Critical fluid light scattering
NASA Technical Reports Server (NTRS)
Gammon, Robert W.
1988-01-01
The objective is to measure the decay rates of critical density fluctuations in a simple fluid (xenon) very near its liquid-vapor critical point using laser light scattering and photon correlation spectroscopy. Such experiments were severely limited on Earth by the presence of gravity which causes large density gradients in the sample when the compressibility diverges approaching the critical point. The goal is to measure fluctuation decay rates at least two decades closer to the critical point than is possible on earth, with a resolution of 3 microK. This will require loading the sample to 0.1 percent of the critical density and taking data as close as 100 microK to the critical temperature. The minimum mission time of 100 hours will allow a complete range of temperature points to be covered, limited by the thermal response of the sample. Other technical problems have to be addressed such as multiple scattering and the effect of wetting layers. The experiment entails measurement of the scattering intensity fluctuation decay rate at two angles for each temperature and simultaneously recording the scattering intensities and sample turbidity (from the transmission). The analyzed intensity and turbidity data gives the correlation length at each temperature and locates the critical temperature. The fluctuation decay rate data from these measurements will provide a severe test of the generalized hydrodynamic theories of transport coefficients in the critical regions. When compared to equivalent data from binary liquid critical mixtures they will test the universality of critical dynamics.
ZALIZNYAK,I.A.; LEE,S.H.
2004-07-30
Much of our understanding of the atomic-scale magnetic structure and the dynamical properties of solids and liquids was gained from neutron-scattering studies. Elastic and inelastic neutron spectroscopy provided physicists with an unprecedented, detailed access to spin structures, magnetic-excitation spectra, soft-modes and critical dynamics at magnetic-phase transitions, which is unrivaled by other experimental techniques. Because the neutron has no electric charge, it is an ideal weakly interacting and highly penetrating probe of matter's inner structure and dynamics. Unlike techniques using photon electric fields or charged particles (e.g., electrons, muons) that significantly modify the local electronic environment, neutron spectroscopy allows determination of a material's intrinsic, unperturbed physical properties. The method is not sensitive to extraneous charges, electric fields, and the imperfection of surface layers. Because the neutron is a highly penetrating and non-destructive probe, neutron spectroscopy can probe the microscopic properties of bulk materials (not just their surface layers) and study samples embedded in complex environments, such as cryostats, magnets, and pressure cells, which are essential for understanding the physical origins of magnetic phenomena. Neutron scattering is arguably the most powerful and versatile experimental tool for studying the microscopic properties of the magnetic materials. The magnitude of the cross-section of the neutron magnetic scattering is similar to the cross-section of nuclear scattering by short-range nuclear forces, and is large enough to provide measurable scattering by the ordered magnetic structures and electron spin fluctuations. In the half-a-century or so that has passed since neutron beams with sufficient intensity for scattering applications became available with the advent of the nuclear reactors, they have became indispensable tools for studying a variety of important areas of modern science
Krishnamurthy, V. V.; Adroja, D. T.; Butch, N. P.; Osborn, R.; Sinha, S. K.; Robertson, J. L.; Aronson, M. C.; Nagler, S. E.; Maple, M. B.; ORNL; Rutherford Appleton Lab.; Univ. California at San Diego; Univ. Michigan
2008-01-01
The spin dynamics of uranium ions in the non-Fermi liquid compounds URu{sub 2-x}Re{sub x}Si{sub 2}, for x=0.2 to 0.6, have been investigated using inelastic neutron scattering. The wave vector (q) dependence of the magnetic scattering provides evidence of short-range antiferromagnetic correlations at low temperatures for x=0.2,0.25, but the scattering is nearly q independent at x=0.35,0.6. The magnetic response, {bar S}({omega}), obtained from the q-independent part of neutron scattering, varies as {omega}{sup -{alpha}} with a composition-dependent exponent {alpha} = 0.2-0.5. The dynamic magnetic susceptibility {chi}{double_prime}(q,{omega}) of the q-independent part exhibits {omega}/T scaling for the energy transfer {bar h}{omega} between 3.5 and 17 meV in the temperature (T) range of 5-300 K at all the compositions. This scaling, which indicates local quantum criticality, breaks down in the q range, 0.6-1.1 {angstrom}{sup -1} at x = 0.2 and 0.25, that is dominated by short-range antiferromagnetic correlations. The appearance of power laws in the magnetic response measured by inelastic neutron scattering over a wide Re doping region indicates a disorder driven non-Fermi liquid mechanism for the low-temperature physical properties in these compounds.
Critical concentrations of cumulative scattered damage
Ignatovich, S.R.
1995-12-01
A statistical model is constructed to describe the formation of associations (clusters) of several defects randomly scattered within a limited region of the material. The dependence of the number of such clusters on the total concentration of defects is determined. Two criteria of the limiting state are established for multiple fracture, these criteria corresponding to the critical concentrations of cumulative scattered damage. The critical concentrations are the threshold concentration at which individual defects begin to merge and the concentration characterizing the transition to the stage in which defects coalesce on a massive scale.
Spin and orbital magnetization loops obtained using magnetic Compton scattering
Itou, M.; Sakurai, Y.; Koizumi, A.
2013-02-25
We present an application of magnetic Compton scattering (MCS) to decompose a total magnetization loop into spin and orbital magnetization contributions. A spin magnetization loop of SmAl{sub 2} was measured by recording the intensity of magnetic Compton scattering as a function of applied magnetic field. Comparing the spin magnetization loop with the total magnetization one measured by a vibrating sample magnetometer, the orbital magnetization loop was obtained. The data display an anti-coupled behavior between the spin and orbital magnetizations and confirm that the orbital part dominates the magnetization.
Multiple magnetic scattering in small-angle neutron scattering of Nd–Fe–B nanocrystalline magnet
Ueno, Tetsuro; Saito, Kotaro; Yano, Masao; Ito, Masaaki; Shoji, Tetsuya; Sakuma, Noritsugu; Kato, Akira; Manabe, Akira; Hashimoto, Ai; Gilbert, Elliot P.; Keiderling, Uwe; Ono, Kanta
2016-01-01
We have investigated the influence of multiple scattering on the magnetic small-angle neutron scattering (SANS) from a Nd–Fe–B nanocrystalline magnet. We performed sample-thickness- and neutron-wavelength-dependent SANS measurements, and observed the scattering vector dependence of the multiple magnetic scattering. It is revealed that significant multiple scattering exists in the magnetic scattering rather than the nuclear scattering of Nd–Fe–B nanocrystalline magnet. It is considered that the mean free path of the neutrons for magnetic scattering is rather short in Nd–Fe–B magnets. We analysed the SANS data by the phenomenological magnetic correlation model considering the magnetic microstructures and obtained the microstructural parameters. PMID:27321149
Multiple magnetic scattering in small-angle neutron scattering of Nd-Fe-B nanocrystalline magnet.
Ueno, Tetsuro; Saito, Kotaro; Yano, Masao; Ito, Masaaki; Shoji, Tetsuya; Sakuma, Noritsugu; Kato, Akira; Manabe, Akira; Hashimoto, Ai; Gilbert, Elliot P; Keiderling, Uwe; Ono, Kanta
2016-01-01
We have investigated the influence of multiple scattering on the magnetic small-angle neutron scattering (SANS) from a Nd-Fe-B nanocrystalline magnet. We performed sample-thickness- and neutron-wavelength-dependent SANS measurements, and observed the scattering vector dependence of the multiple magnetic scattering. It is revealed that significant multiple scattering exists in the magnetic scattering rather than the nuclear scattering of Nd-Fe-B nanocrystalline magnet. It is considered that the mean free path of the neutrons for magnetic scattering is rather short in Nd-Fe-B magnets. We analysed the SANS data by the phenomenological magnetic correlation model considering the magnetic microstructures and obtained the microstructural parameters. PMID:27321149
Light scattering and birefrigence by magnetic bacteria
Johnston, R.G.; Jacobson, P.L.
1990-01-01
The bacterium Aquaspirillum magnetotacticum grows its own internal single domain magnets. For a number of reasons, these magnets make the bacterium an extremely interesting scattering particle. We are engaging in light scattering and birefringence studies on Aquaspirillum magnetotacticum. 9 refs., 4 figs.
Quantum Criticality in an Organic Magnet
Stone, Matthew B; Broholm, C. L.; Reich, D. H.; Tchemyshyov, O.; Vorderwisch, P.; Harrison, N.
2006-01-01
Exchange interactions between S=1/2 sites in piperazinium hexachlorodicuprate produce a frustrated bilayer magnet with a singlet ground state. We have determined the field-temperature phase diagram by high field magnetization and neutron scattering experiments. There are two quantum critical points: H{sub c1}=7.5 T separates a quantum paramagnet phase from a three dimensional, antiferromagnetically ordered state while H{sub c2}=37 T marks the onset of a fully polarized state. The ordered phase, which we describe as a magnon Bose-Einstein condensate (BEC), is embedded in a quantum critical regime with short range correlations. A low temperature anomaly in the BEC phase boundary indicates that additional low energy features of the material become important near H{sub c1}.
Critical phenomena in magnetic nanowires.
Kamalakar, M Venkata; Raychaudhuri, A K
2009-09-01
In this paper we report the first experimental study of critical phenomena in case of magnetic nanowires of nickel near the ferromagnetic-paramagnetic transition from the electrical transport properties. Nickel nanowire arrays, prepared by potentiostatic electrodeposition of nickel inside pores of nanoporous anodic alumina template were well characterized by X-ray Diffraction, Transmission electron microscopy and Energy dispersive Spectroscopy. Precise electrical resistance measurement of the nanowire arrays of wire diameter 20 nm have been done in the temperature range between 300 K to 700 K. We see a drop in the Curie temperature as observed from the resistivity anomaly. We analyzed the resistance data near the critical region and extracted the critical exponent alpha directly from the resistance. We observed a decrease in the critical part of the resistivity including a decrease in the magnitude of the critical exponent alpha and severe modification in the correction to scaling. PMID:19928208
Magnetized stimulated scattering in pulsar winds
NASA Technical Reports Server (NTRS)
Sincell, Mark W.; Krolik, Julian H.
1992-01-01
The effects of stimulated scattering on a collimated high brightness temperature beam of photons traversing a relativistically streaming magnetized plasma are studied. Under the assumption that the center of the photon beam is parallel to the bulk motion, we calculate the scattering rate as a function of the angular spread of the beam and the Lorentz factor gamma. Magnetization changes the photon recoil, without which stimulated scattering has no effect. It also introduces a strong dependence on frequency and polarization: if the photon frequency matches the electron cyclotron frequency, the scattering rate of photons polarized perpendicular to the magnetic field can be substantially enhanced relative to Thomson, and if the photon frequency is much less than the cyclotron frequency, the scattering is suppressed. Applying these calculations to pulsars, we find that stimulated scattering of the radio beam in the magnetized wind believed to exist outside the light cylinder can substantially alter the spectrum and polarization state of the radio signal. We suggest that the scattering rate is so high in some pulsars that the ability of the radio signal to penetrate the pulsar magnetosphere requires modification of either the conventional model of the magnetosphere or assumptions about the effects of stimulated scattering upon a beam.
Magnetization dissipation in ferromagnets from scattering theory
NASA Astrophysics Data System (ADS)
Brataas, Arne; Tserkovnyak, Yaroslav; Bauer, Gerrit E. W.
2011-08-01
The magnetization dynamics of ferromagnets is often formulated in terms of the Landau-Lifshitz-Gilbert (LLG) equation. The reactive part of this equation describes the response of the magnetization in terms of effective fields, whereas the dissipative part is parametrized by the Gilbert damping tensor. We formulate a scattering theory for the magnetization dynamics and map this description on the linearized LLG equation by attaching electric contacts to the ferromagnet. The reactive part can then be expressed in terms of the static scattering matrix. The dissipative contribution to the low-frequency magnetization dynamics can be described as an adiabatic energy pumping process to the electronic subsystem by the time-dependent magnetization. The Gilbert damping tensor depends on the time derivative of the scattering matrix as a function of the magnetization direction. By the fluctuation-dissipation theorem, the fluctuations of the effective fields can also be formulated in terms of the quasistatic scattering matrix. The theory is formulated for general magnetization textures and worked out for monodomain precessions and domain-wall motions. We prove that the Gilbert damping from scattering theory is identical to the result obtained by the Kubo formalism.
Inelastic magnetic X-ray scattering
NASA Astrophysics Data System (ADS)
Platzman, P. M.; Tzoar, N.
1985-04-01
The theory of magnetic X-ray scattering is used to discuss the possibilities for employing inelastic scattering to probe the magnetic properties of condensed matter systems. In particular, it is shown how the interference between the nonmagnetic (Compton) and magnetic scattering arising from the use of circularly polarized X-rays is absolutely essential in such experiments. The very beautiful preliminary experiments by Sakai and Ono (1976) on Fe which use circularly polarized Moessbauer gamma-rays will be discussed. They already show the sensitivity of the technique to the 'magnetic form factor'. In addition, the physics of a unique quarter wave plate employed in obtaining circularly polarized X-rays is considered, and the implications of this advance for doing such experiments on existing synchrotron X-ray sources are discussed.
Probing fine magnetic particles with neutron scattering
Pynn, R.
1991-12-31
Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and colloidal suspensions of magnetic particles, known as ferrofluids. Diffraction, surface reflection, and small angle neutron scattering (SANS) are the techniques used. With the exception of surface reflection, these methods are described in this article. The combination of SANS with refractive-index matching and neutron polarisation analysis is particularly powerful because it allows the magnetic and atomic structures to be determined independently. This technique has been used to study both dilute and concentrated ferrofluid suspensions of relatively monodisperse cobalt particles, subjected to a series of applied magnetic fields. The size of the cobalt particle core and the surrounding surfactant layer were determined. The measured interparticle structure factor agrees well with a recent theory that allows correlations in binary mixtures of magnetic particles to be calculated in the case of complete magnetic alignment. When one of the species in such a binary mixture is a nonmagnetic, cyclindrical macromolecule, application of a magnetic field leads to some degree of alignment of the nonmagnetic species. This result has been demonstrated with tobacco mosaic virus suspended in a water-based ferrofluid.
Probing fine magnetic particles with neutron scattering
Pynn, R.
1991-01-01
Because thermal neutrons are scattered both by nuclei and by unpaired electrons, they provide an ideal probe for studying the atomic and magnetic structures of fine-grained magnetic materials, including nanocrystalline solids, thin epitaxial layers, and colloidal suspensions of magnetic particles, known as ferrofluids. Diffraction, surface reflection, and small angle neutron scattering (SANS) are the techniques used. With the exception of surface reflection, these methods are described in this article. The combination of SANS with refractive-index matching and neutron polarisation analysis is particularly powerful because it allows the magnetic and atomic structures to be determined independently. This technique has been used to study both dilute and concentrated ferrofluid suspensions of relatively monodisperse cobalt particles, subjected to a series of applied magnetic fields. The size of the cobalt particle core and the surrounding surfactant layer were determined. The measured interparticle structure factor agrees well with a recent theory that allows correlations in binary mixtures of magnetic particles to be calculated in the case of complete magnetic alignment. When one of the species in such a binary mixture is a nonmagnetic, cyclindrical macromolecule, application of a magnetic field leads to some degree of alignment of the nonmagnetic species. This result has been demonstrated with tobacco mosaic virus suspended in a water-based ferrofluid.
Compton scattering in strong magnetic fields
NASA Technical Reports Server (NTRS)
Daugherty, Joseph K.; Harding, Alice K.
1986-01-01
The relativistic cross section for Compton scattering by electrons in strong magnetic fields is derived. The results confirm and extend earlier work which has treated only transitions to the lowest or first excited Landau levels. For the teragauss field strengths expected in neutron star magnetospheres, the relative rates for excited state transitions are found to be significant, especially for incident photon energies several times the cyclotron frequency. Since these transitions must result in the rapid emission of one or more cyclotron photons as well as the Compton-scattered photon, the scattering process actually becomes a photon 'splitting' mechanism which acts to soften hard photon spectra, and also provides a specific mechanism for populating higher Landau levels in the electron distribution function. The results should be significant for models of gamma-ray bursters and pulsating X-ray sources.
Raman Scattering in the Magnetized Semiconductor Plasma
NASA Astrophysics Data System (ADS)
Jankauskas, Zigmantas; Kvedaras, Vygaudas; Balevičius, Saulius
2005-04-01
Radio frequency (RF) magnetoplasmic waves known as helicons will propagate in solid-state plasmas when a strong magnetic field is applied. In our device the helicons were excited by RFs (the range 100-2000 MHz) much higher than the helicon generation frequency (the main peak at 20 MHz). The excitation of helicons in this case may be described by the effect similar to the Combination Scattering (Raman effect) when a part of the high RF wave energy that passes through the active material is absorbed and re-emitted by the magnetized solid-state plasma. It is expedient to call this experimental device a Helicon Maser (HRM) and the higher frequency e/m field - a pumping field. In full analogy with the usual Raman maser (or laser) the magnetized semiconductor sample plays the role of active material and the connecting cable - the role of high quality external resonator.
Raman Scattering in the Magnetized Semiconductor Plasma
NASA Astrophysics Data System (ADS)
Jankauskas, Zigmantas; Kvedaras, Vygaudas; Balevičius, Saulius
Radio frequency (RF) magnetoplasmic waves known as helicons will propagate in solid-state plasmas when a strong magnetic field is applied. In our device the helicons were excited by RFs (the range 100-2000 MHz) much higher than the helicon generation frequency (the main peak at 20 MHz). The excitation of helicons in this case may be described by the effect similar to the Combination Scattering (Raman effect) when a part of the high RF wave energy that passes through the active material is absorbed and re-emitted by the magnetized solid-state plasma. It is expedient to call this experimental device a Helicon Maser (HRM) and the higher frequency e/m field - a pumping field. In full analogy with the usual Raman maser (or laser) the magnetized semiconductor sample plays the role of active material and the connecting cable - the role of high quality external resonator.
Scattering of Ions beyond the Single Scattering Critical Angle in HIERDA
Johnston, P.N.; Bubb, I.F.; Franich, R.; Cohen, D.D.; Dytlewski, N.; Arstila, K.; Sajavaara, T.
2003-08-26
In Heavy Ion Elastic Recoil Detection Analysis (HIERDA), Rutherford scattering determines the number of scattered and recoiled ions that reach the detector. Because plural scattering is a major contributor to the spectrum and can mask important features and otherwise distort the spectrum it needs to be described correctly. Scattering more than once is a frequent occurrence so many ions scatter beyond the maximum scattering angle possible by a single scattering event. In this work we have chosen projectile/target combinations which enable the exploitation of the scattering critical angle to obtain spectra which are from ions which have all been scattered more than once. Monte Carlo simulation of the ion transport is used to study the plural scattering using a fast FORTRAN version of TRIM. The results of the simulations are compared with experimental measurements on samples of Si, V and Co performed with 20-100 MeV beams of Br, I and Au ions using ToF-E HIERDA facilities at Lucas Heights and Helsinki.
Critical Magnetic Field Determination of Superconducting Materials
Canabal, A.; Tajima, T.; Dolgashev, V.A.; Tantawi, S.G.; Yamamoto, T.; /Tsukuba, Natl. Res. Lab. Metrol.
2011-11-04
Superconducting RF technology is becoming more and more important. With some recent cavity test results showing close to or even higher than the critical magnetic field of 170-180 mT that had been considered a limit, it is very important to develop a way to correctly measure the critical magnetic field (H{sup RF}{sub c}) of superconductors in the RF regime. Using a 11.4 GHz, 50-MW, <1 {mu}s, pulsed power source and a TE013-like mode copper cavity, we have been measuring critical magnetic fields of superconductors for accelerator cavity applications. This device can eliminate both thermal and field emission effects due to a short pulse and no electric field at the sample surface. A model of the system is presented in this paper along with a discussion of preliminary experimental data.
Scatter-based magnetic resonance elastography
NASA Astrophysics Data System (ADS)
Papazoglou, Sebastian; Xu, Chao; Hamhaber, Uwe; Siebert, Eberhard; Bohner, Georg; Klingebiel, Randolf; Braun, Jürgen; Sack, Ingolf
2009-04-01
Elasticity is a sensitive measure of the microstructural constitution of soft biological tissues and increasingly used in diagnostic imaging. Magnetic resonance elastography (MRE) uniquely allows in vivo measurement of the shear elasticity of brain tissue. However, the spatial resolution of MRE is inherently limited as the transformation of shear wave patterns into elasticity maps requires the solution of inverse problems. Therefore, an MRE method is introduced that avoids inversion and instead exploits shear wave scattering at elastic interfaces between anatomical regions of different shear compliance. This compliance-weighted imaging (CWI) method can be used to evaluate the mechanical consistency of cerebral lesions or to measure relative stiffness differences between anatomical subregions of the brain. It is demonstrated that CWI-MRE is sensitive enough to reveal significant elasticity variations within inner brain parenchyma: the caudate nucleus (head) was stiffer than the lentiform nucleus and the thalamus by factors of 1.3 ± 0.1 and 1.7 ± 0.2, respectively (P < 0.001). CWI-MRE provides a unique method for characterizing brain tissue by identifying local stiffness variations.
Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn5
NASA Astrophysics Data System (ADS)
Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; Shakeripour, H.; Petrovic, C.; Taillefer, Louis
2016-07-01
The thermal conductivity κ of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H , for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc 2, κ /T is found to increase as T →0 , just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ /T with field reveals that the electron-electron scattering (or transport mass m⋆) of those unpaired electrons diverges as H →Hc 2 from below, in the same way that it does in the normal state as H →Hc 2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn5 at H⋆=Hc 2 even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k -space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.
Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn_{5}.
Paglione, Johnpierre; Tanatar, M A; Reid, J-Ph; Shakeripour, H; Petrovic, C; Taillefer, Louis
2016-07-01
The thermal conductivity κ of the heavy-fermion metal CeCoIn_{5} was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field H_{c2}, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ/T with field reveals that the electron-electron scattering (or transport mass m^{⋆}) of those unpaired electrons diverges as H→H_{c2} from below, in the same way that it does in the normal state as H→H_{c2} from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn_{5} at H^{⋆}=H_{c2} even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations. PMID:27419578
Resonant Raman scattering from silicon nanoparticles enhanced by magnetic response.
Dmitriev, Pavel A; Baranov, Denis G; Milichko, Valentin A; Makarov, Sergey V; Mukhin, Ivan S; Samusev, Anton K; Krasnok, Alexander E; Belov, Pavel A; Kivshar, Yuri S
2016-05-01
Enhancement of optical response with high-index dielectric nanoparticles is attributed to the excitation of their Mie-type magnetic and electric resonances. Here we study Raman scattering from crystalline silicon nanoparticles and reveal that magnetic dipole modes have a much stronger effect on the scattering than electric modes of the same order. We demonstrate experimentally a 140-fold enhancement of the Raman signal from individual silicon spherical nanoparticles at the magnetic dipole resonance. Our results confirm the importance of the optically-induced magnetic response of subwavelength dielectric nanoparticles for enhancing light-matter interactions. PMID:27113352
Magnetic diffuse scattering in artificial kagome spin ice
NASA Astrophysics Data System (ADS)
Sendetskyi, Oles; Anghinolfi, Luca; Scagnoli, Valerio; Möller, Gunnar; Leo, Naëmi; Alberca, Aurora; Kohlbrecher, Joachim; Lüning, Jan; Staub, Urs; Heyderman, Laura Jane
2016-06-01
The study of magnetic correlations in dipolar-coupled nanomagnet systems with synchrotron x-ray scattering provides a means to uncover emergent phenomena and exotic phases, in particular in systems with thermally active magnetic moments. From the diffuse signal of soft x-ray resonant magnetic scattering, we have measured magnetic correlations in a highly dynamic artificial kagome spin ice with sub-70-nm Permalloy nanomagnets. On comparing experimental scattering patterns with Monte Carlo simulations based on a needle-dipole model, we conclude that kagome ice I phase correlations exist in our experimental system even in the presence of moment fluctuations, which is analogous to bulk spin ice and spin liquid behavior. In addition, we describe the emergence of quasi-pinch-points in the magnetic diffuse scattering in the kagome ice I phase. These quasi-pinch-points bear similarities to the fully developed pinch points with singularities of a magnetic Coulomb phase, and continually evolve into the latter on lowering the temperature. The possibility to measure magnetic diffuse scattering with soft x rays opens the way to study magnetic correlations in a variety of nanomagnetic systems.
Fano resonance generated by magnetic scatterer in micro metal slit
NASA Astrophysics Data System (ADS)
Zhou, Yun-Song; Wang, Pei-Jie; Wang, Hai; Feng, Sheng-Fei
2014-09-01
A micro metal slit/magnetic scatterer structure is proposed to generate electromagnetic Fano resonance. The magnetic scatterer is formed by infinite long split cylinder resonator array. The analytical transmissivity formulas are deduced from Maxwell electromagnetic theory and the Fano resonance transmission is achieved by the theoretical calculations. The enhancement of environment refractive index leads to an ultrasensitive and linear red shift of resonance peak in the THz range.
Resonant Raman scattering from silicon nanoparticles enhanced by magnetic response
NASA Astrophysics Data System (ADS)
Dmitriev, Pavel A.; Baranov, Denis G.; Milichko, Valentin A.; Makarov, Sergey V.; Mukhin, Ivan S.; Samusev, Anton K.; Krasnok, Alexander E.; Belov, Pavel A.; Kivshar, Yuri S.
2016-05-01
Enhancement of optical response with high-index dielectric nanoparticles is attributed to the excitation of their Mie-type magnetic and electric resonances. Here we study Raman scattering from crystalline silicon nanoparticles and reveal that magnetic dipole modes have a much stronger effect on the scattering than electric modes of the same order. We demonstrate experimentally a 140-fold enhancement of the Raman signal from individual silicon spherical nanoparticles at the magnetic dipole resonance. Our results confirm the importance of the optically-induced magnetic response of subwavelength dielectric nanoparticles for enhancing light-matter interactions.Enhancement of optical response with high-index dielectric nanoparticles is attributed to the excitation of their Mie-type magnetic and electric resonances. Here we study Raman scattering from crystalline silicon nanoparticles and reveal that magnetic dipole modes have a much stronger effect on the scattering than electric modes of the same order. We demonstrate experimentally a 140-fold enhancement of the Raman signal from individual silicon spherical nanoparticles at the magnetic dipole resonance. Our results confirm the importance of the optically-induced magnetic response of subwavelength dielectric nanoparticles for enhancing light-matter interactions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07965a
REACT: Alternatives to Critical Materials in Magnets
2012-01-01
REACT Project: The 14 projects that comprise ARPA-E’s REACT Project, short for “Rare Earth Alternatives in Critical Technologies”, are developing cost-effective alternatives to rare earths, the naturally occurring minerals with unique magnetic properties that are used in electric vehicle (EV) motors and wind generators. The REACT projects will identify low-cost and abundant replacement materials for rare earths while encouraging existing technologies to use them more efficiently. These alternatives would facilitate the widespread use of EVs and wind power, drastically reducing the amount of greenhouse gases released into the atmosphere.
Quantum critical state in a magnetic quasicrystal.
Deguchi, Kazuhiko; Matsukawa, Shuya; Sato, Noriaki K; Hattori, Taisuke; Ishida, Kenji; Takakura, Hiroyuki; Ishimasa, Tsutomu
2012-12-01
Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. in 1984, there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states--whether they are extended as in periodic crystals or localized as in amorphous materials--are still unresolved. Here we report the first observation of quantum (T = 0) critical phenomena of the Au-Al-Yb quasicrystal--the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T→0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals. PMID:23042414
Thomson scattering in a magnetic field. II - Arbitrary field orientation
NASA Technical Reports Server (NTRS)
Whitney, Barbara A.
1991-01-01
This paper presents solutions to the equation of transfer for Thomson scattering in a constant magnetic field of arbitrary orientation. Results from several atmospheres are combined to give the flux from a dipole star. The results are compared to the polarization data of the magnetic white dwarf Grw + 70 deg 8247. The fit is good, though it implies a very large polarization in the ultraviolet. Thomson scattering is not thought to be an important opacity source in white dwarfs, so the good fit is either fortuitous or is perhaps explained by assuming the magnetic field affects the polarization processes in all opacities similarly.
Elastic Scattering of Electron Vortex Beams in Magnetic Matter
NASA Astrophysics Data System (ADS)
Edström, Alexander; Lubk, Axel; Rusz, Ján
2016-03-01
Elastic scattering of electron vortex beams on magnetic materials leads to a weak magnetic contrast due to Zeeman interaction of orbital angular momentum of the beam with magnetic fields in the sample. The magnetic signal manifests itself as a redistribution of intensity in diffraction patterns due to a change of sign of the orbital angular momentum of the electron vortex beam. While in the atomic resolution regime the magnetic signal is most likely under the detection limits of present transmission electron microscopes, for electron probes with high orbital angular momenta, and correspondingly larger spatial extent, its detection is predicted to be feasible.
Critical hysteresis for n-component magnets
NASA Astrophysics Data System (ADS)
Silveira, Ravá Da; Kardar, Mehran
1999-02-01
Earlier work on dynamical critical phenomena in the context of magnetic hysteresis for uniaxial (scalar) spins is extended to the case of a multicomponent (vector) field. From symmetry arguments and a perturbative renormalization-group approach (in the path-integral formalism), it is found that the generic behavior at long time and length scales is described by the scalar fixed point (reached for a given value of the magnetic field and of the quenched disorder), with the corresponding Ising-like exponents. By tuning an additional parameter, however, a fully rotationally invariant fixed point can be reached, at which all components become critical simultaneously, with O(n)-like exponents. Furthermore, the possibility of a spontaneous nonequilibrium transverse ordering, controlled by a distinct fixed point, is unveiled and the associated exponents calculated. In addition to these central results, a didactic ``derivation'' of the equations of motion for the spin field are given, the scalar model is revisited and treated in a more direct fashion, and some issues pertaining to time dependences and the problem of multiple solutions within the path-integral formalism are clarified.
