Paramagnetic Solution Research Articles

GW correlation effects on plutonium quasiparticle energies: Changes in crystal-field splitting

We present results for the electronic structure of plutonium by using a recently developed quasiparticle self-consistent GW method (QSGW). We consider a paramagnetic solution without spin-orbit interaction as a function of volume for the face-centred cubic (fcc) unit cell. We span unit-cell volumes ranging from 10% greater than the equilibrium volume of the δ phase to 90% of the equivalent for the α phase of Pu. The self-consistent GW quasiparticle energies are compared to those obtained within the Local Density Approximation (LDA). The goal of the calculations is to understand systematic trends in the effects of electronic correlations on the quasiparticle energy bands of Pu as a function of the localisation of the f orbitals. We show that correlation effects narrow the f bands in two significantly different ways. Besides the expected narrowing of individual f bands (flatter dispersion), we find that an even more significant effect on the f bands is a decrease in the crystal-field splitting of the different bands.

Insulating behavior with spin and charge order in the ionic Hubbard model

Paramagnetic solutions of the ionic Hubbard model at half-filling in dimensions $Dg2$ indicate that the band and the Mott insulator phases are separated by a metallic phase. We present zero-temperature dynamical mean-field theory solutions, which include antiferromagnetic long-range order and show that the one-particle spectral functions always possess an energy gap, and therefore the system is insulating for all interaction strengths. The staggered charge-density modulation coexists with antiferromagnetic long-range order of N\'eel type.

Using Magnetic Levitation To Distinguish Atomic-Level Differences in Chemical Composition of Polymers, and To Monitor Chemical Reactions on Solid Supports

This communication describes a density-based method that uses magnetic levitation for monitoring solid-supported reactions and for distinguishing differences in chemical composition of polymers. The method is simple, rapid, and inexpensive and is similar to thin-layer chromatography (TLC; for solution-phase chemistry) in its potential for monitoring reactions in solid-phase chemistry. The technique involves levitating a sample of beads (taken from a reaction mixture) in a cuvette containing a paramagnetic solution (e.g., GdCl(3) dissolved in H(2)O) positioned between two NdFeB magnets. The vertical position at which the beads levitate corresponds to the density of the beads and correlates with the progress of a chemical reaction on a solid support. The method is particularly useful for monitoring the kinetics of reactions occurring on polymer beads.

Zero temperature solutions of the Edwards-Anderson model in random Husimi lattices

We solve the Edwards-Anderson model (EA) in different Husimi lattices using the cavity method at replica symmetric (RS) and 1-step of replica symmetry breaking (1RSB) levels. We show that, at T = 0, the structure of the solution space depends on the parity of the loop sizes. Husimi lattices with odd loop sizes may have a trivial paramagnetic solution thermodynamically relevant for highly frustrated systems while, in Husimi lattices with even loop sizes, this solution is absent. The range of stability under 1RSB perturbations of this and other RS solutions is computed analytically (when possible) or numerically. We also study the transition from 1RSB solutions to paramagnetic and ferromagnetic RS solutions. Finally we compare the solutions of the EA model in Husimi lattices with that on the (short loops free) Bethe lattices, showing that already for loop sizes of order 8 both models behave similarly.

Magnetically driven hydrodynamic interactions of magnetic and non-magnetic particles

