Dipolar magnetism in ordered and disordered low-dimensional nanoparticle assemblies

DEFF Research Database (Denmark)

Varón, M.; Beleggia, M; Kasama, T

2013-01-01

order at ambient temperature in assemblies of closely-spaced nanoparticles with magnetic moments of ≥ 100 μ(B). Here we use electron holography with sub-particle resolution to reveal the correlation between particle arrangement and magnetic order in self-assembled 1D and quasi-2D arrangements of 15 nm...... cobalt nanoparticles. In the initial states, we observe dipolar ferromagnetism, antiferromagnetism and local flux closure, depending on the particle arrangement. Surprisingly, after magnetic saturation, measurements and numerical simulations show that overall ferromagnetic order exists in the present...... nanoparticle assemblies even when their arrangement is completely disordered. Such direct quantification of the correlation between topological and magnetic order is essential for the technological exploitation of magnetic quasi-2D nanoparticle assemblies....

Hidden magnetism in periodically modulated one dimensional dipolar fermions

Science.gov (United States)

Fazzini, S.; Montorsi, A.; Roncaglia, M.; Barbiero, L.

2017-12-01

The experimental realization of time-dependent ultracold lattice systems has paved the way towards the implementation of new Hubbard-like Hamiltonians. We show that in a one-dimensional two-components lattice dipolar Fermi gas the competition between long range repulsion and correlated hopping induced by periodically modulated on-site interaction allows for the formation of hidden magnetic phases, with degenerate protected edge modes. The magnetism, characterized solely by string-like nonlocal order parameters, manifests in the charge and/or in the spin degrees of freedom. Such behavior is enlighten by employing Luttinger liquid theory and numerical methods. The range of parameters for which hidden magnetism is present can be reached by means of the currently available experimental setups and probes.

Dynamic effects of dipolar interactions on the magnetic behavior of magnetite nanoparticles

Science.gov (United States)

Allia, Paolo; Tiberto, Paola

2011-12-01

Isothermal magnetization and initial dc susceptibility of spheroidal, nearly monodisperse magnetite nanoparticles (typical diameter: 8 nm) prepared by a standard thermo-chemical route have been measured between 10 and 300 K. The samples contained magnetite nanoparticles in the form of either a dried powder (each nanoparticle being surrounded by a stable oleic acid shell as a result of the preparation procedure) or a solid dispersion in PEGDA-600 polymer; different nanoparticle (NP) concentrations in the polymer were studied. In all samples the NPs were not tightly agglomerated nor their ferromagnetic cores were directly touching. The high-temperature inverse magnetic susceptibility is always found to follow a linear law as a function of T, crossing the horizontal axis at negative temperatures ranging from 175 to about 1,000 K. The deviation from the standard superparamagnetic behavior is related to dipolar interaction among NPs; however, a careful analysis makes it hard to conclude that such a behavior originates from a dominant antiferromagnetic character of the interaction. The results are well explained considering that the studied samples are in the interacting superparamagnetic (ISP) regime. The ISP model is basically a mean field theory which allows one to straightforwardly account for the role of magnetic dipolar interaction in a NP system. The model predicts the existence of specific scaling laws for the reduced magnetization which have been confirmed in all studied samples. The interaction of each magnetic dipole moment with the local, random dipolar field produced by the other dipoles results in the presence of a large fluctuating energy term whose magnitude is comparable to the static barrier for magnetization reversal/rotation related to magnetic anisotropy. On the basis of the existing theories on thermal crossing of a barrier whose height randomly fluctuates in time it is predicted that the rate of barrier crossing is substantially driven by the rate

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

Science.gov (United States)

Chang, Zhiwei; Halle, Bertil

2017-08-01

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

Dispersion characteristics of electromagnetic waves in dipolar (m=±1) modes travelling along a magnetized plasma column

International Nuclear Information System (INIS)

Benova, E.; Ghanashev, I.; Zhelyazkov, I.

1992-01-01

The modelling of isotropic plasma columns sustained by travelling electromagnetic waves in the dipolar mode (angular dependence exp imφ, m=±1) shows that the m=±1 modes have identical dispersion characteristics. In the presence of an external static magnetic field, however, the modes behave rather differently. This observation arose in studying the axial structures of magnetized plasma columns surrounded by vacuum and produced by travelling electromagnetic waves in the dipolar modes. We examine the propagation of electromagnetic waves along a homogeneous cold plasma column of radius R and electron number density n immersed in an axial constant magnetic field. (author) 3 refs., 3 figs

The role of magnetic field fluctuations in nonadiabatic acceleration of ions during dipolarization

Science.gov (United States)

Ono, Y.; Nosé, M.; Christon, S. P.; Lui, A. T. Y.

2009-05-01

We statistically examine changes in the composition of two different ion species, proton and oxygen ions, in the near-Earth plasma sheet (X = -16 R E ˜ -6 R E ) during substorm-associated dipolarization. We use 10 years of energetic (9-212 keV/e) ion data obtained by the suprathermal ion composition spectrometer (STICS) sensor of the energetic particles and ion composition (EPIC) instrument on board the Geotail spacecraft. The results are as follows: (1) Although the percentage increase in the energy density of O+ ions before and after a dipolarization exceeds that of H+ ions in the low-energy range (9-36 keV/e), this property is not evident in the high-energy range (56-212 keV/e); (2) the energy spectrum of H+ and that of O+ become harder after dipolarization in almost all events; and (3) in some events the energy spectrum of O+ becomes harder than that of H+ as reported by previous studies, and, importantly, in other events, the spectrum of H+ becomes harder than that of O+. In order to investigate what mechanism causes these observational results, we focus on magnetic field fluctuations during dipolarization. It is found that the increase of the spectrum slope is positively correlated with the power of waves whose frequencies are close to the gyrofrequency of H+ or O+, respectively (the correlation coefficient is 0.48 for H+ and 0.68 for O+). In conclusion, ions are nonadiabatically accelerated by the electric field induced by the magnetic field fluctuations whose frequencies are close to their gyrofrequencies.

Imaging using long range dipolar field effects

International Nuclear Information System (INIS)

Gutteridge, Sarah

2002-01-01

The work in this thesis has been undertaken by the author, except where indicated in reference, within the Magnetic Resonance Centre, at the University of Nottingham during the period from October 1998 to March 2001. This thesis details the different characteristics of the long range dipolar field and its application to magnetic resonance imaging. The long range dipolar field is usually neglected in nuclear magnetic resonance experiments, as molecular tumbling decouples its effect at short distances. However, in highly polarised samples residual long range components have a significant effect on the evolution of the magnetisation, giving rise to multiple spin echoes and unexpected quantum coherences. Three applications utilising these dipolar field effects are documented in this thesis. The first demonstrates the spatial sensitivity of the signal generated via dipolar field effects in structured liquid state samples. The second utilises the signal produced by the dipolar field to create proton spin density maps. These maps directly yield an absolute value for the water content of the sample that is unaffected by relaxation and any RF inhomogeneity or calibration errors in the radio frequency pulses applied. It has also been suggested that the signal generated by dipolar field effects may provide novel contrast in functional magnetic resonance imaging. In the third application, the effects of microscopic susceptibility variation on the signal are studied and the relaxation rate of the signal is compared to that of a conventional spin echo. (author)

Anisotropic relaxation dynamics in a dipolar Fermi gas driven out of equilibrium

DEFF Research Database (Denmark)

Aikawa, K.; Frisch, A.; Mark, M.

2014-01-01

We report on the observation of a large anisotropy in the rethermalization dynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our system consists of an ultracold sample of strongly magnetic $^{167}$Er fermions, spin-polarized in the lowest Zeeman sublevel. In this system, elastic...

Energetic electron injections and dipolarization events in Mercury's magnetotail: Substorm dynamics

Science.gov (United States)

Dewey, R. M.; Slavin, J. A.; Raines, J. M.; Imber, S.; Baker, D. N.; Lawrence, D. J.

2017-12-01

Despite its small size, Mercury's terrestrial-like magnetosphere experiences brief, yet intense, substorm intervals characterized by features similar to at Earth: loading/unloading of the tail lobes with open magnetic flux, dipolarization of the magnetic field at the inner edge of the plasma sheet, and, the focus of this presentation, energetic electron injection. We use the Gamma-Ray Spectrometer's high-time resolution (10 ms) energetic electron measurements to determine the relationship between substorm activity and energetic electron injections coincident with dipolarization fronts in the magnetotail. These dipolarizations were detected on the basis of their rapid ( 2 s) increase in the northward component of the tail magnetic field (ΔBz 30 nT), which typically persists for 10 s. We estimate the typical flow channel to be 0.15 RM, planetary convection speed of 750 km/s, cross-tail potential drop of 7 kV, and flux transport of 0.08 MWb for each dipolarization event, suggesting multiple simultaneous and sequential dipolarizations are required to unload the >1 MWb of magnetic flux typically returned to the dayside magnetosphere during a substorm interval. Indeed, while we observe most dipolarization-injections to be isolated or in small chains of events (i.e., 1-3 events), intervals of sawtooth-like injections with >20 sequential events are also present. The typical separation between dipolarization-injection events is 10 s. Magnetotail dipolarization, in addition to being a powerful source of electron acceleration, also plays a significant role in the substorm process at Mercury.

Strong Interlayer Magnon-Magnon Coupling in Magnetic Metal-Insulator Hybrid Nanostructures

Science.gov (United States)

Chen, Jilei; Liu, Chuanpu; Liu, Tao; Xiao, Yang; Xia, Ke; Bauer, Gerrit E. W.; Wu, Mingzhong; Yu, Haiming

2018-05-01

We observe strong interlayer magnon-magnon coupling in an on-chip nanomagnonic device at room temperature. Ferromagnetic nanowire arrays are integrated on a 20-nm-thick yttrium iron garnet (YIG) thin film strip. Large anticrossing gaps up to 1.58 GHz are observed between the ferromagnetic resonance of the nanowires and the in-plane standing spin waves of the YIG film. Control experiments and simulations reveal that both the interlayer exchange coupling and the dynamical dipolar coupling contribute to the observed anticrossings. The coupling strength is tunable by the magnetic configuration, allowing the coherent control of magnonic devices.

Evidence of magnetic dipolar interaction in micrometric powders of the Fe50Mn10Al40 system: Melted alloys

International Nuclear Information System (INIS)

Pérez Alcázar, G.A.; Zamora, L.E.; Tabares, J.A.; Piamba, J.F.; González, J.M.; Greneche, J.M.; Martinez, A.; Romero, J.J.; Marco, J.F.

2013-01-01

Powders of melted disordered Fe 50 Mn 10 Al 40 alloy were separated at different mean particle sizes as well as magnetically and structurally characterized. All the samples are BCC and show the same nanostructure. Particles larger than 250 μm showed a lamellar shape compared to smaller particles, which exhibited a more regular form. All the samples are ferromagnetic at room temperature and showed reentrant spin-glass (RSG) and superparamagnetic (SP)-like behaviors between 30 and 60 K and 265 and > 280 K, respectively, as a function of frequency and particle size. The freezing temperature increases with increasing particle size while the blocking one decreases with particle size. The origin of these magnetic phenomena relies in the internal disordered character of samples and the competitive interaction of Fe and Mn atoms. The increase of their critical freezing temperature with increasing mean particle size is due to the increase of the magnetic dipolar interaction between the magnetic moment of each particle with the field produced by the other magnetic moments of their surrounding particles. - Highlights: ► The effect of particle size in microsized powders of Fe 50 Mn 10 Al 40 melted disordered alloy is studied. ► Dipolar magnetic interaction between particles exists and this changes with the particle size. ► For all the particle sizes the reentrant spin- glass and the superparamagnetic-like phases exist. ► RSG and SP critical temperatures increase with increasing the dipolar magnetic interaction (the mean particle size).

Ordering and thermal excitations in dipolar coupled single domain magnet arrays (Presentation Recording)

Science.gov (United States)

Östman, Erik; Arnalds, Unnar; Kapaklis, Vassilios; Hjörvarsson, Björgvin

2015-09-01

For a small island of a magnetic material the magnetic state of the island is mainly determined by the exchange interaction and the shape anisotropy. Two or more islands placed in close proximity will interact through dipolar interactions. The state of a large system will thus be dictated by interactions at both these length scales. Enabling internal thermal fluctuations, e.g. by the choice of material, of the individual islands allows for the study of thermal ordering in extended nano-patterned magnetic arrays [1,2]. As a result nano-magnetic arrays represent an ideal playground for the study of physical model systems. Here we present three different studies all having used magneto-optical imaging techniques to observe, in real space, the order of the systems. The first study is done on a square lattice of circular islands. The remanent magnetic state of each island is a magnetic vortex structure and we can study the temperature dependence of the vortex nucleation and annihilation fields [3]. The second are long chains of dipolar coupled elongated islands where the magnetization direction in each island only can point in one of two possible directions. This creates a system which in many ways mimics the Ising model [4] and we can relate the correlation length to the temperature. The third one is a spin ice system where elongated islands are placed in a square lattice. Thermal excitations in such systems resemble magnetic monopoles [2] and we can investigate their properties as a function of temperature and lattice parameters. [1] V. Kapaklis et al., New J. Phys. 14, 035009 (2012) [2] V. Kapaklis et al., Nature Nanotech 9, 514(2014) [3] E. Östman et al.,New J. Phys. 16, 053002 (2014) [4] E. Östman et al.,Thermal ordering in mesoscopic Ising chains, In manuscript.

Nuclear dipolar magnetism around one microkelvin in calciumhydroxide

International Nuclear Information System (INIS)

Marks, J.

1985-01-01

This thesis is devoted to a study of dipolar magnetism of the proton spins in Ca(OH) 2 . First, cooling techniques are described. The energy of different spin configurations are calculated in the Weiss-field approximation. Crystallographic characteristics of Ca(OH) 2 are described, as well as a method to produce monocrystals and a method for crystal doping using 1.5 MeV electron beams. It is shown that the polarization mechanism of the proton spins in Ca(OH) 2 doped with O 2 - centra is the 'Solid Effect'. Susceptibility measurements are presented as a function of the polarization. Results imply that both at positive and at negative temperatures state ordering sets in, characterized by a plateau in the susceptibility. (Auth/G.J.P.)

Synchronization of spin torque nano-oscillators through dipolar interactions

International Nuclear Information System (INIS)

Chen, Hao-Hsuan; Wu, Jong-Ching; Horng, Lance; Lee, Ching-Ming; Chang, Ching-Ray; Chang, Jui-Hang

2014-01-01

In an array of spin-torque nano-oscillators (STNOs) that combine a perpendicular polarized fixed layer with strong in-plane anisotropy in the free layers, magnetic dipolar interactions can effectively phase-lock the array, thus further enhancing the power of the output microwave signals. We perform a qualitative analysis of the synchronization of an array based on the Landau-Lifshitz-Gilbert equation, with a spin-transfer torque that assumes strong in-plane anisotropy. Finally, we present the numerical results for four coupled STNOs to provide further evidence for the proposed theory

Synchronization of spin torque nano-oscillators through dipolar interactions

Energy Technology Data Exchange (ETDEWEB)

Chen, Hao-Hsuan, E-mail: d95222014@ntu.edu.tw; Wu, Jong-Ching, E-mail: phjcwu@cc.ncue.edu.tw; Horng, Lance [Department of Physics, National Changhua University of Education, Changhua 500, Taiwan (China); Lee, Ching-Ming [Graduate School of Materials Science, National Yunlin University of Science and Technology, Douliou, 64002, Taiwan (China); Chang, Ching-Ray, E-mail: crchang@phys.ntu.edu.tw; Chang, Jui-Hang [Department of Physics and Center for Quantum Sciences and Engineering, National Taiwan University, Taipei 10617, Taiwan (China)

2014-04-07

In an array of spin-torque nano-oscillators (STNOs) that combine a perpendicular polarized fixed layer with strong in-plane anisotropy in the free layers, magnetic dipolar interactions can effectively phase-lock the array, thus further enhancing the power of the output microwave signals. We perform a qualitative analysis of the synchronization of an array based on the Landau-Lifshitz-Gilbert equation, with a spin-transfer torque that assumes strong in-plane anisotropy. Finally, we present the numerical results for four coupled STNOs to provide further evidence for the proposed theory.

Electron dynamics during substorm dipolarization in Mercury's magnetosphere

Directory of Open Access Journals (Sweden)

D. C. Delcourt

2005-11-01

Full Text Available We examine the nonlinear dynamics of electrons during the expansion phase of substorms at Mercury using test particle simulations. A simple model of magnetic field line dipolarization is designed by rescaling a magnetic field model of the Earth's magnetosphere. The results of the simulations demonstrate that electrons may be subjected to significant energization on the time scale (several seconds of the magnetic field reconfiguration. In a similar manner to ions in the near-Earth's magnetosphere, it is shown that low-energy (up to several tens of eV electrons may not conserve the second adiabatic invariant during dipolarization, which leads to clusters of bouncing particles in the innermost magnetotail. On the other hand, it is found that, because of the stretching of the magnetic field lines, high-energy electrons (several keVs and above do not behave adiabatically and possibly experience meandering (Speiser-type motion around the midplane. We show that dipolarization of the magnetic field lines may be responsible for significant, though transient, (a few seconds precipitation of energetic (several keVs electrons onto the planet's surface. Prominent injections of energetic trapped electrons toward the planet are also obtained as a result of dipolarization. These injections, however, do not exhibit short-lived temporal modulations, as observed by Mariner-10, which thus appear to follow from a different mechanism than a simple convection surge.

Asymptotic behavior of local dipolar fields in thin films

Energy Technology Data Exchange (ETDEWEB)

Bowden, G.J., E-mail: gjb@phys.soton.ac.uk [School of Physics and Astronomy, University of Southampton, SO17 1BJ (United Kingdom); Stenning, G.B.G., E-mail: Gerrit.vanderlaan@diamond.ac.uk [Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom); Laan, G. van der, E-mail: gavin.stenning@stfc.ac.uk [ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot OX11 0QX (United Kingdom)

2016-10-15

A simple method, based on layer by layer direct summation, is used to determine the local dipolar fields in uniformly magnetized thin films. The results show that the dipolar constants converge ~1/m where the number of spins in a square film is given by (2m+1){sup 2}. Dipolar field results for sc, bcc, fcc, and hexagonal lattices are presented and discussed. The results can be used to calculate local dipolar fields in films with either ferromagnetic, antiferromagnetic, spiral, exponential decay behavior, provided the magnetic order only changes normal to the film. Differences between the atomistic (local fields) and macroscopic fields (Maxwellian) are also examined. For the latter, the macro B-field inside the film is uniform and falls to zero sharply outside, in accord with Maxwell boundary conditions. In contrast, the local field for the atomistic point dipole model is highly non-linear inside and falls to zero at about three lattice spacing outside the film. Finally, it is argued that the continuum field B (used by the micromagnetic community) and the local field B{sub loc}(r) (used by the FMR community) will lead to differing values for the overall demagnetization energy. - Highlights: • Point-dipolar fields in uniformly magnetized thin films are characterized by just three numbers. • Maxwell's boundary condition is partially violated in the point-dipole approximation. • Asymptotic values of point dipolar fields in circular monolayers scale as π/r.

Designing Hysteresis with Dipolar Chains

Science.gov (United States)

Concha, Andrés; Aguayo, David; Mellado, Paula

2018-04-01

Materials that have hysteretic response to an external field are essential in modern information storage and processing technologies. A myriad of magnetization curves of several natural and artificial materials have previously been measured and each has found a particular mechanism that accounts for it. However, a phenomenological model that captures all the hysteresis loops and at the same time provides a simple way to design the magnetic response of a material while remaining minimal is missing. Here, we propose and experimentally demonstrate an elementary method to engineer hysteresis loops in metamaterials built out of dipolar chains. We show that by tuning the interactions of the system and its geometry we can shape the hysteresis loop which allows for the design of the softness of a magnetic material at will. Additionally, this mechanism allows for the control of the number of loops aimed to realize multiple-valued logic technologies. Our findings pave the way for the rational design of hysteretical responses in a variety of physical systems such as dipolar cold atoms, ferroelectrics, or artificial magnetic lattices, among others.

Ground state configurations in antiferromagnetic ultrathin films with dipolar anisotropy

International Nuclear Information System (INIS)

León, H.

2013-01-01

The formalism developed in a previous work to calculate the dipolar energy in quasi-two-dimensional crystals with ferromagnetic order is now extended to collinear antiferromagnetic order. Numerical calculations of the dipolar energy are carried out for systems with tetragonally distorted fcc [001] structures, the case of NiO and MnO ultrathin film grown in non-magnetic substrates, where the magnetic phase is a consequence of superexchange and dipolar interactions. The employed approximation allows to demonstrate that dipolar coupling between atomic layers is responsible for the orientation of the magnetization when it differs from the one in a single layer. The ground state energy of a given NiO or MnO film is found to depend not only on the strain, but also on how much the interlayer separation and the 2D lattice constant are changed with respect to the ideal values corresponding to the non-distorted cubic structure. Nevertheless, it is shown that the orientation of the magnetization in the magnetic phase of any of these films is determined by the strain exclusively. A striped phase with the magnetization along the [112 ¯ ] direction appears as the ground state configuration of NiO and MnO ultrathin films. In films with equally oriented stripes along the layers this magnetic phase is twofold degenerate, while in films with multidomain layers it is eightfold degenerate. These results are not in contradiction with experimentally observed out-of-plane or in-plane magnetization of striped phases in NiO and MnO ultrathin films. - Highlights: ► Dipolar energy in collinear antiferromagnetic ultrathin films is calculated. ► Numerical results are presented for distorted fcc [001] structures. ► The lowest energy of a system depends on how the tetragonal distortion is achieved. ► A striped phase with magnetization in the [112 ¯ ] direction is the ground state. ► In multidomain NiO and MnO films it is eightfold degenerate.

Large-scale flows, sheet plumes and strong magnetic fields in a rapidly rotating spherical dynamo

Science.gov (United States)

Takahashi, F.

2011-12-01

Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell is investigated. Bearing dynamos of the Eartn and planets in mind, the Ekman number is set at 10-5. A strong dipolar solution with magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small viscosity and inertia with the strong magnetic field, convection structure consists of a few large-scale retrograde flows in the azimuthal direction and sporadic thin sheet-like plumes. The magnetic field is amplified through stretching of magnetic lines, which occurs typically through three types of flow: the retrograde azimuthal flow near the outer boundary, the downwelling flow of the sheet plume, and the prograde azimuthal flow near the rim of the tangent cylinder induced by the downwelling flow. It is found that either structure of current loops or current sheets is accompanied in each flow structure. Current loops emerge as a result of stretching the magnetic lines along the magnetic field, wheres the current sheets are formed to counterbalance the Coriolis force. Convection structure and processes of magnetic field generation found in the present model are distinct from those in models at larger/smaller Ekman number.

Observation of roton mode population in a dipolar quantum gas

Science.gov (United States)

Chomaz, L.; van Bijnen, R. M. W.; Petter, D.; Faraoni, G.; Baier, S.; Becher, J. H.; Mark, M. J.; Wächtler, F.; Santos, L.; Ferlaino, F.

2018-05-01

The concept of a roton, a special kind of elementary excitation forming a minimum of energy at finite momentum, has been essential for the understanding of the properties of superfluid 4He (ref. 1). In quantum liquids, rotons arise from the strong interparticle interactions, whose microscopic description remains debated2. In the realm of highly controllable quantum gases, a roton mode has been predicted to emerge due to magnetic dipole-dipole interactions despite their weakly interacting character3. This prospect has raised considerable interest4-12; yet roton modes in dipolar quantum gases have remained elusive to observations. Here we report experimental and theoretical studies of the momentum distribution in Bose-Einstein condensates of highly magnetic erbium atoms, revealing the existence of the long-sought roton mode. Following an interaction quench, the roton mode manifests itself with the appearance of symmetric peaks at well-defined finite momentum. The roton momentum follows the predicted geometrical scaling with the inverse of the confinement length along the magnetization axis. From the growth of the roton population, we probe the roton softening of the excitation spectrum in time and extract the corresponding imaginary roton gap. Our results provide a further step in the quest towards supersolidity in dipolar quantum gases13.

Existence of solitary waves in dipolar quantum gases

KAUST Repository

Antonelli, Paolo; Sparber, Christof

2011-01-01

We study a nonlinear Schrdinger equation arising in the mean field description of dipolar quantum gases. Under the assumption of sufficiently strong dipolar interactions, the existence of standing waves, and hence solitons, is proved together with some of their properties. This gives a rigorous argument for the possible existence of solitary waves in BoseEinstein condensates, which originate solely due to the dipolar interaction between the particles. © 2010 Elsevier B.V. All rights reserved.

Existence of solitary waves in dipolar quantum gases

KAUST Repository

Antonelli, Paolo

2011-02-01

We study a nonlinear Schrdinger equation arising in the mean field description of dipolar quantum gases. Under the assumption of sufficiently strong dipolar interactions, the existence of standing waves, and hence solitons, is proved together with some of their properties. This gives a rigorous argument for the possible existence of solitary waves in BoseEinstein condensates, which originate solely due to the dipolar interaction between the particles. © 2010 Elsevier B.V. All rights reserved.

Laser induced magnetization switching in a TbFeCo ferrimagnetic thin film: discerning the impact of dipolar fields, laser heating and laser helicity by XPEEM

International Nuclear Information System (INIS)

Gierster, L.; Ünal, A.A.; Pape, L.; Radu, F.; Kronast, F.

2015-01-01

We investigate laser induced magnetic switching in a ferrimagnetic thin film of Tb_2_2Fe_6_9Co_9 by PEEM. Using a small laser beam with a spot size of 3–5 µm in diameter in combination with high resolution magnetic soft X-ray microscopy we are able to discriminate between different effects that govern the microscopic switching process, namely the influence of the laser heating, of the helicity dependent momentum transfer, and of the dipolar coupling. Applying a sequence of femtosecond laser pulses to a previously saturated TbFeCo film leads to the formation of ring shaped magnetic structures in which all three effects can be observed. Laser helicity assisted switching is only observed in a narrow region within the Gaussian profile of the laser spot. Whereas in the center of the laser spot we find clear evidence for thermal demagnetization and in the outermost areas magnetic switching is determined by dipolar coupling with the surrounding film. Our findings demonstrate that by reducing the laser spot size the influence of dipolar coupling on laser induced switching is becoming increasingly important. - Highlights: • With a new PEEM sample holder a laser spot size of 3–5 µm in diameter is reached. • Spatial resolved imaging of laser induced magnetization reversal. • A single femtosecond laser pulse leads to a multi-domain state in TbFeCo. • A pulse sequence results in a ring-shaped magnetic pattern caused by dipolar fields. • Laser helicity dependent effects appear only in a narrow fluence region.

Evidence of magnetic dipolar interaction in micrometric powders of the Fe{sub 50}Mn{sub 10}Al{sub 40} system: Melted alloys

Energy Technology Data Exchange (ETDEWEB)

Perez Alcazar, G.A., E-mail: gpgeperez@gmail.com [Departamento de Fisica, Universidad del Valle, A. A. 25360, Cali (Colombia); Unidad Asociada ICMM-IMA, Apdo. 155, 28230 Las Rozas, Madrid (Spain); Zamora, L.E. [Departamento de Fisica, Universidad del Valle, A. A. 25360, Cali (Colombia); Unidad Asociada ICMM-IMA, Apdo. 155, 28230 Las Rozas, Madrid (Spain); Tabares, J.A.; Piamba, J.F. [Departamento de Fisica, Universidad del Valle, A. A. 25360, Cali (Colombia); Gonzalez, J.M. [Unidad Asociada ICMM-IMA, Apdo. 155, 28230 Las Rozas, Madrid (Spain); Greneche, J.M. [LUNAM, Universite du Maine, Institut des Molecules et Materiaux du Mans, UMR CNRS 6283, 72085 Le Mans Cedex 9 (France); Martinez, A. [Instituto de Magnetismo Aplicado, P.O. Box 155, 28230 Las Rozas (Spain); Romero, J.J. [Instituto de Ceramica y Vidrio, CSIC, C/Kelsen 5, 28049, Madrid (Spain); Marco, J.F. [Instituto de Quimica Fisica Rocasolano, CSIC, C/Serrano 119, 28006 Madrid (Spain)

2013-02-15

Powders of melted disordered Fe{sub 50}Mn{sub 10}Al{sub 40} alloy were separated at different mean particle sizes as well as magnetically and structurally characterized. All the samples are BCC and show the same nanostructure. Particles larger than 250 {mu}m showed a lamellar shape compared to smaller particles, which exhibited a more regular form. All the samples are ferromagnetic at room temperature and showed reentrant spin-glass (RSG) and superparamagnetic (SP)-like behaviors between 30 and 60 K and 265 and > 280 K, respectively, as a function of frequency and particle size. The freezing temperature increases with increasing particle size while the blocking one decreases with particle size. The origin of these magnetic phenomena relies in the internal disordered character of samples and the competitive interaction of Fe and Mn atoms. The increase of their critical freezing temperature with increasing mean particle size is due to the increase of the magnetic dipolar interaction between the magnetic moment of each particle with the field produced by the other magnetic moments of their surrounding particles. - Highlights: Black-Right-Pointing-Pointer The effect of particle size in microsized powders of Fe{sub 50}Mn{sub 10}Al{sub 40} melted disordered alloy is studied. Black-Right-Pointing-Pointer Dipolar magnetic interaction between particles exists and this changes with the particle size. Black-Right-Pointing-Pointer For all the particle sizes the reentrant spin- glass and the superparamagnetic-like phases exist. Black-Right-Pointing-Pointer RSG and SP critical temperatures increase with increasing the dipolar magnetic interaction (the mean particle size).

Nuclear magnetic resonance studies of quadrupolar nuclei and dipolar field effects

Energy Technology Data Exchange (ETDEWEB)

Urban, Jeffry Todd [Univ. of California, Berkeley, CA (United States)

2004-01-01

Experimental and theoretical research conducted in two areas in the field of nuclear magnetic resonance (NMR) spectroscopy is presented: (1) studies of the coherent quantum-mechanical control of the angular momentum dynamics of quadrupolar (spin I > 1/2) nuclei and its application to the determination of molecular structure; and (2) applications of the long-range nuclear dipolar field to novel NMR detection methodologies.The dissertation is organized into six chapters. The first two chapters and associated appendices are intended to be pedagogical and include an introduction to the quantum mechanical theory of pulsed NMR spectroscopy and the time dependent theory of quantum mechanics. The third chapter describes investigations of the solid-state multiple-quantum magic angle spinning (MQMAS) NMR experiment applied to I = 5/2 quadrupolar nuclei. This work reports the use of rotary resonance-matched radiofrequency irradiation for sensitivity enhancement of the I = 5/2 MQMAS experiment. These experiments exhibited certain selective line narrowing effects which were investigated theoretically.The fourth chapter extends the discussion of multiple quantum spectroscopy of quadrupolar nuclei to a mostly theoretical study of the feasibility of enhancing the resolution of nitrogen-14 NMR of large biomolecules in solution via double-quantum spectroscopy. The fifth chapter continues to extend the principles of multiple quantum NMR spectroscopy of quadrupolar nuclei to make analogies between experiments in NMR/nuclear quadrupolar resonance (NQR) and experiments in atomic/molecular optics (AMO). These analogies are made through the Hamiltonian and density operator formalism of angular momentum dynamics in the presence of electric and magnetic fields.The sixth chapter investigates the use of the macroscopic nuclear dipolar field to encode the NMR spectrum of an analyte nucleus indirectly in the magnetization of a sensor nucleus. This technique could potentially serve as an

Nuclear magnetic resonance studies of quadrupolar nuclei and dipolar field effects

International Nuclear Information System (INIS)

Urban, Jeffry Todd

2004-01-01

Experimental and theoretical research conducted in two areas in the field of nuclear magnetic resonance (NMR) spectroscopy is presented: (1) studies of the coherent quantum-mechanical control of the angular momentum dynamics of quadrupolar (spin I > 1/2) nuclei and its application to the determination of molecular structure; and (2) applications of the long-range nuclear dipolar field to novel NMR detection methodologies.The dissertation is organized into six chapters. The first two chapters and associated appendices are intended to be pedagogical and include an introduction to the quantum mechanical theory of pulsed NMR spectroscopy and the time dependent theory of quantum mechanics. The third chapter describes investigations of the solid-state multiple-quantum magic angle spinning (MQMAS) NMR experiment applied to I 5/2 quadrupolar nuclei. This work reports the use of rotary resonance-matched radiofrequency irradiation for sensitivity enhancement of the I = 5/2 MQMAS experiment. These experiments exhibited certain selective line narrowing effects which were investigated theoretically.The fourth chapter extends the discussion of multiple quantum spectroscopy of quadrupolar nuclei to a mostly theoretical study of the feasibility of enhancing the resolution of nitrogen-14 NMR of large biomolecules in solution via double-quantum spectroscopy. The fifth chapter continues to extend the principles of multiple quantum NMR spectroscopy of quadrupolar nuclei to make analogies between experiments in NMR/nuclear quadrupolar resonance (NQR) and experiments in atomic/molecular optics (AMO). These analogies are made through the Hamiltonian and density operator formalism of angular momentum dynamics in the presence of electric and magnetic fields.The sixth chapter investigates the use of the macroscopic nuclear dipolar field to encode the NMR spectrum of an analyte nucleus indirectly in the magnetization of a sensor nucleus. This technique could potentially serve as an encoding

Role of dipolar interactions on morphologies and tunnel magnetoresistance in assemblies of magnetic nanoparticles

Science.gov (United States)

Anand, Manish; Carrey, Julian; Banerjee, Varsha

2018-05-01

We undertake comprehensive simulations of 2d arrays (Lx ×Ly) of magnetic nanoparticles (MNPs) with dipole-dipole interactions by solving LLG equations. Our primary interest is to understand the correspondence between equilibrium spin (ES) morphologies and tunnel magnetoresistance (TMR) as a function of Θ - the ratio of the dipolar to the anisotropy strength, sample size Lx , aspect ratio Ar =Ly /Lx and the direction of the applied field H → = HêH . The parameter Θ is varied by choosing three distinct particles: (i) α -Fe2O3 (Θ ≃ 0) , (ii) Co (Θ ≃ 0.37) and (iii) Fe3O4 (Θ ≃ 1.28) . Our main observations are as follows: (a) For weakly interacting spins (Θ ≃ 0) , the morphology has randomly oriented magnetic moments for all sample sizes and aspect ratios. The TMR exhibits a peak value of 50% at the coercive field Hc . It is robust with respect to Lx and Ar , and isotropic with respect to êH . (b) For strong interactions (Θ > 1) , the moments order in the plane of the sample. The ES morphology comprises of magnetically aligned regions interspersed with flux closure loops. For fields along x or y, the maximum TMR amplitude decrease to ∼30%. For êH = z ̂ , it drops to ∼3%. The TMR is robust with respect to Lx and Ar and isotropic in the x and y directions only. (c) In strongly interacting samples (Θ > 1) with Lx comparable to the size of a flux closure loop, increasing Ar creates ferromagnetic chains in the sample oriented along y or - y . Consequently, for êH = y ̂ , the TMR magnitude for Ar = 1 is ∼33% while that for Ar = 32 drops to ∼16%. For êH = x ̂ on the other hand, it is ∼30% and independent of Ar . The TMR of long ribbons of MNPs has a strong dependence on Ar and is anisotropic in all three directions.

Energetic Electron Acceleration and Injection During Dipolarization Events in Mercury's Magnetotail

Science.gov (United States)

Dewey, Ryan M.; Slavin, James A.; Raines, Jim M.; Baker, Daniel N.; Lawrence, David J.

2017-12-01

Energetic particle bursts associated with dipolarization events within Mercury's magnetosphere were first observed by Mariner 10. The events appear analogous to particle injections accompanying dipolarization events at Earth. The Energetic Particle Spectrometer (3 s resolution) aboard MESSENGER determined the particle bursts are composed entirely of electrons with energies ≳ 300 keV. Here we use the Gamma-Ray Spectrometer high-time-resolution (10 ms) energetic electron measurements to examine the relationship between energetic electron injections and magnetic field dipolarization in Mercury's magnetotail. Between March 2013 and April 2015, we identify 2,976 electron burst events within Mercury's magnetotail, 538 of which are closely associated with dipolarization events. These dipolarizations are detected on the basis of their rapid ( 2 s) increase in the northward component of the tail magnetic field (ΔBz 30 nT), which typically persists for 10 s. Similar to those at Earth, we find that these dipolarizations appear to be low-entropy, depleted flux tubes convecting planetward following the collapse of the inner magnetotail. We find that electrons experience brief, yet intense, betatron and Fermi acceleration during these dipolarizations, reaching energies 130 keV and contributing to nightside precipitation. Thermal protons experience only modest betatron acceleration. While only 25% of energetic electron events in Mercury's magnetotail are directly associated with dipolarization, the remaining events are consistent with the Near-Mercury Neutral Line model of magnetotail injection and eastward drift about Mercury, finding that electrons may participate in Shabansky-like closed drifts about the planet. Magnetotail dipolarization may be the dominant source of energetic electron acceleration in Mercury's magnetosphere.

Electron dynamics during substorm dipolarization in Mercury's magnetosphere

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D. C. Delcourt

2005-11-01

Full Text Available We examine the nonlinear dynamics of electrons during the expansion phase of substorms at Mercury using test particle simulations. A simple model of magnetic field line dipolarization is designed by rescaling a magnetic field model of the Earth's magnetosphere. The results of the simulations demonstrate that electrons may be subjected to significant energization on the time scale (several seconds of the magnetic field reconfiguration. In a similar manner to ions in the near-Earth's magnetosphere, it is shown that low-energy (up to several tens of eV electrons may not conserve the second adiabatic invariant during dipolarization, which leads to clusters of bouncing particles in the innermost magnetotail. On the other hand, it is found that, because of the stretching of the magnetic field lines, high-energy electrons (several keVs and above do not behave adiabatically and possibly experience meandering (Speiser-type motion around the midplane. We show that dipolarization of the magnetic field lines may be responsible for significant, though transient, (a few seconds precipitation of energetic (several keVs electrons onto the planet's surface. Prominent injections of energetic trapped electrons toward the planet are also obtained as a result of dipolarization. These injections, however, do not exhibit short-lived temporal modulations, as observed by Mariner-10, which thus appear to follow from a different mechanism than a simple convection surge.

Energy conversion and dissipation at dipolarization fronts: Theory, modeling and MMS observations

Science.gov (United States)

Sitnov, M. I.; Motoba, T.; Merkin, V. G.; Ohtani, S.; Cohen, I. J.; Mauk, B.; Vines, S. K.; Anderson, B. J.; Moore, T. E.; Torbert, R. B.; Giles, B. L.; Burch, J. L.

2017-12-01

Magnetic reconnection is one of the most important energy conversion mechanisms in space plasmas. In the classical picture it converts the energy of antiparallel magnetic fields into the kinetic and thermal energy of accelerated plasma particles in reconnection exhausts. It also involves energy dissipation near the X-line. This classical picture may be substantially modified in real space plasma configurations, such as the dayside magnetopause and the magnetotail. In particular, in the magnetotail the flows of accelerated particles may be strongly asymmetric along the tail with the domination of earthward flows. At the same time, strong energy conversion and even dissipation may occur away from the X-line, in particular, at dipolarization fronts. Here we present a theoretical picture of spontaneous magnetotail reconnection based on 3-D PIC simulations with the focus on plasma bulk flows, energy conversion and dissipation. This picture is compared with some observations from the MMS tail season. An important finding from these observations is that dipolarizations fronts may not only be regions of the total energy conversion with jE>0, but they may also be the sites of energy dissipation, both positive (jE'>0, E' is the electric field E in the system moving with one of the plasma species) and negative (jE'braking).

Dipolar Antiferromagnetism and Quantum Criticality in LiErF4

International Nuclear Information System (INIS)

Kraemer, Conradin; Nikseresht, Neda; Piatek, Julian; Tsyrulin, Nikolay; Piazza, Bastien; Kiefer, Klaus; Klemke, Bastian; Rosenbaum, Thomas; Aeppli, Gabriel; Gannarelli, Che; Prokes, Karel; Straessle, Thierry; Keller, Lukas; Zaharko, Oksana; Kraemer, Karl; Ronnow, Henrik

2012-01-01

Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF 4 , establishing it as a model dipolar-coupled antiferromagnet with planar spin-anisotropy and a quantum phase transition in applied field H c# parallel# = 4.0 ± 0.1 kilo-oersteds. We discovered non-mean-field critical scaling for the classical phase transition at the antiferromagnetic transition temperature that is consistent with the two-dimensional XY/h 4 universality class; in accord with this, the quantum phase transition at H c exhibits three-dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which strengthens the role of fluctuations.

MMS observations of magnetic reconnection signatures of dissipating ion inertial-scale flux ropes associated with dipolarization events

Science.gov (United States)

Poh, G.; Slavin, J. A.; Lu, S.; Le, G.; Cassak, P.; Eastwood, J. P.; Ozturk, D. S.; Zou, S.; Nakamura, R.; Baumjohann, W.; Russell, C. T.; Gershman, D. J.; Giles, B. L.; Pollock, C.; Moore, T. E.; Torbert, R. B.; Burch, J. L.

2017-12-01

The formation of flux ropes is thought to be an integral part of the process that may have important consequences for the onset and subsequent rate of reconnection in the tail. Earthward flows, i.e. bursty bulk flows (BBFs), generate dipolarization fronts (DFs) as they interact with the closed magnetic flux in their path. Global hybrid simulations and THEMIS observations have shown that earthward-moving flux ropes can undergo magnetic reconnection with the near-Earth dipole field in the downtail region between the Near Earth Neutral Line and the near-Earth dipole field to create DFs-like signatures. In this study, we analyzed sequential "chains" of earthward-moving, ion-scale flux ropes embedded within DFs observed during MMS first tail season. MMS high-resolution plasma measurements indicate that these earthward flux ropes embedded in DFs have a mean bulk flow velocity and diameter of 250 km/s and 1000 km ( 2‒3 ion inertial length λi), respectively. Magnetic reconnection signatures preceding the flux rope/DF encounter were also observed. As the southward-pointing magnetic field in the leading edge of the flux rope reconnects with the northward-pointing geomagnetic field, the characteristic quadrupolar Hall magnetic field in the ion diffusion region and electron outflow jets in the north-south direction are observed. Our results strongly suggest that the earthward moving flux ropes brake and gradually dissipate due to magnetic reconnection with the near Earth magnetic field. We have also examined the occurrence rate of these dissipating flux ropes/DF events as a function of downtail distances.

Magnetic history dependence of metastable states in thin films with dipolar interactions

International Nuclear Information System (INIS)

Iglesias, Oscar; Labarta, Amilcar

2000-01-01

We present the results of a Monte Carlo simulation of the ground state and magnetic relaxation of a model of a thin film consisting of a two-dimensional square lattice of Heisenberg spins with perpendicular anisotropy K, exchange J and long-range dipolar interactions g. We have studied the ground state configurations of this system for a wide range of the interaction parameters J/g, K/g by means of the simulated annealing procedure, showing that the model is able to reproduce the different magnetic configurations found in real samples. We have found the existence of a certain range of K/g, J/g values for which in-plane and out-of-plane configurations are quasi-degenerated in energy. We show that when a system in this region of parameters is perturbed by an external force that is subsequently removed, different kinds of ordering may be induced depending on the followed procedure. In particular, simulations of relaxations from saturation under an AC demagnetizing field or in zero field are in qualitative agreement with recent experiments on epitaxial and granular alloy thin films, which show a wide variety of magnetic patterns depending on their magnetic history

Effects of the competition between the exchange and dipolar interactions in the spin-wave spectrum of two-dimensional circularly magnetized nanodots

International Nuclear Information System (INIS)

Mamica, S; Krawczyk, M; Lévy, J-C S

2014-01-01

We use a microscopic theory taking into account the dipolar and nearest-neighbour exchange interactions for exploring spin-wave excitations in two-dimensional magnetic dots in the vortex state. Normal modes of different profiles are observed: azimuthal and radial modes, as well as fundamental (quasiuniform) and highly localized modes. We examine the dependence of the frequencies and profiles of these modes on the dipolar-to-exchange interaction ratio and the size of the dot. Special attention is paid to some particular modes, including the lowest mode in the spectrum and the evolution of its profile, and the fundamental mode, the frequency of which proves almost independent of the dipolar-to-exchange interaction ratio. We also provide a selective overview of the experimental, analytical and numerical results from the literature, where different profiles of the lowest mode are reported. We attribute this diversity to the competition between the dipolar and exchange interactions. Finally, we study the hybridization of the modes, show the multi-mode hybridization and explain the selection rules. (paper)

Minute splitting of magnetic excitations in CsFeCl{sub 3} due to dipolar interaction observed by polarised neutrons

Energy Technology Data Exchange (ETDEWEB)

Dorner, B [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France); Baehr, M [HMI, Berlin (Germany); Petitgrand, D [Laboratoire Leon Brillouin (LLB) - Centre d` Etudes de Saclay, 91 - Gif-sur-Yvette (France)

1997-04-01

Using inelastic neutron scattering with polarisation analysis it was possible, for the first time, to observe simultaneously the two magnetic modes split due to dipolar interaction. This would not have been possible with energy resolution only. An analysis of eigenvectors was also performed. (author). 4 refs.

Ultracold chromium: a dipolar quantum gas

International Nuclear Information System (INIS)

Pfau, T.; Stuhler, J.; Griesmaier, A.; Fattori, M.; Koch, T.

2005-01-01

We report on our recent achievement of a Bose-Einstein condensate in a gas of chromium atoms. Peculiar electronic and magnetic properties of chromium require the implementation of novel cooling strategies. We observe up to ∼ 10 5 condensed 52 Cr atoms after forced evaporation within a crossed optical dipole trap. Due to its large magnetic moment (6μ B ), the dipole-dipole interaction strength in chromium is comparable with the one of the van der Waals interaction. We prove the anisotropic nature of the dipolar interaction by releasing the condensate from a cigar shaped trap and observe, in time of flight measurements, the change of the aspect-ratio for different in-trap orientations of the atomic dipoles. We also report on the recent observation of 14 Feshbach resonances in elastic collisions between polarized ultra-cold 52 Cr atoms. This is the first Ballistic expansion of a dipolar quantum gas: The anisotropic interaction leads to a different expansion dynamics for the case of the magnetic dipoles aligned with the symmetry axis of the cigar shaped trap as compared with the dipoles oriented perpendicular to the axis of the cigar. The straight lines correspond to the theoretical expectation according to mean field theory without free parameters. observation of collisional Feshbach resonances in an atomic species with more than one valence electron. Moreover, such resonances constitute an important tool towards the realization of a purely dipolar interacting gas because they can be used to change strength and sign of the van der Waals interaction. (author)

Impact of nucleic acid self-alignment in a strong magnetic field on the interpretation of indirect spin–spin interactions

International Nuclear Information System (INIS)

Vavřinská, Andrea; Zelinka, Jiří; Šebera, Jakub; Sychrovský, Vladimír; Fiala, Radovan; Boelens, Rolf; Sklenář, Vladimír; Trantírek, Lukáš

2016-01-01

Heteronuclear and homonuclear direct (D) and indirect (J) spin–spin interactions are important sources of structural information about nucleic acids (NAs). The Hamiltonians for the D and J interactions have the same functional form; thus, the experimentally measured apparent spin–spin coupling constant corresponds to a sum of J and D. In biomolecular NMR studies, it is commonly presumed that the dipolar contributions to Js are effectively canceled due to random molecular tumbling. However, in strong magnetic fields, such as those employed for NMR analysis, the tumbling of NA fragments is anisotropic because the inherent magnetic susceptibility of NAs causes an interaction with the external magnetic field. This motional anisotropy is responsible for non-zero D contributions to Js. Here, we calculated the field-induced D contributions to 33 structurally relevant scalar coupling constants as a function of magnetic field strength, temperature and NA fragment size. We identified two classes of Js, namely 1 J CH and 3 J HH couplings, whose quantitative interpretation is notably biased by NA motional anisotropy. For these couplings, the magnetic field-induced dipolar contributions were found to exceed the typical experimental error in J-coupling determinations by a factor of two or more and to produce considerable over- or under-estimations of the J coupling-related torsion angles, especially at magnetic field strengths >12 T and for NA fragments longer than 12 bp. We show that if the non-zero D contributions to J are not properly accounted for, they might cause structural artifacts/bias in NA studies that use solution NMR spectroscopy

Dipolarization Fronts from Reconnection Onset

Science.gov (United States)

Sitnov, M. I.; Swisdak, M. M.; Merkin, V. G.; Buzulukova, N.; Moore, T. E.

2012-12-01

Dipolarization fronts observed in the magnetotail are often viewed as signatures of bursty magnetic reconnection. However, until recently spontaneous reconnection was considered to be fully prohibited in the magnetotail geometry because of the linear stability of the ion tearing mode. Recent theoretical studies showed that spontaneous reconnection could be possible in the magnetotail geometries with the accumulation of magnetic flux at the tailward end of the thin current sheet, a distinctive feature of the magnetotail prior to substorm onset. That result was confirmed by open-boundary full-particle simulations of 2D current sheet equilibria, where two magnetotails were separated by an equilibrium X-line and weak external electric field was imposed to nudge the system toward the instability threshold. To investigate the roles of the equilibrium X-line, driving electric field and other parameters in the reconnection onset process we performed a set of 2D PIC runs with different initial settings. The investigated parameter space includes the critical current sheet thickness, flux tube volume per unit magnetic flux and the north-south component of the magnetic field. Such an investigation is critically important for the implementation of kinetic reconnection onset criteria into global MHD codes. The results are compared with Geotail visualization of the magnetotail during substorms, as well as Cluster and THEMIS observations of dipolarization fronts.

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

Science.gov (United States)

Chang, Zhiwei; Halle, Bertil

2016-02-28

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

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. II. Dipolar, Quadrupolar, and Octupolar Topologies

Science.gov (United States)

Finley, Adam J.; Matt, Sean P.

2018-02-01

During the lifetime of Sun-like or low-mass stars a significant amount of angular momentum is removed through magnetized stellar winds. This process is often assumed to be governed by the dipolar component of the magnetic field. However, observed magnetic fields can host strong quadrupolar and/or octupolar components, which may influence the resulting spin-down torque on the star. In Paper I, we used the MHD code PLUTO to compute steady-state solutions for stellar winds containing a mixture of dipole and quadrupole geometries. We showed the combined winds to be more complex than a simple sum of winds with these individual components. This work follows the same method as Paper I, including the octupole geometry, which not only increases the field complexity but also, more fundamentally, looks for the first time at combining the same symmetry family of fields, with the field polarity of the dipole and octupole geometries reversing over the equator (unlike the symmetric quadrupole). We show, as in Paper I, that the lowest-order component typically dominates the spin-down torque. Specifically, the dipole component is the most significant in governing the spin-down torque for mixed geometries and under most conditions for real stars. We present a general torque formulation that includes the effects of complex, mixed fields, which predicts the torque for all the simulations to within 20% precision, and the majority to within ≈5%. This can be used as an input for rotational evolution calculations in cases where the individual magnetic components are known.

Supra Arcade Downflows with XRT Informed by Dipolarization Fronts with THEMIS

Science.gov (United States)

Kobelski, Adam; Savage, Sabrina L.; Malaspina, David M.

2016-01-01

Magnetic reconnection can rapidly reconfigure the magnetic field of the corona, accelerating plasma through the site of reconnection. Ambiguities due to the nature of remote sensing have complicated the interpretation of observations of the inflowing and outflowing plasma in reconnecting regions. In particular, the interpretation of sunward moving density depletions above flare arcades (known as Supra Arcade Downflows - SADs) is still debated. Hinode/XRT has provided a wealth of observations for SADs and helped inform our current understanding of these structures. SADs have been interpreted as wakes behind newly reconnected and outflowing loops (Supra Arcade Downflowing Loops - SADLs). Models have shown the plausibility of this interpretation, though this interpretation has not yet been fully accepted. We present here observations of newly reconnected outflowing loops observed via in situ instruments in the magnetosphere. These observations, provided by five THEMIS spacecraft, show that around retracting loops (dipolarization fronts in this context) similar dynamic temperature and density structures are found as seen in SADs. We compare data from multiple SADs and dipolarization fronts to show that the observational signatures implied in the corona can be directly observed in similar plasma regimes in the magnetosphere, strongly favoring the interpretation of SADs as wakes behind retracting loops.

Bose-Einstein condensation and study of inelastic collisions due to dipolar interactions

International Nuclear Information System (INIS)

Beaufils, Q.

2009-01-01

Its large magnetic moment in the ground state makes chromium a good candidate for the study of dipolar interactions in a degenerate gas. We have built an experimental setup for trapping and cooling atoms of "5"2Cr down to Bose-Einstein condensation (BEC). Evaporative cooling takes place in a purely optical trap, which is loaded from the magneto-optical trap using a novel process of continuous accumulation of metastable states. We produce a condensate of typically 15000 atoms in a time of 15 s. We have studied the possibility to bring all the Zeeman substates of a chromium BEC to degeneracy in a non-zero static magnetic field, using a radiofrequency (rf) magnetic field, and demonstrated a new process of rf-assisted dipolar relaxation. We have also studied a narrow Feshbach resonance induced by dipolar interaction, which implies a d-wave collisional channel. We analyzed this resonance in the presence of a rf magnetic field and we reinterpreted rf association of molecules as a mere Feshbach resonance between rf dressed states. Finally, we have set up an optical lattice in the perspective of studying the effects of dipole-dipole interactions in reduced dimension. (author)

Particle-in-cell Simulation of Dipolarization Front Associated Whistlers

Science.gov (United States)

Lin, D.; Scales, W.; Ganguli, G.; Crabtree, C. E.

2017-12-01

Dipolarization fronts (DFs) are dipolarized magnetic field embedded in the Earthward propagating bursty bulk flows (BBFs), which separates the hot, tenuous high-speed flow from the cold, dense, and slowly convecting surrounding plasma [Runov et al. 2011]. Broadband fluctuations have been observed at DFs including the electromagnetic whistler waves and electrostatic lower hybrid waves in the Very Low Frequency (VLF) range [e.g., Zhou et al. 2009, Deng et al. 2010]. There waves are suggested to be able heat electrons and play a critical role in the plasma sheet dynamics [Chaston et al., 2012, Angelopoulos et al., 2013]. However, their generation mechanism and role in the energy conversion are still under debate. The gradient scale of magnetic field, plasma density at DFs in the near-Earth magnetotail is comparable to or lower than the ion gyro radius [Runov et al., 2011, Fu et al., 2012, Breuillard et al., 2016]. Such strongly inhomogeneous configuration could be unstable to the electron-ion hybrid (EIH) instability, which arises from strongly sheared transverse flow and is in the VLF range [Ganguli et al. 1988, Ganguli et al. 2014]. The equilibrium of the EIH theory implies an anisotropy of electron temperature, which are likely to drive the whistler waves observed in DFs [Deng et al., 2010, Gary et al., 2011]. In order to better understand how the whistler waves are generated in DFs and whether the EIH theory is applicable, a fully electromagnetic particle-in-cell (EMPIC) model is used to simulate the EIH instability with similar equilibrium configurations in DF observations. The EMPIC model deals with three dimensions in the velocity space and two dimensions in the configuration space, which is quite ready to include the third configuration dimension. Simulation results will be shown in this presentation.

Tunnel-induced Dipolar Resonances in a Double-well Potential.