Neutron-scattering studies of magnetic superconductors
Sinha, S.K.; Crabtree, G.W.; Hinks, D.G.; Mook, H.A.; Pringle, O.A.
1982-01-01
Results obtained in the last few years obtained by neutron diffraction on the nature of the magnetic ordering in magnetic superconductors are reviewed. Emphasis is given to studies of the complex intermediate phase in ferromagnetic superconductors where both superconductivity and ferromagnetism appear to coexist.
Wei, H. X.; Qin, Q. H.; Ma, Q. L.; Zhang, Xiaoguang; Han, Prof. X. F.
2010-01-01
Analytic expressions for contributions to the inelastic electron tunneling spectrum (IETS) from surface magnon scattering and magnetic impurity scattering are obtained. It is shown that surface magnon scattering alone does not lead to peaks in the IETS. The peaks at small bias often observed in the IETS of magnetic junctions are due to magnetic impurity scattering, in agreement with the traditional model for zero bias anomaly. These impurity resonance peaks can sometimes split due to the impurities' magnetic coupling to the electrodes. Measurements of AlO and MgO barrier junctions yield excellent agreement to the theory. The experiment further shows that the magnetic impurities in MgO barriers are strongly coupled to the electrodes but those in AlO barriers are not magnetically coupled to the electrodes.
Resonant Compton Scattering in Highly-Magnetized Pulsars
NASA Astrophysics Data System (ADS)
Wadiasingh, Zorawar
Soft gamma repeaters and anomalous X-ray pulsars are subset of slow-rotating neutron stars, known as magnetars, that have extremely high inferred surface magnetic fields, of the order 100-1000 TeraGauss. Hard, non-thermal and pulsed persistent X-ray emission extending between 10 keV and 230 keV has been seen in a number of magnetars by RXTE, INTEGRAL, and Suzaku. In this thesis, the author considers inner magnetospheric models of such persistent hard X-ray emission where resonant Compton upscattering of soft thermal photons is anticipated to be the most efficient radiative process. This high efficiency is due to the relative proximity of the surface thermal photons, and also because the scattering becomes resonant at the cyclotron frequency. At the cyclotron resonance, the effective cross section exceeds the classical Thomson one by over two orders of magnitude, thereby enhancing the efficiency of continuum production and cooling of relativistic electrons. In this thesis, a new Sokolov and Ternov formulation of the QED Compton scattering cross section for strong magnetic fields is employed in electron cooling and emission spectra calculations. This formalism is formally correct for treating spin-dependent effects and decay rates that are important at the cyclotron resonance. The author presents electron cooling rates at arbitrary interaction points in a magnetosphere using the QED cross sections. The QED effects reduce the rates below high-field extrapolations of older magnetic Thomson results. The author also computes angle-dependent upscattering model spectra, formed using collisional integrals, for uncooled monoenergetic relativistic electrons injected in inner regions of pulsar magnetospheres. These spectra are integrated over closed field lines and obtained for different observing perspectives. The spectral cut-off energies are critically dependent on the observer viewing angles and electron Lorentz factor. It is found that electrons with energies less than
Polarized neutron reflectivity and scattering studies of magnetic heterostructures
NASA Astrophysics Data System (ADS)
Zabel, H.; Theis-Bröhl, K.
2003-02-01
The current interest in the magnetism of ultrathin films and multilayers is driven by their manifold applications in the magneto-and spin-electronic areas, for instance as magnetic field sensors or as information storage devices. In this regard, there is a large interest in exploring spin structures and spin disorder at the interface of magnetic heterostructures, to investigate magnetic domains in thin films and superlattices, and to understand remagnetization processes of various laterally shaped magnetic nanostructures. Traditionally neutron scattering has played a dominant role in the determination of spin structures, phase transitions and magnetic excitations in bulk materials. Today, its potential for the investigation of thin magnetic films has to be redefined. Polarized neutron reflectivity (PNR) at small wavevectors can provide precise information on the magnetic field distribution parallel to the film plane and on layer resolved magnetization vectors. In addition, PNR is not only sensitive to structural interface roughness but also to the magnetic roughness. Furthermore, magnetic hysteresis measurements from polarized small angle Bragg reflections allows us to filter out correlation effects during magnetization reversals of magnetic stripes and islands. An overview is provided on most recent PNR investigations of magnetic heterostructures.
Scattering of high-energy magnons off a magnetic skyrmion
NASA Astrophysics Data System (ADS)
Schroeter, Sarah; Garst, Markus
2015-10-01
We discuss the scattering of high-energy magnons off a single magnetic skyrmion within the field-polarized ground state of a two-dimensional chiral magnet. For wavevectors larger than the inverse skyrmion radius, krs ≫ 1 the magnon scattering is dominated by an emerging magnetic field whose flux density is essentially determined by the topological charge density of the skyrmion texture. This leads to skew and rainbow scattering characterized by an asymmetric and oscillating differential cross section. We demonstrate that the transversal momentum transfer to the skyrmion is universal due to the quantization of the total emerging flux while the longitudinal momentum transfer is negligible in the high-energy limit. This results in a magnon-driven skyrmion motion approximately antiparallel to the incoming magnon current and a universal relation between current and skyrmion-velocity.
Electromagnetic scattering by magnetic spheres: Theory and algorithms
NASA Astrophysics Data System (ADS)
Milham, Merill E.
1994-10-01
The theory for the scattering of magnetic spheres is developed by means of scaling functions. This theory leads in a natural way to the development of scattering algorithms which use exponential scaling to overcome computational overflow problems. The design and testing of the algorithm is described. Fortran codes which implement the algorithmic design are presented and examples of code use are given. Listings of the code are included.
Spin-flip scattering of critical quasiparticles and the phase diagram of YbRh2Si2
NASA Astrophysics Data System (ADS)
Wölfle, Peter; Abrahams, Elihu
2015-10-01
Several observed transport and thermodynamic properties of the heavy-fermion compound YbRh2Si2 in the quantum critical regime are unusual and suggest that the fermionic quasiparticles are critical, characterized by a scale-dependent diverging effective mass. A theory based on the concept of critical quasiparticles scattering off antiferromagnetic spin fluctuations in a strong-coupling regime has been shown to successfully explain the unusual existing data and to predict a number of so far unobserved properties. In this paper, we point out a new feature of a magnetic field-tuned quantum critical point of a heavy-fermion metal: anomalies in the transport and thermodynamic properties caused by the freezing out of spin-flip scattering of critical quasiparticles and the scattering off collective spin excitations. We show a steplike behavior as a function of magnetic field of, e.g., the Hall coefficient and magnetoresistivity results, which accounts quantitatively for the observed behavior of these quantities. That behavior has been described as a crossover line T*(H ) in the T -H phase diagram of YbRh2Si2 . Whereas some authors have interpreted this observation as signaling the breakdown of Kondo screening and an associated abrupt change of the Fermi surface, our results suggest that the T* line may be quantitatively understood within the picture of robust critical quasiparticles.
Magnetic Structure of NiCr2O4 Studied by Neutron Scattering and Magnetization Measurements
NASA Astrophysics Data System (ADS)
Tomiyasu, Keisuke; Kagomiya, Isao
2004-09-01
The magnetic ordering of the normal spinel ferrimagnet NiCr2O4 below TC = 74 K was reinvestigated by neutron scattering and magnetization measurements on a powder specimen. We found another magnetic transition at TS = 31 K besides TC in both experiments. The ordering of a ferrimagnetic (longitudinal) component and that of an antiferromagnetic (transverse) component occur at TC and TS, separately. A new magnetic structure model of NiCr2O4 below TS with a spontaneous magnetization of about 0.3 μB/formula is proposed based on experimental neutron scattering intensity.
Stimulated Brillouin Scatter in a Magnetized Ionospheric Plasma
Bernhardt, P. A.; Selcher, C. A.; Lehmberg, R. H.; Rodriguez, S. P.; Thomason, J. F.; Groves, K. M.; McCarrick, M. J.; Frazer, G. J.
2010-04-23
High power electromagnetic waves transmitted from the HAARP facility in Alaska can excite low-frequency electrostatic waves by magnetized stimulated Brillouin scatter. Either an ion-acoustic wave with a frequency less than the ion cyclotron frequency (f{sub CI}) or an electrostatic ion cyclotron (EIC) wave just above f{sub CI} can be produced. The coupled equations describing the magnetized stimulated Brillouin scatter instability show that the production of both ion-acoustic and EIC waves is strongly influenced by the wave propagation relative to the background magnetic field. Experimental observations of stimulated electromagnetic emissions using the HAARP transmitter have confirmed that only ion-acoustic waves are excited for propagation along the magnetic zenith and that EIC waves can only be detected with oblique propagation angles. The ion composition can be obtained from the measured EIC frequency.
Stimulated Brillouin scatter in a magnetized ionospheric plasma.
Bernhardt, P A; Selcher, C A; Lehmberg, R H; Rodriguez, S P; Thomason, J F; Groves, K M; McCarrick, M J; Frazer, G J
2010-04-23
High power electromagnetic waves transmitted from the HAARP facility in Alaska can excite low-frequency electrostatic waves by magnetized stimulated Brillouin scatter. Either an ion-acoustic wave with a frequency less than the ion cyclotron frequency (f(CI)) or an electrostatic ion cyclotron (EIC) wave just above f(CI) can be produced. The coupled equations describing the magnetized stimulated Brillouin scatter instability show that the production of both ion-acoustic and EIC waves is strongly influenced by the wave propagation relative to the background magnetic field. Experimental observations of stimulated electromagnetic emissions using the HAARP transmitter have confirmed that only ion-acoustic waves are excited for propagation along the magnetic zenith and that EIC waves can only be detected with oblique propagation angles. The ion composition can be obtained from the measured EIC frequency. PMID:20482059
NASA Astrophysics Data System (ADS)
Metlov, Konstantin L.; Michels, Andreas
2016-04-01
Using analytical expressions for the magnetization textures of thin submicron-sized magnetic cylinders in vortex state, we derive closed-form algebraic expressions for the ensuing small-angle neutron scattering (SANS) cross sections. Specifically, for the perpendicular and parallel scattering geometries, we have computed the cross sections for the case of small vortex-center displacements without formation of magnetic charges on the side faces of the cylinder. The results represent a significant qualitative and quantitative step forward in SANS-data analysis on isolated magnetic nanoparticle systems, which are commonly assumed to be homogeneously or stepwise-homogeneously magnetized. We suggest a way to extract the fine details of the magnetic vortex structure during the magnetization process from the SANS measurements in order to help resolving the long-standing question of the magnetic vortex displacement mode.
Metlov, Konstantin L.; Michels, Andreas
2016-01-01
Using analytical expressions for the magnetization textures of thin submicron-sized magnetic cylinders in vortex state, we derive closed-form algebraic expressions for the ensuing small-angle neutron scattering (SANS) cross sections. Specifically, for the perpendicular and parallel scattering geometries, we have computed the cross sections for the case of small vortex-center displacements without formation of magnetic charges on the side faces of the cylinder. The results represent a significant qualitative and quantitative step forward in SANS-data analysis on isolated magnetic nanoparticle systems, which are commonly assumed to be homogeneously or stepwise-homogeneously magnetized. We suggest a way to extract the fine details of the magnetic vortex structure during the magnetization process from the SANS measurements in order to help resolving the long-standing question of the magnetic vortex displacement mode. PMID:27112640
Critical phenomena of emergent magnetic monopoles in a chiral magnet.
Kanazawa, N; Nii, Y; Zhang, X-X; Mishchenko, A S; De Filippis, G; Kagawa, F; Iwasa, Y; Nagaosa, N; Tokura, Y
2016-01-01
Second-order continuous phase transitions are characterized by symmetry breaking with order parameters. Topological orders of electrons, characterized by the topological index defined in momentum space, provide a distinct perspective for phase transitions, which are categorized as quantum phase transitions not being accompanied by symmetry breaking. However, there are still limited observations of counterparts in real space. Here we show a real-space topological phase transition in a chiral magnet MnGe, hosting a periodic array of hedgehog and antihedgehog topological spin singularities. This transition is driven by the pair annihilation of the hedgehogs and antihedgehogs acting as monopoles and antimonopoles of the emergent electromagnetic field. Observed anomalies in the magnetoresistivity and phonon softening are consistent with the theoretical prediction of critical phenomena associated with enhanced fluctuations of emergent field near the transition. This finding reveals a vital role of topology of the spins in strongly correlated systems. PMID:27181484
Critical phenomena of emergent magnetic monopoles in a chiral magnet
Kanazawa, N.; Nii, Y.; Zhang, X. -X.; Mishchenko, A. S.; De Filippis, G.; Kagawa, F.; Iwasa, Y.; Nagaosa, N.; Tokura, Y.
2016-01-01
Second-order continuous phase transitions are characterized by symmetry breaking with order parameters. Topological orders of electrons, characterized by the topological index defined in momentum space, provide a distinct perspective for phase transitions, which are categorized as quantum phase transitions not being accompanied by symmetry breaking. However, there are still limited observations of counterparts in real space. Here we show a real-space topological phase transition in a chiral magnet MnGe, hosting a periodic array of hedgehog and antihedgehog topological spin singularities. This transition is driven by the pair annihilation of the hedgehogs and antihedgehogs acting as monopoles and antimonopoles of the emergent electromagnetic field. Observed anomalies in the magnetoresistivity and phonon softening are consistent with the theoretical prediction of critical phenomena associated with enhanced fluctuations of emergent field near the transition. This finding reveals a vital role of topology of the spins in strongly correlated systems. PMID:27181484
Critical phenomena of emergent magnetic monopoles in a chiral magnet
NASA Astrophysics Data System (ADS)
Kanazawa, N.; Nii, Y.; Zhang, X.-X.; Mishchenko, A. S.; de Filippis, G.; Kagawa, F.; Iwasa, Y.; Nagaosa, N.; Tokura, Y.
2016-05-01
Second-order continuous phase transitions are characterized by symmetry breaking with order parameters. Topological orders of electrons, characterized by the topological index defined in momentum space, provide a distinct perspective for phase transitions, which are categorized as quantum phase transitions not being accompanied by symmetry breaking. However, there are still limited observations of counterparts in real space. Here we show a real-space topological phase transition in a chiral magnet MnGe, hosting a periodic array of hedgehog and antihedgehog topological spin singularities. This transition is driven by the pair annihilation of the hedgehogs and antihedgehogs acting as monopoles and antimonopoles of the emergent electromagnetic field. Observed anomalies in the magnetoresistivity and phonon softening are consistent with the theoretical prediction of critical phenomena associated with enhanced fluctuations of emergent field near the transition. This finding reveals a vital role of topology of the spins in strongly correlated systems.
Thomson scattering in magnetic fields. [of white dwarf stars
NASA Technical Reports Server (NTRS)
Whitney, Barbara
1989-01-01
The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.
Heat capacity and magnetization of CoNb2O6 near quantum critical point
NASA Astrophysics Data System (ADS)
Liang, Tian; Koohpayeh, Seyed; Krizan, Jason; Dutton, Sian; McQueen, Tyrel; Cava, Robert; Phuan Ong, N.
2012-02-01
CoNb2O6 is a quasi-1D quantum magnet in which magnetic Co^2+ ions are ferromagnetically arranged into nearly isolated chains along the c axis with the magnetic moment confined in the ac-plane. By applying transverse magnetic field along b-axis, quantum phase transition from magnetically ordered phase to paramagnetic phase occurs. Evidence for emergent E8 symmetry was recently obtained by neutron scattering near the quantum critical point (QCP) in an applied transverse magnetic field of 5.5 T We will report on experiments to investigate the behavior of the heat capacity and torque magnetization in the vicinity of the QCP and discuss their implications.
Chaotic Scattering In Magnetic Current Sheets
NASA Astrophysics Data System (ADS)
Martin, R.; Holland, D.; Matsuoka, H.; Rappa, R.
We revisit the subject of nonlinear charged particle dynamics and chaos in current sheet magnetic fields using the modified Harris magnetic field. While much has been written on this subject in the last decade we feel there are some as-yet-unanswered fundamental questions as well as some "folklore" which is in need of clarification. We begin by demonstrating that the general behavior of the average exponential di- vergence rate (AEDR) of individual orbits is strongly correlated with the phase space partitions, i.e. the AEDR for integrable orbits goes to zero for long times, the AEDR of stochastic orbits approaches an asymptotic value for long times, and the AEDR of transient orbits (and short lived stochastic orbits) is not well defined. Furthermore, we show that the Lyapunov exponent for a distribution of particles only has well de- fined values at the resonant energy surfaces defined by Burkhart and Chen. Next it is shown that the "chaos" of the system is maximum at = 1 only in the sense that a lot of particles enter the stochastic region of phase space for this energy. The average Lyapunov exponent at = 1 actually approaches zero, and for those energies where the Lyapunov exponent is defined, it increases as the ratio of normal component of the field to the asymptotic field strength increases. Finally, we present particle escape rate and fractal invariant set results corroborating these conclusions and consider the consequences for anomalous transport in these fields.
Magnetic behavior of dirty multiband superconductors near the upper critical field
NASA Astrophysics Data System (ADS)
Silaev, Mikhail
2016-06-01
Magnetic properties of dirty multiband superconductors near the upper critical field are studied. The parameter κ2 characterizing magnetization slope is shown to have a significant temperature variation which is quite sensitive to the pairing interactions and relative strengths of intraband impurity scattering. In contrast to single-band superconductors the increase of κ2 at low temperatures can be arbitrarily large determined by the ratio of maximal and minimal diffusion coefficients in different bands. Temperature dependencies of κ2(T ) in two-band MgB2 and iron-based superconductors are shown to be much more sensitive to the multiband effects than the upper critical field Hc 2(T ) .
Surface Raman scattering from effervescent magnetic peroxyborates
NASA Astrophysics Data System (ADS)
Walrafen, G. E.; Krishnan, P. N.; Griscom, D. L.; Munro, R.
1982-06-01
Surface Raman scattering using a spinning technique was investigated for solid NaBO3.4H2O and NaBO3.H2O as well as for electron bombarded peroxyborates heated for various times and at temperatures form 110-180 deg C, and for solid Na2O2 and BaO2. The Raman spectra indicate that the breakdown of peroxy groups is accompanied by the formation of trapped molecular O2. Quantitative Raman intensity data were also obtained as functions of heating time at 115 deg C for the 1556 cm-1 line from O2 and for the 890 and 705 cm-1 lines whose intensities scale with the peroxy concentration. These intensity data were treated by logistics theory, and they were found to be consistent with a second-order auto-catalyzed forward reaction dependent on the product of the peroxy and O2 concentrations, plus a first-order reverse reaction dependent only on the O2 concentration.
Surface Raman scattering from effervescent magnetic peroxyborates
NASA Astrophysics Data System (ADS)
Walrafen, G. E.; Krishnan, P. N.; Hokmabadi, M.; Griscom, D. L.; Munro, R. G.
1982-10-01
Surface Raman scattering using a spinning technique was investigated for solid NaBO3ṡ4H2O and NaBO3ṡH2O, as well as for electron bombarded peroxyborates, for peroxyborates heated for various times and at temperatures for 110-180 °C, and for solid Na2O2 and BaO2. The Raman spectra indicate that the breakdown of peroxy groups is accompanied by the formation of trapped molecular O2. Quantitative Raman intensity data were also obtained as functions of heating time at 115 °C for the 1556 cm-1 line from O2 and for the 890 and 705 cm-1 lines whose intensities scale with the peroxy concentration. These intensity data were treated by logistics theory, and they were found to be consistent with a second-order autocatalyzed forward reaction dependent on the product of the peroxy and O2 concentrations, plus a first-order reverse reaction dependent only on the O2 concentration.
Resonant magnetic scattering of polarized soft x rays
Sacchi, M.; Hague, C.F.; Gullikson, E.M.; Underwood, J.
1997-04-01
Magnetic effects on X-ray scattering (Bragg diffraction, specular reflectivity or diffuse scattering) are a well known phenomenon, and they also represent a powerful tool for investigating magnetic materials since it was shown that they are strongly enhanced when the photon energy is tuned across an absorption edge (resonant process). The resonant enhancement of the magnetic scattering has mainly been investigated at high photon energies, in order to match the Bragg law for the typical lattice spacings of crystals. In the soft X-ray range, even larger effects are expected, working for instance at the 2p edges of transition metals of the first row or at the 3d edges of rare earths (300-1500 eV), but the corresponding long wavelengths prevent the use of single crystals. Two approaches have been recently adopted in this energy range: (i) the study of the Bragg diffraction from artificial structures of appropriate 2d spacing; (ii) the analysis of the specular reflectivity, which contains analogous information but has no constraints related to the lattice spacing. Both approaches have their own specific advantages: for instance, working under Bragg conditions provides information about the (magnetic) periodicity in ordered structures, while resonant reflectivity can easily be related to electronic properties and absorption spectra. An important aspect common to all the resonant X-ray scattering techniques is the element selectivity inherent to the fact of working at a specific absorption edge: under these conditions, X-ray scattering becomes in fact a spectroscopy. Results are presented for films of iron and cobalt.
Inelastic neutron scattering studies of novel quantum magnets
NASA Astrophysics Data System (ADS)
Plumb, Kemp W.
Inelastic neutron scattering was used to study the magnetic excitation spectrum of three quantum magnets: (i) the double perovskite Ba2FeReO 6; (ii) the two-dimensional square lattice Heisenberg antiferromagnet Sr2CuO2Cl2; and (iii) the quasi-two-dimensional frustrated two-leg ladder BiCu2PO6. We have conducted inelastic neutron scattering measurements on powder samples of the double perovskite compound Ba2FeReO6. The measurements revealed two well defined dispersing spin wave modes. No excitation gap was observable and the spectrum can be explained with a local moment model incorporating the interactions of Fe spins with spin-orbital locked degrees of freedom on the Re site. The results reveal that both significant electronic correlations and spin-orbit coupling on the Re site play a significant role in the spin dynamics of Ba2FeReO6. High resolution neutron scattering measurements of magnetic excitations in the parent cuprate Sr2CuO2Cl2 reveal a significant dispersion and momentum dependent damping of the zone boundary magnons. We directly compare our measurements with previous resonant inelastic x-ray scattering measurements and find a ~25 meV discrepancy between the two techniques for the measured zone boundary energy at (1/2, 0). The deviations are greatest precisely in the region of phase space where the magnon damping is strongest. This comparison shows that the inelastic x-ray spectrum must contain significant contributions from higher energy excitations not previously considered. Our measurements demonstrate that the high energy continuum of magnetic fluctuations is a ubiquitous feature of the magnetic spectrum among insulating monolayer cuprates, and that these excitations couple to both inelastic neutron and light scattering. A comprehensive series of inelastic neutron scattering measurements was used to investigate spin excitations in the frustrated two-leg ladder compound BiCu2PO6. The measurements revealed six branches of steeply dispersing triplon
NASA Astrophysics Data System (ADS)
Waldmann, O.; Carver, G.; Dobe, C.; Biner, D.; Sieber, A.; Güdel, H. U.; Mutka, H.; Ollivier, J.; Chakov, N. E.
2006-01-01
Time-resolved inelastic neutron scattering measurements on an array of single-crystals of the single-molecule magnet Mn12ac are presented. The data facilitate a spectroscopic investigation of the slow relaxation of the magnetization in this compound in the time domain.
CPP magnetoresistance of magnetic multilayers: A critical review
NASA Astrophysics Data System (ADS)
Bass, Jack
2016-06-01
We present a comprehensive, critical review of data and analysis of Giant (G) Magnetoresistance (MR) with Current-flow Perpendicular-to-the-layer-Planes (CPP-MR) of magnetic multilayers [F/N]n (n=number of repeats) composed of alternating nanoscale layers of ferromagnetic (F) and non-magnetic (N) metals, or of spin-valves that allow control of anti-parallel (AP) and parallel (P) orientations of the magnetic moments of adjacent F-layers. GMR, a large change in resistance when an applied magnetic field changes the moment ordering of adjacent F-layers from AP to P, was discovered in 1988 in the geometry with Current flow in the layer-Planes (CIP). The CPP-MR has two advantages over the CIP-MR: (1) relatively simple two-current series-resistor (2CSR) and more general Valet-Fert (VF) models allow more direct access to the underlying physics; and (2) it is usually larger, which should be advantageous for devices. When the first CPP-MR data were published in 1991, it was not clear whether electronic transport in GMR multilayers is completely diffusive or at least partly ballistic. It was not known whether the properties of layers and interfaces would vary with layer thickness or number. It was not known whether the CPP-MR would be dominated by scattering within the F-metals or at the F/N interfaces. Nothing was known about: (1) spin-flipping within F-metals, characterized by a spin-diffusion length, lsfF; (2) interface specific resistances (AR=area A times resistance R) for N1/N2 interfaces; (3) interface specific resistances and interface spin-dependent scattering asymmetry at F/N and F1/F2 interfaces; and (4) spin-flipping at F/N, F1/F2 and N1/N2 interfaces. Knowledge of spin-dependent scattering asymmetries in F-metals and F-alloys, and of spin-flipping in N-metals and N-alloys, was limited. Since 1991, CPP-MR measurements have quantified the scattering and spin-flipping parameters that determine GMR for a wide range of F- and N-metals and alloys and of F/N pairs. This
Thomson scattering in a magnetic field. I - Field along z
NASA Technical Reports Server (NTRS)
Whitney, Barbara A.
1991-01-01
The Monte Carlo method is used here to solve the radiative transfer equation for Thomson scattering in a constant magnetic field perpendicular to the atmosphere. Emergent radiation and polarization are presented for various atmospheric thicknesses. The circular polarization peaks at frequencies near the cyclotron, omega(c), and for propagation direction along the field. At low field strengths, the circular polarization is roughly proportional to omega(c)/omega; the linear polarization is proportional to the square of omega(c)/omega and the amount of circular polarization present at each scatter and is therefore much smaller than the circular polarization. The linear polarization is large for propagation direction perpendicular to the magnetic field and at frequencies near the cyclotron and in the strong-field limit. The position angle of the linear polarization undergoes a rotation of 90 deg at a value of omega(c)/omega near the square root of three.
Magnetic-Polaron-Induced Enhancement of Surface Raman Scattering.
Shao, Qi; Liao, Fan; Ruotolo, Antonio
2016-01-01
The studies of the effects of magnetic field on surface enhanced Raman scattering (SERS) have been so far limited to the case of ferromagnetic/noble-metal, core/shell nano-particles, where the influence was always found to be negative. In this work, we investigate the influence of magnetic field on a diluted magnetic semiconductor/metal SERS system. Guided by three dimensional finite-difference time-domain simulations, a high efficient SERS substrate was obtained by diluting Mn into Au-capped ZnO, which results in an increase of the dielectric constant and, therefore, an enhancement of Raman signals. More remarkably, an increase of intensities as well as a reduction of the relative standard deviation (RSD) of Raman signals have been observed as a function of the external magnetic strength. We ascribe these positive influences to magnetic-field induced nucleation of bound magnetic polarons in the Mn doped ZnO. The combination of diluted magnetic semiconductors and SERS may open a new avenue for future magneto-optical applications. PMID:26754049
Magnetic-Polaron-Induced Enhancement of Surface Raman Scattering
Shao, Qi; Liao, Fan; Ruotolo, Antonio
2016-01-01
The studies of the effects of magnetic field on surface enhanced Raman scattering (SERS) have been so far limited to the case of ferromagnetic/noble-metal, core/shell nano-particles, where the influence was always found to be negative. In this work, we investigate the influence of magnetic field on a diluted magnetic semiconductor/metal SERS system. Guided by three dimensional finite-difference time-domain simulations, a high efficient SERS substrate was obtained by diluting Mn into Au-capped ZnO, which results in an increase of the dielectric constant and, therefore, an enhancement of Raman signals. More remarkably, an increase of intensities as well as a reduction of the relative standard deviation (RSD) of Raman signals have been observed as a function of the external magnetic strength. We ascribe these positive influences to magnetic-field induced nucleation of bound magnetic polarons in the Mn doped ZnO. The combination of diluted magnetic semiconductors and SERS may open a new avenue for future magneto-optical applications. PMID:26754049
High-pressure neutron scattering of Prussian blue analogue magnets
NASA Astrophysics Data System (ADS)
Pajerowski, Daniel
Pressure sensitive magnetism is known to be useful in sensors, and while applications tend to use metallic alloys, molecule based magnets (MBMs) have been shown to have large inverse magnetostrictive (IMS) response. A promising group of MBMs are the Prussian blue analogues (PBAs), in which magnetic ordering can be tuned by external stimuli such as light, electric field, and pressure. Previously, high pressure neutron scattering of nickel hexacyanochromate hydrate has shown direct evidence for isomerization of the cyanide linkage with applied pressure. Other probes have suggested a similar effect in iron hexacyanochromate hydrate, although there has yet to be direct crystallographic evidence. Neutron diffraction is sensitive to organic elements, even while in the presence of metals, and we have performed experiments above 1 GPa to look for linkage isomerism in iron hexacyanochromate. These results are supported by bulk probes and calculations.
Charge-magnetic interference resonant scattering studies of ferromagnetic crystals and thin films
Haskel, D.; Kravtsov, E.; Choi, Y.; Lang, J.C.; Islam, Z.; Srajer, G.; Jiang, J.S.; Bader, S.D.; Canfield, Paul C.
2012-06-15
The element- and site-specificity of X-ray resonant magnetic scattering (XRMS) makes it an ideal tool for furthering our understanding of complex magnetic systems. In the hard X-rays, XRMS is readily applied to most antiferromagnets where the relatively weak resonant magnetic scattering (10 −2–10 −6Ic) is separated in reciprocal space from the stronger, Bragg charge scattered intensity, Ic. In ferro(ferri)magnetic materials, however, such separation does not occur and measurements of resonant magnetic scattering in the presence of strong charge scattering are quite challenging. We discuss the use of charge-magnetic interference resonant scattering for studies of ferromagnetic (FM) crystals and layered films. We review the challenges and opportunities afforded by this approach, particularly when using circularly polarized X-rays.We illustrate current capabilities at the Advanced Photon Source with studies aimed at probing site-specific magnetism in ferromagnetic crystals, and interfacial magnetism in films.