The influence of magnetic forces on (i) the motion of magnetisable particles in a non-magnetisable fluid and (ii) the motion of non-magnetisable particles in a magnetisable fluid was investigated. A non-uniform magnetic field was used to induce a strong magnetic field gradient. The study was conducted at low particle Reynolds numbers allowing independent evaluation of the hydrodynamic forces along the tangential and normal directions, which in turn were used to deduce the strength and variation of the magnetic forces. Two iron spheres placed in a non-magnetisable fluid showed strong mutual attraction in the normal direction, consistent with an inverse distance to the power four law. The velocity of each sphere in the tangential direction prior to aggregation was constant. Upon aggregation, the velocity of the dumbbell in the tangential direction was approximately two times higher. This sudden increase in velocity was attributed to an increase in the magnetisation following aggregation of the two spheres. It was concluded that a dumbbell has a larger concentration of matter along the direction of the magnetic field and hence, with respect to motion in the tangential direction, a higher magnetisation. For the two acrylic spheres in a magnetised fluid the attractive force was found to be negligible, most probably because of the low magnetisation of the paramagnetic salt solution used. The two spheres did migrate towards each other because of the local field gradients that develop in the normal direction. Interestingly, the spheres developed a constant velocity prior to aggregation, which was also maintained after aggregation. Two acrylic spheres glued together also travelled in the tangential direction at the velocity observed for the individual spheres. It was concluded that there was no change in the magnetisation of the fluid following the aggregation of the spheres.

Cellular dynamical mean-field theory of the periodic Anderson model

We develop a cluster dynamical mean field theory of the periodic Anderson model in three dimensions, taking a cluster of two sites as a basic reference frame. The mean field theory displays the basic features of the Doniach phase diagram: a paramagnetic Fermi liquid state, an antiferromagnetic state and a transition between them. In contrast with spin density wave theories, the transition is accompanied by a large increase of the effective mass everywhere on the Fermi surface and a substantial change of the Fermi surface shape across the transition. To understand the nature and the origin of the phases near the transition, we investigate the paramagnetic solution underlying the antiferromagnetic state, and identify the transition as a point where the $f$ electrons decouple from the conduction electrons undergoing an orbitally selective Mott transition. This point turns out to be intimately related to the two impurity Kondo model quantum critical point. In this regime, non local correlations become important and result in significant changes in the photoemission spectra and the de Haas-van Alphen frequencies. The transition involves considerable $f$ spectral weight transfer from the Fermi level to its immediate vicinity, rather than to the Hubbard bands as in single site DMFT.

Differences in magnetically induced motion of diamagnetic, paramagnetic, and superparamagnetic microparticles detected by cell tracking velocimetry

Magnetic separation in biomedical applications is based on differential magnetophoretic mobility (MM) of microparticulate matter in viscous media. Typically, the difference in MM is obtained by selectively labeling the target cells with superparamagnetic iron oxide nanoparticles (SPIONs). We have measured the MM of monodisperse, polystyrene microspheres (PSMs), with and without attached SPIONs as a model of cell motion induced by nanoparticle magnetization, using variable H field and cell tracking velocimetry (CTV). As a model of paramagnetic microparticle motion, the MM measurements were performed on the same PSMs in paramagnetic gadolinium solutions, and on spores of a prokaryotic organism, Bacillus globigii (shown to contain paramagnetic manganese). The CTV analysis was sensitive to the type of the microparticle magnetization, producing a value of MM independent of the applied H field for the paramagnetic species, and a decreasing MM value with an increasing field for superparamagnetic species, as predicted from theory. The SPION-labeled PSMs exhibited a saturation magnetization above H approximately = 64,000 A m(-1) (or 0.08 tesla). Based on those data, the average saturation magnetizations of the SPIONs was calculated and shown to vary between different commercial sources. The results demonstrate sensitivity of the CTV analysis to different magnetization mechanisms of the microparticles.

Magneto-vibratory separation of glass and bronze granular mixtures immersed in a paramagnetic liquid

A fluid-immersed granular mixture may spontaneously separate when subjected to vertical vibration, separation occurring when the ratio of particle inertia to fluid drag is sufficiently different between the component species of the mixture. Here, we describe how fluid-driven separation is influenced by magneto-Archimedes buoyancy, the additional buoyancy force experienced by a body immersed in a paramagnetic fluid when a strong inhomogeneous magnetic field is applied. In our experiments glass and bronze mixtures immersed in paramagnetic aqueous solutions of MnCl2 have been subjected to sinusoidal vertical vibration. In the absence of a magnetic field the separation is similar to that observed when the interstitial fluid is water. However, at modest applied magnetic fields, magneto-Archimedes buoyancy may balance the inertia/fluid-drag separation mechanism, or it may dominate the separation process. We identify the vibratory and magnetic conditions for four granular configurations, each having distinctive granular convection. Abrupt transitions between these states occur at well-defined values of the magnetic and vibrational parameters. In order to gain insight into the dynamics of the separation process we use computer simulations based on solutions of the Navier-Stokes' equations. The simulations reproduce the experimental results revealing the important role of convection and gap formation in the stability of the different states.

