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Magnetic Coupling (magnetic + coupling)
Selected AbstractsMagnetic and viscous coupling at the core,mantle boundary: inferences from observations of the Earth's nutationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2007B. A. Buffett SUMMARY Dissipative core,mantle coupling is evident in observations of the Earth's nutations, although the source of this coupling is uncertain. Magnetic coupling occurs when conducting materials on either side of the boundary move through a magnetic field. In order to explain the nutation observations with magnetic coupling, we must assume a high (metallic) conductivity on the mantle side of the boundary and a rms radial field of 0.69 mT. Much of this field occurs at short wavelengths, which cannot be observed directly at the surface. High levels of short-wavelength field impose demands on the power needed to regenerate the field through dynamo action in the core. We use a numerical dynamo model from the study of Christensen & Aubert (2006) to assess whether the required short-wavelength field is physically plausible. By scaling the numerical solution to a model with sufficient short-wavelength field, we obtain a total ohmic dissipation of 0.7,1 TW, which is within current uncertainties. Viscous coupling is another possible explanation for the nutation observations, although the effective viscosity required for this is 0.03 m2 s,1 or higher. Such high viscosities are commonly interpreted as an eddy viscosity. However, physical considerations and laboratory experiments limit the eddy viscosity to 10,4 m2 s,1, which suggests that viscous coupling can only explain a few percent of the dissipative torque between the core and the mantle. [source] Studies of the magnetic structure at the ferromagnet,antiferromagnet interfaceJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001A. Scholl Antiferromagnetic layers are a scientifically challenging component in magnetoelectronic devices, such as magnetic sensors in hard-disk heads, or magnetic random-access memory (RAM) elements. In this paper, it is shown that photoelectron emission microscopy (PEEM) is capable of determining the magnetic structure at the interface of ferromagnets and antiferromagnets with high spatial resolution (down to 20,nm). Dichroism effects at the L edges of the magnetic 3d transition metals, using circularly or linearly polarized soft X-rays from a synchrotron source, give rise to a magnetic image contrast. Images, acquired with the PEEM2 experiment at the Advanced Light Source, show magnetic contrast for antiferromagnetic LaFeO3, microscopically resolving the magnetic domain structure in an antiferromagnetically ordered thin film for the first time. Magnetic coupling between LaFeO3 and an adjacent Co layer results in a complete correlation of their magnetic domain structures. From field-dependent measurements, a unidirectional anisotropy resulting in a local exchange bias of up to 30,Oe in single domains could be deduced. The elemental specificity and the quantitative magnetic sensitivity render PEEM a perfect tool to study magnetic coupling effects in multilayered thin-film samples. [source] Origin of the Paramagnetic Properties of the Mixed-Valence Polyoxometalate [GeV14O40]8, Reduced by Two Electrons: Wave Function Theory and Model Hamiltonian CalculationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 34 2009N. Suaud Abstract The aim of the work is to give an explanation of the magnetic properties of a mixed-valence [GeV14O40]8, polyoxometalate reduced by two electrons, which, in contrast to what happens in other two-electron-reduced polyoxometalates, does not show any magnetic coupling between the two unpaired electrons. For this purpose, a quantitative evaluation of the microscopic electronic parameters (electron transfer, magnetic coupling, magnetic orbital energy, and Coulomb repulsion) of the mixed-valence polyoxometalate cluster is performed. The parameters are extracted from valence-spectroscopy large configuration interaction (CI) calculations on embedded fragments. Then, these parameters are used in an extended t - J model Hamiltonian suited to model the properties of the whole anion. The analysis of the wave functions of the lowest singlet and triplet states and of the microscopic parameters emphasizes that the electron delocalization in this mixed-valence cluster is such that each unpaired electron is almost trapped in a different half of the polyoxovanadate, thus disabling any exchange interaction between them.