Science.gov (United States)

Schulz, Bruno; Saenz, Alejandro

2016-11-18

A system of two dipolar particles that are confined in a double-well potential and interact via a realistic isotropic interaction potential is investigated as a protoype for ultracold atoms with a magnetic dipole moment or ultracold dipolar heteronuclear diatomic molecules in double-well traps or in optical lattices. The resulting energy spectrum is discussed as a function of the dipole-dipole interaction strength. The variation of the strength of the dipole-dipole interaction is found to lead to various resonance phenomena. Among those are the previously discussed inelastic confinement-induced resonances as well as the dipole-induced resonances. It is found that the double-well potential gives rise to a new type of resonances, tunnel-induced dipolar ones. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simulation of transverse beam splitting using time-dependent dipolar or quadrupolar kicks

CERN Document Server

Capoani, Federico

2017-01-01

Two simple systems with high relevance for accelerator physics have been studied in detail in the context of this Summer Student Project. These systems describe the motion under the influence of detuning with amplitude due to non-linear magnets and an external, time-dependent force of dipolar or quadrupolar nature.Two simple systems with high relevance for accelerator physics have been studied in detail in the context of this Summer Student Project. These systems describe the motion under the influence of detuning with amplitude due to non-linear magnets and an external, time-dependent force of dipolar or quadrupolar nature.

Different approaches to analyze the dipolar interaction effects on diluted and concentrated granular superparamagnetic systems

Energy Technology Data Exchange (ETDEWEB)

Moscoso-Londoño, O., E-mail: omoscoso@ifi.unicamp.br [Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas (UNICAMP), CEP13083-859 Campinas, São Paulo (Brazil); Tancredi, P. [Laboratorio de Sólidos Amorfos, INTECIN, Facultad de Ingeniería, Universidad de Buenos Aires (UBA), CONICET, C1063ACV Buenos Aires (Argentina); Muraca, D. [Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas (UNICAMP), CEP13083-859 Campinas, São Paulo (Brazil); Centro de Ciencias Naturais e Humanas, Universidade Federal do ABC (UFABC), Av. Dos Estados, 5001, Santo André, SP (Brazil); Mendoza Zélis, P.; Coral, D.; Fernández van Raap, M.B. [Instituto de Física, Universidad Nacional de La Plata (UNLP), CONICET, CC.67, 1900 La Plata, Buenos Aires (Argentina); Wolff, U.; Neu, V.; Damm, C. [IFW Dresden, Leibniz Institute for Solid State and Materials Research, Dresden, Helmholtzstrasse 20, 01069 Dresden (Germany); Oliveira, C.L.P. de [Instituto de Física, Universidade de São Paulo, São Paulo 05314970 (Brazil); Pirota, K.R. [Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas (UNICAMP), CEP13083-859 Campinas, São Paulo (Brazil); and others

2017-04-15

Controlled magnetic granular materials with different concentrations of magnetite nanoparticles immersed in a non-conducting polymer matrix were synthesized and, their macroscopic magnetic observables analyzed in order to advance towards a better understanding of the magnetic dipolar interactions and its effects on the obtained magnetic parameters. First, by means of X-ray diffraction, transmission electron microscopy, small angle X-ray scattering and X-ray absorption fine structure an accurate study of the structural properties was carried out. Then, the magnetic properties were analyzed by means of different models, including those that consider the magnetic interactions through long-range dipolar forces as: the Interacting Superparamagnetic Model (ISP) and the Vogel-Fulcher law (V-F). In systems with larger nanoparticle concentrations, magnetic results clearly indicate that the role played by the dipolar interactions affects the magnetic properties, giving rise to obtaining magnetic and structural parameters without physical meaning. Magnetic parameters as the effective anisotropic constant, magnetic moment relaxation time and mean blocking temperature, extracted from the application of the ISP model and V-F Law, were used to simulate the zero-field-cooling (ZFC) and field-cooling curves (FC). A comparative analysis of the simulated, fitted and experimental ZFC/FC curves suggests that the current models depict indeed our dilute granular systems. Notwithstanding, for concentrated samples, the ISP model infers that clustered nanoparticles are being interpreted as single entities of larger magnetic moment and volume, effect that is apparently related to a collective and complex magnetic moment dynamics within the cluster. - Highlights: • Nanoparticle architecture into matrices determines the composite magnetic response. • Magnetically diluted or compacted systems are useful to study magnetism at nanoscale. • Particle aggregation into the matrices was examined

Low-loss metamaterial electromagnetically induced transparency based on electric toroidal dipolar response

Energy Technology Data Exchange (ETDEWEB)

Li, Hai-ming; Liu, Shao-bin, E-mail: lsb@nuaa.edu.cn; Liu, Si-yuan; Ding, Guo-wen; Yang, Hua; Yu, Zhi-yang; Zhang, Hai-feng [Key Laboratory of Radar Imaging and Microwave Photonics, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016 (China); Wang, Shen-yun [Research Center of Applied Electromagnetic, Nanjing University of Information Science and Technology, Nanjing, 210044 (China)

2015-02-23

In this paper, a low-loss and high transmission analogy of electromagnetically induced transparency based on electric toroidal dipolar response is numerically and experimentally demonstrated. It is obtained by the excitation of the low-loss electric toroidal dipolar response, which confines the magnetic field inside a dielectric substrate with toroidal geometry. The metamaterial electromagnetically induced transparency (EIT) structure is composed of the cut wire and asymmetric split-ring resonators. The transmission level is as high as 0.88, and the radiation loss is greatly suppressed, which can be proved by the surface currents distributions, the magnetic field distributions, and the imaginary parts of the effective permeability and permittivity. It offers an effective way to produce low-loss and high transmission metamaterial EIT.

A practical strategy for the accurate measurement of residual dipolar couplings in strongly aligned small molecules

Science.gov (United States)

Liu, Yizhou; Cohen, Ryan D.; Martin, Gary E.; Williamson, R. Thomas

2018-06-01

Accurate measurement of residual dipolar couplings (RDCs) requires an appropriate degree of alignment in order to optimize data quality. An overly weak alignment yields very small anisotropic data that are susceptible to measurement errors, whereas an overly strong alignment introduces extensive anisotropic effects that severely degrade spectral quality. The ideal alignment amplitude also depends on the specific pulse sequence used for the coupling measurement. In this work, we introduce a practical strategy for the accurate measurement of one-bond 13C-1H RDCs up to a range of ca. -300 to +300 Hz, corresponding to an alignment that is an order of magnitude stronger than typically employed for small molecule structural elucidation. This strong alignment was generated in the mesophase of the commercially available poly-γ-(benzyl-L-glutamate) polymer. The total coupling was measured by the simple and well-studied heteronuclear two-dimensional J-resolved experiment, which performs well in the presence of strong anisotropic effects. In order to unequivocally determine the sign of the total coupling and resolve ambiguities in assigning total couplings in the CH2 group, coupling measurements were conducted at an isotropic condition plus two anisotropic conditions of different alignment amplitudes. Most RDCs could be readily extracted from these measurements whereas more complicated spectral effects resulting from strong homonuclear coupling could be interpreted either theoretically or by simulation. Importantly, measurement of these very large RDCs actually offers significantly improved data quality and utility for the structure determination of small organic molecules.

Field dipolarization in Saturn's magnetotail with planetward ion flows and energetic particle flow bursts: Evidence of quasi-steady reconnection.

Science.gov (United States)

Jackman, C M; Thomsen, M F; Mitchell, D G; Sergis, N; Arridge, C S; Felici, M; Badman, S V; Paranicas, C; Jia, X; Hospodarksy, G B; Andriopoulou, M; Khurana, K K; Smith, A W; Dougherty, M K

2015-05-01

We present a case study of an event from 20 August (day 232) of 2006, when the Cassini spacecraft was sampling the region near 32 R S and 22 h LT in Saturn's magnetotail. Cassini observed a strong northward-to-southward turning of the magnetic field, which is interpreted as the signature of dipolarization of the field as seen by the spacecraft planetward of the reconnection X line. This event was accompanied by very rapid (up to ~1500 km s -1 ) thermal plasma flow toward the planet. At energies above 28 keV, energetic hydrogen and oxygen ion flow bursts were observed to stream planetward from a reconnection site downtail of the spacecraft. Meanwhile, a strong field-aligned beam of energetic hydrogen was also observed to stream tailward, likely from an ionospheric source. Saturn kilometric radiation emissions were stimulated shortly after the observation of the dipolarization. We discuss the field, plasma, energetic particle, and radio observations in the context of the impact this reconnection event had on global magnetospheric dynamics.

The phase transition in the anisotropic Heisenberg model with long range dipolar interactions

International Nuclear Information System (INIS)

Mól, L.A.S.; Costa, B.V.

2014-01-01

In this work we have used extensive Monte Carlo calculations to study the planar to paramagnetic phase transition in the two-dimensional anisotropic Heisenberg model with dipolar interactions (AHd) considering the true long-range character of the dipolar interactions by means of the Ewald summation. Our results are consistent with an order–disorder phase transition with unusual critical exponents in agreement with our previous results for the Planar Rotator model with dipolar interactions. Nevertheless, our results disagree with the Renormalization Group results of Maier and Schwabl [Phys. Rev. B, 70, 134430 (2004)] [13] and the results of Rapini et al. [Phys. Rev. B, 75, 014425 (2007)] [12], where the AHd was studied using a cut-off in the evaluation of the dipolar interactions. We argue that besides the long-range character of dipolar interactions their anisotropic character may have a deeper effect in the system than previously believed. Besides, our results show that the use of a cut-off radius in the evaluation of dipolar interactions must be avoided when analyzing the critical behavior of magnetic systems, since it may lead to erroneous results. - Highlights: • The anisotropic Heisenberg model with dipolar interactions is studied. • True long-range interactions were considered by means of Ewald summation. • We found an order–disorder phase transition with unusual critical exponents. • Previous results show a different behavior when a cut-off radius is introduced. • The use of a cut-off radius must be avoided when dealing with dipolar systems

Propagation of Dipolarization Signatures Observed by the Van Allen Probes in the Inner Magnetosphere

Science.gov (United States)

Ohtani, S.; Motoba, T.; Gkioulidou, M.; Takahashi, K.; Kletzing, C.

2017-12-01

Dipolarization, the change of the local magnetic field from a stretched to a more dipolar configuration, is one of the most fundamental processes of magnetospheric physics. It is especially critical for the dynamics of the inner magnetosphere. The associated electric field accelerates ions and electrons and transports them closer to Earth. Such injected ions intensify the ring current, and electrons constitute the seed population of the radiation belt. Those ions and electrons may also excite various waves that play important roles in the enhancement and loss of the radiation belt electrons. Despite such critical consequences, the general characteristics of dipolarization in the inner magnetosphere still remain to be understood. The Van Allen Probes mission, which consists of two probes that orbit through the equatorial region of the inner magnetosphere, provides an ideal opportunity to examine dipolarization signatures in the core of the ring current. In the present study we investigate the spatial expansion of the dipolarization region by examining the correlation and time delay of dipolarization signatures observed by the two probes. Whereas in general it requires three-point measurements to deduce the propagation of a signal on a certain plane, we statically examined the observed time delays and found that dipolarization signatures tend to propagate radially inward as well as away from midnight. In this paper we address the propagation of dipolarization signatures quantitatively and compare with the propagation velocities reported previously based on observations made farther away from Earth. We also discuss how often and under what conditions the dipolarization region expands.

Single-molecule magnets ``without'' intermolecular interactions

Science.gov (United States)

Wernsdorfer, W.; Vergnani, L.; Rodriguez-Douton, M. J.; Cornia, A.; Neugebauer, P.; Barra, A. L.; Sorace, L.; Sessoli, R.

2012-02-01

Intermolecular magnetic interactions (dipole-dipole and exchange) affect strongly the magnetic relaxation of crystals of single-molecule magnets (SMMs), especially at low temperature, where quantum tunneling of the magnetization (QTM) dominates. This leads to complex many-body problems [l]. Measurements on magnetically diluted samples are desirable to clearly sort out the behaviour of magnetically-isolated SMMs and to reveal, by comparison, the effect of intermolecular interactions. Here, we diluted a Fe4 SMM into a diamagnetic crystal lattice, affording arrays of independent and iso-oriented magnetic units. We found that the resonant tunnel transitions are much sharper, the tunneling efficiency changes significantly, and two-body QTM transitions disappear. These changes have been rationalized on the basis of a dipolar shuffling mechanism and of transverse dipolar fields, whose effect has been analyzed using a multispin model. Our findings directly prove the impact of intermolecular magnetic couplings on the SMM behaviour and disclose the magnetic response of truly-isolated giant spins in a diamagnetic crystalline environment.[4pt] [1] W. Wernsdorfer, at al, PRL 82, 3903 (1999); PRL 89, 197201 (2002); Nature 416, 406 (2002); IS Tupitsyn, PCE Stamp, NV Prokof'ev, PRB 69, 132406 (2004).

Dipolar particles in a double-trap confinement: Response to tilting the dipolar orientation

Science.gov (United States)

Bjerlin, J.; Bengtsson, J.; Deuretzbacher, F.; Kristinsdóttir, L. H.; Reimann, S. M.

2018-02-01

We analyze the microscopic few-body properties of dipolar particles confined in two parallel quasi-one-dimensional harmonic traps. In particular, we show that an adiabatic rotation of the dipole orientation about the trap axes can drive an initially nonlocalized few-fermion state into a localized state with strong intertrap pairing. With an instant, nonadiabatic rotation, however, localization is inhibited and a highly excited state is reached. This state may be interpreted as the few-body analog of a super-Tonks-Girardeau state, known from one-dimensional systems with contact interactions.

Strong and superstrong pulsed magnetic fields generation

CERN Document Server

Shneerson, German A; Krivosheev, Sergey I

2014-01-01

Strong pulsed magnetic fields are important for several fields in physics and engineering, such as power generation and accelerator facilities. Basic aspects of the generation of strong and superstrong pulsed magnetic fields technique are given, including the physics and hydrodynamics of the conductors interacting with the field as well as an account of the significant progress in generation of strong magnetic fields using the magnetic accumulation technique. Results of computer simulations as well as a survey of available field technology are completing the volume.

Advances in magnetic resonance 9

CERN Document Server

Waugh, John S

2013-01-01

Advances in Magnetic Resonance, Volume 9 describes the magnetic resonance in split constants and dipolar relaxation. This book discusses the temperature-dependent splitting constants in the ESR spectra of organic free radicals; temperature-dependent splittings in ion pairs; and magnetic resonance induced by electrons. The electron impact excitation of atoms and molecules; intramolecular dipolar relaxation in multi-spin systems; and dipolar cross-correlation problem are also elaborated. This text likewise covers the NMR studies of molecules oriented in thermotropic liquid crystals and diffusion

Strongly interacting matter in magnetic fields

CERN Document Server

Landsteiner, Karl; Schmitt, Andreas; Yee, Ho-Ung

2013-01-01

The physics of strongly interacting matter in an external magnetic field is presently emerging as a topic of great cross-disciplinary interest for particle, nuclear, astro- and condensed matter physicists. It is known that strong magnetic fields are created in heavy ion collisions, an insight that has made it possible to study a variety of surprising and intriguing phenomena that emerge from the interplay of quantum anomalies, the topology of non-Abelian gauge fields, and the magnetic field. In particular, the non-trivial topological configurations of the gluon field induce a non-dissipative electric current in the presence of a magnetic field. These phenomena have led to an extended formulation of relativistic hydrodynamics, called chiral magnetohydrodynamics. Hitherto unexpected applications in condensed matter physics include graphene and topological insulators. Other fields of application include astrophysics, where strong magnetic fields exist in magnetars and pulsars. Last but not least, an important ne...

Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations

Science.gov (United States)

Le Contel, O.; Roux, A.; Jacquey, C.; Robert, P.; Berthomier, M.; Chust, T.; Grison, B.; Angelopoulos, V.; Sibeck, D.; Chaston, C. C.; Cully, C. M.; Ergun, B.; Glassmeier, K.-H.; Auster, U.; McFadden, J.; Carlson, C.; Larson, D.; Bonnell, J. W.; Mende, S.; Russell, C. T.; Donovan, E.; Mann, I.; Singer, H.

2009-06-01

We report on quasi-parallel whistler emissions detected by the near-earth satellites of the THEMIS mission before, during, and after local dipolarization. These emissions are associated with an electron temperature anisotropy α=T⊥e/T||e>1 consistent with the linear theory of whistler mode anisotropy instability. When the whistler mode emissions are observed the measured electron anisotropy varies inversely with β||e (the ratio of the electron parallel pressure to the magnetic pressure) as predicted by Gary and Wang (1996). Narrow band whistler emissions correspond to the small α existing before dipolarization whereas the broad band emissions correspond to large α observed during and after dipolarization. The energy in the whistler mode is leaving the current sheet and is propagating along the background magnetic field, towards the Earth. A simple time-independent description based on the Liouville's theorem indicates that the electron temperature anisotropy decreases with the distance along the magnetic field from the equator. Once this variation of α is taken into account, the linear theory predicts an equatorial origin for the whistler mode. The linear theory is also consistent with the observed bandwidth of wave emissions. Yet, the anisotropy required to be fully consistent with the observations is somewhat larger than the measured one. Although the discrepancy remains within the instrumental error bars, this could be due to time-dependent effects which have been neglected. The possible role of the whistler waves in the substorm process is discussed.

Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations

Directory of Open Access Journals (Sweden)

O. Le Contel

2009-06-01

Full Text Available We report on quasi-parallel whistler emissions detected by the near-earth satellites of the THEMIS mission before, during, and after local dipolarization. These emissions are associated with an electron temperature anisotropy α=T⊥e/T||e>1 consistent with the linear theory of whistler mode anisotropy instability. When the whistler mode emissions are observed the measured electron anisotropy varies inversely with β||e (the ratio of the electron parallel pressure to the magnetic pressure as predicted by Gary and Wang (1996. Narrow band whistler emissions correspond to the small α existing before dipolarization whereas the broad band emissions correspond to large α observed during and after dipolarization. The energy in the whistler mode is leaving the current sheet and is propagating along the background magnetic field, towards the Earth. A simple time-independent description based on the Liouville's theorem indicates that the electron temperature anisotropy decreases with the distance along the magnetic field from the equator. Once this variation of α is taken into account, the linear theory predicts an equatorial origin for the whistler mode. The linear theory is also consistent with the observed bandwidth of wave emissions. Yet, the anisotropy required to be fully consistent with the observations is somewhat larger than the measured one. Although the discrepancy remains within the instrumental error bars, this could be due to time-dependent effects which have been neglected. The possible role of the whistler waves in the substorm process is discussed.

Thermal entanglement and teleportation in a dipolar interacting system

Energy Technology Data Exchange (ETDEWEB)

Castro, C.S., E-mail: ccastro@if.uff.br [Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza s/n, Gragoatá, 24210-346 Niterói, RJ (Brazil); Centro de Formação de Professores, Universidade Federal do Recôncavo da Bahia, Av. Nestor de Mello Pita, n. 535, 45.300-000 Amargosa, BA (Brazil); Duarte, O.S.; Pires, D.P.; Soares-Pinto, D.O. [Instituto de Física de São Carlos, Universidade de São Paulo, P.O. Box 369, São Carlos, 13560-970 SP (Brazil); Reis, M.S. [Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza s/n, Gragoatá, 24210-346 Niterói, RJ (Brazil)

2016-04-22

Quantum teleportation, which depends on entangled states, is a fascinating subject and an important branch of quantum information processing. The present work reports the use of a dipolar spin thermal system as a noisy quantum channel to perform quantum teleportation. Non-locality, tested by violation of Bell's inequality and thermal entanglement, measured by negativity, shows that for the present model all entangled states, even those that do not violate Bell's inequality, are useful for teleportation. - Highlights: • The effects of a dipolar interaction between two spins on their degree of entanglement and non-locality is reported. • The model presents some degree of non-locality and entanglement at a given coupling parameters. • It is shown how the magnetic anisotropies can influence the fidelity of teleportation.

Cooling Curve of Strange Star in Strong Magnetic Field

Institute of Scientific and Technical Information of China (English)

WANG Xiao-Qin; LUO Zhi-Quan

2008-01-01

In this paper, firstly, we investigate the neutrino emissivity from quark Urca process in strong magnetic field. Then, we discuss the heat capacity of strange stars in strong magnetic field. Finally, we give the cooling curve in strong magnetic field. In order to make a comparison, we also give the corresponding cooling curve in the case of null magnetic field. It turns out that strange stars cool faster in strong magnetic field than that without magnetic field.

The effect of noncollinearity of 15N-1H dipolar and 15N CSA tensors and rotational anisotropy on 15N relaxation, CSA/dipolar cross correlation, and TROSY

International Nuclear Information System (INIS)

Fushman, David; Cowburn, David

1999-01-01

Current approaches to 15N relaxation in proteins assume that the 15N-1H dipolar and 15N CSA tensors are collinear. We show theoretically that, when there is significant anisotropy of molecular rotation, different orientations of the two tensors, experimentally observed in proteins, nucleic acids, and small peptides, will result in differences in site- specific correlation functions and spectral densities. The standard treatments of the rates of longitudinal and transverse relaxation of amide 15N nuclei, of the 15N CSA/15N-1H dipolar cross correlation, and of the TROSY experiment are extended to account for the effect of noncollinearity of the 15N-1H dipolar and 15N CSA (chemical shift anisotropy) tensors. This effect, proportional to the degree of anisotropy of the overall motion, (D-parallel /D-perpendicular -1), is sensitive to the relative orientation of the two tensors and to the orientation of the peptide plane with respect to the diffusion coordinate frame. The effect is negligible at small degrees of anisotropy, but is predicted to become significant for D-parallel /D-perpendicular ≥1.5, and at high magnetic fields. The effect of noncollinearity of 15N CSA and 15N-1H dipolar interaction is sensitive to both gross (hydrodynamic) properties and atomic-level details of protein structure. Incorporation of this effect into relaxation data analysis is likely to improve both precision and accuracy of the derived characteristics of protein dynamics, especially at high magnetic fields and for molecules with a high degree of anisotropy of the overall motion. The effect will also make TROSY efficiency dependent on local orientation in moderately anisotropic systems

Thermodynamics of Dipolar Chain Systems

DEFF Research Database (Denmark)

R. Armstrong, J.; Zinner, Nikolaj Thomas; V. Fedorov, D.

2012-01-01

The thermodynamics of a quantum system of layers containing perpendicularly oriented dipolar molecules is studied within an oscillator approximation for both bosonic and fermionic species. The system is assumed to be built from chains with one molecule in each layer. We consider the effects...... numerically. Our findings indicate that thermodynamic observables, such as the heat capacity, can be used to probe the signatures of the intralayer interaction between chains. This should be relevant for near future experiments on polar molecules with strong dipole moments....

Dipolar interaction in arrays of magnetic nanotubes

International Nuclear Information System (INIS)

Velázquez-Galván, Y; Martínez-Huerta, J M; Encinas, A; De La Torre Medina, J; Danlée, Y; Piraux, L

2014-01-01

The dipolar interaction field in arrays of nickel nanotubes has been investigated on the basis of expressions derived from the effective demagnetizing field of the assembly as well as magnetometry measurements. The model incorporates explicitly the wall thickness and aspect ratio, as well as the spatial order of the nanotubes. The model and experiment show that the interaction field in nanotubes is smaller than that in solid nanowires due to the packing fraction reduction in tubes related to their inner cavity. Finally, good agreement between the model and experiment is found for the variation of the interaction field as a function of the tube wall thickness. (paper)

Cluster Observations of Multiple Dipolarization Fronts

Science.gov (United States)

Hwang, Kyoung-Joo; Goldstein, Melvyn L.; Lee, Ensang; Pickett, Jolene S.

2011-01-01

We present Cluster observations of a series of dipolarization fronts (DF 1 to 6) at the central current sheet in Earth's magnetotail. The velocities of fast earthward flow following behind each DF 1-3, are comparable to the Alfven velocity, indicating that the flow bursts might have been generated by bursty reconnection that occurred tailward of the spacecraft. Based on multi-spacecraft timing analysis, DF normals are found to propagate mainly earthward at $160-335$ km/s with a thickness of 900-1500 km, which corresponds to the ion inertial length or gyroradius scale. Each DF is followed by significant fluctuations in the $x$ and $y$ components of the magnetic field whose peaks are found 1-2 minutes after the DF passage. These $(B_{x},B_{y} )$-fluctuations propagate dawnward (mainly) and earthward. Strongly enhanced field-aligned beams are observed coincidently with $(B_{x},B_{y})$ fluctuations, while an enhancement of cross-tail currents is associated with the DFs. From the observed pressure imbalance and flux-tube entropy changes between the two regions separated by the DF, we speculate that interchange instability destabilizes the DFs and causes the deformation of the mid-tail magnetic topology. This process generates significant field-aligned currents, and might power the auroral brightening in the ionosphere. However, this event is neither associated with the main substorm auroral breakup nor the poleward expansion, which might indicate that the observed multiple DFs have been dissipated before they reach the inner plasma sheet boundary.

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. I. Interaction of Dipolar and Quadrupolar Fields

Energy Technology Data Exchange (ETDEWEB)

Finley, Adam J.; Matt, Sean P., E-mail: af472@exeter.ac.uk [University of Exeter (UK), Department of Physics and Astronomy, Stoker Road, Devon, Exeter, EX4 4QL (United Kingdom)

2017-08-10

Cool stars with outer convective envelopes are observed to have magnetic fields with a variety of geometries, which on large scales are dominated by a combination of the lowest-order fields such as the dipole, quadrupole, and octupole modes. Magnetized stellar wind outflows are primarily responsible for the loss of angular momentum from these objects during the main sequence. Previous works have shown the reduced effectiveness of the stellar wind braking mechanism with increasingly complex but singular magnetic field geometries. In this paper, we quantify the impact of mixed dipolar and quadrupolar fields on the spin-down torque using 50 MHD simulations with mixed fields, along with 10 each of the pure geometries. The simulated winds include a wide range of magnetic field strength and reside in the slow-rotator regime. We find that the stellar wind braking torque from our combined geometry cases is well described by a broken power-law behavior, where the torque scaling with field strength can be predicted by the dipole component alone or the quadrupolar scaling utilizing the total field strength. The simulation results can be scaled and apply to all main-sequence cool stars. For solar parameters, the lowest-order component of the field (dipole in this paper) is the most significant in determining the angular momentum loss.

Resonance double magnetic bremsstrahlung in a strong magnetic field

International Nuclear Information System (INIS)

Fomin, P.I.; Kholodov, R.I.

2003-01-01

The possibility of resonance double magnetic bremsstrahlung in the approximation of weakly excited electron states in a strong external magnetic field is analyzed. The differential probability of this process in the Breit-Wigner form is obtained. The probability of double magnetic bremsstrahlung (second-order process of perturbation theory) is compared with the probability of magnetic bremsstrahlung (first-order process of perturbation theory)

Luttinger hydrodynamics of confined one-dimensional Bose gases with dipolar interactions

International Nuclear Information System (INIS)

Citro, R; Palo, S De; Orignac, E; Pedri, P; Chiofalo, M-L

2008-01-01

Ultracold bosonic and fermionic quantum gases confined to quasi-one-dimensional (1D) geometry are promising candidates for probing fundamental concepts of Luttinger liquid (LL) physics. They can also be exploited for devising applications in quantum information processing and precision measurements. Here, we focus on 1D dipolar Bose gases, where evidence of super-strong coupling behavior has been demonstrated by analyzing the low-energy static and dynamical structures of the fluid at zero temperature by a combined reptation quantum Monte Carlo (RQMC) and bosonization approach. Fingerprints of LL behavior emerge in the whole crossover from the already strongly interacting Tonks-Girardeau at low density to a dipolar density wave regime at high density. We have also shown that a LL framework can be effectively set up and utilized to describe this strongly correlated crossover physics in the case of confined 1D geometries after using the results for the homogeneous system in LL hydrodynamic equations within a local density approximation. This leads to the prediction of observable quantities such as the frequencies of the collective modes of the trapped dipolar gas under the more realistic conditions that could be found in ongoing experiments. The present paper provides a description of the theoretical framework in which the above results have been worked out, making available all the detailed derivations of the hydrodynamic Luttinger equations for the inhomogeneous trapped gas and of the correlation functions for the homogeneous system

Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations

Directory of Open Access Journals (Sweden)

O. Le Contel

2009-06-01

Full Text Available We report on quasi-parallel whistler emissions detected by the near-earth satellites of the THEMIS mission before, during, and after local dipolarization. These emissions are associated with an electron temperature anisotropy α=T_⊥e/T_||e>1 consistent with the linear theory of whistler mode anisotropy instability. When the whistler mode emissions are observed the measured electron anisotropy varies inversely with β_||e (the ratio of the electron parallel pressure to the magnetic pressure as predicted by Gary and Wang (1996. Narrow band whistler emissions correspond to the small α existing before dipolarization whereas the broad band emissions correspond to large α observed during and after dipolarization. The energy in the whistler mode is leaving the current sheet and is propagating along the background magnetic field, towards the Earth. A simple time-independent description based on the Liouville's theorem indicates that the electron temperature anisotropy decreases with the distance along the magnetic field from the equator. Once this variation of α is taken into account, the linear theory predicts an equatorial origin for the whistler mode. The linear theory is also consistent with the observed bandwidth of wave emissions. Yet, the anisotropy required to be fully consistent with the observations is somewhat larger than the measured one. Although the discrepancy remains within the instrumental error bars, this could be due to time-dependent effects which have been neglected. The possible role of the whistler waves in the substorm process is discussed.

Hypernuclear matter in strong magnetic field

Energy Technology Data Exchange (ETDEWEB)

Sinha, Monika [Institute for Theoretical Physics, J.W. Goethe-University, D-60438 Frankfurt am Main (Germany); Indian Institute of Technology Rajasthan, Old Residency Road, Ratanada, Jodhpur 342011 (India); Mukhopadhyay, Banibrata [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Sedrakian, Armen, E-mail: sedrakian@th.physik.uni-frankfurt.de [Institute for Theoretical Physics, J.W. Goethe-University, D-60438 Frankfurt am Main (Germany)

2013-01-17

Compact stars with strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 10{sup 14}–10{sup 15} G, the implied internal field strength being several orders larger. We study the equation of state and composition of dense hypernuclear matter in strong magnetic fields in a range expected in the interiors of magnetars. Within the non-linear Boguta–Bodmer–Walecka model we find that the magnetic field has sizable influence on the properties of matter for central magnetic field B⩾10{sup 17} G, in particular the matter properties become anisotropic. Moreover, for the central fields B⩾10{sup 18} G, the magnetized hypernuclear matter shows instability, which is signalled by the negative sign of the derivative of the pressure parallel to the field with respect to the density, and leads to vanishing parallel pressure at the critical value B{sub cr}≃10{sup 19} G. This limits the range of admissible homogeneously distributed fields in magnetars to fields below the critical value B{sub cr}.

A liquid crystalline medium for measuring residual dipolar couplings over a wide range of temperatures

Energy Technology Data Exchange (ETDEWEB)

Wang Hong; Eberstadt, Matthias; Olejniczak, Edward T.; Meadows, Robert P.; Fesik, Stephen W. [Abbott Laboratories (United States)

1998-10-15

A mixture of dilauroyl phosphatidylcholine (DLPC) and 3-(cholamidopropyl)dimethylammonio-2-hydroxyl-1-propane sulfonate (CHAPSO) in water forms disc shaped bicelles that become ordered at high magnetic fields over a wide range of temperatures. As illustrated for the FK506 binding protein (FKBP), large residual dipolar couplings can be measured for proteins dissolved in low concentrations (5% w/v) of a DLPC/CHAPSO medium at a molar ratio of 4.2:1. This system is especially useful for measuring residual dipolar couplings for molecules that are only stable at low temperatures.

Physics of Substorm Growth Phase, Onset, and Dipolarization

Energy Technology Data Exchange (ETDEWEB)

C.Z. Cheng

2003-10-22

A new scenario of substorm growth phase, onset, and depolarization during expansion phase and the corresponding physical processes are presented. During the growth phase, as a result of enhanced plasma convection, the plasma pressure and its gradient are continued to be enhanced over the quiet-time values in the plasma sheet. Toward the late growth phase, a strong cross-tail current sheet is formed in the near-Earth plasma sheet region, where a local magnetic well is formed, the plasma beta can reach a local maximum with value larger than 50 and the cross-tail current density can be enhanced to over 10nA/m{sup 2} as obtained from 3D quasi-static magnetospheric equilibrium solutions for the growth phase. The most unstable kinetic ballooning instabilities (KBI) are expected to be located in the tailward side of the strong cross-tail current sheet region. The field lines in the most unstable KBI region map to the transition region between the region-1 and region-2 currents in the ionosphere, which is consistent with the observed initial brightening location of the breakup arc in the intense proton precipitation region. The KBI explains the AMPTE/CCE observations that a low-frequency instability with a wave period of 50-75 seconds is excited about 2-3 minutes prior to substorm onset and grows exponentially to a large amplitude at the onset of current disruption (or current reduction). At the current disruption onset higher frequency instabilities are excited so that the plasma and electromagnetic field fluctuations form a strong turbulent state. Plasma transport takes place due to the strong turbulence to relax the ambient plasma pressure profile so that the plasma pressure and current density are reduced and the ambient magnetic field intensity increases by more than a factor of 2 in the high-beta(sub)eq region and the field line geometry recovers from tail-like to dipole-like dipolarization.

Physics of Substorm Growth Phase, Onset, and Dipolarization

International Nuclear Information System (INIS)

Cheng, C.Z.

2003-01-01

A new scenario of substorm growth phase, onset, and depolarization during expansion phase and the corresponding physical processes are presented. During the growth phase, as a result of enhanced plasma convection, the plasma pressure and its gradient are continued to be enhanced over the quiet-time values in the plasma sheet. Toward the late growth phase, a strong cross-tail current sheet is formed in the near-Earth plasma sheet region, where a local magnetic well is formed, the plasma beta can reach a local maximum with value larger than 50 and the cross-tail current density can be enhanced to over 10nA/m 2 as obtained from 3D quasi-static magnetospheric equilibrium solutions for the growth phase. The most unstable kinetic ballooning instabilities (KBI) are expected to be located in the tailward side of the strong cross-tail current sheet region. The field lines in the most unstable KBI region map to the transition region between the region-1 and region-2 currents in the ionosphere, which is consistent with the observed initial brightening location of the breakup arc in the intense proton precipitation region. The KBI explains the AMPTE/CCE observations that a low-frequency instability with a wave period of 50-75 seconds is excited about 2-3 minutes prior to substorm onset and grows exponentially to a large amplitude at the onset of current disruption (or current reduction). At the current disruption onset higher frequency instabilities are excited so that the plasma and electromagnetic field fluctuations form a strong turbulent state. Plasma transport takes place due to the strong turbulence to relax the ambient plasma pressure profile so that the plasma pressure and current density are reduced and the ambient magnetic field intensity increases by more than a factor of 2 in the high-beta(sub)eq region and the field line geometry recovers from tail-like to dipole-like dipolarization

Atom-Pair Kinetics with Strong Electric-Dipole Interactions.

Science.gov (United States)

Thaicharoen, N; Gonçalves, L F; Raithel, G

2016-05-27

Rydberg-atom ensembles are switched from a weakly to a strongly interacting regime via adiabatic transformation of the atoms from an approximately nonpolar into a highly dipolar quantum state. The resultant electric dipole-dipole forces are probed using a device akin to a field ion microscope. Ion imaging and pair-correlation analysis reveal the kinetics of the interacting atoms. Dumbbell-shaped pair-correlation images demonstrate the anisotropy of the binary dipolar force. The dipolar C_{3} coefficient, derived from the time dependence of the images, agrees with the value calculated from the permanent electric-dipole moment of the atoms. The results indicate many-body dynamics akin to disorder-induced heating in strongly coupled particle systems.

Contrasting dynamics of electrons and protons in the near-Earth plasma sheet during dipolarization

Science.gov (United States)

Malykhin, Andrey Y.; Grigorenko, Elena E.; Kronberg, Elena A.; Koleva, Rositza; Ganushkina, Natalia Y.; Kozak, Ludmila; Daly, Patrick W.

2018-05-01

The fortunate location of Cluster and the THEMIS P3 probe in the near-Earth plasma sheet (PS) (at X ˜ -7-9 RE) allowed for the multipoint analysis of properties and spectra of electron and proton injections. The injections were observed during dipolarization and substorm current wedge formation associated with braking of multiple bursty bulk flows (BBFs). In the course of dipolarization, a gradual growth of the BZ magnetic field lasted ˜ 13 min and it was comprised of several BZ pulses or dipolarization fronts (DFs) with duration ≤ 1 min. Multipoint observations have shown that the beginning of the increase in suprathermal ( > 50 keV) electron fluxes - the injection boundary - was observed in the PS simultaneously with the dipolarization onset and it propagated dawnward along with the onset-related DF. The subsequent dynamics of the energetic electron flux was similar to the dynamics of the magnetic field during the dipolarization. Namely, a gradual linear growth of the electron flux occurred simultaneously with the gradual growth of the BZ field, and it was comprised of multiple short ( ˜ few minutes) electron injections associated with the BZ pulses. This behavior can be explained by the combined action of local betatron acceleration at the BZ pulses and subsequent gradient drifts of electrons in the flux pile up region through the numerous braking and diverting DFs. The nonadiabatic features occasionally observed in the electron spectra during the injections can be due to the electron interactions with high-frequency electromagnetic or electrostatic fluctuations transiently observed in the course of dipolarization. On the contrary, proton injections were detected only in the vicinity of the strongest BZ pulses. The front thickness of these pulses was less than a gyroradius of thermal protons that ensured the nonadiabatic acceleration of protons. Indeed, during the injections in the energy spectra of protons the pronounced bulge was clearly observed in a

Coherent manipulation of dipolar coupled spins in an anisotropic environment

Science.gov (United States)

Baibekov, E. I.; Gafurov, M. R.; Zverev, D. G.; Kurkin, I. N.; Malkin, B. Z.; Barbara, B.

2014-11-01

We study coherent dynamics in a system of dipolar coupled spin qubits diluted in a solid and subjected to a driving microwave field. In the case of rare earth ions, an anisotropic crystal background results in anisotropic g tensor and thus modifies the dipolar coupling. We develop a microscopic theory of spin relaxation in a transient regime for the frequently encountered case of axially symmetric crystal field. The calculated decoherence rate is nonlinear in the Rabi frequency. We show that the direction of a static magnetic field that corresponds to the highest spin g factor is preferable in order to obtain a higher number of coherent qubit operations. The results of calculations are in excellent agreement with our experimental data on Rabi oscillations recorded for a series of CaW O4 crystals with different concentrations of N d3 + ions.

Arrays of dipolar molecular rotors in Tris(o-phenylenedioxy) cyclotriphosphazene.

Science.gov (United States)

Zhao, Ke; Dron, Paul I; Kaleta, Jiří; Rogers, Charles T; Michl, Josef

2014-01-01

Regular two-dimensional or three-dimensional arrays of mutually interacting dipolar molecular rotors represent a worthy synthetic objective. Their dielectric properties, including possible collective behavior, will be a sensitive function of the location of the rotors, the orientation of their axes, and the size of their dipoles. Host-guest chemistry is one possible approach to gaining fine control over these factors. We describe the progress that has been achieved in recent years using tris (o-phenylenedioxy)cyclotriphosphazene as a host and a series of rod-shaped dipolar molecular rotors as guests. Structures of both surface and bulk inclusion compounds have been established primarily by solid-state nuclear magnetic resonance (NMR) and powder X-ray diffraction (XRD) techniques. Low-temperature dielectric spectroscopy revealed rotational barriers as low as 1.5 kcal/mol, but no definitive evidence for collective behavior has been obtained so far.

Fluctuation and dipolar interaction effects on the pinning of domain walls

International Nuclear Information System (INIS)

Chui, S.T.

2001-01-01

We discuss the effect of the dipolar interaction on the pinning of domain walls. Domain walls are usually pinned near the boundaries between grains. Magnetic charges accumulated at the domain wall make the wall more unstable and easier to depin. We discuss how the grain-orientation and thermal fluctuations affect these magnetic charges and hence the depinning of the domain walls. Our results are illustrated by finite temperature Monte Carlo simulation on periodic arrays of large cells separated by walls consisting of faces of pyramids

Mechanics of magnetic fluid column in strong magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Polunin, V.M.; Ryapolov, P.A., E-mail: r-piter@yandex.ru; Platonov, V.B.

2017-06-01

Elastic-and magnetic properties of magnetic fluid confined by ponderomotive force in a tube fixed in horizontal position are considered. The system is placed in a strong magnetic field under the influence of external static and dynamic perturbations. An experimental setup has been developed. A theoretical basis of the processes of magnetic colloid elastic deformation has been proposed. The values of the static ponderomotive elasticity coefficient and the elasticity coefficient under dynamic action are experimentally determined. The calculations of the saturation magnetization for two magnetic fluid samples, carried out according to the equation containing the dynamic elasticity coefficient, are in good agreement with the experimental magnetization curve. The described method is of interest when studying magnetophoresis and aggregation of nanoparticles in magnetic colloids.

Magnetospheric Multiscale (MMS) Observations of Energetic Ion Response to Magnetotail Dipolarization Events

Science.gov (United States)

Cohen, I. J.; Mauk, B.; Anderson, B. J.; Sitnov, M. I.; Motoba, T.; Ohtani, S.; Gkioulidou, M.; Fuselier, S. A.; Giles, B. L.; Strangeway, R. J.; Torbert, R. B.; Burch, J. L.

2017-12-01

Observations from the Energetic Ion Spectrometer (EIS) instruments aboard MMS have shown angular (pitch, elevation, azimuthal) asymmetries of energetic (>10s of keV) ions corresponding to dipolarization events in the near-Earth and distant magnetotail. In particular, EIS distinguishes the species composition of these ions (protons, helium, oxygen) and reveals apparent species-based differences in their response. This study presents analysis of the dynamic injection and mass-dependent response of energetic ions that likely result from the kinetic response of the ions to the time-varying electric and magnetic fields associated with injection process. Analysis is focused on discriminating between truly kinetic responses to the dynamics and the features that arise from large gyro-radii particles in the vicinity of strong spatial gradients. The study will focus on EIS measurements and include supplementary data from the FIELDS, FPI, and HPCA instruments.

Absence of Long-Range Order in a Triangular Spin System with Dipolar Interactions

Science.gov (United States)

Keleş, Ahmet; Zhao, Erhai

2018-05-01

The antiferromagnetic Heisenberg model on the triangular lattice is perhaps the best known example of frustrated magnets, but it orders at low temperatures. Recent density matrix renormalization group (DMRG) calculations find that the next nearest neighbor interaction J2 enhances the frustration, and it leads to a spin liquid for J2/J1∈(0.08 ,0.15 ). In addition, a DMRG study of a dipolar Heisenberg model with longer range interactions gives evidence for a spin liquid at a small dipole tilting angle θ ∈[0 ,1 0 ° ). In both cases, the putative spin liquid region appears to be small. Here, we show that for the triangular lattice dipolar Heisenberg model, a robust quantum paramagnetic phase exists in a surprisingly wide region, θ ∈[0 ,5 4 ° ) , for dipoles tilted along the lattice diagonal direction. We obtain the phase diagram of the model by functional renormalization group (RG), which treats all magnetic instabilities on equal footing. The quantum paramagnetic phase is characterized by a smooth continuous flow of vertex functions and spin susceptibility down to the lowest RG scale, in contrast to the apparent breakdown of RG flow in phases with stripe or spiral order. Our finding points to a promising direction to search for quantum spin liquids in ultracold dipolar molecules.

Characterizing Ion Flows Across a Dipolarization Front

Science.gov (United States)

Arnold, H.; Drake, J. F.; Swisdak, M.

2017-12-01

In light of the Magnetospheric Multiscale Mission (MMS) moving to study predominately symmetric magnetic reconnection in the Earth's magnetotail, it is of interest to investigate various methods for determining the relative location of the satellites with respect to the x line or a dipolarization front. We use a 2.5 dimensional PIC simulation to explore the dependence of various characteristics of a front, or flux bundle, on the width of the front in the dawn-dusk direction. In particular, we characterize the ion flow in the x-GSM direction across the front. We find a linear relationship between the width of a front, w, and the maximum velocity of the ion flow in the x-GSM direction, Vxi, for small widths: Vxi/VA=w/di*1/2*(mVA2)/Ti*Bz/Bxwhere m, VA, di, Ti, Bz, and Bx are the ion mass, upstream Alfven speed, ion inertial length, ion temperature, and magnetic fields in the z-GSM and x-GSM directions respectively. However, once the width reaches around 5 di, the relationship gradually approaches the well-known theoretical limit for ion flows, the upstream Alfven speed. Furthermore, we note that there is a reversal in the Hall magnetic field near the current sheet on the positive y-GSM side of the front. This reversal is most likely due to conservation of momentum in the y-GSM direction as the ions accelerate towards the x-GSM direction. This indicates that while the ions are primarily energized in the x-GSM direction by the front, they transfer energy to the electromagnetic fields in the y-GSM direction. The former energy transfer is greater than the latter, but the reversal of the Hall magnetic field drags the frozen-in electrons along with it outside of the front. These simulations should better able researchers to determine the relative location of a satellite crossing a dipolarization front.

Magnetic dipolar coupling and collective effects for binary information codification in cost-effective logic devices

International Nuclear Information System (INIS)

Chiolerio, Alessandro; Allia, Paolo; Graziano, Mariagrazia

2012-01-01

Physical limitations foreshadow the eventual end to traditional Complementary Metal Oxide Semiconductor (CMOS) scaling. Therefore, interest has turned to various materials and technologies aimed to succeed to traditional CMOS. Magnetic Quantum dot Cellular Automata (MQCA) are one of these technologies. Working MQCA arrays require very complex techniques and an excellent control on the geometry of the nanomagnets and on the quality of the magnetic thin film, thus limiting the possibility for MQCA of representing a definite solution to cost-effective, high density and low power consumption device demand. Counter-intuitively, moving towards bigger sizes and lighter technologies it is still possible to develop multi-state logic devices, as we demonstrated, whose main advantage is cost-effectiveness. Applications may be seen in low cost logic devices where integration and computational power are not the main issue, eventually using flexible substrates and taking advantage of the intrinsic mechanical toughness of systems where long range interactions do not need wirings. We realized cobalt micrometric MQCA arrays by means of Electron Beam Lithography, exploiting cost-effective processes such as lift-off and RF sputtering that usually are avoided due to their low control on array geometry and film roughness. Information relative to the magnetic configuration of MQCA elements including their eventual magnetic interactions was obtained from Magnetic Force Microscope (MFM) images, enhanced by means of a numerical procedure and presented in differential maps. We report the existence of bi-stable magnetic patterns, as detected by MFM while sampling the z-component of magnetic induction field, arising from dipolar inter-element magnetostatic coupling, able to store and propagate binary information. This is achieved despite the array quality and element magnetic state, which are low and multi-domain, respectively. We discuss in detail shape, inter-element spacing and dot profile

Interlayer exchange coupling, dipolar coupling and magnetoresistance in Fe/MgO/Fe trilayers with a subnanometer MgO barrier

Energy Technology Data Exchange (ETDEWEB)

Kozioł-Rachwał, A. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków (Poland); National Institute of Advanced Industrial Science and Technology, Spintronics Research Center, Tsukuba, Ibaraki 305-8568 (Japan); Skowroński, W.; Frankowski, M. [AGH University of Science and Technology, Department of Electronics, al. Mickiewicza 30, 30-059 Kraków (Poland); Chęciński, J. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków (Poland); AGH University of Science and Technology, Department of Electronics, al. Mickiewicza 30, 30-059 Kraków (Poland); Ziętek, S.; Rzeszut, P. [AGH University of Science and Technology, Department of Electronics, al. Mickiewicza 30, 30-059 Kraków (Poland); Ślęzak, M.; Matlak, K.; Ślęzak, T. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków (Poland); Stobiecki, T. [AGH University of Science and Technology, Department of Electronics, al. Mickiewicza 30, 30-059 Kraków (Poland); Korecki, J. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków (Poland); Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Kraków (Poland)

2017-02-15

Fe/MgO/Fe trilayers with a subnanometer MgO tunnel barrier were grown by molecular beam epitaxy. Longitudinal magnetooptic Kerr effect measurements confirmed the existence of the antiferromagnetic interlayer exchange coupling (IEC) between the Fe layers for 2 Åmagnetic characterization, the sample was patterned into circular-shaped pillars with diameters ranging from 200 nm to 520 nm. We showed that the dipolar coupling that appeared after the nanofabrication process modified the effective coupling between layers, and we determined dependence of the dipolar coupling on the pillar diameter. Finally, magnetoresistance (MR) was measured as a function of MgO thickness (d{sub MgO}), and a non-zero MR was found for the MgO as thin as 3.4 Å. Extrapolation of the MR (d{sub MgO}) dependence to MR=0 allowed us to determine the length of the pinholes in our sample, which was estimated to be (3.2±0.5) Å. - Highlights: • Strong antiferromagnetic (AFM) interlayer exchange coupling (IEC) between Fe layers in Fe/MgO/Fe. • After nanofabrication the effective AFM IEC is enhanced due to the dipolar coupling. • The dipolar coupling that appeared after the nanofabrication process modified the effective coupling between layers. • Non-zero magnetoresistance values registered for the Fe/MgO/Fe trilayers with the MgO spacers as thin as 3.4 Å.

Watermelon-like iron nanoparticles: Cr doping effect on magnetism and magnetization interaction reversal

Energy Technology Data Exchange (ETDEWEB)

Kaur, Maninder; Dai, Qilin; Bowden, Mark E.; Engelhard, Mark H.; Wu, Yaqiao; Tang, Jinke; Qiang, You

2013-06-26

Chromium (Cr) forms a solid solution with iron (Fe) lattice when doped in core-shell iron -iron oxide nanocluster (NC) and shows a mixed phase of sigma (σ) FeCr and bcc Fe. The Cr dopant affects heavily the magnetization and magnetic reversal process, and causes the hysteresis loop to shrink near the zero field axis. Dramatic transformation happens from dipolar interaction (0 at. % Cr) to strong exchange interaction (8 at. % of Cr) is confirmed from the Henkel plot and delta M plot, and is explained by a water-melon model of core-shell NC system.

Direct Observation of Field and Temperature Induced Domain Replication in Dipolar Coupled Perpendicular Anisotropy Films

Energy Technology Data Exchange (ETDEWEB)

Hauet, T.; Gunther, C.M.; Pfau, B.; Eisebitt, S.; Fischer, P.; Rick, R. L.; Thiele, J.-U.; Hellwig, O.; Schabes, M.E.

2007-07-01

Dipolar interactions in a soft/Pd/hard [CoNi/Pd]{sub 30}/Pd/[Co/Pd]{sub 20} multilayer system, where a thick Pd layer between two ferromagnetic units prevents direct exchange coupling, are directly revealed by combining magnetometry and state-of-the-art layer resolving soft x-ray imaging techniques with sub-100-nm spatial resolution. The domains forming in the soft layer during external magnetic field reversal are found to match the domains previously trapped in the hard layer. The low Curie temperature of the soft layer allows varying its intrinsic parameters via temperature and thus studying the competition with dipolar fields due to the domains in the hard layer. Micromagnetic simulations elucidate the role of [CoNi/Pd] magnetization, exchange, and anisotropy in the duplication process. Finally, thermally driven domain replication in remanence during temperature cycling is demonstrated.

Longitudinal expansion of field line dipolarization

Science.gov (United States)

Saka, O.; Hayashi, K.

2017-11-01

We examine the substorm expansions that started at 1155 UT 10 August 1994 in the midnight sector focusing on the longitudinal (eastward) expansion of field line dipolarization in the auroral zone. Eastward expansion of the dipolarization region was observed in all of the H, D, and Z components. The dipolarization that started at 1155 UT (0027 MLT) from 260° of geomagnetic longitude (CMO) expanded to 351°(PBQ) in about 48 min. The expansion velocity was 0.03-0.04°/s, or 1.9 km/s at 62°N of geomagnetic latitude. The dipolarization region expanding to the east was accompanied by a bipolar event at the leading edge of the expansion in latitudes equatorward of the westward electrojet (WEJ). In the midnight sector at the onset meridian, the Magnetospheric Plasma Analyzer (MAP) on board geosynchronous satellite L9 measured electrons and ions between 10 eV and 40 keV. We conclude from the satellite observations that this dipolarization was characterized by the evolution of temperature anisotropies, an increase of the electron and ion temperatures, and a rapid change in the symmetry axis of the temperature tensor. The field line dipolarization and its longitudinal expansion were interpreted in terms of the slow MHD mode triggered by the current disruption. We propose a new magnetosphere-ionosphere coupling (MI-coupling) mechanism based on the scenario that transmitted westward electric fields from the magnetosphere in association with expanding dipolarization produced electrostatic potential (negative) in the ionosphere through differences in the mobility of collisional ions and collisionless electrons. The field-aligned currents that emerged from the negative potential region are arranged in a concentric pattern around the negative potential region, upward toward the center and downward on the peripheral.

Influence of static and dynamic dipolar fields in bulk YIG/thin film NiFe systems probed via spin rectification effect

Energy Technology Data Exchange (ETDEWEB)

Soh, Wee Tee, E-mail: a0046479@u.nus.edu [Center for Superconducting and Magnetic Materials, Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551 (Singapore); Tay, Z.J. [Center for Superconducting and Magnetic Materials, Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551 (Singapore); Yakovlev, N.L. [Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore); Peng, Bin [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China); Ong, C.K. [Center for Superconducting and Magnetic Materials, Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551 (Singapore); Temasek Laboratories, National University of Singapore, 5A Engineering Drive 2, Singapore 117411 (Singapore)

2017-03-15

The characteristics of the static and dynamic components of the dipolar fields originating from a bulk polycrystalline yttrium iron garnet (YIG) substrate are probed by depositing a NiFe (Permalloy) layer on it, which acts as a detector. By measuring dc voltages generated via spin rectification effect (SRE) within the NiFe layer under microwave excitation, we characterize the influence of dipolar fields from bulk YIG on the NiFe layer. It is found that the dynamic YIG dipolar fields modify the self-SRE of NiFe, driving its own rectification voltages within the NiFe layer, an effect we term as non-local SRE. This non-local SRE only occurs near the simultaneous resonance of both YIG and NiFe. On the other hand, the static dipolar field from YIG manifests itself as a negative anisotropy in the NiFe layer which shifts the latter’s ferromagnetic resonance frequency. - Highlights: • We demonstrate the quantification of both the static and dynamic components of the dipolar fields due to a YIG slab. • The detection and characterisation of such dipolar fields are important in many magnetic applications such as magnonics. • The dipolar fields can pose potential pitfalls if not properly considered in certain spin-electronics systems.

Acceleration and Precipitation of Electrons during Substorm Dipolarization Events

Science.gov (United States)

Ashour-Abdalla, Maha; Richard, Robert; Donovan, Eric; Zhou, Meng; Goldstein, Mevlyn; El-Alaoui, Mostafa; Schriver, David; Walker, Raymond

Observations and modeling have established that during geomagnetically disturbed times the Earth’s magnetotail goes through large scale changes that result in enhanced electron precipitation into the ionosphere and earthward propagating dipolarization fronts that contain highly energized plasma. Such events originate near reconnection regions in the magnetotail at about 20-30 R_E down tail. As the dipolarization fronts propagate earthward, strong acceleration of both ions and electrons occurs due to a combination of non-adiabatic and adiabatic (betatron and Fermi) acceleration, with particle energies reaching up to 100 keV within the dipolarization front. One consequence of the plasma transport that occurs during these events is direct electron precipitation into the ionosphere, which form auroral precipitation. Using global kinetic simulations along with spacecraft and ground-based data, causes of electron precipitation are determined during well-documented, disturbed events. It is found that precipitation of keV electrons in the pre-midnight sector at latitudes around 70(°) occur due to two distinct physical processes: (1) higher latitude (≥72(°) ) precipitation due to electrons that undergo relatively rapid non-adiabatic pitch angle scattering into the loss cone just earthward of the reconnection region at around 20 R_E downtail, and (2) lower latitude (≤72(°) ) precipitation due to electrons that are more gradually accelerated primarily parallel to the geomagnetic field during its bounce motion by Fermi acceleration and enter the loss cone much closer to the Earth at 10-15 R_E, somewhat tailward of the dipolarization front. As the dipolarization fronts propagate earthward, the electron precipitation shifts to lower latitudes and occurs over a wider region in the auroral ionosphere. Our results show a direct connection between electron acceleration in the magnetotail and electron precipitation in the ionosphere during disturbed times. The electron

Non-dipolar gauge links for transverse-momentum-dependent pion wave functions

International Nuclear Information System (INIS)

Wang, Y.M.

