Magnetic Susceptibility Effects Research Articles

Magnetic shape-memory effects in a crystal.

Magnetic fields affect the motion of electrons and the orientation of spins in solids, but are thought to have little impact on crystal structure, particularly in compounds with low magnetic susceptibility, such as antiferromagnets. Here we describe an unexpected magnetic effect on crystal shape, in which the direction of the crystal's axes are swapped and the shape changes when a magnetic field is applied; this in turn induces curious memory effects in resistivity and magnetic susceptibility. Ironically, this phenomenon occurs in one of the most well-studied two-dimensional antiferromagnets, La(2-x)Sr(x)CuO(4).

NMR Chemical Shift Methods for Binding Constant Determination of an Organic Anion and α-Cyclodextrin

Abstract Internal reference compounds suitable for proton chemical shift measurements of organic anions in deuterium oxide solutions are proposed and used to determine the binding constant of sodium hexane-1-sulfonate (SHS) and α-cyclodextrin (α-CD). The chemical shift of the methyl proton of sodium methyl sulfate (MeS), referred to external sodium 4,4-dimethyl-4-silapentane-1-sulfonate (DSS), changes linearly with the α-CD concentration, because of the volume magnetic susceptibility effect. The chemical shifts of the SHS methyl proton, referred to external DSS and corrected for this magnetic susceptibility effect, as well as referred to internal MeS and methanol (MeOH), provide reliable binding constants of SHS and α-CD. Therefore, MeS and MeOH are appropriate internal standards for organic anions. The present results serve not only for choosing appropriate internal references and the internal or external standard method for chemical shift measurements but also for correcting the chemical shift referred to an external standard.

Superparamagnetic iron oxide-mediated hepatic signal intensity change in patients with and without cirrhosis: pulse sequence effects and Kupffer cell function.

To analyze superparamagnetic iron oxide (SPIO)-mediated hepatic signal intensity change in cirrhotic and noncirrhotic liver and to investigate the relationship between pulse sequence effects in SPIO-enhanced magnetic resonance (MR) imaging for hepatic cirrhosis. Twelve patients with and 12 patients without cirrhosis underwent T2-weighted fast spin-echo, T2*-weighted gradient-echo (GRE), and T1-weighted GRE MR imaging before and twice (early and late phase) after SPIO administration. To assess the effect of SPIO, postcontrast relative signal-to-noise ratio (SNR) changes were statistically analyzed with repeated measurements analysis of variance for each pulse sequence. No interaction was shown between groups and data time points for any pulse sequence. There was no significant difference in mean hepatic relative SNR change on T2-weighted fast spin-echo images between the cirrhotic group and noncirrhotic group (-38.6% and -40.7%, early phase; -42.2% and -49.6%, late phase, respectively). For GRE images, statistically significant differences in mean hepatic relative SNR change were found between the cirrhotic group and noncirrhotic group (-14.2% and -44.5%, early phase; -28.5% and -56.4%, late phase on T2*-weighted GRE images (P <.001); 31.8% and 12.9%, early phase; 23.8% and 2.2%, late phase on T1-weighted GRE images (P <.05), respectively. Decreased overall phagocytic activity in cirrhotic liver is more likely due to Kupffer cell dysfunction than to Kupffer cell depletion, since magnetic susceptibility effects on T2*-weighted GRE images depend on intracellular SPIO cluster size.

Dynamic and magnetic susceptibility effects on the MAS NMR linewidth of a tetrapeptide bound to different resins

AbstractUnder magic angle spinning, the NMR spectrum of the tetrapeptide Ala‐Ile‐Gly‐Met bound to a Wang resin, and swollen in DMF, exhibits proton and carbon linewidths that are sharp enough to allow the complete characterization of the peptide using classical liquid‐state NMR methods. The proton linewidths of the bound peptide remain, however, about three times larger than those of the free peptide in solution. The residual NMR linewidth originates essentially from incompletely averaged magnetic susceptibility effects due to the Wang resin. Replacing the aromatic Wang resin with a PEGA or POEPOP resin removes this effect. To investigate the contribution to line broadening of the peptide dynamics, relaxation studies were performed on the peptide bound to Wang and POEPOP resins. Copyright © 2001 John Wiley &amp; Sons, Ltd.

High-resolution BOLD venographic imaging: a window into brain function.

This paper reviews the recent development of a new high-resolution magnetic resonance imaging approach to visualizing small veins in the human brain with diameters in the sub-millimeter range, which is smaller than a voxel. It briefly introduces the physical background of the underlying bulk magnetic susceptibility effects, on which this approach is based, and it demonstrates the successful application of the method for imaging different intracranial lesions, like venous anomalies, arteriovenous malformations and brain tumors. The susceptibility difference between venous blood and the surrounding tissue is used to generate contrast. Using this method it is possible to visualize draining veins in lesions better than conventional magnetic resonance imaging methods, which often require application of a contrast medium or even conventional catheter angiography. Limitations of the method are discussed. The ability to highlight deoxygenated blood with high spatial resolution yields important vascular parameters which may be helpful for improved modeling of MR signal changes during functional brain activation, it may lead to a better understanding of brain function in diseased states, or it may even offer the possibility of differentiating benign from malignant tumors non-invasively.