NASA Astrophysics Data System (ADS)
Agui, Akane; Masuda, Ryo; Kobayashi, Yasuhiro; Kato, Tadashi; Emoto, Shun; Suzuki, Kosuke; Sakurai, Hiroshi
2016-06-01
The magnetization process of Fe (110) film was investigated using the field dependence of magnetic Compton scattering and Mössbauer spectroscopy. The spin and orbital magnetic moment specific magnetization versus magnetizing field curves were obtained from the magnetic Compton profiles, and the angles between the magnetizing field and the magnetic moment, θ, were obtained from the Mössbauer spectra. It was found that the magnetizing field dependence of the ratio between orbital moment and spin moment was related to θ. We indicate that the magnetic field dependence of the orbital magnetic moment plays a role in the magnetization process.
COOLING RATES FOR RELATIVISTIC ELECTRONS UNDERGOING COMPTON SCATTERING IN STRONG MAGNETIC FIELDS
Baring, Matthew G.; Wadiasingh, Zorawar; Gonthier, Peter L. E-mail: zw1@rice.edu
2011-05-20
For inner magnetospheric models of hard X-ray and gamma-ray emission in high-field pulsars and magnetars, resonant Compton upscattering is anticipated to be the most efficient process for generating continuum radiation. This is in part due to the proximity of a hot soft photon bath from the stellar surface to putative radiation dissipation regions in the inner magnetosphere. Moreover, because the scattering process becomes resonant at the cyclotron frequency, the effective cross section exceeds the classical Thomson value by over two orders of magnitude, thereby enhancing the efficiency of continuum production and the cooling of relativistic electrons. This paper presents computations of the electron cooling rates for this process, which are needed for resonant Compton models of non-thermal radiation from such highly magnetized pulsars. The computed rates extend previous calculations of magnetic Thomson cooling to the domain of relativistic quantum effects, sampled near and above the quantum critical magnetic field of 44.13 TG. This is the first exposition of fully relativistic, quantum magnetic Compton cooling rates for electrons, and it employs both the traditional Johnson and Lippmann cross section and a newer Sokolov and Ternov (ST) formulation of Compton scattering in strong magnetic fields. Such ST formalism is formally correct for treating spin-dependent effects that are important in the cyclotron resonance and has not been addressed before in the context of cooling by Compton scattering. The QED effects are observed to profoundly lower the rates below extrapolations of the familiar magnetic Thomson results, as expected, when recoil and Klein-Nishina reductions become important.
Analytical expression for critical frequency of microwave assisted magnetization switching
NASA Astrophysics Data System (ADS)
Arai, Hiroko; Imamura, Hiroshi
2016-02-01
The microwave-assisted switching (MAS) of magnetization in a perpendicularly magnetized circular disk is studied based on the macrospin model in a rotating frame. The analytical expression for the critical frequency of MAS is derived by analyzing the presence of a quasiperiodic mode. The critical frequency is expressed as a function of the radio frequency (rf) field Hrf and the effective anisotropy field H\\text{k}\\text{eff}. For a small rf field such that H\\text{rf} \\ll H\\text{k}\\text{eff}, the critical frequency is approximately equal to (γ /π )\\root 3 \\of{\\smash{H\\text{k}\\text{eff}H\\text{rf}2}\\mathstrut}.
Magnetic properties of Ga doped cobalt ferrite: Compton scattering study
Sharma, Arvind Mund, H. S.; Ahuja, B. L.; Sahariya, Jagrati; Itou, M.; Sakurai, Y.
2014-04-24
We present the spin momentum density of Ga doped CoFe{sub 2}O{sub 4} at 100 K using magnetic Compton scattering. The measurement has been performed using circularly polarized synchrotron radiations of 182.65 keV at SPring8, Japan. The experimental profile is decomposed into its constituent profile to determine the spin moment at individual sites. Co atom has the maximum contribution (about 58%) in the total spin moment of the doped CoFe{sub 2}O{sub 4}.
Neutron and synchrotron radiation scattering by nonpolar magnetic fluids
NASA Astrophysics Data System (ADS)
Aksenov, V. L.; Avdeev, M. V.; Shulenina, A. V.; Zubavichus, Y. V.; Veligzhanin, A. A.; Rosta, L.; Garamus, V. M.; Vekas, L.
2011-09-01
The complex approach (which comprises different physical methods, including neutron and synchrotron radiation scattering) is justified in the structural analysis of magnetic fluids (MFs). Investigations of MFs based on nonpolar organic solvents with magnetite nanoparticles (2-20 nm in size) coated by various monocarboxylic acids have been performed. It is shown that the use of saturated linear acids with various alkyl chain (C12-C18) lengths instead of unsaturated oleic acid (alkyl chain C18 with a kink in the middle due to the double bond in the cis-configuration) in the classical stabilization procedure for the given type of magnetic fluids leads to a decrease in the mean size and polydispersity of nanoparticles in the final systems.
Characterization of magnetic nanoparticle by dynamic light scattering
2013-01-01
Here we provide a complete review on the use of dynamic light scattering (DLS) to study the size distribution and colloidal stability of magnetic nanoparticles (MNPs). The mathematical analysis involved in obtaining size information from the correlation function and the calculation of Z-average are introduced. Contributions from various variables, such as surface coating, size differences, and concentration of particles, are elaborated within the context of measurement data. Comparison with other sizing techniques, such as transmission electron microscopy and dark-field microscopy, revealed both the advantages and disadvantages of DLS in measuring the size of magnetic nanoparticles. The self-assembly process of MNP with anisotropic structure can also be monitored effectively by DLS. PMID:24011350
Neutron and synchrotron radiation scattering by nonpolar magnetic fluids
Aksenov, V. L.; Avdeev, M. V.; Shulenina, A. V.; Zubavichus, Y. V.; Veligzhanin, A. A.; Rosta, L.; Garamus, V. M.; Vekas, L.
2011-09-15
The complex approach (which comprises different physical methods, including neutron and synchrotron radiation scattering) is justified in the structural analysis of magnetic fluids (MFs). Investigations of MFs based on nonpolar organic solvents with magnetite nanoparticles (2-20 nm in size) coated by various monocarboxylic acids have been performed. It is shown that the use of saturated linear acids with various alkyl chain (C12-C18) lengths instead of unsaturated oleic acid (alkyl chain C18 with a kink in the middle due to the double bond in the cis-configuration) in the classical stabilization procedure for the given type of magnetic fluids leads to a decrease in the mean size and polydispersity of nanoparticles in the final systems.
Tuning Mie scattering resonances in soft materials with magnetic fields.
Brunet, Thomas; Zimny, Kevin; Mascaro, Benoit; Sandre, Olivier; Poncelet, Olivier; Aristégui, Christophe; Mondain-Monval, Olivier
2013-12-27
An original approach is proposed here to reversibly tune Mie scattering resonances occurring in random media by means of external low induction magnetic fields. This approach is valid for both electromagnetic and acoustic waves. The experimental demonstration is supported by ultrasound experiments performed on emulsions made of fluorinated ferrofluid spherical droplets dispersed in a Bingham fluid. We show that the electromagnet-induced change of droplet shape into prolate spheroids, with a moderate aspect ratio of 2.5, drastically affects the effective properties of the disordered medium. Its effective acoustic attenuation coefficient is shown to vary by a factor of 5, by controlling both the flux density and orientation of the applied magnetic field. PMID:24483797
Critical Current Measurements in Commercial Tapes, Coils, and Magnets.
NASA Astrophysics Data System (ADS)
Gubser, D. U.; Soulen, R. J., Jr.; Fuller-Mora, W. W.; Francavilla, T. L.
1996-03-01
We have measured a number of tapes, coils, and magnets produced by commercial vendors and determined their properties as functions of magnetic field and temperature. The tapes were measured at the National High Magnetic Field Laboratory in magnetic fields to 20 tesla and at temperatures of 4.2 K, 27 K, 65 K, and 77 K. For the tapes we report critical currents and current-voltage characteristics. Six inch diameter coils were measured at NRL in zero magnetic field. Critical currents, current-voltage characteristics, and reliability studies are reported for the coils. Larger 10 inch diameter coils, which are to be used in a 200 hp superconducting motor, were also measured and results will be presented. The talk will also review the status of the most recent tests of the superconducting motor.
Magnetically modulated critical current densities of Co/Nb hybrid
NASA Astrophysics Data System (ADS)
Li, Zhigang; Wang, Weike; Zhang, Li; Yang, Zhaorong; Tian, Mingliang; Zhang, Yuheng
2015-12-01
By tuning morphology and size of magnetic subsystem, ferromagnet-superconductor (F/S) hybrid system provides an effective way to modulate superconductivity due to the interaction between superconducting and magnetic-order parameters at the mesoscopic length scale. In this work, we report on investigations of critical current density in a large-area Co/Nb hybrid via facile colloidal lithography. Here, Co hexagon shell array as a magnetic template build on Nb film to modulate the critical current density. A novel superconducting transition has been observed in I-V curve with two metastable transition states: double-transition and binary-oscillation-transition states. Importantly, such unusual behavior can be adjusted by temperature, magnetic field and contact area of F/S. Such hybrid film has important implications for understanding the role of magnetic subsystem modulating superconductivity, as well as applied to low-energy electronic devices such as superconducting current fault limiters.
Magnetically modulated critical current densities of Co/Nb hybrid
Li, Zhigang; Wang, Weike; Zhang, Li; Yang, Zhaorong; Tian, Mingliang; Zhang, Yuheng
2015-01-01
By tuning morphology and size of magnetic subsystem, ferromagnet-superconductor (F/S) hybrid system provides an effective way to modulate superconductivity due to the interaction between superconducting and magnetic-order parameters at the mesoscopic length scale. In this work, we report on investigations of critical current density in a large-area Co/Nb hybrid via facile colloidal lithography. Here, Co hexagon shell array as a magnetic template build on Nb film to modulate the critical current density. A novel superconducting transition has been observed in I-V curve with two metastable transition states: double-transition and binary-oscillation-transition states. Importantly, such unusual behavior can be adjusted by temperature, magnetic field and contact area of F/S. Such hybrid film has important implications for understanding the role of magnetic subsystem modulating superconductivity, as well as applied to low-energy electronic devices such as superconducting current fault limiters. PMID:26678595
Determination of liquid-liquid critical point composition using 90∘ laser light scattering
NASA Astrophysics Data System (ADS)
Williamson, J. Charles; Brown, Allison M.; Helvie, Elise N.; Dean, Kevin M.
2016-04-01
Despite over a century of characterization efforts, liquid-liquid critical point compositions are difficult to identify with good accuracy. Reported values vary up to 10% for even well-studied systems. Here, a technique is presented for high-precision determination of the critical composition of a partially miscible binary liquid system. Ninety-degree laser light-scattering intensities from single-phase samples are analyzed using an equation derived from nonclassical power laws and the pseudospinodal approximation. Results are reported for four liquid-liquid systems (aniline + hexane, isobutyric acid + water, methanol + cyclohexane, and methanol + carbon disulfide). Compared to other methods, the 90∘ light-scattering approach has a strong dependence on composition near the critical point, is less affected by temperature fluctuations, and is insensitive to the presence of trace impurities in the samples. Critical compositions found with 90∘ light scattering are precise to the parts-per-thousand level and show long-term reproducibility.
Chen, Bao-Qin; Zhang, Chao; Li, Jiafang; Li, Zhi-Yuan; Xia, Younan
2016-08-25
Electromagnetic and chemical enhancement mechanisms are commonly used to account for single-molecule surface-enhanced Raman scattering (SM-SERS). Due to many practical limitations, however, the overall enhancement factor summed up from these two mechanisms is typically 5-6 orders of magnitude below the level of 10(14)-10(15) required for SM-SERS. Here, we demonstrate that the multiple elastic Rayleigh scattering of a molecule could play a critical role in further enhancing the Raman signal, when the molecule is trapped in a 2 nm gap between two Ag nanoparticles, pushing the overall enhancement factor close to the level needed for SM-SERS. As a universal physical process for all molecules interacting with light, we believe that Rayleigh scattering plays a pivotal and as yet unrecognized role in SERS, in particular, for enabling single-molecule sensitivity. PMID:27526632
Attraction, merger, reflection, and annihilation in magnetic droplet soliton scattering
NASA Astrophysics Data System (ADS)
Maiden, M. D.; Bookman, L. D.; Hoefer, M. A.
2014-05-01
The interaction behaviors of solitons are defining characteristics of these nonlinear, coherent structures. Due to recent experimental observations, thin ferromagnetic films offer a promising medium in which to study the scattering properties of two-dimensional magnetic droplet solitons, particle-like, precessing dipoles. Here, a rich set of two-droplet interaction behaviors are classified through micromagnetic simulations. Repulsive and attractive interaction dynamics are generically determined by the relative phase and speeds of the two droplets and can be classified into four types: (1) merger into a breather bound state, (2) counterpropagation trapped along the axis of symmetry, (3) reflection, and (4) violent droplet annihilation into spin wave radiation and a breather. Utilizing a nonlinear method of images, it is demonstrated that these dynamics describe repulsive/attractive scattering of a single droplet off of a magnetic boundary with pinned/free spin boundary conditions, respectively. These results explain the mechanism by which propagating and stationary droplets can be stabilized in a confined ferromagnet.
NASA Astrophysics Data System (ADS)
Piecuch, Michel
The goal of this chapter is to present three traditional methods for the study of magnetic properties : Mössbauer effect, neutron diffraction and nuclear magnetic resonance. It begins by recalling the basic properties of atomic nuclei and describing the hyperfine interactions between the nucleus and its surrounding. Then, the recoilless absorption of γ-rays by crystal, the Mössbauer effect is presented, we discuss the main parameters measured and show one example of application. Next we present neutron interactions with matter, the interaction of neutrons with the atomic nucleus and the interaction of the neutron magnetic moment with the magnetic moment of electrons. The use of polarized neutron and the inelastic scattering of neutrons are also discussed. The comparison between neutron experiments and synchrotron radiation techniques is briefly reviewed. One example of the use of neutron scattering in the domain of thin film magnetism is shown. Finally, we present the basic theory of nuclear magnetic resonance and one application of this technique to the study of Co/Cu multilayers.
NASA Astrophysics Data System (ADS)
Köber, Mariana; Moros, Maria; Grazú, Valeria; de la Fuente, Jesus M.; Luna, Mónica; Briones, Fernando
2012-04-01
The increasing use of biofunctionalized magnetic nanoparticles in biomedical applications calls for further development of characterization tools that allow for determining the interactions of the nanoparticles with the biological medium in situ. In cell-incubating conditions, for example, nanoparticles may aggregate and serum proteins adsorb on the particles, altering the nanoparticles’ performance and their interaction with cell membranes. In this work we show that the aggregation of spherical magnetite nanoparticles can be detected with high sensitivity in dense, highly light scattering media by making use of magnetically induced birefringence. Moreover, the hydrodynamic particle diameter distribution of anisometric nanoparticle aggregates can be determined directly in these media by monitoring the relaxation time of the magnetically induced birefringence. As a proof of concept, we performed measurements on nanoparticles included in an agarose gel, which scatters light in a similar way as a more complex biological medium but where particle-matrix interactions are weak. Magnetite nanoparticles were separated by agarose gel electrophoresis and the hydrodynamic diameter distribution was determined in situ. For the different particle functionalizations and agarose concentrations tested, we could show that gel electrophoresis did not yield a complete separation of monomers and small aggregates, and that the electrophoretic mobility of the aggregates decreased linearly with the hydrodynamic diameter. Furthermore, the rotational particle diffusion was not clearly affected by nanoparticle-gel interactions. The possibility to detect nanoparticle aggregates and their hydrodynamic diameters in complex scattering media like cell tissue makes transient magnetic birefringence an interesting technique for biological applications.
Köber, Mariana; Moros, Maria; Grazú, Valeria; de la Fuente, Jesus M; Luna, Mónica; Briones, Fernando
2012-04-20
The increasing use of biofunctionalized magnetic nanoparticles in biomedical applications calls for further development of characterization tools that allow for determining the interactions of the nanoparticles with the biological medium in situ. In cell-incubating conditions, for example, nanoparticles may aggregate and serum proteins adsorb on the particles, altering the nanoparticles' performance and their interaction with cell membranes. In this work we show that the aggregation of spherical magnetite nanoparticles can be detected with high sensitivity in dense, highly light scattering media by making use of magnetically induced birefringence. Moreover, the hydrodynamic particle diameter distribution of anisometric nanoparticle aggregates can be determined directly in these media by monitoring the relaxation time of the magnetically induced birefringence. As a proof of concept, we performed measurements on nanoparticles included in an agarose gel, which scatters light in a similar way as a more complex biological medium but where particle-matrix interactions are weak. Magnetite nanoparticles were separated by agarose gel electrophoresis and the hydrodynamic diameter distribution was determined in situ. For the different particle functionalizations and agarose concentrations tested, we could show that gel electrophoresis did not yield a complete separation of monomers and small aggregates, and that the electrophoretic mobility of the aggregates decreased linearly with the hydrodynamic diameter. Furthermore, the rotational particle diffusion was not clearly affected by nanoparticle-gel interactions. The possibility to detect nanoparticle aggregates and their hydrodynamic diameters in complex scattering media like cell tissue makes transient magnetic birefringence an interesting technique for biological applications. PMID:22456180
Critical Casimir forces in a magnetic system: An experimental protocol
NASA Astrophysics Data System (ADS)
Lopes Cardozo, David; Jacquin, Hugo; Holdsworth, Peter C. W.
2014-11-01
We numerically test an experimentally realizable method for the extraction of the critical Casimir force based on its thermodynamic definition as the derivative of the excess free energy with respect to system size. Free energy differences are estimated for different system sizes by integrating the order parameter along an isotherm. The method could be developed for experiments on magnetic systems and could give access to the critical Casimir force for any universality class. By choosing an applied field that opposes magnetic ordering at the boundaries, the Casimir force is found to increase by an order of magnitude over zero-field results.
NASA Astrophysics Data System (ADS)
Weier, C.; Adam, R.; Rudolf, D.; Frömter, R.; Grychtol, P.; Winkler, G.; Kobs, A.; Oepen, H. P.; Kapteyn, H. C.; Murnane, M. M.; Schneider, C. M.
2015-01-01
We characterize the magnetic domain structure of Co/Pt multilayer films on length scales below one hundred nanometers using resonant magnetic scattering and magnetic force microscopy. The extreme ultraviolet light for the scattering experiment is created by a laser-based high-order harmonic generation source. After illumination with intense ultrashort infrared laser pulses, we observe pronounced changes in the magnetic structure and morphology. This study points out the importance of a detailed analysis of the different laser-induced modifications of a magnetic thin film that influence the scattering patterns.
Compton scattering in strong magnetic fields: Spin-dependent influences at the cyclotron resonance
NASA Astrophysics Data System (ADS)
Gonthier, Peter L.; Baring, Matthew G.; Eiles, Matthew T.; Wadiasingh, Zorawar; Taylor, Caitlin A.; Fitch, Catherine J.
2014-08-01
The quantum electrodynamical (QED) process of Compton scattering in strong magnetic fields is commonly invoked in atmospheric and inner magnetospheric models of x-ray and soft gamma-ray emission in high-field pulsars and magnetars. A major influence of the field is to introduce resonances at the cyclotron frequency and its harmonics, where the incoming photon accesses thresholds for the creation of virtual electrons or positrons in intermediate states with excited Landau levels. At these resonances, the effective cross section typically exceeds the classical Thomson value by over 2 orders of magnitude. Near and above the quantum critical magnetic field of 44.13 TeraGauss, relativistic corrections must be incorporated when computing this cross section. This profound enhancement underpins the anticipation that resonant Compton scattering is a very efficient process in the environs of highly magnetized neutron stars. This paper presents formalism for the QED magnetic Compton differential cross section valid for both subcritical and supercritical fields, yet restricted to scattered photons that are below pair creation threshold. Calculations are developed for the particular case of photons initially propagating along the field, and in the limit of zero vacuum dispersion, mathematically simple specializations that are germane to interactions involving relativistic electrons frequently found in neutron star magnetospheres. This exposition of relativistic, quantum, magnetic Compton cross sections treats electron spin dependence fully, since this is a critical feature for describing the finite decay lifetimes of the intermediate states. Such lifetimes are introduced to truncate the resonant cyclotronic divergences via standard Lorentz profiles. The formalism employs both the traditional Johnson and Lippmann (JL) wave functions and the Sokolov and Ternov (ST) electron eigenfunctions of the magnetic Dirac equation. The ST states are formally correct for self
Interference between magnetism and surface roughness in coherent soft X-ray scattering
Rahmim, A.; Tixier, S.; Tiedje, T.; Eisebitt, S.; Lorgen, M.; Scherer, R.; Eberhardt, W.; Luning, J.; Scholl, A.
2002-06-15
In coherent soft x-ray scattering from magnetically ordered surfaces there are contributions to the scattering from the magnetic domains, from the surface roughness, and from the diffraction associated with the pinhole aperture used as a coherence filter. In the present work, we explore the interplay between these contributions by analyzing speckle patterns in diffusely scattered x rays from the surface of magnetic thin films. Magnetic contrast from the surface of anti ferro magnetically ordered LaFeO3 films is caused by magnetic linear dichroism in resonant x-ray scattering. The samples studied possess two types of domains with their magnetic orientations perpendicular to each other. By tuning the x-ray energy from one of the two Fe-L3 resonant absorption peaks to the other, the relative amplitudes of the x-ray scattering from the two domains is inverted which results in speckle pattern changes. A theoretical expression is derived for the intensity correlation between the speckle patterns with the magnetic contrast inverted and not inverted. The model is found to be in good agreement with the x-ray-scattering observations and independent measurements of the surface roughness. An analytical expression for the correlation function gives an explicit relation between the change in the speckle pattern and the roughness, and magnetic and aperture scattering. Changes in the speckle pattern are shown to arise from beating of magnetic scattering with the roughness scattering and diffraction from the aperture. The largest effect is found when the surface roughness scatter is comparable in intensity to the magnetic scatter.
Replacing critical rare earth materials in high energy density magnets
NASA Astrophysics Data System (ADS)
McCallum, R. William
2012-02-01
High energy density permanent magnets are crucial to the design of internal permanent magnet motors (IPM) for hybride and electric vehicles and direct drive wind generators. Current motor designs use rare earth permanent magnets which easily meet the performance goals, however, the rising concerns over cost and foreign control of the current supply of rare earth resources has motivated a search for non-rare earth based permanent magnets alloys with performance metrics which allow the design of permanent magnet motors and generators without rare earth magnets. This talk will discuss the state of non-rare-earth permanent magnets and efforts to both improve the current materials and find new materials. These efforts combine first principles calculations and meso-scale magnetic modeling with advance characterization and synthesis techniques in order to advance the state of the art in non rare earth permanent magnets. The use of genetic algorithms in first principle structural calculations, combinatorial synthesis in the experimental search for materials, atom probe microscopy to characterize grain boundaries on the atomic level, and other state of the art techniques will be discussed. In addition the possibility of replacing critical rare earth elements with the most abundant rare earth Ce will be discussed.
Neutron scattering studies of the magnetic structure of cupric oxide
NASA Astrophysics Data System (ADS)
Yang, B. X.; Tranquada, J. M.; Shirane, G.
1988-07-01
In light of the recent discovery of copper oxide high-Tc superconductors, we have reexamined the early neutron diffraction measurements on CuO by Brockhouse [B. N. Brockhouse, Phys. Rev. 94, A781 (1954)]. Our measurement confirmed the antiferromagnetic ordering in CuO below 225 K. The magnetic unit cell has a volume double that of the chemical unit cell. The ordered moment is 0.68μB per Cu, significantly smaller than 1μB expected for a spin-only Cu2+ ion. The diffuse scattering was also studied well above the Néel temperature, and was found to be mostly elastic, in clear contrast to that of La2CuO4.
Neutron scattering studies of the magnetic structure of cupric oxide
Yang, B.X.; Tranquada, J.M.; Shirane, G.
1988-07-01
In light of the recent discovery of copper oxide high-T/sub c/ superconductors, we have reexamined the early neutron diffraction measurements on CuO by Brockhouse (B. N. Brockhouse, Phys. Rev. 94, A781 (1954)). Our measurement confirmed the antiferromagnetic ordering in CuO below 225 K. The magnetic unit cell has a volume double that of the chemical unit cell. The ordered moment is 0.68..mu../sub B/ per Cu, significantly smaller than 1..mu../sub B/ expected for a spin-only Cu/sup 2+/ ion. The diffuse scattering was also studied well above the Neel temperature, and was found to be mostly elastic, in clear contrast to that of La/sub 2/CuO/sub 4/.
Critical current destabilizing perpendicular magnetization by the spin Hall effect
NASA Astrophysics Data System (ADS)
Taniguchi, Tomohiro; Mitani, Seiji; Hayashi, Masamitsu
2015-07-01
The critical current needed to destabilize the magnetization of a perpendicular ferromagnet via the spin Hall effect is studied. Both the dampinglike and fieldlike torques associated with the spin current generated by the spin Hall effect are included in the Landau-Lifshitz-Gilbert equation to model the system. In the absence of the fieldlike torque, the critical current is independent of the damping constant and is much larger than that of conventional spin torque switching of collinear magnetic systems, as in magnetic tunnel junctions. With the fieldlike torque included, we find that the critical current scales with the damping constant as α0 (i.e., damping independent), α , and α1 /2 depending on the sign of the fieldlike torque and other parameters such as the external field. Numerical and analytical results show that the critical current can be significantly reduced when the fieldlike torque possesses the appropriate sign, i.e., when the effective field associated with the fieldlike torque is pointing opposite to the spin direction of the incoming electrons. These results provide a pathway to reducing the current needed to switch magnetization using the spin Hall effect.
Superconductivity in Strong Magnetic Field (Greater Than Upper Critical Field)
Tessema, G.X.; Gamble, B.K.; Skove, M.J.; Lacerda, A.H.; Mielke, C.H.
1998-08-22
The National High Magnetic Field Laboratory, funded by the National Science Foundation and other US federal Agencies, has in recent years built a wide range of magnetic fields, DC 25 to 35 Tesla, short pulse 50 - 60 Tesla, and quasi-continuous 60 Tesla. Future plans are to push the frontiers to 45 Tesla DC and 70 to 100 Tesla pulse. This user facility, is open for national and international users, and creates an excellent tool for materials research (metals, semiconductors, superconductors, biological systems ..., etc). Here we present results of a systematic study of the upper critical field of a novel superconducting material which is considered a promising candidate for the search for superconductivity beyond H{sub c2} as proposed by several new theories. These theories predict that superconductors with low carrier density can reenter the superconducting phase beyond the conventional upper critical field H{sub c2}. This negates the conventional thinking that superconductivity and magnetic fields are antagonistic.
Finite-temperature Dynamics and Quantum Criticality in a Model for Insulating Magnets
NASA Astrophysics Data System (ADS)
Wu, Jianda; Yang, Wang; Wu, Congjun; Si, Qimiao
Theoretical understanding of the finite-temperature dynamics in quantum critical systems is a challenging problem, due to the mixing of thermal and quantum fluctuations. Recently, neutron scattering experiments in the three-dimensional quantum dimmer material TlCuCl3 under pressure tuning have mapped out the magnetic dynamics at finite temperatures in the quantum critical regime, thereby providing the opportunity for systematic understandings. In this work, we calculate the spin spectral function of an O (n) symmetric field theory using a field-theory procedure to two loops. We calculate the temperature dependence of the energy and damping rate of the spin excitations in the quantum critical regime, demonstrate a good agreement with the experimental results, and determine the parameter regime of the field theory that is appropriate for TlCuCl3. From our calculations we can also suggest further experimental means to test the applicability of the underlying field theory in this and related systems.
Theory of magnetic circular dichroism of nonresonant x-ray Raman scattering
NASA Astrophysics Data System (ADS)
Takahashi, Manabu; Hiraoka, Nozomu
2015-09-01
We develop a theory of magnetic circular dichroism (MCD) of hard x-ray Raman scattering (XRS) to analyze the MCD signal at iron L edge from pure ferromagnetic iron. The obtained formula of scattering amplitude has terms corresponding to the charge (Thomson) scattering process, and the orbital and spin scattering processes in the elastic x-ray magnetic scattering. The total scattering intensity is almost independent of incident photon helicity since it is mainly produced by the charge scattering. The weak MCD signals are caused primarily by interference between the charge scattering amplitude and each of the orbital and spin scattering amplitudes. The shape of the MCD spectra depends on angle αM between the wave vector of the incident photon and the magnetization vector. At αM=0∘ , the spin scattering is suppressed so that the MCD spectrum becomes analogous to that observed in the x-ray absorption spectroscopy. At αM=135∘ , the orbital scattering is suppressed, and the spin scattering plays central roles in producing the MCD signal. The magnitude of the MCD signal turns out to be proportional to the spin density of states projected onto the 3 d states in the unoccupied state. Consequently, the value of the integrated MCD signal is proportional to the spin moment in the 3 d states at the scattering site. The calculated MCD spectra with the help of a band structure calculation well reproduce the observed spectra.
Excitation spectra of disordered dimer magnets near quantum criticality.