2016-01-01

I discuss the factorization-compatible definitions of transverse-momentum-dependent (TMD) pion wave functions which are fundamental theory inputs entering QCD factorization formulae for many hard exclusive processes. I will first demonstrate that the soft subtraction factor introduced to remove both rapidity and pinch singularities can be greatly reduced by making the maximal use of the freedom to construct the Wilson-line paths when defining the TMD wave functions. I will then turn to show that the newly proposed TMD definition with non-dipolar Wilson lines is equivalent to the one with dipolar gauge links and with a complicated soft function, to all orders of the perturbative expansion in the strong coupling, as far as the infrared behavior is concerned. (author)

Curie temperature and magnetic phase transition of nanostructured ultrathin Fe/GaAs (001). Size dependence and relevance of dipolar coupling

Energy Technology Data Exchange (ETDEWEB)

Meier, Roland

2009-07-01

In the present work the impact of lateral patterning of ultrathin ferromagnetic films down to the nanometer range on the magnetic phase transition has been investigated. In this respect on the one hand a size effect on the Curie temperature and, referring to that, the relevance of dipolar coupling were a matter of particular interest. On the other hand the characteristics of the critical behavior itself, becoming apparent by the accurate evaluation of the curvature shape of the magnetization as a function of temperature at T{sub c}, were analyzed with regard to potential and expected size effects. The investigation of similar nanostructures with respect to an effect on Curie temperature respectively phase transition may draw up a correlation. Therefore more than hundred samples were fabricated for this work extensively by means of MBE (Molecular Beam Epitaxy) and ESL (Electron Beam Epitaxy) methods, measured by MOKE (Magneto-Optical Kerr Effect) technique and systematically evaluated. (orig.)

Hydrogen atoms in a strong magnetic field

International Nuclear Information System (INIS)

Santos, R.R. dos.

1975-07-01

The energies and wave functions of the 14 lowest states of a Hydrogen atom in a strong magnetic field are calculated, using a variational scheme. The equivalence between the atomic problem and the problems related with excitons and impurities in semiconductors in the presence of a strong magnetic field are shown. The calculations of the energies and wave functions have been divided in two regions: the first, for the magnetic field ranging between zero and 10 9 G; in the second the magnetic field ranges between 10 9 and 10 11 G. The results have been compared with those obtained by previous authors. The computation time necessary for the calculations is small. Therefore this is a convenient scheme to obtain the energies and wave functions for the problem. Transition probabilities, wavelengths and oscillator strengths for some allowed transitions are also calculated. (Author) [pt

Frictional Coulomb drag in strong magnetic fields

DEFF Research Database (Denmark)

Bønsager, Martin Christian; Flensberg, Karsten; Hu, Ben Yu-Kuang

1997-01-01

A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21) is eval......A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity rho(21...

The quantum coherence of disordered dipolar bosonic gas

International Nuclear Information System (INIS)

Wang Jiguo; Zhang Aixia; Tang Rongan; Gao Jimin; Xue Jukui

2013-01-01

We investigate the coherence of correlated dipolar gas in the presence of disorder within a three-site Bose–Hubbard model. We show that the interplay between the on-site interaction, the inter-site dipole–dipole interactions (DDI) and the disorder exhibits new and interesting coherence characters that cannot take place in a non-dipolar system. The ratio between the on-site interaction and DDI plays a dominant role in the phase coherence. The resonance character of the coherence against both disorder and interactions emerges. DDI can enhance the coherence at certain values of the disorder and on-site interaction. In the coherence region, the enhancement of the coherence by disorder in a dipolar system is more significant than that in a non-dipolar system. In particular, the on-site interaction and DDI together can enhance the coherence even in the clean dipolar system (i.e. a dipolar system without disorder). However, without the on-site interaction, disorder, DDI or both together suppress the coherence. Furthermore, the relationship between the coherence and the energy gap and the compressibility of the system is also discussed. (paper)

MAXIMIZING MAGNETIC ENERGY STORAGE IN THE SOLAR CORONA

International Nuclear Information System (INIS)

Wolfson, Richard; Drake, Christina; Kennedy, Max

2012-01-01

The energy that drives solar eruptive events such as coronal mass ejections (CMEs) almost certainly originates in coronal magnetic fields. Such energy may build up gradually on timescales of days or longer before its sudden release in an eruptive event, and the presence of free magnetic energy capable of rapid release requires nonpotential magnetic fields and associated electric currents. For magnetic energy to power a CME, that energy must be sufficient to open the magnetic field to interplanetary space, to lift the ejecta against solar gravity, and to accelerate the material to speeds of typically several hundred km s –1 . Although CMEs are large-scale structures, many originate from relatively compact active regions on the solar surface—suggesting that magnetic energy storage may be enhanced when it takes place in smaller magnetic structures. This paper builds on our earlier work exploring energy storage in large-scale dipolar and related bipolar magnetic fields. Here we consider two additional cases: quadrupolar fields and concentrated magnetic bipoles intended to simulate active regions. Our models yield stored energies whose excess over that of the corresponding open field state can be greater than 100% of the associated potential field energy; this contrasts with maximum excess energies of only about 20% for dipolar and symmetric bipolar configurations. As in our previous work, energy storage is enhanced when we surround a nonpotential field with a strong overlying potential field that acts to 'hold down' the nonpotential flux as its magnetic energy increases.

Nonlinear Electron Waves in Strongly Magnetized Plasmas

DEFF Research Database (Denmark)

Pécseli, Hans; Juul Rasmussen, Jens

1980-01-01

Weakly nonlinear dispersive electron waves in strongly magnetized plasma are considered. A modified nonlinear Schrodinger equation is derived taking into account the effect of particles resonating with the group velocity of the waves (nonlinear Landau damping). The possibility of including the ion...... dynamics in the analysis is also demonstrated. As a particular case the authors investigate nonlinear waves in a strongly magnetized plasma filled wave-guide, where the effects of finite geometry are important. The relevance of this problem to laboratory experiments is discussed....

NMR studies on 1,3-dipolar cycloaddition of nitrile oxides to norbornenes

International Nuclear Information System (INIS)

Gucma, Mirosław; Gołębiewski, W. Marek; Krawczyk, Maria

2013-01-01

The 1,3-dipolar cycloaddition reaction of nitrile oxides to norbornenes substituted with an acrylate-derived moiety was examined. Only adducts to norbornene system were formed with a good exo selectivity and complete site-selectivity. Structures of the products were elucidated by an extensive application of electrospray ionization-mass spectrometry (ESI-MS) and 2D 1 H and 13 C nuclear magnetic resonance (NMR). (author)

NMR studies on 1,3-dipolar cycloaddition of nitrile oxides to norbornenes

Energy Technology Data Exchange (ETDEWEB)

Gucma, Miroslaw; Golebiewski, W. Marek; Krawczyk, Maria, E-mail: golebiewski@ipo.waw.pl [Institute of Industrial Organic Chemistry, Warsaw (Poland)

2013-05-15

The 1,3-dipolar cycloaddition reaction of nitrile oxides to norbornenes substituted with an acrylate-derived moiety was examined. Only adducts to norbornene system were formed with a good exo selectivity and complete site-selectivity. Structures of the products were elucidated by an extensive application of electrospray ionization-mass spectrometry (ESI-MS) and 2D {sup 1}H and {sup 13}C nuclear magnetic resonance (NMR). (author)

Dipolar modulation of Large-Scale Structure

Science.gov (United States)

Yoon, Mijin

For the last two decades, we have seen a drastic development of modern cosmology based on various observations such as the cosmic microwave background (CMB), type Ia supernovae, and baryonic acoustic oscillations (BAO). These observational evidences have led us to a great deal of consensus on the cosmological model so-called LambdaCDM and tight constraints on cosmological parameters consisting the model. On the other hand, the advancement in cosmology relies on the cosmological principle: the universe is isotropic and homogeneous on large scales. Testing these fundamental assumptions is crucial and will soon become possible given the planned observations ahead. Dipolar modulation is the largest angular anisotropy of the sky, which is quantified by its direction and amplitude. We measured a huge dipolar modulation in CMB, which mainly originated from our solar system's motion relative to CMB rest frame. However, we have not yet acquired consistent measurements of dipolar modulations in large-scale structure (LSS), as they require large sky coverage and a number of well-identified objects. In this thesis, we explore measurement of dipolar modulation in number counts of LSS objects as a test of statistical isotropy. This thesis is based on two papers that were published in peer-reviewed journals. In Chapter 2 [Yoon et al., 2014], we measured a dipolar modulation in number counts of WISE matched with 2MASS sources. In Chapter 3 [Yoon & Huterer, 2015], we investigated requirements for detection of kinematic dipole in future surveys.

Phase transitions in random uniaxial systems with dipolar interactions

International Nuclear Information System (INIS)

Schuster, H.G.

1977-01-01

The critical behaviour of random uniaxial ferromagnetic (ferroelectric) systems with both short range and long range dipolar interactions is investigated, using the field theoretic renormalization method of Brezin et al. for the free energy above and below transition point Tsub(c). The randomness is due to externally introduced fluctuations in the short range interactions (quenched case) or (and) magneto-elastic coupling to the lattice (annealed case). Strong deviations in the critical behaviour with respect to the pure systems are found. In the quenched case, e.g., the specific heat C and the coefficient f 2 (of M 3 in the equation of state, where M is the magnetization) change from C proportional to abs ln abs t abs abssup(1/3), f 2 proportional to abs ln abs t abs abs sup(1/3), f 2 proportional to abs ln abs t abs abs -1 in the pure system to C = A+- + C+-exp[-4√ 3 106 abs ln abs t abs abs], f 2 proportional to abs ln abs t abs abs sup(-1/2) (where t = (T-Tsub(c)) / Tsub(c) is the reduced temperature and A+-, C+- are constants) in the random situation. (orig.) [de

Jeans instability of self-gravitating magnetized strongly coupled plasma

International Nuclear Information System (INIS)

Prajapati, R P; Sharma, P K; Sanghvi, R K; Chhajlani, R K

2012-01-01

We investigate the Jeans instability of self-gravitating magnetized strongly coupled plasma. The equations of the problem are formulated using the generalized hydrodynamic model and a general dispersion relation is obtained using the normal mode analysis. This dispersion relation is discussed for transverse and longitudinal mode of propagations. The modified condition of Jeans instability is obtained for magnetized strongly coupled plasma. We find that strong coupling of plasma particles modify the fundamental criterion of Jeans gravitational instability. In transverse mode it is found that Jeans instability criterion gets modified due to the presence of magnetic field, shear viscosity and fluid viscosity but in longitudinal mode it is unaffected due to the presence of magnetic field. From the curves we found that all these parameters have stabilizing influence on the growth rate of Jeans instability.

Magnetization of dense neutron matter in a strong magnetic field

International Nuclear Information System (INIS)

Isaev, A.A.; Yang, J.

2010-01-01

Spin polarized states in neutron matter at a strong magnetic field up to 1018 G are considered in the model with the Skyrme effective interaction. Analyzing the self consistent equations at zero temperature, it is shown that a thermodynamically stable branch of solutions for the spin polarization parameter as a function of the density corresponds to the negative spin polarization when the majority of neutron spins are oriented oppositely to the direction of the magnetic field. In addition, beginning from some threshold density dependent on the magnetic field strength, the self-consistent equations have also two other branches of solutions for the spin polarization parameter with the positive spin polarization. The free energy corresponding to one of these branches turns out to be very close to the free energy corresponding to the thermodynamically preferable branch with the negative spin polarization. As a consequence, at a strong magnetic field, the state with the positive spin polarization can be realized as a metastable state at the high density region in neutron matter which changes into a thermodynamically stable state with the negative spin polarization with decrease in the density at some threshold value. The calculations of the neutron spin polarization parameter, energy per neutron, and chemical potentials of spin-up and spin-down neutrons as functions of the magnetic field strength show that the influence of the magnetic field remains small at the field strengths up to 1017 G.

Radiative properties of strongly magnetized plasmas

International Nuclear Information System (INIS)

Weisheit, J.C.

1993-11-01

The influence of strong magnetic fields on quantum phenomena continues to be a topic of much interest to physicists and astronomers investigating a wide array of problems - the formation of high energy-density plasmas in pulsed power experiments, the crustal structure and radiative properties of neutron stars, transport coefficients of matter irradiated by subpicosecond lasers, the spectroscopy of magnetic white dwarf stars, the quantum Hall effect, etc. The passage of time finds more questions being asked than being answered in this subject, where even the hydrogen atom open-quotes paradigmclose quotes remains a major challenge. This theoretical program consists of two distinct parts: (1) investigation into the structure and transport properties of many-electron atoms in fields B > 10 8 Gauss; and (2) extension of spectral lineshape methods for diagnosing fields in strongly magnetized plasmas. Research during the past year continued to be focused on the first topic, primarily because of the interest and skills of Dr. E.P. Lief, the postdoctoral research associate who was hired to work on the proposal

The effect of temperature on the magnetization reversal mechanism in sintered PrFeB

International Nuclear Information System (INIS)

Crew, D. C.; Lewis, L. H.; Welch, D. O.; Pourarian, F.

2000-01-01

To understand the effects of nucleation fields and intergranular dipolar interactions on the magnetization reversal mechanism, recoil curves from the major hysteresis loop have been measured on a sample of sintered PrFeB as a function of temperature from 150 to 300 K. At room temperature the reversible magnetization behavior indicates a reversal mechanism of nucleation of domain walls whose motion after nucleation is resisted by dipolar fields. As the temperature is reduced, the coercivity, and hence the nucleation field, is observed to increase while the dipolar fields, dependent on microstructure and saturation magnetization, remain approximately constant. These temperature-dependent changes in the relative magnitudes of the dipolar field and nucleation field cause the reversible magnetization behavior to change from domain wall motion to rotation. This change in behavior is attributed to the supposition that at temperatures where the nucleation field exceeds the dipolar field, once nucleated, domain walls are swept out of the material. (c) 2000 American Institute of Physics

LDA+DMFT Approach to Magnetocrystalline Anisotropy of Strong Magnets

Directory of Open Access Journals (Sweden)

Jian-Xin Zhu

2014-05-01

Full Text Available The new challenges posed by the need of finding strong rare-earth-free magnets demand methods that can predict magnetization and magnetocrystalline anisotropy energy (MAE. We argue that correlated electron effects, which are normally underestimated in band-structure calculations, play a crucial role in the development of the orbital component of the magnetic moments. Because magnetic anisotropy arises from this orbital component, the ability to include correlation effects has profound consequences on our predictive power of the MAE of strong magnets. Here, we show that incorporating the local effects of electronic correlations with dynamical mean-field theory provides reliable estimates of the orbital moment, the mass enhancement, and the MAE of YCo_{5}.

Matter and Radiation in Strong Magnetic Fields of Neutron Stars

International Nuclear Information System (INIS)

Lai, D

2006-01-01

Neutron stars are found to possess magnetic fields ranging from 10 8 G to 10 15 G, much larger than achievable in terrestrial laboratories. Understanding the properties of matter and radiative transfer in strong magnetic fields is essential for the proper interpretation of various observations of magnetic neutron stars, including radio pulsars and magnetars. This paper reviews the atomic/molecular physics and condensed matter physics in strong magnetic fields, as well as recent works on modeling radiation from magnetized neutron star atmospheres/surface layers

Harmonically trapped dipolar fermions in a two-dimensional square lattice

DEFF Research Database (Denmark)

Larsen, Anne-Louise G.; Bruun, Georg

2012-01-01

We consider dipolar fermions in a two-dimensional square lattice and a harmonic trapping potential. The anisotropy of the dipolar interaction combined with the lattice leads to transitions between phases with density order of different symmetries. We show that the attractive part of the dipolar...

Electron Jet Detected by MMS at Dipolarization Front

Science.gov (United States)

Liu, C. M.; Fu, H. S.; Vaivads, A.; Khotyaintsev, Y. V.; Gershman, D. J.; Hwang, K.-J.; Chen, Z. Z.; Cao, D.; Xu, Y.; Yang, J.; Peng, F. Z.; Huang, S. Y.; Burch, J. L.; Giles, B. L.; Ergun, R. E.; Russell, C. T.; Lindqvist, P.-A.; Le Contel, O.

2018-01-01

Using MMS high-resolution measurements, we present the first observation of fast electron jet (Ve 2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale comparable to the DF thickness ( 0.9 di), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E × B drift motion; it contributes significantly to the current system at the DF, including a localized ring-current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron-jet-driven current (E ṡ je ≈ 2 E ṡ ji), rather than the ion current suggested in previous studies.

Magnetization reversal processes in bonded magnets made from a mixture of Nd–(Fe,Co)–B and strontium ferrite powders

International Nuclear Information System (INIS)

Dospial, M.; Plusa, D.

2013-01-01

Isotropic epoxy-resin bonded magnets composed of different amounts of Magnequench MQP-B and strontium ferrite powders have been prepared using a compression molding technique. The magnetic parameters for magnets with different amounts of strontium ferrite and magnetization reversal processes have been studied by the measurement of the initial magnetization curves, the major hysteresis loops measured at a field up to 14 T and sets of recoil loops. The enhancement of μ 0 M R and μ 0 H C is observed in comparison with the calculated values. From the recoil loops the field dependences of the reversible, irreversible and total magnetization components and the differential susceptibilities were derived. From the dependence of the irreversible magnetization component versus an applied field it was deduced that the main mechanism of magnetization reversal process is the pinning of domain walls in MQP-B and strontium ferrite grains. The interactions between the magnetic particles and grains have been examined by the analysis of the δM plot. The δM behavior of magnets with ferrite has been interpreted as being composed of magnetizing exchange coupling and demagnetizing dipolar interactions. - Highlights: ► SrFe 12 O 19 addition causes a decrease in the H c , J R and (BH) max . ► H c and J R changes are not in agreement with dilution law. ► Main mechanism of the coercivity is the pinning of domain walls. ► In both magnets from pure powders dominant role plays long range dipolar interactions. ► Dipolar and exchange interaction are simultaneously present in hybrids but the dipolar are weaker.

Partial alignment and measurement of residual dipolar couplings of proteins under high hydrostatic pressure

Energy Technology Data Exchange (ETDEWEB)

Fu, Yinan; Wand, A. Joshua, E-mail: wand@mail.med.upenn.edu [University of Pennsylvania, Department of Biochemistry and Biophysics, Johnson Research Foundation (United States)

2013-08-15

High-pressure NMR spectroscopy has emerged as a complementary approach for investigating various structural and thermodynamic properties of macromolecules. Noticeably absent from the array of experimental restraints that have been employed to characterize protein structures at high hydrostatic pressure is the residual dipolar coupling, which requires the partial alignment of the macromolecule of interest. Here we examine five alignment media that are commonly used at ambient pressure for this purpose. We find that the spontaneous alignment of Pf1 phage, d(GpG) and a C12E5/n-hexnanol mixture in a magnetic field is preserved under high hydrostatic pressure. However, DMPC/DHPC bicelles and collagen gel are found to be unsuitable. Evidence is presented to demonstrate that pressure-induced structural changes can be identified using the residual dipolar coupling.

Long-range dipolar order and dispersion forces in polar liquids

Science.gov (United States)

Besford, Quinn Alexander; Christofferson, Andrew Joseph; Liu, Maoyuan; Yarovsky, Irene

2017-11-01

Complex solvation phenomena, such as specific ion effects, occur in polar liquids. Interpretation of these effects in terms of structure and dispersion forces will lead to a greater understanding of solvation. Herein, using molecular dynamics, we probe the structure of polar liquids through specific dipolar pair correlation functions that contribute to the potential of mean force that is "felt" between thermally rotating dipole moments. It is shown that unique dipolar order exists at separations at least up to 20 Å for all liquids studied. When the structural order is compared with a dipolar dispersion force that arises from local co-operative enhancement of dipole moments, a strong agreement is found. Lifshitz theory of dispersion forces was compared with the structural order, where the theory is validated for all liquids that do not have significant local dipole correlations. For liquids that do have significant local dipole correlations, specifically liquid water, Lifshitz theory underestimates the dispersion force by a factor of 5-10, demonstrating that the force that leads to the increased structure in liquid water is missed by Lifshitz theory of van der Waals forces. We apply similar correlation functions to an ionic aqueous system, where long-range order between water's dipole moment and a single chloride ion is found to exist at 20 Å of separation, revealing a long-range perturbation of water's structure by an ion. Furthermore, we found that waters within the 1st, 2nd, and 3rd solvation shells of a chloride ion exhibit significantly enhanced dipolar interactions, particularly with waters at larger distances of separation. Our results provide a link between structures, dispersion forces, and specific ion effects, which may lead to a more robust understanding of solvation.

Magnetic Reconnection in Strongly Magnetized Regions of the Low Solar Chromosphere

Science.gov (United States)

Ni, Lei; Lukin, Vyacheslav S.; Murphy, Nicholas A.; Lin, Jun

2018-01-01

Magnetic reconnection in strongly magnetized regions around the temperature minimum region of the low solar atmosphere is studied by employing MHD-based simulations of a partially ionized plasma within a reactive 2.5D multi-fluid model. It is shown that in the absence of magnetic nulls in a low β plasma, the ionized and neutral fluid flows are well-coupled throughout the reconnection region. However, non-equilibrium ionization–recombination dynamics play a critical role in determining the structure of the reconnection region, leading to much lower temperature increases and a faster magnetic reconnection rate as compared to simulations that assume plasma to be in ionization–recombination equilibrium. The rate of ionization of the neutral component of the plasma is always faster than recombination within the current sheet region even when the initial plasma β is as high as {β }0=1.46. When the reconnecting magnetic field is in excess of a kilogauss and the plasma β is lower than 0.0145, the initially weakly ionized plasmas can become fully ionized within the reconnection region and the current sheet can be strongly heated to above 2.5× {10}4 K, even as most of the collisionally dissipated magnetic energy is radiated away. The Hall effect increases the reconnection rate slightly, but in the absence of magnetic nulls it does not result in significant asymmetries or change the characteristics of the reconnection current sheet down to meter scales.

Suppression of cooling by strong magnetic fields in white dwarf stars.

Science.gov (United States)

Valyavin, G; Shulyak, D; Wade, G A; Antonyuk, K; Zharikov, S V; Galazutdinov, G A; Plachinda, S; Bagnulo, S; Machado, L Fox; Alvarez, M; Clark, D M; Lopez, J M; Hiriart, D; Han, Inwoo; Jeon, Young-Beom; Zurita, C; Mujica, R; Burlakova, T; Szeifert, T; Burenkov, A

2014-11-06

Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young.

Thermodynamics of Dipolar Chain Systems

International Nuclear Information System (INIS)

Armstrong, J.R.; Zinner, N.T.; Fedorov, D.V.; Jensen, A.S.

2013-01-01

The thermodynamics of a quantum system of layers containing perpendicularly oriented dipolar molecules is studied within an oscillator approximation for both bosonic and fermionic species. The system is assumed to be built from chains with one molecule in each layer. We consider the effects of the intralayer repulsion and quantum statistical requirements in systems with more than one chain. Specifically, we consider the case of two chains and solve the problem analytically within the harmonic Hamiltonian approach which is accurate for large dipole moments. The case of three chains is calculated numerically. Our findings indicate that thermodynamic observables, such as the heat capacity, can be used to probe the signatures of the intralayer interaction between chains. This should be relevant for near future experiments on polar molecules with strong dipole moments. (author)

Off-equatorial current-driven instabilities ahead of approaching dipolarization fronts

Science.gov (United States)

Zhang, Xu; Angelopoulos, V.; Pritchett, P. L.; Liu, Jiang

2017-05-01

Recent kinetic simulations have revealed that electromagnetic instabilities near the ion gyrofrequency and slightly away from the equatorial plane can be driven by a current parallel to the magnetic field prior to the arrival of dipolarization fronts. Such instabilities are important because of their potential contribution to global electromagnetic energy conversion near dipolarization fronts. Of the several instabilities that may be consistent with such waves, the most notable are the current-driven electromagnetic ion cyclotron instability and the current-driven kink-like instability. To confirm the existence and characteristics of these instabilities, we used observations by two Time History of Events and Macroscale Interactions during Substorms satellites, one near the neutral sheet observing dipolarization fronts and the other at the boundary layer observing precursor waves and currents. We found that such instabilities with monochromatic signatures are rare, but one of the few cases was selected for further study. Two different instabilities, one at about 0.3 Hz and the other at a much lower frequency, 0.02 Hz, were seen in the data from the off-equatorial spacecraft. A parallel current attributed to an electron beam coexisted with the waves. Our instability analysis attributes the higher-frequency instability to a current-driven ion cyclotron instability and the lower frequency instability to a kink-like instability. The current-driven kink-like instability we observed is consistent with the instabilities observed in the simulation. We suggest that the currents needed to excite these low-frequency instabilities are so intense that the associated electron beams are easily thermalized and hence difficult to observe.

Neutrino oscillations in strong magnetic fields

International Nuclear Information System (INIS)

Likhachev, G.G.; Studenikin, A.I.

1994-07-01

Neutrino conversion processes between two neutrino species and the corresponding oscillations induced by strong magnetic fields are considered. The value of the critical strength of magnetic field B cr as a function of characteristics of neutrinos in vacuum (Δm 2 ν , mixing angle θ), effective particle density of matter n eff , neutrino (transition) magnetic moment μ-tilde and energy E is introduced. It is shown that the neutrino conversion and oscillations effects induced by magnetic fields B ≥ B cr are important and may result in the depletion of the initial type of ν's in the bunch. A possible increase of these effects in the case when neutrinos pass through a sudden decrease of density of matter (''cross-boundary effect'') and applications to neutrinos from neutron stars and supernova are discussed. (author). 25 refs

Characterization and modeling of multi-dipolar microwave plasmas: application to multi-dipolar plasma assisted sputtering; Caracterisation et modelisation des plasmas micro-onde multi-dipolaires: application a la pulverisation assistee par plasma multi-dipolaire

Energy Technology Data Exchange (ETDEWEB)

Tran, T.V

2006-12-15

The scaling up of plasma processes in the low pressure range remains a question to be solved for their rise at the industrial level. One solution is the uniform distribution of elementary plasma sources where the plasma is produced via electron cyclotron resonance (ECR) coupling. These elementary plasma sources are made up of a cylindrical permanent magnet (magnetic dipole) set at the end of a coaxial microwave line. Although of simple concept, the optimisation of these dipolar plasma sources is in fact a complex problem. It requires the knowledge, on one hand, of the configurations of static magnetic fields and microwave electric fields, and, on the other hand, of the mechanisms of plasma production in the region of high intensity magnetic field (ECR condition), and of plasma diffusion. Therefore, the experimental characterisation of the operating ranges and plasma parameters has been performed by Langmuir probes and optical emission spectroscopy on different configurations of dipolar sources. At the same time, in a first analytical approach, calculations have been made on simple magnetic field configurations, motion and trajectory of electrons in these magnetic fields, and the acceleration of electrons by ECR coupling. Then, the results have been used for the validation of the numerical modelling of the electron trajectories by using a hybrid PIC (particle-in-cell) / MC (Monte Carlo) method. The experimental study has evidenced large operating domains, between 15 and 200 W of microwave power, and from 0.5 to 15 mtorr argon pressure. The analysis of plasma parameters has shown that the region of ECR coupling is localised near the equatorial plane of the magnet and dependent on magnet geometry. These characterizations, applied to a cylindrical reactor using 48 sources, have shown that densities between 10{sup 11} and 10{sup 12} cm{sup -3} could be achieved in the central part of the volume at a few mtorr argon pressures. The modelling of electron trajectories near

Magnetic resonance in zero-field: construction of a spectrometer, evaluation of a method for structure studies

International Nuclear Information System (INIS)

Llor, M.

1987-01-01

The method known as Nuclear Resonance in the zero-field, applied to the spectral analysis of powders, is discussed. In the method, the anisotropy due to the preferential direction of the magnetic field is suppressed, but a high sensitivity is keeped. For powders spectra, the process allows the obtention resolutions, of dipolar and quadrupolar couplings, in the range of those only obtained on monocrystals under strong fields. By suitable magnetic field oscillations, and by the effect of the high field on the RMN signal, the transient evolutions of the spins are obtained. Concerning the absence of a preferred direction in the zero-field, a powder or the monocrystals show nearly the same behavior. In such conditions, a much more interesting spectra than those from a powder in a strong field, can be obtained. The RMN spectrometer is described. The possibilities, the experimental and theoretical limits of the proposed method, are analyzed. Applications on dipolar (proton and phosphor) and quadrupolar (deuterium) interactions, on hydrated salts and on cyclophasphazenes are carried out [fr

One-loop QCD thermodynamics in a strong homogeneous and static magnetic field

Science.gov (United States)

Rath, Shubhalaxmi; Patra, Binoy Krishna

2017-12-01

We have studied how the equation of state of thermal QCD with two light flavors is modified in a strong magnetic field. We calculate the thermodynamic observables of hot QCD matter up to one-loop, where the magnetic field affects mainly the quark contribution and the gluon part is largely unaffected except for the softening of the screening mass. We have first calculated the pressure of a thermal QCD medium in a strong magnetic field, where the pressure at fixed temperature increases with the magnetic field faster than the increase with the temperature at constant magnetic field. This can be understood from the dominant scale of thermal medium in the strong magnetic field, being the magnetic field, in the same way that the temperature dominates in a thermal medium in the absence of magnetic field. Thus although the presence of a strong magnetic field makes the pressure of hot QCD medium larger, the dependence of pressure on the temperature becomes less steep. Consistent with the above observations, the entropy density is found to decrease with the temperature in the presence of a strong magnetic field which is again consistent with the fact that the strong magnetic field restricts the dynamics of quarks to two dimensions, hence the phase space becomes squeezed resulting in the reduction of number of microstates. Moreover the energy density is seen to decrease and the speed of sound of thermal QCD medium increases in the presence of a strong magnetic field. These findings could have phenomenological implications in heavy ion collisions because the expansion dynamics of the medium produced in non-central ultra-relativistic heavy ion collisions is effectively controlled by both the energy density and the speed of sound.

Ultracold Dipolar Gases in Optical Lattices

OpenAIRE

Trefzger, C.; Menotti, C.; Capogrosso-Sansone, B.; Lewenstein, M.

2011-01-01

This tutorial is a theoretical work, in which we study the physics of ultra-cold dipolar bosonic gases in optical lattices. Such gases consist of bosonic atoms or molecules that interact via dipolar forces, and that are cooled below the quantum degeneracy temperature, typically in the nK range. When such a degenerate quantum gas is loaded into an optical lattice produced by standing waves of laser light, new kinds of physical phenomena occur. These systems realize then extended Hubbard-type m...

Two dimensional dipolar coupling in monolayers of silver and gold nanoparticles on a dielectric substrate.

Science.gov (United States)

Liu, Yu; Begin-Colin, Sylvie; Pichon, Benoît P; Leuvrey, Cedric; Ihiawakrim, Dris; Rastei, Mircea; Schmerber, Guy; Vomir, Mircea; Bigot, Jean Yves

2014-10-21

The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices.

Characteristics of high-latitude precursor flows ahead of dipolarization fronts

Science.gov (United States)

Li, Jia-Zheng; Zhou, Xu-Zhi; Runov, Andrei; Angelopoulos, Vassilis; Liu, Jiang; Pan, Dong-Xiao; Zong, Qiu-Gang

2017-05-01

Dipolarization fronts (DFs), earthward propagating structures in the magnetotail current sheet characterized by sharp enhancements of northward magnetic field, are capable of converting electromagnetic energy into particle kinetic energy. The ions previously accelerated and reflected at the DFs can contribute to plasma flows ahead of the fronts, which have been identified as DF precursor flows in both the near-equatorial plasma sheet and far from it, near the plasma sheet boundary. Using observations from the THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft, we show that the earthward particle and energy flux enhancements ahead of DFs are statistically larger farther away from the neutral sheet (at high latitudes) than in the near-equatorial region. High-latitude particle and energy fluxes on the DF dawnside are found to be significantly greater than those on the duskside, which is opposite to the dawn-dusk asymmetries previously found near the equatorial region. Using forward and backward tracing test-particle simulations, we then explain and reproduce the observed latitude-dependent characteristics of DF precursor flows, providing a better understanding of ion dynamics associated with dipolarization fronts.

Dipolar ferromagnets and glasses (invited)

International Nuclear Information System (INIS)

Rosenbaum, T.F.; Wu, W.; Ellman, B.; Yang, J.; Aeppli, G.; Reich, D.H.

1991-01-01

What is the ground state and what are the dynamics of 10 23 randomly distributed Ising spins? We have attempted to answer these questions through magnetic susceptibility, calorimetric, and neutron scattering studies of the randomly diluted dipolar-coupled Ising magnet LiHo x Y 1-x F 4 . The material is ferromagnetic for dipole concentrations at least as low as x=0.46, with a Curie temperature obeying mean-field scaling relative to that of pure LiHoF 4 . In the dilute spin limit, an x=0.045 crystal shows very unusual glassy properties characterized by decreasing barriers to relaxation as T→0. Its properties are consistent with a single low degeneracy ground state with a large gap for excitations. A slightly more concentrated x=0.167 sample, however, supports a complex ground state with no appreciable gap, in accordance with prevailing theories of spin glasses. The underlying causes of such disparate behavior are discussed in terms of random clusters as probed by neutron studies of the x=0.167 sample. In addition to tracing the evolution of the glassy and ferromagnetic states with dipole concentration, we investigate the effects of a transverse magnetic field on the Ising spin glass, LiHo 0.167 Y 0.833 F 4 . The transverse field mixes the eigenfunctions of the ground-state Ising doublet with the otherwise inaccessible excited-state levels. We observe a rapid decrease in the characteristic relaxation times, large changes in the spectral form of the relaxation, and a depression of the spin-glass transition temperature with the addition of quantum fluctuations

Mechanism and regioselectivity of 1,3-dipolar cycloaddition ...

Indian Academy of Sciences (India)

1,3-Dipolar cycloaddition; sulphur-centred 1,3-dipoles; regioselectivity; DFT reactivity indices;. FMO theory. 1. Introduction. Five-membered heterocyclic compounds can be gene- rated by addition of a 1,3-dipole to a dipolarophile under a 1,3-dipolar cycloaddition (1,3-DC) reaction which is well known as pericyclic reaction.

Dipolar oscillations in a quantum degenerate Fermi-Bose atomic mixture

International Nuclear Information System (INIS)

Ferlaino, F; Brecha, R J; Hannaford, P; Riboli, F; Roati, G; Modugno, G; Inguscio, M

2003-01-01

We study the dynamics of coupled dipolar oscillations in a Fermi-Bose mixture of 40 K and 87 Rb atoms. This low-energy collective mode is strongly affected by the interspecies interactions. Measurements are performed in the classical and quantum degenerate regimes and reveal the crucial role of the statistical properties of the mixture. At the onset of quantum degeneracy, we investigate the role of Pauli blocking and superfluidity for K and Rb atoms, respectively, resulting in a change in the collisional interactions

Wigner functions for fermions in strong magnetic fields

Science.gov (United States)

Sheng, Xin-li; Rischke, Dirk H.; Vasak, David; Wang, Qun

2018-02-01

We compute the covariant Wigner function for spin-(1/2) fermions in an arbitrarily strong magnetic field by exactly solving the Dirac equation at non-zero fermion-number and chiral-charge densities. The Landau energy levels as well as a set of orthonormal eigenfunctions are found as solutions of the Dirac equation. With these orthonormal eigenfunctions we construct the fermion field operators and the corresponding Wigner-function operator. The Wigner function is obtained by taking the ensemble average of the Wigner-function operator in global thermodynamical equilibrium, i.e., at constant temperature T and non-zero fermion-number and chiral-charge chemical potentials μ and μ_5, respectively. Extracting the vector and axial-vector components of the Wigner function, we reproduce the currents of the chiral magnetic and separation effect in an arbitrarily strong magnetic field.

Magnetic field modification of optical magnetic dipoles.

Science.gov (United States)

Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David

2015-03-11

Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate.

Understanding the anisotropic ion distributions within magnetotail dipolarizing flux bundles

Science.gov (United States)

Zhou, X.; Runov, A.; Angelopoulos, V.; Birn, J.

2017-12-01

Dipolarizing flux bundles (DFBs), earthward-propagating structures with enhanced northward magnetic field (Bz) component, are usually believed to carry a different plasma population from that in the ambient magnetotail plasma sheet. The ion distribution functions within the DFB, however, are recently found to be largely controlled by the ion adiabaticity parameter κ in the ambient plasma sheet outside the DFBs. According to these observations, the ambient κ values of 2-3 usually correspond to a strong perpendicular anisotropy of suprathermal ions within the DFBs, whereas for lower κ values the ions inside the DFBs become more isotropic. Here we utilize a simple, test-particle model to explore the nature of the anisotropy and its dependence on the ambient κ values. We find that the ion anisotropy originates from successive ion reflections and reentries to the DFBs, during which the ions can be consecutively accelerated in the perpendicular direction by the DFB-carried electric field. This acceleration process may be interrupted, however, when the magnetic field lines are highly curved in the ambient plasma sheet. In this case, the ion trajectories are most stochastic outside the DFB region, which makes the reflected ions less likely to return to the DFBs for another cycle of acceleration; as a consequence, the perpendicular ion anisotropy does not appear. Given that the DFB ions are a free energy source for instabilities when they are injected towards Earth, our simple model (that reproduces most observational features on the anisotropic DFB ion distributions) may shed new lights on the coupling process between the magnetotail and the inner magneosphere.

When Ethyl Isocyanoacetate Meets Isatins: A 1,3-Dipolar/Inverse 1,3-Dipolar/Olefination Reaction for Access to 3-Ylideneoxindoles.

Science.gov (United States)

Yuan, Wen-Kui; Cui, Tao; Liu, Wei; Wen, Li-Rong; Li, Ming

2018-03-16

A new CuI/1,10-phen-catalyzed reaction for the synthesis of 3-ylideneoxindoles from readily available isatins and ethyl isocyanoacetate, in which ethyl isocyanoacetate acts as a latent two-carbon donor like the Wittig reagent, is reported. A tandem procedure including 1,3-dipolar cycloaddition/inverse 1,3-dipolar ring opening/olefination allows the preparation of 3-ylideneoxindoles with broad functional group tolerance.

Dipolar and spinor bosonic systems

Science.gov (United States)

Yukalov, V. I.

2018-05-01

The main properties and methods of describing dipolar and spinor atomic systems, composed of bosonic atoms or molecules, are reviewed. The general approach for the correct treatment of Bose-condensed atomic systems with nonlocal interaction potentials is explained. The approach is applied to Bose-condensed systems with dipolar interaction potentials. The properties of systems with spinor interaction potentials are described. Trapped atoms and atoms in optical lattices are considered. Effective spin Hamiltonians for atoms in optical lattices are derived. The possibility of spintronics with cold atom is emphasized. The present review differs from the previous review articles by concentrating on a thorough presentation of basic theoretical points, helping the reader to better follow mathematical details and to make clearer physical conclusions.

Canonical Transform Method for Treating Strongly Anisotropy Magnets

DEFF Research Database (Denmark)

Cooke, J. F.; Lindgård, Per-Anker

1977-01-01

An infinite-order perturbation approach to the theory of magnetism in magnets with strong single-ion anisotropy is given. This approach is based on a canonical transformation of the system into one with a diagonal crystal field, an effective two-ion anisotropy, and reduced ground-state corrections....... A matrix-element matching procedure is used to obtain an explicit expression for the spin-wave energy to second order. The consequences of this theory are illustrated by an application to a simple example with planar anisotropy and an external magnetic field. A detailed comparison between the results...

Magnetic core-shell silica particles

NARCIS (Netherlands)

Claesson, E.M.

2007-01-01

This thesis deals with magnetic silica core-shell colloids and related functionalized silica structures. Synthesis routes have been developed and optimized. The physical properties of these colloids have been investigated, such as the magnetic dipole moment, dipolar structure formation and

Finite-size corrections in simulation of dipolar fluids

Science.gov (United States)

Belloni, Luc; Puibasset, Joël

2017-12-01

Monte Carlo simulations of dipolar fluids are performed at different numbers of particles N = 100-4000. For each size of the cubic cell, the non-spherically symmetric pair distribution function g(r,Ω) is accumulated in terms of projections gmnl(r) onto rotational invariants. The observed N dependence is in very good agreement with the theoretical predictions for the finite-size corrections of different origins: the explicit corrections due to the absence of fluctuations in the number of particles within the canonical simulation and the implicit corrections due to the coupling between the environment around a given particle and that around its images in the neighboring cells. The latter dominates in fluids of strong dipolar coupling characterized by low compressibility and high dielectric constant. The ability to clean with great precision the simulation data from these corrections combined with the use of very powerful anisotropic integral equation techniques means that exact correlation functions both in real and Fourier spaces, Kirkwood-Buff integrals, and bridge functions can be derived from box sizes as small as N ≈ 100, even with existing long-range tails. In the presence of dielectric discontinuity with the external medium surrounding the central box and its replica within the Ewald treatment of the Coulombic interactions, the 1/N dependence of the gmnl(r) is shown to disagree with the, yet well-accepted, prediction of the literature.

Laser propagation and soliton generation in strongly magnetized plasmas

Energy Technology Data Exchange (ETDEWEB)

Feng, W.; Li, J. Q.; Kishimoto, Y. [Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)

2016-03-15

The propagation characteristics of various laser modes with different polarization, as well as the soliton generation in strongly magnetized plasmas are studied numerically through one-dimensional (1D) particle-in-cell (PIC) simulations and analytically by solving the laser wave equation. PIC simulations show that the laser heating efficiency substantially depends on the magnetic field strength, the propagation modes of the laser pulse and their intensities. Generally, large amplitude laser can efficiently heat the plasma with strong magnetic field. Theoretical analyses on the linear propagation of the laser pulse in both under-dense and over-dense magnetized plasmas are well confirmed by the numerical observations. Most interestingly, it is found that a standing or moving soliton with frequency lower than the laser frequency is generated in certain magnetic field strength and laser intensity range, which can greatly enhance the laser heating efficiency. The range of magnetic field strength for the right-hand circularly polarized (RCP) soliton formation with high and low frequencies is identified by solving the soliton equations including the contribution of ion's motion and the finite temperature effects under the quasi-neutral approximation. In the limit of immobile ions, the RCP soliton tends to be peaked and stronger as the magnetic field increases, while the enhanced soliton becomes broader as the temperature increases. These findings in 1D model are well validated by 2D simulations.

Application of orbital strong magnet in the extraction of deep orbital magnetic foreign bodies

Directory of Open Access Journals (Sweden)

Jin-Chen Jia

2017-12-01

Full Text Available AIM: To investigate the surgical method and efficacy of extraction of deep orbital magnetic foreign bodies by mean of an orbital strong magnet. METHODS: A retrospective analysis of clinical data of patients with deep orbital magnetic foreign bodies(OMFBin Hebei Eye Hospital from June 2014 to May 2017 was processed. A total of 23 eyes were enrolled, among them, 14 eyes of extraorbital OMFB, 9 eyes of intraorbital OMFB. The rate of extraction of foreign bodies and the postoperative complications were observed. RESULTS: All eyes of intraorbital foreign bodies were successfully extracted with 100% success rate. Twelve of 14 eyes of extraorbital foreign bodies were extracted with 86% success rate. Mild orbital hemorrhage were found in 2 eyes. There was no other obvious complication such as visual loss, orbital massive hemorrhage or limited ocular movement. CONCLUSION: It's an ideal surgical method to extract the deep orbital magnetic foreign bodies by mean of an orbital strong magnet, with mini-injury, high success rate, short duration and few complications.

Phase transitions to dipolar clusters and charge density waves in high T_c superconductors

International Nuclear Information System (INIS)

Saarela, M.; Kusmartsev, F.V.

2017-01-01

We show that doping of hole charge carriers leads to formation of electric dipolar clusters in cuprates. They are created by many-body interactions between the dopant ion outside and holes inside the CuO planes. Because of the two-fold degeneracy holes in the CuO plane cluster into four-particles resonance valence bond plaquettes bound with dopant ions. Such dipoles may order into charge-density waves (CDW) or stripes or form a disordered state depending on doping and temperature. The lowest energy of the ordered system corresponds to a local anti-ferroelectric ordering. The mobility of individual disordered dipoles is very low at low temperatures and they prefer first to bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly with electric dipoles and when the sample is subjected to it the mobility changes significantly. This leads to a fractal growth of dipolar clusters. The existence of electric dipoles and CDW induce two phase transitions with increasing temperature, melting of the ordered state and disappearance of the dipolar state. Ferroelectricity at low doping is a natural consequence of such dipole moments. We develop a theory based on two-level systems and dipole-dipole interaction to explain the behavior of the polarization as a function of temperature and electric field.

Exact solutions for chemical bond orientations from residual dipolar couplings

International Nuclear Information System (INIS)

Wedemeyer, William J.; Rohl, Carol A.; Scheraga, Harold A.

2002-01-01

New methods for determining chemical structures from residual dipolar couplings are presented. The fundamental dipolar coupling equation is converted to an elliptical equation in the principal alignment frame. This elliptical equation is then combined with other angular or dipolar coupling constraints to form simple polynomial equations that define discrete solutions for the unit vector(s). The methods are illustrated with residual dipolar coupling data on ubiquitin taken in a single anisotropic medium. The protein backbone is divided into its rigid groups (namely, its peptide planes and C α frames), which may be solved for independently. A simple procedure for recombining these independent solutions results in backbone dihedral angles φ and ψ that resemble those of the known native structure. Subsequent refinement of these φ-ψ angles by the ROSETTA program produces a structure of ubiquitin that agrees with the known native structure to 1.1 A C α rmsd

Magnetic separation technique for environmental water purification by strong magnetic field generator loading HTS bulk magnets

International Nuclear Information System (INIS)

Oka, T.; Tanaka, K.; Kimura, T.; Mimura, D.; Fukui, S.; Ogawa, J.; Sato, T.; Ooizumi, M.; Yokoyama, K.; Yamaguchi, M.

2010-01-01

The magnetic separation technique in combination with high temperature superconducting bulk magnets has been investigated to purify the ground water which has been used in the coolant system for the incinerator furnace to cool the burning gas. The experiment has been operated by means of the newly-built alternating channel type magnetic separating device. The separation ratios of ferromagnetic flocks including fine magnetite powder have been estimated by means of the high gradient magnetic separation method with small iron balls filled in the water channels. As the magnetic force acting on the magnetic particle is given by the product of a magnetization of the material and a gradient of magnetic field, and as the ferromagnetic stainless steel balls yield the steep gradient of magnetic field around them in a strong magnetic field, the system has exhibited a quite excellent performance with respect to the separation ratios. The separation ratios of the flocks which contain the magnetite powder with the values more than 50 ppm have remained over 80% for under the flow rates less than 5 L/min.

Chiral-glass transition in a diluted dipolar-interaction Heisenberg system

International Nuclear Information System (INIS)

Zhang Kaicheng; Liu Guibin; Zhu Yan

2011-01-01

Recently, numerical simulations reveal that a spin-glass transition can occur in the three-dimensional diluted dipolar system. By defining the chirality of triple spins in a diluted dipolar Heisenberg spin glass, we study the chiral ordering in the system using parallel tempering algorithm and heat bath method. The finite-size scaling analysis reveals that the system undergoes a chiral-glass transition at finite temperature. - Highlights: → We define the chirality in a diluted dipolar Heisenberg system. → The system undergoes a chiral-glass transition at finite temperature. → We extract the critical exponents of the chiral-glass transition.

Highly stable and finely tuned magnetic fields generated by permanent magnet assemblies.

Science.gov (United States)

Danieli, E; Perlo, J; Blümich, B; Casanova, F

2013-05-03

Permanent magnetic materials are the only magnetic source that can be used to generate magnetic fields without power consumption or maintenance. Such stand-alone magnets are very attractive for many scientific and engineering areas, but they suffer from poor temporal field stability, which arises from the strong sensitivity of the magnetic materials and mechanical support to temperature variation. In this work, we describe a highly efficient method useful to cancel the temperature coefficient of permanent magnet assemblies in a passive and accurate way. It is based on the combination of at least two units made of magnetic materials with different temperature coefficients arranged in such a way that the ratio of the fields generated by each unit matches the ratio of their effective temperature coefficients defined by both the magnetic and mechanical contributions. Although typically available magnetic materials have negative temperature coefficients, the cancellation is achieved by aligning the fields generated by each unit in the opposite direction. We demonstrate the performance of this approach by stabilizing the field generated by a dipolar Halbach magnet, recently proposed to achieve high field homogeneity. Both the field drift and the homogeneity are monitored via nuclear magnetic resonance spectroscopy experiments. The results demonstrate the compatibility of the thermal compensation approach with existing strategies useful to fine-tune the spatial dependence of the field generated by permanent magnet arrays.

Chiral magnetism of magnetic adatoms generated by Rashba electrons

Science.gov (United States)

Bouaziz, Juba; dos Santos Dias, Manuel; Ziane, Abdelhamid; Benakki, Mouloud; Blügel, Stefan; Lounis, Samir

2017-02-01

We investigate long-range chiral magnetic interactions among adatoms mediated by surface states spin-splitted by spin-orbit coupling. Using the Rashba model, the tensor of exchange interactions is extracted wherein a thepseudo-dipolar interaction is found, in addition to the usual isotropic exchange interaction and the Dzyaloshinskii-Moriya interaction. We find that, despite the latter interaction, collinear magnetic states can still be stabilized by the pseudo-dipolar interaction. The interadatom distance controls the strength of these terms, which we exploit to design chiral magnetism in Fe nanostructures deposited on a Au(111) surface. We demonstrate that these magnetic interactions are related to superpositions of the out-of-plane and in-plane components of the skyrmionic magnetic waves induced by the adatoms in the surrounding electron gas. We show that, even if the interatomic distance is large, the size and shape of the nanostructures dramatically impacts on the strength of the magnetic interactions, thereby affecting the magnetic ground state. We also derive an appealing connection between the isotropic exchange interaction and the Dzyaloshinskii-Moriya interaction, which relates the latter to the first-order change of the former with respect to spin-orbit coupling. This implies that the chirality defined by the direction of the Dzyaloshinskii-Moriya vector is driven by the variation of the isotropic exchange interaction due to the spin-orbit interaction.

BaZr.sub.0.5./sub.Ti.sub.0.5./sub.O.sub.3./sub.: Lead-free relaxor ferroelectric or dipolar glass

Czech Academy of Sciences Publication Activity Database

Filipič, C.; Kutnjak, Z.; Pirc, R.; Canu, G.; Petzelt, Jan

2016-01-01

Roč. 93, č. 22 (2016), 1-7, č. článku 224105. ISSN 2469-9950 Institutional support: RVO:68378271 Keywords : relaxor ferroelectric * dipolar glass * dielectric relaxation * Edwards-Anderson parameter Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.836, year: 2016

Radial oscillations of neutron stars in strong magnetic fields

Indian Academy of Sciences (India)

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to ...

Electron-Cloud Pinch Dynamics in Presence of Lattice Magnet Fields

CERN Document Server

Franchetti, G

2011-01-01

The pinch of the electron cloud due to a passing proton bunch was extensively studied in a field free region and in a dipolar magnetic field. For the latter study, a strong field approximation helped to formulate the equations of motion and to understand the complex electron pinch dynamics, which exhibited some similarities with the field-free situation. Here we extend the analysis to the case of electron pinch in quadrupoles and in sextupoles. We discuss the limits of validity for the strong field approximation and we evaluate the relative magnitude of the peak tune shift along the bunch expected for the different fields.

Electromagnetic modes in cold magnetized strongly coupled plasmas

OpenAIRE

Tkachenko, I. M.; Ortner, J.; Rylyuk, V. M.

1999-01-01

The spectrum of electromagnetic waves propagating in a strongly coupled magnetized fully ionized hydrogen plasma is found. The ion motion and damping being neglected, the influence of the Coulomb coupling on the electromagnetic spectrum is analyzed.

Evidence for several dipolar quasi-invariants in liquid crystals

Science.gov (United States)

Bonin, C. J.; González, C. E.; Segnorile, H. H.; Zamar, R. C.

2013-10-01

The quasi-equilibrium states of an observed quantum system involve as many constants of motion as the dimension of the operator basis which spans the blocks of all the degenerate eigenvalues of the Hamiltonian that drives the system dynamics, however, the possibility of observing such quasi-invariants in solid-like spin systems in Nuclear Magnetic Resonance (NMR) is not a strictly exact prediction. The aim of this work is to provide experimental evidence of several quasi-invariants, in the proton NMR of small spin clusters, like nematic liquid crystal molecules, in which the use of thermodynamic arguments is not justified. We explore the spin states prepared with the Jeener-Broekaert pulse sequence by analyzing the time-domain signals yielded by this sequence as a function of the preparation times, in a variety of dipolar networks, solids, and liquid crystals. We observe that the signals can be explained with two dipolar quasi-invariants only within a range of short preparation times, however at longer times liquid crystal signals show an echo-like behaviour whose description requires assuming more quasi-invariants. We study the multiple quantum coherence content of such signals on a basis orthogonal to the z-basis and see that such states involve a significant number of correlated spins. Therefore, we show that the NMR signals within the whole preparation time-scale can only be reconstructed by assuming the occurrence of multiple quasi-invariants which we experimentally isolate.

Magnetic interactions in anisotropic Nd-Dy-Fe-Co-B/α-Fe multilayer magnets

Science.gov (United States)

Dai, Z. M.; Liu, W.; Zhao, X. T.; Han, Z.; Kim, D.; Choi, C. J.; Zhang, Z. D.

2016-10-01

The magnetic properties and the possible interaction mechanisms of anisotropic soft- and hard-magnetic multilayers have been investigated by altering the thickness of different kinds of spacer layers. The metal Ta and the insulating oxides MgO, Cr2O3 have been chosen as spacer layers to investigate the characteristics of the interactions between soft- and hard-magnetic layers in the anisotropic Nd-Dy-Fe-Co-B/α-Fe multilayer system. The dipolar and exchange interaction between hard and soft phases are evaluated with the help of the first order reversal curve method. The onset of the nucleation field and the magnetization reversal by domain wall movement are also evident from the first-order-reversal-curve measurements. Reversible/irreversible distributions reveal the natures of the soft- and hard-magnetic components. Incoherent switching fields are observed and the calculations show the semiquantitative contributions of hard and soft components to the system. An antiferromagnetic spacer layer will weaken the interaction between ferromagnetic layers and the effective interaction length decreases. As a consequence, the dipolar magnetostatic interaction may play an important role in the long-range interaction in anisotropic multilayer magnets.