Density-Based Diamagnetic Separation: Devices for Detecting Binding Events and for Collecting Unlabeled Diamagnetic Particles in Paramagnetic Solutions

This paper describes the fabrication of a fluidic device for detecting and separating diamagnetic materials that differ in density. The basis for the separation is the balance of the magnetic and gravitational forces on diamagnetic materials suspended in a paramagnetic medium. The paper demonstrates two applications of separations involving particles suspended in static fluids for detecting the following: (i) the binding of streptavidin to solid-supported biotin and (ii) the binding of citrate-capped gold nanoparticles to amine-modified polystyrene spheres. The paper also demonstrates a microfluidic device in which polystyrene particles that differ in their content of CH2Cl groups are continuously separated and collected in a flowing stream of an aqueous solution of GdCl3. The procedures for separation and detection described in this paper require only gadolinium salts, two NdFeB magnets, and simple microfluidic devices fabricated from poly(dimethylsiloxane). This device requires no power, has no moving parts, and may be suitable for use in resource-poor environments.

Orbital density functional as a means to restore the discontinuities in the total-energyderivative and the exchange–correlation potential

The local density approximation (LDA) to the density functional theory (DFT) has acontinuous derivative of the total energy as a function of the number of electrons andcontinuous exchange–correlation potential, while in exact DFT both functions should bediscontinuous as the number of electrons goes through an integer value. We propose an adhoc orbital density functional (ODF) (with orbitals defined as Wannier functions)that by construction obeys this discontinuity condition. Taking its variation, theone-electron equations are obtained with a potential in the form of a projectionoperator. This operator increases the separation between occupied and empty bands,thus curing an LDA deficiency—systematic underestimation of the energy gapvalue. The minimization of the ODF gives the ground-state orbital and totalelectron densities. In addition to that we define the ODF fluctuation Hamiltonianthat allows one to treat dynamical correlation effects. The dynamical mean-fieldtheory (DMFT) with the quantum Monte Carlo (QMC) method for an effectiveimpurity problem was used to solve this Hamiltonian. We have applied the ODFmethod to the problem of the metal–insulator transition in lanthanum trihydrideLaH3−x. In the LDA calculations for all values of hydrogen nonstoichiometryx the ground state of this material is metallic, while experimentally the system is insulating forx<0.3. The ODF method gave a paramagnetic insulator solution forLaH3 andLaH2.75 but metallicstate for LaH2.5.

A new flow-type cell by the application of magnetic microfluidic chip

Using a magnetically formed channel called a magnetic channel, a new flow-type cell is proposed. The magnetic channel consists of magnetic walls that are formed by heterogeneous distributions of magnetic flux density around a ferromagnetic track under a magnetic field. The magnetic wall separates the paramagnetic oxidant solution from the diamagnetic reductant solution at a liquid–liquid interface without any solid membranes. In the magnetic channel formed on the cathode, the oxidant solution flows in a quasi-frictionless mode. The anode is placed in the reductant solution surrounding the magnetic channel. Such a geometrical configuration between the oxidant and reductant solutions is interchangeable depending on the magnetism of the solutions. To examine this concept, a Daniel cell system was adopted, where the copper ion in copper sulfate solution is employed as the oxidant and the zinc atom of zinc electrode as the reductant. The copper ion is paramagnetic, so that 1 mol dm−3 copper sulfate solution is injected into the magnetic channel formed on the copper cathode. Zinc sulfate solution (1 mol dm−3; diamagnetic) together with the zinc anode are placed surrounding the magnetic channel. The performance of this flow-type battery was examined up to a current density of 22 mA cm−2.