Vojta, Matthias
2013-08-30
For coupled-dimer magnets with quenched disorder, we introduce a generalization of the bond-operator method, appropriate to describe both singlet and magnetically ordered phases. This allows for a numerical calculation of the magnetic excitations at all energies across the phase diagram, including the strongly inhomogeneous Griffiths regime near quantum criticality. We apply the method to the bilayer Heisenberg model with bond randomness and characterize both the broadening of excitations and the transfer of spectral weight induced by disorder. Inside the antiferromagnetic phase this model features the remarkable combination of sharp magnetic Bragg peaks and broad magnons, the latter arising from the tendency to localization of low-energy excitations. PMID:24033066
Distributed Hybridization Model for Quantum Critical Behavior in Magnetic Quasicrystals
NASA Astrophysics Data System (ADS)
Otsuki, Junya; Kusunose, Hiroaki
2016-07-01
A quantum critical behavior of the magnetic susceptibility was observed in a quasicrystal containing ytterbium. At the same time, a mixed-valence feature of Yb ions was reported, which appears to be incompatible with the magnetic instability. We derive the magnetic susceptibility by expressing the quasiperiodicity as the distributed hybridization strength between Yb 4f and conduction electrons. Assuming a wide distribution of the hybridization strength, the most f electrons behave as renormalized paramagnetic states in the Kondo or mixed-valence regime, but a small number of f moments remain unscreened. As a result, the bulk magnetic susceptibility exhibits a nontrivial power-law-like behavior, while the average f-electron occupation is that of mixed-valence systems. This model thus resolves two contradictory properties of Yb quasicrystals.
NASA Astrophysics Data System (ADS)
Milham, Merrill E.
1994-10-01
In this report, relevant parts of the scattering theory for magnetic spheres are presented. Mass extinction coefficients, and the lognormal size distribution are defined. The theory and algorithms for integrating scattering parameters over size distributions are developed. The integrations are carried out in terms of dimensionless scattering, and size distribution parameters, which are simply related to the usual mass scattering coefficients. Fortran codes, which implement the algorithmic design, are presented, and examples of code use are given. Code listings are included.
Artemyev, A. V. Vasiliev, A. A.; Mourenas, D.; Krasnoselskikh, V. V.
2014-10-15
In this paper, we consider high-energy electron scattering and nonlinear trapping by oblique whistler waves via the Landau resonance. We use recent spacecraft observations in the radiation belts to construct the whistler wave model. The main purpose of the paper is to provide an estimate of the critical wave amplitude for which the nonlinear wave-particle resonant interaction becomes more important than particle scattering. To this aim, we derive an analytical expression describing the particle scattering by large amplitude whistler waves and compare the corresponding effect with the nonlinear particle acceleration due to trapping. The latter is much more rare but the corresponding change of energy is substantially larger than energy jumps due to scattering. We show that for reasonable wave amplitudes ∼10–100 mV/m of strong whistlers, the nonlinear effects are more important than the linear and nonlinear scattering for electrons with energies ∼10–50 keV. We test the dependencies of the critical wave amplitude on system parameters (background plasma density, wave frequency, etc.). We discuss the role of obtained results for the theoretical description of the nonlinear wave amplification in radiation belts.
Optimization and self-organized criticality in a magnetic system
NASA Astrophysics Data System (ADS)
Onody, Roberto N.; de Castro, Paulo A.
2003-05-01
We propose a kind of Bak-Sneppen dynamics as a general optimization technique to treat magnetic systems. The resulting dynamics shows self-organized criticality with power-law scaling of the spatial and temporal correlations. An alternative method of the extremal optimization (EO) is also analyzed here. We provided a numerical confirmation that, for any possible value of its free parameter τ, the EO dynamics exhibits a non-critical behavior with an infinite spatial range and exponential decay of the avalanches. Using the chiral clock model as our test system, we compare the efficiency of the two dynamics with regard to their abilities to find the system's ground state.
Scattering of core-shell nanowires with the interference of electric and magnetic resonances.
Liu, Wei; Miroshnichenko, Andrey E; Oulton, Rupert F; Neshev, Dragomir N; Hess, Ortwin; Kivshar, Yuri S
2013-07-15
We study the scattering of normally incident waves by core-shell nanowires, which support both electric and magnetic resonances. Within such nanowires, for p-polarized incident waves, each electric resonance corresponds to two degenerate scattering channels while the magnetic resonance corresponds to only one channel. Consequently, when the electric dipole (ED) and magnetic dipole (MD) are tuned to overlap spectrally, the magnitude of the ED is twice that of the magnetic one, leading to a pair of angles of vanishing scattering. We further demonstrate that the scattering features of nanowires are polarization dependent, and vanishing scattering angles also can be induced by Fano resonances due to the interference of higher-order electric modes with the broad MD mode. PMID:23939129
Neutron Scattering Study of Low Dimensional Quantum Magnets
NASA Astrophysics Data System (ADS)
Broholm, Collin
1997-03-01
I review three neutron scattering experiments which have uncovered unusual magnetic phenomena in non-metallic low dimensional quantum antiferromagnets. (Work done in collaboration with M. Adams, G. Aeppli, C. Carlile, S.-W. Cheong, D. Davidović), D. C. Dender, J. F. DiTusa, P. R. Hammar, B. Hessen, T. Ito, S. H. Lee, K. Lefmann, K. Oka, T. G. Perring, A. P. Ramirez, Daniel H. Reich, H. Takagi, A. Taylor, and Guangyong Xu. I present evidence that the low temperature short-range ordered spin configuration in the kagomé bi-layer system SrCr_9pGa_12-9pO_19 is composed of small groups of spins whose dipole moments cancel. I report the first observation of field induced incommensurate spin correlations in the uniform spin 1/2 antiferromagnetic chain copper benzoate, and I discuss new results concerning sub-gap excitations in a spin 1 antiferromagnetic chain with impurity bonds, (Y_1-xCa_x)_2BaNiO_5.
Qiu, Hui-Bin; Song, Hai-Ying; Liu, Shi-Bing
2015-09-15
Nonlinear Raman forward scattering of an intense short laser pulse with a duration shorter than the plasma period propagating through a homogenous collisional nonextensive distributed plasma in the presence of a uniform magnetic field perpendicular to both the direction of propagation and electric vector of the radiation field is investigated theoretically when ponderomotive, relativistic, and collisional nonlinearities are taken into account. The governing equations for nonlinear wave in the context of nonextensive statistics are given, the nonextensive coupled equations describing the nonlinear Raman forward scattering instability are solved by the Fourier transformation method, and the growth rate of the nonlinear Raman forward scattering instability is obtained. The results in the case q → 1 are consistent with those in the framework of the Maxwellian distribution. It is found that the instability growth rate first decreases on increasing electron thermal velocity, minimizes at a critical thermal velocity, and then increases steeply; the critical temperature dependents on the nonextensive parameter, and the greater nonextensive parameter, correspond to the greater critical temperature; when the thermal velocity of electron is less than the critical speed, the instability growth rate is found to be enhanced as the nonextensive parameter increases; but when the thermal velocity is greater than the critical speed, the instability growth rate decreases on increasing the nonextensive parameter.
Weissmüller, J.; McMichael, R. D.; Michels, A.; Shull, R. D.
1999-01-01
The paper presents a theoretical analysis of elastic magnetic small-angle neutron scattering (SANS) due to the nonuniform magnetic microstructure in nanocrystalline ferromagnets. The reaction of the magnetization to the magnetocrystalline and magnetoelastic anisotropy fields is derived using the theory of micromagnetics. In the limit where the scattering volume is a single magnetic domain, and the magnetization is nearly aligned with the direction of the magnetic field, closed form solutions are given for the differential scattering cross-section as a function of the scattering vector and of the magnetic field. These expressions involve an anisotropy field scattering function, that depends only on the Fourier components of the anisotropy field microstructure, not on the applied field, and a micromagnetic response function for SANS, that can be computed from tabulated values of the materials parameters saturation magnetization and exchange stiffness constant or spin wave stiffness constant. Based on these results, it is suggested that the anisotropy field scattering function SH can be extracted from experimental SANS data. A sum rule for SH suggests measurement of the volumetric mean square anisotropy field. When magnetocrystalline anisotropy is dominant, then a mean grain size or the grain size distribution may be determined by analysis of SH.
Zou, L.; Gong, X.G.; Zheng, Q. |; Pan, C.Y.
1996-04-01
We present the study of the giant magnetoresistance effect in ferromagnetically ordered thin film and bulk based on the Hund{close_quote}s rule coupling between the mobile {ital d} electron and the core spin of Mn ions. It has been shown that the resistivity is proportional to the spin{endash}spin correlation functions, a maximum resistivity appears near the critical point in absence of magnetic field and an applied field drives the resistivity peak to higher temperature and reduces the peak value, which is in agreement with the experiments. The giant magnetoresistance effect in thin film is attributed to the spin-correlation-dependent scattering and the low-dimensional character. {copyright} {ital 1996 American Institute of Physics.}
Neutron Scattering at Highest Magnetic Fields at the Helmholtz Centre Berlin
NASA Astrophysics Data System (ADS)
Smeibidl, P.; Tennant, A.; Ehmler, H.; Bird, M.
2010-04-01
The Helmholtz Centre Berlin (HZB), formerly Hahn-Meitner Institute is a user facility for the study of structure and dynamics with neutrons and synchrotron radiation with special emphasis on experiments under extreme conditions. Neutron scattering is uniquely suited to study magnetic properties on a microscopic length scale, because neutrons have comparable wavelengths and, due to their magnetic moment, they interact with the atomic magnetic moments. At HZB a dedicated instrument for neutron scattering at extreme fields is under construction, the Extreme Environment Diffractometer ExED. It is projected according to the “time-of-flight” principle for elastic and inelastic neutron scattering and for the special geometric constraints of analysing samples in a high field magnet. The new magnet will not only allow for novel experiments, it will be at the forefront of development in magnet technology itself. The design of the magnet will follow the Series Connected Hybrid System Technology (SCH) developed at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida. To compromise between the needs of the magnet design for highest fields and the concept of the neutron instrument, the magnetic field will be generated by means of a coned solenoid with horizontal field orientation. By using resistive insert coils, which are mounted in the room temperature bore of a superconducting cable-in-conduit (CIC) magnet, fields above 30 Tesla can be obtained in a geometry optimised for the demands of neutron scattering.
Critical magnetic transition in TbNi2Mn--magnetization and Mössbauer spectroscopy.
Wang, J L; Campbell, S J; Kennedy, S J; Zeng, R; Dou, S X; Wu, G H
2011-06-01
The structural and magnetic properties of the TbNi(2)Mn(x) series (0.9 ≤ x ≤ 1.10) have been investigated using x-ray diffraction, field- and temperature-dependent AC magnetic susceptibility, DC magnetization (5-340 K; 0-5 T) and (57)Fe Mössbauer spectroscopy (5-300 K). TbNi(2)Mn(x) crystallizes in the MgCu(2)-type structure (space group Fd3m). The additional contributions to the magnetic energy terms from transition-metal-transition-metal interactions (T-T) and rare-earth-transition-metal interactions (R-T) in RNi(2)Mn compounds contribute to their increased magnetic ordering temperatures compared with RNi(2) and RMn(2). Both the lattice constant a and the Curie temperature T(C) exhibit maximal values at the x = 1 composition indicating strong magnetostructural coupling. Analyses of the AC magnetic susceptibility and DC magnetization data of TbNi(2)Mn around the Curie temperature T(C) = 147 K confirm that the magnetic transition is second order with critical exponents β = 0.77 ± 0.12, γ = 1.09 ± 0.07 and δ = 2.51 ± 0.06. These exponents establish that the magnetic interactions in TbNi(2)Mn are long range despite mixed occupancies of Tb and Mn atoms at the 8a site and vacancies. The magnetic entropy - ΔS(M) around T(C) is proportional to (μ(0)H/T(C))(2/3) in agreement with the critical magnetic analyses. The Mössbauer spectra above T(C) are fitted by two sub-spectra in agreement with refinement of the x-ray data while below T(C) three sub-spectra are required to represent the three inequivalent local magnetic environments. PMID:21555840
Critical magnetic transition in TbNi2Mn—magnetization and Mössbauer spectroscopy
NASA Astrophysics Data System (ADS)
Wang, J. L.; Campbell, S. J.; Kennedy, S. J.; Zeng, R.; Dou, S. X.; Wu, G. H.
2011-06-01
The structural and magnetic properties of the TbNi2Mnx series (0.9 <= x <= 1.10) have been investigated using x-ray diffraction, field- and temperature-dependent AC magnetic susceptibility, DC magnetization (5-340 K 0-5 T) and 57Fe Mössbauer spectroscopy (5-300 K). TbNi2Mnx crystallizes in the MgCu2-type structure (space group Fd\\bar {3}m ). The additional contributions to the magnetic energy terms from transition-metal-transition-metal interactions (T-T) and rare-earth-transition-metal interactions (R-T) in RNi2Mn compounds contribute to their increased magnetic ordering temperatures compared with RNi2 and RMn2. Both the lattice constant a and the Curie temperature TC exhibit maximal values at the x = 1 composition indicating strong magnetostructural coupling. Analyses of the AC magnetic susceptibility and DC magnetization data of TbNi2Mn around the Curie temperature TC = 147 K confirm that the magnetic transition is second order with critical exponents β = 0.77 ± 0.12, γ = 1.09 ± 0.07 and δ = 2.51 ± 0.06. These exponents establish that the magnetic interactions in TbNi2Mn are long range despite mixed occupancies of Tb and Mn atoms at the 8a site and vacancies. The magnetic entropy - ΔSM around TC is proportional to (μ0H/TC)2/3 in agreement with the critical magnetic analyses. The Mössbauer spectra above TC are fitted by two sub-spectra in agreement with refinement of the x-ray data while below TC three sub-spectra are required to represent the three inequivalent local magnetic environments.
Static Magnetic Field Therapy: A Critical Review of Treatment Parameters
Wahbeh, Helané; Harling, Noelle; Connelly, Erin; Schiffke, Heather C.; Forsten, Cora; Gregory, William L.; Markov, Marko S.; Souder, James J.; Elmer, Patricia; King, Valerie
2009-01-01
Static magnetic field (SMF) therapy, applied via a permanent magnet attached to the skin, is used by people worldwide for self-care. Despite a lack of established SMF dosage and treatment regimens, multiple studies are conducted to evaluate SMF therapy effectiveness. Our objectives in conducting this review are to:(i) summarize SMF research conducted in humans; (ii) critically evaluate reporting quality of SMF dosages and treatment parameters and (iii) propose a set of criteria for reporting SMF treatment parameters in future clinical trials. We searched 27 electronic databases and reference lists. Only English language human studies were included. Excluded were studies of electromagnetic fields, transcranial magnetic stimulation, magnets placed on acupuncture points, animal studies, abstracts, posters and editorials. Data were extracted on clinical indication, study design and 10 essential SMF parameters. Three reviewers assessed quality of reporting and calculated a quality assessment score for each of the 10 treatment parameters. Fifty-six studies were reviewed, 42 conducted in patient populations and 14 in healthy volunteers. The SMF treatment parameters most often and most completely described were site of application, magnet support device and frequency and duration of application. Least often and least completely described were characteristics of the SMF: magnet dimensions, measured field strength and estimated distance of the magnet from the target tissue. Thirty-four (61%) of studies failed to provide enough detail about SMF dosage to permit protocol replication by other investigators. Our findings highlight the need to optimize SMF dosing parameters for individual clinical conditions before proceeding to a full-scale clinical trial. PMID:18955243
NASA Astrophysics Data System (ADS)
Liman, Christopher; Sunday, Daniel; Ro, Hyun Wook; Richter, Lee; Hannon, Adam; Kline, R. Joseph
Critical dimension small angle X-ray scattering (CDSAXS) is a recently developed technique that enables the characterization of the three-dimensional shape of periodic patterns, such as directed self-assembled (DSA) block copolymer (BCP) lamellae thin films. Information about the polymer patterns is extracted by fitting simulated scattering patterns to the experimental ones using an inverse iterative algorithm. Conducting CDSAXS at resonant energies near the carbon or nitrogen edge can enhance the strength of the scattering, but also causes the scattering to be influenced by any anisotropic orientation of the polymer chains. In this work, to assess the degree to which the scattering may be influenced by orientation, we simulate polarized resonant CDSAXS patterns for BCP lamellae with varying degrees of orientation, as well as orientation as a function of location within the lamellae, for different polarizations of the incident X-rays. Also, to assess the influence of a higher degree of orientation, we use capillary force lithography to pattern nanogratings of two semiconducting homopolymers which are known to orient strongly. We characterize these nanogratings, which have similar length scales to DSA BCP lamellae, with polarized resonant CDSAXS and spectroscopic ellipsometry. Finally, we fit simulated CDSAXS and ellipsometric data to the experimental data to obtain information about the shape and the orientation of the nanogratings.
Waters, Z J; Simpson, H J; Sarkissian, A; Dey, S; Houston, B H; Bucaro, J A; Yoder, T J
2012-11-01
Laboratory grade bistatic scattering measurements are conducted in order to examine the acoustic response of realistic fully buried unexploded ordnance (UXO) from above-critical angle insonification, between 2 and 40 kHz. A 127 mm diameter rocket UXO, a 155 mm diameter artillery shell, a natural rock of approximately the same size, and a cinder block are fully buried in water-saturated medium grained sand (mean grain diameter, 240 μm) at depths of 10 cm below the water-sediment interface. A two-dimensional array of bistatic scattering measurements is generated synthetically by scanning a single hydrophone in steps of 3 cm over a 1 m × 1 m patch directly above the targets at a height of 20 cm above the water-sediment interface. Three-dimensional volumetric acoustic images generated from the return waveforms reveal scattering components attributed to geometric and elastic scattering, as well as multiple-scattering interactions of returns between the sediment-water interface and the buried objects. The far-field target strength of the objects is estimated through extrapolation of the angular spectrum. Agreement is found between experimental data and simulated data generated from a finite-element-based, three-dimensional time-harmonic model (2-25 kHz). Separation of the measured UXO from the clutter objects is demonstrated through exploitation of structural-acoustics-based features. PMID:23145593
Magnetic two-photon scattering and two-photon emission - Cross sections and redistribution functions
NASA Technical Reports Server (NTRS)
Alexander, S. G.; Meszaros, P.
1991-01-01
The magnetic two-photon scattering cross section is discussed within the framework of QED, and the corresponding scattering redistribution function for this process and its inverse, as well as the scattering source function are calculated explicitly. In a similar way, the magnetic two-photon emission process which follows the radiative excitation of Landau levels above ground is calculated. The two-photon scattering and two-photon emission are of the same order as the single-photon magnetic scattering. All three of these processes, and in optically thick cases also their inverses, are included in radiative transport calculations modeling accreting pulsars and gamma-ray bursters. These processes play a prominent role in determining the relative strength of the first two cyclotron harmonics, and their effects extend also to the higher harmonics.
Development of Metallic Magnetic Calorimeters with a Critical Temperature Switch
NASA Astrophysics Data System (ADS)
Kim, S. R.; Choi, J.; Jo, H. S.; Kang, C. S.; Kim, G. B.; Kim, H. L.; Kim, I. W.; Lee, H. J.; Lee, J. H.; Lee, M. K.; Oh, S. Y.; Sala, E.; So, J. H.; Yoon, W. S.; Kim, Y. H.
2016-07-01
We report on the progress in the development of meander-shaped metallic magnetic calorimeters (MMCs) with a critical temperature switch. A niobium meander-shaped coil in an MMC is arranged to form a superconducting loop. It is to measure the change in magnetization and to apply a persistent current that magnetizes the MMC sensor material. In this work, part of the superconducting loop is fabricated with another superconducting material with its transition temperature (T_C) lower than that of niobium. A persistent current can be injected in the loop while reducing the temperature from above to below the T_C of the switch. Aluminum (Al) wires and an alloy of molybdenum and germanium (MoGe) were tested as critical temperature switch. The test with the Al switch demonstrated the temperature switch concept for meander-shaped MMCs that require a large field current. Microfabricated MoGe switches showed a T_C near 4.3 K, but only 7 mA of persistent current could be charged due to MoGe film discontinuity. This issue requires further improvement in the fabrication procedure.
Single-pulse resonant magnetic scattering using a soft x-ray free-electron laser
Gutt, C.; Streit-Nierobisch, S.; Stadler, L.-M.; Faeustlin, R. R.; Treusch, R.; Feldhaus, J.; Weckert, E.; Vartanyants, I. A.; Gruebel, G.; Pfau, B.; Guenther, C. M.; Koennecke, R.; Eisebitt, S.; Froemter, R.; Kobs, A.; Stickler, D.; Oepen, H. P.; Grunze, M.; Rosenhahn, A.; Wilhein, T.
2010-03-01
We report on single-pulse resonant magnetic scattering experiments using soft x-ray pulses generated by the free-electron laser FLASH at DESY. We could record a magnetic diffraction pattern from a Co/Pt multilayer sample at the Co M{sub 2,3} edge with a single 30-fs-long FEL pulse. The analysis of the magnetic small-angle scattering signal for subsequent pulses indicates a threshold energy density below which there is no indication that the magnetic properties of the sample might be altered.
Mitigating stimulated scattering processes in gas-filled Hohlraums via external magnetic fields
Gong, Tao; Zheng, Jian; Li, Zhichao; Ding, Yongkun; Yang, Dong; Hu, Guangyue; Zhao, Bin
2015-09-15
A simple model, based on energy and pressure equilibrium, is proposed to deal with the effect of external magnetic fields on the plasma parameters inside the laser path, which shows that the electron temperature can be significantly enhanced as the intensity of the external magnetic fields increases. With the combination of this model and a 1D three-wave coupling code, the effect of external magnetic fields on the reflectivities of stimulated scattering processes is studied. The results indicate that a magnetic field with an intensity of tens of Tesla can decrease the reflectivities of stimulated scattering processes by several orders of magnitude.
Second-order magnetic critical points at finite magnetic fields: Revisiting Arrott plots
NASA Astrophysics Data System (ADS)
Bustingorry, S.; Pomiro, F.; Aurelio, G.; Curiale, J.
2016-06-01
The so-called Arrott plot, which consists in plotting H /M against M2, with H the applied magnetic field and M the magnetization, is used to extract valuable information in second-order magnetic phase transitions. Besides, it is widely accepted that a negative slope in the Arrott plot is indicative of a first-order magnetic transition. This is known as the Banerjee criterion. In consequence, the zero-field transition temperature T* is reported as the characteristic first-order transition temperature. By carefully analyzing the mean-field Landau model used for studying first-order magnetic transitions, we show in this work that T* corresponds in fact to a triple point where three first-order lines meet. More importantly, this analysis reveals the existence of two symmetrical second-order critical points at finite magnetic field (Tc,±Hc) . We then show that a modified Arrott plot can be used to obtain information about these second-order critical points. To support this idea we analyze experimental data on La2 /3Ca1 /3MnO3 and discuss an estimate for the location of the triple point and the second-order critical points.
Effects of static magnetic fields on light scattering in red chromatophore of goldfish scale
NASA Astrophysics Data System (ADS)
Iwasaka, M.
2010-05-01
Light scattering in a guanine crystal plate of goldfish scales was observed with and without static magnetic field exposure. Under a microscopic image with dark-field-illumination, the structural color of the scale by guanine plates was observed, and isolated chromatophores showed a twinkling which was the intermittent light scattering of the light from the side. The light scattering was quenched by static magnetic fields of more than 0.26 tesla (T). The quenching was reversibly occurred when the applied external magnetic fields were changed between ambient fields and 5 T. The quenched light scattering did not improve when the magnetic field was decreased from 5 to 0.3 T. It recovered to the original twinkling state about one minute after reaching an ambient geomagnetic field level. The mechanism of the quenched light scattering was speculated to be concerned with the possible magnetic orientation of guanine crystal plates, which were sustained by protein fibers in the red chromatophore. The diamagnetic complex of guanine crystal plates and protein fibers are the candidates for the nanosized light scattering controller based on the magnetic orientation mechanism.
Josephson critical current of long SNS junctions in the presence of a magnetic field
NASA Astrophysics Data System (ADS)
Meier, Hendrik; Fal'Ko, Vladimir I.; Glazman, Leonid I.
We evaluate the Josephson critical current of a long and wide two-dimensional superconductor-normal metal-superconductor (SNS) junction, taking into account the effect of electron reflection off the side edges of the junction. Considering clean junctions, we find that the effect of edges alters the usual Fraunhofer-like dependence of the Josephson critical current Ic on the magnetic flux Φ. At relatively weak fields, B <~Φ0 /W2 , the edge effect lifts zeros of the Ic (Φ) dependence and gradually shifts the maxima of that function by Φ0 / 2 . (Here W is the width of the junction and Φ0 the magnetic flux quantum.) At higher fields, B >~Φ0 /W2 , the edge effect leads to an accelerated decay of the critical current Ic (Φ) with increasing Φ. Our results are robust with respect to the roughness of realistic boundaries. Finally, we discuss the role of mesoscopic fluctuations of Ic (Φ) originating from the scattering off the edges, and compare our findings to recent experiments.
Qin, G.; Shalchi, A.
2014-04-15
In the present paper, we re-visit a well-known problem in diffusion theory, namely the 90∘ scattering problem. We use a test-particle code to compute the pitch-angle Fokker-Planck coefficient at 90∘ for different values of the turbulent magnetic field strength and the magnetic rigidity. We consider a slab model and compare our numerical findings with the analytical result provided by second-order quasilinear theory. We show that the latter theory accurately describes 90∘ scattering. We also replace the slab model by a more realistic two-component model to explore the influence of the turbulence model on 90∘ scattering.
Surface and bulk scattering by magnetic and dielectric inhomogeneities: a first-order method.
Dieudonné, É; Malléjac, N; Amra, C; Enoch, S
2013-09-01
The scattering of a magnetodielectric multilayer has been studied by a first-order method. The model reported in this manuscript relies on the equivalence between heterogeneities of the medium and fictitious electric and magnetic sources. Types of inhomogeneities considered are roughness and bulk inhomogeneities and concern both permittivity and permeability. The numerical results are compared to those given in previous papers for optical scattering. It is shown in the microwave spectra that angle-resolved scattering allows identification of the scattering origins (permittivity or permeability spectra). The cases of isotropic films and metamaterials are presented and discussed. PMID:24323258
Magnetization processes in nanostructured metals and small-angle neutron scattering
Loeffler, J.F.; Braun, H.B.; Wagner, W.; Kostorz, G.; Wiedenmann, A.
2005-04-01
The magnetization process in nanostructured (n-) Fe and Co was investigated via small-angle neutron scattering (SANS). In a zero field, the magnetization exhibits correlations extending over several grains. In intermediate applied magnetic fields around 1 kOe, n-Fe and n-Co samples with small grain sizes exhibit an anisotropic scattering profile with an unusual intensity enhancement for scattering vectors parallel to the field direction. Comparing the experimental data with a modeled granular microstructure containing magnetic domains of arbitrary size and orientation, we conclude that magnetic domains extending over several grains are tilted considerably out of the external field direction in intermediate fields. Since the domain size does not change significantly with the magnitude of the external field, we conclude that the magnetization process does not proceed via domain-wall motion. Together with theoretical arguments showing the existence of marginally stable domains within the random-anisotropy model, our SANS data suggests that the magnetization process proceeds by simultaneous reversal of a few adjacent domains, presumably in the form of small avalanches. This resembles the magnetization process predicted for random-field Ising magnets. Our theoretical analysis of SANS data is general and applies to other systems consisting of magnetic nanoclusters embedded in a nonmagnetic matrix.
New high field magnet for neutron scattering at Hahn-Meitner Institute
NASA Astrophysics Data System (ADS)
Steiner, M.; Tennant, D. A.; Smeibidl, P.
2006-11-01
The Berlin Neutron Scattering Center BENSC at the Hahn-Meitner-Institute (HMI) is a user facility for the study of structure and dynamics of condensed matter with neutrons and synchrotron radiation with special emphasis on experiments under extreme conditions. Neutron scattering is uniquely suited to study magnetic properties on a microscopic length scale, because neutrons have comparable wavelengths and, due to their magnetic moment, they interact with the atomic magnetic moments. Magnetic interactions and magnetic phenomena depend on thermodynamic parameters like magnetic field, temperature and pressure. At HMI special efforts are being made to offer outstanding sample environments such as very low temperatures or high magnetic fields or combination of both. For the future a dedicated instrument for neutron scattering at extreme fields is under construction, the Extreme Environment Diffractometer ExED. For this instrument the existing superconducting magnets as well as a future hybrid system can be used. The highest fields, above 30 T will be produced by the planned series-connected hybrid magnet system, designed and constructed in collaboration with the National High Magnetic Field Laboratory, Tallahassee, FL.
Vibration effect on magnetization and critical current density of superconductors
NASA Astrophysics Data System (ADS)
Golovchanskiy, Igor A.; Pan, Alexey V.; George, Jonathan; Wells, Frederick S.; Fedoseev, Sergey A.; Rozenfeld, Anatoly
2016-07-01
In this work the effect of vibrations on critical current density (J c ) of superconductors has been studied. The vibrations are shown to affect J c of all types of superconductors during their measurements, employing a vibrating sample magnetometer (VSM). Increasing vibration frequency (f) and/or amplitude (A) leads to progressive reduction of J c as a function of magnetic field (B a ). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on {J}c({B}a) curves. Analysis of magnetization loops and relaxation of magnetization in YBCO films revealed that the vibration effect can be treated as the effective reduction of pinning potential. The asymmetry of the vibration effect in ascending and descending B a is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A are shown to have rather insignificant influence, while the vibrational vortex dynamics exhibit a strong impact. The irreversibility field ({B}{{irr}}) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of {B}{{irr}} for J c modeling is demonstrated.