Many-body formation and dissociation of a dipolar chain crystal

International Nuclear Information System (INIS)

You, Jhih-Shih; Wang, Daw-Wei

2014-01-01

We propose an experimental scheme to effectively assemble chains of dipolar gases with a uniform length in a multi-layer system. The obtained dipolar chains can form a chain crystal with the system temperature easily controlled by the initial lattice potential and the external field strength during processing. When the density of chains increases, we further observe a second order quantum phase transition for the chain crystal to be dissociated toward layers of 2D crystal, where the quantum fluctuation dominates the classical energy and the compressibility diverges at the phase boundary. The experimental implication of such a dipolar chain crystal and its quantum phase transition is also discussed. (paper)

RADIO POLARIMETRY SIGNATURES OF STRONG MAGNETIC TURBULENCE IN SUPERNOVA REMNANTS

International Nuclear Information System (INIS)

Stroman, Wendy; Pohl, Martin

2009-01-01

We discuss the emission and transport of polarized radio-band synchrotron radiation near the forward shocks of young shell-type supernova remnants, for which X-ray data indicate a strong amplification of turbulent magnetic field. Modeling the magnetic turbulence through the superposition of waves, we calculate the degree of polarization and the magnetic polarization direction which is at 90 deg. to the conventional electric polarization direction. We find that isotropic strong turbulence will produce weakly polarized radio emission even in the absence of internal Faraday rotation. If anisotropy is imposed on the magnetic-field structure, the degree of polarization can be significantly increased, provided internal Faraday rotation is inefficient. Both for shock compression and a mixture with a homogeneous field, the increase in polarization degree goes along with a fairly precise alignment of the magnetic-polarization angle with the direction of the dominant magnetic-field component, implying tangential magnetic polarization at the rims in the case of shock compression. We compare our model with high-resolution radio polarimetry data of Tycho's remnant. Using the absence of internal Faraday rotation we find a soft limit for the amplitude of magnetic turbulence, δB ∼ 0 . An alternative viable scenario involves anisotropic turbulence with stronger amplitudes in the radial direction, as was observed in recent Magnetohydrodynamics simulations of shocks propagating through a medium with significant density fluctuations.

Quantum states with topological properties via dipolar interactions

Energy Technology Data Exchange (ETDEWEB)

Peter, David

2015-06-25

This thesis proposes conceptually new ways to realize materials with topological properties by using dipole-dipole interactions. First, we study a system of ultracold dipolar fermions, where the relaxation mechanism of dipolar spins can be used to reach the quantum Hall regime. Second, in a system of polar molecules in an optical lattice, dipole-dipole interactions induce spin-orbit coupling terms for the rotational excitations. In combination with time-reversal symmetry breaking this leads to topological bands with Chern numbers greater than one.

NMR magnetization exchange dynamics for three spin-1/2 systems

International Nuclear Information System (INIS)

Demco, D.E.; Filip, X.; Filip, C.

1997-01-01

The magnetization exchange dynamics in one-dimensional NMR exchange experiments performed with static samples is analyzed for the relevant case of three spin systems. The magnetization decays recorded in the experiments performed with different chemical shift filters for the short mixing times are derived analytically. In this regime the decay rates depend on the dipolar coupling between the spins belonging to different functional groups. The predictions of the theoretical model are compared with the magnetization exchange data obtained for cross-linked poly(styrene-co-butadiene) samples. The residual dipolar coupling between the functional CH- and CH2-groups of butadiene are measured from the magnetization exchange experiments in the short mixing time regime. (authors)

Phase transitions to dipolar clusters and charge density waves in high T{sub c} superconductors

Energy Technology Data Exchange (ETDEWEB)

Saarela, M., E-mail: Mikko.Saarela@oulu.fi [Department of Physics, University of Oulu, P.O. Box 3000, FIN-90014 (Finland); Kusmartsev, F.V. [Department of Physics, Loughborough University, LE11 3TU (United Kingdom)

2017-02-15

We show that doping of hole charge carriers leads to formation of electric dipolar clusters in cuprates. They are created by many-body interactions between the dopant ion outside and holes inside the CuO planes. Because of the two-fold degeneracy holes in the CuO plane cluster into four-particles resonance valence bond plaquettes bound with dopant ions. Such dipoles may order into charge-density waves (CDW) or stripes or form a disordered state depending on doping and temperature. The lowest energy of the ordered system corresponds to a local anti-ferroelectric ordering. The mobility of individual disordered dipoles is very low at low temperatures and they prefer first to bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly with electric dipoles and when the sample is subjected to it the mobility changes significantly. This leads to a fractal growth of dipolar clusters. The existence of electric dipoles and CDW induce two phase transitions with increasing temperature, melting of the ordered state and disappearance of the dipolar state. Ferroelectricity at low doping is a natural consequence of such dipole moments. We develop a theory based on two-level systems and dipole-dipole interaction to explain the behavior of the polarization as a function of temperature and electric field.

Magnetic and velocity fields in a dynamo operating at extremely small Ekman and magnetic Prandtl numbers

Science.gov (United States)

Šimkanin, Ján; Kyselica, Juraj

2017-12-01

Numerical simulations of the geodynamo are becoming more realistic because of advances in computer technology. Here, the geodynamo model is investigated numerically at the extremely low Ekman and magnetic Prandtl numbers using the PARODY dynamo code. These parameters are more realistic than those used in previous numerical studies of the geodynamo. Our model is based on the Boussinesq approximation and the temperature gradient between upper and lower boundaries is a source of convection. This study attempts to answer the question how realistic the geodynamo models are. Numerical results show that our dynamo belongs to the strong-field dynamos. The generated magnetic field is dipolar and large-scale while convection is small-scale and sheet-like flows (plumes) are preferred to a columnar convection. Scales of magnetic and velocity fields are separated, which enables hydromagnetic dynamos to maintain the magnetic field at the low magnetic Prandtl numbers. The inner core rotation rate is lower than that in previous geodynamo models. On the other hand, dimensional magnitudes of velocity and magnetic fields and those of the magnetic and viscous dissipation are larger than those expected in the Earth's core due to our parameter range chosen.

Structures and dynamics in a two-dimensional dipolar dust particle system

Science.gov (United States)

Hou, X. N.; Liu, Y. H.; Kravchenko, O. V.; Lapushkina, T. A.; Azarova, O. A.; Chen, Z. Y.; Huang, F.

2018-05-01

The effects of electric dipole moment, the number of dipolar particles, and system temperature on the structures and dynamics of a dipolar dust particle system are studied by molecular dynamics simulations. The results show that the larger electric dipole moment is favorable for the formation of a long-chain structure, the larger number of dipolar dust particles promotes the formation of the multi-chain structure, and the higher system temperature can cause higher rotation frequency. The trajectories, mean square displacement (MSD), and the corresponding spectrum functions of the MSDs are also calculated to illustrate the dynamics of the dipolar dust particle system, which is also closely related to the growth of dust particles. Some simulations are qualitatively in agreement with our experiments and can provide a guide for the study on dust growth, especially on the large-sized particles.

How systems of single-molecule magnets magnetize at low temperatures

Science.gov (United States)

Fernández, Julio F.; Alonso, Juan J.

2004-01-01

We model magnetization processes that take place through tunneling in crystals of single-molecule magnets, such as Mn12 and Fe8. These processes take place when a field H is applied after quenching to very low temperatures. Magnetic dipolar interactions and spin-flipping rules are essential ingredients of the model. The results obtained follow from Monte Carlo simulations and from the stochastic model we propose for dipole field diffusion. Correlations established before quenching are shown to later drive the magnetization process. We also show that in simple cubic lattices, m∝√(t) at time t after H is applied, as observed in Fe8, but only for 1+2log10(hd/hw) time decades, where hd is some near-neighbor magnetic dipolar field, and a spin reversal can occur only if the magnetic field acting on it is within some field window (-hw,hw). However, the √(t) behavior is not universal. For bcc and fcc lattices, m∝tp, but p≃0.7. An expression for p in terms of lattice parameters is derived. At later times the magnetization levels off to a constant value. All these processes take place at approximately constant magnetic energy if the annealing energy ɛa is larger than the tunneling window’s energy width (i.e., if ɛa≳gμBhwS). Thermal processes come in only later on to drive further magnetization growth.

The radiofrequency magnetic dipole discharge

Energy Technology Data Exchange (ETDEWEB)

Martines, E., E-mail: emilio.martines@igi.cnr.it; Zuin, M.; Cavazzana, R.; Fassina, A.; Spolaore, M. [Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), Corso Stati Uniti 4, 35127 Padova (Italy); Marcante, M. [Dipartimento di Fisica, Università di Trento, via Sommarive 14, 38123 Povo, TN (Italy); TIFPA, Trento Institute for Fundamental Physics and Applications INFN, 38123 Trento (Italy)

2016-05-15

This paper describes a novel and simple concept of plasma source, which is able to produce a radiofrequency magnetized discharge with minimal power requirements. The source is based on the magnetron concept and uses a permanent magnet as an active electrode. The dipolar field produced by the magnet confines the electrons, which cause further ionization, thus producing a toroidally shaped plasma in the equatorial region around the electrode. A plasma can be ignited with such scheme with power levels as low as 5 W. Paschen curves have been built for four different working gases, showing that in Helium or Neon, plasma breakdown is easily obtained also at atmospheric pressure. The plasma properties have been measured using a balanced Langmuir probe, showing that the electron temperature is around 3–4 eV and higher in the cathode proximity. Plasma densities of the order of 10{sup 16 }m{sup −3} have been obtained, with a good positive scaling with applied power. Overall, the electron pressure appears to be strongly correlated with the magnetic field magnitude in the measurement point.

The radiofrequency magnetic dipole discharge

Science.gov (United States)

Martines, E.; Zuin, M.; Marcante, M.; Cavazzana, R.; Fassina, A.; Spolaore, M.

2016-05-01

This paper describes a novel and simple concept of plasma source, which is able to produce a radiofrequency magnetized discharge with minimal power requirements. The source is based on the magnetron concept and uses a permanent magnet as an active electrode. The dipolar field produced by the magnet confines the electrons, which cause further ionization, thus producing a toroidally shaped plasma in the equatorial region around the electrode. A plasma can be ignited with such scheme with power levels as low as 5 W. Paschen curves have been built for four different working gases, showing that in Helium or Neon, plasma breakdown is easily obtained also at atmospheric pressure. The plasma properties have been measured using a balanced Langmuir probe, showing that the electron temperature is around 3-4 eV and higher in the cathode proximity. Plasma densities of the order of 1016 m-3 have been obtained, with a good positive scaling with applied power. Overall, the electron pressure appears to be strongly correlated with the magnetic field magnitude in the measurement point.

Heavy quark potential in a static and strong homogeneous magnetic field

Energy Technology Data Exchange (ETDEWEB)

Hasan, Mujeeb; Chatterjee, Bhaswar; Patra, Binoy Krishna [Indian Institute of Technology Roorkee, Department of Physics, Roorkee (India)

2017-11-15

We have investigated the properties of quarkonia in a thermal QCD medium in the background of strong magnetic field. For that purpose, we employ the Schwinger proper-time quark propagator in the lowest Landau level to calculate the one-loop gluon self-energy, which in the sequel gives the effective gluon propagator. As an artifact of strong magnetic field approximation (eB >> T{sup 2} and eB >> m{sup 2}), the Debye mass for massless flavors is found to depend only on the magnetic field which is the dominant scale in comparison to the scales prevalent in the thermal medium. However, for physical quark masses, it depends on both magnetic field and temperature in a low temperature and high magnetic field but the temperature dependence is very meager and becomes independent of the temperature beyond a certain temperature and magnetic field. With the above mentioned ingredients, the potential between heavy quark (Q) and anti-quark (anti Q) is obtained in a hot QCD medium in the presence of a strong magnetic field by correcting both short- and long-range components of the potential in the real-time formalism. It is found that the long-range part of the quarkonium potential is affected much more by magnetic field as compared to the short-range part. This observation facilitates us to estimate the magnetic field beyond which the potential will be too weak to bind Q anti Q together. For example, the J/ψ is dissociated at eB ∝ 10 m{sub π}{sup 2} and Υ is dissociated at eB ∝ 100 m{sub π}{sup 2} whereas its excited states, ψ{sup '} and Υ{sup '} are dissociated at smaller magnetic field eB = m{sub π}{sup 2}, 13 m{sub π}{sup 2}, respectively. (orig.)

Equilibrium phases of dipolar lattice bosons in the presence of random diagonal disorder

Science.gov (United States)

Zhang, C.; Safavi-Naini, A.; Capogrosso-Sansone, B.

2018-01-01

Ultracold gases offer an unprecedented opportunity to engineer disorder and interactions in a controlled manner. In an effort to understand the interplay between disorder, dipolar interactions, and quantum degeneracy, we study two-dimensional hard-core dipolar lattice bosons in the presence of on-site bound disorder. Our results are based on large-scale path-integral quantum Monte Carlo simulations by the worm algorithm. We study the ground-state phase diagram at a fixed half-integer filling factor for which the clean system is either a superfluid at a lower dipolar interaction strength or a checkerboard solid at a larger dipolar interaction strength. We find that, even for weak dipolar interactions, superfluidity is destroyed in favor of a Bose glass at a relatively low disorder strength. Interestingly, in the presence of disorder, superfluidity persists for values of the dipolar interaction strength for which the clean system is a checkerboard solid. At a fixed disorder strength, as the dipolar interaction is increased, superfluidity is destroyed in favor of a Bose glass. As the interaction is further increased, the system eventually develops extended checkerboard patterns in the density distribution. Due to the presence of disorder, though, grain boundaries and defects, responsible for a finite residual compressibility, are present in the density distribution. Finally, we study the robustness of the superfluid phase against thermal fluctuations.

Magnetization relaxation of single molecule magnets after field cooling

Science.gov (United States)

Fernandez, Julio F.; Alonso, Juan J.

2004-03-01

Magnetic clusters, such as Fe8 and Mn_12, behave at low temperatures as large single spins S. In crystals, anisotropy energies U allow magnetic relaxation only through tunneling at k_BTstackrelspins with dipolar interactions. To mimic tunneling effects, a spin on a lattice site where h is within some tunnel window -h_wmagnetic dipole field drift.

On the Acceleration and Anisotropy of Ions Within Magnetotail Dipolarizing Flux Bundles

Science.gov (United States)

Zhou, Xu-Zhi; Runov, Andrei; Angelopoulos, Vassilis; Artemyev, Anton V.; Birn, Joachim

2018-01-01

Dipolarizing flux bundles (DFBs), earthward propagating structures with enhanced northward magnetic field Bz, are usually believed to carry a distinctly different plasma population from that in the ambient magnetotail plasma sheet. The ion distribution functions within the DFB, however, have been recently found to be largely controlled by the ion adiabaticity parameter κ in the ambient plasma sheet outside the DFB. According to these observations, the ambient κ values of 2-3 usually correspond to a strong perpendicular anisotropy of suprathermal ions within the DFB, whereas for lower κ values the DFB ions become more isotropic. Here we utilize a simple, test particle model to explore the nature of the anisotropy and its dependence on the ambient κ values. We find that the anisotropy originates from successive ion reflections and reentries to the DFB, during which the ions are consecutively accelerated in the perpendicular direction by the DFB-associated electric field. This consecutive acceleration may be interrupted, however, when magnetic field lines are highly curved in the ambient plasma sheet. In this case, the ion trajectories become stochastic outside the DFB, which makes the reflected ions less likely to return to the DFB for another cycle of acceleration; as a consequence, the perpendicular ion anisotropy does not appear. Given that the DFB ions are a free energy source for instabilities when they are injected toward Earth, our simple model (that reproduces most observational features on the anisotropic DFB ion distributions) may shed new lights on the coupling process between magnetotail and inner magnetosphere.

Dipolar versus octupolar triphenylamine-based fluorescent organic nanoparticles as brilliant one- and two-photon emitters for (bio)imaging.

Science.gov (United States)

Parthasarathy, Venkatakrishnan; Fery-Forgues, Suzanne; Campioli, Elisa; Recher, Gaëlle; Terenziani, Francesca; Blanchard-Desce, Mireille

2011-11-18

Two related triphenylamine-based dipolar and octupolar fluorophores are used to prepare aqueous suspensions of fluorescent organic nanoparticles (FONs) via the reprecipitation method. The obtained spherical nanoparticles (30-40 nm in diameter) are fluorescent in aqueous solution (up to 15% fluorescence quantum yield) and exhibit extremely high one- and two-photon brightness, superior to those obtained for quantum dots. Despite the two chromophores showing similar fluorescence in solution, the fluorescence of FONs made from the octupolar derivative is significantly red-shifted compared to that generated by the dipolar FONs. In addition, the maximum two-photon absorption cross section of the FONs made from the octupolar derivative is 55% larger than that of the dipolar derivative FONs. The experimental observations provide evidence that the different molecular shape (rodlike versus three-branched) and charge distribution (dipolar versus octupolar) of the two chromophores strongly affect the packing inside the nanoparticles as well as their spectroscopic properties and colloidal stability in pure water. The use of these FONs as probes for biphotonic in-vivo imaging is investigated on Xenopus laevis tadpoles to test their utilization for angiography. When using FONs made from the octupolar dye, the formation of microagglomerates (2-5 μm scale) is observed in vivo, with subsequent lethal occlusion of the blood vessels. Conversely, the nanoparticles of the dipolar dye allow acute imaging of blood vessels thanks to their suitable size and brightness, while no toxic effect is observed. Such a goal cannot be achieved with the dissolved dye, which permeates the vessel walls. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ion Motion in a Plasma Interacting with Strong Magnetic Fields

International Nuclear Information System (INIS)

Weingarten, A.; Grabowski, C.; Chakrabarti, N.; Maron, Y.; Fruchtmant, A.

1999-01-01

The interaction of a plasma with strong magnetic fields takes place in many laboratory experiments and astrophysical plasmas. Applying a strong magnetic field to the plasma may result in plasma displacement, magnetization, or the formation of instabilities. Important phenomena in plasma, such as the energy transport and the momentum balance, take a different form in each case. We study this interaction in a plasma that carries a short-duration (80-ns) current pulse, generating a magnetic field of up to 17 kG. The evolution of the magnetic field, plasma density, ion velocities, and electric fields are determined before and during the current pulse. The dependence of the plasma limiting current on the plasma density and composition are studied and compared to theoretical models based on the different phenomena. When the plasma collisionality is low, three typical velocities should be taken into consideration: the proton and heavier-ion Alfven velocities (v A p and v A h , respectively) and the EMHD magnetic-field penetration velocity into the plasma (v EMHD ). If both Alfven velocities are larger than v EMHD the plasma is pushed ahead of the magnetic piston and the magnetic field energy is dissipated into ion kinetic energy. If v EMHD is the largest of three velocities, the plasma become magnetized and the ions acquire a small axial momentum only. Different ion species may drift in different directions along the current lines. In this case, the magnetic field energy is probably dissipated into electron thermal energy. When vs > V EMHD > vi, as in the case of one of our experiments, ion mass separation occurs. The protons are pushed ahead of the piston while the heavier-ions become magnetized. Since the plasma electrons are unmagnetized they cannot cross the piston, and the heavy ions are probably charge-neutralized by electrons originating from the cathode that are 'born' magnetized

A new approach for applying residual dipolar couplings as restraints in structure elucidation

International Nuclear Information System (INIS)

Meiler, Jens; Blomberg, Niklas; Nilges, Michael; Griesinger, Christian

2000-01-01

Residual dipolar couplings are useful global structural restraints. The dipolar couplings define the orientation of a vector with respect to the alignment tensor. Although the size of the alignment tensor can be derived from the distribution of the experimental dipolar couplings, its orientation with respect to the coordinate system of the molecule is unknown at the beginning of structure determination. This causes convergence problems in the simulated annealing process. We therefore propose a protocol that translates dipolar couplings into intervector projection angles, which are independent of the orientation of the alignment tensor with respect to the molecule. These restraints can be used during the whole simulated annealing protocol

Dynamical Properties of a Diluted Dipolar-Interaction Heisenberg Spin Glass

International Nuclear Information System (INIS)

Zhang Kai-Cheng; Liu Yong; Chi Feng

2014-01-01

Up to now the chirality is seldom studied in the diluted spin glass although many investigations have been performed on the site-ordered Edwards—Anderson model. By simulation, we investigate the dynamical properties of both the spin-glass and the chiral-glass phases in a diluted dipolar system, which was manifested to have a spin-glass transition by recent numerical study. By scaling we find that both phases have the same aging behavior and closer aging parameter μ. Similarly, the domains grow in the same way and both phases have a closer barrier exponent Ψ. It means that both the spins and the chirality have the same dynamical properties and they may freeze at the same temperature. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Probing the extreme wind confinement of the most magnetic O star with COS spectroscopy

Science.gov (United States)

Petit, Veronique

2014-10-01

We propose to obtain phase-resolved UV spectroscopy of the recently discovered magnetic O star NGC 1624-2, which has the strongest magnetic field ever detected in a O-star, by an order of magnitude. We will use the strength and variability of the UV resonance line profiles to diagnose the density, velocity, and ionization structure of NGC 1624-2's enormous magnetosphere that results from entrapment of its stellar wind by its strong, nearly dipolar magnetic field. With this gigantic magnetosphere, NGC 1624-2 represents a new regime of extreme wind confinement that will constrain models of magnetized winds and their surface mass flux properties. A detailed understanding of such winds is necessary to study the rotational braking history of magnetic O-stars, which can shed new light on the fundamental origin of magnetism in massive, hot stars.

Non-equilibrium magnetic interactions in strongly correlated systems

Energy Technology Data Exchange (ETDEWEB)

Secchi, A., E-mail: a.secchi@science.ru.nl [Institute for Molecules and Materials, Radboud University Nijmegen, 6525 AJ Nijmegen (Netherlands); Brener, S.; Lichtenstein, A.I. [Institut für Theoretische Physik, Universitat Hamburg, Jungiusstraße 9, D-20355 Hamburg (Germany); Katsnelson, M.I. [Institute for Molecules and Materials, Radboud University Nijmegen, 6525 AJ Nijmegen (Netherlands)

2013-06-15

We formulate a low-energy theory for the magnetic interactions between electrons in the multi-band Hubbard model under non-equilibrium conditions determined by an external time-dependent electric field which simulates laser-induced spin dynamics. We derive expressions for dynamical exchange parameters in terms of non-equilibrium electronic Green functions and self-energies, which can be computed, e.g., with the methods of time-dependent dynamical mean-field theory. Moreover, we find that a correct description of the system requires, in addition to exchange, a new kind of magnetic interaction, that we name twist exchange, which formally resembles Dzyaloshinskii–Moriya coupling, but is not due to spin–orbit, and is actually due to an effective three-spin interaction. Our theory allows the evaluation of the related time-dependent parameters as well. -- Highlights: •We develop a theory for magnetism of strongly correlated systems out of equilibrium. •Our theory is suitable for laser-induced ultrafast magnetization dynamics. •We write time-dependent exchange parameters in terms of electronic Green functions. •We find a new magnetic interaction, a “twist exchange”. •We give general expressions for magnetic noise in itinerant-electron systems.

Theory of Spin Waves in Strongly Anisotropic Magnets

DEFF Research Database (Denmark)

Lindgård, Per-Anker; Cooke, J. F.

1976-01-01

A new infinite-order perturbation approach to the theory of spin waves in strongly anisotropic magnets is introduced. The system is transformed into one with effective two-ion anisotropy and considerably reduced ground-state corrections. A general expression for the spin-wave energy, valid to any...

Understanding the physics of magnetic nanoparticles and their applications in the biomedical field

Science.gov (United States)

Laha, Suvra Santa

The study of magnetic nanoparticles is of great interest because of their potential uses in magnetic-recording, medical diagnostic and therapeutic applications. Additionally, they also offer an opportunity to understand the physics underlying the complex behavior exhibited by these materials. Two of the most important relaxation phenomena occurring in magnetic nanoparticles are superparamagnetic blocking and spin-glass-like freezing. In addition to features attributed to superparamagnetism, these nanoparticles can also exhibit magnetic relaxation effects at very low temperatures (≤ 50 K). Our studies suggest that all structural defects, and not just surface spins, are responsible for the low-temperature glass-like relaxation observed in many magnetic nanoparticles. The characteristic dipolar interaction energy existing in an ensemble of magnetic nanoparticles does not apparently depend on the average spacing between the nanoparticles but is likely to be strongly influenced by the fluctuations in the nanoparticle distribution. Our findings revealed that incorporating a small percentage of boron can stabilize the spinel structure in Mn 3O4 nanoparticles. We have also demonstrated that the dipolar interactions between the magnetic cores can be tuned by introducing non-magnetic nanoparticles. In particular, we studied the magnetic properties of Gd-doped Fe3O4 nanoparticles, a potential applicant for T1--T2 dual-modal MRI contrast agent. We have explored the interactions of BiFeO3 nanoparticles on live cells and the binding of FITC-conjugated Fe3O 4 nanoparticles with artificial lipid membranes to investigate these materials as candidates in medical imaging. Taken together, these studies have advanced our understanding of the fundamental physical principles that governs magnetism in magnetic materials with a focus on developing these nanoparticles for advanced biomedical applications. The materials developed and studied expand the repertoire of tools available for

The evolution of polar caps in magnetic cataclysmic variables

International Nuclear Information System (INIS)

Frank, J.; Chanmugam, G.

1986-01-01

A simple analysis of the evolution of the size of the magnetic polar cap in accreting white dwarfs is made on the basis of current theories of the secular evolution of magnetic cataclysmic variables. For white dwarfs with dipolar fields it is shown that the size of the polar cap in DQ Her binaries is larger than in AM Her binaries. The size of the former is, however, smaller than deduced from interpretation of their X-ray light curves, while that of the latter is in rough agreement. If the dwarf contains an aligned magnetic quadrupole the size of the polar caps of the DQ Her binaries is significantly increased. Magnetic field decay of the quadrupole moment in the older AM Her binaries implies that their fields are predominantly dipolar. (author)

Magnetized Langmuir wave packets excited by a strong beam-plasma interaction

International Nuclear Information System (INIS)

Pelletier, G.; Sol, H.; Asseo, E.

1988-01-01

The physics of beam-plasma interaction, which has been investigated for a long time mostly in relation with solar bursts, is now more widely invoked in various astrophysical contexts such as pulsars, active galactic nuclei, close binaries, cataclysmic variables, γ bursters, and so on. In these situations the interaction is more likely in the spirit of strong Langmuir turbulence rather than in the spirit of quasilinear theory. Many investigations have been done for two opposite extremes, namely, in very weak and in very strong magnetic fields. Very few properties of the strong Langmuir turbulence are known in the most usual astrophysical situation where the magnetic field plays a significant role but is not strong enough to force the electrons into one-dimensional motion. For this case, we analyze the dynamics of Langmuir wave packets and provide new results about the stability of the solitons against transverse perturbations. It turns out that both the averaged Lagrangian method and the adiabatic perturbation method derived from the inverse scattering transform give exactly the same results (which is not obvious in soliton perturbation theory). In particular, they predict the stability of the solitons as long as the electron gyrofrequency is greater than the plasma frequency (strong magnetic field) and their instability against transverse self-modulation in the opposite case (weak magnetic field); moreover, they allow one to deduce the self-similar collapsing oblate cavitons in the latter case. The laws governing the collapse of the wave packets determine the relaxation of the beam in the surrounding medium and we derive a useful formula giving the power loss of the beam. We outline the astrophysical consequences of this investigation

Evolution of the magnetic field structure of the Crab pulsar.

Science.gov (United States)

Lyne, Andrew; Graham-Smith, Francis; Weltevrede, Patrick; Jordan, Christine; Stappers, Ben; Bassa, Cees; Kramer, Michael

2013-11-01

Pulsars are highly magnetized rotating neutron stars and are well known for the stability of their signature pulse shapes, allowing high-precision studies of their rotation. However, during the past 22 years, the radio pulse profile of the Crab pulsar has shown a steady increase in the separation of the main pulse and interpulse components at 0.62° ± 0.03° per century. There are also secular changes in the relative strengths of several components of the profile. The changing component separation indicates that the axis of the dipolar magnetic field, embedded in the neutron star, is moving toward the stellar equator. This evolution of the magnetic field could explain why the pulsar does not spin down as expected from simple braking by a rotating dipolar magnetic field.

Kubo formulas for relativistic fluids in strong magnetic fields

International Nuclear Information System (INIS)

Huang Xuguang; Sedrakian, Armen; Rischke, Dirk H.

2011-01-01

Magnetohydrodynamics of strongly magnetized relativistic fluids is derived in the ideal and dissipative cases, taking into account the breaking of spatial symmetries by a quantizing magnetic field. A complete set of transport coefficients, consistent with the Curie and Onsager principles, is derived for thermal conduction, as well as shear and bulk viscosities. It is shown that in the most general case the dissipative function contains five shear viscosities, two bulk viscosities, and three thermal conductivity coefficients. We use Zubarev's non-equilibrium statistical operator method to relate these transport coefficients to correlation functions of the equilibrium theory. The desired relations emerge at linear order in the expansion of the non-equilibrium statistical operator with respect to the gradients of relevant statistical parameters (temperature, chemical potential, and velocity.) The transport coefficients are cast in a form that can be conveniently computed using equilibrium (imaginary-time) infrared Green's functions defined with respect to the equilibrium statistical operator. - Highlights: → Strong magnetic fields can make charged fluids behave anisotropically. → Magnetohydrodynamics for these fluids contains 5 shear, 2 bulk viscosities, and 3 heat conductivities. → We derive Kubo formulas for these transport coefficients.

Confinining properties of QCD in strong magnetic backgrounds

Directory of Open Access Journals (Sweden)

Bonati Claudio

2017-01-01

Full Text Available Strong magnetic backgrounds are known to modify QCD properties at a nonperturbative level. We discuss recent lattice results, obtained for Nf = 2 + 1 QCD with physical quark masses, concerning in particular the modifications and the anisotropies induced at the level of the static quark-antiquark potential, both at zero and finite temperature.

Dynamical Monte Carlo investigation of spin reversals and nonequilibrium magnetization of single-molecule magnets

OpenAIRE

Liu, Gui-Bin; Liu, Bang-Gui

2010-01-01

In this paper, we combine thermal effects with Landau-Zener (LZ) quantum tunneling effects in a dynamical Monte Carlo (DMC) framework to produce satisfactory magnetization curves of single-molecule magnet (SMM) systems. We use the giant spin approximation for SMM spins and consider regular lattices of SMMs with magnetic dipolar interactions (MDI). We calculate spin reversal probabilities from thermal-activated barrier hurdling, direct LZ tunneling, and thermal-assisted LZ tunnelings in the pr...

Cooling-history effects on magnetic relaxation through quantum tunneling

Science.gov (United States)

Fernandez, Julio; Alonso, Juan

2003-03-01

Magnetic clusters, such as Fe8 and Mn_12, that make up the core of large organometallic molecules, behave at low temperatures as large single spins S. In crystals, magnetic anisotropy energies U inhibit magnetic relaxation of these spins, which can then proceed at very small temperatures (at k_BT tunneling (MQT). Magnetic dipolar interactions then play an essential role. We study how an Ising system of spins that interact through magnetic dipolar fields relaxes. A spin is allowed to flip, at rate Γ, only if the magnetic field h acting on it is within some tunnel window -hw < h< h_w. We let (1) this system be initially held for some time at some temperature Ta that is above both the long-range ordering temperature and T ˜ U/S, and (2) apply a magnetic field at t=0, inmediately after the system is quenched to T < 0.1U/S. This is somewhat as in the experiments of Wernsdorfer et al on Fe_8. The time evolution of the magnetiztion m and field distributions after the field is applied at t=0 is studied. For small applied fields H, m ˜= hw HF(Γ t). In addition, F(Γ t)˜= cΓ t for Γ t < 1 and F(Γ t)˜= cΓ t for 1 <Γ t < (h_d/h_w)^2, where hd is a nearest neighbor dipolar field. We will show how c depends on the cooling protocol. Finally, m saturates at m_s˜= 0.13\\varepsilon_aH.

Electromagnetic pulses in a strongly magnetized electron-positron plasma

International Nuclear Information System (INIS)

Yu, M.Y.; Rao, N.N.

1985-01-01

The conditions for the existence of large-amplitude localized electromagnetic wave pulses in an electron-positron plasma penetrated by a very strong ambient magnetic field are obtained. It is shown that such pulses can exist in pulsar polar magnetospheres. 12 references

Pressure and compressibility factor of bidisperse magnetic fluids

Science.gov (United States)

Minina, Elena S.; Blaak, Ronald; Kantorovich, Sofia S.

2018-04-01

In this work, we investigate the pressure and compressibility factors of bidisperse magnetic fluids with relatively weak dipolar interactions and different granulometric compositions. In order to study these properties, we employ the method of diagram expansion, taking into account two possible scenarios: (1) dipolar particles repel each other as hard spheres; (2) the polymer shell on the surface of the particles is modelled through a soft-sphere approximation. The theoretical predictions of the pressure and compressibility factors of bidisperse ferrofluids at different granulometric compositions are supported by data obtained by means of molecular dynamics computer simulations, which we also carried out for these systems. Both theory and simulations reveal that the pressure and compressibility factors decrease with growing dipolar correlations in the system, namely with an increasing fraction of large particles. We also demonstrate that even if dipolar interactions are too weak for any self-assembly to take place, the interparticle correlations lead to a qualitative change in the behaviour of the compressibility factors when compared to that of non-dipolar spheres, making the dependence monotonic.

Statistical Study of Interplanetary Coronal Mass Ejections with Strong Magnetic Fields

Science.gov (United States)

Murphy, Matthew E.

Coronal Mass Ejections (CMEs) with strong magnetic fields (B ) are typically associated with significant Solar Energetic Particle (SEP) events, high solar wind speed and solar flare events. Successful prediction of the arrival time of a CME at Earth is required to maximize the time available for satellite, infrastructure, and space travel programs to take protective action against the coming flux of high-energy particles. It is known that the magnetic field strength of a CME is linked to the strength of a geomagnetic storm on Earth. Unfortunately, the correlations between strong magnetic field CMEs from the entire sun (especially from the far side or non-Earth facing side of the sun) to SEP and flare events, solar source regions and other relevant solar variables are not well known. New correlation studies using an artificial intelligence engine (Eureqa) were performed to study CME events with magnetic field strength readings over 30 nanoteslas (nT) from January 2010 to October 17, 2014. This thesis presents the results of this study, validates Eureqa to obtain previously published results, and presents previously unknown functional relationships between solar source magnetic field data, CME initial speed and the CME magnetic field. These new results enable the development of more accurate CME magnetic field predictions and should help scientists develop better forecasts thereby helping to prevent damage to humanity's space and Earth assets.

Critical point in the QCD phase diagram for extremely strong background magnetic fields

International Nuclear Information System (INIS)

Endrödi, Gergely

2015-01-01

Lattice simulations have demonstrated that a background (electro)magnetic field reduces the chiral/deconfinement transition temperature of quantum chromodynamics for eB<1 GeV 2 . On the level of observables, this reduction manifests itself in an enhancement of the Polyakov loop and in a suppression of the light quark condensates (inverse magnetic catalysis) in the transition region. In this paper, we report on lattice simulations of 1+1+1-flavor QCD at an unprecedentedly high value of the magnetic field eB=3.25 GeV 2 . Based on the behavior of various observables, it is shown that even at this extremely strong field, inverse magnetic catalysis prevails and the transition, albeit becoming sharper, remains an analytic crossover. In addition, we develop an algorithm to directly simulate the asymptotically strong magnetic field limit of QCD. We find strong evidence for a first-order deconfinement phase transition in this limiting theory, implying the presence of a critical point in the QCD phase diagram. Based on the available lattice data, we estimate the location of the critical point.

Heterogeneous dipolar theory of the exponential pile

International Nuclear Information System (INIS)

Mastrangelo, P.V.

1981-01-01

We present a heterogeneous theory of the exponential pile, closely related to NORDHEIM-SCALETTAR's. It is well adapted to lattice whose pitch is relatively large (D-2O, grahpite) and the dimensions of whose channels are not negligible. The anisotropy of neutron diffusion is taken into account by the introduction of dipolar parameters. We express the contribution of each channel to the total flux in the moderator by means of multipolar coefficients. In order to be able to apply conditions of continuity between the flux and their derivatives, on the side of the moderator, we develop in a Fourier series the fluxes found at the periphery of each channel. Using Wronski's relations of Bessel's functions, we express the multipolar coefficients of the surfaces of each channel, on the side of the moderator, by means of the harmonics of each flux and their derivatives. We retain only monopolar (A 0 sub(g)) and dipolar (A 1 sub(g)) coefficients; those of a higher order are ignored. We deduce from these coefficients the systems of homogeneous equations of the exponential pile with monopoles on their own and monopoles plus dipoles. It should be noted that the systems of homogeneous equations of the critical pile are contained in those of the exponential pile. In another article, we develop the calculation of monopolar and dipolar heterogeneous parameters. (orig.)

Nanomagnets with high shape anisotropy and strong crystalline anisotropy: perspectives on magnetic force microscopy

International Nuclear Information System (INIS)

Campanella, H; Llobet, J; Esteve, J; Plaza, J A; Jaafar, M; Vázquez, M; Asenjo, A; Del Real, R P

2011-01-01

We report on a new approach for magnetic imaging, highly sensitive even in the presence of external, strong magnetic fields. Based on FIB-assisted fabricated high-aspect-ratio rare-earth nanomagnets, we produce groundbreaking magnetic force tips with hard magnetic character where we combine a high aspect ratio (shape anisotropy) together with strong crystalline anisotropy (rare-earth-based alloys). Rare-earth hard nanomagnets are then FIB-integrated to silicon microcantilevers as highly sharpened tips for high-field magnetic imaging applications. Force resolution and domain reversing and recovery capabilities are at least one order of magnitude better than for conventional magnetic tips. This work opens new, pioneering research fields on the surface magnetization process of nanostructures based either on relatively hard magnetic materials—used in magnetic storage media—or on materials like superparamagnetic particles, ferro/antiferromagnetic structures or paramagnetic materials.

Electrons in a strong magnetic field

International Nuclear Information System (INIS)

Itzykson, C.

1985-05-01

We first describe the average one-particle spectrum in the presence of a strong magnetic field together with random impurities for a Gaussian distribution, and generalized using a supersymmetric method. We then study the effect of Coulomb interactions on an electron gas in a strong field, within the approximation of a projection on the lowest Landau level. At maximal density (or filling fraction ν equal to unity) the quantum mechanical problem is equivalent to a soluble classical model for a two-dimensional plasma. As ν decreases, more states come into play. Laughlin has guessed the structure of the ground state and its low lying excitations for certain rational values of the filling fraction. A complete proof is however missing, nor is it clear what happens as ν becomes so small that a ''crystalline'' structure becomes favoured. Our presentation shows a link with functions occurring in combinatorics and analytic number theory, which seems not to have been fully exploited

Nonlocal and nonlinear electrostatics of a dipolar Coulomb fluid.

Science.gov (United States)

Sahin, Buyukdagli; Ralf, Blossey

2014-07-16

We study a model Coulomb fluid consisting of dipolar solvent molecules of finite extent which generalizes the point-like dipolar Poisson-Boltzmann model (DPB) previously introduced by Coalson and Duncan (1996 J. Phys. Chem. 100 2612) and Abrashkin et al (2007 Phys. Rev. Lett. 99 077801). We formulate a nonlocal Poisson-Boltzmann equation (NLPB) and study both linear and nonlinear dielectric response in this model for the case of a single plane geometry. Our results shed light on the relevance of nonlocal versus nonlinear effects in continuum models of material electrostatics.

Interaction between Electron Holes in a Strongly Magnetized Plasma

DEFF Research Database (Denmark)

Lynov, Jens-Peter; Michelsen, Poul; Pécseli, Hans

1980-01-01

The interaction between electron holes in a strongly magnetized, plasma-filled waveguide is investigated by means of computer simulation. Two holes may or may not coalesce, depending on their amplitudes and velocities. The interaction between holes and Trivelpiece-Gould solitons is demonstrated...

On the theory of magnetic field generation by relativistically strong laser radiation

International Nuclear Information System (INIS)

Berezhiani, V.I.; Shatashvili, N.L.; Mahajan, S.M.

1996-07-01

The authors consider the interaction of subpicosecond relativistically strong short laser pulses with an underdense cold unmagnetized electron plasma. It is shown that the strong plasma inhomogeneity caused by laser pulses results in the generation of a low frequency (quasistatic) magnetic field. Since the electron density distribution is determined completely by the pump wave intensity, the generated magnetic field is negligibly small for nonrelativistic laser pulses but increases rapidly in the ultrarelativistic case. Due to the possibility of electron cavitation (complete expulsion of electrons from the central region) for narrow and intense beams, the increase in the generated magnetic field slows down as the beam intensity is increased. The structure of the magnetic field closely resembles that of the field produced by a solenoid; the field is maximum and uniform in the cavitation region, then it falls, changes polarity and vanishes. In extremely dense plasmas, highly intense laser pulses in the self-channeling regime can generate magnetic fields ∼ 100 Mg and greater

Pion Production from Proton Synchrotron Radiation under Strong Magnetic Field in Relativistic Quantum Approach

Directory of Open Access Journals (Sweden)

Maruyama Tomoyuki

2016-01-01

Full Text Available We study pion production from proton synchrotron radiation in the presence of strong magnetic fields by using the exact proton propagator in a strong magnetic field and explicitly including the anomalous magnetic moment. Results in this exact quantum-field approach do not agree with those obtained in the semi-classical approach. Furthermore, we also find that the anomalous magnetic moment of the proton greatly enhances the production rate about by two orders of magnitude, and that the polar angle of an emitted pion is the same as that of an initial proton.

Frequency-Dependent Properties of Magnetic Nanoparticle Crystals

Energy Technology Data Exchange (ETDEWEB)

Majetich, Sara [Carnegie Mellon Univ., Pittsburgh, PA (United States)

2016-05-17

In the proposed research program we will investigate the time- and frequency-dependent behavior of ordered nanoparticle assemblies, or nanoparticle crystals. Magnetostatic interactions are long-range and anisotropic, and this leads to complex behavior in nanoparticle assemblies, particularly in the time- and frequency-dependent properties. We hypothesize that the high frequency performance of composite materials has been limited because of the range of relaxation times; if a composite is a dipolar ferromagnet at a particular frequency, it should have the advantages of a single phase material, but without significant eddy current power losses. Arrays of surfactant-coated monodomain magnetic nanoparticles can exhibit long-range magnetic order that is stable over time. The magnetic domain size and location of domain walls is governed not by structural grain boundaries but by the shape of the array, due to the local interaction field. Pores or gaps within an assembly pin domain walls and limit the domain size. Measurements of the magnetic order parameter as a function of temperature showed that domains can exist at high temoerature, and that there is a collective phase transition, just as in an exchange-coupled ferromagnet. Dipolar ferromagnets are not merely of fundamental interest; they provide an interesting alternative to exchange-based ferromagnets. Dipolar ferromagnets made with high moment metallic particles in an insulating matrix could have high permeability without large eddy current losses. Such nanocomposites could someday replace the ferrites now used in phase shifters, isolators, circulators, and filters in microwave communications and radar applications. We will investigate the time- and frequency-dependent behavior of nanoparticle crystals with different magnetic core sizes and different interparticle barrier resistances, and will measure the magnetic and electrical properties in the DC, low frequency (0.1 Hz - 1 kHz), moderate frequency (10 Hz - 500

SU-E-T-227: Could the Alpha/Beta Ratio Change in a Strong Magnetic Field?

Energy Technology Data Exchange (ETDEWEB)

Pang, G [Odette Cancer Centre, 2075 Bayview Avenue, Toronto M4N 3M5, Canada and Sunnybrook Research Institute and Departments of Radiation Oncology and Medical Biophysics, University of Toronto, Toronto (Canada)

2015-06-15

Purpose: Magnetic resonance imaging (MRI) is being integrated into radiotherapy delivery for MRI-guided radiotherapy. The presence of a strong magnetic field from a MRI machine during radiotherapy delivery presents a new challenge since the trajectories of electrons liberated by ionizing radiation in patients are strongly dependent on the applied magnetic field. The purpose of this work is to explore the potential effect of a strong magnetic field on the α/β ratio, an important radiobiological parameter in radiotherapy. Methods: Based on the theory of dual radiation action, the α/β ratio can be expressed by an integral of the product of two microdosimetry quantities γ(x) and t(x), where γ(x) is the probability that two energy transfers, a distance x apart, results in a lesion, and t(x) is the proximity function, which is the energy-weighted point-pair distribution of distances between energy transfer points in a track. The quantity t(x) depends on the applied magnetic field. An analytical approach has been used to derive a formula that can be used to calculate the α/β ratio in an extremely strong magnetic field. Results: The α/β ratio has been evaluated in the special case when the applied magnetic field approaches infinity, which gives the upper limit of the potential change of the α/β ratio due to the presence of a strong magnetic field. For V79 Chinese hamster cells it has been shown that the α/β ratio could be increased by 2.90 times for Pd-103, 2.97 times for I-125 and about 2.3 times for Co-60 sources when the applied magnetic field approaches infinity. Conclusion: It has been shown theoretically that the α/β ratio can change in a strong magnetic field, and there could be up to a nearly three-fold increase in the α/β ratio, depending on the strength of the applied magnetic field, the cell type and the radiation used.

Critical Time Crystals in Dipolar Systems.

Science.gov (United States)

Ho, Wen Wei; Choi, Soonwon; Lukin, Mikhail D; Abanin, Dmitry A

2017-07-07

We analyze the quantum dynamics of periodically driven, disordered systems in the presence of long-range interactions. Focusing on the stability of discrete time crystalline (DTC) order in such systems, we use a perturbative procedure to evaluate its lifetime. For 3D systems with dipolar interactions, we show that the corresponding decay is parametrically slow, implying that robust, long-lived DTC order can be obtained. We further predict a sharp crossover from the stable DTC regime into a regime where DTC order is lost, reminiscent of a phase transition. These results are in good agreement with the recent experiments utilizing a dense, dipolar spin ensemble in diamond [Nature (London) 543, 221 (2017)NATUAS0028-083610.1038/nature21426]. They demonstrate the existence of a novel, critical DTC regime that is stabilized not by many-body localization but rather by slow, critical dynamics. Our analysis shows that the DTC response can be used as a sensitive probe of nonequilibrium quantum matter.

Bound-state β decay of a neutron in a strong magnetic field

International Nuclear Information System (INIS)

Kouzakov, Konstantin A.; Studenikin, Alexander I.

2005-01-01

The β decay of a neutron into a bound (pe - ) state and an antineutrino in the presence of a strong uniform magnetic field (B > or approx. 10 13 G) is considered. The β decay process is treated within the framework of the standard model of weak interactions. A Bethe-Salpeter formalism is employed for description of the bound (pe - ) system in a strong magnetic field. For the field strengths 10 13 18 G the estimate for the ratio of the bound-state decay rate w b and the usual (continuum-state) decay rate w c is derived. It is found that in such strong magnetic fields w b /w c ∼0.1-0.4. This is in contrast to the field-free case, where w b /w c ≅4.2x10 -6 [J. N. Bahcall, Phys. Rev. 124, 495 (1961); L. L. Nemenov, Sov. J. Nucl. Phys. 15, 582 (1972); X. Song, J. Phys. G: Nucl. Phys. 13, 1023 (1987)]. The dependence of the ratio w b /w c on the magnetic field strength B exhibits a logarithmiclike behavior. The obtained results can be important for applications in astrophysics and cosmology

X-ray magnetic circular dichroism strongly influenced by non-magnetic cover layers

International Nuclear Information System (INIS)

Zafar, K.; Audehm, P.; Schütz, G.; Goering, E.; Pathak, M.; Chetry, K.B.; LeClair, P.R.; Gupta, A.

2013-01-01

Highlights: •Energy filtering gives much larger sampling depth and escape length as expected. •XMCD sum rules could be dramatically altered by this effect. •Strong enhanced effective escape length for buried layers. •A “universal curve” model gives semi quantitative understanding. •Buried layers are more sensitive to self-absorption phenomena. -- Abstract: Total electron yield (TEY) is the dominating measurement mode in soft X-ray absorption spectroscopy (XAS), where the sampling depth is generally assumed to be quite small and constant, and the related self-absorption or saturation phenomena are about to be negligible at normal incidence conditions. From the OK edge to CrL 2,3 edge XAS ratio we determined a strong change in the effective electron escape length between an uncovered and a RuO 2 covered CrO 2 sample. This effect has been explained by a simple electron energy filtering model, providing a semi quantitative description. In addition, this simple model can quantitatively describe the unexpected reduced and positive CrL 2,3 X-ray magnetic circular dichroism (XMCD) signal of a RuO 2 /CrO 2 bilayer, while previous results have identified a clear negative Cr magnetization at the RuO 2 /CrO 2 interface. In our case this escape length enhancement has strong impact on the XMCD sum rule results and in general it provides much deeper sampling depth, but also larger self-absorption or saturation effects

Spin-polarized states in neutron matter in a strong magnetic field

International Nuclear Information System (INIS)

Isayev, A. A.; Yang, J.

2009-01-01

Spin-polarized states in neutron matter in strong magnetic fields up to 10 18 G are considered in the model with the Skyrme effective interaction. By analyzing the self-consistent equations at zero temperature, it is shown that a thermodynamically stable branch of solutions for the spin-polarization parameter as a function of density corresponds to the negative spin polarization when the majority of neutron spins are oriented opposite to the direction of the magnetic field. Besides, beginning from some threshold density dependent on magnetic field strength, the self-consistent equations also have two other branches of solutions for the spin-polarization parameter with the positive spin polarization. The free energy corresponding to one of these branches turns out to be very close to that of the thermodynamically preferable branch. As a consequence, in a strong magnetic field, the state with the positive spin polarization can be realized as a metastable state in the high-density region in neutron matter, which, under decreasing density, at some threshold density changes to a thermodynamically stable state with the negative spin polarization.

Positronium-photon and photon-positronium quantum transitions in strong magnetic fields

International Nuclear Information System (INIS)

Leinson, L.B.; Oraevskii, V.N.; Radio-Wave Propagation, Academy of Sciences of the USSR)

1985-01-01

The wave functions and energy levels of bound electron-positron pairs in a strong magnetic field H>>α 2 H 0 , where H 0 = m 2 0 c 3 /eh = 4.4 x 10 13 G and α = e 2 /hc, are found in the nonrelativistic approximation. The probabilities of one-photon annihilation of positronium and of the inverse transition from a resonance photon to a positronium atom are calculated. It is shown that in a sufficiently strong magnetic field H∼H 0 , when the probability of one-photon annihilation is considerably greater than the probability of two-photon annihilation of positronium, the lifetime of the decay photon with respect to the inverse transformation to a positronium atom is so small that the decay photon cannot propagate freely in the magnetic field. Therefore, the lifetime of the positronium atom in the case H∼H 0 is determined by the two-photon decay. The possibility of the decay γ→γ 1 +γ 2 via intermediate positronium states in a magnetic field with curved field lines is discussed

Magnetic properties of strongly asymmetric nuclear matter

International Nuclear Information System (INIS)

Kutschera, M.; Wojcik, W.

1988-01-01

We investigate stability of neutron matter containing a small proton admixture with respect to spin fluctuations. We establish conditions under which strongly asymmetric nuclear matter could acquire a permanent magnetization. It is shown that if the protons are localized, the system becomes unstable to spin fluctuations for arbitrarily weak proton-neutron spin interactions. For non-localized protons there exists a threshold value of the spin interaction above which the system can develop a spontaneous polarization. 12 refs., 2 figs. (author)

Application of the annihilation and creation operators in magnetic resonance problems

International Nuclear Information System (INIS)

Nosel, W.

1981-01-01

Application of the annihilation and creation operators in the following problems is presented: in the resonance of the free spins in rotating and oscillating magnetic field, in the influence of the nonresonance magnetic fields on magnetic resonance, in the thermodynamics of the spins with dipolar interaction and in the nuclear magnetic relaxation. (author)

Statistical mechanics of a plasma in a very strong magnetic field

International Nuclear Information System (INIS)

Psimopoulos, M.

1980-03-01

Using the guiding centre model the behaviour of a plasma in the presence of a very strong constant magnetic field has been studied. The validity of the model is discussed and the conditions concerning the strength of the magnetic field are derived. Both the equilibrium and the non-equilibrium aspects of the problem are considered. (U.K.)

Magnetic structure of Fe-based amorphous and thermal annealed microwires

International Nuclear Information System (INIS)

Olivera, J.; Provencio, M.; Prida, V.M.; Hernando, B.; Santos, J.D.; Perez, M.J.; Gorria, P.; Sanchez, M.L.; Belzunce, F.J.

2005-01-01

The magnetic structure of amorphous and thermal annealed glass coated microwires is studied by thermomagnetic, DSC, and Bitter domain pattern techniques. The long-range dipolar interaction between parallel aligned microwires and the appearance of large Barkhausen jumps steps in the axially magnetized loops are discussed in terms of reversal magnetization process

Spin coherence in a Mn{sub 3} single-molecule magnet

Energy Technology Data Exchange (ETDEWEB)

Abeywardana, Chathuranga [Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Mowson, Andrew M.; Christou, George [Department of Chemistry, University of Florida, Gainesville, Florida 32611 (United States); Takahashi, Susumu, E-mail: susumu.takahashi@usc.edu [Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Department of Physics, University of Southern California, Los Angeles, California 90089 (United States)

2016-01-25

Spin coherence in single crystals of the spin S = 6 single-molecule magnet (SMM) [Mn{sub 3}O(O{sub 2}CEt){sub 3}(mpko){sub 3}]{sup +} (abbreviated Mn{sub 3}) has been investigated using 230 GHz electron paramagnetic resonance spectroscopy. Coherence in Mn{sub 3} was uncovered by significantly suppressing dipolar contribution to the decoherence with complete spin polarization of Mn{sub 3} SMMs. The temperature dependence of spin decoherence time (T{sub 2}) revealed that the dipolar decoherence is the dominant source of decoherence in Mn{sub 3} and T{sub 2} can be extended up to 267 ns by quenching the dipolar decoherence.

GLOBAL GALACTIC DYNAMO DRIVEN BY COSMIC RAYS AND EXPLODING MAGNETIZED STARS

International Nuclear Information System (INIS)

Hanasz, Michal; Woltanski, Dominik; Kowalik, Kacper

2009-01-01

We report the first results of the first global galactic-scale cosmic ray (CR)-MHD simulations of CR-driven dynamo. We investigate the dynamics of magnetized interstellar medium (ISM), which is dynamically coupled with CR gas. We assume that exploding stars deposit small-scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of CRs, accelerated in supernova shocks. We conduct numerical simulations with the aid of a new parallel MHD code PIERNIK. We find that the initial magnetization of galactic disks by exploding magnetized stars forms favorable conditions for the CR-driven dynamo. We demonstrate that dipolar magnetic fields supplied on small supernova remnant scales can be amplified exponentially by the CR-driven dynamo, to the present equipartition values, and transformed simultaneously to large galactic scales. The resulting magnetic field structure in an evolved galaxy appears spiral in the face-on view and reveals the so-called X-shaped structure in the edge-on view.

Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids

International Nuclear Information System (INIS)

Abedinpour, Saeed H.; Asgari, Reza; Tanatar, B.; Polini, Marco

2014-01-01

We study the ground-state properties of a two-dimensional spin-polarized fluid of dipolar fermions within the Euler–Lagrange Fermi-hypernetted-chain approximation. Our method is based on the solution of a scattering Schrödinger equation for the “pair amplitude” √(g(r)), where g(r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow–Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree–Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation–dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density–density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings. -- Highlights: •We have studied the ground state properties of a strongly correlated two-dimensional fluid of dipolar fermions. •We have calculated the effective inter-particle interaction and the dynamical density–density response function. •We have shown that an undamped zero sound mode exists at any value of the interaction strength

Magnetic fields in Earth-like exoplanets and implications for habitability around M-dwarfs.