Phase separation in the Hubbard model using the dynamical cluster approximation

Phase separation in the Hubbard model is investigated with the dynamical cluster approximation. We find that it is present in the paramagnetic solution for values of filling smaller than 1 and at finite temperature when a positive next-nearest-neighbor hopping is considered. The phase-separated region is characterized by a mixture of a strongly correlated metallic and Mott insulating phases. Our results indicate that phase separation is driven by the formation of doped regions with strong antiferromagnetic correlations and low kinetic energy.

Local Diffusion in Paramagnetic Solutions by NMR Relaxometry at One Frequency

The relative diffusion coefficient D of a paramagnetic species and a diamagnetic probe molecule bearing nuclear spins is obtained from their measured relaxation times T1 and T2 (or T1rho). This is achieved by introducing the longitudinal relaxivity, r1, a linear expression of 1/T1, and the mixed relaxivity, rmix, a linear expression of 1/T1 and 1/T2 (or 1/T1rho). Under weak assumptions, D is proportional to (rmix - r1) to the power -2/3 and to rmix to the power -1, with easy-to-determine proportionality factors. The method is noninvasive and easy to use on standard NMR spectrometers and imagers. It is validated through the study of various solutions of a Gd(III)-based contrast agent for magnetic resonance imaging.

Replica-symmetric solutions of a dilute Ising ferromagnet in a random field

We use the replica method in order to obtain an expression for the variational free energy of an Ising ferromagnet on a Viana-Bray lattice in the presence of random external fields. Introducing a global order parameter, in the replica-symmetric context, the problem is reduced to the analysis of the solutions of a nonlinear integral equation. At zero temperature, and under some restrictions on the form of the random fields, we are able to perform a detailed analysis of stability of the replica-symmetric solutions. In contrast to the behaviour of the Sherrington-Kirkpatrick model for a spin glass in a uniform field, the paramagnetic solution is fully stable in a sufficiently large random field.

Glassy magnetism in mechanically alloyed Fe xCr 90−xMn 10 ( x=18 and 35)

X-ray diffraction (XRD), 57Fe Mössbauer and magnetic measurements were performed on mechanically alloyed Fe x Cr 90− x Mn 10 ( x=18 and 35) alloys. XRD and 57Fe Mössbauer spectra show the systems are non-magnetic BCC phase. The irreversibility between field-cooled and zero-field-cooled magnetization curves at relative high temperature is due to the blocking of some single particles. A correlation between the Fe concentration and T max of ZFC curves can be explained by the fine Fe-rich clusters which are embedded in a paramagnetic solid solution. The Fe 35Cr 55Mn 10 alloy exhibits two type of blocking/freezing in an ensemble of nanoparticles. With the decreasing of temperature, the Fe 18Cr 72Mn 10 alloy shows spin-glass-like behavior and the Fe 35Cr 55Mn 10 alloy goes through two magnetic transitions from paramagnetic phase to ferromagnetic phase and then to re-entrant spin-glass state.

Magnetic properties of nanocrystalline Fe60Cr40 powders prepared by mechanical alloying in vacuum and air

Magnetic properties of nanocrystalline Fe60 Cr40 powders prepared by mechanical alloying in vacuum and air were investigated by utilizing the measurements of magnetization, X-ray diffraction, and 57Fe Mossbauer spectrum. The results show that the Fe60Cr40, powders keep the bcc structure during milling in air and vacuum. The saturation magnetization of the Fe60 Cr40 powders milled in vacuum and air decreases with the increase of the milling time up to 45 h. The decrease of saturation magnetization of the Fe60 Cr40 powders milled in vacuum is due to the formation of Fe-Cr solid solution, while in air it is due to the formation of paramagnetic disorder structure and solid solution.