Magnetic field dependence of critical currents in superconducting polycrystals
Kugel, K.I.; Lisovskaya, T.Y. ); Mints, R.G. )
1992-02-10
The authors study the dependence of critical current j{sub c} on magnetic field H in superconducting polycrystals which are considered as system of superconducting crystallites (isotropic or anisotropic) with Josephson contacts between them. Isotropy or anisotropy of contacts depends on the orientation of their crystallographic axes relatively to edges of contact planes. In this paper it is shown that for a system of randomly oriented isotropic contacts, the dependence j{sub c}(H) in a relatively wide field range has the asymptotic form j{sub c} {approximately} (InH)/H{sup 2}. This differs drastically from j{sub c}(H) for single contacts. Anisotropy effects due to large differences in London penetration depth {lambda} values corresponding to external magnetic field directed along different axes are analyzed in detail. It is shown that for uniaxal crystals with {lambda}{sub 1} = {lambda}{sub 2} {lt} {lambda}{sub 3}, this anisotropy leads to the relation j{sub c} {approximately} {radical}{lambda}{sub 3}/{lambda}{sub 1} for chaotic orientation of crystallites. The form of j{sub c}(H) curves for two different orientations of the magnetic field relatively to the transport current through the sample is found.
Critical Differences of Asymmetric Magnetic Reconnection from Standard Models
NASA Astrophysics Data System (ADS)
Nitta, S.; Wada, T.; Fuchida, T.; Kondoh, K.
2016-09-01
We have clarified the structure of asymmetric magnetic reconnection in detail as the result of the spontaneous evolutionary process. The asymmetry is imposed as ratio k of the magnetic field strength in both sides of the initial current sheet (CS) in the isothermal equilibrium. The MHD simulation is carried out by the HLLD code for the long-term temporal evolution with very high spatial resolution. The resultant structure is drastically different from the symmetric case (e.g., the Petschek model) even for slight asymmetry k = 2. (1) The velocity distribution in the reconnection jet clearly shows a two-layered structure, i.e., the high-speed sub-layer in which the flow is almost field aligned and the acceleration sub-layer. (2) Higher beta side (HBS) plasma is caught in a lower beta side plasmoid. This suggests a new plasma mixing process in the reconnection events. (3) A new large strong fast shock in front of the plasmoid forms in the HBS. This can be a new particle acceleration site in the reconnection system. These critical properties that have not been reported in previous works suggest that we contribute to a better and more detailed knowledge of the reconnection of the standard model for the symmetric magnetic reconnection system.
Analysis of magnetic neutron-scattering data of two-phase ferromagnets
NASA Astrophysics Data System (ADS)
Honecker, Dirk; Dewhurst, Charles D.; Suzuki, Kiyonori; Erokhin, Sergey; Michels, Andreas
2013-09-01
We have analyzed magnetic-field-dependent small-angle neutron scattering (SANS) data of soft magnetic two-phase nanocomposite ferromagnets in terms of a recent micromagnetic theory for the magnetic SANS cross section [Honecker and Michels, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.87.224426 87, 224426 (2013)]. The approach yields a value for the average exchange-stiffness constant and provides the Fourier coefficients of the magnetic anisotropy field and the magnetostatic field, which is related to jumps of the magnetization at internal interfaces.
Nonlinear evolution of stimulated Raman scattering near the quarter-critical density
Xiao, C. Z.; Wu, D.; Liu, Z. J.; Zheng, C. Y. He, X. T.
2015-05-15
Nonlinear evolution of stimulated Raman scattering (SRS) near the quarter-critical density is studied using one-dimensional (1D) and two-dimensional (2D) particle-in-cell simulations in homogeneous plasmas. In 1D configuration, with two-plasmon decay (TPD) instability excluded, the system evolves into two regimes distinguished by whether density cavities have been formed or not. At low temperatures, a cavity regime characterised by high absorption and low reflection, and at high temperatures nonlinear frequency shift regime due to particle trapping, are observed. Furthermore, a competition between SRS and TPD in 2D simulations reveals that the nonlinear SRS does play a significant role near the quarter-critical density, whose influences were mostly neglected before.
Study of multiple scattering in high magnetic fields
NASA Astrophysics Data System (ADS)
Kaplan, Daniel M.; Roberts, Thomas J.
2013-02-01
Muon cooling for a neutrino factory or muon collider can be achieved using low-Z absorbers in strong focusing fields. Proposed cooling lattices place absorbers in solenoidal fields ranging up to 30 to 40 T. The cooling performance of these lattices is determined by the interplay of ionization energy loss and Molière scattering, but Bethe's classic treatment of Moliere scattering ignores the helical motion of charged particles in solenoidal fields. When this motion is taken into account, the performance of these lattices can be better than predicted by simulations using the standard treatment.
Critical phenomena of emergent monopoles in a chiral magnet
NASA Astrophysics Data System (ADS)
Zhang, Xiao-Xiao; Nagaosa, Naoto
A three-dimensional cubic Skyrmion crystal in the bulk, which is simultaneously a lattice of monopole-antimonopole pairs predicted theoretically, has been recently identified experimentally in MnGe. Adopting appropriate temperature Green's function technique for optical conductivity and devising a solvable phonon-magnon interaction, we systematically developed the theory of coupling spin-waves to both itinerant electrons and mechanical degrees of freedom in this chiral magnet, describing the latest experimental observations including anomalies and critical phenomena in magnetotransport and magnetoelasticity, which are identified as hallmarks of fluctuations of the emergent monopolar fields upon the nontrivial monopole dynamics and especially a topological phase transition signifying strong correlation. As a whole, they speak for a crucial role played by the monopole defects and hence the real-space spin topology in this material.
Heikkinen, J.A.; Dumbrajs, O.
1996-02-01
From the general three-wave coupling formalism in magnetized nonrelativistic Vlasov plasma, an expression is derived that gives the differential cross section for the scattering of incident radiation off of thermal fluctuations induced by ions in a hot magnetized plasma. The model is valid to any order in thermal parameters, and can thus generalize the previous theory models to regimes where either the electron Larmor radius or the electron cyclotron resonance are significant for the scattered wave. {copyright} {ital 1996 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Frankowski, Marek; Żywczak, Antoni; Czapkiewicz, Maciej; Zietek, Sławomir; Kanak, Jarosław; Banasik, Monika; Powroźnik, Wiesław; Skowroński, Witold; Checiński, Jakub; Wrona, Jerzy; Głowiński, Hubert; Dubowik, Janusz; Ansermet, Jean-Philippe; Stobiecki, Tomasz
2015-06-01
We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magnetic anisotropy fields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights.
A semi-numerical model for near-critical angle scattering.
Fradkin, Larissa Ju; Darmon, Michel; Chatillon, Sylvain; Calmon, Pierre
2016-01-01
Numerous phenomena in the fields of physics and mathematics as seemingly different as seismology, ultrasonics, crystallography, photonics, relativistic quantum mechanics, and analytical number theory are described by integrals with oscillating integrands that contain three coalescing criticalities, a branch point, stationary phase point, and pole as well as accumulation points at which the speed of integrand oscillation is infinite. Evaluating such integrals is a challenge addressed in this paper. A fast and efficient numerical scheme based on the regularized composite Simpson's rule is proposed, and its efficacy is demonstrated by revisiting the scattering of an elastic plane wave by a stress-free half-plane crack embedded in an isotropic and homogeneous solid. In this canonical problem, the head wave, edge diffracted wave, and reflected (or compensating) wave each can be viewed as a respective contribution of a branch point, stationary phase point, and pole. The proposed scheme allows for a description of the non-classical diffraction effects near the "critical" rays (rays that separate regions irradiated by the head waves from their respective shadow zones). The effects include the spikes present in diffraction coefficients at the critical angles in the far field as well as related interference ripples in the near field. PMID:26827012
MAGNETIC VARIANCES AND PITCH-ANGLE SCATTERING TIMES UPSTREAM OF INTERPLANETARY SHOCKS
Perri, Silvia; Zimbardo, Gaetano E-mail: gaetano.zimbardo@fis.unical.it
2012-07-20
Recent observations of power-law time profiles of energetic particles accelerated at interplanetary shocks have shown the possibility of anomalous, superdiffusive transport for energetic particles throughout the heliosphere. Those findings call for an accurate investigation of the magnetic field fluctuation properties at the resonance frequencies upstream of the shock's fronts. Normalized magnetic field variances, indeed, play a crucial role in the determination of the pitch-angle scattering times and then of the transport regime. The present analysis investigates the time behavior of the normalized variances of the magnetic field fluctuations, measured by the Ulysses spacecraft upstream of corotating interaction region (CIR) shocks, for those events which exhibit superdiffusion for energetic electrons. We find a quasi-constant value for the normalized magnetic field variances from about 10 hr to 100 hr from the shock front. This rules out the presence of a varying diffusion coefficient and confirms the possibility of superdiffusion for energetic electrons. A statistical analysis of the scattering times obtained from the magnetic fluctuations upstream of the CIR events has also been performed; the resulting power-law distributions of scattering times imply long range correlations and weak pitch-angle scattering, and the power-law slopes are in qualitative agreement with superdiffusive processes described by a Levy random walk.
A portable high-field pulsed magnet system for x-ray scattering studies.
Islam, Z.; Ruff, J.P.C.; Nojiri, H.; Matsuda, Y. H.; Ross, K. A.; Gaulin, B. D.; Qu, Z.; Lang, J. C.
2009-01-01
We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields (- 1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.
Spin-flip scattering of a half spin particle by a magnetic impurity in one dimension
NASA Astrophysics Data System (ADS)
Hafeez, Hafeez Y.; Ndikilar, Chifu E.; Adamu, Bala Ismail; Sa'adu, Ibrahim
2016-05-01
In this article, the behavior of a half spin particle is studied. Specifically an electron with mass me, when passing through a magnetic field with fixed strength Bo is examined. A magnetic impurity is considered as a scatterer of a half spin particle in one dimension. This corresponds for example to a defect in the local magnetic structure inducing a magnetic field, e.g. as a result of strong spin-orbit coupling. From this set-up, the spin-flipping scattering processes are observed. Different profiles of Spin-Flip-Rate (SFR) against frequencies ω and amplitudes U are drawn respectively, for angle φ0=0, θ = /π 2 and different values of, μBB0, and radius R.
A high-field (30 Tesla) pulsed magnet instrument for single-crystal scattering studies
NASA Astrophysics Data System (ADS)
Islam, Zahirul; Nojiri, Hiroyuki; Narumi, Yasuo; Lang, Jonathan
2010-03-01
Pulsed magnets have emerged as a viable approach at synchrotron x-ray facilities for studying materials in high magnetic fields. We are developing a new high-field (30 Tesla) pulsed magnet system for single-crystal x-ray diffraction studies. It consists of a single 18mm-bore solenoid, designed and built at Tohoku University using high-tensile-strength and high conductivity CuAg wires. A dual-cryostat scheme has been developed at Advanced Photon Source in order to cool the coil using liquid nitrogen and the sample using a closed-cycle cryostat independently. Liquid nitrogen cooling allows repetition rate of a few minutes for peak fields near 30 Tesla. This scheme is unique in that it allows the applied magnetic field to be parallel to the scattering plane. Time-resolved scattering data are typically collected using a fast one-dimensional strip detector. Opportunities and challenges for experiments and instrumentation will be discussed.
Paillet, Sabrina; Grassl, Bruno; Desbrières, Jacques
2009-03-23
We present the rapid and quantitative characterization of ionic, non-ionic and zwitterionic surfactants based upon the combination of an automatic continuous mixing technique and static light scattering. Collection and subsequent analysis of data are both rapid and semiautomatic, which increases precision, sensitivity, and range of applicability while substantially decreasing the amount of manual intervention required by the investigator. By treating the continuous data, the entire data set may be rapidly analyzed in the context of the closed association model to determine the critical micelle concentration cmc and aggregation number Nag of a detergent; these technique are comparable in the scope and resolution currently obtainable from other conductimetric, fluorescence and surface tension techniques. PMID:19264174
Small-angle neutron scattering correlation functions of bulk magnetic materials
Mettus, Denis; Michels, Andreas
2015-01-01
On the basis of the continuum theory of micromagnetics, the correlation function of the spin-misalignment small-angle neutron scattering cross section of bulk ferromagnets (e.g. elemental polycrystalline ferromagnets, soft and hard magnetic nanocomposites, nanoporous ferromagnets, or magnetic steels) is computed. For such materials, the spin disorder which is related to spatial variations in the saturation magnetization and magnetic anisotropy field results in strong spin-misalignment scattering dΣM/dΩ along the forward direction. When the applied magnetic field is perpendicular to the incoming neutron beam, the characteristics of dΣM/dΩ (e.g. the angular anisotropy on a two-dimensional detector or the asymptotic power-law exponent) are determined by the ratio of magnetic anisotropy field strength H p to the jump ΔM in the saturation magnetization at internal interfaces. Here, the corresponding one- and two-dimensional real-space correlations are analyzed as a function of applied magnetic field, the ratio H p/ΔM, the single-particle form factor and the particle volume fraction. Finally, the theoretical results for the correlation function are compared with experimental data on nanocrystalline cobalt and nickel. PMID:26500464
NASA Astrophysics Data System (ADS)
Hamano, K.; Fukuhara, K.; Kuwahara, N.; Ducros, E.; Benseddik, M.; Rouch, J.; Tartaglia, P.
1995-07-01
Extensive sets of measurements of the shear viscosity, the scattered light intensity, and the relaxation rate of the order-parameter fluctuations lead us to reexamine the static and dynamic critical behaviors of binary solutions of pentaethylene glycol n-dodecylether (C12E5) and water. The scattered intensity, the scattered field correlation function, and the relaxation rate of the order parameter show systematic deviations from the behavior usually observed for simple or molecular binary fluids. A modified version of the Sorensen et al. [Phys. Rev. A 13, 1593 (1976)] dynamical droplet model that assumes that close to the critical point the critical clusters can be treated much like percolating aggregates having a fractal dimension df=2.49 and an associated polydispersity exponent τ=2.21 and which includes the finite size of the micelles, very well accounts for all our experimental results.
NASA Astrophysics Data System (ADS)
Shao, X.; Karavaev, A. V.; Sharma, A. S.; Papadopoulos, K.; Gumerov, N.; Gigliotti, A. F.; Gekelman, W. N.
2009-12-01
Injection of whistler waves into Earth's inner radiation belt to enhance precipitation of energetic electrons has been an active research area, and is referred to as RB Remediation (RBR). Most mechanisms of pitch angle scattering of energetic particles are based on gyro-resonant wave-particle interaction. Recent experiments and simulations show that Rotating Magnetic Field (RMF) antennas in plasmas can be efficient radiation sources of MHD and whistler waves. In experiments conducted in the Large Plasma Device (LAPD) at UCLA, poly-phased current loops drove the RMF antenna. These experiments, as well as simulations show that 75-85% of the radiation generated by the RMF antenna is in guided propagation. The whistler and MHD waves have non-local magnetic field gradients in the transverse direction and these provide ways to break the adiabatic invariants of electrons and precipitate them via a non-resonant scattering. In this paper simulations of non-resonant pitch angle scattering of energetic particles by waves generated by RMF sources are presented. Three-dimensional EMHD simulations are used to model whistlers and the resultant 3D electromagnetic fields are used in particle tracing codes to study pitch angle scattering. The simulations are carried out for a wide range of magnetic fields produced by RMF sources, including fields much larger than the ambient magnetic field in space plasma environments. This work was sponsored by ONR MURI Grant 5-28828
Yang, Yifeng; Urbano, Ricardo; Nicholas, Curro; Pines, David
2009-01-01
We report Knight shift experiments on the superconducting heavy electron material CeCoIn{sub 5} that allow one to track with some precision the behavior of the heavy electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the {sup 115}In nuclear quadrupole resonance (NQR) spin-lattice relaxation rate T{sub 1}{sup -1} measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point (QCP) located at slightly negative pressure in CeCoIn{sub 5} and provide additional evidence for significant similarities between the heavy electron materials and the high T{sub c} cuprates.
NASA Astrophysics Data System (ADS)
Shi, Wei; Paproski, Robert J.; Moore, Ronald; Zemp, Roger
2014-05-01
While more than 90% of cancer deaths are due to metastases, our ability to detect circulating tumor cells (CTCs) is limited by low numbers of these cells in the blood and factors confounding specificity of detection. We propose a magnetic enrichment and detection technique for detecting CTCs with high specificity. We targeted both magnetic and surface-enhanced Raman scattering (SERS) nanoparticles to cancer cells. Only cells that are dual-labeled with both kinds of nanoparticles demonstrate an increasing SERS signal over time due to magnetic trapping.
Electronic scattering of pseudo-magnetic field induced by local bump in graphene
NASA Astrophysics Data System (ADS)
Yang, Mou; Cui, Yan; Wang, Rui-Qiang; Zhao, Hong-Bo
2012-10-01
We investigated the electronic scattering properties of a local bump strain in graphene sheet in frame of Born approximation. The differential scattering cross section is a function of outgoing and incident angles and has the six-fold rotational symmetry with respect to both angles. The incident plane wave is scattered into two backward fan-waves in different directions in low energy limit and is split into two branches spanning the angle reversely proportional to the incident wavevector k in high energy limit. The total scattering cross section depends on incident wavevector by the form k5 in the former limit, while it is independent of k and sensitive to the incident orientation in the latter limit. We explained these features using the symmetry of the strain-induced pseudo-magnetic field.
Stable superconducting magnet. [high current levels below critical temperature
NASA Technical Reports Server (NTRS)
Boom, R. W. (Inventor)
1967-01-01
Operation of a superconducting magnet is considered. A method is described for; (1) obtaining a relatively high current in a superconducting magnet positioned in a bath of a gas refrigerant; (2) operating a superconducting magnet at a relatively high current level without training; and (3) operating a superconducting magnet containing a plurality of turns of a niobium zirconium wire at a relatively high current level without training.
New generation of cryogen free advanced superconducting magnets for neutron scattering experiments
NASA Astrophysics Data System (ADS)
Kirichek, O.; Brown, J.; Adroja, D. T.; Manuel, P.; Kouzmenko, G.; Bewley, R. I.; Wotherspoon, R.
2012-12-01
Recent advances in superconducting technology and cryocooler refrigeration have resulted in a new generation of advanced superconducting magnets for neutron beam applications. These magnets have outstanding parameters such as high homogeneity and stability at highest magnetic fields possible, a reasonably small stray field, low neutron scattering background and larger exposure to neutron detectors. At the same time the pulse tube refrigeration technology provides a complete re-condensing regime which allows to minimise the requirements for cryogens without introducing additional noise and mechanical vibrations. The magnets can be used with dilution refrigerator insert which expands the temperature range from 20mK to 300K. Here we are going to present design, test results and the operational data of the 14T magnet for neutron diffraction and the 9T wide angle chopper magnet for neutron spectroscopy developed by Oxford Instruments in collaboration with ISIS neutron source. First scientific results obtained from the neutron scattering experiments with these magnets are also going to be discussed.
Exact scattering matrix of graphs in magnetic field and quantum noise
Caudrelier, Vincent; Mintchev, Mihail; Ragoucy, Eric
2014-08-15
We consider arbitrary quantum wire networks modelled by finite, noncompact, connected quantum graphs in the presence of an external magnetic field. We find a general formula for the total scattering matrix of the network in terms of its local scattering properties and its metric structure. This is applied to a quantum ring with N external edges. Connecting the external edges of the ring to heat reservoirs, we study the quantum transport on the graph in ambient magnetic field. We consider two types of dynamics on the ring: the free Schrödinger and the free massless Dirac equations. For each case, a detailed study of the thermal noise is performed analytically. Interestingly enough, in presence of a magnetic field, the standard linear Johnson-Nyquist law for the low temperature behaviour of the thermal noise becomes nonlinear. The precise regime of validity of this effect is discussed and a typical signature of the underlying dynamics is observed.
Nucleon-nucleon scattering in a strong external magnetic field and the neutrino emissivity
Bavarsad, E.; Mohammadi, R.; Haghighat, M.
2010-11-15
The nucleon-nucleon scattering in a large magnetic background is considered to find its potential to change the neutrino emissivity of the neutron stars. For this purpose, we consider the one-pion-exchange approximation to find the nucleon-nucleon (NN) cross section in a background field as large as 10{sup 15}-10{sup 18} G. We show that the NN cross section in neutron stars with temperatures in the range 0.1-5 MeV can be changed up to the 1 order of magnitude with respect to the one in the absence of the magnetic field. In the limit of the soft neutrino emission, the neutrino emissivity can be written in terms of the NN-scattering amplitude; therefore, the large magnetic fields can dramatically change the neutrino emissivity of the neutron stars as well.
Levitation force on a permanent magnet over a superconducting plane: Modified critical-state model
Yang, Z.J.
1997-08-01
The authors consider a model system of a permanent magnet above a semi-infinite superconductor. They introduce a modified critical-state model, and carry out derivations of the levitation force acting on the magnet. A key feature of the modification allows the current density to be less than the critical value. The theoretical results show an exponential relationship between the force and the distance. Analytical expressions are developed for permanent magnets in the form of a point dipole, a tip of a magnetic force microscope, and a cylindrical magnet. In the latter case, the exponential relationship has been observed in numerous experiments but without previous interpretation.
NASA Astrophysics Data System (ADS)
Smeibidl, P.; Mezei, F.; Meissner, M.; Prokes, K.; Schröder-Smeibidl, B.; Steiner, M.
2003-05-01
The neutron scattering facility BENSC at Hahn-Meitner-Institut offers outstanding research opportunities to the international scientific user community. Experiments on an advanced suite of instruments can be performed in uniquely high magnetic fields up to 17.5 T at temperatures down to 30 mK simultaneously. To further extend the range of continuous magnetic fields for neutron scattering, HMI has proposed a new facility with resistive magnets up to 40 T.
Scattering-induced quantum correlation in electronic waveguides with static magnetic impurities
NASA Astrophysics Data System (ADS)
Ghanbari-Adivi, E.; Soltani, M.; Alami, Z.; Sheikhali, M.
2016-07-01
Entanglement generation due to low-energy scattering of the transporting electrons in an electronic waveguide by a quantum dot magnetic impurity is theoretically investigated. The transverse confining potential of the waveguide is considered as a two-dimensional harmonic potential, and the interaction of the electron with the impurity is described by a zero-range pseudopotential modulated by an Ising or a Heisenberg spin interaction. Our calculation shows that the scattering process leads to creation of a considerable amount of entanglement in the state of the reflected and transmitted electrons. The situation is extended to the scattering of the electrons by two well-separated magnetic impurities localized on the nanowire axis. It is shown that the scattering process causes the magnetic impurities embedded in the nanowire to share their quantum information; subsequently, they can be entangled by spin interaction with the injected electron. The created entanglement between the impurities is calculated and discussed. It is shown that the exact three-dimensional problem can be approximated as a one-dimensional problem under certain circumstances. The approximate results are compared to exact calculations and discussed.
STUDY MAGNETIC EXCITATIONS IN DOPED TRANSITION METAL OXIDES USING INELASTIC NEUTRON SCATTERING
Dai, Pengcheng
2014-02-18
Understanding the interplay between magnetism and superconductivity continues to be a “hot” topic in modern condensed matter physics. The discovery of high-temperature superconductivity in iron-based materials in 2008 provided an unique opportunity to compare and contrast these materials with traditional high-Tc copper oxide superconductors. Neutron scattering plays an important role in determining the dynamical spin properties in these materials. This proposal is a continuation of previous DOE supported proposal. This report summarizes the final progress we have made over from May 2005 till Aug. 2013. Overall, we continue to carry out extensive neutron scattering experiments on Fe-based materials, focusing on understanding their magnetic properties. In addition, we have established a materials laboratory at UT that has allowed us to grow these superconductors. Because neutron scattering typically demands a large amount of samples, by growing these materials in our own laboratory, we can now pursuit neutron scattering experiments over the entire electronic phase diagram, focusing on regions of interests. The material synthesis laboratory at UT was established entirely with the support of DOE funding. This not only allowed us to carry out neutron scattering experiments, but also permit us to provide samples to other US/International collaborators for studying these materials.
Scattering amplitude of ultracold atoms near the p-wave magnetic Feshbach resonance
Zhang Peng; Naidon, Pascal; Ueda, Masahito
2010-12-15
Most of the current theories on the p-wave superfluid in cold atomic gases are based on the effective-range theory for the two-body scattering, where the low-energy p-wave scattering amplitude f{sub 1}(k) is given by f{sub 1}(k)=-1/[ik+1/(Vk{sup 2})+1/R]. Here k is the incident momentum, V and R are the k-independent scattering volume and effective range, respectively. However, due to the long-range nature of the van der Waals interaction between two colliding ultracold atoms, the p-wave scattering amplitude of the two atoms is not described by the effective-range theory [J. Math. Phys. 4, 54 (1963); Phys. Rev. A 58, 4222 (1998)]. In this paper we provide an explicit calculation for the p-wave scattering of two ultracold atoms near the p-wave magnetic Feshbach resonance. We show that in this case the low-energy p-wave scattering amplitude f{sub 1}(k)=-1/[ik+1/(V{sup eff}k{sup 2})+1/(S{sup eff}k)+1/R{sup eff}] where V{sup eff}, S{sup eff}, and R{sup eff} are k-dependent parameters. Based on this result, we identify sufficient conditions for the effective-range theory to be a good approximation of the exact scattering amplitude. Using these conditions we show that the effective-range theory is a good approximation for the p-wave scattering in the ultracold gases of {sup 6}Li and {sup 40}K when the scattering volume is enhanced by the resonance.
Critical current density and trapped field in HTS with asymmetric magnetization loops
NASA Astrophysics Data System (ADS)
Gokhfeld, D.
2016-03-01
Applications of the extended critical state model are considered. The trapped magnetic field, the penetration field and the field dependence of the critical current density are analysed. The critical current density and the trapped field in superconducting grains depend on the grain size. Asymmetry of the hysteresis curves relative to the M = 0 axis is related to the scale of the current circulation.
Diffuse magnetic neutron scattering in the highly frustrated double perovskite Ba2YRuO6
Nilsen, Gøran. J.; Thompson, Corey M.; Ehlers, Georg; Marjerrison, Casey A.; Greedan, John E.
2015-02-23
Here we investigated diffuse magnetic scattering in the highly frustrated double perovskite Ba2YRuO6 using polarized neutrons. Consistent with previous reports, the material shows two apparent transitions at 47 and 36 K to an eventual type I face-centered-cubic magnetic ground state. The (100) magnetic reflection shows different behavior from the five other observed reflections upon heating from 1.8 K, with the former broadening well beyond the resolution limit near 36 K. Closer examination of the latter group reveals a small, but clear, increase in peak widths between 36 and 47 K, indicating that this regime is dominated by short-range spin correlations.more » Diffuse magnetic scattering persists above 47 K near the position of (100) to at least 200 K, consistent with strong frustration. Reverse Monte Carlo (RMC) modeling of the diffuse scattering from 45 to 200 K finds that the spin-spin correlations between nearest and next-nearest neighbors are antiferromagnetic and ferromagnetic, respectively, at temperatures near the upper ordering temperature, but both become antiferromagnetic and of similar magnitude above 100 K. The significance of this unusual crossover is discussed in light of the super-superexchange interactions between nearest and next-nearest neighbors in this material and the demands of type I order. The dimensionality of the correlations is addressed by reconstructing the scattering in the (hk0) plane using the RMC spin configurations. This indicates that one-dimensional spin correlations dominate at temperatures close to the first transition. In addition, a comparison between mean-field calculations and (hk0) scattering implies that further neighbor couplings play a significant role in the selection of the ground state. Finally, the results and interpretation are compared with those recently published for monoclinic Sr2YRuO6, and similarities and differences are emphasized.« less
Structural and Magnetic Phase Transitions in Minerals: In Situ Studies by Neutron Scattering
NASA Astrophysics Data System (ADS)
Redfern, Simon A. T.; Harrison, Richard J.
The application of neutron scattering to the study of structural and magnetic phase transitions in minerals is discussed. The advantages of neutrons for structural characterization of phase transitions are enumerated and compared with the data that might be obtained from X-ray methods. Elements that are difficult to distinguish by X-ray diffraction can show huge contrasts in neutron diffraction experiments; this contrast has been exploited in studies of site occupancies and intra-mineral partitioning of elements difficult to distinguish by other methods, such as Mg-Al and Fe-Mn pairs. Selected examples of the use of these methods in recent studies are outlined. These include the study of cation order-disorder phase transitions in minerals, ranging in complexity from rather simple silicate structures such as olivine and spinel (where ordering may occur between two sites) to more complex double-chain silicates (where partitioning studies by neutron diffraction have identified the trends over as many as four different crystallographic sites). The ability to build complex sample environments around the minerals under study has been beneficial in cases where extreme high temperatures (as great as 2000 K) are of interest, or where buffering of oxidation states is required. The magnetic moment of the neutron provides a unique tool for the study of the magnetic structures of oxide minerals, and the identification of magnetic ordering schemes in minerals such as magnetite were some of the first examples of the application of this method to magnetic minerals. The principles of magnetic scattering of neutrons are briefly outlined; and applications of magnetic studies by powder diffraction using both unpolarized and polarized neutrons are discussed, including recent studies of nanoscale hematite exsolution in ilmenite by polarized neutron scattering. Finally, the extension of the entire family of such studies in mineralogy to conditions pertinent to deep planetary interiors is
Toroid dipole moment as a signature of hybridization, observability by magnetic neutron scattering
NASA Astrophysics Data System (ADS)
Buin, Andrei; de Chatel, Peter
2002-03-01
The current denstity generated by electrons in Russell-Saunders states within an l^n manifold comprises only even-parity multipoles: 'magnetic' dipoles, octopoles, etc. (L=1,3,...) and 'electric' quadrupoles, etc. (L=2,4,...). If inversion symmetry is broken, e.g., by an odd-parity order parameter, and hybridization between states of different parity becomes possible, odd-parity terms also emerge in the multipole expansion of the magnetic field. The L=1 'electric' term describes the field of toroidal currents, which can be modeled by a solenoid bent in a circle. The magnetic neutron scattering amplitude due to such toroidal currents (or, equivalently, ring-shaped magnetization patterns), has a distinct angular dependence on the scattering vector q. If data covering a sufficient variety of q vectors and neutron-spin orientations are available, magnetic and toroidal moments can be distinguished unambiguously. However, it can be shown that within a limited set of data, notably within a plane in q space, which contains the magnetic dipole moment that enables a satisfactory interpretation, a toroid moment can be found, which gives an equally satisfactory result. The possible relevance of this finding to the order parameter in URu2Si2 will be discussed.