Science.gov (United States)

López-Morales, Mercedes; Gómez-Pérez, Natalia; Ruedas, Thomas

2011-12-01

We present estimations of dipolar magnetic moments for terrestrial exoplanets using the Olson & Christiansen (EPS Lett 250:561-571, 2006) scaling law and assuming their interior structure is similar to Earth. We find that the dipolar moment of fast rotating planets (where the Coriolis force dominates convection in the core), may amount up to ~80 times the magnetic moment of Earth, M ⊕, for at least part of the planets' lifetime. For slow rotating planets (where the force of inertia dominates), the dipolar magnetic moment only reaches up to ~1.5 M [symbol in text]. Applying our calculations to confirmed rocky exoplanets, we find that CoRoT-7b, Kepler-10b and 55 Cnc e can sustain dynamos up to ~18, 15 and 13 M [symbol in text], respectively. Our results also indicate that the magnetic moment of rocky exoplanets not only depends on rotation rate, but also on their formation history, thermal state, age, composition, and the geometry of the field. These results apply to all rocky planets, but have important implications for the particular case of planets in the Habitable Zone of M-dwarfs.

Diffusion of charged particles in strong large-scale random and regular magnetic fields

International Nuclear Information System (INIS)

Mel'nikov, Yu.P.

2000-01-01

The nonlinear collision integral for the Green's function averaged over a random magnetic field is transformed using an iteration procedure taking account of the strong random scattering of particles on the correlation length of the random magnetic field. Under this transformation the regular magnetic field is assumed to be uniform at distances of the order of the correlation length. The single-particle Green's functions of the scattered particles in the presence of a regular magnetic field are investigated. The transport coefficients are calculated taking account of the broadening of the cyclotron and Cherenkov resonances as a result of strong random scattering. The mean-free path lengths parallel and perpendicular to the regular magnetic field are found for a power-law spectrum of the random field. The analytical results obtained are compared with the experimental data on the transport ranges of solar and galactic cosmic rays in the interplanetary magnetic field. As a result, the conditions for the propagation of cosmic rays in the interplanetary space and a more accurate idea of the structure of the interplanetary magnetic field are determined

Characterization of surfactant liquid crystal phases suitable for molecular alignment and measurement of dipolar couplings

International Nuclear Information System (INIS)

Barrientos, Laura G.; Dolan, Caroline; Gronenborn, Angela M.

2000-01-01

Media employed for imparting partial alignment onto solute molecules have recently attracted considerable attention, since they permit the measurement of NMR parameters for solute biomolecules commonly associated with solid state NMR. Here we characterize a medium which is based on a quasi-ternary surfactant system comprising cetylpyridinium bromide/hexanol/sodium bromide. We demonstrate that dilute solutions of this system can exist in liquid crystalline phases which orient in the magnetic field and allow the measurement of residual dipolar couplings under a variety of conditions. The present system is extremely versatile and robust, tolerating different buffer conditions, temperature ranges and concentrations

The structure of the interface in the solvent mediated interaction of dipolar surfaces

International Nuclear Information System (INIS)

Dzhavakhidze, P.G.; Levadny, V.G.

1987-08-01

Interaction of two dipolar surfaces separated by a polar medium is considered within the framework of nonlocal electrostatics. The dipolar surface layers are modelled as regular lattices with fixed orientation of dipoles which are immersed into the solvent; solvent response is characterized by nonlocal dielectric function. The model is elaborated in order to reveal the role of the dipolar layer discreteness in the electric field produced by one surface and the interaction between two surfaces (which gives rise to the so called ''hydration'' or ''structural'' force acting between mineral surfaces and phospholipid bilayers). The discreteness effects are present only for commensurate lattices. Their special mutual arrangement then may lead to considerable reduction of structural forces, viz. the usual repulsion regime may change at short distances to attraction. Conditions are considered when repulsion is entirely replaced by attraction, i.e. the ''hydration barrier'' disappears. In appended note we discuss the role of solvation of surface dipolar groups. We propose an explanation of why two modes of decay (one with oscillative fine structure) may be present in the dependence of the force upon distance if the surface dipolar groups are immersed deep enough in the solvent and how the long-range oscillative mode disappears when the surface is but weakly solvated. (author). 35 refs, 5 figs

The influence of hyperons and strong magnetic field in neutron star properties

International Nuclear Information System (INIS)

Lopes, L.L.; Menezes, D.P.

2012-01-01

Neutron stars are among the most exotic objects in the universe and constitute a unique laboratory to study nuclear matter above the nuclear saturation density. In this work, we study the equation of state (EoS) of the nuclear matter within a relativistic model subject to a strong magnetic field. We then apply this EoS to study and describe some of the physical characteristics of neutron stars, especially the massradius relation and chemical compositions. To study the influence of the magnetic field and the hyperons in the stellar interior, we consider altogether four solutions: two different magnetic fields to obtain a weak and a strong influence; and two configurations: a family of neutron stars formed only by protons, electrons, and neutrons and a family formed by protons, electrons, neutrons, muons, and hyperons. The limit and the validity of the results found are discussed with some care. In all cases, the particles that constitute the neutron star are in ,B equilibrium and zero total net charge. Our work indicates that the effect of a strong magnetic field has to be taken into account in the description of magnetars, mainly if we believe that there are hyperons in their interior, in which case the influence of the magnetic field can increase the mass by more than 10 %. We have also seen that although a magnetar can reach 2.48 M0, a natural explanation of why we do not know pulsars with masses above 2.0 Mo arises. We also discuss how the magnetic field affects the strangeness fraction in some standard neutron star masses, and to conclude our paper, we revisit the direct Urca process related to the cooling of the neutron stars and show how it is affected by the hyperons and the magnetic field. (author)

High electronegativity multi-dipolar electron cyclotron resonance plasma source for etching by negative ions

DEFF Research Database (Denmark)

Stamate, Eugen; Draghici, M.

2012-01-01

A large area plasma source based on 12 multi-dipolar ECR plasma cells arranged in a 3 x 4 matrix configuration was built and optimized for silicon etching by negative ions. The density ratio of negative ions to electrons has exceeded 300 in Ar/SF6 gas mixture when a magnetic filter was used...... to reduce the electron temperature to about 1.2 eV. Mass spectrometry and electrostatic probe were used for plasma diagnostics. The new source is free of density jumps and instabilities and shows a very good stability for plasma potential, and the dominant negative ion species is F-. The magnetic field...... in plasma volume is negligible and there is no contamination by filaments. The etching rate by negative ions measured in Ar/SF6/O-2 mixtures was almost similar with that by positive ions reaching 700 nm/min. (C) 2012 American Institute of Physics...

Cluster analysis in systems of magnetic spheres and cubes

Energy Technology Data Exchange (ETDEWEB)

Pyanzina, E.S., E-mail: elena.pyanzina@urfu.ru [Ural Federal University, Lenin Av. 51, Ekaterinburg (Russian Federation); Gudkova, A.V. [Ural Federal University, Lenin Av. 51, Ekaterinburg (Russian Federation); Donaldson, J.G. [University of Vienna, Sensengasse 8, Vienna (Austria); Kantorovich, S.S. [Ural Federal University, Lenin Av. 51, Ekaterinburg (Russian Federation); University of Vienna, Sensengasse 8, Vienna (Austria)

2017-06-01

In the present work we use molecular dynamics simulations and graph-theory based cluster analysis to compare self-assembly in systems of magnetic spheres, and cubes where the dipole moment is oriented along the side of the cube in the [001] crystallographic direction. We show that under the same conditions cubes aggregate far less than their spherical counterparts. This difference can be explained in terms of the volume of phase space in which the formation of the bond is thermodynamically advantageous. It follows that this volume is much larger for a dipolar sphere than for a dipolar cube. - Highlights: • A comparison of the degree of self-assembly in systems of magnetic spheres and cubes. • Spheres are more likely to form larger clusters than cubes. • Differences in microstructure will manifest in the magnetic response of each system.

Strong Magnetic Field Characterisation

Science.gov (United States)

2012-04-01

an advertised surface field of approximately 0.5 T were used to supply the static magnetic field source. The disc magnet had a diameter of 50 mm and... colour bar indicates the magnetic field strength set to an arbitrary 0.25 T. The white area has a field >0.25 T. The size of the arrow is proportional...9 shows the magnetic field strength along a slice in the XZ plane. The colours represent the total UNCLASSIFIED 10 UNCLASSIFIED DSTO-TR-2699

Pion Production from Proton Synchrotron Radiation under Strong Magnetic Field in a Relativistic Quantum Approach

Directory of Open Access Journals (Sweden)

Maruyama Tomoyuki

2016-01-01

Full Text Available We study pion production from proton synchrotron radiation in the presence of strong magnetic fields by using the exact proton propagator in a strong magnetic field and explicitly including the anomalous magnetic moment. Results in this exact quantum approach do not agree with those obtained in the semi-classical approach. Then, we find that the anomalous magnetic moment of the proton greatly enhances the production rate by about two orders magnitude, and that the decay width satisfies a robust scaling law.

Magnetic ordering in tetragonal FeS: Evidence for strong itinerant spin fluctuations

Energy Technology Data Exchange (ETDEWEB)

Kwon, K.D.; Refson, K.; Bone, S.; Qiao, R.; Yang, W.; Liu, Z.; Sposito, G.

2010-11-01

Mackinawite is a naturally occurring layer-type FeS mineral important in biogeochemical cycles and, more recently, in the development of microbial fuel cells. Conflicting results have been published as to the magnetic properties of this mineral, with Moessbauer spectroscopy indicating no magnetic ordering down to 4.2 K but density functional theory (DFT) predicting an antiferromagnetic ground state, similar to the Fe-based high-temperature superconductors with which it is isostructural and for which it is known that magnetism is suppressed by strong itinerant spin fluctuations. We investigated this latter possibility for mackinawite using photoemission spectroscopy, near-edge x-ray absorption fine structure spectroscopy, and DFT computations. Our Fe 3{sub s} core-level photoemission spectrum of mackinawite showed a clear exchange-energy splitting (2.9 eV) consistent with a 1 {micro}{sub B} magnetic moment on the Fe ions, while the Fe L-edge x-ray absorption spectrum indicated rather delocalized Fe 3{sub d} electrons in mackinawite similar to those in Fe metal. Our DFT computations demonstrated that the ground state of mackinawite is single-stripe antiferromagnetic, with an Fe magnetic moment (2.7 {micro}{sub B}) that is significantly larger than the experimental estimate and has a strong dependence on the S height and lattice parameters. All of these trends signal the existence of strong itinerant spin fluctuations. If spin fluctuations prove to be mediators of electron pairing, we conjecture that mackinawite may be one of the simplest Fe-based superconductors.

Structure refinement of flexible proteins using dipolar couplings: Application to the protein p8MTCP1

International Nuclear Information System (INIS)

Demene, Helene; Ducat, Thierry; Barthe, Philippe; Delsuc, Marc-Andre; Roumestand, Christian

2002-01-01

The present study deals with the relevance of using mobility-averaged dipolar couplings for the structure refinement of flexible proteins. The 68-residue protein p8 MTCP1 has been chosen as model for this study. Its solution state consists mainly of three α-helices. The two N-terminal helices are strapped in a well-determined α-hairpin, whereas, due to an intrinsic mobility, the position of the third helix is less well defined in the NMR structure. To further characterize the degrees of freedom of this helix, we have measured the dipolar coupling constants in the backbone of p8 MTCP1 in a bicellar medium. We show here that including D HN dip dipolar couplings in the structure calculation protocol improves the structure of the α-hairpin but not the positioning of the third helix. This is due to the motional averaging of the dipolar couplings measured in the last helix. Performing two calculations with different force constants for the dipolar restraints highlights the inconstancy of these mobility-averaged dipolar couplings. Alternatively, prior to any structure calculations, comparing the values of the dipolar couplings measured in helix III to values back-calculated from an ideal helix demonstrates that they are atypical for a helix. This can be partly attributed to mobility effects since the inclusion of the 15 N relaxation derived order parameter allows for a better fit

Direct URCA-processes in neutron star quark core with strong magnetic field.

Directory of Open Access Journals (Sweden)

Belyaev Vasily

2017-01-01

In evaluations, the strength of magnetic field corresponds to the case, where the quarks of medium occupy a lot of Landau levels, while the electrons are in ground Landau level. The analytical dependence of neutrino emissivity on chemical potentials of quarks and electrons, temperature and magnetic field strength is obtained and briefly discussed. The result could be important in application to a massive strongly magnetized neutron star with quark core.

Pitch angle distributions of electrons at dipolarization sites during geomagnetic activity: THEMIS observations

Science.gov (United States)

Wang, Kaiti; Lin, Ching-Huei; Wang, Lu-Yin; Hada, Tohru; Nishimura, Yukitoshi; Turner, Drew L.; Angelopoulos, Vassilis

2014-12-01

Changes in pitch angle distributions of electrons with energies from a few eV to 1 MeV at dipolarization sites in Earth's magnetotail are investigated statistically to determine the extent to which adiabatic acceleration may contribute to these changes. Forty-two dipolarization events from 2008 and 2009 observed by Time History of Events and Macroscale Interactions during Substorms probes covering the inner plasma sheet from 8 RE to 12 RE during geomagnetic activity identified by the AL index are analyzed. The number of observed events with cigar-type distributions (peaks at 0° and 180°) decreases sharply below 1 keV after dipolarization because in many of these events, electron distributions became more isotropized. From above 1 keV to a few tens of keV, however, the observed number of cigar-type events increases after dipolarization and the number of isotropic events decreases. These changes can be related to the ineffectiveness of Fermi acceleration below 1 keV (at those energies, dipolarization time becomes comparable to electron bounce time). Model-calculated pitch angle distributions after dipolarization with the effect of betatron and Fermi acceleration tested indicate that these adiabatic acceleration mechanisms can explain the observed patterns of event number changes over a large range of energies for cigar events and isotropic events. Other factors still need to be considered to assess the observed increase in cigar events around 2 keV. Indeed, preferential directional increase/loss of electron fluxes, which may contribute to the formation of cigar events, was observed. Nonadiabatic processes to accelerate electrons in a parallel direction may also be important for future study.

Chiral soliton lattice and charged pion condensation in strong magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Brauner, Tomáš [Faculty of Science and Technology, University of Stavanger,N-4036 Stavanger (Norway); Yamamoto, Naoki [Department of Physics, Keio University,Yokohama 223-8522 (Japan)

2017-04-21

The Chiral Soliton Lattice (CSL) is a state with a periodic array of topological solitons that spontaneously breaks parity and translational symmetries. Such a state is known to appear in chiral magnets. We show that CSL also appears as a ground state of quantum chromodynamics at nonzero chemical potential in a magnetic field. By analyzing the fluctuations of the CSL, we furthermore demonstrate that in strong but achievable magnetic fields, charged pions undergo Bose-Einstein condensation. Our results, based on a systematic low-energy effective theory, are model-independent and fully analytic.

Production of large volume, strongly magnetized laser-produced plasmas by use of pulsed external magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Albertazzi, B. [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau (France); INRS-EMT, Varennes, Quebec J3X 1S2 (Canada); Beard, J.; Billette, J.; Portugall, O. [LNCMI, UPR 3228, CNRS-UFJ-UPS-INSA, 31400 Toulouse (France); Ciardi, A. [LERMA, Observatoire de Paris, Ecole Normale Superieure, Universite Pierre et Marie Curie, CNRS UMR 8112, Paris (France); Vinci, T.; Albrecht, J.; Chen, S. N.; Da Silva, D.; Hirardin, B.; Nakatsutsumi, M.; Romagnagni, L.; Simond, S.; Veuillot, E.; Fuchs, J. [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau (France); Burris-Mog, T.; Dittrich, S.; Herrmannsdoerfer, T.; Kroll, F.; Nitsche, S. [Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany); and others

2013-04-15

The production of strongly magnetized laser plasmas, of interest for laboratory astrophysics and inertial confinement fusion studies, is presented. This is achieved by coupling a 16 kV pulse-power system. This is achieved by coupling a 16 kV pulse-power system, which generates a magnetic field by means of a split coil, with the ELFIE laser facility at Ecole Polytechnique. In order to influence the plasma dynamics in a significant manner, the system can generate, repetitively and without debris, high amplitude magnetic fields (40 T) in a manner compatible with a high-energy laser environment. A description of the system and preliminary results demonstrating the possibility to magnetically collimate plasma jets are given.

VLA observations of dwarf M flare stars and magnetic stars

Science.gov (United States)

Willson, R. F.; Lang, K. R.; Foster, P.

1988-01-01

The VLA has been used to search for 6 cm emission from 16 nearby dwarf M stars, leading to the detection of only one of them - Gliese 735. The dwarf M flare stars AD Leonis and YZ Canis Minoris were also monitored at 6 cm and 20 cm wavelength in order to study variability. Successive oppositely circularly polarized bursts were detected from AD Leo at 6 cm, suggesting the presence of magnetic fields of both magnetic polarities. An impulsive 20-cm burst from YZ CMi preceded slowly varying 6-cm emission. The VLA was also used, unsuccessfully, to search for 6-cm emission from 13 magnetic Ap stars, all of which exhibit kG magnetic fields. Although the Ap magnetic stars have strong dipolar magnetic fields, the failure to detect gyroresonant radiation suggests that these stars do not have hot, dense coronae. The quiescent microwave emission from GL 735 is probably due to nonthermal radiation, since unusually high (H = 50 kG or greater) surface magnetic fields are inferred under the assumption that the 6-cm radiation is the gyroresonant radiation of thermal electrons.

Quantum simulation and quantum information processing with molecular dipolar crystals

International Nuclear Information System (INIS)

Ortner, M.

2011-01-01

In this thesis interactions between dipolar crystals and neutral atoms or separated molecules have been investigated. They were motivated to realize new kinds of lattice models in mixtures of atoms and polar molecules where an MDC functions as an underlying periodic lattice structure for the second species. Such models bring out the peculiar features of MDC's, that include a controllable, potentially sub-optical wavelength periodicity and strong particle phonon interactions. Only stable collisional configurations have been investigated, excluding chemical reactions between the substituents, and crystal distortions beyond the scope of perturbation theory. The system was treated in the polaron picture where particles of the second species are dressed by surrounding crystal phonons. To describe the competition between coherent and incoherent dynamics of the polarons, a master equation in the Brownian motion limit was used with phonons treated as a thermal heat bath. It was shown analytically that in a wide range of realistic parameters the corrections to the coherent time evolution are small, and that the dynamics of the dressed particles can be described by an effective extended Hubbard model with controllable system parameters. The last chapter of this thesis contains a proposal for QIP with cold polar molecules that, in contrast to previous works, uses an MDC as a quantum register. It was motivated by the unique features of dipolar molecules and to exploit the peculiar physical conditions in dipolar crystals. In this proposal the molecular dipole moments were tailored by non-local fields to include a small, switchable, state-dependent dipole moment in addition to the large internal state independent moment that stabilizes the crystal. It was shown analytically that a controllable, non-trivial phonon-mediated interaction can be generated that exceeds non-trivial, direct dipole-dipole couplings. The addressability problem due to high crystal densities was overcome by

Classical anomalous absorption in strongly magnetized plasmas and effective shielding length

International Nuclear Information System (INIS)

Matsuda, K.

1981-01-01

The high-frequency conductivity tensor of a plasma in a magnetic field has been evaluated. An anomalous perpendicular conductivity is obtained for a strongly magnetized plasma. Contrarily to the previous prediction, the effective shielding length is found to be the Debye length even when the Debye length is larger than the electron gyroradius. The effective shielding length is further discussed by presenting the generalized Balescu-Lenard equation

Kubo conductivity of a strongly magnetized two-dimensional plasma.

Science.gov (United States)

Montgomery, D.; Tappert, F.

1971-01-01

The Kubo formula is used to evaluate the bulk electrical conductivity of a two-dimensional guiding-center plasma in a strong dc magnetic field. The particles interact only electrostatically. An ?anomalous' electrical conductivity is derived for this system, which parallels a recent result of Taylor and McNamara for the coefficient of spatial diffusion.

Independent EEG sources are dipolar.

Directory of Open Access Journals (Sweden)

Arnaud Delorme

Full Text Available Independent component analysis (ICA and blind source separation (BSS methods are increasingly used to separate individual brain and non-brain source signals mixed by volume conduction in electroencephalographic (EEG and other electrophysiological recordings. We compared results of decomposing thirteen 71-channel human scalp EEG datasets by 22 ICA and BSS algorithms, assessing the pairwise mutual information (PMI in scalp channel pairs, the remaining PMI in component pairs, the overall mutual information reduction (MIR effected by each decomposition, and decomposition 'dipolarity' defined as the number of component scalp maps matching the projection of a single equivalent dipole with less than a given residual variance. The least well-performing algorithm was principal component analysis (PCA; best performing were AMICA and other likelihood/mutual information based ICA methods. Though these and other commonly-used decomposition methods returned many similar components, across 18 ICA/BSS algorithms mean dipolarity varied linearly with both MIR and with PMI remaining between the resulting component time courses, a result compatible with an interpretation of many maximally independent EEG components as being volume-conducted projections of partially-synchronous local cortical field activity within single compact cortical domains. To encourage further method comparisons, the data and software used to prepare the results have been made available (http://sccn.ucsd.edu/wiki/BSSComparison.

Helium atoms and molecules in strong magnetic fields

Science.gov (United States)

Mori, K.

Recent theoretical studies have shown that the neutron star surface may be composed of helium or heavier elements as hydrogen may be quickly depleted by diffuse nuclear burning Chang Bildsten However while Hydrogen atmospheres have been studied in great details atomic data for helium is available only for He ion Pavlov Bezchastnov 2005 We performed Hartree-Fock type calculation for Helium atom and molecules and computed their binding ionization and dissociation energies in strong magnetic fields B sim10 12 -- 10 15 G We will present ionization balance of Helium atmospheres at typical magnetic field strengths and temperatures to radio-quiet neutron stars and AXPs We will also discuss several implications of helium atmosphere to X-ray data of isolated neutron stars focusing on the detected spectral features

Topological defect formation in rotating binary dipolar Bose–Einstein condensate

International Nuclear Information System (INIS)

Zhang, Xiao-Fei; Han, Wei; Jiang, Hai-Feng; Liu, Wu-Ming; Saito, Hiroki; Zhang, Shou-Gang

2016-01-01

We investigate the topological defects and spin structures of a rotating binary Bose–Einstein condensate, which consists of both dipolar and scalar bosonic atoms confined in spin-dependent optical lattices, for an arbitrary orientation of the dipoles with respect to their plane of motion. Our results show that the tunable dipolar interaction, especially the orientation of the dipoles, can be used to control the direction of stripe phase and its related half-vortex sheets. In addition, it can also be used to obtain a regular arrangement of various topological spin textures, such as meron, circular and cross disgyration spin structures. We point out that such topological defects and regular arrangement of spin structures arise primarily from the long-range and anisotropic nature of dipolar interaction and its competition with the spin-dependent optical lattices and rotation. - Highlights: • Effects of both strength and orientation of the dipoles are discussed. • Various topological defects can be formed in different parameter regions. • Present one possible way to obtain regular arrangements of spin textures.

On Multiple Reconnection X-lines and Tripolar Perturbations of Strong Guide Magnetic Fields

Science.gov (United States)

Eriksson, S.; Lapenta, G.; Newman, D. L.; Phan, T. D.; Gosling, J. T.; Lavraud, B.; Khotyaintsev, Yu. V.; Carr, C. M.; Markidis, S.; Goldman, M. V.

2015-05-01

We report new multi-spacecraft Cluster observations of tripolar guide magnetic field perturbations at a solar wind reconnection exhaust in the presence of a guide field BM which is almost four times as strong as the reversing field BL. The novel tripolar field consists of two narrow regions of depressed BM, with an observed 7%-14% ΔBM magnitude relative to the external field, which are found adjacent to a wide region of enhanced BM within the exhaust. A stronger reversing field is associated with each BM depression. A kinetic reconnection simulation for realistic solar wind conditions and the observed strong guide field reveals that tripolar magnetic fields preferentially form across current sheets in the presence of multiple X-lines as magnetic islands approach one another and merge into fewer and larger islands. The simulated ΔBM/ΔXN over the normal width ΔXN between a BM minimum and the edge of the external region agree with the normalized values observed by Cluster. We propose that a tripolar guide field perturbation may be used to identify candidate regions containing multiple X-lines and interacting magnetic islands at individual solar wind current sheets with a strong guide field.

Quantum phases of dipolar rotors on two-dimensional lattices.

Science.gov (United States)

Abolins, B P; Zillich, R E; Whaley, K B

2018-03-14

The quantum phase transitions of dipoles confined to the vertices of two-dimensional lattices of square and triangular geometry is studied using path integral ground state quantum Monte Carlo. We analyze the phase diagram as a function of the strength of both the dipolar interaction and a transverse electric field. The study reveals the existence of a class of orientational phases of quantum dipolar rotors whose properties are determined by the ratios between the strength of the anisotropic dipole-dipole interaction, the strength of the applied transverse field, and the rotational constant. For the triangular lattice, the generic orientationally disordered phase found at zero and weak values of both dipolar interaction strength and applied field is found to show a transition to a phase characterized by net polarization in the lattice plane as the strength of the dipole-dipole interaction is increased, independent of the strength of the applied transverse field, in addition to the expected transition to a transverse polarized phase as the electric field strength increases. The square lattice is also found to exhibit a transition from a disordered phase to an ordered phase as the dipole-dipole interaction strength is increased, as well as the expected transition to a transverse polarized phase as the electric field strength increases. In contrast to the situation with a triangular lattice, on square lattices, the ordered phase at high dipole-dipole interaction strength possesses a striped ordering. The properties of these quantum dipolar rotor phases are dominated by the anisotropy of the interaction and provide useful models for developing quantum phases beyond the well-known paradigms of spin Hamiltonian models, implementing in particular a novel physical realization of a quantum rotor-like Hamiltonian that possesses an anisotropic long range interaction.

Quantum phases of dipolar rotors on two-dimensional lattices

Science.gov (United States)

Abolins, B. P.; Zillich, R. E.; Whaley, K. B.

2018-03-01

The quantum phase transitions of dipoles confined to the vertices of two-dimensional lattices of square and triangular geometry is studied using path integral ground state quantum Monte Carlo. We analyze the phase diagram as a function of the strength of both the dipolar interaction and a transverse electric field. The study reveals the existence of a class of orientational phases of quantum dipolar rotors whose properties are determined by the ratios between the strength of the anisotropic dipole-dipole interaction, the strength of the applied transverse field, and the rotational constant. For the triangular lattice, the generic orientationally disordered phase found at zero and weak values of both dipolar interaction strength and applied field is found to show a transition to a phase characterized by net polarization in the lattice plane as the strength of the dipole-dipole interaction is increased, independent of the strength of the applied transverse field, in addition to the expected transition to a transverse polarized phase as the electric field strength increases. The square lattice is also found to exhibit a transition from a disordered phase to an ordered phase as the dipole-dipole interaction strength is increased, as well as the expected transition to a transverse polarized phase as the electric field strength increases. In contrast to the situation with a triangular lattice, on square lattices, the ordered phase at high dipole-dipole interaction strength possesses a striped ordering. The properties of these quantum dipolar rotor phases are dominated by the anisotropy of the interaction and provide useful models for developing quantum phases beyond the well-known paradigms of spin Hamiltonian models, implementing in particular a novel physical realization of a quantum rotor-like Hamiltonian that possesses an anisotropic long range interaction.

Permanent magnet assembly producing a strong tilted homogeneous magnetic field: towards magic angle field spinning NMR and MRI.

Science.gov (United States)

Sakellariou, Dimitris; Hugon, Cédric; Guiga, Angelo; Aubert, Guy; Cazaux, Sandrine; Hardy, Philippe

2010-12-01

We introduce a cylindrical permanent magnet design that generates a homogeneous and strong magnetic field having an arbitrary inclination with respect to the axis of the cylinder. The analytical theory of 3 D magnetostatics has been applied to this problem, and a hybrid magnet structure has been designed. This structure contains two magnets producing a longitudinal and transverse component for the magnetic field, whose amplitudes and homogeneities can be fully controlled by design. A simple prototype has been constructed using inexpensive small cube magnets, and its magnetic field has been mapped using Hall and NMR probe sensors. This magnet can, in principle, be used for magic angle field spinning NMR and MRI experiments allowing for metabolic chemical shift profiling in small living animals. Copyright © 2010 John Wiley & Sons, Ltd.

Optical investigation of the strong spin-orbit-coupled magnetic semimetal YbMnBi2

Science.gov (United States)

Chaudhuri, Dipanjan; Cheng, Bing; Yaresko, Alexander; Gibson, Quinn D.; Cava, R. J.; Armitage, N. P.

2017-08-01

Strong spin-orbit coupling (SOC) can result in ground states with nontrivial topological properties. The situation is even richer in magnetic systems where the magnetic ordering can potentially have strong influence over the electronic band structure. The class of A MnBi2 (A = Sr, Ca) compounds are important in this context as they are known to host massive Dirac fermions with strongly anisotropic dispersion, which is believed to be due to the interplay between strong SOC and magnetic degrees of freedom. We report the optical conductivity of YbMnBi2, a newly discovered member of this family and a proposed Weyl semimetal (WSM) candidate with broken time reversal symmetry. Together with density functional theory (DFT) band-structure calculations, we show that the complex conductivity can be interpreted as the sum of an intraband Drude response and interband transitions. We argue that the canting of the magnetic moments that has been proposed to be essential for the realization of the WSM in an otherwise antiferromagnetically ordered system is not necessary to explain the optical conductivity. We believe our data is explained qualitatively by the uncanted magnetic structure with a small offset of the chemical potential from strict stochiometry. We find no definitive evidence of a bulk Weyl nodes. Instead, we see signatures of a gapped Dirac dispersion, common in other members of A MnBi2 family or compounds with similar 2D network of Bi atoms. We speculate that the evidence for a WSM seen in ARPES arises through a surface magnetic phase. Such an assumption reconciles all known experimental data.

Effective Induction Heating around Strongly Magnetized Stars

Science.gov (United States)

Kislyakova, K. G.; Fossati, L.; Johnstone, C. P.; Noack, L.; Lüftinger, T.; Zaitsev, V. V.; Lammer, H.

2018-05-01

Planets that are embedded in the changing magnetic fields of their host stars can experience significant induction heating in their interiors caused by the planet’s orbital motion. For induction heating to be substantial, the planetary orbit has to be inclined with respect to the stellar rotation and dipole axes. Using WX UMa, for which the rotation and magnetic axes are aligned, as an example, we show that for close-in planets on inclined orbits, induction heating can be stronger than the tidal heating occurring inside Jupiter’s satellite Io; namely, it can generate a surface heat flux exceeding 2 W m‑2. An internal heating source of such magnitude can lead to extreme volcanic activity on the planet’s surface, possibly also to internal local magma oceans, and to the formation of a plasma torus around the star aligned with the planetary orbit. A strongly volcanically active planet would eject into space mostly SO2, which would then dissociate into oxygen and sulphur atoms. Young planets would also eject CO2. Oxygen would therefore be the major component of the torus. If the O I column density of the torus exceeds ≈1012 cm‑2, the torus could be revealed by detecting absorption signatures at the position of the strong far-ultraviolet O I triplet at about 1304 Å. We estimate that this condition is satisfied if the O I atoms in the torus escape the system at a velocity smaller than 1–10 km s‑1. These estimates are valid also for a tidally heated planet.

Magnetic dipolar interaction in two-dimensional complex plasmas

International Nuclear Information System (INIS)

Feldmann, J D; Kalman, G J; Rosenberg, M

2006-01-01

Various interactions can play a role between the mesoscopic dust grains of a complex plasma. We study a system composed of dust grains that have both an electric charge and a permanent magnetic dipole moment. It is assumed that the grains occupy lattice sites, as dictated by their Coulomb interaction. In addition, they possess a spin degree of freedom (orientation of magnetic dipole moment) that is not constrained by the Coulomb interaction, thus allowing for the possibility of equilibrium orientational ordering and 'wobbling' about the equilibrium orientations. As a result, collective modes develop. We identify in-plane and out-of-plane wobbling modes and discuss their dispersion characteristics both in the ferromagnetic and in the anti-ferromagnetic ground state

Edge-state-dependent tunneling of dipole-exchange spin waves in submicrometer magnetic strips with an air gap.

Science.gov (United States)

Xing, X J; Zhang, D; Li, S W

2012-12-14

We have investigated the tunneling of dipole-exchange spin waves across an air gap in submicrometer-sized permalloy magnetic strips by means of micromagnetic simulations. The magnetizations beside the gap could form three distinct end-domain states with various strengths of dipolar coupling. Spin-wave tunneling through the gap at individual end-domain states is studied. It is found that the tunneling behavior is strongly dependent on these domain states. Nonmonotonic decay of transmission of spin waves with the increase of the gap width is observed. The underlying mechanism for these behaviors is proposed. The tunneling characteristics of the dipole-exchange spin waves differ essentially from those of the magnetostatic ones reported previously.

Magnetic Properties of Magnetic Nanoparticles for Efficient Hyperthermia

Directory of Open Access Journals (Sweden)

Ihab M. Obaidat

2015-01-01

Full Text Available Localized magnetic hyperthermia using magnetic nanoparticles (MNPs under the application of small magnetic fields is a promising tool for treating small or deep-seated tumors. For this method to be applicable, the amount of MNPs used should be minimized. Hence, it is essential to enhance the power dissipation or heating efficiency of MNPs. Several factors influence the heating efficiency of MNPs, such as the amplitude and frequency of the applied magnetic field and the structural and magnetic properties of MNPs. We discuss some of the physics principles for effective heating of MNPs focusing on the role of surface anisotropy, interface exchange anisotropy and dipolar interactions. Basic magnetic properties of MNPs such as their superparamagnetic behavior, are briefly reviewed. The influence of temperature on anisotropy and magnetization of MNPs is discussed. Recent development in self-regulated hyperthermia is briefly discussed. Some physical and practical limitations of using MNPs in magnetic hyperthermia are also briefly discussed.

Ground-state candidate for the classical dipolar kagome Ising antiferromagnet

Science.gov (United States)

Chioar, I. A.; Rougemaille, N.; Canals, B.

2016-06-01

We have investigated the low-temperature thermodynamic properties of the classical dipolar kagome Ising antiferromagnet using Monte Carlo simulations, in the quest for the ground-state manifold. In spite of the limitations of a single-spin-flip approach, we managed to identify certain ordering patterns in the low-temperature regime and we propose a candidate for this unknown state. This configuration presents some intriguing features and is fully compatible with the extrapolations of the at-equilibrium thermodynamic behavior sampled so far, making it a very likely choice for the dipolar long-range ordered state of the classical kagome Ising antiferromagnet.

Relaxation dynamics of a driven two-level system coupled to a Bose-Einstein condensate: application to quantum dot-dipolar exciton gas hybrid systems.

Science.gov (United States)

Kovalev, Vadim M; Tse, Wang-Kong

2017-11-22

We develop a microscopic theory for the relaxation dynamics of an optically pumped two-level system (TLS) coupled to a bath of weakly interacting Bose gas. Using Keldysh formalism and diagrammatic perturbation theory, expressions for the relaxation times of the TLS Rabi oscillations are derived when the boson bath is in the normal state and the Bose-Einstein condensate (BEC) state. We apply our general theory to consider an irradiated quantum dot coupled with a boson bath consisting of a two-dimensional dipolar exciton gas. When the bath is in the BEC regime, relaxation of the Rabi oscillations is due to both condensate and non-condensate fractions of the bath bosons for weak TLS-light coupling and pre dominantly due to the non-condensate fraction for strong TLS-light coupling. Our theory also shows that a phase transition of the bath from the normal to the BEC state strongly influences the relaxation rate of the TLS Rabi oscillations. The TLS relaxation rate is approximately independent of the pump field frequency and monotonically dependent on the field strength when the bath is in the low-temperature regime of the normal phase. Phase transition of the dipolar exciton gas leads to a non-monotonic dependence of the TLS relaxation rate on both the pump field frequency and field strength, providing a characteristic signature for the detection of BEC phase transition of the coupled dipolar exciton gas.

Axion production from Landau quantization in the strong magnetic field of magnetars

Science.gov (United States)

Maruyama, Tomoyuki; Balantekin, A. Baha; Cheoun, Myung-Ki; Kajino, Toshitaka; Mathews, Grant J.

2018-04-01

We utilize an exact quantum calculation to explore axion emission from electrons and protons in the presence of the strong magnetic field of magnetars. The axion is emitted via transitions between the Landau levels generated by the strong magnetic field. The luminosity of axions emitted by protons is shown to be much larger than that of electrons and becomes stronger with increasing matter density. Cooling by axion emission is shown to be much larger than neutrino cooling by the Urca processes. Consequently, axion emission in the crust may significantly contribute to the cooling of magnetars. In the high-density core, however, it may cause heating of the magnetar.

Magnetic bistability of isolated giant-spin centers in a diamagnetic crystalline matrix.

Science.gov (United States)

Vergnani, Luca; Barra, Anne-Laure; Neugebauer, Petr; Rodriguez-Douton, Maria Jesus; Sessoli, Roberta; Sorace, Lorenzo; Wernsdorfer, Wolfgang; Cornia, Andrea

2012-03-12

Polynuclear single-molecule magnets (SMMs) were diluted in a diamagnetic crystal lattice to afford arrays of independent and iso-oriented magnetic units. Crystalline solid solutions of an Fe(4) SMM and its Ga(4) analogue were prepared with no metal scrambling for Fe(4) molar fractions x down to 0.01. According to high-frequency EPR and magnetic measurements, the guest SMM species have the same total spin (S=5), anisotropy, and high-temperature spin dynamics found in the pure Fe(4) phase. However, suppression of intermolecular magnetic interactions affects magnetic relaxation at low temperature (40 mK), where quantum tunneling (QT) of the magnetization dominates. When a magnetic field is applied along the easy magnetic axis, both pure and diluted (x=0.01) phases display pronounced steps at evenly spaced field values in their hysteresis loops due to resonant QT. The pure Fe(4) phase exhibits additional steps which are firmly ascribed to two-molecule QT transitions. Studies on the field-dependent relaxation rate showed that the zero-field resonance sharpens by a factor of five and shifts from about 8 mT to exactly zero field on dilution, in agreement with the calculated variation of dipolar interactions. The tunneling efficiency also changes significantly as a function of Fe(4) concentration: the zero-field resonance is significantly enhanced on dilution, while tunneling at ±0.45 T becomes less efficient. These changes were rationalized on the basis of a dipolar shuffling mechanism and transverse dipolar fields, whose effect was analyzed by using a multispin model. Our findings directly prove the impact of intermolecular magnetic couplings on SMM behavior and disclose the magnetic response of truly isolated giant spins in a diamagnetic crystalline environment. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Strongly Coupled Magnetic and Electronic Transitions in Multivalent Strontium Cobaltites.

Science.gov (United States)

Lee, J H; Choi, Woo Seok; Jeen, H; Lee, H-J; Seo, J H; Nam, J; Yeom, M S; Lee, H N

2017-11-22

The topotactic phase transition in SrCoO x (x = 2.5-3.0) makes it possible to reversibly transit between the two distinct phases, i.e. the brownmillerite SrCoO 2.5 that is a room-temperature antiferromagnetic insulator (AFM-I) and the perovskite SrCoO 3 that is a ferromagnetic metal (FM-M), owing to their multiple valence states. For the intermediate x values, the two distinct phases are expected to strongly compete with each other. With oxidation of SrCoO 2.5 , however, it has been conjectured that the magnetic transition is decoupled to the electronic phase transition, i.e., the AFM-to-FM transition occurs before the insulator-to-metal transition (IMT), which is still controversial. Here, we bridge the gap between the two-phase transitions by density-functional theory calculations combined with optical spectroscopy. We confirm that the IMT actually occurs concomitantly with the FM transition near the oxygen content x = 2.75. Strong charge-spin coupling drives the concurrent IMT and AFM-to-FM transition, which fosters the near room-T magnetic transition characteristic. Ultimately, our study demonstrates that SrCoO x is an intriguingly rare candidate for inducing coupled magnetic and electronic transition via fast and reversible redox reactions.

Confinement of laser plasma expansion with strong external magnetic field

Science.gov (United States)

Tang, Hui-bo; Hu, Guang-yue; Liang, Yi-han; Tao, Tao; Wang, Yu-lin; Hu, Peng; Zhao, Bin; Zheng, Jian

2018-05-01

The evolutions of laser ablation plasma, expanding in strong (∼10 T) transverse external magnetic field, were investigated in experiments and simulations. The experimental results show that the magnetic field pressure causes the plasma decelerate and accumulate at the plasma-field interface, and then form a low-density plasma bubble. The saturation size of the plasma bubble has a scaling law on laser energy and magnetic field intensity. Magnetohydrodynamic simulation results support the observation and find that the scaling law (V max ∝ E p /B 2, where V max is the maximum volume of the plasma bubble, E p is the absorbed laser energy, and B is the magnetic field intensity) is effective in a broad laser energy range from several joules to kilo-joules, since the plasma is always in the state of magnetic field frozen while expanding. About 15% absorbed laser energy converts into magnetic field energy stored in compressed and curved magnetic field lines. The duration that the plasma bubble comes to maximum size has another scaling law t max ∝ E p 1/2/B 2. The plasma expanding dynamics in external magnetic field have a similar character with that in underdense gas, which indicates that the external magnetic field may be a feasible approach to replace the gas filled in hohlraum to suppress the wall plasma expansion and mitigate the stimulated scattering process in indirect drive ignition.

Comptonization in Ultra-Strong Magnetic Fields: Numerical Solution to the Radiative Transfer Problem

Science.gov (United States)

Ceccobello, C.; Farinelli, R.; Titarchuk, L.

2014-01-01

We consider the radiative transfer problem in a plane-parallel slab of thermal electrons in the presence of an ultra-strong magnetic field (B approximately greater than B(sub c) approx. = 4.4 x 10(exp 13) G). Under these conditions, the magnetic field behaves like a birefringent medium for the propagating photons, and the electromagnetic radiation is split into two polarization modes, ordinary and extraordinary, that have different cross-sections. When the optical depth of the slab is large, the ordinary-mode photons are strongly Comptonized and the photon field is dominated by an isotropic component. Aims. The radiative transfer problem in strong magnetic fields presents many mathematical issues and analytical or numerical solutions can be obtained only under some given approximations. We investigate this problem both from the analytical and numerical point of view, provide a test of the previous analytical estimates, and extend these results with numerical techniques. Methods. We consider here the case of low temperature black-body photons propagating in a sub-relativistic temperature plasma, which allows us to deal with a semi-Fokker-Planck approximation of the radiative transfer equation. The problem can then be treated with the variable separation method, and we use a numerical technique to find solutions to the eigenvalue problem in the case of a singular kernel of the space operator. The singularity of the space kernel is the result of the strong angular dependence of the electron cross-section in the presence of a strong magnetic field. Results. We provide the numerical solution obtained for eigenvalues and eigenfunctions of the space operator, and the emerging Comptonization spectrum of the ordinary-mode photons for any eigenvalue of the space equation and for energies significantly lesser than the cyclotron energy, which is on the order of MeV for the intensity of the magnetic field here considered. Conclusions. We derived the specific intensity of the

ON MULTIPLE RECONNECTION X-LINES AND TRIPOLAR PERTURBATIONS OF STRONG GUIDE MAGNETIC FIELDS

International Nuclear Information System (INIS)

Eriksson, S.; Gosling, J. T.; Lapenta, G.; Newman, D. L.; Goldman, M. V.; Phan, T. D.; Lavraud, B.; Khotyaintsev, Yu. V.; Carr, C. M.; Markidis, S.

2015-01-01

We report new multi-spacecraft Cluster observations of tripolar guide magnetic field perturbations at a solar wind reconnection exhaust in the presence of a guide field B M   which is almost four times as strong as the reversing field B L . The novel tripolar field consists of two narrow regions of depressed B M , with an observed 7%–14% ΔB M magnitude relative to the external field, which are found adjacent to a wide region of enhanced B M within the exhaust. A stronger reversing field is associated with each B M depression. A kinetic reconnection simulation for realistic solar wind conditions and the observed strong guide field reveals that tripolar magnetic fields preferentially form across current sheets in the presence of multiple X-lines as magnetic islands approach one another and merge into fewer and larger islands. The simulated ΔB M /ΔX N over the normal width ΔX N between a B M minimum and the edge of the external region agree with the normalized values observed by Cluster. We propose that a tripolar guide field perturbation may be used to identify candidate regions containing multiple X-lines and interacting magnetic islands at individual solar wind current sheets with a strong guide field

Advances in magnetic resonance 12

CERN Document Server

Waugh, John S

2013-01-01

Advances in Magnetic Resonance, Volume 12, presents a variety of contributions to the theory and practice of magnetic resonance. The book contains six chapters and begins with a discussion of diffusion and self-diffusion measurements by nuclear magnetic resonance. This is followed by separate chapters on spin-lattice relaxation time in hydrogen isotope mixtures; the principles of optical detection of nuclear spin alignment and nuclear quadropole resonance; and the spin-1 behavior, including the relaxation of the quasi-invariants of the motion of a system of pairs of dipolar coupled spin-1/2 nu

Infrared behavior of closed superstrings in strong magnetic and gravitational fields

International Nuclear Information System (INIS)

Kiritsis, E.; Kounnas, C.

1995-01-01

A large class of four-dimensional supersymmetric ground states of closed superstrings with a non-zero mass gap are constructed. For such ground states we turn on chromo-magnetic fields as well as curvature. The exact spectrum as function of the chromo-magnetic fields and curvature is derived. We examine the behavior of the spectrum, and find that there is a maximal value for the magnetic field H max similar M planck 2 . At this value all states that couple to the magnetic field become infinitely massive and decouple. We also find tachyonic instabilities for strong background fields of the order O (μM planck ) where μ is the mass gap of the theory. Unlike the field theory case, we find that such ground states become stable again for magnetic fields of the order O (M 2 planck ). The implications of these results are discussed. (orig.)

Transport coefficients of InSb in a strong magnetic field

International Nuclear Information System (INIS)

Nakamura, Hiroaki; Ikeda, Kazuaki; Yamaguchi, Satarou

1998-02-01

Improvement of a superconducting magnet system makes induction of a strong magnetic field easier. This fact gives us a possibility of energy conversion by the Nernst effect. As the first step to study the Nernst element, we measured the conductivity, the Hall coefficient, the thermoelectric power and the Nernst coefficient of the InSb, which is one of candidates of the Nernst elements. From this experiment, it is concluded that the Nernst coefficient is smaller than the theoretical values. On the other hand, the conductivity, the Hall coefficient and the thermoelectric power has the values expected by the theory. (author)

Nonlinear localized modes in dipolar Bose–Einstein condensates in two-dimensional optical lattices

International Nuclear Information System (INIS)

Rojas-Rojas, Santiago; Naether, Uta; Delgado, Aldo; Vicencio, Rodrigo A.

2016-01-01

Highlights: • We study discrete two-dimensional breathers in dipolar Bose–Einstein Condensates. • Important differences in the properties of three fundamental modes are found. • Norm threshold for existence of 2D breathers varies with dipolar interaction. • The Effective Potential Method is implemented for stability analysis. • Uncommon mobility of 2D discrete solitons is observed. - Abstract: We analyze the existence and properties of discrete localized excitations in a Bose–Einstein condensate loaded into a periodic two-dimensional optical lattice, when a dipolar interaction between atoms is present. The dependence of the Number of Atoms (Norm) on the energy of solutions is studied, along with their stability. Two important features of the system are shown, namely, the absence of the Norm threshold required for localized solutions to exist in finite 2D systems, and the existence of regions in the parameter space where two fundamental solutions are simultaneously unstable. This feature enables mobility of localized solutions, which is an uncommon feature in 2D discrete nonlinear systems. With attractive dipolar interaction, a non-trivial behavior of the Norm dependence is obtained, which is well described by an analytical model.

Nonlinear localized modes in dipolar Bose–Einstein condensates in two-dimensional optical lattices

Energy Technology Data Exchange (ETDEWEB)

Rojas-Rojas, Santiago, E-mail: srojas@cefop.cl [Center for Optics and Photonics and MSI-Nucleus on Advanced Optics, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Naether, Uta [Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain); Delgado, Aldo [Center for Optics and Photonics and MSI-Nucleus on Advanced Optics, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Vicencio, Rodrigo A. [Center for Optics and Photonics and MSI-Nucleus on Advanced Optics, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Departamento de Física, Facultad de Ciencias, Universidad de Chile, Santiago (Chile)

2016-09-16

Highlights: • We study discrete two-dimensional breathers in dipolar Bose–Einstein Condensates. • Important differences in the properties of three fundamental modes are found. • Norm threshold for existence of 2D breathers varies with dipolar interaction. • The Effective Potential Method is implemented for stability analysis. • Uncommon mobility of 2D discrete solitons is observed. - Abstract: We analyze the existence and properties of discrete localized excitations in a Bose–Einstein condensate loaded into a periodic two-dimensional optical lattice, when a dipolar interaction between atoms is present. The dependence of the Number of Atoms (Norm) on the energy of solutions is studied, along with their stability. Two important features of the system are shown, namely, the absence of the Norm threshold required for localized solutions to exist in finite 2D systems, and the existence of regions in the parameter space where two fundamental solutions are simultaneously unstable. This feature enables mobility of localized solutions, which is an uncommon feature in 2D discrete nonlinear systems. With attractive dipolar interaction, a non-trivial behavior of the Norm dependence is obtained, which is well described by an analytical model.

Strongly interacting Fermi gases

Directory of Open Access Journals (Sweden)

Bakr W.

2013-08-01

Full Text Available Strongly interacting gases of ultracold fermions have become an amazingly rich test-bed for many-body theories of fermionic matter. Here we present our recent experiments on these systems. Firstly, we discuss high-precision measurements on the thermodynamics of a strongly interacting Fermi gas across the superfluid transition. The onset of superfluidity is directly observed in the compressibility, the chemical potential, the entropy, and the heat capacity. Our measurements provide benchmarks for current many-body theories on strongly interacting fermions. Secondly, we have studied the evolution of fermion pairing from three to two dimensions in these gases, relating to the physics of layered superconductors. In the presence of p-wave interactions, Fermi gases are predicted to display toplogical superfluidity carrying Majorana edge states. Two possible avenues in this direction are discussed, our creation and direct observation of spin-orbit coupling in Fermi gases and the creation of fermionic molecules of 23Na 40K that will feature strong dipolar interactions in their absolute ground state.

Modified coulomb law in a strongly magnetized vacuum.

Science.gov (United States)

Shabad, Anatoly E; Usov, Vladimir V

2007-05-04

We study the electric potential of a charge placed in a strong magnetic field B>B(0) approximately 4.4x10(13) G, as modified by the vacuum polarization. In such a field the electron Larmour radius is much less than its Compton length. At the Larmour distances a scaling law occurs, with the potential determined by a magnetic-field-independent function. The scaling regime implies short-range interaction, expressed by the Yukawa law. The electromagnetic interaction regains its long-range character at distances larger than the Compton length, the potential decreasing across B faster than along. Correction to the nonrelativistic ground-state energy of a hydrogenlike atom is found. In the limit B = infinity, the modified potential becomes the Dirac delta function plus a regular background. With this potential the ground-state energy is finite--the best pronounced effect of the vacuum polarization.

Equation of state of strange quark matter in a strong magnetic field

International Nuclear Information System (INIS)

Isayev, A.A.; Yang, J.

2012-01-01

Thermodynamic properties of strange quark matter (SQM) in strong magnetic fields H up to 10 20 G are considered at zero temperature within the MIT bag model. The effects of the pressure anisotropy, exhibiting in the difference between the pressures along and perpendicular to the field direction, become essential at H>H t h , with the estimate 10 17 t h 18 G. The longitudinal pressure vanishes in the critical field H c , which can be somewhat less or larger than 10 18 G, depending on the total baryon number density and bag pressure. As a result, the longitudinal instability occurs in strongly magnetized SQM. The appearance of such instability sets the upper bound on the magnetic field strength which can be reached in the interior of a neutron star with the quark core. The longitudinal and transverse pressures as well as the anisotropic equation of state of SQM are determined under the conditions relevant for the cores of magnetars

Electron gas interacting in a metal, submitted to a strong magnetic field

International Nuclear Information System (INIS)

Alcaraz, Francisco Castilho

1977-01-01

Using the propagator's technique in the grand ensemble developed by Montroll and Ward we investigate the magnetic properties of an interacting electron gas in a strong magnetic field. The free propagator properly constructed shows that the spin paramagnetism does not have a term with strong temperature dependence, contrary to the result of Isihara. Considering the electron density to be constant, the dHVA oscillations in the magnetic susceptibility and sound velocity, considering the effects of first exchange interactions, show only one phase in agreement with experimental result, while Ichimura and Isihara obtained two phases differing by π/2. The effects of first order exchange interactions in the dHVA oscillations of the magnetic susceptibility and sound velocity give rise to an exponential factor in the amplitudes of oscillator (Dingle factor), being the Dingle temperature linearly dependent of the Fermi velocity. The calculations of the ring diagram contribution to the grand partition function, show that the approximation used by Isihara for this calculations is not good and the dHVA oscillations of the contributions from the ring diagrams for the grand partition function have a phase differing by π/2 from that obtained by Isihara. (author)

Sedimentation equilibria of ferrofluids: II. Experimental osmotic equations of state of magnetite colloids

International Nuclear Information System (INIS)

Luigjes, Bob; Thies-Weesie, Dominique M E; Erné, Ben H; Philipse, Albert P

2012-01-01

The first experimental osmotic equation of state is reported for well-defined magnetic colloids that interact via a dipolar hard-sphere potential. The osmotic pressures are determined from the sedimentation equilibrium concentration profiles in ultrathin capillaries using a low-velocity analytical centrifuge, which is the subject of the accompanying paper I. The pressures of the magnetic colloids, measured accurately to values as low as a few pascals, obey Van ’t Hoff’s law at low concentrations, whereas at increasing colloid densities non-ideality appears in the form of a negative second virial coefficient. This virial coefficient corresponds to a dipolar coupling constant that agrees with the coupling constant obtained via independent magnetization measurements. The coupling constant manifests an attractive potential of mean force that is significant but yet not quite strong enough to induce dipolar chain formation. Our results disprove van der Waals-like phase behavior of dipolar particles for reasons that are explained. (paper)

STRONG SOLAR WIND DYNAMIC PRESSURE PULSES: INTERPLANETARY SOURCES AND THEIR IMPACTS ON GEOSYNCHRONOUS MAGNETIC FIELDS

International Nuclear Information System (INIS)

Zuo, Pingbing; Feng, Xueshang; Wang, Yi; Xie, Yanqiong; Xu, Xiaojun

2015-01-01

In this investigation, we first present a statistical result of the interplanetary sources of very strong solar wind dynamic pressure pulses (DPPs) detected by WIND during solar cycle 23. It is found that the vast majority of strong DPPs reside within solar wind disturbances. Although the variabilities of geosynchronous magnetic fields (GMFs) due to the impact of positive DPPs have been well established, there appears to be no systematic investigations on the response of GMFs to negative DPPs. Here, we study both the decompression effects of very strong negative DPPs and the compression from strong positive DPPs on GMFs at different magnetic local time sectors. In response to the decompression of strong negative DPPs, GMFs on the dayside near dawn and near dusk on the nightside, are generally depressed. But near the midnight region, the responses of GMF are very diverse, being either positive or negative. For part of the events when GOES is located at the midnight sector, the GMF is found to abnormally increase as the result of magnetospheric decompression caused by negative DPPs. It is known that under certain conditions magnetic depression of nightside GMFs can be caused by the impact of positive DPPs. Here, we find that a stronger pressure enhancement may have a higher probability of producing the exceptional depression of GMF at the midnight region. Statistically, both the decompression effect of strong negative DPPs and the compression effect of strong positive DPPs depend on the magnetic local time, which are stronger at the noon sector

STRONG SOLAR WIND DYNAMIC PRESSURE PULSES: INTERPLANETARY SOURCES AND THEIR IMPACTS ON GEOSYNCHRONOUS MAGNETIC FIELDS

Energy Technology Data Exchange (ETDEWEB)

Zuo, Pingbing; Feng, Xueshang; Wang, Yi [SIGMA Weather Group, State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing (China); Xie, Yanqiong [College of Meteorology and Oceanography, PLA University of Science and Technology, Nanjing (China); Xu, Xiaojun, E-mail: pbzuo@spaceweather.ac.cn, E-mail: fengx@spaceweather.ac.cn [Space Science Institute, Macau University of Science and Technology, Macao (China)

2015-10-20

In this investigation, we first present a statistical result of the interplanetary sources of very strong solar wind dynamic pressure pulses (DPPs) detected by WIND during solar cycle 23. It is found that the vast majority of strong DPPs reside within solar wind disturbances. Although the variabilities of geosynchronous magnetic fields (GMFs) due to the impact of positive DPPs have been well established, there appears to be no systematic investigations on the response of GMFs to negative DPPs. Here, we study both the decompression effects of very strong negative DPPs and the compression from strong positive DPPs on GMFs at different magnetic local time sectors. In response to the decompression of strong negative DPPs, GMFs on the dayside near dawn and near dusk on the nightside, are generally depressed. But near the midnight region, the responses of GMF are very diverse, being either positive or negative. For part of the events when GOES is located at the midnight sector, the GMF is found to abnormally increase as the result of magnetospheric decompression caused by negative DPPs. It is known that under certain conditions magnetic depression of nightside GMFs can be caused by the impact of positive DPPs. Here, we find that a stronger pressure enhancement may have a higher probability of producing the exceptional depression of GMF at the midnight region. Statistically, both the decompression effect of strong negative DPPs and the compression effect of strong positive DPPs depend on the magnetic local time, which are stronger at the noon sector.