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Monomeric and Dimeric Copper(II) Complexes of a Pyrrole-Containing Tridentate Schiff-Base LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2009Rongqing Li Abstract Three copper(II) complexes of (L1),, [CuL1Cl] (1), [CuL1Br]n (2) and [Cu2(L1)2(,1,3 -NCS)2] (3), and two copper(II) complexes of HL1, [Cu(HL1)X2] (X = Cl,, 4; X = Br,, 5), have been prepared and characterised [where HL1 is the Schiff-base ligand derived from pyrrole-2-carbaldehyde and 2-aminomethylpyridine]. The removal of a chloride ion and deprotonation of [Cu(HL1)Cl2] (4) to form [CuL1Cl] (1) worked well. However, attempts to protonate [CuL1Cl] with HCl to re-form [Cu(HL1)Cl2] were not successful. X-ray structure determinations revealed that 1 is a N3Cl-coordinated square-planar copper(II) monomer [CuL1Cl], whereas 3 is a doubly end-to-end thiocyanate-bridged square-pyramidal copper(II) dimer [Cu2(L1)2(,1,3 -NCS)2]. The structure determinations on 4 and 5 showed that in both cases the copper(II) ion is in a distorted square-planar N2X2 environment, with the pyrrole NH remaining non-deprotonated and uncoordinated. Variable-temperature magnetic susceptibility investigations carried out on the end-to-end thiocyanate doubly bridged square-pyramidal copper(II) dimer 3 showed that no magnetic coupling occurs between the two copper(II) ions; it exhibits Curie-like magnetic behaviour.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Synthesis, Structural, Thermal and Magnetic Characterization of a Pyrophosphato-Bridged Cobalt(II) ComplexEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2008Oluwatayo F. Ikotun Abstract The reaction in water of CoII sulfate heptahydrate with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na4P2O7) in a 2:4:1 stoichiometric ratio resulted in the crystallization of a neutral dinuclear CoII complex, {[Co(phen)2]2(,-P2O7)}·6MeOH (1), as revealed by a single-crystal X-ray diffraction study. The bridging pyrophosphato ligand between the two [Co(phen)2]2+ units in a bis(bidentate) coordination mode places the adjacent metal centers at 4.857 Å distance, and its conformation gives rise to intramolecular ,,, stacking interaction between adjacent phen ligands. Indeed, intermolecular ,,, stacking interactions between phen ligands from adjacent dinuclear complexes create a supramolecular 2D network in 1. Magnetic susceptibility measurements on a polycrystalline sample of 1 in the temperature range 1.9,295 K are typical of an overall antiferromagnetic coupling with a maximum of the magnetic susceptibility at 3.0 K. The analysis of the magnetic data in the whole temperature range allows the determination of the value of the intramolecular magnetic coupling (J = ,1.23 cm,1). The ability of the pyrophosphato ligand to mediate magnetic interactions between different first-row transition-metal ions when adopting the bis(bidentate) bridging mode is analyzed and discussed in the light of the small number of magneto-structural reports on this type of compound, bearing in mind the number of unpaired electrons and type of magnetic orbitals on each metal center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Solid-State Anion,Guest Encapsulation by Metallosupramolecular Capsules Made from Two Tetranuclear Copper(II) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2007Emilio Pardo Abstract A new cationic tetranuclear copper(II) complex self-assembles from one 1,3-phenylenebis(oxamato) (mpba) bridging ligand and four CuII ions partially blocked with N,N,N,,N, -tetramethylethylenediamine (tmen) terminal ligands. In the solid state, two of these tetracopper(II) oxamato complexes of bowl-like shape and helical conformation then serve as a building block for the generation of either hetero- (MP) or homochiral (MM/PP) dimeric capsules depending on the nature of the encapsulated anion guest, perchlorate or hexafluorophosphate. The overall magnetic behaviour of these metallosupramolecular capsules does not depend on the nature of the encapsulated anion guest, but it is consistent with the dimer-of-dimer structure of the tetracopper(II) cation host, where the interdimer magnetic coupling through the meta -phenylenediamidate bridge is negligibly smallrelative to the reasonably strong intradimer one across the oxamato bridge.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] [CuII4] Clusters From the Self-Assembly of Two Imidazolidinyl 2-Phenolate-Bridged [CuII2] Units: The Role of the Chloride BridgeEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2007Alok Ranjan Paital Abstract A new family of tetracopper clusters [Cu4(,4 -X)L2]ClO4·nH2O (1a,c) [X = Cl, Br, I; n = 12, 2, 2; H3L = 2-(2,-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine] have been synthesised and characterised. The X-ray crystal structure of 1a reveals that the template action of the spherical Cl, anion (,4 -Cl,), which features a unique rectangular planar bridging mode, is responsible for the self-assembly of two [Cu2L]+ units in complex 1a. In this family of complexes the spherical halides serve as templates to assemble the dimeric unit into tetrameric complexes, which gives an insight into the role of the halide bridge in tetranuclear complex formation. The capacity of this bridge to mediate magnetic coupling has been examined by bulk magnetic measurements for complex 1a. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis, Structure and Magnetic Properties of a Novel Linear CuII -Trimer ComplexEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2005Vladimir Pashchenko Abstract A new hexanuclear copper(II) sandwich complex based on two 10-membered macrocyclic phenylsiloxanolate ligands, {Cu6[(C6H5SiO2)5]2(OH)2(C10H8N2)2}·4(DMF)·3(H2O) (1), was synthesized and characterized by single-crystal X-ray diffraction and measurements of the magnetic susceptibility and isothermal magnetization. The cluster compound crystallizes in the triclinic system, space group P (No. 2), with a = 14.925(3) Å, b = 16.745(2) Å, c = 23.053(3) Å, , = 83.079(9)°, , = 84.836(13)°, , = 65.019(17)°, and Z = 2. The unit cell contains two identical molecules, each consisting of six interacting Cu2+ (S = 1/2) ions. Within the molecule, the six Cu2+ ions are arranged in two almost linear, parallel trimers. While pairs of oxygen atoms link the Cu2+ ions within the trimers, single oxygen atoms residing at the ends of the trimers provide the strongest intertrimer bonds. Magnetic measurements reveal an antiferromagnetic intratrimer exchange interaction, J/kB = 85 K, as the dominant magnetic coupling of the complex. By introducing a weak antiferromagnetic intertrimer coupling, J,/kB = 3.5 K, a satisfactory description of the magnetic behavior over a wide range of temperature and magnetic field is obtained. The departure of the model curves from the data at the lowest available temperature indicates the presence of additional, weak intra - and/or intermolecular interactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Magnetic and viscous coupling at the core,mantle boundary: inferences from observations of the Earth's nutationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2007B. A. Buffett SUMMARY Dissipative core,mantle coupling is evident in observations of the Earth's nutations, although the source of this coupling is uncertain. Magnetic coupling occurs when conducting materials on either side of the boundary move through a magnetic field. In order to explain the nutation observations with magnetic coupling, we must assume a high (metallic) conductivity on the mantle side of the boundary and a rms radial field of 0.69 mT. Much of this field occurs at short wavelengths, which cannot be observed directly at the surface. High levels of short-wavelength field impose demands on the power needed to regenerate the field through dynamo action in the core. We use a numerical dynamo model from the study of Christensen & Aubert (2006) to assess whether the required short-wavelength field is physically plausible. By scaling the numerical solution to a model with sufficient short-wavelength field, we obtain a total ohmic dissipation of 0.7,1 TW, which is within current uncertainties. Viscous coupling is another possible explanation for the nutation observations, although the effective viscosity required for this is 0.03 m2 s,1 or higher. Such high viscosities are commonly interpreted as an eddy viscosity. However, physical considerations and laboratory experiments limit the eddy viscosity to 10,4 m2 s,1, which suggests that viscous coupling can only explain a few percent of the dissipative torque between the core and the mantle. [source] Magnetic and Electrical Properties of (Mn, La)-Codoped SrTiO3 Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Song-Yin Zhang Mn-doped SrTiO3 -based thin films have been prepared by a simple sol,gel spin-coating method on silicon substrate. X-ray diffraction and high-resolution transmission electron microscopy reveal that these thin films are composed of amorphous and crystalline SrTiO3 phases. Optical and electrical measurements indicate that La codoping can make the band gap of SrTiO3 narrow and cause the leakage current to increase. Ferromagnetic behavior can be observed in these Mn- and/or La-codoped SrTiO3 -based thin films at room temperature, which should be ascribed to the magnetic coupling between the induced free electrons and Mn 3d spins. [source] Iron K, line profiles and the inner boundary condition of accretion flowsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003A. Merloni ABSTRACT Recent X-ray observations have shown evidence