NASA Astrophysics Data System (ADS)
Settens, Charles M.
Simultaneous migration of planar transistors to FinFET architectures, the introduction of a plurality of materials to ensure suitable electrical characteristics, and the establishment of reliable multiple patterning lithography schemes to pattern sub-10 nm feature sizes imposes formidable challenges to current in-line dimensional metrologies. Because the shape of a FinFET channel cross-section immediately influences the electrical characteristics, the evaluation of 3D device structures requires measurement of parameters beyond traditional critical dimension (CD), including their sidewall angles, top corner rounding and footing, roughness, recesses and undercuts at single nanometer dimensions; thus, metrologies require sub-nm and approaching atomic level measurement uncertainty. Synchrotron critical dimension small angle X-ray scattering (CD-SAXS) has unique capabilities to non-destructively monitor the cross-section shape of surface structures with single nanometer uncertainty and can perform overlay metrology to sub-nm uncertainty. In this dissertation, we perform a systematic experimental investigation using CD-SAXS metrology on a hierarchy of semiconductor 3D device architectures including, high-aspect-ratio contact holes, H 2 annealed Si fins, and a series of grating type samples at multiple points along a FinFET fabrication process increasing in structural intricacy and ending with fully fabricated FinFET. Comparative studies between CD-SAXS metrology and other relevant semiconductor dimensional metrologies, particularly CD-SEM, CD-AFM and TEM are used to determine physical limits of CD-SAXS approach for advanced semiconductor samples. CD-SAXS experimental tradeoffs, advice for model-dependent analysis and thoughts on the compatibility with a semiconductor manufacturing environment are discussed.
NASA Astrophysics Data System (ADS)
Serrano Ruiz, D.; Alonso Cristobal, P.; Laurenti, M.; Rubio Retama, J.; Lopez-Cabarcos, E.
2014-11-01
Poly(acrylic-acrylamide) interpenetrated microgels present continuous phase transition from collapsed to swollen state around 42 °C. The upper critical solution temperature (UCST) of this polymeric system has prompted scientists to consider them candidates for its use in biological applications such as smart drug delivery devices since the swelling of the polymer matrix would permit the release of the drug previously entrapped within the microgels. In these systems the increment of the temperature can break inter-chain interactions, mainly hydrogen bonds, which reduce the elastic tension that stabilizes the microgel, favoring the polymer swelling. The microgel molecular dynamics at the UCST can be investigated using Incoherent Elastic (IENS) and Quasielastic Neutron Scattering (IQNS). From the analysis of the IQNS data we obtained that the diffusion coefficient of the polymer segments depends on the composition of the interpenetrated matrix. Thus, at room temperature, microgels with a polymer composition of 50% of each component present a diffusion coefficient 1·10-12 m2/s, while for the microgels formed by only one component the diffusion coefficient is 5.10-10 m2/s. This huge difference in the diffusion coefficient is conspicuously reduced when temperature increases, and we attribute this effect to the breaking of the inter-chain interaction. By means of FTIR-ATR analysis we have identified the groups that are involved in this phenomenon and we associate the breaking of the polyacrylic-polyacrylamide interactions with the swelling of the microgels.
Magnetic Field Dependence of the Critical Current in S-N Bilayer Thin Films
NASA Technical Reports Server (NTRS)
Sadleir, John E.; Lee, Sang-Jun; Smith, Stephen James; Bandler, Simon; Chervenak, James; Kilbourne, Caroline A.; Finkbeiner, Fred M.; Porter, Frederick S.; Kelley, Richard L.; Adams, Joseph S.; Eckart, Megan E.; Busch, Sarah; Porst, Jan-Patrick
2013-01-01
Here we investigate the effects a non-uniform applied magnetic field has on superconducting transition-edge sensors (TESs) critical current. This has implications on TES optimization. It has been shown that TESs resistive transition can be altered by magnetic fields. We have observed critical current rectification effects and explained these effects in terms of a magnetic self-field arising from asymmetric current injection into the sensor. Our TES physical model shows that this magnetic self-field can result in significantly degraded or improved TES performance. In order for this magnetically tuned TES strategy to reach its full potential we are investigating the effect a non-uniform applied magnetic field has on the critical current.
Pan, Albert C; Rappl, Timothy J; Chandler, David; Balsara, Nitash P
2006-03-01
We have used a combination of neutron scattering experiments and Monte Carlo simulations to study the initial stages of first-order phase transitions. We focus on quenches wherein the nascent phase is formed by homogeneous nucleation, and we approach the spinodal, i.e., the quench depth at which the original phase becomes unstable. In this regime, we show how critical nuclei sizes are determined from neutron scattering structure factors. Prevailing thought is that the size of the critical nucleus should increase with increasing quench depth and diverge at the spinodal. To the contrary, our experiments and simulations indicate that the critical nucleus size decreases monotonically as quench depth is increased and is finite at the spinodal. PMID:16494425
NASA Astrophysics Data System (ADS)
Erokhin, Sergey; Berkov, Dmitry; Gorn, Nataliya; Michels, Andreas
2012-01-01
A new methodology for micromagnetic simulations of magnetic nanocomposites is presented. The methodology is especially suitable for simulations of two-phase composites consisting of magnetically hard inclusions in a soft magnetic matrix phase. The proposed technique allows us to avoid unnecessary discretization of the “hard” inclusions (these are normally in a single-domain state) but enables arbitrary fine discretization of the “soft” phase. The method is applied to the determination of the equilibrium magnetization state of an iron-based nanocomposite from the Nanoperm (FeZrBCu) family of alloys and to the calculation of the corresponding small-angle neutron scattering (SANS) cross-section. The results of our simulations exhibit a remarkable agreement with nontrivial “clover-leaf” SANS cross-sections observed experimentally.
Neutron scattering study on the magnetic and superconducting phases of MnP
NASA Astrophysics Data System (ADS)
Yano, Shinichiro; Lancon, Diane; Ronnow, Henrik; Hansen, Thomas; Gardner, Jason
We have performed series of neutron scattering experiments on MnP. MnP has been investigated for decades because of its rich magnetic phase diagram. The magnetic structure of MnP is ferromagnetic (FM) below TC = 291 K. It transforms into a helimagnetic structure at TS = 47 K with a propagation vector q = 0 . 117a* . Superconductivity was found in MnP under pressures of 8 GPa with a TSC around 1 K by J.-G. Cheng. Since Mn-based superconductors are rare, and the superconducting phase occurs in the vicinity of FM, new magnetic and helimagnetic phases, there is a need to understand how the magnetism evolves as one approach the superconducting state. MnP is believed to be a double helix magnetic structure at TS = 47 K. We observed new 2 δ and 3 δ satellite peaks whose intensity are 200 ~ 1000 times smaller than these of 1 δ satellite peaks on the cold triple axis spectrometer SIKA under zero magnetic fields. We also found the periods of helimagnetic structure changes as a function of temperature. If time permits, we will discuss recent experiments under pressure. However, we have complete picture of magnetic structure of this system with and without applied pressure, revealing the interplay between the magnetic and superconducting phases.
Quantum correlations of magnetic impurities by a multiple electron scattering in carbon nanotubes
NASA Astrophysics Data System (ADS)
Gamboa Angulo, Didier; Cordourier Maruri, Guillermo; de Coss Gómez, Romeo
In this work we analyze the quantum correlations and polarizations states of magnetic impurities spins, when a multiple electron scattering was taken place. A sequence of non-correlated electrons interacts through scattering producing quantum correlation which will have an impact on the electronic transmission. We consider a short range Heisenberg interaction between ballistic electron and static impurities. We analyze the cases when the electron scattering is produce by one and two impurities, obtaining the electronic transmission rates. Concurrence and fidelity calculations are performed to obtain the level of quantum entanglement and polarization correlations. We also discuss the possible application of this model to metallic and semiconductor carbon nanotubes, which could have important implications on spintronics and quantum information devices.
Scattering of electromagnetic waves from a magnetized plasma column at oblique incidence
Ghaffari-Oskooei, Sara S.; Aghamir, Farzin M.
2015-07-14
Scattering of electromagnetic waves from a magnetized plasma column is investigated using Maxwell's equations and applying boundary conditions. Backscattering cross section is evaluated by analytic solution of electric fields inside and outside of plasma column. Plots of backscattering cross section versus frequency, for the range up to J band, reveal two main peaks and two sidebands. Effects of plasma density and radius, as main parameters determining the characteristics of plasma column, on backscattering are discussed. Furthermore, the effect of electromagnetic wave incidence angle on backscattering of plasma column is included in the analysis. The influence of wave incidence angle and frequency, as well as, plasma density and radius on scattering pattern, which is an indicator of the distribution of scattered power in different azimuthal angles, is discussed.
Compton scattering S matrix and cross section in strong magnetic field
NASA Astrophysics Data System (ADS)
Mushtukov, Alexander A.; Nagirner, Dmitrij I.; Poutanen, Juri
2016-05-01
Compton scattering of polarized radiation in a strong magnetic field is considered. The recipe for calculation of the scattering matrix elements, the differential and total cross sections based on quantum electrodynamic second-order perturbation theory is presented for the case of arbitrary initial and final Landau level, electron momentum along the field and photon momentum. Photon polarization and electron spin state are taken into account. The correct dependence of natural Landau level width on the electron spin state is taken into account in a general case of arbitrary initial photon momentum for the first time. A number of steps in the calculations were simplified analytically making the presented recipe easy to use. The redistribution functions over the photon energy, momentum and polarization states are presented and discussed. The paper generalizes already known results and offers a basis for the accurate calculation of radiation transfer in a strong B field, for example, in strongly magnetized neutron stars.
Light scattering from liquid crystal director fluctuations in steady magnetic fields up to 25 tesla
NASA Astrophysics Data System (ADS)
Challa, Pavan K.; Curtiss, O.; Williams, J. C.; Twieg, R.; Toth, J.; McGill, S.; Jákli, A.; Gleeson, J. T.; Sprunt, S. N.
2012-07-01
We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (QαβBαBβ) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may be expected from the mean field scaling of these quantities with the magnitude of Q and the predicted variation of Q with field.
Light scattering from liquid crystal director fluctuations in steady magnetic fields up to 25 tesla.
Challa, Pavan K; Curtiss, O; Williams, J C; Twieg, R; Toth, J; McGill, S; Jákli, A; Gleeson, J T; Sprunt, S N
2012-07-01
We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (Q(αβ)B(α)B(β)) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may be expected from the mean field scaling of these quantities with the magnitude of Q and the predicted variation of Q with field. PMID:23005438
Stimulated Raman scattering of a laser beam in a plasma with azimuthal magnetic field
NASA Astrophysics Data System (ADS)
Sajal, Vivek; Tripathi, V. K.
2004-09-01
A strong azimuthal magnetic field localizes the lower hybrid waves radially in laser produced plasmas. The laser pump parametrically excites a lower hybrid wave and a backscattered electromagnetic sideband wave. The density perturbation due to the lower hybrid wave couples with the oscillatory velocity of electrons due to the pump wave, to produce a nonlinear current driving the sideband. The pump and sideband waves exert a ponderomotive force on electrons driving the lower hybrid wave. The local effects reduce the growth rate of stimulated Raman scattering. The fundamental radial eigenmode (p=0) of the lower hybrid wave is the maximally growing mode. The scattering process can be used as a diagnostic for the azimuthal magnetic field.
Paknezhad, Alireza
2013-01-15
Nonlinear Raman forward scattering (NRFS) of an intense short laser pulse with a duration shorter than the plasma period through a homogenous collisional transversely magnetized plasma is investigated theoretically when ponderomotive, relativistic and collioninal nonlinearities are taken into account. The plasma is embedded in a uniform magnetic field perpendicular to both, the direction of propagation and electric vector of the radiation field. Nonlinear wave equation is set up and Fourier transformation method is used to solve the coupled equations describing NRFS instability. Finally, the growth rate of this instability is obtained. Thermal effects of plasma electrons and effect of the electron-ion collisions are examined. It is found that the growth rate of Raman forward scattering first decreases on increasing electron thermal velocity, minimizes at an optimum value, and then increases. Our results also show that the growth rate increases by increasing the electron-ion collisions.
Amorphous soft-magnetic ribbons studied by ultra-small-angle polarized neutron scattering
NASA Astrophysics Data System (ADS)
Badurek, G.; Jericha, E.; Grössinger, R.; Sato-Turtelli, R.
2010-02-01
When we investigated the magnetic structure of a variety of soft-magnetic amorphous ribbons by means of ultra-small-angle neutron scattering (USANSPOL) we were confronted with one particularly interesting Fe65.7Co18Si0.8B15.5 ribbon, provided by VAC Hanau. Due to a special thermal treatment during production a field- and stress-induced transverse domain texture was expected. Although the USANSPOL technique encountered its resolution limits during the investigation of this specific sample ribbon, such a texture could indeed be verified.
NASA Astrophysics Data System (ADS)
Günther, Stefan; Spezzani, Carlo; Ciprian, Roberta; Grazioli, Cesare; Ressel, Barbara; Coreno, Marcello; Poletto, Luca; Miotti, Paolo; Sacchi, Maurizio; Panaccione, Giancarlo; Uhlíř, Vojtěch; Fullerton, Eric E.; De Ninno, Giovanni; Back, Christian H.
2014-11-01
We use element-resolved IR-pump/extreme ultraviolet-probe experiments to disentangle the ultrafast interplay of the magnetic sublattices of an ordered crystalline magnetic alloy. As a paradigmatic example, we investigate the case of the FeRh alloy, which shows a delayed response for the different components. Furthermore, a detailed time-resolved magneto-optic study shows that the data can be analyzed by only assuming Elliot-Yafet-like scattering, as the underlying mechanism for ultrafast demagnetization, resulting in an unexpected nonmonotonic dependence of the spin-flip rate, as a function of quenching.
Extended reciprocal space observation of artificial spin ice with x-ray resonant magnetic scattering
NASA Astrophysics Data System (ADS)
Perron, J.; Anghinolfi, L.; Tudu, B.; Jaouen, N.; Tonnerre, J.-M.; Sacchi, M.; Nolting, F.; Lüning, J.; Heyderman, L. J.
2013-12-01
Soft x-ray resonant magnetic scattering is an element-sensitive technique that enables the characterization of the magnetic properties of a wide variety of systems. Here we apply this technique to study lithographically produced artificial spin ice, a particular class of magnetically frustrated systems comprising arrays of nanomagnets. Using a CCD detector we can access a large fraction of the reciprocal space at once, allowing us to easily distinguish the signatures of the magnetic ground-state ordering. Comparing the dichroic signal at the position of the Bragg peaks with model calculations based on the kinematical theory of x-ray diffraction, we are able to determine the number of reversed moments as a function of applied magnetic field for each of the two sublattices. This study demonstrates the benefit of having direct access to a significant fraction of the reciprocal space, and opens the way towards more sophisticated x-ray based experiments on artificial spin ice such as scattering of coherent x-ray beams to explore the dynamics of thermally activated systems.
Magnetic Diffuse Scattering in the Frustrated Kagome Antiferromagnet YBaCo4O7
NASA Astrophysics Data System (ADS)
Manuel, Pascal; Chapon, Laurent; Radaelli, Paolo; Mitchell, John; Zheng, Hong
2008-03-01
Cobalt oxides of composition RBaCo4O7 (R=Y, Tb-Lu) crystallize with a lattice structure topologically related to that of the pyrochlore. Considering only the magnetic transition metal sublattice, R-114 appears as Kagome sheets linked by triangular layers and is therefore expected to provide a new materials class for exploring geometric magnetic frustration. We have recently shown that stoichiometric R-114 compound orders antiferromagnetically into a long-range ordered (LRO) structure with features common to the √3 *√3 negative chirality spin arrangements often found in Kagome net systems. In contrast, small excesses of O added to the system, as little as 0.1, destroys this LRO state. To explore the nature of the frustrated magnetism in this novel system, we have measured magnetic diffuse scattering on YBaCo4O7 and YBaCo4O7.1 single crystals at the ISIS facility. Large maps of reciprocal space in several planes have been recorded showing a very structured diffuse scattering. The data compared to models obtained by the Monte-Carlo method using the metropolis algorithm, reveal the exact nature of the disordered ground state in this new class of frustrated magnets.
Quantum Criticality and Unconventional Order in Magnetic and Dielectric Material
NASA Astrophysics Data System (ADS)
Rowley, S. E.; Smith, R.; Sutherland, M. L.; Alireza, P.; Saxena, S. S.; Lonzarich, G. G.
2012-12-01
We present an overview of unconventional phenomena arising close to ferromagnetic and ferroelectric quantum phase transitions. The applicability and potential breakdown of traditional field theories of quantum criticality and the emergence of a multiplicity of critical fields in particular will be discussed.
NASA Astrophysics Data System (ADS)
Jiang, Y.; Nozaki, T.; Abe, S.; Ochiai, T.; Hirohata, A.; Tezuka, N.; Inomata, K.
2004-06-01
Great interest in current-induced magnetic excitation and switching in a magnetic nanopillar has been caused by the theoretical predictions of these phenomena. The concept of using a spin-polarized current to switch the magnetization orientation of a magnetic layer provides a possible way to realize future 'current-driven' devices: in such devices, direct switching of the magnetic memory bits would be produced by a local current application, instead of by a magnetic field generated by attached wires. Until now, all the reported work on current-induced magnetization switching has been concentrated on a simple ferromagnet/Cu/ferromagnet trilayer. Here we report the observation of current-induced magnetization switching in exchange-biased spin valves (ESPVs) at room temperature. The ESPVs clearly show current-induced magnetization switching behaviour under a sweeping direct current with a very high density. We show that insertion of a ruthenium layer between an ESPV nanopillar and the top electrode effectively decreases the critical current density from about 108 to 107 A cm-2. In a well-designed 'antisymmetric' ESPV structure, this critical current density can be further reduced to 2 × 106 A cm-2. We believe that the substantial reduction of critical current could make it possible for current-induced magnetization switching to be directly applied in spintronic devices, such as magnetic random-access memory.
Resonant Scattering off Magnetic Impurities in Graphene: Mechanism for Ultrafast Spin Relaxation
NASA Astrophysics Data System (ADS)
Kochan, D.; Gmitra, M.; Fabian, J.
We give a tutorial account of our recently proposed mechanism for spin relaxation based on spin-flip resonant scattering off local magnetic moments. The mechanism is rather general, working in any material with a resonant local moment, but we believe that its particular niche is graphene, whose measured spin relaxation time is 100-1000 ps. Conventional spin-orbit coupling based mechanisms (Elliott-Yafet or Dyakonov-Perel) would require large concentrations (1000 ppm) of impurities to explain this. Our mechanism needs only 1 ppm of resonant local moments, as these act as local spin hot spots: the resonant scatterers do not appear to substantially affect graphene's measured resistivity, but are dominating spin relaxation. In principle, the local moments can come from a variety of sources. Most likely would be organic molecule adsorbants or metallic adatoms. As the representative model, particularly suited for a tutorial, we consider hydrogen adatoms which are theoretically and experimentally demonstrated to yield local magnetic moments when chemisorbed on graphene. We introduce the scattering formalism and apply it to graphene, to obtain the T-matrix and spin-flip scattering rates using the generalized Fermi golden rule.
NASA Astrophysics Data System (ADS)
Kotera, Kumiko; Lemoine, Martin
2008-06-01
This paper provides an analytical description of the transport of ultrahigh energy cosmic rays in an inhomogeneously magnetized intergalactic medium. The latter is modeled as a collection of magnetized scattering centers, such as radio cocoons, magnetized galactic winds, clusters or magnetized filaments of large scale structure, with negligible magnetic fields in between. Magnetic deflection is no longer a continuous process, it is rather dominated by scattering events. We study the interaction between high-energy cosmic rays and the scattering agents. We then compute the optical depth of the Universe to cosmic ray scattering and discuss the phenomenological consequences for various source scenarios. For typical parameters of the scattering centers, the optical depth is greater than unity at 5×1019eV, but the total angular deflection is smaller than unity. One important consequence of this scenario is the possibility that the last scattering center encountered by a cosmic ray be mistaken with the source of this cosmic ray. In particular, we suggest that part of the correlation recently reported by the Pierre Auger Observatory may be affected by such delusion: this experiment may be observing in part the last scattering surface of ultrahigh energy cosmic rays rather than their source population. Since the optical depth falls rapidly with increasing energy, one should probe the arrival directions of the highest energy events beyond 1020eV on an event by event basis to circumvent this effect.
Kotera, Kumiko; Lemoine, Martin
2008-06-15
This paper provides an analytical description of the transport of ultrahigh energy cosmic rays in an inhomogeneously magnetized intergalactic medium. The latter is modeled as a collection of magnetized scattering centers, such as radio cocoons, magnetized galactic winds, clusters or magnetized filaments of large scale structure, with negligible magnetic fields in between. Magnetic deflection is no longer a continuous process, it is rather dominated by scattering events. We study the interaction between high-energy cosmic rays and the scattering agents. We then compute the optical depth of the Universe to cosmic ray scattering and discuss the phenomenological consequences for various source scenarios. For typical parameters of the scattering centers, the optical depth is greater than unity at 5x10{sup 19} eV, but the total angular deflection is smaller than unity. One important consequence of this scenario is the possibility that the last scattering center encountered by a cosmic ray be mistaken with the source of this cosmic ray. In particular, we suggest that part of the correlation recently reported by the Pierre Auger Observatory may be affected by such delusion: this experiment may be observing in part the last scattering surface of ultrahigh energy cosmic rays rather than their source population. Since the optical depth falls rapidly with increasing energy, one should probe the arrival directions of the highest energy events beyond 10{sup 20} eV on an event by event basis to circumvent this effect.
Magnetic spectra in the tridiminished-icosahedron {Fe9} nanocluster by inelastic neutron scattering
Vaknin, David; Demmel, Franz
2014-05-01
Inelastic neutron scattering (INS) experiments under applied magnetic field at low temperatures show detailed low-lying magnetic excitations in the so-called tridiminshed iron icosahedron magnetic molecule. The magnetic molecule consists of nine iron Fe3+ (s=5/2) and three phosphorous atoms that are situated on the 12 vertices of a nearly perfect icosahedron. The three phosphorous atoms form a plane that separates the iron cluster into two weakly coupled three- and six-ion fragments, {Fe3} and {Fe6}, respectively. The magnetic field INS results exhibit an S=1/2 ground state expected from a perfect equilateral triangle of the {Fe3} triad with a powder averaged g value =2.00. Two sets of triplet excitations whose temperature and magnetic field dependence indicate an S=0 ground state with two nondegenerate S=1 states are attributed to the {Fe6} fragment. The splitting may result from a finite coupling between the two fragments, single-ion anisotropy, antisymmetric exchange couplings, or from magnetic frustration of its triangular building blocks.
NASA Astrophysics Data System (ADS)
Kharkov, Yaroslav; Oleg P Sushkov Team
We consider two spin 1 / 2 fermions in a two-dimensional magnetic system that is close to the O (3) magnetic quantum critical point (QCP) which separates magnetically ordered and disordered phases. Focusing on the disordered phase in the vicinity of the QCP, we demonstrate that the criticality results in a strong long range attraction between the fermions, with potential V (r) ~ - 1 /rα , α ~ 0 . 75 , where r is separation between the fermions. The mechanism of the enhanced attraction is similar to Casimir effect and corresponds to multi-magnon exchange processes between the fermions. While we consider a model system, the problem is originally motivated by recent experimental establishment of magnetic QCP in hole doped cuprates under the superconducting dome at doping of about 10%. We suggest the mechanism of magnetic critical enhancement of pairing in cuprates.
NASA Technical Reports Server (NTRS)
Goldstein, M. L.; Klimas, A. J.; Sandri, G.
1974-01-01
The Fokker-Planck coefficient for pitch angle scattering, appropriate for cosmic rays in homogeneous, stationary, magnetic turbulence, is computed from first principles. No assumptions are made concerning any special statistical symmetries the random field may have. This result can be used to compute the parallel diffusion coefficient for high energy cosmic rays moving in strong turbulence, or low energy cosmic rays moving in weak turbulence. Becuase of the generality of the magnetic turbulence which is allowed in this calculation, special interplanetary magnetic field features such as discontinuities, or particular wave modes, can be included rigorously. The reduction of this results to previously available expressions for the pitch angle scattering coefficient in random field models with special symmetries is discussed. The general existance of a Dirac delta function in the pitch angle scattering coefficient is demonstrated. It is proved that this delta function is the Fokker-Planck prediction for pitch angle scattering due to mirroring in the magnetic field.
NASA Astrophysics Data System (ADS)
Wu, B.; Zhu, D.; Acremann, Y.; Miller, T. A.; Lindenberg, A. M.; Hellwig, O.; Stöhr, J.; Scherz, A.
2011-12-01
We report on time-resolved coherent x-ray scattering experiments of laser induced magnetization dynamics in Co/Pd multilayers with a high repetition rate optical pump x-ray probe setup. Starting from a multi-domain ground state, the magnetization is uniformly reduced after excitation by an intense 50 fs laser pulse. Using the normalized time correlation, we study the magnetization recovery on a picosecond timescale. The dynamic scattering intensity is separated into an elastic portion at length scales above 65 nm, which retains memory of the initial domain magnetization, and a fluctuating portion at smaller length scales corresponding to domain boundary motion during recovery.
NASA Astrophysics Data System (ADS)
Lister, S. J.; Thomson, T.; Kohlbrecher, J.; Takano, K.; Venkataramana, V.; Ray, S. J.; Wismayer, M. P.; de Vries, M. A.; Do, H.; Ikeda, Y.; Lee, S. L.
2010-09-01
Polarized small-angle neutron scattering has been used to measure the magnetic structure of a CoCrPt-SiOx thin-film data storage layer, contained within a writable perpendicular recording media, at granular (<10 nm) length scales. The magnetic contribution to the scattering is measured as the magnetization is reversed by an external field, providing unique spatial information on the switching process. A simple model of noninteracting nanomagnetic grains provides a good description of the data and an analysis of the grain-size dependent reversal provides strong evidence for an increase in magnetic anisotropy with grain diameter.
Wu, Benny
2012-04-05
We report on time-resolved coherent x-ray scattering experiments of laser induced magnetization dynamics in Co/Pd multilayers with a high repetition rate optical pump x-ray probe setup. Starting from a multi-domain ground state, the magnetization is uniformly reduced after excitation by an intense 50 fs laser pulse. Using the normalized time correlation, we study the magnetization recovery on a picosecond timescale. The dynamic scattering intensity is separated into an elastic portion at length scales above 65 nm which retains memory of the initial domain magnetization, and a fluctuating portion at smaller length scales corresponding to domain boundary motion during recovery.
Small-angle neutron scattering of nanocrystalline terbium with random paramagnetic susceptibility.
Balaji, G; Ghosh, S; Döbrich, F; Eckerlebe, H; Weissmüller, J
2008-06-01
We report magnetic small-angle neutron scattering (SANS) data for the nanocrystalline rare earth metal Terbium in its paramagnetic state. Whereas critical scattering dominates at large momentum transfer, q, the (magnetic-) field response of the scattering at small q arises from the spatial nonuniformity of the paramagnetic susceptibility tensor. The finding of an interrelation between SANS and the susceptibility suggests a way for characterizing the nonuniform magnetic interactions in hard magnets by neutron scattering. PMID:18643454
IRMA-2 at SOLEIL: a set-up for magnetic and coherent scattering of polarized soft x-rays
NASA Astrophysics Data System (ADS)
Sacchi, M.; Popescu, H.; Gaudemer, R.; Jaouen, N.; Avila, A.; Delaunay, R.; Fortuna, F.; Maier, U.; Spezzani, C.
2013-03-01
We have designed, built and tested a new instrument for soft x-ray scattering experiments. IRMA-2 is a UHV set-up for elastic and coherent scattering experiments developed at the SEXTANTS beamline of the SOLEIL synchrotron. Applications will be in the field of solid state physics, with emphasis on the investigation of the magnetic properties of artificially structured materials.
Magnetic Rotation and Chirality and X(5) Critical Symmetry in Nucleus
Zhu, L. H.; Wu, X. G.; He, C. Y.; Hao, X.; Wang, L. L.; Zheng, Y.; Li, G. S.
2010-05-12
The magnetic and chiral rotation, the critical symmetry are fundamental problems in the study of nuclear structure. Here we report the recent results from the experiments on the magnetic and electric rotations in {sup 106}Ag, the chiral rotation in {sup 130}Cs and the evolution of X(5) symmetry in {sup 176}Os.
Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; James, R. D.; Leighton, C.
2012-04-27
The Heusler-derived multiferroic alloy Ni50–xCoxMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390 K. Themore » static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.« less
Magnetic Field and Pressure Dependence of Small Angle Neutron Scattering in MnSi
Pfleiderer, C.; Reznik, D.; Pintschovius, L.; Haug, J.
2007-10-12
We report small angle neutron scattering of spontaneous and magnetic field aligned components of the helical spin polarization in MnSi for temperatures T down to 0.35 K, at pressures p up to 21 kbar, and magnetic field B up to 0.7 T. The parameter range of our study spans the first order transition between helical order and partial magnetic order at p{sub c}=14.6 kbar, which coincides with the onset of an extended regime of non-Fermi liquid resistivity. Our study suggests that MnSi above p{sub c} is not dominated by the remnants of the first order transition at p{sub c}, but that an unidentified mechanism favors stabilization of a new ground state other than helical order.