Spin interactions in Graphene-Single Molecule Magnets Hybrids

Science.gov (United States)

Cervetti, Christian; Rettori, Angelo; Pini, Maria Gloria; Cornia, Andrea; Repollés, Aña; Luis, Fernando; Rauschenbach, Stephan; Dressel, Martin; Kern, Klaus; Burghard, Marko; Bogani, Lapo

2014-03-01

Graphene is a potential component of novel spintronics devices owing to its long spin diffusion length. Besides its use as spin-transport channel, graphene can be employed for the detection and manipulation of molecular spins. This requires an appropriate coupling between the sheets and the single molecular magnets (SMM). Here, we present a comprehensive characterization of graphene-Fe4 SMM hybrids. The Fe4 clusters are anchored non-covalently to the graphene following a diffusion-limited assembly and can reorganize into random networks when subjected to slightly elevated temperature. Molecules anchored on graphene sheets show unaltered static magnetic properties, whilst the quantum dynamics is profoundly modulated. Interaction with Dirac fermions becomes the dominant spin-relaxation channel, with observable effects produced by graphene phonons and reduced dipolar interactions. Coupling to graphene drives the spins over Villain's threshold, allowing the first observation of strongly-perturbative tunneling processes. Preliminary spin-transport experiments at low-temperature are further presented.

New Developments in Spin Labels for Pulsed Dipolar EPR

Directory of Open Access Journals (Sweden)

Alistair J. Fielding

2014-10-01

Full Text Available Spin labelling is a chemical technique that enables the integration of a molecule containing an unpaired electron into another framework for study. Given the need to understand the structure, dynamics, and conformational changes of biomacromolecules, spin labelling provides a relatively non-intrusive technique and has certain advantages over X-ray crystallography; which requires high quality crystals. The technique relies on the design of binding probes that target a functional group, for example, the thiol group of a cysteine residue within a protein. The unpaired electron is typically supplied through a nitroxide radical and sterically shielded to preserve stability. Pulsed electron paramagnetic resonance (EPR techniques allow small magnetic couplings to be measured (e.g., <50 MHz providing information on single label probes or the dipolar coupling between multiple labels. In particular, distances between spin labels pairs can be derived which has led to many protein/enzymes and nucleotides being studied. Here, we summarise recent examples of spin labels used for pulse EPR that serve to illustrate the contribution of chemistry to advancing discoveries in this field.

The structure of ions and zwitterionic lipids regulates the charge of dipolar membranes.

Science.gov (United States)

Szekely, Or; Steiner, Ariel; Szekely, Pablo; Amit, Einav; Asor, Roi; Tamburu, Carmen; Raviv, Uri

2011-06-21

In pure water, zwitterionic lipids form lamellar phases with an equilibrium water gap on the order of 2 to 3 nm as a result of the dominating van der Waals attraction between dipolar bilayers. Monovalent ions can swell those neutral lamellae by a small amount. Divalent ions can adsorb onto dipolar membranes and charge them. Using solution X-ray scattering, we studied how the structure of ions and zwitterionic lipids regulates the charge of dipolar membranes. We found that unlike monovalent ions that weakly interact with all of the examined dipolar membranes, divalent and trivalent ions adsorb onto membranes containing lipids with saturated tails, with an association constant on the order of ∼10 M(-1). One double bond in the lipid tail is sufficient to prevent divalent ion adsorption. We suggest that this behavior is due to the relatively loose packing of lipids with unsaturated tails that increases the area per lipid headgroup, enabling their free rotation. Divalent ion adsorption links two lipids and limits their free rotation. The ion-dipole interaction gained by the adsorption of the ions onto unsaturated membranes is insufficient to compensate for the loss of headgroup free-rotational entropy. The ion-dipole interaction is stronger for cations with a higher valence. Nevertheless, polyamines behave as monovalent ions near dipolar interfaces in the sense that they interact weakly with the membrane surface, whereas in the bulk their behavior is similar to that of multivalent cations. Advanced data analysis and comparison with theory provide insight into the structure and interactions between ion-induced regulated charged interfaces. This study models biologically relevant interactions between cell membranes and various ions and the manner in which the lipid structure governs those interactions. The ability to monitor these interactions creates a tool for probing systems that are more complex and forms the basis for controlling the interactions between dipolar

Relativistic stability of interacting Fermi gas in a strong magnetic field

International Nuclear Information System (INIS)

Wang Lilin; Tian Jincheng; Men Fudian; Zhang Yipeng

2013-01-01

By means of the single particle energy spectrum of weak interaction between fermions and Poisson formula, the thermodynamic potential function of relativistic Fermi gas in a strong magnetic field is derived. Based on this, we obtained the criterion of stability for the system. The results show that the mechanics stability of a Fermi gas with weak interacting is influenced by the interacting. While the magnetic field is able to regulate the influence and the relativistic effect has almost no effect on it. (authors)

Functionalization of Graphene via 1,3-Dipolar Cycloaddition

NARCIS (Netherlands)

Quintana, Mildred; Spyrou, Konstantinos; Grzelczak, Marek; Browne, Wesley R.; Rudolf, Petra; Prato, Maurizio

Few-layer graphenes (FLG) produced by dispersion and exfoliation of graphite in N-methylpyrrolidone were successfully functionalized using the 1,3-dipolar cycloaddition of azomethine ylides. The amino functional groups attached to graphene sheets were quantified by the Kaiser test. These amino

Dipolar fluid-wall systems. Beyond the image potential

International Nuclear Information System (INIS)

Boudh-hir, M.E.

1989-02-01

The case of dipolar fluid in front of an ideal wall is examined. The surface-fluid system is introduced as a limit case of a binary mixture Using the diagrammatic development, the expansion of the one-particle distribution function is given. 16 refs

Resonances of the helium atom in a strong magnetic field

DEFF Research Database (Denmark)

Lühr, Armin Christian; Al-Hujaj, Omar-Alexander; Schmelcher, Peter

2007-01-01

We present an investigation of the resonances of a doubly excited helium atom in a strong magnetic field covering the regime B=0–100  a.u. A full-interaction approach which is based on an anisotropic Gaussian basis set of one-particle functions being nonlinearly optimized for each field strength...

Monte Carlo simulation of magnetic multi-core nanoparticles

International Nuclear Information System (INIS)

Schaller, Vincent; Wahnstroem, Goeran; Sanz-Velasco, Anke; Enoksson, Peter; Johansson, Christer

2009-01-01

In this paper, a Monte Carlo simulation is carried out to evaluate the equilibrium magnetization of magnetic multi-core nanoparticles in a liquid and subjected to a static magnetic field. The particles contain a magnetic multi-core consisting of a cluster of magnetic single-domains of magnetite. We show that the magnetization of multi-core nanoparticles cannot be fully described by a Langevin model. Inter-domain dipolar interactions and domain magnetic anisotropy contribute to decrease the magnetization of the particles, whereas the single-domain size distribution yields an increase in magnetization. Also, we show that the interactions affect the effective magnetic moment of the multi-core nanoparticles.

The Mechanics of a Chain or Ring of Spherical Magnets

KAUST Repository

Hall, Cameron L.; Vella, Dominic; Goriely, Alain

2013-01-01

Strong magnets, such as neodymium-iron-boron magnets, are increasingly being manufactured as spheres. Because of their dipolar characters, these spheres can easily be arranged into long chains that exhibit mechanical properties reminiscent of elastic strings or rods. While simple formulations exist for the energy of a deformed elastic rod, it is not clear whether or not they are also appropriate for a chain of spherical magnets. In this paper, we use discrete-to-continuum asymptotic analysis to derive a continuum model for the energy of a deformed chain of magnets based on the magnetostatic interactions between individual spheres. We find that the mechanical properties of a chain of magnets differ significantly from those of an elastic rod: while both magnetic chains and elastic rods support bending by change of local curvature, nonlocal interaction terms also appear in the energy formulation for a magnetic chain. This continuum model for the energy of a chain of magnets is used to analyze small deformations of a circular ring of magnets and hence obtain theoretical predictions for the vibrational modes of a circular ring of magnets. Surprisingly, despite the contribution of nonlocal energy terms, we find that the vibrations of a circular ring of magnets are governed by the same equation that governs the vibrations of a circular elastic ring. Copyright © by SIAM.

Nonlinear localized modes in dipolar Bose-Einstein condensates in optical lattices

International Nuclear Information System (INIS)

Rojas-Rojas, S.; Vicencio, R. A.; Molina, M. I.; Abdullaev, F. Kh.

2011-01-01

Modulational instability and discrete matter wave solitons in dipolar BECs, loaded into a deep optical lattice, are investigated analytically and numerically. The process of modulational instability of nonlinear plane matter waves in a dipolar nonlinear lattice is studied and the regions of instability are established. The existence and stability of bulk discrete solitons are analyzed analytically and confirmed by numerical simulations. In marked contrast with the usual discrete nonlinear Schroedinger behavior (no dipolar interactions), we found a region where the two fundamental modes are simultaneously unstable, allowing enhanced mobility across the lattice for large norm values. To study the existence and properties of surface discrete solitons, an analysis of the dimer configuration is performed. The properties of symmetric and antisymmetric modes including stability diagrams and bifurcations are investigated in closed form. For the case of a bulk medium, properties of fundamental on-site and intersite localized modes are analyzed. On-site and intersite surface localized modes are studied, and we find that they do not exist when nonlocal interactions predominate with respect to local ones.

Self-organized patterns of macroscopic quantum tunneling in molecular magnets.

Science.gov (United States)

Garanin, D A; Chudnovsky, E M

2009-03-06

We study low temperature resonant spin tunneling in molecular magnets induced by a field sweep with account of dipole-dipole interactions. Numerical simulations uncovered formation of self-organized patterns of the magnetization and of the ensuing dipolar field that provide resonant conditions inside a finite volume of the crystal. This effect is robust with respect to disorder and should be relevant to the dynamics of the magnetization steps observed in molecular magnets.

Magnetic properties of metallic impurities with strongly correlated electrons

Czech Academy of Sciences Publication Activity Database

Janiš, Václav; Ringel, Matouš

2009-01-01

Roč. 115, č. 1 (2009), s. 30-35 ISSN 0587-4246 R&D Projects: GA ČR GA202/07/0644 Institutional research plan: CEZ:AV0Z10100520 Keywords : And erson impurity * strong electron correlations * spin-polarized solution * three-channel parquet equations * magnetic field Subject RIV: BE - Theoretical Physics Impact factor: 0.433, year: 2009 http://przyrbwn.icm.edu.pl/APP/ABSTR/115/a115-1-5.html

ON MULTIPLE RECONNECTION X-LINES AND TRIPOLAR PERTURBATIONS OF STRONG GUIDE MAGNETIC FIELDS

Energy Technology Data Exchange (ETDEWEB)

Eriksson, S.; Gosling, J. T. [Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO (United States); Lapenta, G. [Center for Mathematical Plasma Astrophysics, Department of Mathematics, University of Leuven, Leuven (Belgium); Newman, D. L.; Goldman, M. V. [Center for Integrated Plasma Studies, University of Colorado, Boulder, CO (United States); Phan, T. D. [Space Sciences Laboratory, University of California, Berkeley, CA (United States); Lavraud, B. [Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, Toulouse (France); Khotyaintsev, Yu. V. [Swedish Institute of Space Physics, Uppsala (Sweden); Carr, C. M. [The Blackett Laboratory, Imperial College London, London (United Kingdom); Markidis, S., E-mail: eriksson@lasp.colorado.edu [High Performance Computing and Visualization Department, KTH, Stockholm (Sweden)

2015-05-20

We report new multi-spacecraft Cluster observations of tripolar guide magnetic field perturbations at a solar wind reconnection exhaust in the presence of a guide field B{sub M} {sub  }which is almost four times as strong as the reversing field B{sub L}. The novel tripolar field consists of two narrow regions of depressed B{sub M}, with an observed 7%–14% ΔB{sub M} magnitude relative to the external field, which are found adjacent to a wide region of enhanced B{sub M} within the exhaust. A stronger reversing field is associated with each B{sub M} depression. A kinetic reconnection simulation for realistic solar wind conditions and the observed strong guide field reveals that tripolar magnetic fields preferentially form across current sheets in the presence of multiple X-lines as magnetic islands approach one another and merge into fewer and larger islands. The simulated ΔB{sub M}/ΔX{sub N} over the normal width ΔX{sub N} between a B{sub M} minimum and the edge of the external region agree with the normalized values observed by Cluster. We propose that a tripolar guide field perturbation may be used to identify candidate regions containing multiple X-lines and interacting magnetic islands at individual solar wind current sheets with a strong guide field.

The exotic molecular ion H43+ in a strong magnetic field

International Nuclear Information System (INIS)

Olivares P, H.

2006-01-01

Using the variational method, a detailed study of the lowest m = 0, -1 electronic states of the exotic molecular ion H3+ 4 in a strong magnetic field, in the linear symmetric configuration parallel to the direction of the magnetic field is carried out. A extended study of the 1σg ground state (J.C. Lopez and A.Turbiner, Phys. Rev A 62, 022510, 2000) was performed obtaining that the potential energy curve displays a sufficiently deep minimum for finite internuclear distances, indicating the possible existence of the molecular ion H 4 3+ , for magnetic fields of strength B > ∼ 3 x 10 13 G. It is demonstrated that the excited state 1π u , can exist for a magnetic field B = 4.414 x 10 13 G corresponding to the limit of applicability of the non-relativistic theory. (Author)

Structure-independent cross-validation between residual dipolar couplings originating from internal and external orienting media

International Nuclear Information System (INIS)

Barbieri, Renato; Bertini, Ivano; Lee, Yong-Min; Luchinat, Claudio; Velders, Aldrik H.

2002-01-01

Lanthanide-substituted calcium binding proteins are known to partially orient in high magnetic fields. Orientation provides residual dipolar couplings (rdc's). Two of these systems, Tm 3+ - and Dy 3+ -substituted calbindin D 9k , dissolved in an external orienting medium (nonionic liquid crystalline phase) provide rdc values which are the sum of those induced by the lanthanides and by the liquid crystalline phase on the native calcium binding protein. This structure-independent check shows the innocence of the orienting medium with respect to the structure of the protein in solution. Furthermore, the simultaneous use of lanthanide substitution and external orienting media provides a further effective tool to control and tune the orientation tensor

Statistical mechanics of molecular fluids. The RHNC theory applied to hard dipolar spheres

International Nuclear Information System (INIS)

Lombardero, M.; Lado, F.; Abascal, J.L.F.; Lago, S.; Enciso, E.

1988-01-01

The RHNC (reference hipernetted chain) equation, together with an optimization criterion which extremalizes the Helmholtz free energy, is used to obtain structural, thermodynamic, and dielectric properties of a system made up of hard dipolar spheres. The comparison with simulation results is made in the same boundary conditions and then the properties of an infinite system are evaluated for a variaty of states at different densities and dipolar moments. (Author)

Diamagnetic (cyclotron) resonance in semiconductors using strong magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Sosniak, J

1962-07-01

Diamagnetic (cyclotron) resonance experiments have been carried out in the semiconductors indium-antimonide (InSb), the indium-arsenide (InAs). Pulsed magnetic fields up to 300,000 gauss and monochromatic infrared radiation of 9 to 13.5 microns wavelength were used to measure the effective mass of the conduction electrons in those materials. The samples were n-type single crystals, with a room temperature electron concentration of 1.9 x 10{sup 16} and 6 x 10{sup 16} per cm{sup 3} in InSb and InAs respectively. Both the InSb and InAs samples showed a strong dependence of the effective mass on the magnetic field. The results show that the conduction bands in those solids are highly non-parabolic. Measurements were also made of the resonance absorption coefficients, which were found to be considerably smaller than the values obtained from simple theory. The effect is explained by assuming that the magnetic field reduces the intrinsic electron density, and that the absorption coefficient depends on the shape of the conduction band. It is postulated as a consequence that the relaxation time of diamagnetic energy levels at high magnetic fields does not differ appreciably from the relaxation time used in the description of conduction processes. (author)

In-medium covariant propagator of baryons under a strong magnetic field: Effect of the intrinsic magnetic moments

Energy Technology Data Exchange (ETDEWEB)

Aguirre, R.M.; Paoli, A.L. de [Universidad Nacional de La Plata, and IFLP, Departamento de Fisica, Facultad de Ciencias Exactas, La Plata (Argentina)

2016-11-15

We obtain the covariant propagator at finite temperature for interacting baryons immersed in a strong magnetic field. The effect of the intrinsic magnetic moments on the Green function are fully taken into account. We make an expansion in terms of eigenfunctions of a Dirac field, which leads us to a compact form of its propagator. We present some simple applications of these propagators, where the statistical averages of nuclear currents and energy density are evaluated. (orig.)

Metal-insulator crossover in superconducting cuprates in strong magnetic fields

International Nuclear Information System (INIS)

Marchetti, P.A.; Su Zhaobin; Yu Lu

2001-02-01

The metal-insulator crossover of the in-plane resistivity upon temperature decrease, recently observed in several classes of cuprate superconductors, when a strong magnetic field suppresses the superconductivity, is explained using the U(1)xSU(2) Chern-Simons gauge field theory. The origin of this crossover is the same as that for a similar phenomenon observed in heavily underdoped cuprates without magnetic field. It is due to the interplay between the diffusive motion of the charge carriers and the 'peculiar' localization effect due to short-range antiferromagnetic order. We also calculate the in-plane transverse magnetoresistance which is in a fairly good agreement with available experimental data. (author)

Viscosity of two-dimensional strongly coupled dusty plasma modified by a perpendicular magnetic field

Science.gov (United States)

Feng, Yan; Lin, Wei; Murillo, M. S.

2017-11-01

Transport properties of two-dimensional (2D) strongly coupled dusty plasmas have been investigated in detail, but never for viscosity with a strong perpendicular magnetic field; here, we examine this scenario using Langevin dynamics simulations of 2D liquids with a binary Yukawa interparticle interaction. The shear viscosity η of 2D liquid dusty plasma is estimated from the simulation data using the Green-Kubo relation, which is the integration of the shear stress autocorrelation function. It is found that, when a perpendicular magnetic field is applied, the shear viscosity of 2D liquid dusty plasma is modified substantially. When the magnetic field is increased, its viscosity increases at low temperatures, while at high temperatures its viscosity diminishes. It is determined that these different variational trends of η arise from the different behaviors of the kinetic and potential parts of the shear stress under external magnetic fields.

The structure of the interface in the solvent-mediated interaction of dipolar surfaces

International Nuclear Information System (INIS)

Dzhavakhidze, P.G.; Kornyshev, A.A.; Levadny, V.G.

1988-01-01

Interaction of two dipolar surfaces separated by a polar medium is considered within the framework of nonlocal electrostatics. The dipolar-surface layers are modelled as regular lattices with fixed orientation of dipoles which are immersed into the solvent; solvent response is characterized by nonlocal dielectric function. The model is elaborated in order to reveal the role of the dypolar-layer discreteness in the electric field produced by one surface and the interaction between two surfaces (which gives rise to the so-called ''hydration'' or ''structural'' force acting between mineral surfaces and phospholipid bilayers). The discreteness effects are present only for commensurate lattices. Their special mutual arrangement then may lead to considerable reduction of structural forces, viz. the usual repulsion regime may change at short distances to attraction. Conditions are considered when repulsion is entirely replaced by attraction, i.e. the ''hydration barrier'' disappears. In appended note it is discussed the role of solvation of surface dipolar groups. It is proposed an explanation of why two modes of decay (one with oscillative fine structure) may be present in the dependence of the force upon distance, if the surface dipolar groups are immersed deep enough in the solvent, and how the long-range oscillative mode disappears when the surface is but weakly solvated

Comparison of the Supercooled Spin Liquid States in the Pyrochlore Magnets Dy2Ti2O7 and Ho2Ti2O7

Science.gov (United States)

Eyal, Anna; Eyvazov, Azar B.; Dusad, Ritika; Munsie, Timothy J. S.; Luke, Graeme M.; Davis, J. C. Séamus

Despite a well-ordered crystal structure and strong magnetic interactions between the Dy or Ho ions, no long-range magnetic order has been detected in the pyrochlore titanates Ho2Ti2O7 and Dy2Ti2O7. The low temperature state in these materials is governed by spin-ice rules. These constrain the Ising like spins in the materials, yet does not result in a global broken symmetry state. To explore the actual magnetic phases, we simultaneously measure the time- and frequency-dependent magnetization dynamics of Dy2Ti2O7 and Ho2Ti2O7 using toroidal, boundary-free magnetization transport techniques. We demonstrate a distinctive behavior of the magnetic susceptibility of both compounds, that is indistinguishable in form from the permittivity of supercooled dipolar liquids. Moreover, we show that the microscopic magnetic relaxation times for both materials increase along a super-Arrhenius trajectory also characteristic of supercooled glass-forming liquids. Both materials therefore exhibit characteristics of a supercooled spin liquid. Strongly-correlated dynamics of loops of spins is suggested as a possible mechanism which could account for these findings. Potential connections to many-body spin localization will also be discussed.

1,3-Dipolar Cycloadditions of Diazo Compounds in the Presence of Azides.

Science.gov (United States)

Aronoff, Matthew R; Gold, Brian; Raines, Ronald T

2016-04-01

The diazo group has untapped utility in chemical biology. The tolerance of stabilized diazo groups to cellular metabolism is comparable to that of azido groups. However, chemoselectivity has been elusive, as both groups undergo 1,3-dipolar cycloadditions with strained alkynes. Removing strain and tuning dipolarophile electronics yields diazo group selective 1,3-dipolar cycloadditions that can be performed in the presence of an azido group. For example, diazoacetamide but not its azido congener react with dehydroalanine residues, as in the natural product nisin.

Magnetic dichroism and spin structure of antiferromagnetic NiO(001) films

NARCIS (Netherlands)

Altieri, S; Finazzi, M; Hsieh, HH; Lin, HJ; Chen, CT; Hibma, T; Valeri, S; Sawatzky, GA

2003-01-01

We find that Ni L-2 edge x-ray magnetic linear dichroism is fully reversed for NiO(001) films on materials with reversed lattice mismatch. We relate this phenomenon to a preferential stabilization of magnetic S domains with main spin component either in or out of the plane, via dipolar interactions.

Thermal conductivity of magnetic insulators with strong spin-orbit coupling

Science.gov (United States)

Stamokostas, Georgios; Lapas, Panteleimon; Fiete, Gregory A.

We study the influence of spin-orbit coupling on the thermal conductivity of various types of magnetic insulators. In the absence of spin-orbit coupling and orbital-degeneracy, the strong-coupling limit of Hubbard interactions at half filling can often be adequately described in terms of a pure spin Hamiltonian of the Heisenberg form. However, in the presence of spin-orbit coupling the resulting exchange interaction can become highly anisotropic. The effect of the atomic spin-orbit coupling, taken into account through the effect of magnon-phonon interactions and the magnetic order and excitations, on the lattice thermal conductivity of various insulating magnetic systems is studied. We focus on the regime of low temperatures where the dominant source of scattering is two-magnon scattering to one-phonon processes. The thermal current is calculated within the Boltzmann transport theory. We are grateful for financial support from NSF Grant DMR-0955778.

Superconductivity and magnetic fluctuations developing in the vicinity of strong first-order magnetic transition in CrAs

International Nuclear Information System (INIS)

Kotegawa, H; Matsushima, K; Nakahara, S; Tou, H; Kaneyoshi, J; Nishiwaki, T; Matsuoka, E; Sugawara, H; Harima, H

2017-01-01

We report single crystal preparation, resistivity, and nuclear quadrupole resonance (NQR) measurements for new pressure-induced superconductor CrAs. In the first part, we present the difference between crystals made by different thermal sequences and methods, and show the sample dependence of superconductivity in CrAs. In the latter part, we show NQR data focusing the microscopic electronic state at the phase boundary between the helimagnetic and the paramagnetic phases. They suggest strongly that a quantum critical point is absent on the pressure-temperature phase diagram of CrAs, because of the strong first-order character of the magnetic transition; however, the spin fluctuations are observed in the paramagnetic phase. The close relationship between the spin fluctuations and superconductivity can be seen even in the vicinity of the first-order magnetic transition in CrAs. (paper)

Exchange bias properties of 140 nm-sized dipolarly interacting circular dots with ultrafine IrMn and NiFe layers

Energy Technology Data Exchange (ETDEWEB)

Spizzo, F., E-mail: spizzo@fe.infn.it [Dipartimento di Fisica e Scienze della Terra and CNISM, Università di Ferrara, I-44122 Ferrara (Italy); Tamisari, M. [Dipartimento di Fisica e Scienze della Terra and CNISM, Università di Ferrara, I-44122 Ferrara (Italy); Dipartimento di Fisica e Geologia and CNISM, Università di Perugia, I-06123 Perugia (Italy); Chinni, F.; Bonfiglioli, E. [Dipartimento di Fisica e Scienze della Terra and CNISM, Università di Ferrara, I-44122 Ferrara (Italy); Gerardino, A. [Istituto di Fotonica e Nanotecnologie, CNR, I-00156 Roma (Italy); Barucca, G. [Dipartimento SIMAU, Università Politecnica delle Marche, I-60131 Ancona (Italy); Bisero, D.; Fin, S.; Del Bianco, L. [Dipartimento di Fisica e Scienze della Terra and CNISM, Università di Ferrara, I-44122 Ferrara (Italy)

2016-02-15

We studied the exchange bias effect in an array of IrMn(3 nm)/NiFe(3 nm) circular dots (size ~140 nm and center-to-center distance ~200 nm, as revealed by microscopy analyses), prepared on a large area (3×3 mm{sup 2}) by electron beam lithography and lift-off, using dc sputtering deposition. Hysteresis loops were measured by SQUID magnetometer at increasing values of temperature T (in the 5–300 K range) after cooling from 300 K down to 5 K in zero field (ZFC mode) and in a saturating magnetic field (FC mode). The exchange bias effect disappears above T~200 K and, at each temperature, the exchange field H{sub EX} measured in ZFC is substantially lower than the FC one. Micromagnetic calculations indicate that, at room temperature, each dot is in high-remanence ground state, but magnetic dipolar interactions establish a low-remanence configuration of the array as a whole. Hence, at low temperature, following the ZFC procedure, the exchange anisotropy in the dot array is averaged out, tending to zero. However, even the FC values of H{sub EX} and of the coercivity H{sub C} are definitely smaller compared to those measured in a reference continuous film with the same stack configuration (at T=5 K, H{sub EX}~90 Oe and H{sub C}~180 Oe in the dots and H{sub EX}~1270 Oe and H{sub C}~860 Oe in the film). Our explanation is based on the proven glassy magnetic nature of the ultrathin IrMn layer, implying the existence of magnetic correlations among the spins, culminating in a collective freezing below T~100 K. We propose, also by the light of micromagnetic simulations, that the small dot size imposes a spatial constraint on the magnetic correlation length among the IrMn spins so that, even at the lowest temperature, their thermal stability, especially at the dot border, is compromised. - Highlights: • Exchange bias in 140 nm-sized IrMn(3 nm)/NiFe(3 nm) dots much weaker than in a film. • Glassy magnetic nature of the IrMn phase and collective spin freezing at T<100 K �

Exchange bias properties of 140 nm-sized dipolarly interacting circular dots with ultrafine IrMn and NiFe layers

International Nuclear Information System (INIS)

Spizzo, F.; Tamisari, M.; Chinni, F.; Bonfiglioli, E.; Gerardino, A.; Barucca, G.; Bisero, D.; Fin, S.; Del Bianco, L.

2016-01-01

We studied the exchange bias effect in an array of IrMn(3 nm)/NiFe(3 nm) circular dots (size ~140 nm and center-to-center distance ~200 nm, as revealed by microscopy analyses), prepared on a large area (3×3 mm"2) by electron beam lithography and lift-off, using dc sputtering deposition. Hysteresis loops were measured by SQUID magnetometer at increasing values of temperature T (in the 5–300 K range) after cooling from 300 K down to 5 K in zero field (ZFC mode) and in a saturating magnetic field (FC mode). The exchange bias effect disappears above T~200 K and, at each temperature, the exchange field H_E_X measured in ZFC is substantially lower than the FC one. Micromagnetic calculations indicate that, at room temperature, each dot is in high-remanence ground state, but magnetic dipolar interactions establish a low-remanence configuration of the array as a whole. Hence, at low temperature, following the ZFC procedure, the exchange anisotropy in the dot array is averaged out, tending to zero. However, even the FC values of H_E_X and of the coercivity H_C are definitely smaller compared to those measured in a reference continuous film with the same stack configuration (at T=5 K, H_E_X~90 Oe and H_C~180 Oe in the dots and H_E_X~1270 Oe and H_C~860 Oe in the film). Our explanation is based on the proven glassy magnetic nature of the ultrathin IrMn layer, implying the existence of magnetic correlations among the spins, culminating in a collective freezing below T~100 K. We propose, also by the light of micromagnetic simulations, that the small dot size imposes a spatial constraint on the magnetic correlation length among the IrMn spins so that, even at the lowest temperature, their thermal stability, especially at the dot border, is compromised. - Highlights: • Exchange bias in 140 nm-sized IrMn(3 nm)/NiFe(3 nm) dots much weaker than in a film. • Glassy magnetic nature of the IrMn phase and collective spin freezing at T<100 K • Confinement of IrMn magnetic

Magnetic anisotropy in the incommensurate ScFe{sub 4}Al{sub 8} system

Energy Technology Data Exchange (ETDEWEB)

Rećko, K., E-mail: k.recko@uwb.edu.pl [Faculty of Physics, University of Białystok, K. Ciołkowskiego 1L, 15-245 Białystok (Poland); Dobrzyński, L. [National Centre for Nuclear Research, A. Soltan 7, 05-400 Otwock-Świerk (Poland); Waliszewski, J.; Szymański, K. [Faculty of Physics, University of Białystok, K. Ciołkowskiego 1L, 15-245 Białystok (Poland)

2015-08-15

Neutron scattering and magnetization data are used for estimation of the spin ordering in ScFe{sub 4}Al{sub 8}. Results of experimental measurements are compared with the ground state configurations obtained by simulated annealing algorithms. The origins of the magnetocrystalline anisotropy of the scandium intermetallic alloy and the conditions of the coexistence of two different magnetic modulations as a function of the exchange integrals are discussed. The influence of the dipolar interactions for the noncollinearity and incommensurability in ScFe{sub 4}Al{sub 8} was determined. - Highlights: • We found dipolar and DM interactions as the anisotropy origins of 3d–3d–3p alloy. • We covered the explanation of incommensurability and noncollinearity of ScFe{sub 4}Al{sub 8}. • We discussed the magnetism resulting from competitiveness of exchange effects.

Spontaneous Magnetization in the Dipolar Ising Ferromagnet LiTbF4

DEFF Research Database (Denmark)

Als-Nielsen, Jens Aage; Holmes, L. M.; Krebs Larsen, F.

1975-01-01

The spontaneous magnetization μ in Bohr magnetons below TC=2.874 K in LiTbF4 has been measured by magnetic Bragg scattering of neutrons. The data were normalized by comparing the magnetic Bragg scattering to the nuclear Bragg scattering at T>TC. The nuclear structure factors as well...

The Plasma Sheet as Natural Symmetry Plane for Dipolarization Fronts in the Earth's Magnetotail

Science.gov (United States)

Frühauff, D.; Glassmeier, K.-H.

2017-11-01

In this work, observations of multispacecraft mission Time History of Events and Macroscale Interactions during Substorms are used for statistical investigation of dipolarization fronts in the near-Earth plasma sheet of the magnetotail. Using very stringent criteria, 460 events are detected in almost 10 years of mission data. Minimum variance analysis is used to determine the normal directions of the phase fronts, providing evidence for the existence of a natural symmetry of these phenomena, given by the neutral sheet of the magnetotail. This finding enables the definition of a local coordinate system based on the Tsyganenko model, reflecting the intrinsic orientation of the neutral sheet and, therefore, the dipolarization fronts. In this way, the comparison of events with very different background conditions is improved. Through this study, the statistical results of Liu, Angelopoulos, Runov, et al. (2013) are both confirmed and extended. In a case study, the knowledge of this plane of symmetry helps to explain the concave curvature of dipolarization fronts in the XZ plane through phase propagation speeds of magnetoacoustic waves. A second case study is presented to determine the central current system of a passing dipolarization front through a constellation of three spacecraft. With this information, a statistical analysis of spacecraft observations above and below the neutral sheet is used to provide further evidence for the neutral sheet as the symmetry plane and the central current system. Furthermore, it is shown that the signatures of dipolarization fronts are under certain conditions closely related to that of flux ropes, indicating a possible relationship between these two transient phenomena.

Combined Conformal Strongly-Coupled Magnetic Resonance for Efficient Wireless Power Transfer

Directory of Open Access Journals (Sweden)

Matjaz Rozman

2017-04-01

Full Text Available This paper proposes a hybrid circuit between a conformal strongly-coupled magnetic resonance (CSCMR and a strongly-coupled magnetic resonance (SCMR, for better wireless power transmission (WPT. This combination promises to enhance the flexibility of the proposed four-loop WPT system. The maximum efficiency at various distances is achieved by combining coupling-matching between the source and transmitting coils along with the coupling factor between the transmitting and receiving coils. Furthermore, the distance between transmitting and receiving coils is investigated along with the distance relationship between the source loop and transmission coil, in order to achieve the maximum efficiency of the proposed hybrid WPT system. The results indicate that the proposed approach can be effectively employed at distances comparatively smaller than the maximum distance without frequency matching. The achievable efficiency can be as high as 84% for the whole working range of the transmitter. In addition, the proposed hybrid system allows more spatial freedom compared to existing chargers.

Cluster analysis in systems of magnetic spheres and cubes

Science.gov (United States)

Pyanzina, E. S.; Gudkova, A. V.; Donaldson, J. G.; Kantorovich, S. S.

2017-06-01

In the present work we use molecular dynamics simulations and graph-theory based cluster analysis to compare self-assembly in systems of magnetic spheres, and cubes where the dipole moment is oriented along the side of the cube in the [001] crystallographic direction. We show that under the same conditions cubes aggregate far less than their spherical counterparts. This difference can be explained in terms of the volume of phase space in which the formation of the bond is thermodynamically advantageous. It follows that this volume is much larger for a dipolar sphere than for a dipolar cube.

Yeast cells proliferation on various strong static magnetic fields and temperatures

International Nuclear Information System (INIS)

Otabe, E S; Kuroki, S; Nikawa, J; Matsumoto, Y; Ooba, T; Kiso, K; Hayashi, H

2009-01-01

The effect of strong magnetic fields on activities of yeast cells were investigated. Experimental yeast cells were cultured in 5 ml of YPD(Yeast extract Peptone Dextrose) for the number density of yeast cells of 5.0 ±0.2 x 10 6 /ml with various temperatures and magnetic fields up to 10 T. Since the yeast cells were placed in the center of the superconducting magnet, the effect of magnetic force due to the diamagnetism and magnetic gradient was negligibly small. The yeast suspension was opened to air and cultured in shaking condition. The number of yeast cells in the yeast suspension was counted by a counting plate with an optical microscope, and the time dependence of the number density of yeast cells was measured. The time dependence of the number density of yeast cells, ρ, of initial part is analyzed in terms of Malthus equation as given by ρ = ρo exp(kt), where k is the growth coefficient. It is found that, the growth coefficient under the magnetic field is suppressed compared with the control. The growth coefficient decreasing as increasing magnetic field and is saturated at about 5 T. On the other hand, it is found that the suppression of growth of yeast cells by the magnetic field is diminished at high temperatures.

Dipolar Quinoidal Acene Analogues as Stable Isoelectronic Structures of Pentacene and Nonacene

KAUST Repository

Shi, Xueliang

2015-10-08

Quinoidal thia-acene analogues, as the respective isoelectronic structures of pentacene and nonacene, were synthesized and an unusual 1,2-sulfur migration was observed during the Friedel-Crafts alkylation reaction. The analogues display a closed-shell quinoidal structure in the ground state with a distinctive dipolar character. In contrast to their acene isoelectronic structures, both compounds are stable because of the existence of more aromatic sextet rings, a dipolar character, and kinetic blocking. They exhibit unique packing in single crystals resulting from balanced dipole-dipole and [C-H⋯π]/[C-H⋯S] interactions.

Coulomb Impurity Problem of Graphene in Strong Coupling Regime in Magnetic Fields.

Science.gov (United States)

Kim, S C; Yang, S-R Eric

2015-10-01

We investigate the Coulomb impurity problem of graphene in strong coupling limit in the presence of magnetic fields. When the strength of the Coulomb potential is sufficiently strong the electron of the lowest energy boundstate of the n = 0 Landau level may fall to the center of the potential. To prevent this spurious effect the Coulomb potential must be regularized. The scaling function for the inverse probability density of this state at the center of the impurity potential is computed in the strong coupling regime. The dependence of the computed scaling function on the regularization parameter changes significantly as the strong coupling regime is approached.

Dielectric response of a relativistic degenerate electron plasma in a strong magnetic field

International Nuclear Information System (INIS)

Delsante, A.E.; Frankel, N.E.

1979-01-01

The longitudinal dielectric response of a relativistic ultradegenerate electron plasma in a strong magnetic field is obtained via a relativistic generalization of the Hartree self-consistent field method. Dispersion relations and damping conditions for plasma oscillations both parallel and perpendicular to the magnetic field are obtained. Detailed results for the zero-field case, and applications to white dwarf stars and pulsars are given

Strongly anisotropic and complex magnetic behavior in EuRhGe{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Bednarchuk, Oleksandr; Kaczorowski, Dariusz, E-mail: D.Kaczorowski@int.pan.wroc.pl

2015-10-15

Single crystals of EuRhGe{sub 3} were studied by means of magnetic susceptibility, magnetization, heat capacity, resistivity and magnetoresistance measurements, performed in wide ranges of temperature and magnetic field strength. The compound was characterized as a Curie–Weiss paramagnet, due to divalent Eu ions, that orders antiferromagnetically at T{sub N} = 11.3 K. In the ordered state, EuRhGe{sub 3} exhibits strong magnetic anisotropy. The magnetic moments are probably nearly confined within the ab plane of the tetragonal crystallographic unit cell, and the magnetic propagation vector is likely perpendicular to this plane. The bulk thermodynamic and transport data concordantly suggest that in zero magnetic field the magnetic structure of EuRhGe{sub 3} is incommensurate with the chemical one and bears an amplitude-modulated character. In external magnetic field applied within the easy magnetization plane, two other magnetic structures were detected, each of them having an antiferromagnetic nature. - Highlights: • High-quality single crystals of EuRhGe{sub 3} were prepared. • Low-temperature physical behavior was studied along the main crystallographic directions. • Magnetic phase diagrams for B || ab and B || c were derived • EuRhGe{sub 3} was found highly anisotropic despite L = 0 electronic ground state. • As many as three distinct AFM phases were evidenced for B || ab.

Magnetism of one-dimensional strongly repulsive spin-1 bosons with antiferromagnetic spin-exchange interaction

International Nuclear Information System (INIS)

Lee, J. Y.; Guan, X. W.; Batchelor, M. T.; Lee, C.

2009-01-01

We investigate magnetism and quantum phase transitions in a one-dimensional system of integrable spin-1 bosons with strongly repulsive density-density interaction and antiferromagnetic spin-exchange interaction via the thermodynamic Bethe ansatz method. At zero temperature, the system exhibits three quantum phases: (i) a singlet phase of boson pairs when the external magnetic field H is less than the lower critical field H c1 ; (ii) a ferromagnetic phase of atoms in the hyperfine state |F=1, m F =1> when the external magnetic field exceeds the upper critical field H c2 ; and (iii) a mixed phase of singlet pairs and unpaired atoms in the intermediate region H c1 c2 . At finite temperatures, the spin fluctuations affect the thermodynamics of the model through coupling the spin bound states to the dressed energy for the unpaired m F =1 bosons. However, such spin dynamics is suppressed by a sufficiently strong external field at low temperatures. Thus the singlet pairs and unpaired bosons may form a two-component Luttinger liquid in the strong coupling regime.

Quantum-well exciton dipolar interaction: Polarization-dependence and Z-LT splitting

International Nuclear Information System (INIS)

Nguyen Ba An.

1996-12-01

We calculate the exciton dipolar interaction in a semiconductor quantum well. The explicit polarization-dependence, i.e, the dependence on both the exciton dipole moment μ-vector and its inplane wavevector k-vector is derived. The obtained results for the three modes (L, T and Z modes) of the long-range part of the dipolar interaction satisfy the polarization sum rule for any parameters. In the long wavelength limit there is a Z-LT splitting which decreases as the well width increases reflecting a crossover from strict 2D to quasi-2D. A rough crossover from quasi-2D to 3D is also described. (author). 18 refs, 4 figs

An initial boundary value problem for modeling a piezoelectric dipolar body

Science.gov (United States)

Marin, Marin; Öchsner, Andreas

2018-03-01

This study deals with the first initial boundary value problem in elasticity of piezoelectric dipolar bodies. We consider the most general case of an anisotropic and inhomogeneous elastic body having a dipolar structure. For two different types of restrictions imposed on the problem data, we prove two results regarding the uniqueness of solution, by using a different but accessible method. Then, the mixed problem is transformed in a temporally evolutionary equation on a Hilbert space, conveniently constructed based on the problem data. With the help of a known result from the theory of semigroups of operators, the existence and uniqueness of the weak solution for this equation are proved.

Accurate measurement of heteronuclear dipolar couplings by phase-alternating R-symmetry (PARS) sequences in magic angle spinning NMR spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Hou, Guangjin, E-mail: hou@udel.edu, E-mail: tpolenov@udel.edu; Lu, Xingyu, E-mail: luxingyu@udel.edu, E-mail: lexvega@comcast.net; Vega, Alexander J., E-mail: luxingyu@udel.edu, E-mail: lexvega@comcast.net; Polenova, Tatyana, E-mail: hou@udel.edu, E-mail: tpolenov@udel.edu [Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA and Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh School of Medicine, 1051 Biomedical Science Tower 3, 3501 Fifth Ave., Pittsburgh, Pennsylvania 15261 (United States)

2014-09-14

We report a Phase-Alternating R-Symmetry (PARS) dipolar recoupling scheme for accurate measurement of heteronuclear {sup 1}H-X (X = {sup 13}C, {sup 15}N, {sup 31}P, etc.) dipolar couplings in MAS NMR experiments. It is an improvement of conventional C- and R-symmetry type DIPSHIFT experiments where, in addition to the dipolar interaction, the {sup 1}H CSA interaction persists and thereby introduces considerable errors in the dipolar measurements. In PARS, phase-shifted RN symmetry pulse blocks applied on the {sup 1}H spins combined with π pulses applied on the X spins at the end of each RN block efficiently suppress the effect from {sup 1}H chemical shift anisotropy, while keeping the {sup 1}H-X dipolar couplings intact. Another advantage over conventional DIPSHIFT experiments, which require the signal to be detected in the form of a reduced-intensity Hahn echo, is that the series of π pulses refocuses the X chemical shift and avoids the necessity of echo formation. PARS permits determination of accurate dipolar couplings in a single experiment; it is suitable for a wide range of MAS conditions including both slow and fast MAS frequencies; and it assures dipolar truncation from the remote protons. The performance of PARS is tested on two model systems, [{sup 15}N]-N-acetyl-valine and [U-{sup 13}C,{sup 15}N]-N-formyl-Met-Leu-Phe tripeptide. The application of PARS for site-resolved measurement of accurate {sup 1}H-{sup 15}N dipolar couplings in the context of 3D experiments is presented on U-{sup 13}C,{sup 15}N-enriched dynein light chain protein LC8.

Dirac particles in the field of magnetic monopoles and of strong electric charges

International Nuclear Information System (INIS)

Schafer, A.; Muller, B.; Greiner, W.

1985-01-01

The field of a magnetic pointlike monopole acts in a similar way on a charged Dirac particle as the field of a very strong electric point charge. To explore this parallel it is constructed a field solution for an extended magnetic-charge distribution. In contrast to what is found for extended electric charges, the Hamiltonian remains nonself-adjoint for an extended magnetic monopole. This suggests that there exist a fundamental difference between the two cases. In particular, the appearance of undefined states for point monopoles is not a consequence of the mere strength of the magnetic-monopole charge, which has a minimum value fixed by Dirac's quantization condition

Cluster and Double Star observations of dipolarization

Directory of Open Access Journals (Sweden)

R. Nakamura

2005-11-01

Full Text Available We studied two types of dipolarization events with different IMF conditions when Cluster and Double Star (TC-1 were located in the same local time sector: 7 August 2004, 18:00-24:00 UT, during a disturbed southward/northward IMF interval, and 14 August 2004, 21:00-24:00 UT, when the IMF was stably northward. Cluster observed dipolarization as well as fast flows during both intervals, but this was not the case for TC-1. For both events the satellites crossed near the conjugate location of the MIRACLE stations. By using multi-point analysis techniques, the direction/speed of the propagation is determined using Cluster and is then compared with the disturbances at TC-1 to discuss its spatial/temporal scale. The propagation direction of the B_Z disturbance at Cluster was mainly dawnward with a tailward component for 7 August and with a significant Earthward component for 14 August associated with fast flows. We suggest that the role of the midtail fast flows can be quite different in the dissipation process depending on the condition of the IMF and resultant configuration of the tail.

Geomagnetic and strong static magnetic field effects on growth and chlorophyll a fluorescence in Lemna minor.

Science.gov (United States)

Jan, Luka; Fefer, Dušan; Košmelj, Katarina; Gaberščik, Alenka; Jerman, Igor

2015-04-01

The geomagnetic field (GMF) varies over Earth's surface and changes over time, but it is generally not considered as a factor that could influence plant growth. The effects of reduced and enhanced GMFs and a strong static magnetic field on growth and chlorophyll a (Chl a) fluorescence of Lemna minor plants were investigated under controlled conditions. A standard 7 day test was conducted in extreme geomagnetic environments of 4 µT and 100 µT as well as in a strong static magnetic field environment of 150 mT. Specific growth rates as well as slow and fast Chl a fluorescence kinetics were measured after 7 days incubation. The results, compared to those of controls, showed that the reduced GMF significantly stimulated growth rate of the total frond area in the magnetically treated plants. However, the enhanced GMF pointed towards inhibition of growth rate in exposed plants in comparison to control, but the difference was not statistically significant. This trend was not observed in the case of treatments with strong static magnetic fields. Our measurements suggest that the efficiency of photosystem II is not affected by variations in GMF. In contrast, the strong static magnetic field seems to have the potential to increase initial Chl a fluorescence and energy dissipation in Lemna minor plants. © 2015 Wiley Periodicals, Inc.

MULTI-WAVELENGTH STUDY OF A DELTA-SPOT. I. A REGION OF VERY STRONG, HORIZONTAL MAGNETIC FIELD

Energy Technology Data Exchange (ETDEWEB)

Jaeggli, S. A., E-mail: sarah.jaeggli@nasa.gov [NASA Goddard Space Flight Center, Solar Physics Laboratory, Code 671, Greenbelt, MD 20771 (United States)

2016-02-10

Active region NOAA 11035 appeared in 2009 December, early in the new solar activity cycle. This region achieved a delta sunspot (δ spot) configuration when parasitic flux emerged near the rotationally leading magnetic polarity and traveled through the penumbra of the largest sunspot in the group. Both visible and infrared imaging spectropolarimetry of the magnetically sensitive Fe i line pairs at 6302 and 15650 Å show large Zeeman splitting in the penumbra between the parasitic umbra and the main sunspot umbra. The polarized Stokes spectra in the strongest field region display anomalous profiles, and strong blueshifts are seen in an adjacent region. Analysis of the profiles is carried out using a Milne–Eddington inversion code capable of fitting either a single magnetic component with stray light or two independent magnetic components to verify the field strength. The inversion results show that the anomalous profiles cannot be produced by the combination of two profiles with moderate magnetic fields. The largest field strengths are 3500–3800 G in close proximity to blueshifts as strong as 3.8 km s{sup −1}. The strong, nearly horizontal magnetic field seen near the polarity inversion line in this region is difficult to understand in the context of a standard model of sunspot magnetohydrostatic equilibrium.

MULTI-WAVELENGTH STUDY OF A DELTA-SPOT. I. A REGION OF VERY STRONG, HORIZONTAL MAGNETIC FIELD

International Nuclear Information System (INIS)

Jaeggli, S. A.

2016-01-01

Active region NOAA 11035 appeared in 2009 December, early in the new solar activity cycle. This region achieved a delta sunspot (δ spot) configuration when parasitic flux emerged near the rotationally leading magnetic polarity and traveled through the penumbra of the largest sunspot in the group. Both visible and infrared imaging spectropolarimetry of the magnetically sensitive Fe i line pairs at 6302 and 15650 Å show large Zeeman splitting in the penumbra between the parasitic umbra and the main sunspot umbra. The polarized Stokes spectra in the strongest field region display anomalous profiles, and strong blueshifts are seen in an adjacent region. Analysis of the profiles is carried out using a Milne–Eddington inversion code capable of fitting either a single magnetic component with stray light or two independent magnetic components to verify the field strength. The inversion results show that the anomalous profiles cannot be produced by the combination of two profiles with moderate magnetic fields. The largest field strengths are 3500–3800 G in close proximity to blueshifts as strong as 3.8 km s −1 . The strong, nearly horizontal magnetic field seen near the polarity inversion line in this region is difficult to understand in the context of a standard model of sunspot magnetohydrostatic equilibrium

Bound states in strongly correlated magnetic and electronic systems

International Nuclear Information System (INIS)

Trebst, S.

2002-02-01

A novel strong coupling expansion method to calculate two-particle spectra of quantum lattice models is developed. The technique can be used to study bosonic and fermionic models and in principle it can be applied to systems in any dimension. A number of strongly correlated magnetic and electronic systems are examined including the two-leg spin-half Heisenberg ladder, the dimerized Heisenberg chain with a frustrating next-nearest neighbor interaction, coupled Heisenberg ladders, and the one-dimensional Kondo lattice model. In the various models distinct bound states are found below the two-particle continuum. Quantitative calculations of the dispersion, coherence length and binding energy of these bound states are used to describe spectroscopic experiments on (Ca,La) 14 Cu 24 O 41 and NaV 2 O 5 . (orig.)

Unexpected strong magnetism of Cu doped single-layer MoS₂ and its origin.

Science.gov (United States)

Yun, Won Seok; Lee, J D

2014-05-21

The magnetism of the 3d transition-metal (TM) doped single-layer (1L) MoS2, where the Mo atom is partially replaced by the 3d TM atom, is investigated using the first-principles density functional calculations. In a series of 3d TM doped 1L-MoS2's, the induced spin polarizations are negligible for Sc, Ti, and Cr dopings, while the induced spin polarizations are confirmed for V, Mn, Fe, Co, Ni, Cu, and Zn dopings and the systems become magnetic. Especially, the Cu doped system shows unexpectedly strong magnetism although Cu is nonmagnetic in its bulk state. The driving force is found to be a strong hybridization between Cu 3d states and 3p states of neighboring S, which results in an extreme unbalanced spin-population in the spin-split impurity bands near the Fermi level. Finally, we also discuss further issues of the Cu induced magnetism of 1L-MoS2 such as investigation of additional charge states, the Cu doping at the S site instead of the Mo site, and the Cu adatom on the layer (i.e., 1L-MoS2).

The Of?p stars of the Magellanic Clouds: Are they strongly magnetic?

Science.gov (United States)

Munoz, M.; Wade, G. A.; Nazé, Y.; Bagnulo, S.; Puls, J.

2018-01-01

All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric (Nazé et al., 2015) and spectroscopic (Walborn et al., 2015) variability compatible with the Oblique Rotator Model (ORM). However, their magnetic fields have yet to be directly detected. We have developed an algorithm allowing for the synthesis of photometric observables based on the Analytic Dynamical Magnetosphere (ADM) model by Owocki et al. (2016). We apply our model to OGLE photometry in order to constrain their magnetic geometries and surface dipole strengths. We predict that the field strengths for some of theses candidate extra-Galactic magnetic stars may be within the detection limits of the FORS2 instrument

Localized Electron Heating by Strong Guide-Field Magnetic Reconnection

Science.gov (United States)

Guo, Xuehan; Sugawara, Takumichi; Inomoto, Michiaki; Yamasaki, Kotaro; Ono, Yasushi; UTST Team

2015-11-01

Localized electron heating of magnetic reconnection was studied under strong guide-field (typically Bt 15Bp) using two merging spherical tokamak plasmas in Univ. Tokyo Spherical Tokamak (UTST) experiment. Our new slide-type two-dimensional Thomson scattering system documented for the first time the electron heating localized around the X-point. The region of high electron temperature, which is perpendicular to the magnetic field, was found to have a round shape with radius of 2 [cm]. Also, it was localized around the X-point and does not agree with that of energy dissipation term Et .jt . When we include a guide-field effect term Bt / (Bp + αBt) for Et .jt where α =√{ (vin2 +vout2) /v∥2 } , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus,'' a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) Fellows 15J03758.

Dipolar interaction induced band gaps and flat modes in surface-modulated magnonic crystals

Science.gov (United States)

Gallardo, R. A.; Schneider, T.; Roldán-Molina, A.; Langer, M.; Fassbender, J.; Lenz, K.; Lindner, J.; Landeros, P.

