with the increase in size of the spheres. Results are compared with the experimentally observed scattering effects in a dispersion of magnetite spheres in a ferrofluid.

  14. Short- and long-range magnetic order in LaMnAsO

    DOE PAGES

    McGuire, Michael A.; Garlea, Vasile Ovidiu

    2016-02-02

    The magnetic properties of the layered oxypnictide LaMnAsO have been revisited using neutron scattering and magnetization measurements. The present measurements identify the Néel temperature TN = 360(1) K. Below TN the critical exponent describing the magnetic order parameter is β=0.33–0.35 , consistent with a three-dimensional Heisenberg model. Above this temperature, diffuse magnetic scattering indicative of short-range magnetic order is observed, and this scattering persists up to TSRO = 650(10) K. Morevoer, the magnetic susceptibility shows a weak anomaly at TSRO and no anomaly at TN. Analysis of the diffuse scattering data using a reverse Monte Carlo algorithm indicates that abovemore » TN nearly two-dimensional, short-range magnetic order is present with a correlation length of 9.3(3) Å within the Mn layers at 400 K. The inelastic scattering data reveal a spin gap of 3.5 meV in the long-range ordered state, and strong, low-energy (quasielastic) magnetic excitations emerging in the short-range ordered state. When we compared it with other related compounds correlates the distortion of the Mn coordination tetrahedra to the sign of the magnetic exchange along the layer-stacking direction, and suggests that short-range order above TN is a common feature in the magnetic behavior of layered Mn-based pnictides and oxypnictides.« less

  15. Short- and long-range magnetic order in LaMnAsO

    NASA Astrophysics Data System (ADS)

    McGuire, Michael A.; Garlea, V. Ovidiu

    2016-02-01

    The magnetic properties of the layered oxypnictide LaMnAsO have been revisited using neutron scattering and magnetization measurements. The present measurements identify the Néel temperature TN=360 (1 ) K. Below TN the critical exponent describing the magnetic order parameter is β =0.33 -0.35 , consistent with a three-dimensional Heisenberg model. Above this temperature, diffuse magnetic scattering indicative of short-range magnetic order is observed, and this scattering persists up to TSRO=650 (10 ) K. The magnetic susceptibility shows a weak anomaly at TSRO and no anomaly at TN. Analysis of the diffuse scattering data using a reverse Monte Carlo algorithm indicates that above TN nearly two-dimensional, short-range magnetic order is present with a correlation length of 9.3(3) Å within the Mn layers at 400 K. The inelastic scattering data reveal a spin gap of 3.5 meV in the long-range ordered state, and strong, low-energy (quasielastic) magnetic excitations emerging in the short-range ordered state. Comparison with other related compounds correlates the distortion of the Mn coordination tetrahedra to the sign of the magnetic exchange along the layer-stacking direction, and suggests that short-range order above TN is a common feature in the magnetic behavior of layered Mn-based pnictides and oxypnictides.

  16. Magnetic fusion energy plasma interactive and high heat flux components. Volume I. Technical assessment of the critical issues and problem areas in the plasma materials interaction field

    SciTech Connect

    Conn, R.W.; Gauster, W.B.; Heifetz, D.; Marmar, E.; Wilson, K.L.

    1984-01-01

    A technical assessment of the critical issues and problem areas in the field of plasma materials interactions (PMI) in magnetic fusion devices shows these problems to be central for near-term experiments, for intermediate-range reactor devices including D-T burning physics experiments, and for long-term reactor machines. Critical technical issues are ones central to understanding and successful operation of existing and near-term experiments/reactors or devices of great importance for the long run, i.e., ones which will require an extensive, long-term development effort and thus should receive attention now. Four subgroups were formed to assess the critical PMI issues along four major lines: (1) PMI and plasma confinement physics experiments; (2) plasma-edge modelling and theory; (3) surface physics; and (4) materials technology for in-vessel components and the first wall. The report which follows is divided into four major sections, one for each of these topics.