Lee, Dukhyung; Kim, Dai-Sik
2016-01-01
We study light scattering off rectangular slot nano antennas on a metal film varying incident polarization and incident angle, to examine which field vector of light is more important: electric vector perpendicular to, versus magnetic vector parallel to the long axis of the rectangle. While vector Babinet's principle would prefer magnetic field along the long axis for optimizing slot antenna function, convention and intuition most often refer to the electric field perpendicular to it. Here, we demonstrate experimentally that in accordance with vector Babinet's principle, the incident magnetic vector parallel to the long axis is the dominant component, with the perpendicular incident electric field making a small contribution of the factor of 1/|ε|, the reciprocal of the absolute value of the dielectric constant of the metal, owing to the non-perfectness of metals at optical frequencies. PMID:26740335
Clustering in Water Based Magnetic Nanofluids: Investigations by Light Scattering Methods
NASA Astrophysics Data System (ADS)
Socoliuc, Vlad; Taculescu, Alina; Podaru, Camelia; Dobra, Andreea; Daia, Camelia; Marinica, Oana; Turcu, Rodica; Vekas, Ladislau
2010-12-01
Nanosized magnetite particles, with mean physical diameter of about 7 nm, obtained by chemical coprecipitation procedure were dispersed in water carrier by applying sterical stabilization of particles in order to prevent their aggregation and to ensure colloidal stability of the systems. Different chain length (C12, C14, C18) carboxylic acids (lauric (LA), myristic (MA) and oleic (OA)) were used for double layer coating of magnetite nanoparticles. Structural and magnetic properties were investigated by electron microscopy (TEM), dynamical and static light scattering (DLS, SLS) and magnetometry (VSM) to evaluate the role of chain length and of the saturated/unsaturated nature of surfactant layers. Also investigated were two water based magnetic nanocomposites obtained by encapsulating the magnetic nanoparticles in polymers with different functional properties.
Lee, Dukhyung; Kim, Dai-Sik
2016-01-01
We study light scattering off rectangular slot nano antennas on a metal film varying incident polarization and incident angle, to examine which field vector of light is more important: electric vector perpendicular to, versus magnetic vector parallel to the long axis of the rectangle. While vector Babinet’s principle would prefer magnetic field along the long axis for optimizing slot antenna function, convention and intuition most often refer to the electric field perpendicular to it. Here, we demonstrate experimentally that in accordance with vector Babinet’s principle, the incident magnetic vector parallel to the long axis is the dominant component, with the perpendicular incident electric field making a small contribution of the factor of 1/|ε|, the reciprocal of the absolute value of the dielectric constant of the metal, owing to the non-perfectness of metals at optical frequencies. PMID:26740335
Magnetic resonance imaging in entomology: a critical review
Hart, A.G.; Bowtell, R.W.; Köckenberger, W.; Wenseleers, T.; Ratnieks, F.L.W.
2003-01-01
Magnetic resonance imaging (MRI) enables in vivo imaging of organisms. The recent development of the magnetic resonance microscope (MRM) has enabled organisms within the size range of many insects to be imaged. Here, we introduce the principles of MRI and MRM and review their use in entomology. We show that MRM has been successfully applied in studies of parasitology, development, metabolism, biomagnetism and morphology, and the advantages and disadvantages relative to other imaging techniques are discussed. In addition, we illustrate the images that can be obtained using MRM. We conclude that although MRM has significant potential, further improvements to the technique are still desirable if it is to become a mainstream imaging technology in entomology. Abbreviation: CSI chemical shift imaging. The dependence of the resonance frequency of a nucleus on the chemical binding of the atom or molecule in which it is contained. (N)MRI (nuclear) magnetic resonance imaging MRM magnetic resonance microscopy Voxel A contraction for volume element, which is the basic unit of MR reconstruction; represented as a pixel in the display of the MR image. PMID:15841222
NASA Astrophysics Data System (ADS)
Madsen, A.; Als-Nielsen, J.; Hallmann, J.; Roth, T.; Lu, W.
2016-07-01
β -brass exhibits an archetypical example of an order-disorder transition with a critical behavior that was previously investigated by neutron scattering. The data were well described by the three-dimensional (3d) Ising model but the relatively crude experimental resolution prevented an in-depth examination of the single-length scaling hypothesis, a cornerstone in the theory of critical phenomena. With the development of synchrotron x-ray experiments, high-resolution data could be recorded and surprisingly it was found that the single-length scaling did not hold in most critical systems, possibly due to strain originating from surface defects and/or impurities. In this paper we demonstrate single-length critical behavior using high-resolution x-ray scattering in β -brass. The investigations confirm that β -brass behaves like a 3d Ising system over a wide range of length scales comprising correlated clusters of millions of atoms. To vary the surface sensitivity, experiments have been performed both in Bragg reflection and Laue transmission geometries but without any substantial differences observed in the scaling and critical behavior.
Yano, M. Manabe, A.; Shoji, T.; Kato, A.; Ono, K.; Harada, M.; Kohlbrecher, J.
2014-05-07
The magnetic reversal behaviors of single domain sized Nd-Fe-B permanent magnets, with and without isolation between the Nd{sub 2}Fe{sub 14}B grains, was clarified using small-angle neutron scattering (SANS). The SANS patterns obtained arose from changes in the magnetic domains and were analyzed using the Teubner–Stray model, a phenomenological correlation length model, to quantify the periodicity and morphology of the magnetic domains. The results indicated that the magnetic reversal evolved with the magnetic domains that had similar sized grains. The grain isolation enabled us to realize the reversals of single domains.
Peterson, J. L.; Hammet, G. W.; Mikkelsen, D. R.; Yuh, H. Y.; Candy, J.; Guttenfelder, W.; Kaye, S. M.; LeBlanc, B.
2011-05-11
The first nonlinear gyrokinetic simulations of electron internal transport barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed magnetic shear can suppress thermal transport by increasing the nonlinear critical gradient for electron-temperature-gradient-driven turbulence to three times its linear critical value. An interesting feature of this turbulence is non- linearly driven off-midplane radial streamers. This work reinforces the experimental observation that magnetic shear is likely an effective way of triggering and sustaining e-ITBs in magnetic fusion devices.
Reactivity Impact of 2H and 16O Elastic Scattering Nuclear Data on Critical Systems with Heavy Water
NASA Astrophysics Data System (ADS)
Roubtsov, D.; Kozier, K. S.; Chow, J. C.; Plompen, A. J. M.; Kopecky, S.; Svenne, J. P.; Canton, L.
2014-04-01
The accuracy of deuterium nuclear data is important for reactor physics simulations of heavy water (D2O) reactors. The elastic neutron scattering cross section data at thermal energies, σs,th, have been observed to have noticeable impact on the reactivity values in simulations of critical systems involving D2O. We discuss how the uncertainties in the thermal scattering cross sections of 2H(n,n)2H and 16O(n,n)16O propagate to the uncertainty of the calculated neutron multiplication factor, keff, in thermal critical assemblies with heavy water neutron moderator/reflector. The method of trial evaluated nuclear data files, in which specific cross sections are individually perturbed, is used to calculate the sensitivity coefficients of keff to the microscopic nuclear data, such as σs(E) characterized by σs,th. Large reactivity differences of up to ≃ 5-10 mk (500-1000 pcm) were observed using 2H and 16O data files with different elastic scattering data in MCNP5 simulations of the LANL HEU heavy-water solution thermal critical experiments included in the ICSBEP handbook.
NASA Astrophysics Data System (ADS)
Kim, Jong-Woo
2005-11-01
The x-ray magnetic scattering (XRMS) intensities of the Gd, Tb, Dy, Ho, Er, and Tm L2,3 edges were investigated using two isostructural samples [Gd1/4Tb1/4Dy1/4Ho 1/4]Ni2Ge2 and [Gd1/3Er1/3Tm 1/3]Ni2Ge2 in order to elucidate systematics in the underlying resonance process. Taken together with theoretical linearized augmented planewave (LAPW) calculations employing LDA + U, we found that the XRMS intensity at the heavy rare-earth L edges is strongly related to the 4f-5d exchange interaction and that the branching ratio arises from the effects of spin orbit coupling in the 5d band. For Gd, the 4f-5 d exchange interaction is large and dominant over not only the spin orbit coupling but also other interactions. Therefore, the XRMS intensity of Gd L3 and L2 edges most closely reflects the state of 4f moments. In the pure GdNi2Ge2 compound, large antiferromagnetic (AFM) domains were found, comparable to the x-ray beam size. Single domain scattering was measured carefully with a very small beam size for various azimuth angles and temperatures. From this measurement, a second transition at 16 K in bulk measurements was identified as a transformation from a collinear squared-up structure at high temperature, to a tilted helical structure below 16 K. Since the XRMS scattering cross-section is strongly dependent on the magnetic moment direction, the AFM domain structure was imaged by the XRMS intensity. From single domain scattering data, the ratio of the spin moments in the collinear and the spiral structure of GdNi2Ge2 at the second magnetic transition temperature were derived and used to estimate the magnetic anisotropy energy of Gd. Surprisingly, the estimated magnetic anisotropy energy of Gd in this compound is much higher than that of pure Gd metal (about a order of magnitude). This is expected to be the effect of the anisotropy in 5d conduction band. More theoretical study is necessary to understand this observation.
Magnetocaloric effect and critical behavior in Mn2-imidazole-[Nb(CN)8] molecular magnetic sponge
NASA Astrophysics Data System (ADS)
Fitta, Magdalena; Pełka, Robert; Gajewski, Marcin; Mihalik, Marian; Zentkova, Maria; Pinkowicz, Dawid; Sieklucka, Barbara; Bałanda, Maria
2015-12-01
A comprehensive study of magnetocaloric effect (MCE) and critical behavior in the {Mn2(imH)2(H2O)4[Nb(CN)8]·4H2O}n molecular magnet is reported. The compound is an example of a magnetic sponge, where structural changes provoked by dehydration process lead to the increase of Tc critical temperature from 25 K for the as-synthesized sample (1) up to 60 K for the anhydrous one (2). MCE and critical behavior were investigated by magnetization measurements. The maximum value of magnetic entropy change ΔS, determined by the magnetization measurements for 1 is 6.70 J mol-1 K-1 (8.95 J kg-1 K-1) at μ0ΔH=5 T, while for 2 it is equal to 4.02 J mol-1 K-1 (7.73 J kg-1 K-1) at the same magnetic field change. The field dependence of MCE at Tc for 1 and 2 was consistent with critical exponents, which allowed to classify both phases to 3D Heisenberg universality class. The Tc-2/3 dependence of the maximum entropy change has been tested using data of 1 and 2 together with MCE data previously reported for other members of the ferrimagnetic Mn2-L-[Nb(CN)8] (L=imidazole, pyridazine and pyrazole) series. Experimental MCE results have been compared with the spin contribution to the magnetic entropy change estimated using a molecular field approximation.
Siphon flows in isolated magnetic flux tubes. IV - Critical flows with standing tube shocks
NASA Technical Reports Server (NTRS)
Thomas, John H.; Montesinos, Benjamin
1991-01-01
Critical siphon flows in arched, isolated magnetic flux tubes are studied within the thin flux tube approximation, with a view toward applications to intense magnetic flux concentrations in the solar photosphere. The results of calculations of the strength and position of the standing tube shock in the supercritical downstream branch of a critical siphon flow are presented, as are calculations of the flow variables all along the flux tube and the equilibrium path of the flux tube in the surrounding atmosphere. It is suggested that arched magnetic flux tubes, with magnetic field strength increased by a siphon flow, may be associated with some of the intense, discrete magnetic elements observed in the solar photosphere.
NASA Astrophysics Data System (ADS)
Fuss, M. C.; Sanz, A. G.; Blanco, F.; Oiler, J. C.; Limão-Vieira, P.; Brunger, M. J.; García, G.
2014-04-01
In this paper, a recently constructed apparatus for measuring electron scattering cross sections while applying a strong axial magnetic field is utilized for determining total scattering cross sections. The first molecules studied with this setup are pyrimidine (1,3-diazine) and pyrazine (1,4-diazine), whose total cross sections are obtained for the incident electron energy range of 8-500 eV. Quite good agreement with earlier theoretical predictions is found after accounting for the angular acceptance (angular resolution for forward scattering) of the apparatus. However, no other experimental total cross sections for electron scattering from pyrimidine or pyrazine have been found in the literature for comparison.
NASA Astrophysics Data System (ADS)
Lillis, Robert J.; Fang, Xiaohua
2015-07-01
Precipitating electrons are typically the dominant source of energy input into Mars' nighttime upper atmosphere, with consequences for atmospheric and ionospheric structure, composition, chemistry, and electrodynamics. Mars' spatially heterogeneous crustal magnetic fields affect the fluxes of precipitating electrons, via both the magnetic mirror force and Gauss' law of conservation of magnetic flux. We use a kinetic electron transport model to examine ionization rate profiles that result from the combination of these magnetic effects and elastic and inelastic scattering by atmospheric neutrals. Specifically, we calculate ionization rates as a function of altitude, crustal magnetic field strength, and the initial energy and pitch angle of the precipitating electrons, covering the relevant ranges of these parameters. Several complex behaviors are exhibited, including bifurcating ionization peaks with distinct characteristics and energy-dependent and crustal field strength-dependent increases in ionization with decreasing pitch angle. Elucidating such behavior is important for understanding the effect of Mars' unique crustal fields on the Mars upper atmosphere and ionosphere, both to predict the consequences of measured electron precipitation and to enable, for the first time, downward coupling of global plasma models with thermosphere-ionosphere models.
Depth dependence of strain, mosaicity and sharp component in the critical scattering of SrTiO3
NASA Astrophysics Data System (ADS)
Rütt, U.; Diederichs, A.; Schneider, J. R.; Shirane, G.
1997-08-01
The sharp component observed in the critical scattering above the cubic-to-tetragonal phase transition in SrTiO3 is now generally considered as a surface-related phenomenon. In the present paper, for the first time, the structural difference between the bulk and a skin layer of a highly perfect crystal has been shown quantitatively by diffraction methods. High-resolution measurements have been performed with highly penetrating 121 keV synchrotron radiation X-rays. The lattice parameter d, its fluctuations Δd/d, the crystal mosaicity and the critical scattering were found to be depth dependent. The two-length-scale behaviour in the critical fluctuations is confined to a skin layer approximately 100 μm thick and related to an increase in strain. Approaching the crystal surface the lattice parameter decreases by 6.2·10-5 Å, Δd/d increases from the bulk value of 5.2·10-5 to 13·10-5, the mosaicity increases from 1.0 to 8.2 seconds of arc. In addition the critical temperature determined from the temperature dependence of the 1/2(511) reflection at the surface and 150 μm below, is smaller than the bulk value by 1.7 and 2.4 K, respectively.
Magnetic transitions and quantum criticality in the three-dimensional Hubbard model
NASA Astrophysics Data System (ADS)
Schäfer, Thomas; Katanin, Andrey; Held, Karsten; Toschi, Alessandro
We analyze the (quantum) critical properties of the simplest model for electronic correlations, the Hubbard model, in three spatial dimensions by means of the dynamical mean field theory (DMFT, including all local correlations) and the dynamical vertex approximation (D ΓA, including non-local correlations on all length scales). Both in the half-filled/unfrustrated and in the hole-doped system the transition temperature is significantly lowered by including non-local fluctuations.In the latter case, however, the magnetic order becomes incommensurate, eventually leading to a complete suppression of the order and giving rise to a magnetic quantum critical point (QCP) at zero temperature. We analyze the (quantum) critical properties of this QCP (e.g. critical exponents) and relate our findings to the standard theory of quantum criticality in metals, the Hertz-Millis-Moriya theory. Solids4Fun, Austrian Science Fund (FWF, Project ID 1243).
Magnetic and superconducting quantum critical behavior of itinerant electronic systems
NASA Astrophysics Data System (ADS)
Sknepnek, Rastko
Quantum phase transitions occur at zero temperature as a function of some non-thermal parameter, e.g., pressure or chemical composition. In addition to being of fundamental interest, quantum phase transitions are important because they are believed to underlie a number of interesting low temperature phenomena. Quantum phase transitions differ from the classical phase transitions in many important aspects, two of them being (i) the mode-coupling effects and (ii) the behavior in the presence of disorder. We devote two projects of this dissertation to each of the two. First, we investigate the quantum phase transition of itinerant electrons from a paramagnet to a state which displays long-period helical structures due to a Dzyaloshinskii instability of the ferromagnetic state. In particular, we study how the self generated effective long-range interaction recently identified in itinerant quantum ferromagnets is cut-off by the helical ordering. Second, we discuss a quantum phase transition between a disordered metal and an exotic (non-s-wave) superconductor. Like in the case of ferromagnetic quantum phase transition mode coupling effects lead to an effective long-range interaction between the anomalous density fluctuations. We find that the asymptotic critical region is characterized by run-away flow to large disorder. However, for weak coupling, this region is very narrow, and it is preempted by a wide crossover regime with mean-field critical behavior. Then, we present results of large-scale Monte Carlo simulations for a 3d Ising model with short range interactions and planar defects. We show that the phase transition in this system is smeared, i.e., there is no single critical temperature, but different parts of the system order at different temperatures. Our Monte-Carlo results are in good agreement with a recent theory. Finally, we present large-scale Monte-Carlo simulations of a 2d bilayer quantum Heisenberg antiferromagnet with random dimer dilution. In contrast
Blum, Thomas; Chowdhury, Saumitra; Hayakawa, Masashi; Izubuchi, Taku
2015-01-07
The form factor that yields the light-by-light scattering contribution to the muon anomalous magnetic moment is computed in lattice QCD+QED and QED. A non-perturbative treatment of QED is used and is checked against perturbation theory. The hadronic contribution is calculated for unphysical quark and muon masses, and only the diagram with a single quark loop is computed. Statistically significant signals are obtained. Initial results appear promising, and the prospect for a complete calculation with physical masses and controlled errors is discussed.
Observation of spin-wave dispersion in Nd-Fe-B magnets using neutron Brillouin scattering
Ono, K. Inami, N.; Saito, K.; Takeichi, Y.; Kawana, D.; Yokoo, T.; Itoh, S.; Yano, M.; Shoji, T.; Manabe, A.; Kato, A.; Kaneko, Y.
2014-05-07
The low-energy spin-wave dispersion in polycrystalline Nd-Fe-B magnets was observed using neutron Brillouin scattering (NBS). Low-energy spin-wave excitations for the lowest acoustic spin-wave mode were clearly observed. From the spin-wave dispersion, we were able to determine the spin-wave stiffness constant D{sub sw} (100.0 ± 4.9 meV.Å{sup 2}) and the exchange stiffness constant A (6.6 ± 0.3 pJ/m)
Endstation for ultrafast magnetic scattering experiments at the free-electron laser in Hamburg.
Müller, L; Gutt, C; Streit-Nierobisch, S; Walther, M; Schaffert, S; Pfau, B; Geilhufe, J; Büttner, F; Flewett, S; Günther, C M; Eisebitt, S; Kobs, A; Hille, M; Stickler, D; Frömter, R; Oepen, H P; Lüning, J; Grübel, G
2013-01-01
An endstation for pump-probe small-angle X-ray scattering (SAXS) experiments at the free-electron laser in Hamburg (FLASH) is presented. The endstation houses a solid-state absorber, optical incoupling for pump-probe experiments, time zero measurement, sample chamber, and detection unit. It can be used at all FLASH beamlines in the whole photon energy range offered by FLASH. The capabilities of the setup are demonstrated by showing the results of resonant magnetic SAXS measurements on cobalt-platinum multilayer samples grown on freestanding Si(3)N(4) membranes and pump-laser-induced grid structures in multilayer samples. PMID:23387667
X-ray Resonant Scattering Study of the Magnetic Phase Diagram of Multiferroic TbMnO3
Wilkins, S.B.; Walker, H.C.; Ewings, R.A.; Fabrizi, F.; Mannix, D.; Mazzoli, C.; Paolasini, L.; Prabhakaran, D.; Boothroyd, A.T.; McMorrowa, D.F.
2009-10-15
We present the magnetic phase diagram of multiferroic TbMnO{sub 3} for H {parallel} b determined using X-ray resonant scattering at the Tb L{sub 3}-edge. Investigations of two different magnetic domains, C-type and F-type, demonstrate very similar behavior in high applied magnetic fields, with a low temperature incommensurate to commensurate transition at H {approx_equal} 4.5 T, concurrent with the polarization flop observed in bulk magnetoelectric measurements.
NASA Astrophysics Data System (ADS)
Nagornyi, A. V.; Petrenko, V. I.; Bulavin, L. A.; Avdeev, M. V.; Almásy, L.; Rosta, L.; Aksenov, V. L.
2014-01-01
Structural parameters of the magnetite-oleic acid-decalin magnetic fluid at various excesses of oleic acid (up to 25 vol %) have been determined using small-angle neutron scattering. Based on the comparison of the behavior of oleic acid in the magnetic fluid and in the pure solvent (decalin), it has been concluded that the interaction between the molecules of free (unadsorbed) surfactant changes in the presence of magnetic nanoparticles. However, the system remains stable and does not form aggregates of magnetic particles or free oleic acid. These results are compared with the previously presented data for similar benzene-based magnetic fluids.
NASA Astrophysics Data System (ADS)
Kamble, Bhaskar; Akbari, Alireza; Eremin, Ilya
2016-04-01
We employ a five-orbital tight-binding model to develop the mean-field solution for various possible spin density wave states in the iron-chalcogenides. The quasiparticle interference (QPI) technique is applied to detect signatures of these states due to scatterings arising from non-magnetic impurities. Apart from the experimentally observed double-striped structure with ordering vector (π/2,π/2) , the QPI method is investigated for the extended-stripe as well as the orthogonal double-stripe phase. We discuss QPI as a possible tool to detect and classify various magnetic structures with different electronic structure reconstruction within the framework of the \\text{Fe}1+y\\text{Te} compound.
Development and application of setup for ac magnetic field in neutron scattering experiments.
Klimko, Sergey; Zhernenkov, Kirill; Toperverg, Boris P; Zabel, Hartmut
2010-10-01
We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm(3) and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed. PMID:21034083
Development and application of setup for ac magnetic field in neutron scattering experiments
Klimko, Sergey; Zhernenkov, Kirill; Toperverg, Boris P.; Zabel, Hartmut
2010-10-15
We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm{sup 3} and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed.
NASA Astrophysics Data System (ADS)
Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.; Tian, Di; Kim, J.; Upton, M. H.; Casa, D.; Gog, T.; Islam, Z.; Jeon, Byung-Gu; Kim, Kee Hoon; Desgreniers, S.; Kim, Yong Baek; Julian, S. J.; Kim, Young-June
2016-07-01
We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu2Ir2O7 and Pr2Ir2O7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu2Ir2O7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (˜6 to 300 K) and pressures (˜0.1 to 17 GPa) studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of Eu2Ir2O7 and Pr2Ir2O7 using high-resolution Ir L3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ˜3 -5 eV, spin-orbit excitations at ˜0.5 -1 eV, and broad low-lying excitations below ˜0.15 eV. In single-crystal samples of "Eu-rich" Eu2Ir2O7 (found to possess an actual stoichiometry of Eu2.18Ir1.82O7.06 ) we observe highly damped magnetic excitations at ˜45 meV, which display significant momentum dependence. We compare these results with recent dynamical structure factor calculations.
NASA Astrophysics Data System (ADS)
Swadling, George
2015-11-01
Ion interpenetration driven by high velocity plasma collisions is an important phenomenon in high energy density environments such as the interiors of ICF vacuum hohlraums and fast z-pinches. The presence of magnetic fields frozen into these colliding flows further complicates the interaction dynamics. This talk focuses on an experimental investigation of ion interpenetration in collisions between cylindrically convergent, supersonic, magnetized flows (M ~10, Vflow ~ 100km/s, ni ~ 1017cm-3) . The flows used in this study were plasma ablation streams produced by tungsten wire array z-pinches, driven by the 1.4MA, 240ns Magpie facility at Imperial College, and diagnosed using a combination of optical Thomson scattering, Faraday rotation and interferometry. Optical Thomson scattering (TS) provides time-resolved measurements of local flow velocity and plasma temperature across multiple (7 to 14) spatial positions. TS spectra are recorded simultaneously from multiple directions with respect to the probing beam, resulting in separate measurements of the rates of transverse diffusion and slowing-down of the ion velocity distribution. The measurements demonstrate flow interpenetration through the array axis at early time, and also show an axial deflection of the ions towards the anode. This deflection is induced by a toroidal magnetic field (~ 10T), frozen into the plasma that accumulates near the axis. Measurements obtained later in time show a change in the dynamics of the stream interactions, transitioning towards a collisional, shock-like interaction of the streams, and rapid radial collapse of the magnetized plasma column. The quantitative nature of the spatial profiles of the density, flow velocities and ion temperatures measured in these experiments will allow detailed verification of MHD and PIC codes used by the HEDP community. Work Supported by EPSRC (Grant No. EP/G001324/1), DOE (Cooperative Agreement Nos. DE-F03-02NA00057 & DE-SC-0001063) & Sandia National
Jain, Dr Nirmesh; Liu, Dr C K; Hawkett, Dr B. S.; Warr, G. G.; Hamilton, William A
2014-01-01
The optical magnetic chaining technique (MCT) developed by Leal-Calderon, Bibette and co-workers in the 1990 s allows precise measurements of force profiles between droplets in monodisperse ferrofluid emulsions. However, the method lacks an in-situ determination of droplet size and therefore requires the combination of separately acquired measurements of droplet chain periodicity versus an applied magnetic field from optical Bragg scattering and droplet diameter inferred from dynamic light scattering (DLS) to recover surface force-distance profiles between the colloidal particles. Compound refractive lens (CRL) focussed small-angle scattering (SANS) MCT should result in more consistent measurements of droplet size (form factor measurements in the absence of field) and droplet chaining period (from structure factor peaks when the magnetic field is applied); and, with access to shorter length scales, extend force measurements to closer approaches than possible by optical measurements. We report on CRL-SANS measurements of monodisperse ferrofluid emulsion droplets aligned in straight chains by an applied field perpendicular to the incident beam direction. Analysis of the scattering from the closely spaced droplets required algorithms that carefully treated resolution and its effect on mean scattering vector magnitudes in order to determine droplet size and chain periods to sufficient accuracy. At lower applied fields scattering patterns indicate structural correlations transverse to the magnetic field direction due to the formation of intermediate structures in early chain growth.
NASA Astrophysics Data System (ADS)
Lovesey, Stephen W.; Balcar, Ewald
1996-12-01
The scattering length common to the attenuation coefficient and cross-sections for the resonance-enhanced scattering of x-rays suffers from a dependence on a spectrum of virtual, intermediate states which contain next to no useful information about the environment of the atoms. It is the dependence of the scattering length on intermediate states that sets the x-ray techniques apart from neutron scattering and other techniques which directly probe properties of magnetic materials, and limits the usefulness of physical intuition in the interpretation of empirical x-ray data. As a step toward a legible interpretation, in a language of standard atomic variables, an investigation is reported of a modified scattering length constructed to possess a structure similar to the scattering length for magnetic neutron scattering, namely, it has the mathematical structure of a spherical tensor operator, to which all Racah's methods for electrons in an open valence shell can be applied. In the process of reaching this goal, the influence of the intermediate states on the scattering length is reduced by summing over a limited set of quantum numbers for the intermediate states. Topics covered in the investigation include the attenuation coefficient for x-rays passing through a foil of magnetic material, dichroism, and the cross-sections for resonance-enhanced elastic (Bragg) and inelastic scattering of x-rays by magnetic materials. The treatment of polarization in the primary beam admits states of partial polarization, described by a Stokes vector. Both jj-coupling and Russell - Saunders coupling schemes for the valence states are explored.
Magnetic-field control of quantum critical points of valence transition.
Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques
2008-06-13
We study the mechanism of how critical end points of first-order valence transitions are controlled by a magnetic field. We show that the critical temperature is suppressed to be a quantum critical point (QCP) by a magnetic field, and unexpectedly, the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to the emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be cooperative phenomena of the Zeeman and Kondo effects, which create a distinct energy scale from the Kondo temperature. This mechanism explains the peculiar magnetic response in CeIrIn(5) and the metamagnetic transition in YbXCu(4) for X=In as well as the sharp contrast between X=Ag and Cd. PMID:18643524
Photon production from the scattering of axions out of a solenoidal magnetic field
Guendelman, Eduardo I.; Shilon, Idan; Cantatore, Giovanni; Zioutas, Konstantin E-mail: silon@bgu.ac.il E-mail: Konstantin.Zioutas@cern.ch
2010-06-01
We calculate the total cross section for the production of photons from the scattering of axions by a strong inhomogeneous magnetic field in the form of a 2D δ-function, a cylindrical step function and a 2D Gaussian distribution, which can be approximately produced by a solenoidal current. The theoretical result is used to estimate the axion-photon conversion probability which could be expected in a reasonable experimental situation. Comparison between the 2D conversion probabilities for QCD inspired axions and those derived by applying the celebrated 1D calculation of the (inverse) coherent Primakoff effect is made using an averaging prescription procedure of the 1D case. We also consider scattering at a resonance E{sub axion} ∼ m{sub axion}, which corresponds to the scattering from a δ-function and gives the most enhanced results. Finally, we analyze the results of this work in the astrophysical extension to suggest a way in which they may be directed to a solution to some basic solar physics problems and, in particular, the coronal heating problem.
Cerium-Based Magnets: Novel High Energy Permanent Magnet Without Critical Elements
2012-01-01
REACT Project: Ames Laboratory will develop a new class of permanent magnets based on the more commonly available element cerium for use in both EVs and renewable power generators. Cerium is 4 times more abundant and significantly less expensive than the rare earth element neodymium, which is frequently used in today’s most powerful magnets. Ames Laboratory will combine other metal elements with cerium to create a new magnet that can remain stable at the high temperatures typically found in electric motors. This new magnetic material will ultimately be demonstrated in a prototype electric motor, representing a cost-effective and efficient alternative to neodymium-based motors.
Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.