2018-04-01

Theoretical results for the magnetization dynamics of a magnonic crystal formed by grooves on the surface of a ferromagnetic film, called a surface-modulated magnonic crystal, are presented. For such a system, the role of the periodic dipolar field induced by the geometrical modulation is addressed by using the plane-wave method. The results reveal that, under the increasing of the depth of the grooves, zones with magnetizing and demagnetizing fields act on the system in such a way that magnonic band gaps are observed in both Damon-Eshbach and backward volume geometries. Particularly, in the backward volume configuration, high-frequency band gaps and low-frequency flat modes are obtained. By taking into account the properties of the internal field induced by the grooves, the flattening of the modes and their shift towards low frequencies are discussed and explained. To test the validity of the model, the theoretical results of this work are confirmed by micromagnetic simulations, and good agreement between both methods is achieved. The theoretical model allows for a detailed understanding of the physics underlying these kinds of systems, thereby providing an outlook for potential applications on magnonic devices.

Electron cyclotron maser instability (ECMI in strong magnetic guide field reconnection

Directory of Open Access Journals (Sweden)

R. A. Treumann

2017-08-01

Full Text Available The ECMI model of electromagnetic radiation from electron holes is shown to be applicable to spontaneous magnetic reconnection. We apply it to reconnection in strong current-aligned magnetic guide fields. Such guide fields participate only passively in reconnection, which occurs in the antiparallel components to both sides of the guide-field-aligned current sheets with current carried by kinetic Alfvén waves. Reconnection generates long (the order of hundreds of electron inertial scales electron exhaust regions at the reconnection site X point, which are extended perpendicular to the current and the guide fields. Exhausts contain a strongly density-depleted hot electron component and have properties similar to electron holes. Exhaust electron momentum space distributions are highly deformed, exhibiting steep gradients transverse to both the reconnecting and guide fields. Such properties suggest application of the ECMI mechanism with the fundamental ECMI X-mode emission beneath the nonrelativistic guide field cyclotron frequency in localized source regions. An outline of the mechanism and its prospects is given. Potential applications are the kilometric radiation (AKR in auroral physics, solar radio emissions during flares, planetary emissions and astrophysical scenarios (radiation from stars and compact objects involving the presence of strong magnetic fields and field-aligned currents. Drift of the exhausts along the guide field maps the local field and plasma properties. Escape of radiation from the exhaust and radiation source region still poses a problem. The mechanism can be studied in 2-D particle simulations of strong guide field reconnection which favours 2-D, mapping the deformation of the electron distribution perpendicular to the guide field, and using it in the numerical calculation of the ECMI growth rate. The mechanism suggests also that reconnection in general may become a source of the ECMI with or without guide fields. This is

Electron cyclotron maser instability (ECMI) in strong magnetic guide field reconnection

Science.gov (United States)

Treumann, Rudolf A.; Baumjohann, Wolfgang

2017-08-01

The ECMI model of electromagnetic radiation from electron holes is shown to be applicable to spontaneous magnetic reconnection. We apply it to reconnection in strong current-aligned magnetic guide fields. Such guide fields participate only passively in reconnection, which occurs in the antiparallel components to both sides of the guide-field-aligned current sheets with current carried by kinetic Alfvén waves. Reconnection generates long (the order of hundreds of electron inertial scales) electron exhaust regions at the reconnection site X point, which are extended perpendicular to the current and the guide fields. Exhausts contain a strongly density-depleted hot electron component and have properties similar to electron holes. Exhaust electron momentum space distributions are highly deformed, exhibiting steep gradients transverse to both the reconnecting and guide fields. Such properties suggest application of the ECMI mechanism with the fundamental ECMI X-mode emission beneath the nonrelativistic guide field cyclotron frequency in localized source regions. An outline of the mechanism and its prospects is given. Potential applications are the kilometric radiation (AKR) in auroral physics, solar radio emissions during flares, planetary emissions and astrophysical scenarios (radiation from stars and compact objects) involving the presence of strong magnetic fields and field-aligned currents. Drift of the exhausts along the guide field maps the local field and plasma properties. Escape of radiation from the exhaust and radiation source region still poses a problem. The mechanism can be studied in 2-D particle simulations of strong guide field reconnection which favours 2-D, mapping the deformation of the electron distribution perpendicular to the guide field, and using it in the numerical calculation of the ECMI growth rate. The mechanism suggests also that reconnection in general may become a source of the ECMI with or without guide fields. This is of particular

Polarized X-Ray Emission from Magnetized Neutron Stars: Signature of Strong-Field Vacuum Polarization

Science.gov (United States)

Lai, Dong; Ho, Wynn C.

2003-08-01

In the atmospheric plasma of a strongly magnetized neutron star, vacuum polarization can induce a Mikheyev-Smirnov-Wolfenstein type resonance across which an x-ray photon may (depending on its energy) convert from one mode into the other, with significant changes in opacities and polarizations. We show that this vacuum resonance effect gives rise to a unique energy-dependent polarization signature in the surface emission from neutron stars. The detection of polarized x rays from neutron stars can provide a direct probe of strong-field quantum electrodynamics and constrain the neutron star magnetic field and geometry.

Polarized x-ray emission from magnetized neutron stars: signature of strong-field vacuum polarization.

Science.gov (United States)

Lai, Dong; Ho, Wynn C G

2003-08-15

In the atmospheric plasma of a strongly magnetized neutron star, vacuum polarization can induce a Mikheyev-Smirnov-Wolfenstein type resonance across which an x-ray photon may (depending on its energy) convert from one mode into the other, with significant changes in opacities and polarizations. We show that this vacuum resonance effect gives rise to a unique energy-dependent polarization signature in the surface emission from neutron stars. The detection of polarized x rays from neutron stars can provide a direct probe of strong-field quantum electrodynamics and constrain the neutron star magnetic field and geometry.

Stepwise π-extension of meso-alkylidenyl porphyrins through sequential 1,3-dipolar cycloaddition and redox reactions.

Science.gov (United States)

Park, Dowoo; Jeong, Seung Doo; Ishida, Masatoshi; Lee, Chang-Hee

2014-08-25

Several regioselectively π-extended, pyrrole fused porphyrinoids have been synthesized by the 1,3-dipolar cycloaddition of meso-alkylidene-(benzi)porphyrins. Pd(II) complexes gave oxidation resistant, bis-pyrrole fused adducts. The repeated 1,3-dipolar cycloaddition followed by oxidation-reduction of pentaphyrin analogs afforded π-extended porphyrin analogs.

Perturbation theories for the dipolar fluids

International Nuclear Information System (INIS)

Lee, L.L.; Chung, T.H.

1983-01-01

We derive here four different perturbation equations for the calculation of the angular pair correlation functions of dipolar fluids; namely, the first order y-expansion, the modified Percus--Yevik (MPY) expansion, the modified hypernetted chain (MHNC) expansion, and the modified linearized hypernetted chain (MLHNC) equation. Both the method of the functional expansion and the method of the cluster integrals are utilized. Comparison with other perturbation theories (e.g., the Melnyk--Smith equation) is made. While none of the theories is exact, as shown by the cluster diagrams, the MLHNC and the MHNC contain more diagrams than, say, the MPY and y-expansion. The y-expansion equation can be improved by including the correction terms to the Kirkwood superposition approximation for the triplet correlation function. For example, the inclusion of the correction term rho∫d4h(14)h(24)h(34) in a formula given by Henderson, is shown to improve substantially the y-expansion equation. We examine the performance of two of the theories: the y-expansion and the MLHNC equation for a Stockmayer (dipolar) fluid with a reduced dipole moment μ/sup asterisk2/ [ = μ 2 /(epsilonsigma 3 )] = 1.0. Comparison with Monte Carlo simulation results of Adams et al. and with other theories (e.g., the QHNC equation) shows that our results are reasonable. Further improvements of the equations are also pointed out

Self-assembly and flux closure studies of magnetic nanoparticle rings

DEFF Research Database (Denmark)

Wei, Alexander; Kasama, Takeshi; Dunin-Borkowski, Rafal E.

2011-01-01

Thermoremanent magnetic nanoparticles (MNPs) can self-assemble into rings through dipolar interactions, when dispersed under appropriate conditions. Analysis of individual MNP rings and clusters by off-axis electron holography reveals bistable flux closure (FC) states at ambient temperatures...

Effective magnetic moment of neutrinos in strong magnetic fields

International Nuclear Information System (INIS)

Perez M, A.; Perez R, H.; Masood, S.S.; Gaitan, R.; Rodriguez R, S.

2002-01-01

In this paper we compute the effective magnetic moment of neutrinos propagating in dense high magnetized medium. Taking typical values of magnetic field and densities of astrophysical objects (such as the cores of supernovae and neutron stars) we obtain an effective type of dipole magnetic moment in agreement with astrophysical and cosmological bounds. (Author)

Charge transfer of He2+ with H in a strong magnetic field

International Nuclear Information System (INIS)

Liu Chun-Lei; Zou Shi-Yang; He Bin; Wang Jian-Guo

2015-01-01

By solving a time-dependent Schrödinger equation (TDSE), we studied the electron capture process in the He 2+ +H collision system under a strong magnetic field in a wide projectile energy range. The strong enhancement of the total charge transfer cross section is observed for the projectile energy below 2.0 keV/u. With the projectile energy increasing, the cross sections will reduce a little and then increase again, compared with those in the field-free case. The cross sections to the states with different magnetic quantum numbers are presented and analyzed where the influence due to Zeeman splitting is obviously found, especially in the low projectile energy region. The comparison with other models is made and the tendency of the cross section varying with the projectile energy is found closer to that from other close coupling models. (paper)

Charged perfect fluid tori in strong central gravitational and dipolar magnetic fields

Czech Academy of Sciences Publication Activity Database

Kovář, J.; Slaný, P.; Cremaschini, C.; Stuchlík, Z.; Karas, Vladimír; Trova, Audrey

2016-01-01

Roč. 93, June (2016), 124055/1-124055/20 ISSN 1550-7998 R&D Projects: GA ČR GB14-37086G; GA MŠk(CZ) LH14049 Grant - others:GA ČR(CZ) GP14-07753P Institutional support: RVO:67985815 Keywords : black holes * accretion discscretion discs Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.643, year: 2014

Phosphorus nuclear magnetic resonance imaging in solid bone

International Nuclear Information System (INIS)

Li, Limin.

1990-01-01

Phosphorus ( 31 P) nuclear magnetic resonance (NMR) double-pulse transient experiments of solid bone have shown that the spins dephased by the dipolar spin-spin interactions can be refocused with a 90 degree-β pulse sequence so that an echo is observable at some time following the second pulse. The decay time constant of the maximum echo amplitude is larger than that of the free induction decay (FID) signal from a single 90 degree pulse. Depending on the nutation angle of the second pulse, the former decay time constant is about three-five times as long as the latter one. The dipolar-echo properties of the bone may be relevant with the interpair dipolar interactions. The experiments have also show that, in general, the time for the transient signal from the double pulses to reach the maximum amplitude is not equal to the pulse separation. This can be attributed to the effect of the heteronuclear dipolar interactions. In addition, it is found experimentally that refocused gradients applied only in a time interval of the formation of an echo have the capability of phase-encoding spatial information. Based on this, a new imaging method was proposed. With the method, several 31 P images of the solid bone samples have been obtained. The picture element size is 1-1.5 mm with very good signal-to-noise ratios. The imaging ability of the refocused gradients may be relevant with the inhomogeneous local field produced by the interpair dipolar interactions

Defect characterization and magnetic properties in un-doped ZnO thin film annealed in a strong magnetic field

International Nuclear Information System (INIS)

Ning Shuai; Zhan Peng; Wang Wei-Peng; Li Zheng-Cao; Zhang Zheng-Jun

2014-01-01

Highly c-axis oriented un-doped zinc oxide (ZnO) thin films, each with a thickness of ∼ 100 nm, are deposited on Si (001) substrates by pulsed electron beam deposition at a temperature of ∼ 320 °C, followed by annealing at 650 °C in argon in a strong magnetic field. X-ray photoelectron spectroscopy (XPS), positron annihilation analysis (PAS), and electron paramagnetic resonance (EPR) characterizations suggest that the major defects generated in these ZnO films are oxygen vacancies. Photoluminescence (PL) and magnetic property measurements indicate that the room-temperature ferromagnetism in the un-doped ZnO film originates from the singly ionized oxygen vacancies whose number depends on the strength of the magnetic field applied in the thermal annealing process. The effects of the magnetic field on the defect generation in the ZnO films are also discussed. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Consequence of total lepton number violation in strongly magnetized iron white dwarfs

Energy Technology Data Exchange (ETDEWEB)

Belyaev, V.B. [Bogolyubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Ricci, P. [Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, I-50019 Sesto Fiorentino (Firenze) (Italy); Šimkovic, F. [Department of Nuclear Physics and Biophysics, Comenius University, Mlynská dolina F1, SK-842 15, Bratislava (Slovakia); Bogolyubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Adam, J.; Tater, M. [Institute of Nuclear Physics ASCR, CZ-250 68 Řež (Czech Republic); Truhlík, E., E-mail: truhlik@ujf.cas.cz [Institute of Nuclear Physics ASCR, CZ-250 68 Řež (Czech Republic)

2015-05-15

The influence of a neutrinoless electron to positron conversion on a cooling of strongly magnetized iron white dwarfs is studied. It is shown that they can be good candidates for soft gamma-ray repeaters and anomalous X-ray pulsars.

MAGNETIC NULL POINTS IN KINETIC SIMULATIONS OF SPACE PLASMAS

International Nuclear Information System (INIS)

Olshevsky, Vyacheslav; Innocenti, Maria Elena; Cazzola, Emanuele; Lapenta, Giovanni; Deca, Jan; Divin, Andrey; Peng, Ivy Bo; Markidis, Stefano

2016-01-01

We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic particle-in-cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind, and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly (LMA) and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3–9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and LMA simulations are rather stable and do not exhibit any energy dissipation. Energy dissipation is more powerful in the vicinity of spiral nulls enclosed by magnetic flux ropes with strong currents at their axes (their cross sections resemble 2D magnetic islands). These null lines reminiscent of Z-pinches efficiently dissipate magnetic energy due to secondary instabilities such as the two-stream or kinking instability, accompanied by changes in magnetic topology. Current enhancements accompanied by spiral nulls may signal magnetic energy conversion sites in the observational data

Dipolar dark matter with massive bigravity

International Nuclear Information System (INIS)

Blanchet, Luc; Heisenberg, Lavinia

2015-01-01

Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the two metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model

Dynamics of long-period irregular pulsations in high latitudes during strong magnetic storms

International Nuclear Information System (INIS)

Kurazhkovskaya, N.A.; Klajn, B.I.

1995-01-01

Effects of strong magnetic storms within np type high-latitudinal long-period irregular pulsations at Mirny studied using data obtained at observatory of the magnetosphere south hemisphere. Variation of long-period irregular pulsation amplitude is shown to depend essentially on duration of storm initial phase and on the nature of solar wind heterogeneity enabling growth of strong storm. 14 refs

Analysis of the giant magnetostrictive actuator with strong bias magnetic field

Energy Technology Data Exchange (ETDEWEB)

Xue, Guangming, E-mail: yy0youxia@163.com; He, Zhongbo; Li, Dongwei; Yang, Zhaoshu; Zhao, Zhenglong

2015-11-15

Giant magnetostrictive actuator with strong bias magnetic field is designed to control the injector bullet valve opening and closing. The relationship between actuator displacement amplitude and input signal direction is analyzed. And based on the approximate linearity of strain-magnetic field, second-order system model of the actuator displacement is established. Experimental system suitable for the actuator is designed. The experimental results show that, the square voltage amplitude being 12 V, the actuator displacement amplitude is about 17 μm with backward direction signal input while being 1.5 μm under forward direction signal. From the results, the suitable input direction is confirmed to be backward. With exciting frequncy lower than 200 Hz, the error between the model and experimental result is less than 1.7 μm. So the model is validated under the low-frequency signal input. The testing displacement-voltage curves are approximately straight lines. But due to the biased position, the line slope and the displacement-voltage linearity change as the input voltage changes. - Highlights: • Giant magnetostrictive actuator with strong bias magnetic field is designed. • The relationship between actuator displacement amplitude and input current direction is analyzed. • The model of the actuator displacement is established and its accuracy is verified by the test. • The actuator displacement-voltage curves are achieved by the test, and the curves’ characteristics are analyzed theoretically.

Sound absorption in a field of a strong electromagnetic wave in a quantizied magnetic field

International Nuclear Information System (INIS)

Chajkovskij, I.A.

1974-01-01

A coefficient of sound absorption GAMMA in a semiconductor and semi-metal in the quantized magnetic field is calculated for a system exposed to a field of strong electromagnetic radiation. The cases E parallel H and E orthogonal H are considered. Along with the already known strong oscillations of sound absorption in magnetic fields, the absorption spectrum GAMMAsub(par) and GAMMAsub(orth) shows new oscillations representing a manifestation of the quasi-energetic electron spectrum in the field of a strong electromagnetic wave. The oscillation height at E parallel H is modulated by the electromagnetic field. It is shown that the ratio GAMMAsub(par)/GAMMAsub(orth) allows the determination of the effective mass of the carriers

Cluster-cluster aggregation of Ising dipolar particles under thermal noise

KAUST Repository

Suzuki, Masaru; Kun, Ferenc; Ito, Nobuyasu

2009-01-01

The cluster-cluster aggregation processes of Ising dipolar particles under thermal noise are investigated in the dilute condition. As the temperature increases, changes in the typical structures of clusters are observed from chainlike (D1

Magnetization Dynamics in Two Novel Current-Driven Spintronic Memory Cell Structures

KAUST Repository

Velazquez-Rizo, Martin

2017-01-01

In this work, two new spintronic memory cell structures are proposed. The first cell uses the diffusion of polarized spins into ferromagnets with perpendicular anisotropy to tilt their magnetization followed by their dipolar coupling to a fixed

Exchange interaction of strongly anisotropic tripodal erbium single-ion magnets with metallic surfaces

DEFF Research Database (Denmark)

Dreiser, Jan; Wäckerlin, Christian; Ali, Md. Ehesan

2014-01-01

We present a comprehensive study of Er(trensal) single-ion magnets deposited in ultrahigh vacuum onto metallic surfaces. X-ray photoelectron spectroscopy reveals that the molecular structure is preserved after sublimation, and that the molecules are physisorbed on Au(111) while they are chemisorbed...... on a Ni thin film on Cu(100) single-crystalline surfaces. X-ray magnetic circular dichroism (XMCD) measurements performed on Au(111) samples covered with molecular monolayers held at temperatures down to 4 K suggest that the easy axes of the strongly anisotropic molecules are randomly oriented...... pathways toward optical addressing of surface-deposited single-ion magnets....

Micellar dipolar rearrangement is sensitive to hydrophobic chain length: Implication for structural switchover of piroxicam.

Science.gov (United States)

Sethy, Dasaratha; Chakraborty, Hirak

2016-10-01

The interfacial properties of the membrane are exceptionally vital in drug-membrane interaction. They not only select out a particular prototropic form of the drug molecule for incorporation, but are also potent enough to induce structural switchover of these drugs in several cases. In this work, we quantitatively monitored the change in dipolar rearrangement of the micellar interface (as a simplified membrane mimic) by measuring the dielectric constant and dipole potential with the micellization of SDS at pH 3.6. The dielectric constant and dipole potential were measured utilizing the fluorescence of polarity sensitive probe, pyrene and potential-sensitive probe, di-8-ANEPPS, respectively. Our study demonstrates that the change in dipolar rearrangement directly influences the switchover equilibrium between the anionic and neutral from of piroxicam. We have further extended our work to evaluate the effect of hydrophobic chain length of the surfactants on the dipolar rearrangement and its effect on the structural switchover of piroxicam. It is interesting that the extent of switchover of piroxicam is directly correlated with the dipolar rearrangement induced bythe varying hydrophobic chain length of the surfactants. To the best of our knowledge, our results constitute the first report to show the dependence of dipole potential on the hydrophobic chain length of the surfactant and demonstrate that the dipolar rearrangement directly tunes the extent of structural switchover of piroxicam, which was so far only intuitive. We consider that this new finding would have promising implication in drug distribution and drug efficacy. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Optimal laser heating of plasmas confined in strong solenoidal magnetic fields

International Nuclear Information System (INIS)

Vitela, J.; Akcasu, A.Z.

1987-01-01

Optimal Control Theory is used to analyze the laser-heating of plasmas confined in strong solenoidal magnetic fields. Heating strategies that minimize a linear combination of heating time and total energy spent by the laser system are found. A numerical example is used to illustrate the theory. Results of this example show that by an appropriate modulation of the laser intensity, significant savings in the laser energy are possible with only slight increases in the heating time. However, results may depend strongly on the initial state of the plasma and on the final ion temperature. (orig.)

Anisotropy of the nuclear magnetic relaxation times induced in solid 3He by modulation of the dipolar interactions

International Nuclear Information System (INIS)

Deville, G.

1976-01-01

Anisotropic nuclear relaxation times have been measured in solid 3 He samples grown at constant pressure, in the Larmor frequency range 1.5MHz-5MHz where the main relaxation mechanism is the modulation of the dipolar interaction by exchange or by motion of the vacancies. The second order calculation made by Harris for the exchange induced relaxation regime is extended to the regime where vacancy motion dominates. The theory is further refined by considering the fourth moment anisotropy effect on the spectral densities. This latter calculation yields a frequency dependent anisotropic contribution to T 1 which agrees qualitatively with the data, unlike the simpler results by Harris [fr

Defect characterization and magnetic properties in un-doped ZnO thin film annealed in a strong magnetic field

Science.gov (United States)

Ning, Shuai; Zhan, Peng; Wang, Wei-Peng; Li, Zheng-Cao; Zhang, Zheng-Jun

2014-12-01

Highly c-axis oriented un-doped zinc oxide (ZnO) thin films, each with a thickness of ~ 100 nm, are deposited on Si (001) substrates by pulsed electron beam deposition at a temperature of ~ 320 °C, followed by annealing at 650 °C in argon in a strong magnetic field. X-ray photoelectron spectroscopy (XPS), positron annihilation analysis (PAS), and electron paramagnetic resonance (EPR) characterizations suggest that the major defects generated in these ZnO films are oxygen vacancies. Photoluminescence (PL) and magnetic property measurements indicate that the room-temperature ferromagnetism in the un-doped ZnO film originates from the singly ionized oxygen vacancies whose number depends on the strength of the magnetic field applied in the thermal annealing process. The effects of the magnetic field on the defect generation in the ZnO films are also discussed.

Photoionization of the hydrogen atom in strong magnetic fields

Science.gov (United States)

Potekhin, Aleksandr IU.; Pavlov, George G.

1993-01-01

The photoionization of the hydrogen atom in magnetic fields B about 10 exp 11 - 10 exp 13 G typical of the surface layers of neutron stars is investigated analytically and numerically. We consider the photoionization from various tightly bound and hydrogen-like states of the atom for photons with arbitrary polarizations and wave-vector directions. It is shown that the length form of the interaction matrix elements is more appropriate in the adiabatic approximation than the velocity form, at least in the most important frequency range omega much less than omega(B), where omega(B) is the electron cyclotron frequency. Use of the length form yields nonzero cross sections for photon polarizations perpendicular to the magnetic field at omega less than omega(B); these cross sections are the ones that most strongly affect the properties of the radiation escaping from an optically thick medium, e.g., from the atmosphere of a neutron star. The results of the numerical calculations are fitted by simple analytical formulas.

Numerical analysis of blood flow in realistic arteries subjected to strong non-uniform magnetic fields

International Nuclear Information System (INIS)

Kenjeres, Sasa

2008-01-01

The paper reports on a comprehensive mathematical model for simulations of blood flow under the presence of strong non-uniform magnetic fields. The model consists of a set of Navier-Stokes equations accounting for the Lorentz and magnetisation forces, and a simplified set of Maxwell's equations (Biot-Savart/Ampere's law) for treating the imposed magnetic fields. The relevant hydrodynamic and electromagnetic properties of human blood were taken from the literature. The model is then validated for different test cases ranging from a simple cylindrical geometry to real-life right-coronary arteries in humans. The time-dependency of the wall-shear-stress for different stenosis growth rates and the effects of the imposed strong non-uniform magnetic fields on the blood flow pattern are presented and analysed. It is concluded that an imposed non-uniform magnetic field can create significant changes in the secondary flow patterns, thus making it possible to use this technique for optimisations of targeted drug delivery

The mean energy loss by neutrino with magnetic moment in strong magnetic field with consideration of positronium contribution to photon dispersion

Science.gov (United States)

Mosichkin, A. F.

2017-11-01

The process of radiative decay of the neutrino with a magnetic moment in a strong magnetic field with consideration of positronium influence on photon dispersion has been studied. Positronium contribution to the photon polarization operator induces significant modifications of the photon dispersion law and neutrino radiative decay amplitude. It has been shown that the mean energy loss of a neutrino with magnetic a moment significantly increases, when the positronium contribution to photon dispersion is taken into account.

Spatially correlated disorder in striped precursor magnetic modulations

International Nuclear Information System (INIS)

Porta, Marcel; Castan, Teresa; LLoveras, Pol; Planes, Antoni; Saxena, Avadh

2007-01-01

We use a Ginzburg-Landau model that includes long-range dipolar interactions and spatially correlated quenched-in disorder coupled to the local magnetization to study the properties of the precursor magnetic modulations as a function of the characteristics of the disorder. We find that although the modulation pattern is very robust and does not depend on details of the pair correlation function G(r), the scaling behaviour of the characteristic length of the striped magnetic modulations depends on the behaviour of G(r) for small values of r

A new purely growing instability in a strongly magnetized nonuniform pair plasma

International Nuclear Information System (INIS)

Shukla, Nitin; Shukla, P.K.

2007-01-01

It is shown that a strongly magnetized nonuniform electron-positron (hereafter referred to as e-p or pair) plasma is unstable against low-frequency (in comparison with the electron gyrofrequency) electrostatic oscillations. For this purpose, a dispersion relation is derived by using the Poisson equation as well as the electron and positron continuity equations with the guiding center drifts for the electron and positron fluids. The dispersion relation admits a purely growing instability in the presence of the equilibrium density and magnetic field inhomogeneities. Physically, instability arises because of the inhomogeneous magnetic field induced differential electron and positron density fluctuations, which do not keep in phase with the electrostatic potential arising from the charge separation in our nonuniform pair plasmas

Nanoscale layer-selective readout of magnetization direction from a magnetic multilayer using a spin-torque oscillator

International Nuclear Information System (INIS)

Suto, Hirofumi; Nagasawa, Tazumi; Kudo, Kiwamu; Mizushima, Koichi; Sato, Rie

2014-01-01

Technology for detecting the magnetization direction of nanoscale magnetic material is crucial for realizing high-density magnetic recording devices. Conventionally, a magnetoresistive device is used that changes its resistivity in accordance with the direction of the stray field from an objective magnet. However, when several magnets are near such a device, the superposition of stray fields from all the magnets acts on the sensor, preventing selective recognition of their individual magnetization directions. Here we introduce a novel readout method for detecting the magnetization direction of a nanoscale magnet by use of a spin-torque oscillator (STO). The principles behind this method are dynamic dipolar coupling between an STO and a nanoscale magnet, and detection of ferromagnetic resonance (FMR) of this coupled system from the STO signal. Because the STO couples with a specific magnet by tuning the STO oscillation frequency to match its FMR frequency, this readout method can selectively determine the magnetization direction of the magnet. (papers)

Coulomb effects on the transport properties of quantum dots in strong magnetic field

International Nuclear Information System (INIS)

Moldoveanu, V.; Aldea, A.; Manolescu, A.; Nita, M.

2000-08-01

We investigate the transport properties of quantum dots placed in strong magnetic field using a quantum-mechanical approach based on the 2D tight-binding Hamiltonian with direct Coulomb interaction and the Landauer-Buettiker (LB) formalism. The electronic transmittance and the Hall resistance show Coulomb oscillations and also prove multiple addition processes. We identify this feature as the 'bunching' of electrons observed in recent experiments and give an elementary explanation in terms of spectral characteristics of the dot. The spatial distribution of the added electrons may distinguish between edge and bulk states and it has specific features for bunched electrons. The dependence of the charging energy on the number of electrons is discussed for strong magnetic field. The crossover from the tunneling to quantum Hall regime is analyzed in terms of dot-lead coupling. (author)

Manifestation of spin selection rules on the quantum tunneling of magnetization in a single-molecule magnet.

Science.gov (United States)

Henderson, J J; Koo, C; Feng, P L; del Barco, E; Hill, S; Tupitsyn, I S; Stamp, P C E; Hendrickson, D N

2009-07-03

We present low temperature magnetometry measurements on a new Mn3 single-molecule magnet in which the quantum tunneling of magnetization (QTM) displays clear evidence for quantum mechanical selection rules. A QTM resonance appearing only at high temperatures demonstrates tunneling between excited states with spin projections differing by a multiple of three. This is dictated by the C3 molecular symmetry, which forbids pure tunneling from the lowest metastable state. Transverse field resonances are understood by correctly orienting the Jahn-Teller axes of the individual manganese ions and including transverse dipolar fields. These factors are likely to be important for QTM in all single-molecule magnets.

The Equation of State of Neutron Star Matter in Strong Magnetic Fields

International Nuclear Information System (INIS)

Broderick, A.; Prakash, M.; Lattimer, J. M.

2000-01-01

We study the effects of very strong magnetic fields on the equation of state (EOS) in multicomponent, interacting matter by developing a covariant description for the inclusion of the anomalous magnetic moments of nucleons. For the description of neutron star matter, we employ a field-theoretical approach, which permits the study of several models that differ in their behavior at high density. Effects of Landau quantization in ultrastrong magnetic fields (B>10 14 G) lead to a reduction in the electron chemical potential and a substantial increase in the proton fraction. We find the generic result for B>10 18 G that the softening of the EOS caused by Landau quantization is overwhelmed by stiffening due to the incorporation of the anomalous magnetic moments of the nucleons. In addition, the neutrons become completely spin polarized. The inclusion of ultrastrong magnetic fields leads to a dramatic increase in the proton fraction, with consequences for the direct Urca process and neutron star cooling. The magnetization of the matter never appears to become very large, as the value of |H/B| never deviates from unity by more than a few percent. Our findings have implications for the structure of neutron stars in the presence of large frozen-in magnetic fields. (c) 2000 The American Astronomical Society

The Equation of State of Neutron Star Matter in Strong Magnetic Fields

Energy Technology Data Exchange (ETDEWEB)

Broderick, A; Prakash, M; Lattimer, J M

2000-07-01

We study the effects of very strong magnetic fields on the equation of state (EOS) in multicomponent, interacting matter by developing a covariant description for the inclusion of the anomalous magnetic moments of nucleons. For the description of neutron star matter, we employ a field-theoretical approach, which permits the study of several models that differ in their behavior at high density. Effects of Landau quantization in ultrastrong magnetic fields (B>10{sup 14} G) lead to a reduction in the electron chemical potential and a substantial increase in the proton fraction. We find the generic result for B>10{sup 18} G that the softening of the EOS caused by Landau quantization is overwhelmed by stiffening due to the incorporation of the anomalous magnetic moments of the nucleons. In addition, the neutrons become completely spin polarized. The inclusion of ultrastrong magnetic fields leads to a dramatic increase in the proton fraction, with consequences for the direct Urca process and neutron star cooling. The magnetization of the matter never appears to become very large, as the value of |H/B| never deviates from unity by more than a few percent. Our findings have implications for the structure of neutron stars in the presence of large frozen-in magnetic fields. (c) 2000 The American Astronomical Society.

On the reversal of the dipolar field of the sun and its possible implication for the reversal of the earth's field

International Nuclear Information System (INIS)

Saito, T.; Akasofu, S.

1987-01-01

Changes of the neutral line on the source surface (analogous to the magnetic dip equator of the earth) during the period between 1976 and 1983 are examined on the basis of the Stanford solar magnetic field data. Instead of the standard Mercator-like projection, the neutral line is shown on a spherical surface for 16 selected Carrington rotations. In spite of great complexity of the field variations, this presentation depicts clearly a fairly systematic rotational reversal of the dipolar field on the source surface during the sunspot maximum years. It is suggested that this solar situation is somewhat analogous to the planet earth in the sense that the core surface and the earth's surface may correspond to the photosphere and the source surface, respectively. Copyright American Geophysical Union 1987

Absence of magnetic ordering and field-induced phase diagram in the gadolinium aluminum garnet

Science.gov (United States)

Florea, O.; Lhotel, E.; Jacobsen, H.; Knee, C. S.; Deen, P. P.

2017-12-01

The robustness of spin liquids with respect to small perturbations, and the way magnetic frustration can be lifted by slight changes in the balance between competing magnetic interactions, remains a rich and open issue. We address this question through the study of the gadolinium aluminum garnet Gd3Al5O12 , a related compound to the extensively studied Gd3Ga5O12 . We report on its magnetic properties at very low temperatures. We show that despite a freezing at about 300 mK, no magnetic transition is observed, suggesting the presence of a spin-liquid state down to the lowest temperatures, similarly to Gd3Ga5O12 , in spite of a larger ratio between exchange and dipolar interactions. Finally, the phase diagram as a function of field and temperature is strongly reminiscent of the one reported in Gd3Ga5O12 . This study reveals the robust nature of the spin-liquid phase for Gd ions on the garnet lattice, in stark contrast to Gd ions on the pyrochlore lattice for which a slight perturbation drives the compound into a range of magnetically ordered states.

Quark-gluon plasma in strong magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Kalaydzhyan, Tigran

2013-04-15

One of the fundamental problems in subatomic physics is the determination of properties of matter at extreme temperatures, densities and electromagnetic fields. The modern ultrarelativistic heavy-ion experiments are able to study such states (the quark-gluon plasma) and indicate that the physics at extreme conditions differs drastically from what is known from the conventional observations. Also the theoretical methods developed mostly within the perturbative framework face various conceptual problems and need to be replaced by a nonperturbative approach. In this thesis we study the physics of the strongly-coupled quark-gluon plasma in external magnetic fields as well as general electromagnetic and topological properties of the QCD and QCD-like systems. We develop and apply various nonperturbative techniques, based on e.g. gauge-gravity correspondence, lattice QCD simulations, relativistic hydrodynamics and condensed-matter-inspired models.

Quark-gluon plasma in strong magnetic fields

International Nuclear Information System (INIS)

Kalaydzhyan, Tigran

2013-04-01

One of the fundamental problems in subatomic physics is the determination of properties of matter at extreme temperatures, densities and electromagnetic fields. The modern ultrarelativistic heavy-ion experiments are able to study such states (the quark-gluon plasma) and indicate that the physics at extreme conditions differs drastically from what is known from the conventional observations. Also the theoretical methods developed mostly within the perturbative framework face various conceptual problems and need to be replaced by a nonperturbative approach. In this thesis we study the physics of the strongly-coupled quark-gluon plasma in external magnetic fields as well as general electromagnetic and topological properties of the QCD and QCD-like systems. We develop and apply various nonperturbative techniques, based on e.g. gauge-gravity correspondence, lattice QCD simulations, relativistic hydrodynamics and condensed-matter-inspired models.

Magnetic dipolar ordering and hysteresis of geometrically defined nanoparticle clusters

DEFF Research Database (Denmark)

Kure, Mathias; Beleggia, Marco; Frandsen, Cathrine

2017-01-01

Magnetic nanoparticle clusters have several biomedical and engineering applications, and revealing the basic interplay between particle configuration and magnetic properties is important for tuning the clusters for specific uses. Here, we consider the nanoparticles as macrospins and use computer...... of the polyhedra, the central moment relaxes along one of the principal axes and induces partial alignment of the surrounding moments. The resulting net moment is up to nearly four times that of the single moment added. Furthermore, we model quasi-static hysteresis loops for structures with and without a central...

Micromagnetics of antiskyrmions in ultrathin films

Science.gov (United States)

Camosi, Lorenzo; Rougemaille, Nicolas; Fruchart, Olivier; Vogel, Jan; Rohart, Stanislas

2018-04-01

We present a combined analytical and numerical micromagnetic study of the equilibrium energy, size, and shape of antiskyrmionic magnetic configurations. Antiskyrmions can be stabilized when the Dzyaloshinskii-Moriya interaction has opposite signs along two orthogonal in-plane directions, breaking the magnetic circular symmetry. We compare the equilibrium energy, size, and shape of antiskyrmions and skyrmions that are stabilized in environments with anisotropic and isotropic Dzyaloshinskii-Moriya interactions, respectively, but with the same strength of the magnetic interactions. When the dipolar interactions are neglected, the skyrmion and the antiskyrmion have the same energy, shape, and size in their respective environments. However, when dipolar interactions are considered, the energy of the antiskyrmion is strongly reduced, and its equilibrium size increases with respect to that of the skyrmion. While the skyrmion configuration shows homochiral Néel magnetization rotations, antiskyrmions show partly Néel and partly Bloch rotations. The latter do not produce magnetic charges and thus cost less dipolar energy. Both magnetic configurations are stable when the magnetic energies almost cancel each other, which means that a small variation of one parameter can drastically change their configurations, sizes, and energies.

Buoyant convection during Czochralski silicon growth with a strong, non-uniform, axisymmetric magnetic field

Science.gov (United States)

Khine, Y. Y.; Walker, J. S.

1995-02-01

This paper treats the buoyant convection during the Czochralski growth of silicon crystals with a steady, strong, non-uniform, axisymmetric magnetic field. We consider a family of magnetic fields which includes a uniform axial magnetic field and a "cusp" field which is produced by identical solenoids placed symmetrically above and below the plane of the crystal-melt interface and free surface. We investigate the evolution of the buoyant convection as the magnetic field is changed continuously from a uniform axial field to a cusp field, with a constant value of the root-mean-squared magnetic flux density in the melt. We also investigate changes as the magnetic flux density is increased. While the cusp field appears very promising, perfect alignment between the local magnetic field vector and the crystal-melt interface or free surface is not possible, so the effects of a slight misalignment are also investigated.

Properties of color-flavor locked strange quark matter in an external strong magnetic field

Institute of Scientific and Technical Information of China (English)

崔帅帅; 彭光雄; 陆振烟; 彭程; 徐建峰

2015-01-01

The properties of color-flavor locked strange quark matter in an external strong magnetic field are investigated in a quark model with density-dependent quark masses. Parameters are determined by stability arguments. It is found that the minimum energy per baryon of the color-flavor locked (MCFL) matter decreases with increasing magnetic-field strength in a certain range, which makes MCFL matter more stable than other phases within a proper magnitude of the external magnetic field. However, if the energy of the field itself is added, the total energy per baryon will increase.

Generation of strong pulsed magnetic fields using a compact, short pulse generator

Science.gov (United States)

Yanuka, D.; Efimov, S.; Nitishinskiy, M.; Rososhek, A.; Krasik, Ya. E.

2016-04-01

The generation of strong magnetic fields (˜50 T) using single- or multi-turn coils immersed in water was studied. A pulse generator with stored energy of ˜3.6 kJ, discharge current amplitude of ˜220 kA, and rise time of ˜1.5 μs was used in these experiments. Using the advantage of water that it has a large Verdet constant, the magnetic field was measured using the non-disturbing method of Faraday rotation of a polarized collimated laser beam. This approach does not require the use of magnetic probes, which are sensitive to electromagnetic noise and damaged in each shot. It also avoids the possible formation of plasma by either a flashover along the conductor or gas breakdown inside the coil caused by an induced electric field. In addition, it was shown that this approach can be used successfully to investigate the interesting phenomenon of magnetic field enhanced diffusion into a conductor.

Charged Tori in Spherical Gravitational and Dipolar Magnetic Fields

Czech Academy of Sciences Publication Activity Database

Slaný, P.; Kovář, J.; Stuchlík, Z.; Karas, Vladimír

2013-01-01

Roč. 205, č. 1 (2013), 3/1-3/16 ISSN 0067-0049 R&D Projects: GA ČR(CZ) GC13-00070J Institutional support: RVO:67985815 Keywords : accretion * accretion disks * magnetic fields Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 14.137, year: 2013

An encodable lanthanide binding tag with reduced size and flexibility for measuring residual dipolar couplings and pseudocontact shifts in large proteins

Energy Technology Data Exchange (ETDEWEB)

Barb, Adam W., E-mail: abarb@iastate.edu; Subedi, Ganesh P. [Iowa State University, Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology (United States)

2016-01-15

Metal ions serve important roles in structural biology applications from long-range perturbations seen in magnetic resonance experiments to electron-dense signatures in X-ray crystallography data; however, the metal ion must be secured in a molecular framework to achieve the maximum benefit. Polypeptide-based lanthanide-binding tags (LBTs) represent one option that can be directly encoded within a recombinant protein expression construct. However, LBTs often exhibit significant mobility relative to the target molecule. Here we report the characterization of improved LBTs sequences for insertion into a protein loop. These LBTs were inserted to connect two parallel alpha helices of an immunoglobulin G (IgG)-binding Z domain platform. Variants A and B bound Tb{sup 3+} with high affinity (0.70 and 0.13 μM, respectively) and displayed restricted LBT motion. Compared to the parent construct, the metal-bound A experienced a 2.5-fold reduction in tag motion as measured by magnetic field-induced residual dipolar couplings and was further studied in a 72.2 kDa complex with the human IgG1 fragment crystallizable (IgG1 Fc) glycoprotein. The appearance of both pseudo-contact shifts (−0.221 to 0.081 ppm) and residual dipolar couplings (−7.6 to 14.3 Hz) of IgG1 Fc resonances in the IgG1 Fc:(variant A:Tb{sup 3+}){sub 2} complex indicated structural restriction of the LBT with respect to the Fc. These studies highlight the applicability of improved LBT sequences with reduced mobility to probe the structure of macromolecular systems.

An encodable lanthanide binding tag with reduced size and flexibility for measuring residual dipolar couplings and pseudocontact shifts in large proteins

International Nuclear Information System (INIS)

Barb, Adam W.; Subedi, Ganesh P.

2016-01-01

Metal ions serve important roles in structural biology applications from long-range perturbations seen in magnetic resonance experiments to electron-dense signatures in X-ray crystallography data; however, the metal ion must be secured in a molecular framework to achieve the maximum benefit. Polypeptide-based lanthanide-binding tags (LBTs) represent one option that can be directly encoded within a recombinant protein expression construct. However, LBTs often exhibit significant mobility relative to the target molecule. Here we report the characterization of improved LBTs sequences for insertion into a protein loop. These LBTs were inserted to connect two parallel alpha helices of an immunoglobulin G (IgG)-binding Z domain platform. Variants A and B bound Tb 3+ with high affinity (0.70 and 0.13 μM, respectively) and displayed restricted LBT motion. Compared to the parent construct, the metal-bound A experienced a 2.5-fold reduction in tag motion as measured by magnetic field-induced residual dipolar couplings and was further studied in a 72.2 kDa complex with the human IgG1 fragment crystallizable (IgG1 Fc) glycoprotein. The appearance of both pseudo-contact shifts (−0.221 to 0.081 ppm) and residual dipolar couplings (−7.6 to 14.3 Hz) of IgG1 Fc resonances in the IgG1 Fc:(variant A:Tb 3+ ) 2 complex indicated structural restriction of the LBT with respect to the Fc. These studies highlight the applicability of improved LBT sequences with reduced mobility to probe the structure of macromolecular systems

Polarized neutron reflectivity from monolayers of self-assembled magnetic nanoparticles.

Science.gov (United States)

Mishra, D; Petracic, O; Devishvili, A; Theis-Bröhl, K; Toperverg, B P; Zabel, H

2015-04-10

We prepared monolayers of iron oxide nanoparticles via self-assembly on a bare silicon wafer and on a vanadium film sputter deposited onto a plane sapphire substrate. The magnetic configuration of nanoparticles in such a dense assembly was investigated by polarized neutron reflectivity. A theoretical model fit shows that the magnetic moments of nanoparticles form quasi domain-like configurations at remanence. This is attributed to the dipolar coupling amongst the nanoparticles.

Quantum magnetism in strongly interacting one-dimensional spinor Bose systems

DEFF Research Database (Denmark)

Salami Dehkharghani, Amin; Volosniev, A. G.; Lindgren, E. J.

2015-01-01

-range inter-species interactions much larger than their intra-species interactions and show that they have novel energetic and magnetic properties. In the strongly interacting regime, these systems have energies that are fractions of the basic harmonic oscillator trap quantum and have spatially separated......Strongly interacting one-dimensional quantum systems often behave in a manner that is distinctly different from their higher-dimensional counterparts. When a particle attempts to move in a one-dimensional environment it will unavoidably have to interact and 'push' other particles in order...... ground states with manifestly ferromagnetic wave functions. Furthermore, we predict excited states that have perfect antiferromagnetic ordering. This holds for both balanced and imbalanced systems, and we show that it is a generic feature as one crosses from few- to many-body systems....

Multicomponent synthesis of spiropyrrolidine analogues derived from vinylindole/indazole by a 1,3-dipolar cycloaddition reaction

Directory of Open Access Journals (Sweden)

Manjunatha Narayanarao

2016-12-01

Full Text Available A new series of spiropyrrolidine compounds containing indole/indazole moieties as side chains have been accomplished via a one-pot multicomponent synthesis. The method uses the 1,3-dipolar cycloaddition reaction between N-alkylvinylindole/indazole and azomethine ylides, prepared in situ from cyclic/acyclic amino acids. The 1,3-dipolar cycloaddition proceeds efficiently under thermal conditions to afford the regio- and stereospecific cyclic adducts.

Strong exchange and magnetic blocking in N₂³⁻-radical-bridged lanthanide complexes.

Science.gov (United States)

Rinehart, Jeffrey D; Fang, Ming; Evans, William J; Long, Jeffrey R

2011-05-22

Single-molecule magnets approach the ultimate size limit for spin-based devices. These complexes can retain spin information over long periods of time at low temperature, suggesting possible applications in high-density information storage, quantum computing and spintronics. Notably, the success of most such applications hinges upon raising the inherent molecular spin-inversion barrier. Although recent advances have shown the viability of lanthanide-containing complexes in generating large barriers, weak or non-existent magnetic exchange coupling allows fast relaxation pathways that mitigate the full potential of these species. Here, we show that the diffuse spin of an N(2)(3-) radical bridge can lead to exceptionally strong magnetic exchange in dinuclear Ln(III) (Ln = Gd, Dy) complexes. The Gd(III) congener exhibits the strongest magnetic coupling yet observed for that ion, while incorporation of the high-anisotropy Dy(III) ion gives rise to a molecule with a record magnetic blocking temperature of 8.3 K at a sweep rate of 0.08 T s(-1).

Effect of horizontal strong static magnetic field on swimming behaviour of Paramecium caudatum

Science.gov (United States)

Fujiwara, Yoshihisa; Tomishige, Masahiko; Itoh, Yasuhiro; Fujiwara, Masao; Shibata, Naho; Kosaka, Toshikazu; Hosoya, Hiroshi; Tanimoto, Yoshifumi

2006-05-01

Effect of horizontal strong static magnetic field on swimming behaviour of Paramecium caudatum was studied by using a superconducting magnet. Around a centre of a round vessel, random swimming at 0 T and aligned swimming parallel to the magnetic field (MF) of 8 T were observed. Near a wall of the vessel, however, swimming round and round along the wall at 0 T and aligned swimming of turning at right angles upon collision with the wall, which was remarkable around 1-4 T, were detected. It was experimentally revealed that the former MF-induced parallel swimming at the vessel centre was caused physicochemically by the parallel magnetic orientation of the cell itself. From magnetic field dependence of the extent of the orientation, the magnetic susceptibility anisotropy (χ ∥-χ ⊥) was first obtained to be 3.4× 10-23 emu cell-1 at 298 K for Paramecium caudatum. The orientation of the cell was considered to result from the magnetic orientation of the cell membrane. On the other hand, although mechanisms of the latter swimming near the vessel wall regardless of the absence and presence of the magnetic field are unclear at present, these experimental results indicate that whether the cell exists near the wall alters the magnetic field effect on the swimming in the horizontal magnetic field.

Semicalssical quantization of interacting anyons in a strong magnetic field

International Nuclear Information System (INIS)

Levit, S.; Sivan, N.

1992-01-01

We represent a semiclassical theory of charged interacting anyons in strong magnetic fields. We apply this theory to a number of few anyons systems including two interacting anyons in the presence of an impurity and three interacting anyons. We discuss the dependence of their energy levels on the statistical parameter and find regions in which this dependence follows very different patterns. The semiclassical arguments allow to correlate these patterns with the change in the character of the classical motion of the system. (author)

Can a Hexapole magnet of an ECR Ion Source be too strong?

CERN Document Server

Drentje, A G; Kremers, H R; Meyer, D; Mulder, J; Sijbring, J

1999-01-01

Experience of many ECRIS designers and users during more than a decade has given a few experimental rules, or "scaling laws". Many of these have been discussed at the ECRIS workshops. After the 1993 workshop it was concluded that the properties of the magnetic trap, in particular the strength of the radial component, determine to a great deal the confinement characteristics. For that reason it was decided at the KVI to choose a very strong magnet for the new 14 GHz ECRIS4 to be used in the Atomic Physics experiments. The hexapole magnet designed by the Giessen group is a good example. The induction, measured 2.5 mm inside the pole tips (i.e. at the wall of the plasma chamber) amounts more than 1.2 T. The measured radial field component Br obeys closely the expression Br= 0.00136 r2. (with B in T, r in mm). The quality of the magnetic trap can be given by the "radial mirror ratio", which is usually defined as R = Bmax / Breson, with Breson equal 0.5 T for a 14 GHz ECRIS. For the KVI magnet this would give R= 2...

Theory of a four-electron 2-D system in a strong magnetic field

International Nuclear Information System (INIS)

Yuandong Dai; Bingjian Ni; Fusui Liu.

1985-10-01

An orthogonal and complete set for relative motion of four-electron 2-D system in strong magnetic field is given, the energy of ground state of relative motion is calculated. This paper also calculates the energy of ground state whose maximum of single electron angular momentum is limited by the degeneracy under a given magnetic field, obtains the energy minimums corresponding to a fractional quantized Hall effect of 2/5, 2/7, and from it the physical meaning of 'magic number' is interpreted. (author)

Chemical spots on the surface of the strongly magnetic Herbig Ae star HD 101412

DEFF Research Database (Denmark)

Järvinen, S. P.; Hubrig, S.; Schöller, M.

2016-01-01

Due to the knowledge of the rotation period and the presence of a rather strong surface magnetic field, the sharp-lined young Herbig Ae star HD 101412 with a rotation period of 42 d has become one of the most well-studied targets among the Herbig Ae stars. High-resolution HARPS polarimetric spectra...... that is opposite to the behaviour of the other elements studied. Since classical Ap stars usually show a relationship between the magnetic field geometry and the distribution of element spots, we used in our magnetic field measurements different line samples belonging to the three elements with the most numerous...

Off-specular polarized neutron reflectometry study of magnetic dots with a strong shape anisotropy

CERN Document Server

Temst, K; Moshchalkov, V V; Bruynseraede, Y; Fritzsche, H; Jonckheere, R

2002-01-01

We have measured the off-specular polarized neutron reflectivity of a regular array of rectangular magnetic polycrystalline Co dots, which were prepared by a combination of electron-beam lithography, molecular beam deposition, and lift-off processes. The dots have a length-to-width ratio of 4:1 imposing a strong shape anisotropy. The intensity of the off-specular satellite reflection was monitored as a function of the magnetic field applied parallel to the rows of dots and in the plane of the sample, allowing us to analyze the magnetization-reversal process using the four spin-polarized cross sections. (orig.)

DIPOLE COLLAPSE AND DYNAMO WAVES IN GLOBAL DIRECT NUMERICAL SIMULATIONS

Energy Technology Data Exchange (ETDEWEB)

Schrinner, Martin; Dormy, Emmanuel [MAG (ENS/IPGP), LRA, Ecole Normale Superieure, 24 Rue Lhomond, 75252 Paris Cedex 05 (France); Petitdemange, Ludovic, E-mail: martin@schrinner.eu [Previously at Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany. (Germany)

2012-06-20

Magnetic fields of low-mass stars and planets are thought to originate from self-excited dynamo action in their convective interiors. Observations reveal a variety of field topologies ranging from large-scale, axial dipoles to more structured magnetic fields. In this article, we investigate more than 70 three-dimensional, self-consistent dynamo models in the Boussinesq approximation obtained by direct numerical simulations. The control parameters, the aspect ratio, and the mechanical boundary conditions have been varied to build up this sample of models. Both strongly dipolar and multipolar models have been obtained. We show that these dynamo regimes in general can be distinguished by the ratio of a typical convective length scale to the Rossby radius. Models with a predominantly dipolar magnetic field were obtained, if the convective length scale is at least an order of magnitude larger than the Rossby radius. Moreover, we highlight the role of the strong shear associated with the geostrophic zonal flow for models with stress-free boundary conditions. In this case the above transition disappears and is replaced by a region of bistability for which dipolar and multipolar dynamos coexist. We interpret our results in terms of dynamo eigenmodes using the so-called test-field method. We can thus show that models in the dipolar regime are characterized by an isolated 'single mode'. Competing overtones become significant as the boundary to multipolar dynamos is approached. We discuss how these findings relate to previous models and to observations.

Spin Diffusion and Spin Lattice Relaxation of Dipolar Order in Solids Containing Paramagnetic Impurities

International Nuclear Information System (INIS)

Furman, G.B.; Panich, A.M.; Goren, S.D.

1998-01-01

The phenomena of spin diffusion and spin lattice relaxation of nuclear dipolar order in solids containing paramagnetic impurities (PI) is considered. We show that at the beginning of the relaxation process the diffusion vanishing regime realizes with non-exponential time dependence, R(t) ∼ exp [- (t/T 1d ) α ], where T 1d ∼ C p -1/α , C p is PI's concentration. For a homogeneous distribution of Pis and nuclear spins, α=Q/6, where Q is the sample dimensionality; for an inhomogeneous distribution, the sample is divided into q-dimensional subsystems, each containing one PI, yield- ing α= (Q + q) /6. This result coincides with experimental data for CaF 2 doped with 0.8 - 10 -3 ωt % of Mn 2+ , where the non-exponential decay of the dipolar signal with α= 0.83 has been observed [3]. Fitting the experimental data yields a good agreement with T 1d = 66 ms . For another independent check of the obtained results we use dependence of the relaxation time on impurities concentration. In accordance that 1/α=1.2 , we have T 1d ∼ C p -1 '. 2 . Exactly this dependence on impurity concentration of the relaxation time has been found in the experiment. Then the relaxation regime starts as a non-exponential time dependent, proceed asymptotically to an to an exponential function of time, to so called diffusion limited relaxation regime with relaxation time T 1d D is inversely depends on impurities concentration. This kind of relaxation behavior of the dipolar order takes place in the experiment [2]. Using experimental results [2] from this two regime we can estimate the diffusion coefficient of the nuclear dipolar order in CaF 2 , which gives for typical values of impurity concentration C p ∼ 10 18 cm 3 the diffusion coefficient of dipolar order in the interval D ∼ 10 -11 -i- 10 -12 cm 2 /sec which is coincide to the case of Zeeman energy spin diffusion

Working with MRI: An investigation of occupational exposure to strong static magnetic fields and associated symptoms

NARCIS (Netherlands)

Schaap, K.

2015-01-01

Magnetic resonance imaging (MRI) makes use of electromagnetic fields in the non-ionizing radiation frequency ranges. One of them is a continuously present strong static magnetic field (SMF), which extends up to several meters around the scanner. Each time an MRI worker performs tasks near the

Design, construction and test of a corrector coil set for magnetic field homogenization of a dipolar magnet

International Nuclear Information System (INIS)

Pires, L.R.