for exceptionally broad and skewed iron K, emission lines from several accreting black hole systems. The lines are assumed to be due to fluorescence of the accretion disc illuminated by a surrounding corona and require a steep emissivity profile increasing into the innermost radius. This appears to question both standard accretion disc theory and the zero-torque assumption for the inner boundary condition, both of which predict a much less extreme profile. Instead it argues that a torque may be present due to magnetic coupling with matter in the plunging region or even to the spinning black hole itself. Discussion so far has centred on the torque acting on the disc. However, the crucial determinant of the iron line profile is the radial variation of the power radiated in the corona. Here we study the effects of different inner boundary conditions on the coronal emissivity and on the profiles of the observable Fe K, lines. We argue that in the extreme case where a prominent highly redshifted component of the iron line is detected, requiring a steep emissivity profile in the innermost part and a flatter one outside, energy from the gas plunging into the black hole is being fed directly to the corona. [source] Effect of hydrostatic pressure on the transport properties in magnetic semiconductorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004M. Csontos Abstract The effect of pressure on the ferromagnetic phase transition has been studied in manganese doped III-V semiconductors by electrical conductance and Hall measurements. We found that the application of hydrostatic pressure shifts the transition temperature upwards both in (In,Mn)Sb and (Ga,Mn)As. The anomalous-Hall coefficient shows a dramatic increase in the hysteresis loops in the ferromagnetic phase and an enhanced magnetization both below and above the phase transition. As the normal-Hall results suggest that the pressure does not change the carrier density [in (In,Mn)Sb] or rather decreases it [in (Ga,Mn)As], all the above observations are indicative of a pressure-induced enhancement of magnetic coupling. [source] Phenomenology of magnetic second harmonic generation from low symmetry surfaces and interfacesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2003L. Carroll Abstract Low dimensional magnetic structures show interesting and novel phenomena such as oscillatory magnetic coupling and giant magnetoresistance. Magnetic second harmonic generation (MSHG) can provide unique information on magnetic surfaces and interfaces because, within the dipole approximation, broken space-inversion symmetry at the surface or interface of centrosymmetric media, and broken time-reversal symmetry arising from the magnetization, are both required in order to observe a magnetic-field-dependent second harmonic response. However, the additional reduction in symmetry arising from the magetization produces many non-zero susceptibility tensor components, particularly in the case of vicinal, stepped surfaces of 1m symmetry, and care is needed in designing experiments that will produce readily interpretable results. Phenomenological expressions for the MSHG response from systems of 1m symmetry are presented, where combinations of input and output polarizations and magnetic field orientations allow the essential physics of these systems to be explored, particularly in relation to distinguishing terrace and step contributions to the magnetization from vicinal surfaces and interfaces. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Superparamagnetic iron oxide particles: contrast media for magnetic resonance imaging,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2004Rüdiger Lawaczeck Abstract The mainstream magnetic iron oxide particles used as contrast media for magnetic resonance (MR) imaging are composed of a magnetic iron oxide core surrounded by a dextran or carboxydextran coat. The core size ranges from 2 nm to less than 10 nm, and the hydrodynamic diameter ranges from 20 nm to about 120 nm. The coat prevents aggregation and sedimentation of the particles in aqueous solutions, achieves high biological tolerance, and prevents toxic side effects. Two kinds of particles are considered: (i) large particles (>30 nm), called superparamagnetic iron oxide particles (SPIOs) for liver imaging; (ii) smaller particles (<30 nm hydrodynamic diameter), called ultrasmall SPIOs (USPIOs), e.g. for MR angiography. To characterize the particles, Mössbauer spectra are presented for the two particle ensembles. These spectra allow insight into the magnetic coupling, the valency of the iron ions and a rough estimate of the core size to be deduced. On the basis of the concentration dependence of the MR signal