2014-12-08
Here, we present x-ray resonant magnetic dichroism and x-ray resonant magnetic scattering measurements of the temperature dependence of magnetism in Pr-doped La-Ca-Mn-O films grown on (110) NdGaO3 substrates. We observed thermal hysteresis of the ferromagnetism in one film that also showed large thermal hysteresis of ~18K in transport measurements. While in a second film of a different nominal chemistry, which showed very small thermal hysteresis ~3K in transport measurements, no thermal hysteresis of the ferromagnetism was observed. As a result, these macroscopic properties are correlated with evolution of surface magnetization across metal insulator transition for these films as observed bymore » soft x-ray resonant magnetic scattering measurements.« less
Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.
2014-12-08
Here, we present x-ray resonant magnetic dichroism and x-ray resonant magnetic scattering measurements of the temperature dependence of magnetism in Pr-doped La-Ca-Mn-O films grown on (110) NdGaO3 substrates. We observed thermal hysteresis of the ferromagnetism in one film that also showed large thermal hysteresis of ~18K in transport measurements. While in a second film of a different nominal chemistry, which showed very small thermal hysteresis ~3K in transport measurements, no thermal hysteresis of the ferromagnetism was observed. As a result, these macroscopic properties are correlated with evolution of surface magnetization across metal insulator transition for these films as observed by soft x-ray resonant magnetic scattering measurements.
Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.
2014-12-14
Here, we present x-ray resonant magnetic dichroism and x-ray resonant magnetic scattering measurements of the temperature dependence of magnetism in Pr-doped La-Ca-Mn-O films grown on (110) NdGaO{sub 3} substrates. We observed thermal hysteresis of the ferromagnetism in one film that also showed large thermal hysteresis of ∼18 K in transport measurements. While in a second film of a different nominal chemistry, which showed very small thermal hysteresis ∼3 K in transport measurements, no thermal hysteresis of the ferromagnetism was observed. These macroscopic properties are correlated with evolution of surface magnetization across metal insulator transition for these films as observed by soft x-ray resonant magnetic scattering measurements.
High-field magnets using high-critical-temperature superconducting thin films
Mitlitsky, F.; Hoard, R.W.
1994-05-10
High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla are disclosed. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field. 4 figures.
High-field magnets using high-critical-temperature superconducting thin films
Mitlitsky, Fred; Hoard, Ronald W.
1994-01-01
High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field.
Self-Magnetic Field Effects on Electron Emission as the Critical Current is Approached
Ottinger, P. F.; Cooperstein, G.; Schumer, J. W.; Swanekamp, S. B.
2001-09-28
The self-magnetic field associated with the current in a planar diode is shown to reduce electron emission below the Child-Langmuir current density. As the magnetic field increases, the diode current is limited to the critical current. Here, a ID analysis is carried out to calculate the suppressed current density in the presence of a transverse magnetic field. The problem is shown to be similar to that of the limiting current (i.e., Hull current) calculated in a crossed field gap, in which a constant transverse magnetic field is applied across the gap to insulate the electron flow. In the case considered here, the magnetic field is produced by the diode current itself and this self-magnetic field decreases with distance along the gap. It is shown that the emitted current density is only modestly reduced from the Child-Langmuir current density. The 1-D analysis remains valid until critical current is approached, at which point orbit crossing occurs and a 2-D kinetic analysis is required. The minimum diode length required to reach critical current is also derived.
Magnetic relaxation and lower critical field in MgB2 wires
NASA Astrophysics Data System (ADS)
Y, Feng; G, Yan; Y, Zhao; Pradhan, A. K.; F, Liu C.; X, Zhang P.; L, Zhou
2003-09-01
Magnetic relaxation behaviour, critical current density Jc and lower critical field Hc1 have been investigated in MgB2/Ta/Cu wires. It is found that Jc and Hc1 decrease linearly with temperature in the whole temperature region below Tc. The relaxation rate is very small and has a weak temperature dependence compared to high-Tc superconductors. Also, the pinning potential is much larger and the temperature and field dependences of the pinning potential are briefly discussed.
Wen, H.; Yan, R.; Maximov, A. V.; Ren, C.
2015-05-15
A model for the interaction between the laser light and the plasma waves near the quarter-critical density in plasmas has been studied. This model includes, but is not limited to, the instabilities of two-plasmon decay (TPD) and stimulated Raman scattering (SRS). The full simulation results show the instability growth in the wavevector domains corresponding to TPD and SRS, respectively, and the domain between those two. The instability growth rates and thresholds can be calculated in our model for the parameters of the inertial confinement fusion experiments without the approximations common in analytical theories.
Limits on low energy photon-photon scattering from an experiment on magnetic vacuum birefringence
Bregant, M.; Cantatore, G.; Della Valle, F.; Lozza, V.; Milotti, E.; Raiteri, G.; Zavattini, E.; Carusotto, S.; Polacco, E.; Cimino, R.; Di Domenico, G.; Zavattini, G.; Gastaldi, U.; Ruoso, G.; Karuza, M.
2008-08-01
Experimental bounds on induced vacuum magnetic birefringence can be used to improve present photon-photon scattering limits in the electronvolt energy range. Measurements with the Polarizzazione del Vuoto con Laser apparatus [E. Zavattini et al., Phys. Rev. D 77, 032006 (2008)] at both {lambda}=1064 and 532 nm lead to bounds on the parameter A{sub e}, describing nonlinear effects in QED, of A{sub e}{sup (1064)}<6.6x10{sup -21} T{sup -2}-1064 nm and A{sub e}{sup (532)}<6.3x10{sup -21} T{sup -2}-532 nm, respectively, at 95% confidence level, compared to the predicted value of A{sub e}=1.32x10{sup -24} T{sup -2}. The total photon-photon scattering cross section may also be expressed in terms of A{sub e}, setting bounds for unpolarized light of {sigma}{sub {gamma}}{sub {gamma}}{sup (1064)}<4.6x10{sup -62} m{sup 2} and {sigma}{sub {gamma}}{sub {gamma}}{sup (532)}<2.7x10{sup -60} m{sup 2}. Compared to the expected QED scattering cross section these results are a factor of {approx_equal}2x10{sup 7} higher and represent an improvement of a factor about 500 on previous bounds based on ellipticity measurements and of a factor of about 10{sup 10} on bounds based on direct stimulated scattering measurements.
High-Energy Ions from Near-Critical Density Plasmas via Magnetic Vortex Acceleration
Nakamura, Tatsufumi; Bulanov, Sergei V.; Esirkepov, Timur Zh.; Kando, Masaki
2010-09-24
Ultraintense laser pulses propagating in near-critical density plasmas generate magnetic dipole vortex structures. In the region of decreasing plasma density, the vortex expands both in forward and lateral directions. The magnetic field pressure pushes electrons and ions to form a density jump along the vortex axis and induces a longitudinal electric field. This structure moves together with the expanding dipole vortex. The background ions located ahead of the electric field are accelerated to high energies. The energy scaling of ions generated by this magnetic vortex acceleration mechanism is derived and corroborated using particle-in-cell simulations.
NASA Astrophysics Data System (ADS)
Roshchin, Igor V.; Lapa, Pavel N.; Krycka, Kathryn L.; Maranville, Brian B.; Monroe, James A.; Franco, Brian E.; Karaman, Ibrahim
In Ni-Mn-In- and Ni-Mn-Sn-based alloys, two magnetic phases with ferromagnetic and antiferromagnetic exchange couplings between two nearest Mn atoms can coexist. The interaction between these phases results in exchange bias (EB). The EB field depends on the cluster sizes. Using the first order reversal curve (FORC) analysis of magnetization for Ni-Co-Mn-Sn and Ni-Co-Mn-In samples with different heat treatment, we can obtain information about cluster sizes of the structural phases in these alloys. This is especially important for polycrystalline alloy samples where dark-field images showing different phases are hard to obtain. Such a Ni-Co-Mn-Sn polycrystalline sample was characterized with small angle neutron scattering (SANS). Analyses of the scattering as a function of wavevector transfer in 50 Oe and 15 kOe applied field yield the average magnetic domain size of 21.2 +/-6.6 nm and a polydispersity of 0.32 +/-0.02 at 300 K, in good agreement with our prediction. The temperature evolution of the domain size will be discussed. Using an off-specular reflectometer in transmission geometry, the same sample was measured at a field of 270 Oe and 5.15 kOe. The fit of the 270 Oe data yields grain sizes of approximately 0.11-0.12 μm with polydispersities between 0.98 and 1.27. Supported by Texas A&M University, US-DOE, and US NSF-DMR.
Scattering theory for the radial H˙1/2-critical wave equation with a cubic convolution
NASA Astrophysics Data System (ADS)
Miao, Changxing; Zhang, Junyong; Zheng, Jiqiang
2015-12-01
In this paper, we study the global well-posedness and scattering for the wave equation with a cubic convolution ∂t2 u - Δu = ± (| x | - 3 *| u | 2) u in dimensions d ≥ 4. We prove that if the radial solution u with life-span I obeys (u, ut) ∈ Lt∞ (I ; H˙x 1 / 2 (Rd) × H˙x - 1 / 2 (Rd)), then u is global and scatters. By the strategy derived from concentration compactness, we show that the proof of the global well-posedness and scattering is reduced to disprove the existence of two scenarios: soliton-like solution and high to low frequency cascade. Making use of the No-waste Duhamel formula and double Duhamel trick, we deduce that these two scenarios enjoy the additional regularity by the bootstrap argument of [7]. This together with virial analysis implies the energy of such two scenarios is zero and so we get a contradiction.
NASA Astrophysics Data System (ADS)
Nakatani, Alan I.; Kim, Hongdoo; Takahashi, Yoshiaki; Matsushita, Yushu; Takano, Atsushi; Bauer, Barry J.; Han, Charles C.
1990-07-01
The small angle neutron scattering (SANS) technique has been used to study the concentration fluctuations of binary polymer mixtures under shear. Two different polymer systems, deuterated polystyrene/poly(vinylmethylether) and deuterated polystyrene/polybutadiene, have been studied as a function of temperature and shear rate. Due to the small wavelength of the incident neutron radiation compared with light, the shear dependence of concentration fluctuations in the one-phase region and in the strong shear limit has been obtained from the q dependence of the scattering structure factor for the first time. From a detailed analysis of the scattering structure factor S(q) a crossover value of the wave number qs has been obtained as a function of temperature and shear rate. This crossover wave number represents the inverse of the lowest fluctuation mode which is not affected by shear. The temperature, viscosity, and shear rate dependence of this experimentally determined qs agree well with a simple rotatory diffusion model and also the dynamic mode-mode coupling analysis of Kawasaki and Ferrell. The apparent spinodal temperature as a function of shear rate is shown to be consistent with the prediction of Onuki.
Saito, Kotaro Ono, Kanta; Ueno, Tetsuro; Yano, Masao; Shoji, Tetsuya; Sakuma, Noritsugu; Manabe, Akira; Kato, Akira; Harada, Masashi; Keiderling, Uwe
2015-05-07
The magnetization reversal process of Nd-Fe-B nanocrystalline magnets infiltrated with Nd-Cu alloy was examined using small-angle neutron scattering (SANS). The magnetic-field dependence of SANS intensity revealed a qualitative difference between Nd-Cu-infiltrated samples and as-deformed samples. Insufficient magnetic isolation along the direction perpendicular to the nominal c-axis is expected from comparable SANS intensities for different ranges of q values along this direction. For small q values near the coercivity field, Nd-Cu-infiltrated samples show a noticeable reduction in SANS intensity along the nominal c-axis, which is parallel to the external magnetic field. This indicates less spatial fluctuation of magnetic moments in Nd-Cu-infiltrated samples, owing to magnetically isolated Nd{sub 2}Fe{sub 14}B grains.
Magnetic structure determination of Ca3LiOsO6 using neutron and x-ray scattering
Calder, Stuart A; Lumsden, Mark D; Garlea, Vasile O; Kim, Jong-Woo; Shi, Y. G.; Yamaura, K.; Christianson, Andrew D
2012-01-01
We present a neutron and x-ray scattering investigation of Ca3LiOsO6, a material that has been predicted to host magnetic ordering through an extended superexchange pathway involving two anions. Despite the apparent 1D nature and triangular units of magnetic osmium ions the onset of magnetic correlations has been observed at a high temperature of 117 K in bulk measurements. We experimentally determine the magnetically ordered structure and show it to be long range and three dimensional. Our results support the model of extended superexchange interaction.
NASA Astrophysics Data System (ADS)
Jang, H.; Nojiri, H.; Gerber, S.; Lee, W.-S.; Zhu, D.; Lee, J.-S.; Kao, C.-C.
X-ray scattering under high magnetic fields provides unique opportunities for solving many scientific puzzles in quantum materials, such as strongly correlated electron systems. Incorporating high magnetic field capability presents serious challenges at an x-ray facility, including the limitation on the maximum magnetic field even with a DC magnet (up to ~20 Tesla), expensive cost in development, radiation damage, and limited flexibility in the experimental configuration. These challenges are especially important when studying the symmetry broken state induced by the high magnetic field are necessary, for example, exploring intertwined orders between charge density wave (CDW) and high Tc superconductivity. Moreover, a gap in magnetic field strengths has led to many discrepancies and puzzling issues for understanding strongly correlated systems - is a CDW competing or more intimately intertwined with high-temperature superconductivity. To bridge this gap and resolve these experimental discrepancies, one needs an innovative experimental approach. Here, we will present a new approach to x-ray scattering under high magnetic field up to 28 Teals by taking advantage of brilliant x-ray free electron laser (FEL). The FEL generates sufficiently high photon flux for single shot x-ray scattering experiment. In this talk, we will also present the first demonstration about the field induced CDW order in YBCO Ortho-VIII with 28 Tesla, which show the totally unexpected three-dimensional behavior.
Okube, Maki; Kaneko, Yuhei; Ohsawa, Seiji; Sasaki, Satoshi; Toyoda, Takeshi; Mori, Takeharu
2010-06-23
Synchrotron radiation intensity measurements were made for single crystals of ferrimagnetic BaTiCoFe{sub 10}O{sub 19} at the BL-6C(3A) beamline of the Photon Factory. The resonant x-ray magnetic scattering (RXMS) method at the Fe K edge makes it possible to determine the magnetic crystal structure, having the magnetic helices for Fe ions in tetrahedral 4f{sub 1}, bipyramidal 2b, and octahedral 2a, 4f{sub 2} and 12k sites. Based on the information on x-ray magnetic circular dichroism (XMCD) and a resonant magnetic scattering factor f''{sub m} ( = 0.23) estimated from BaFe{sub 12}O{sub 19} at E = 7128.2 eV, the magnetic structures have been determined from an asymmetrical ratio {Delta}R (Y{sup +}-Y{sup -})/(Y{sup +}+Y{sup -}), where Y{sup +} and Y{sup -} are scattering intensities for left- and right-circular polarizations, respectively. Spin orientations were estimated in the least-squares procedure to minimize a residual factor of {Sigma}({Delta}R{sub obs}-{Delta}R{sub calc}){sup 2}. The canting angles estimated in this study are 180 deg., 19 deg., 118 deg., 180 deg. and 65 deg. for the magnetic moments of Fe ions in 4f{sub 1}, 2b, 2a, 4f{sub 2} and 12k sites, respectively.
Ulfat Jafri, A D; Lakhtakia, Akhlesh
2014-01-01
An exact transition matrix was formulated for electromagnetic scattering by an orthorhombic dielectric-magnetic sphere whose permeability dyadic is a scalar multiple of its permittivity dyadic. Calculations were made for plane waves incident on the sphere. As the size parameter increases, the role of anisotropy evolves; multiple lobes appear in the plots of the differential scattering efficiency in any scattering plane; the total scattering, extinction, and forward-scattering efficiencies exhibit a prominent maximum each; and the absorption efficiency generally increases with weak undulations. Certain orientations of the sphere with respect to the directions of propagation and the electric field of the incident plane wave make it highly susceptible to detection in a monostatic configuration, whereas other orientations make it much less vulnerable to detection. Impedance match to the ambient free space decreases backscattering efficiency significantly, although anisotropy prevents null backscattering. PMID:24561944
Electron back scattered diffraction characterization of Sm(CoFeCuZr){sub z} magnets
Yonamine, T.; Fukuhara, M.; Archanjo, B. S.; Missell, F. P.
2011-04-01
In permanent magnets based on the Sm{sub 2}Co{sub 17} phase, the high coercivity depends on the presence of a complex microstructure, consisting of a Sm{sub 2}(Co,Fe){sub 17} cell phase, a cell boundary phase Sm(Co,Cu){sub 5}, and a Zr-rich platelet or lamellae phase. The aim of this work is to use electron back scatter diffraction (EBSD) in order to identify the different phases present in the isotropic magnets produced from cast alloys with the composition of Sm(Co{sub bal}Fe{sub 0.2}Cu{sub 0.1}Zr{sub x}){sub 8}, where x = 0, 0.02, or 0.06, and correlate them with the different phases observed in scanning electron microscopy (SEM) images. Due to the combination of careful surface preparation and high resolution microscopy, it was possible to observe the cellular structure characteristic of the 2:17 magnets in the SEM images. Until now, only transmission electron microscopy (TEM) had been used. Composition maps, energy dispersive spectroscopy (EDS), and EBSD measurements were used for doing the phase identification.
NASA Astrophysics Data System (ADS)
Cabrera, Ivelisse; Thompson, Jordan; Coldea, Radu; Robinson, Neil; Essler, Fabian; Prabhakaran, Dharmalingam; Bewley, Robert; Guidi, Tatiana
2013-03-01
The Ising chain in a transverse magnetic field is one of the canonical examples of a quantum phase transition. We have recently realized this model experimentally in the quasi-one-dimensional (1D) Ising-like ferromagnet CoNb2O6. Here, we present single-crystal inelastic neutron scattering measurements of the magnetic dispersion relations in the full three-dimensional (3D) Brillouin zone for magnetic fields near the critical point and in the high field paramagnetic phase. We explore the gap dependence as a function of field and quantify the cross-over to 3D physics at the lowest energies due to the finite interchain couplings. We parametrize the dispersion relations in the high-field paramagnetic phase to a spin wave model to quantify the sub-leading terms in the spin Hamiltonian beyond the dominant 1D Ising exchange.
Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake.
Hayakawa, Masashi; Schekotov, Alexander; Potirakis, Stelios; Eftaxias, Kostas
2015-01-01
The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) Fh (horizontal magnetic field), (2) Fz (vertical magnetic field), and (3) Dh (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03-0.05 Hz was averaged for nighttime hours. The analysis results indicate that Fh fulfilled all criticality conditions on March 3-5, 2011, and that the additional parameter, Dh reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ. PMID:25743063
Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake
NASA Astrophysics Data System (ADS)
Hayakawa, Masashi; Schekotov, Alexander; Potirakis, Stelios; Eftaxias, Kostas
2015-01-01
The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) Fh (horizontal magnetic field), (2) Fz (vertical magnetic field), and (3) Dh (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03-0.05 Hz was averaged for nighttime hours. The analysis results indicate that Fh fulfilled all criticality conditions on March 3-5, 2011, and that the additional parameter, Dh reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ.
Critical Currents of MgB2 Wire and Tape in Magnetic Field under Bending Deformations
NASA Astrophysics Data System (ADS)
Abin, D. A.; Mineev, N. A.; Osipov, M. A.; Pokrovsky, S. V.; Rudnev, I. A.
Nowadays MgB2 wires are attractive for designing real devices like motors and magnets. The latest production technologies allow to increase critical current value of wires. However, there is a problem of wire performance degradation under bending strain. Thus, there is a problem of manufacturing solenoids with small diameters, especially from ex situ MgB2 wires produced by powder-in-tube (PIT) technology. In this work, influence of bending on critical current Ic multifilament PIT ex situ MgB2 tape and wire has been studied. Critical current dependencies on external magnetic field Ic(H) were measured at liquid helium temperature in the range of fields from 2.5 T up to 8 T. Measurements were carried out in parallel (H||), and perpendicular (H⊥) orientation of external magnetic field to the sample surface. Voltage current characteristics (V-I) on tape samples were measured with bending on diameters D=30; 40; 60; 70; 80; 90;100 mm. It was shown that critical current density (Jc) decreases by 24% and by 28% for tape and wire respectively with decreasing bending diameter from 100 mm to 60 mm. It was found that the tape still had superconductive properties even with bending diameter D=30 mm, but its Jc decreased by 44% in comparison with Jc(D=100 mm). One more feature that was found is the appearance of resistive component in the voltage current characteristics for all bend diameters in magnetic fields H>3.5 T.
Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake
HAYAKAWA, Masashi; SCHEKOTOV, Alexander; POTIRAKIS, Stelios; EFTAXIAS, Kostas
2015-01-01
The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) Fh (horizontal magnetic field), (2) Fz (vertical magnetic field), and (3) Dh (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03–0.05 Hz was averaged for nighttime hours. The analysis results indicate that Fh fulfilled all criticality conditions on March 3–5, 2011, and that the additional parameter, Dh reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ. PMID:25743063
NASA Astrophysics Data System (ADS)
Muxworthy, Adrian R.; Williams, Wyn
2015-07-01
Kamacite particles (Fe-Ni, Ni < 5 per cent), are very common in extra-terrestrial materials, such as meteorites. It is normally assumed that for kamacite particles to be reliable recorders of magnetic fields, they need to be magnetically uniform (single domain, SD) and thermally stable. Larger particles subdivide into non-uniform multidomain (MD) magnetic structures that produce weaker magnetic signals, while small SD particles become magnetically unstable due to thermal fluctuations and exhibit superparamagnetic behaviour. In this paper we determine the first micromagnetic calculation of the stable SD range domain-state phase diagram for metallic iron; previous calculations were analytical. There is a significant increase in the critical size for the SD/MD threshold size, for example, for cube-shaped iron particles, the critical SD/MD threshold has now been estimated to be 25 nm, compared to 17 nm for previous estimates. The larger critical SD/MD threshold size for iron, agrees better with previously published nanometric observations of domain state for FeNi particles, then early analytical models.
NASA Astrophysics Data System (ADS)
Follett, R. K.; Michel, D. T.; Hu, S. X.; Myatt, J. F.; Henchen, R. J.; Katz, J.; Froula, D. H.
2013-10-01
Thomson scattering (TS) was used to probe electron plasma waves (EPW's) driven by the two-plasmon-decay (TPD) instability near quarter-critical density. TPD-driven EPW's were observed at densities consistent with the common-wave TPD model. Five laser beams (λ3ω = 351nm) produced 400- μm-diam (FWHM) laser spots with overlapped intensities up to 3 ×1014W/cm2 . A 263-nm TS beam was used to probe densities ranging from 0.18 to 0.26 nc, where nc is the critical density for 351-nm light. The experimental geometry was chosen to match the five-beam TPD common wave k vector. The TS spectrum shows a large amplitude, narrow (~1.6-nm FHWM) feature centered around 423.4 nm. This wavelength corresponds to scattering from EPW's with a normalized wave vector k / k3 ω = 1 . 3 , a density of ne/nc = 0.243, and a temperature of Te = 2 keV. This is consistent with the predicted values given by the dispersion relations and TPD maximum growth hyperbola. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.
Kozier, K. S.; Roubtsov, D.; Plompen, A. J. M.; Kopecky, S.
2012-07-01
The thermal neutron-elastic-scattering cross-section data for {sup 16}O used in various modern evaluated-nuclear-data libraries were reviewed and found to be generally too high compared with the best available experimental measurements. Some of the proposed revisions to the ENDF/B-VII.0 {sup 16}O data library and recent results from the TENDL system increase this discrepancy further. The reactivity impact of revising the {sup 16}O data downward to be consistent with the best measurements was tested using the JENDL-3.3 {sup 16}O cross-section values and was found to be very small in MCNP5 simulations of the UO{sub 2} and reactor-recycle MOX-fuel cases of the ANS Doppler-defect numerical benchmark. However, large reactivity differences of up to about 14 mk (1400 pcm) were observed using {sup 16}O data files from several evaluated-nuclear-data libraries in MCNP5 simulations of the Los Alamos National Laboratory HEU heavy-water solution thermal critical experiments, which were performed in the 1950's. The latter result suggests that new measurements using HEU in a heavy-water-moderated critical facility, such as the ZED-2 zero-power reactor at the Chalk River Laboratories, might help to resolve the discrepancy between the {sup 16}O thermal elastic-scattering cross-section values and thereby reduce or better define its uncertainty, although additional assessment work would be needed to confirm this. (authors)
Zou, S N; Gu, C; Qu, T M; Han, Z
2013-10-01
The critical current (I(c)) of high-temperature superconductor (HTS) tapes has to be examined not only for short samples, but also for the entire tape, because local weak points can possibly lead to the quenching of the whole HTS device. Some methods were reported for continuous I(c) measurement along the length of a HTS tape, but few of them were applicable to tapes with magnetic substrates represented by YBa2Cu3O(7-δ)(YBCO)-coated conductors based on Ni5W alloy substrate by rolling assisted bi-axially textured substrate process. We previously presented a contact-free method using magnetic circuits to measure I(c) continuously of long HTS tapes, namely the magnetic-circuit (MC) method. This method has been previously applied with high speed and resolution to measure I(c) of HTS tapes with non-magnetic substrates, due to its resistance to noise aroused by mechanical vibration. In this work, its ability to measure HTS tapes with magnetic substrates is demonstrated both theoretically and experimentally. A 100 m long commercial YBCO tape based on Ni5W alloy substrate was measured and regular I(c) fluctuations were discovered. The MC method can be a powerful tool for quality control of HTS tapes, especially for tapes with magnetic substrates. PMID:24182162
NASA Astrophysics Data System (ADS)
Jacobs, Donald T.; Becker, James S.
1993-06-01
Critical phenomena has been the subject of physics research for many years. However, only in recent years has the research effort become intense. The current intensity has caused the study of critical phenomena to be grouped into a previous older era and a present contemporary era. Turbidity cell filling with methanol cyclohexane is one of the first steps toward a further understanding of critical phenomena. Work performed during the research period is outlined. During this period, research was spent developing apparatus and techniques that will make it possible to study critical phenomena through turbidity measurements on methanol cyclohexane. Topics covered range from the orientation of turbidity cell parts for assembly to the filling apparatus and procedure used when th cell is built. The last section will briefly cover some of the observations made when viewing the cell in a controlled water bath. However, before mention is made of the specifics of the summer research, a short introduction to critical phenomena and turbidity and how they relate to this experiment is provided.
NASA Technical Reports Server (NTRS)
Jacobs, Donald T.; Becker, James S.
1993-01-01
Critical phenomena has been the subject of physics research for many years. However, only in recent years has the research effort become intense. The current intensity has caused the study of critical phenomena to be grouped into a previous older era and a present contemporary era. Turbidity cell filling with methanol cyclohexane is one of the first steps toward a further understanding of critical phenomena. Work performed during the research period is outlined. During this period, research was spent developing apparatus and techniques that will make it possible to study critical phenomena through turbidity measurements on methanol cyclohexane. Topics covered range from the orientation of turbidity cell parts for assembly to the filling apparatus and procedure used when th cell is built. The last section will briefly cover some of the observations made when viewing the cell in a controlled water bath. However, before mention is made of the specifics of the summer research, a short introduction to critical phenomena and turbidity and how they relate to this experiment is provided.
Critical entropies for magnetic ordering in bosonic mixtures on a lattice
Capogrosso-Sansone, B.; Soeyler, S. G.; Prokof'ev, N. V.; Svistunov, B. V.
2010-05-15
We perform a numeric study (Worm algorithm Monte Carlo simulations) of ultracold two-component bosons in two- and three-dimensional optical lattices. At strong enough interactions and low enough temperatures the system features magnetic ordering. We compute critical temperatures and entropies for the disappearance of the Ising antiferromagnetic and the xy-ferromagnetic order and find that the largest possible entropies per particle are {approx} 0.5k{sub B}. We also estimate (optimistically) the experimental hold times required to reach equilibrium magnetic states to be on a scale of seconds. Low critical entropies and long hold times render the experimental observations of magnetic phases challenging and call for increased control over heating sources.
A portable high-field pulsed-magnet system for single-crystal x-ray scattering studies
NASA Astrophysics Data System (ADS)
Islam, Zahirul; Ruff, Jacob P. C.; Nojiri, Hiroyuki; Matsuda, Yasuhiro H.; Ross, Kathryn A.; Gaulin, Bruce D.; Qu, Zhe; Lang, Jonathan C.
2009-11-01
We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields (˜1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.
A portable high-field pulsed-magnet system for single-crystal x-ray scattering studies.
Islam, Zahirul; Ruff, Jacob P C; Nojiri, Hiroyuki; Matsuda, Yasuhiro H; Ross, Kathryn A; Gaulin, Bruce D; Qu, Zhe; Lang, Jonathan C
2009-11-01
We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields (approximately 1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state. PMID:19947737
A portable high-field pulsed-magnet system for single-crystal x-ray scattering studies
Islam, Zahirul; Lang, Jonathan C.; Ruff, Jacob P. C.; Ross, Kathryn A.; Gaulin, Bruce D.; Nojiri, Hiroyuki; Matsuda, Yasuhiro H.; Qu Zhe
2009-11-15
We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields ({approx}1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.
NASA Astrophysics Data System (ADS)
Maruyama, R.; Bigault, T.; Wildes, A. R.; Dewhurst, C. D.; Soyama, K.; Courtois, P.
2016-05-01
The in-plane magnetic structure of a layered system with a polycrystalline grain size less than the ferromagnetic exchange length was investigated using polarized neutron off-specular scattering and grazing incidence small angle scattering measurements to gain insight into the mechanism that controls the magnetic properties which are different from the bulk. These complementary measurements with different length scales and the data analysis based on the distorted wave Born approximation revealed the lateral correlation on a length scale of sub- μm due to the fluctuating orientation of the magnetization in the layer. The obtained in-plane magnetic structure is consistent with the random anisotropy model, i.e. competition between the exchange interactions between neighboring spins and the local magnetocrystalline anisotropy.