  17. Intergranular pinning potential and critical current in the magnetic superconductor Ru Sr2 Gd1.5 Ce0.5 Cu2 O10

    NASA Astrophysics Data System (ADS)

    Das Virgens, M. G.; García, S.; Continentino, M. A.; Ghivelder, L.

    2005-02-01

    The intergranular pinning potential U and the critical current density JC for polycrystalline RuSr2Gd1.5Ce0.5Cu2O10 ruthenate-cuprate were determined at zero magnetic field and temperature through the frequency shift in the peak of the imaginary part of the ac magnetic susceptibility, χ″ . A critical state model, including a flux creep term, was found to accurately describe the χ″ behavior. The obtained values, U(H=0,T=0)≅30meV and JC(H=0,T=0)≅110A/cm2 are about two orders of magnitude and four times lower, respectively, in comparison with the high- TC cuprate YBa2Cu3O7 . These results were ascribed to the effects of the Ru magnetization on the connectivity of the weak-linked network, giving an intrinsic local field at the junctions of ˜15Oe . The impact on JC is less intense because of the small average grain radius (˜1μm) . The intragranular London penetration length at T=0[λL(0)≅2μm] was derived using a Kim-type expression for the field dependence of JC . A possible source for the large value of λL in comparison to the high- Tc cuprates is suggested to come from a strong intragrain granularity, due to structural domains of coherent-rotated RuO6 octahedra separated by antiphase boundaries.

  18. Magnetic exchange interactions and critical temperature of the nanolaminate M n2GaC from first-principles supercell methods

    NASA Astrophysics Data System (ADS)

    Thore, A.; Dahlqvist, M.; Alling, B.; Rosen, J.

    2016-02-01

    In this work, we employ and critically evaluate a first-principles approach based on supercell calculations for predicting the magnetic critical order-disorder temperature Tc. As a model material we use the recently discovered nanolaminate M n2GaC . First, we derive the exchange interaction parameters Ji j between pairs of Mn atoms on sites i and j of the bilinear Heisenberg Hamiltonian using the novel magnetic direct cluster averaging method (MDCA), and then compare the J's from the MDCA calculations to the same parameters calculated using the Connolly-Williams method. We show that the two methods yield closely matching results, but observe that the MDCA method is computationally less effective when applied to highly ordered phases such as M n2GaC . Secondly, Monte Carlo simulations are used to derive the magnetic energy, specific heat, and Tc. For M n2GaC , we find Tc=660 K . The uncertainty in the calculated Tc caused by possible uncertainties in the J's is discussed and exemplified in our case by an analysis of the impact of the statistical uncertainties of the MDCA-derived J's , resulting in a Tc distribution with a standard deviation of 133 K.

  19. Stripe order of La1.64Eu0.2Sr0.16CuO4 in magnetic fields studied by resonant soft x-ray scattering

    NASA Astrophysics Data System (ADS)

    Zwiebler, M.; Schierle, E.; Weschke, E.; Büchner, B.; Revcolevschi, A.; Ribeiro, Patrick; Geck, J.; Fink, J.

    2016-10-01

    We present results on the magnetic field dependence of the stripe order in La1.64Eu0.2Sr0.16CuO4 (LESCO). Using resonant soft x-ray scattering at the oxygen K edge to probe the (0.259,0,0.648) superlattice reflection, which is commonly associated to charge stripes, we found no pronounced difference in the wave vector, peak widths, and integrated intensity for magnetic fields up to B =6 T. This is in strong contrast to the behavior observed for La1.875Sr0.125CuO4 , where a stabilization of the charge modulation in high magnetic fields has been demonstrated.

  20. MAGNETS

    DOEpatents

    Hofacker, H.B.

    1958-09-23

    This patent relates to nmgnets used in a calutron and more particularly to means fur clamping an assembly of magnet coils and coil spacers into tightly assembled relation in a fluid-tight vessel. The magnet comprises windings made up of an assembly of alternate pan-cake type coils and spacers disposed in a fluid-tight vessel. At one end of the tank a plurality of clamping strips are held firmly against the assembly by adjustable bolts extending through the adjacent wall. The foregoing arrangement permits taking up any looseness which may develop in the assembly of coils and spacers.