intensities, two applications are discussed together with two representative clinical examples. Future indications for MR diagnostics, e.g. the labeling and tracking of stem cells during stem-cell therapy control, are outlined. Copyright © 2004 John Wiley & Sons, Ltd. [source] Disposable MagLev Centrifugal Blood Pump Utilizing a Cone-Shaped ImpellerARTIFICIAL ORGANS, Issue 8 2010Wataru Hijikata Abstract To enhance the durability and reduce the blood trauma of a conventional blood pump with a cone-shaped impeller, a magnetically levitated (MagLev) technology has been applied to the BioPump BPX-80 (Medtronic Biomedicus, Inc., Minneapolis, MN, USA), whose impeller is supported by a mechanical bearing. The MagLev BioPump (MagLev BP), which we have developed, has a cone-shaped impeller, the same as that used in the BPX-80. The suspension and driving system, which is comprised of two degrees of freedom, radial-controlled magnetic bearing, and a simply structured magnetic coupling, eliminates any physical contact between the impeller and the housing. To reduce both oscillation of the impeller and current in the coils, the magnetic bearing system utilizes repetitive and zero-power compensators. In this article, we present the design of the MagLev mechanism, measure the levitational accuracy of the impeller and pressure-flow curves (head-quantity [HQ] characteristics), and describe in vitro experiments designed to measure hemolysis. For the flow-induced hemolysis of the initial design to be reduced, the blood damage index was estimated by using computational fluid dynamics (CFD) analysis. Stable rotation of the impeller in a prototype MagLev BP from 0 to 2750 rpm was obtained, yielding a flow rate of 5 L/min against a head pressure in excess of 250 mm Hg. Because the impeller of the prototype MagLev BP is levitated without contact, the normalized index of hemolysis was 10% less than the equivalent value with the BPX-80. The results of the CFD analysis showed that the shape of the outlet and the width of the fluid clearances have a large effect on blood damage. The prototype MagLev BP satisfied the required HQ characteristics (5 L/min, 250 mm Hg) for extracorporeal circulation support with stable levitation of the impeller and showed an acceptable level of hemolysis. The simulation results of the CFD analysis indicated the possibility of further reducing the blood damage of the prototype MagLev BP. [source] On the applicability of multireference second-order perturbation theory to study weak magnetic coupling in molecular complexes,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2008Núria Queralt Abstract The performance of multiconfigurational second-order perturbation techniques is established for the calculation of small magnetic couplings in heterobinuclear complexes. Whereas CASPT2 gives satisfactory results for relatively strong magnetic couplings, the method shows important deviations from the expected Heisenberg spectrum for couplings smaller than 15,20 cm,1. The standard choice of the zeroth-order CASPT2 Hamiltonian is compared to alternative definitions published in the literature and the stability of the results is tested against increasing level shifts. Furthermore, we compare CASPT2 with an alternative implementation of multiconfigurational perturbation theory, namely NEVPT2 and with variational calculations based on the difference dedicated CI technique. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Electron-density studies of molecular magnetic materialsACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2004Sébastien Pillet For more than forty years, the experimental determination and analysis of electron densities have played a fundamental role in advances in the chemical bond concept. The present paper illustrates the application of this approach to the field of molecular magnetism with examples that recently appeared in the literature. Particular attention is attached to several classes of materials, purely organic free radicals, coordination compounds and organometallic complexes, which exhibit specific magnetic behaviors. It is shown to what extent the electron-density analysis can shed light on bonding aspects that are closely related to magnetic couplings. Relations between spin delocalization, spin polarization, superexchange and the characteristics of the electron density are described. The use of the topological theory of `atoms in molecules' allows the possible magnetic interaction pathways to be located and defined, especially through weak intermolecular contacts. The complementarity with polarized neutron diffraction and spin-density modeling techniques is particularly evident from the chosen examples. [source] | |||||||||||||