1987-01-01

A method to improve the homogeneity of the distribution of the magnetic flux density in the gap of a dipole magnet. It is based on correcting the magnetic field by means of a system of coils, which employs etching thin copper foils, similarly as those for electronic circuits, is presented. The advantage of this method lies on its simplicity, its small space use, and its low price. The method was applied to correct the field of a dipole magnet, and it worked properly. (author) [pt

Development and characterization of a multi-layer magnetorheological elastomer isolator based on a Halbach array

Science.gov (United States)

Przybylski, Michal; Sun, Shuaishuai; Li, Weihua

2016-10-01

Most existing vibration isolators and dampers based on magnetorheological (MR) materials need electrical power to feed magnetic coils to stimulate the MR material, so if there is a loss of power, such as during a strong earthquake or system failure, they are unable to protect the structure. This paper outlines the design and test of a controllable multilayered magnetorheological elastomer (MRE) isolator based on a circular dipolar Halbach array; which is a set of magnets that generates a strong and uniform magnetic field. Combining an MRE layered isolator system with the Halbach array allows for constant vibration isolation with very low power consumption, where the power generated is only used to adjust the Halbach position. When this system was tested it successfully altered the lateral stiffness and damping force by 81.13% and 148.72%, respectively. This paper also includes an extended analysis of the magnetic field generated by the circular dipolar Halbach array and a discussion of the improvements that may potentially improve the range of magnetic fields generated.

Strong magnetic fields, galaxy formation, and the Galactic engine

International Nuclear Information System (INIS)

Greyber, H.D.

1989-01-01

The strong-magnetic-field model proposed as an energy source for AGN and quasars by Greyber (1961, 1962, 1964, 1967, 1984, 1988, and 1989) is discussed. The basic principles of the model are reviewed; its advantages (in explaining the observed features of AGN and quasars) over models based on a rotating accretion disk are indicated in a table; and its implications for galaxy and quasar formation are explored. The gravitationally bound current loops detected in nearby spiral galaxies are interpreted as weak remnants of the current loops present during their formation. An observational search for a similar loop near the Galactic center is proposed. 27 refs

Non-equilibrium magnetic properties of Sm0.43Ca0.57MnO3 nanoparticles

International Nuclear Information System (INIS)

Markovich, V.; Dolgin, B.; Puzniak, R.; Wisniewski, A.; Fita, I.; Mogilyansky, D.; Dvir, E.; Gorodetsky, G.; Jung, G.

2014-01-01

Highlights: • SCMO nanoparticles (15–60 nm) were prepared by glycine–nitrate method. • The charge ordering is progressively suppressed with decreasing particle size. • The dynamic properties of SCMO nanoparticles was studied. • Super spin glass state in 15 nm particles stems from dipole–dipole interactions. - Abstract: Non-equilibrium magnetic properties of the near half-doped Sm 0.43 Ca 0.57 MnO 3 nanoparticles with an average size as small as 15 nm have been investigated by measuring temperature dependence of zero field cooled (ZFC) magnetization, ac-susceptibility, time dependence of ZFC magnetization, relaxation of the remanent magnetization, and memory effects in ZFC magnetization. For the studied particles, charge ordering, characteristic for the bulk, is gradually suppressed with decreasing particle size and fully disappears in 15 nm particles, while the Néel temperature decreases slightly from 73 K for 60 nm to 58 K for 15 nm particles. It was found that dipolar interaction between 15 nm nanoparticles is enough to leads to the formation of a superspin glass state. Characteristic features of superspin glass state, such as aging and memory effects have been observed in 15 nm samples. In a difference to atomic spin glasses, no strong rejuvenation of magnetization has been observed at low temperatures

Residual dipolar couplings in sup 3 sup 1 P MAS spectra of PPh sub 3 substituted cobalt complexes

CERN Document Server

Szalontai, G

2002-01-01

Residual dipolar couplings between sup 3 sup 1 P- sup 5 sup 9 Co spin pairs were studied in sup 3 sup 1 P MAS spectra of mono- and dinuclear cobalt-triphenylphosphine complexes. These spectra can provide important information such as the scalar coupling between the dipolar phosphorus and the quadrupolar cobalt nuclei normally not available from solution phase studies. In case of complementary (NQR or x-ray) data even the relative orientation of the interacting shielding, dipolar, scalar couplings, and electric field gradient tensors or internuclear distances can be determined. Examples are shown both for well resolved and practically unresolved cases, factors which possibly control the spectral resolution are discussed in detail. (author)

A kinetic study of 1,3-dipolar cycloadditions in micellar media

NARCIS (Netherlands)

Rispens, T; Engberts, JBFN

2003-01-01

The kinetics of the 1,3-dipolar cycloadditions (DC) of benzonitrile oxide with a series of N-substituted maleimides in micellar media have been investigated. Surfactants studied include anionic sodium dodecyl sulfate, cationic cetyltrimethylammonium bromide, and a series of nonionic alkyl

Statistical Plasma Physics in a Strong Magnetic Field: Paradigms and Problems

Energy Technology Data Exchange (ETDEWEB)

J.A. Krommes

2004-03-19

An overview is given of certain aspects of fundamental statistical theories as applied to strongly magnetized plasmas. Emphasis is given to the gyrokinetic formalism, the historical development of realizable Markovian closures, and recent results in the statistical theory of turbulent generation of long-wavelength flows that generalize and provide further physical insight to classic calculations of eddy viscosity. A Hamiltonian formulation of turbulent flow generation is described and argued to be very useful.

Diazo Compounds as Highly Tunable Reactants in 1,3-Dipolar Cycloaddition Reactions with Cycloalkynes†

Science.gov (United States)

McGrath, Nicholas A.

2012-01-01

Diazo compounds, which can be accessed directly from azides by deimidogenation, are shown to be extremely versatile dipoles in 1,3-dipolar cycloaddition reactions with a cyclooctyne. The reactivity of a diazo compound can be much greater or much less than its azide analog, and is enhanced markedly in polar-protic solvents. These reactivities are predictable from frontier molecular orbital energies. The most reactive diazo compound exhibited the highest known second-order rate constant to date for a dipolar cycloaddition with a cycloalkyne. These data provide a new modality for effecting chemoselective reactions in a biological context. PMID:23227302

Dipolar and quadrupolar defects in a transport line

International Nuclear Information System (INIS)

Leleux, G.; Nghiem, P.

1991-01-01

The defects on a transport line of linear accelerator are studied. A transport line where the elements are influenced by the design or position defects is analyzed. Only dipolar and quadrupolar defects are considered, and the coupling betwen transversal motions are excluded. The data from the literature and those calculated by transfer matrices are compared. The defects on a line are considered from an analytical point of view. Closed optical structures are also studied [fr

Magnetic massive stars as progenitors of `heavy' stellar-mass black holes

Science.gov (United States)

Petit, V.; Keszthelyi, Z.; MacInnis, R.; Cohen, D. H.; Townsend, R. H. D.; Wade, G. A.; Thomas, S. L.; Owocki, S. P.; Puls, J.; ud-Doula, A.

2017-04-01

The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of 'heavy' stellar-mass BHs with masses >25 M⊙. Initial characterization of the system by Abbott et al. supposes that the formation of BHs with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z ≲ 0.25-0.5 Z⊙) environments. However, strong surface magnetic fields also provide a powerful mechanism for modifying mass-loss and rotation of massive stars, independent of environmental metallicity. In this paper, we explore the hypothesis that some heavy BHs, with masses >25 M⊙ such as those inferred to compose GW150914, could be the natural end-point of evolution of magnetic massive stars in a solar-metallicity environment. Using the MESA code, we developed a new grid of single, non-rotating, solar-metallicity evolutionary models for initial zero-age main sequence masses from 40 to 80 M⊙ that include, for the first time, the quenching of the mass-loss due to a realistic dipolar surface magnetic field. The new models predict terminal-age main-sequence (TAMS) masses that are significantly greater than those from equivalent non-magnetic models, reducing the total mass lost by a strongly magnetized 80 M⊙ star during its main-sequence evolution by 20 M⊙. This corresponds approximately to the mass-loss reduction expected from an environment with metallicity Z = 1/30 Z⊙.

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

International Nuclear Information System (INIS)

Fahmi, A.; Qachaou, A.

2009-01-01

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

Centrifugal pumping during Czochralski silicon growth with a strong, non-uniform, axisymmetric magnetic field

Science.gov (United States)

Khine, Y. Y.; Walker, J. S.

1996-08-01

Centrifugal pumping flows are produced in the melt by the rotations of crystal and crucible during the Czochralski growth of silicon crystals. This paper treats the centrifugal pumping effects with a steady, strong, non-uniform axisymmetric magnetic field. We consider a family of magnetic fields ranging from a uniform axial field to a "cusp" field, which has a purely radial field at the crystal-melt interface and free surface. We present the numerical solutions for the centrifugal pumping flows as the magnetic field is changed continuously from a uniform axial field to a cusp one, and for arbitrary Hartmann number. Since the perfect alignment between the local magnetic field vector and the crystal-melt interface or free surface is not likely, we also investigate the effects of a slight misalignment.

Spin polarization in high density quark matter under a strong external magnetic field

DEFF Research Database (Denmark)

Tsue, Yasuhiko; Da Providência, João; Providência, Constança

2016-01-01

In high density quark matter under a strong external magnetic field, possible phases are investigated by using the two-flavor Nambu-Jona-Lasinio (NJL) model with tensor-type four-point interaction between quarks, as well as the axial-vector-type four-point interaction. In the tensor-type interact...

Tris-o-phenylenedioxycyclotriphosphazene (TPP) Inclusion Compounds Containing a Dipolar Molecular Rotor

Czech Academy of Sciences Publication Activity Database

Kobr, L.; Zhao, K.; Shen, Y.; Shoemaker, R. K.; Rogers, C. T.; Michl, Josef

2014-01-01

Roč. 14, č. 2 (2014), s. 559-568 ISSN 1528-7483 EU Projects: European Commission(XE) 227756 - DIPOLAR ROTOR ARRAY Institutional support: RVO:61388963 Keywords : aromatic nanochannels * single-molecule * dynamics Subject RIV: CC - Organic Chemistry Impact factor: 4.891, year: 2014

Role of lower hybrid waves in ion heating at dipolarization fronts

Science.gov (United States)

Greco, A.; Artemyev, A.; Zimbardo, G.; Angelopoulos, V.; Runov, A.

2017-05-01

One of the important sources of hot ions in the magnetotail is the bursty bulk flows propagating away from the reconnection region and heating the ambient plasma. Charged particles interact with nonlinear magnetic field pulses (dipolarization fronts, DFs) embedded into these flows. The convection electric fields associated with DF propagation are known to reflect and accelerate ambient ions. Moreover, a wide range of waves is observed within/near these fronts, the electric field fluctuations being dominated by the lower hybrid drift (LHD) instability. Here we investigate the potential role of these waves in the further acceleration of ambient ions. We use a LHD wave emission profile superimposed on the leading edge of a two-dimensional model profile of a DF and a test particle approach. We show that LHD waves with realistic amplitudes can significantly increase the upper limit of energies gained by ions. Wave-particle interaction near the front is more effective in producing superthermal ions than in increasing the flux of thermal ions. Comparison of test particle simulations and Time History of Events and Macroscale Interactions during Substorms observations show that ion acceleration by LHD waves is more important for slower DFs.

Rapid characterization of superconducting wires and tapes in strong pulsed magnetic fields

International Nuclear Information System (INIS)

Bockstal, L. van; Keyser, A. de; Deschagt, J.; Hopkins, S.C.; Glowacki, B.A.

2007-01-01

A new measurement system for rapid characterization of superconducting wires and tapes is developed. The CryoPulse-BI is a system to provide a direct measurement of critical material parameters for superconducting materials when high long pulsed magnetic fields and strong currents are applied. In the experiments, synchronized magnetic fields up to 30 T and current pulses up to 5 kA are generated with adjustable timing. Varying the magnetic field strength, the current through the sample and the BI timing allows for a thorough characterization of the sample and the determination of critical currents. The rapid cycle time of the experiments yields a rapid and thorough determination of the critical parameters. The method has been tested on low T c as well as high T c materials with the field parallel or perpendicular to the current. The discussion covers the current state of the art including a comparison of our results to classical DC characterization measurements

Zero Sound in Neutron Stars with Dense Quark Matter under Strong Magnetic Fields

DEFF Research Database (Denmark)

Kouvaris, Christoforos

2009-01-01

We study a neutron star with a quark matter core under extremely strong magnetic fields. We investigate the possibility of an Urca process as a mechanism for the cooling of such a star. We found that apart from very particular cases, the Urca process cannot occur. We also study the stability...

4f and 5d magnetism in samarium

International Nuclear Information System (INIS)

Stunault, A.; Bernhoeft, N.; Vettier, C.; Dumesnil, K.; Dufour, C.

2001-01-01

We report on resonant magnetic X-ray scattering studies of a samarium epitaxial film at the samarium L 3 edge. We observe one quadrupolar resonance below the edge, reflecting the polarization of the 4f electrons, and two dipolar resonances above the edge, related to the polarization of the 5d band. We demonstrate, by following the thermal evolution of resonant magnetic intensities of both types, that the polarization of the 4f and 5d electrons present exactly the same temperature dependence, even very close to the ordering temperature, in agreement with the RKKY model for long-range magnetic order in rare earths

The thermodynamic spin magnetization of strongly correlated 2d electrons in a silicon inversion layer

OpenAIRE

Prus, O.; Yaish, Y.; Reznikov, M.; Sivan, U.; Pudalov, V.

2002-01-01

A novel method invented to measure the minute thermodynamic spin magnetization of dilute two dimensional fermions is applied to electrons in a silicon inversion layer. Interplay between the ferromagnetic interaction and disorder enhances the low temperature susceptibility up to 7.5 folds compared with the Pauli susceptibility of non-interacting electrons. The magnetization peaks in the vicinity of the density where transition to strong localization takes place. At the same density, the suscep...

Quantum Femtosecond Magnetism: Phase Transition in Step with Light in a Strongly Correlated Manganese Oxide

Science.gov (United States)

Wang, Jigang

2014-03-01

Research of non-equilibrium phase transitions of strongly correlated electrons is built around addressing an outstanding challenge: how to achieve ultrafast manipulation of competing magnetic/electronic phases and reveal thermodynamically hidden orders at highly non-thermal, femtosecond timescales? Recently we reveal a new paradigm called quantum femtosecond magnetism-photoinduced femtosecond magnetic phase transitions driven by quantum spin flip fluctuations correlated with laser-excited inter-atomic coherent bonding. We demonstrate an antiferromagnetic (AFM) to ferromagnetic (FM) switching during about 100 fs laser pulses in a colossal magneto-resistive manganese oxide. Our results show a huge photoinduced femtosecond spin generation, measured by magnetic circular dichroism, with photo-excitation threshold behavior absent in the picosecond dynamics. This reveals an initial quantum coherent regime of magnetism, while the optical polarization/coherence still interacts with the spins to initiate local FM correlations that compete with the surrounding AFM matrix. Our results thus provide a framework that explores quantum non-equilibrium kinetics to drive phase transitions between exotic ground states in strongly correlated elecrons, and raise fundamental questions regarding some accepted rules, such as free energy and adiabatic potential surface. This work is in collaboration with Tianqi Li, Aaron Patz, Leonidas Mouchliadis, Jiaqiang Yan, Thomas A. Lograsso, Ilias E. Perakis. This work was supported by the National Science Foundation (contract no. DMR-1055352). Material synthesis at the Ames Laboratory was supported by the US Department of Energy-Basic Energy Sciences (contract no. DE-AC02-7CH11358).

Exploring strain-promoted 1,3-dipolar cycloadditions of end functionalized polymers

NARCIS (Netherlands)

Ledin, Petr A; Kolishetti, Nagesh; Hudlikar, Manish S; Boons, Geert-Jan

2014-01-01

Strain-promoted 1,3-dipolar cycloaddition of cyclooctynes with 1,3-dipoles such as azides, nitrones, and nitrile oxides, are of interest for the functionalization of polymers. In this study, we have explored the use of a 4-dibenzocyclooctynol (DIBO)-containing chain transfer agent in reversible

Solid-state NMR detection of 14N-13C dipolar couplings between amino acid side groups provides constraints on amyloid fibril architecture.

Science.gov (United States)

Middleton, David A

2011-02-01

Solid-state nuclear magnetic resonance (SSNMR) is a powerful technique for the structural analysis of amyloid fibrils. With suitable isotope labelling patterns, SSNMR can provide constraints on the secondary structure, alignment and registration of β-strands within amyloid fibrils and identify the tertiary and quaternary contacts defining the packing of the β-sheet layers. Detection of (14)N-(13)C dipolar couplings may provide potentially useful additional structural constraints on β-sheet packing within amyloid fibrils but has not until now been exploited for this purpose. Here a frequency-selective, transfer of population in double resonance SSNMR experiment is used to detect a weak (14)N-(13)C dipolar coupling in amyloid-like fibrils of the peptide H(2)N-SNNFGAILSS-COOH, which was uniformly (13)C and (15)N labelled across the four C-terminal amino acids. The (14)N-(13)C interatomic distance between leucine and asparagine side groups is constrained between 2.4 and 3.8 Å, which allows current structural models of the β-spine arrangement within the fibrils to be refined. This procedure could be useful for the general structural analysis of other proteins in condensed phases and environments, such as biological membranes. Copyright © 2011 John Wiley & Sons, Ltd.

On the Gross–Pitaevskii equation for trapped dipolar quantum gases

KAUST Repository

Carles, Ré mi; Markowich, Peter A; Sparber, Christof

2008-01-01

We study the time-dependent Gross-Pitaevskii equation describing Bose-Einstein condensation of trapped dipolar quantum gases. Existence and uniqueness as well as the possible blow-up of solutions are studied. Moreover, we discuss the problem of dimension reduction for this nonlinear and nonlocal Schrödinger equation. © 2008 IOP Publishing Ltd and London Mathematical Society.

On the Gross–Pitaevskii equation for trapped dipolar quantum gases

KAUST Repository

Carles, Rémi

2008-09-29

We study the time-dependent Gross-Pitaevskii equation describing Bose-Einstein condensation of trapped dipolar quantum gases. Existence and uniqueness as well as the possible blow-up of solutions are studied. Moreover, we discuss the problem of dimension reduction for this nonlinear and nonlocal Schrödinger equation. © 2008 IOP Publishing Ltd and London Mathematical Society.

The mass limit of white dwarfs with strong magnetic fields in general relativity

International Nuclear Information System (INIS)

Wen De-Hua; Liu He-Lei; Zhang Xiang-Dong

2014-01-01

Recently, U. Das and B. Mukhopadhyay proposed that the Chandrasekhar limit of a white dwarf could reach a new high level (2.58M⊙) if a superstrong magnetic field were considered (Das U and Mukhopadhyay B 2013 Phys. Rev. Lett. 110 071102), where the structure of the strongly magnetized white dwarf (SMWD) is calculated in the framework of Newtonian theory (NT). As the SMWD has a far smaller size, in contrast with the usual expectation, we found that there is an obvious general relativistic effect (GRE) in the SMWD. For example, for the SMWD with a one Landau level system, the super-Chandrasekhar mass limit in general relativity (GR) is approximately 16.5% lower than that in NT. More interestingly, the maximal mass of the white dwarf will be first increased when the magnetic field strength keeps on increasing and reaches the maximal value M = 2.48M⊙ with B D = 391.5. Then if we further increase the magnetic fields, surprisingly, the maximal mass of the white dwarf will decrease when one takes the GRE into account. (geophysics, astronomy, and astrophysics)

Complete devil's staircase and crystal-superfluid transitions in a dipolar XXZ spin chain: a trapped ion quantum simulation

International Nuclear Information System (INIS)

Hauke, Philipp; Cucchietti, Fernando M; Lewenstein, Maciej; Mueller-Hermes, Alexander; Banuls, Mari-Carmen; Ignacio Cirac, J

2010-01-01

Systems with long-range interactions show a variety of intriguing properties: they typically accommodate many metastable states, they can give rise to spontaneous formation of supersolids, and they can lead to counterintuitive thermodynamic behavior. However, the increased complexity that comes with long-range interactions strongly hinders theoretical studies. This makes a quantum simulator for long-range models highly desirable. Here, we show that a chain of trapped ions can be used to quantum simulate a one-dimensional (1D) model of hard-core bosons with dipolar off-site interaction and tunneling, equivalent to a dipolar XXZ spin-1/2 chain. We explore the rich phase diagram of this model in detail, employing perturbative mean-field theory, exact diagonalization and quasi-exact numerical techniques (density-matrix renormalization group and infinite time-evolving block decimation). We find that the complete devil's staircase-an infinite sequence of crystal states existing at vanishing tunneling-spreads to a succession of lobes similar to the Mott lobes found in Bose-Hubbard models. Investigating the melting of these crystal states at increased tunneling, we do not find (contrary to similar 2D models) clear indications of supersolid behavior in the region around the melting transition. However, we find that inside the insulating lobes there are quasi-long-range (algebraic) correlations, as opposed to models with nearest-neighbor tunneling, that show exponential decay of correlations.

Improvement of hydrogen bond geometry in protein NMR structures by residual dipolar couplings - an assessment of the interrelation of NMR restraints

Energy Technology Data Exchange (ETDEWEB)

Jensen, Pernille Rose; Axelsen, Jacob Bock [University of Copenhagen, Institute of Molecular Biology (Denmark); Lerche, Mathilde Hauge [Amersham Health (Sweden); Poulsen, Flemming M. [University of Copenhagen, Institute of Molecular Biology (Denmark)], E-mail: fmp@apk.molbio.ku.dk

2004-01-15

We have examined how the hydrogen bond geometry in three different proteins is affected when structural restraints based on measurements of residual dipolar couplings are included in the structure calculations. The study shows, that including restraints based solely on {sup 1}H{sup N}-{sup 15}N residual dipolar couplings has pronounced impact on the backbone rmsd and Ramachandran plot but does not improve the hydrogen bond geometry. In the case of chymotrypsin inhibitor 2 the addition of {sup 13}CO-{sup 13}C{sup {alpha}} and {sup 15}N-{sup 13}CO one bond dipolar couplings as restraints in the structure calculations improved the hydrogen bond geometry to a quality comparable to that obtained in the 1.8 A resolution X-ray structure of this protein. A systematic restraint study was performed, in which four types of restraints, residual dipolar couplings, hydrogen bonds, TALOS angles and NOEs, were allowed in two states. This study revealed the importance of using several types of residual dipolar couplings to get good hydrogen bond geometry. The study also showed that using a small set of NOEs derived only from the amide protons, together with a full set of residual dipolar couplings resulted in structures of very high quality. When reducing the NOE set, it is mainly the side-chain to side-chain NOEs that are removed. Despite of this the effect on the side-chain packing is very small when a reduced NOE set is used, which implies that the over all fold of a protein structure is mainly determined by correct folding of the backbone.

Race for novel high-index all-dielectric and hybrid metal-dielectric nanophotonic materials: Pit-stop optical tests

Science.gov (United States)

Kudryashov, S. I.; Saraeva, I. N.; Ivanova, A. K.; Kudryavtseva, A. D.; Tchiernega, N. V.; Ionin, A. A.; Kuchmizhak, A. A.; Zayarny, D. A.

2017-09-01

Magnetic dipolar Mie-resonance of nanodiamonds supports their highly-efficient stimulated low-frequency Raman scattering via nanosecond laser excitation of their fundamental breathing mode, with strong additional plasmonic enhancement of the Raman conversion efficiency upon ablative capping of the resonant nanodiamond core by a silver nanoshell with a broad overlapping electrical dipolar Mie-resonance. Also, crystalline selenium nanoparticles, exhibiting the high refractive index in the visible/near-IR ranges, were demonstrated as promising all-dielectric sensing building nanoblocks in nanophotonics.

Temperature Variation of the Magnetic Structure of HoSb

DEFF Research Database (Denmark)

Andersen, Nils Axel; Kjems, Jørgen; Vogt, O.

1980-01-01

Neutron diffraction has been used to show that the magnetic moment vector in the antiferromagnet HoSb changes direction as a function of temperature below TN=5.7K. The experimental results are in qualitative agreement with a recent theoretical prediction by Jensen et al. (1980) which ascribe the ...... the changing directions to a competition between the crystal fields and the dipolar interactions....

Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe.

Science.gov (United States)

Parker, David S

2017-06-13

We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large T c value is unlikely.

Microwave Synthesis and Magnetic Properties of High Tc Superconductor MGB2

International Nuclear Information System (INIS)

Koeseoglu, Y.

2004-01-01

Polycrystalline powders of MgB 2 have been synthesized by microwave synthesis technique. Crystallographic information of the sample was investigated by powder X-ray diffraction (XRD). The main phase was determined as MgB2, and secondary phases as MgB4 and MgO. The temperature dependence of magnetic properties of polycrystalline MgB2, synthesized by using microwave heating of the constituents have been characterized by SQUID magnetometer and X-band EPR spectrometer. The transition temperature to the superconducting phase is observed as 39K for both measurements. An isotropic, strong and very narrow EPR signal corresponding to free electron g-value (ge=2.0023) is observed. The observed line broadening with decreasing temperature might arise from the dipolar interactions between the superparamagnetic nanoparticles. Normally, the internal magnetic field originating from magnetic entities is expected to be more uniform as a result of highly ordered magnetic moments at low temperatures; giving narrower ESR line in contrary in our case. While the ESR line is broadened, the signal intensity is drastically decreased just below T c =39 K corresponding to a transition temperature from normal to superconducting state. Some minor changes in both intensity and line width curves might be taken as signs for changes of local crystalline field symmetry around weakly localized conduction electrons or holes, which are the sources of ESR signal in MgB 2 compound

Two-dimensional discrete solitons in dipolar Bose-Einstein condensates

International Nuclear Information System (INIS)

Gligoric, Goran; Stepic, Milutin; Hadzievski, Ljupco; Maluckov, Aleksandra; Malomed, Boris A.

2010-01-01

We analyze the formation and dynamics of bright unstaggered solitons in the disk-shaped dipolar Bose-Einstein condensate, which features the interplay of contact (collisional) and long-range dipole-dipole (DD) interactions between atoms. The condensate is assumed to be trapped in a strong optical-lattice potential in the disk's plane, hence it may be approximated by a two-dimensional (2D) discrete model, which includes the on-site nonlinearity and cubic long-range (DD) interactions between sites of the lattice. We consider two such models, which differ by the form of the on-site nonlinearity, represented by the usual cubic term, or more accurate nonpolynomial one, derived from the underlying three-dimensional Gross-Pitaevskii equation. Similar results are obtained for both models. The analysis is focused on the effects of the DD interaction on fundamental localized modes in the lattice (2D discrete solitons). The repulsive isotropic DD nonlinearity extends the existence and stability regions of the fundamental solitons. New families of on-site, inter-site, and hybrid solitons, built on top of a finite background, are found as a result of the interplay of the isotropic repulsive DD interaction and attractive contact nonlinearity. By themselves, these solutions are unstable, but they evolve into robust breathers which exist on an oscillating background. In the presence of the repulsive contact interactions, fundamental localized modes exist if the DD interaction (attractive isotropic or anisotropic) is strong enough. They are stable in narrow regions close to the anticontinuum limit, while unstable solitons evolve into breathers. In the latter case, the presence of the background is immaterial.

Strongly correlated electron systems and neutron scattering. Magnetism, superconductivity, structural phase transition

Energy Technology Data Exchange (ETDEWEB)

Katano, Susumu [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1998-03-01

Neutron scattering experiments in our group on strongly correlated electron systems are reviewed Metal-insulator transitions caused by structural phase transitions in (La{sub 1-x}Sr{sub x}) MnO{sub 3}, a novel magnetic transition in the CeP compound, correlations between antiferromagnetism and superconductivity in UPd{sub 2}Al{sub 3} and so forth are discussed. Here, in this note, the phase transition of Mn-oxides was mainly described. (author)

Critical behaviour of nanocrystalline gadolinium: evidence for random uniaxial dipolar universality class

International Nuclear Information System (INIS)

Ferdinand, A; Probst, A-C; Birringer, R; Michels, A; Kaul, S N

2014-01-01

We report on how nanocrystal size affects the critical behaviour of the rare-earth metal Gd near the ferromagnetic-to-paramagnetic phase transition. The asymptotic critical behaviour of the coarse-grained polycrystalline sample (with an average crystallite size of L≅100 μm) is that of a (pure) uniaxial dipolar ferromagnet, as is the case with single crystal Gd, albeit the width of the asymptotic critical region (ACR) is reduced. As the grain size approaches ∼30 nm, the ACR is so narrow that it could not be accessed in the present experiments. Inaccessibly narrow ACR for L ∼ 30 nm and continuous increase in the width of the ACR as L decreases from 16 to 9.5 nm basically reflect a crossover to the random uniaxial dipolar fixed point caused by the quenched random exchange disorder prevalent at the internal interfaces (grain boundaries). (paper)

A search for strong, ordered magnetic fields in Herbig Ae/Be stars

Science.gov (United States)

Wade, G. A.; Bagnulo, S.; Drouin, D.; Landstreet, J. D.; Monin, D.

2007-04-01

The origin of magnetic fields in intermediate- and high-mass stars is fundamentally a mystery. Clues towards solving this basic astrophysical problem can likely be found at the pre-main-sequence (PMS) evolutionary stage. With this work, we perform the largest and most sensitive search for magnetic fields in PMS Herbig Ae/Be (HAeBe) stars. We seek to determine whether strong, ordered magnetic fields, similar to those of main-sequence Ap/Bp stars, can be detected in these objects, and if so, to determine the intensities, geometrical characteristics, and statistical incidence of such fields. 68 observations of 50 HAeBe stars have been obtained in circularly polarized light using the FORS1 spectropolarimeter at the ESO VLT. An analysis of both Balmer and metallic lines reveals the possible presence of weak longitudinal magnetic fields in photospheric lines of two HAeBe stars, HD 101412 and BF Ori. Results for two additional stars, CPD-53 295 and HD 36112, are suggestive of the presence of magnetic fields, but no firm conclusions can be drawn based on the available data. The intensity of the longitudinal fields detected in HD 101412 and BF Ori suggest that they correspond to globally ordered magnetic fields with surface intensities of order 1 kG. On the other hand, no magnetic field is detected in 4 other HAeBe stars in our sample in which magnetic fields had previously been confirmed. Monte Carlo simulations of the longitudinal field measurements of the undetected stars allow us to place an upper limit of about 300 G on the general presence of aligned magnetic dipole magnetic fields, and of about 500 G on perpendicular dipole fields. Taking into account the results of our survey and other published results, we find that the observed bulk incidence of magnetic HAeBe stars in our sample is 8-12 per cent, in good agreement with that of magnetic main-sequence stars of similar masses. We also find that the rms longitudinal field intensity of magnetically detected HAe

Scaling parallels in the non-Debye dielectric relaxation of ionic glasses and dipolar supercooled liquids

International Nuclear Information System (INIS)

Sidebottom, D.L.; Green, P.F.; Brow, R.K.

1997-01-01

We compare the dielectric response of ionic glasses and dipolar liquids near the glass transition. Our work is divided into two parts. In the first section we examine ionic glasses and the two prominent approaches to analyzing the dielectric response. The conductivity of ion-conducting glasses displays a power law dispersion σ(ω)∝ω n , where n∼0.67, but frequently the dielectric response is analyzed using the electrical modulus M * (ω)=1/var-epsilon * (ω), where var-epsilon * (ω)=var-epsilon(ω)-iσ(ω)/ω is the complex permittivity. We reexamine two specific examples where the shape of M * (ω) changes in response to changes in (a) temperature and (b) ion concentration, to suggest fundamental changes in ion dynamics are occurring. We show, however, that these changes in the shape of M * (ω) occur in the absence of changes in the scaling properties of σ(ω), for which n remains constant. In the second part, we examine the dielectric relaxation found in dipolar liquids, for which var-epsilon * (ω) likewise exhibits changes in shape on approach to the glass transition. Guided by similarities of M * (ω) in ionic glasses and var-epsilon * (ω) in dipolar liquids, we demonstrate that a recent scaling approach proposed by Dixon and co-workers for var-epsilon * (ω) of dipolar relaxation also appears valid for M * (ω) in the ionic case. While this suggests that the Dixon scaling approach is more universal than previously recognized, we demonstrate how the dielectric response can be scaled in a linear manner using an alternative data representation. copyright 1997 The American Physical Society

Regular and chaotic motion of two dimensional electrons in a strong magnetic field

International Nuclear Information System (INIS)

Bar-Lev, Oded; Levit, Shimon.

1992-05-01

For two dimensional system of electrons in a strong magnetic field a standard approximation is the projection on a single Landau level. The resulting Hamiltonian is commonly treated semiclassically. An important element in applying the semiclassical approximation is the integrability of the corresponding classical system. We discuss the relevant integrability conditions and give a simple example of a non-integrable system-two interacting electrons in the presence of two impurities-which exhibits a coexistence of regular and chaotic classical motions. Since the inverse of the magnetic field plays the role of the Planck constant in these problems, one has the opportunity to control the 'closeness' of chaotic physical systems to the classical limit. (author)

Wide aperture multipole magnets of the kinematic separator COMBAS. Correcting pair of multipole magnets M3M4 (M5M6) with compensation for higher order aberrations

International Nuclear Information System (INIS)

Artyukh, A.G.; Gridnev, G.F.; Teterev, Yu.G.

1999-01-01

The high-resolving large aperture separator COMBAS has been created and commissioned. The magneto-optical structure of the separator is based on the strong focusing principle. The separator consists of eight wide aperture multipole magnets M1-M8. The magnets M1, M2, M7, M8 forming the 1 st order optics together with some higher order optical corrections and M3-M6 being dedicated to higher order corrections of the chromatic and spherical aberrations at the intermediate and exit foci of the separator. The multipole correctors M3-M6 contain the dipolar, sextupole and octupole components in their magnetic field distributions. It was the use of the rectangular dipoles M3-M6 as carriers of sextupole and octupole field components that let achieve high values of the separator angular and momentum acceptances. Measurements of the magnetic field distributions in the median planes of the pairs of magnets M3M6 (M4M5) have been performed. These measurements allowed one to analyze the magnets manufacturing quality. Based on the analysis, shimming of pole pieces of the pair of magnets M3M6 have been done. Pole surface correcting coils for the magnets M4M5 have been foreseen to compensate for small deviations (within a few percents) of the 2 nd and 3 rd order field components from the design values, which are probable due to manufacturing errors in all the magnets M1-M8. The measured magnetic field distributions are supposed to be used for particle trajectory simulations throughout the entire separator

Magnetic nanoparticles in fluid environment: combining molecular dynamics and Lattice-Boltzmann

Energy Technology Data Exchange (ETDEWEB)

Melenev, Petr, E-mail: melenev@icmm.ru [Ural Federal University, 4, Turgeneva str., 620000 Ekaterinburg (Russian Federation); Institute of Continuous Media Mechanics, 1, Koroleva str., 614013 Perm (Russian Federation)

2017-06-01

Hydrodynamic interactions between magnetic nanoparticles suspended in the Newtonian liquid are accounted for using a combination of the lattice Boltzmann method and molecular dynamics simulations. Nanoparticle is modelled by the system of molecular dynamics material points (which form structure resembles raspberry) coupled to the lattice Boltzmann fluid. The hydrodynamic coupling between the colloids is studied by simulations of the thermo-induced rotational diffusion of two raspberry objects. It was found that for the considered range of model parameters the approaching of the raspberries leads to slight retard of the relaxation process. The presence of the weak magnetic dipolar interaction between the objects leads to modest decrease of the relaxation time and the extent of the acceleration of the diffusion is intensified along with magnetic forces. - Highlights: • The combination of molecular dynamics and lattice Boltzmann method is utilized for the reveal of the role of hydrodynamic interaction in rotational dynamics of colloid particles. • The verification of the model parameters is done based on the comparison with the results of Langevin dynamics. • For the task of free rotational diffusion of the pair of colloid particles the influence of the hydrodynamic interactions on the relaxation time is examined in the case of nonmagnetic particles and at the presence of weak dipolar interaction.

The magnetic field dependent dynamic properties of magnetorheological elastomers based on hard magnetic particles

Science.gov (United States)

Wen, Qianqian; Wang, Yu; Gong, Xinglong

2017-07-01

In this study, novel magnetorheological elastomers based on hard magnetic particles (H-MREs) were developed and the magnetic field dependent dynamic properties of the H-MREs were further investigated. The storage modulus of H-MREs could not only be increased by increasing magnetic field but also be decreased by the increasing magnetic field of opposite orientation. For the anisotropic H-MREs with 80 wt% NdFeB particles, the field-induced increasing and decreasing modulus was 426 kPa and 118 kPa respectively. Moreover, the dynamic performances of H-MREs significantly depended on the pre-structure magnetic field, magnetizing field and test magnetic field. The H-MREs were initially magnetized and formed the chain-like microstructure by the pre-structure magnetic field. The field-induced increasing and decreasing modulus of H-MREs both raised with increasing of the magnetizing field. When the magnetizing field increased from 400 to 1200 kA m-1, the field induced decreasing modulus of the 80 wt% isotropic H-MREs raised from 3 to 47 kPa. The magnetic field dependent curves of H-MREs’ storage modulus were asymmetric if the magnetizing field was higher than the test magnetic field. Based on the dipolar model of MREs and magnetic properties of hard magnetic material, a reasonable explanation was proposed to understand the H-MREs’ field dependent mechanical behaviors.

Molecular, dynamic, and structural origin of inhomogeneous magnetization transfer in lipid membranes.

Science.gov (United States)

Swanson, Scott D; Malyarenko, Dariya I; Fabiilli, Mario L; Welsh, Robert C; Nielsen, Jon-Fredrik; Srinivasan, Ashok

2017-03-01

To elucidate the dynamic, structural, and molecular properties that create inhomogeneous magnetization transfer (ihMT) contrast. Amphiphilic lipids, lamellar phospholipids with cholesterol, and bovine spinal cord (BSC) specimens were examined along with nonlipid systems. Magnetization transfer (MT), enhanced MT (eMT, obtained with double-sided radiofrequency saturation), ihMT (MT - eMT), and dipolar relaxation, T 1D , were measured at 2.0 and 11.7 T. The amplitude of ihMT ratio (ihMTR) is positively correlated with T 1D values. Both ihMTR and T 1D increase with increasing temperature in BSC white matter and in phospholipids and decrease with temperature in other lipids. Changes in ihMTR with temperature arise primarily from alterations in MT rather than eMT. Spectral width of MT, eMT, and ihMT increases with increasing carbon chain length. Concerted motions of phospholipids in white matter decrease proton spin diffusion leading to increased proton T 1D times and increased ihMT amplitudes, consistent with decoupling of Zeeman and dipolar spin reservoirs. Molecular specificity and dynamic sensitivity of ihMT contrast make it a suitable candidate for probing myelin membrane disorders. Magn Reson Med 77:1318-1328, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe

Energy Technology Data Exchange (ETDEWEB)

Parker, David S. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-06-13

We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large T_c value is unlikely.

Improved ring potential of QED at finite temperature and in the presence of weak and strong magnetic fields

International Nuclear Information System (INIS)

Sadooghi, N.; Anaraki, K. Sohrabi

2008-01-01

Using the general structure of the vacuum polarization tensor Π μν (k 0 ,k) in the infrared (IR) limit, k 0 →0, the ring contribution to the QED effective potential at finite temperature and the nonzero magnetic field is determined beyond the static limit, (k 0 →0, k→0). The resulting ring potential is then studied in weak and strong magnetic field limits. In the weak magnetic field limit, at high temperature and for α→0, the improved ring potential consists of a term proportional to T 4 α 5/2 , in addition to the expected T 4 α 3/2 term arising from the static limit. Here, α is the fine structure constant. In the limit of the strong magnetic field, where QED dynamics is dominated by the lowest Landau level, the ring potential includes a novel term consisting of dilogarithmic function (eB)Li 2 (-(2α/π)(eB/m 2 )). Using the ring improved (one-loop) effective potential including the one-loop effective potential and ring potential in the IR limit, the dynamical chiral symmetry breaking of QED is studied at finite temperature and in the presence of the strong magnetic field. The gap equation, the dynamical mass and the critical temperature of QED in the regime of the lowest Landau level dominance are determined in the improved IR as well as in the static limit. For a given value of the magnetic field, the improved ring potential is shown to be more efficient in decreasing the critical temperature arising from the one-loop effective potential.

Numerical simulation of dipolar magnetic field inflation due to equatorial ring-current

International Nuclear Information System (INIS)

Kajimura, Yoshihiro; Funaki, Ikkoh; Shinohara, Iku; Usui, Hideyuki; Matsumoto, Masaharu; Yamakawa, Hiroshi

2014-01-01

Magneto Plasma Sail (MPS) is one of the next generation space propulsion systems which generates a propulsive force using the interaction between the solar wind plasma and an artificial inflated magnetosphere generated by a superconductive coil. In the MPS system, the magnetosphere as a sail must be inflated by the plasma injection from the spacecraft in order to obtain the thrust gain. In the present study, the magnetic inflation concept is numerically tested by so-called ion one-component plasma model. As a simulation result, the magnetic moment of the system is drastically increased up to 45 times that of the coil current at plasma-β = 20 and r Li /L (radius of gyro motion / characteristics length of the magnetic field) = 0.01, and this is the first successful magnetosphere inflation obtained by numerical simulation. Corresponding maximum thrust gain is also estimated to be about 45. (author)

Rigorous numerical study of strong microwave photon-magnon coupling in all-dielectric magnetic multilayers

Energy Technology Data Exchange (ETDEWEB)

Maksymov, Ivan S., E-mail: ivan.maksymov@uwa.edu.au [School of Physics M013, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); ARC Centre of Excellence for Nanoscale BioPhotonics, School of Applied Sciences, RMIT University, Melbourne, VIC 3001 (Australia); Hutomo, Jessica; Nam, Donghee; Kostylev, Mikhail [School of Physics M013, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia)

2015-05-21

We demonstrate theoretically a ∼350-fold local enhancement of the intensity of the in-plane microwave magnetic field in multilayered structures made from a magneto-insulating yttrium iron garnet (YIG) layer sandwiched between two non-magnetic layers with a high dielectric constant matching that of YIG. The enhancement is predicted for the excitation regime when the microwave magnetic field is induced inside the multilayer by the transducer of a stripline Broadband Ferromagnetic Resonance (BFMR) setup. By means of a rigorous numerical solution of the Landau-Lifshitz-Gilbert equation consistently with the Maxwell's equations, we investigate the magnetisation dynamics in the multilayer. We reveal a strong photon-magnon coupling, which manifests itself as anti-crossing of the ferromagnetic resonance magnon mode supported by the YIG layer and the electromagnetic resonance mode supported by the whole multilayered structure. The frequency of the magnon mode depends on the external static magnetic field, which in our case is applied tangentially to the multilayer in the direction perpendicular to the microwave magnetic field induced by the stripline of the BFMR setup. The frequency of the electromagnetic mode is independent of the static magnetic field. Consequently, the predicted photon-magnon coupling is sensitive to the applied magnetic field and thus can be used in magnetically tuneable metamaterials based on simultaneously negative permittivity and permeability achievable thanks to the YIG layer. We also suggest that the predicted photon-magnon coupling may find applications in microwave quantum information systems.

Magnetic separation from superparamagnetic particle suspensions

International Nuclear Information System (INIS)

Sinha, Ashok; Ganguly, Ranjan; Puri, Ishwar K.

2009-01-01

We investigate the magnetophoretic separation of magnetic microparticles from a non-dilute flow in a microfluidic channel and their subsequent field-induced aggregation under the influence of an externally applied magnetic force. This force induces dipolar interactions between the particles that aid in their separation from the flow. Existing analytical models for dilute suspensions cannot be extended to non-dilute suspensions in which interparticle magnetic interactions play an important role. We therefore conduct a parametric investigation of the mechanics of this problem in a microcapillary flow through simulations and experimental visualization. When a magnetic field is applied, the magnetic microparticles form an aggregate on the channel wall that is influenced by the competition between the holding magnetic force and the aggregate-depleting flow shear force. Microparticle collection in the aggregate increases linearly with increasing magnetic field strength and is characterized by distinct buildup and washaway phases. The collected microparticle volume fraction in an aggregate is found to depend on a single dimensional group that depends upon characteristic system parameters.

Electromagnetic fields of rotating magnetized NUT stars

International Nuclear Information System (INIS)

Ahmedov, B.J.; Khugaev, A.V.; Ahmedov, B.J.

2004-01-01

Full text: Analytic general relativistic expressions for the electromagnetic fields external to a slowly-rotating magnetized NUT star with nonvanishing gravitomagnetic charge have been presented. Solutions for the electric and magnetic fields have been found after separating the Maxwell equations in the external background spacetime of a slowly rotating NUT star into angular and radial parts in the lowest order approximation. The star is considered isolated and in vacuum, with different models for stellar magnetic field: i) monopolar magnetic field and II) dipolar magnetic field aligned with the axis of rotation. We have shown that the general relativistic corrections due to the dragging of reference frames and gravitomagnetic charge are not present in the form of the magnetic fields but emerge only in the form of the electric fields. In particular, we have shown that the frame-dragging and gravitomagnetic charge provide an additional induced electric field which is analogous to the one introduced by the rotation of the star in the flat spacetime limit

Magnetic properties of Kramers rare earth ions in aluminium and gallium garnets

International Nuclear Information System (INIS)

Capel, H.

1964-01-01

The magnetic properties of Kramers rare earth ions in aluminium and gallium garnets (MAlG and MGaG) are discussed by means of a molecular field treatment. The symmetry properties of the space group permit to establish a parametrization for the magnetic dipolar and exchange couplings. The magnetic properties of the system can be expressed in terms of these parameters and the g factors of the rare earth ions. We have calculated the transition temperatures, the sub-lattice magnetizations, the susceptibility in the paramagnetic region and the antiferromagnetic susceptibility for a special type of magnetic ordering. The influence of the excited Kramers doublets is described by means of a generalization of the usual g tensor. (authors) [fr

Wave Vector Dependent Susceptibility at T>Tc in a Dipolar Ising Ferromagnet

DEFF Research Database (Denmark)

Als-Nielsen, Jens Aage; Holmes, L. M:; Guggenheim, H. J.

1974-01-01

The wave-vector-dependent susceptibility of LiTbF4 has been investigated by means of neutron scattering. The observations show a singularity of the susceptibility near wave vector Q=0 which is characteristic of the dipolar Coulomb interaction and good agreement with theory is obtained...

Micromagnetic simulation of two-body magnetic nanoparticles

Science.gov (United States)

Li, Fei; Lu, Jincheng; Yang, Yu; Lu, Xiaofeng; Tang, Rujun; Sun, Z. Z.

2017-05-01

Field-induced magnetization dynamics was investigated in a system of two magnetic nanoparticles with uniaxial anisotropies and magnetostatic interaction. By using the micromagnetic simulation, ultralow switching field strength was found when the separation distance between the two particles reaches a critical small value on nanometer scale in the perpendicular configuration where the anisotropic axes of the two particles are perpendicular to the separation line. The switching field increases sharply when the separation is away from the critical distance. The same results were observed when varying the radius of particles. The micromagnetic results are consistent with the previous theoretical prediction where dipolar interaction between two single-domain magnetic particles was considered. Our present simulations offered further proofs and possibilities for the low-power applications of information storage as the two-body magnetic nanoparticles could be implemented as a composite information bit.

Regio- and stereochemistry of 1,3-dipolar cycloaddition of nitrile oxides to alkenes

International Nuclear Information System (INIS)

Litvinovskaya, Raisa P; Khripach, Vladimir A

2001-01-01

The published data on the chemistry of intermolecular 1,3-dipolar cycloaddition of nitrile oxides to different types of alkene derivatives are systematised. Various aspects of stereo- and regiochemistry of this reaction are considered. The bibliography includes 182 references.

Spin ordered phase transitions in neutron matter under the presence of a strong magnetic field

International Nuclear Information System (INIS)

Isayev, A.A.; Yang, J.

2011-01-01

In dense neutron matter under the presence of a strong magnetic field, considered in the model with the Skyrme effective interaction, there are possible two types of spin ordered states. In one of them the majority of neutron spins are aligned opposite to magnetic field (thermodynamically preferable state), and in other one the majority of spins are aligned along the field (metastable state). The equation of state, incompressibility modulus and velocity of sound are determined in each case with the aim to find the peculiarities allowing to distinguish between two spin ordered phases.

The effect of the size of the system, aspect ratio and impurities concentration on the dynamic of emergent magnetic monopoles in artificial spin ice systems

Energy Technology Data Exchange (ETDEWEB)

León, Alejandro, E-mail: alejandro.leon@udp.cl

2013-08-15

In this work we study the dynamical properties of a finite array of nanomagnets in artificial kagome spin ice at room temperature. The dynamic response of the array of nanomagnets is studied by implementing a “frustrated celular autómata” (FCA), based in the charge model and dipolar model. The FCA simulations allow us to study in real-time and deterministic way, the dynamic of the system, with minimal computational resource. The update function is defined according to the coordination number of vertices in the system. Our results show that for a set geometric parameters of the array of nanomagnets, the system exhibits high density of Dirac strings and high density emergent magnetic monopoles. A study of the effect of disorder in the arrangement of nanomagnets is incorporated in this work. - Highlights: • The dynamics of magnetic monopoles in spin ice systems strongly dependent on the size of the system. • Number of emerging magnetic monopoles, in the phase of magnetic reversal, depend of the aspect. • Different systems can be created based on this idea, for information technology.

A many-particle adiabatic invariant of strongly magnetized pure electron plasmas

International Nuclear Information System (INIS)

Hjorth, P.G.

1988-01-01

A pure electron plasma is said to be strongly magnetized if the cyclotron radius of the electrons is much smaller than the classical distance of closest approach. In this parameter regime a many-particle adiabatic invariant constrains the collisional dynamics. For the case of a uniform magnetic field, the adiabatic invariant is the total kinetic energy associated with the electron velocity components that are perpendicular to the magnetic field (i.e., Σ j mv 2 j perpendicular/2). Were the adiabatic invariant an exact constant of the motion, no exchange of energy would be possible between the parallel and the perpendicular degrees of freedom, and the plasma could develop and maintain two different temperatures T parallel and T perpendicular. An adiabatic invariant, however, is not strictly conserved. In the present case, each collision produces an exponentially small exchange of energy between the parallel and the perpendicular degrees of freedom, and these act cumulatively in such a way that T parallel and T perpendicular eventually relax to a common value. The rate of equilibrium is calculated, both in the case where the collisions are described by classical mechanics and in the case where the collisions are described by quantum mechanics, the two calculations giving essentially the same result. A molecular dynamics simulation has been carried out, verifying the existence of this unusual invariant, and verifying the theoretically predicted rate equation

Method for Transformation of Weakly Magnetic Minerals (Hematite, Goethite into Strongly Magnetic Mineral (Magnetite to Improve the Efficiency of Technologies for Oxidized Iron Ores Benefication

Directory of Open Access Journals (Sweden)

Ponomarenko, O.

2015-03-01

Full Text Available A new method for relatively simple transformation of weakly magnetic minerals (goethite (α-FeOOH and hematite (α-Fe2O3 into strongly magnetic mineral (magnetite (Fe3O4 was developed. It was shown, that transformation of structure and magnetic characteristics of go ethite and hematite are realized in the presence of starch at relatively low temperatures (in the range of 300—600 °С. Obtained results open up new possibilities for development of effective technologies for oxidized iron ore beneficiation.

Linear theory of a cold relativistic beam in a strongly magnetized finite-geometry plasma

International Nuclear Information System (INIS)

Gagne, R.R.J.; Shoucri, M.M.

1976-01-01

The linear theory of a finite-geometry cold relativistic beam propagating in a cold homogeneous finite-geometry plasma, is investigated in the case of a strongly magnetized plasma. The beam is assumed to propagate parallel to the external magnetic field. It is shown that the instability which takes place at the Cherenkov resonance ωapprox. =k/subz/v/subb/ is of the convective type. The effect of the finite geometry on the instability growth rate is studied and is shown to decrease the growth rate, with respect to the infinite geometry, by a factor depending on the ratio of the beam-to-plasma radius

Polarization of electron-positron vacuum by strong magnetic field in theory with fundamental mass

International Nuclear Information System (INIS)

Kadyshevskij, V.G.; ); Rodionov, V.N.

2003-01-01

The exact Lagrangian function of the intensive constant magnetic field, replacing the Heisenberg-Euler Lagrangian in the traditional quantum electrodynamics, is calculated within the frames of the theory with the fundamental mass in the single-loop approximation. It is established that the obtained generalization of the Lagrangian function is substantial by arbitrary values of the magnetic field. The calculated Lagrangian in the weak field coincides with the known Heisenberg-Euler formula. The Lagrangian dependence on the field in the extremely strong fields completely disappears and it tends in this area to the threshold value, which is determined by the fundamental and lepton mass ratio [ru

Numerical simulation of trapped dipolar quantum gases: Collapse studies and vortex dynamics

KAUST Repository

Sparber, Christof; Markowich, Peter; Huang, Zhongyi

2010-01-01

We numerically study the three dimensional Gross-Pitaevskii equation for dipolar quantum gases using a time-splitting algorithm. We are mainly concerned with numerical investigations of the possible blow-up of solutions, i.e. collapse of the condensate, and the dynamics of vortices. © American Institute of Mathematical Sciences.

Synthesis of Ferrofluids Made of Iron Oxide Nanoflowers: Interplay between Carrier Fluid and Magnetic Properties

Directory of Open Access Journals (Sweden)

Federico Spizzo

2017-11-01

Full Text Available Ferrofluids are nanomaterials consisting of magnetic nanoparticles that are dispersed in a carrier fluid. Their physical properties, and hence their field of application are determined by intertwined compositional, structural, and magnetic characteristics, including interparticle magnetic interactions. Magnetic nanoparticles were prepared by thermal decomposition of iron(III chloride hexahydrate (FeCl3·6H2O in 2-pyrrolidone, and were then dispersed in two different fluids, water and polyethylene glycol 400 (PEG. A number of experimental techniques (especially, transmission electron microscopy, Mössbauer spectroscopy and superconducting quantum interference device (SQUID magnetometry were employed to study both the as-prepared nanoparticles and the ferrofluids. We show that, with the adopted synthesis parameters of temperature and FeCl3 relative concentration, nanoparticles are obtained that mainly consist of maghemite and present a high degree of structural disorder and strong spin canting, resulting in a low saturation magnetization (~45 emu/g. A remarkable feature is that the nanoparticles, ultimately due to the presence of 2-pyrrolidone at their surface, are arranged in nanoflower-shape structures, which are substantially stable in water and tend to disaggregate in PEG. The different arrangement of the nanoparticles in the two fluids implies a different strength of dipolar magnetic interactions, as revealed by the analysis of their magnetothermal behavior. The comparison between the magnetic heating capacities of the two ferrofluids demonstrates the possibility of tailoring the performances of the produced nanoparticles by exploiting the interplay with the carrier fluid.

The realization of strong, stray static magnetic fields

Czech Academy of Sciences Publication Activity Database

Žežulka, Václav; Straka, Pavel

2012-01-01

Roč. 9, č. 1 (2012), s. 71-77 ISSN 1214-9705 Institutional research plan: CEZ:AV0Z30460519 Keywords : magnetic fields * magnetic circuits * permanent NdFeB magnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.530, year: 2011 http://www.irsm.cas.cz/materialy/acta_content/2012_01/7_Zezulka.pdf