Indirect detection of lung perfusion using susceptibility‐based hyperpolarized gas imaging

To address the problem of inadequate signal-to-noise ratio (SNR) encountered in lung perfusion magnetic resonance imaging (MRI) by developing an indirect detection based on the strong hyperpolarized (HP) gas signal. Our model is based on detecting the effects of gadolinium (Gd) flowing through lung capillaries by recording the phase of the nearby alveolar HP gas. In a HP gas 3He phantom we imaged gas phases before and after removing tubes containing paramagnetic solution away from the phantom. We also imaged HP gas phases in pig lungs before and after injection of Gd. Finally, parenchymal spin phase in excised lungs was measured as a function of Gd concentration. In the phantom, the differential phase map displayed a pattern characteristic of a susceptibility-induced dipole field, showing the possibility of an indirect detection. In vivo, the differential phase map showed homogeneous appearance, as expected for uniform perfusion in healthy lungs. Ex vivo, the parenchymal spin phases were shown to depend linearly on Gd concentration. Our method should allow indirect perfusion (Q) and direct ventilation (V) to be assessed simultaneously, thus allowing for diagnosis of V/Q mismatches. The linear dependency of parenchymal spin phase vs. Gd concentration may allow for quantification of lung perfusion.

Noninvasive measurement and imaging of liver iron concentrations using proton magnetic resonance

AbstractMeasurement of liver iron concentration (LIC) is necessary for a range of iron-loading disorders such as hereditary hemochromatosis, thalassemia, sickle cell disease, aplastic anemia, and myelodysplasia. Currently, chemical analysis of needle biopsy specimens is the most common accepted method of measurement. This study presents a readily available noninvasive method of measuring and imaging LICs in vivo using clinical 1.5-T magnetic resonance imaging units. Mean liver proton transverse relaxation rates (R2) were measured for 105 humans. A value for the LIC for each subject was obtained by chemical assay of a needle biopsy specimen. High degrees of sensitivity and specificity of R2 to biopsy LICs were found at the clinically significant LIC thresholds of 1.8, 3.2, 7.0, and 15.0 mg Fe/g dry tissue. A calibration curve relating liver R2 to LIC has been deduced from the data covering the range of LICs from 0.3 to 42.7 mg Fe/g dry tissue. Proton transverse relaxation rates in aqueous paramagnetic solutions were also measured on each magnetic resonance imaging unit to ensure instrument-independent results. Measurements of proton transverse relaxivity of aqueous MnCl2 phantoms on 13 different magnetic resonance imaging units using the method yielded a coefficient of variation of 2.1%.

Electron-phonon interaction in the three-band model

We study the half-breathing phonon in the three-band model of a high temperature superconductor, allowing for vibrations of atoms and resulting changes of hopping parameters. Two different approaches are compared. From the three-band model a t-J model with phonons can be derived, and phonon properties can be calculated. To make contact to density functional calculations, we also study the three-band model in the Hartree-Fock (HF) approximation. The paramagnetic HF solution, appropriate for the doped cuprates, has similarities to the local-density approximation (LDA). However, in contrast to the LDA, the existence of an antiferromagnetic insulating solution for the undoped system makes it possible to study the softening of the half-breathing phonon under doping. We find that although the HF approximation and the t-J model give similar softenings, these softenings happen in quite different ways. We also find that the HF approximation gives an incorrect doping and q dependence for the softening and too small a width for the (half-)breathing phonon.

First-order phase transitions in spin-glass models with multiple paramagnetic solutions

The paramagnetic and the one-step replica-symmetry-breaking spin-glass solutions of a p-spin-glass model in the presence of a transverse field are studied in the neighborhood of the phase transition curve. Two qualitatively different regions are found in the phase diagram. For a transition temperature higher than a certain value T c , the thermodynamic transition is of second order, otherwise it is of first order with latent heat. The temperature T c is joined to a point in the phase diagram where a transition between two paramagnetic solutions happens. A discussion about the order of the thermodynamic-phase transition in the quantum random orthogonal model is presented.