Cross correlation between the dipole-dipole interaction and the Curie spin relaxation: the effect of anisotropic magnetic susceptibility.

Cross-correlated relaxation caused by the interference of nuclear dipole-dipole interaction and the Curie spin relaxation (DD-CSR cross relaxation) is generalized to treat the case of anisotropic magnetic susceptibility, including the important case where the latter originates from zero-field splitting. It is shown that the phenomenon of DD-CSR cross relaxation is absolutely general and to be expected under any electronic configuration. The results of the generalization are presented for a model system, and the consequences for paramagnetic metalloproteins are illustrated with an example of cerium(III)-substituted calbindin. The effects of the magnetic anisotropy are found to be substantial.

Magnetic Susceptibility Effects on 13C MAS NMR Spectra of Carbon Materials and Graphite

13C high-resolution solid-state nuclear magnetic resonance (NMR) was employed to study carbon materials prepared through the thermal decomposition of four different organic precursors (rice hulls, endocarp of babassu coconut, peat, and PVC). For heat treatment temperatures (HTTs) above about 600°C, all materials presented 13C NMR spectra composed of a unique resonance line associated with carbon atoms in aromatic planes. With increasing HTT, a continuous broadening of this resonance and a diamagnetic shift in its central frequency were verified for all samples. The evolution of the magnitude and anisotropy of the magnetic susceptibility of the heat-treated carbon samples with HTT explains well these findings. It is shown that these results are better understood when a comparison is made with the features of the 13C NMR spectrum of polycrystalline graphite, for which the magnetic susceptibility effect is also present and is much more pronounced.

Magnetic transitions in Cu 2− xSe below room temperature

We have measured the magnetic susceptibility, resistivity, magnetoresistivity and Hall effect of nonstoichiometric cuprous selenide between 5 and 350 K. Our results show that below 170 K Cu 2− x Se is a mixture of diamagnetic Cu 1.995Se and paramagnetic Cu 3Se 2. The phase diagram of the Cu–Se system, in which 170 K represents the eutectic isotherm, governs the relative content of the two phases. For the Cu 3Se 2 phase a transition to an antiferromagnetic state is observed at about 50 K, with the corresponding Weiss temperature Θ=120 K. On heating above 170 K Cu 2− x Se becomes completely diamagnetic, but the transformation is slow and strongly time dependent. The complicated magnetic behaviour is ascribed to a broad temperature hysteresis of the process.

In vivo Magnetic Resonance Imaging and Surgical Histopathology of Intracardiac Masses: Distinct Features of Subacute Thrombi

We evaluated intracardiac masses in vivo, in situ and histologically to determine tissue properties revealed by magnetic resonance (MR) imaging. In 15 consecutive patients scheduled for cardiotomy, the cardiac chambers were studied preoperatively with MR imaging and echocardiography. Visual examination of one or more chambers was performed during cardiotomy for mitral valve replacement, aneurysmectomy, atrial septal repair and atriotomy. Six thrombi (1 atrial appendage, 5 ventricular) and 2 atrial myxomas were removed and subjected to histological analysis. All masses were detected preoperatively by MR imaging. The smallest was a subacute 3-mm mural clot in the left ventricle and was undetected by transesophageal and transthoracic echocardiography. The 3 subacute clots had homogeneously low MR signals, did not enhance with gadolinium and exhibited magnetic susceptibility effects; histopathology confirmed these clots to be avascular and laden with dense iron deposition related to hemoglobin breakdown products. The 3 organized clots had intermediate and heterogeneous MR signals and multiple areas of gadolinium enhancement. The 2 myxomas had low MR signals and gadolinium enhancement in the core and septal attachment; these areas had dense neovascular channels. Subacute thrombi appear to have MR features that are distinct from organized thrombi and myxomas, and MR images of subacute thrombi contrast sharply with normal cardiac structures, enabling detection of thin mural clots that may be echographically occult. These findings may be of value, because a subacute clot may be more likely than an organized thrombus to give rise to an embolus.

MR Imaging of Vascular Stents: Effects of Susceptibility, Flow, and Radiofrequency Eddy Currents

The purpose of this in vitro study was to examine the various sources of artifacts in magnetic resonance (MR) imaging and angiography of vascular stents. Five low-artifact stents-Wallstent (cobalt alloy), Memotherm (nitinol), Perflex (stainless steel), Passager (tantalum), and Smart (nitinol)-were imaged in a vascular flow phantom, consisting of a thin-walled cellulose vessel model connected to a pump system. The echo time and the angulation of the stents with respect to the direction of the main magnetic field were varied. Spin echo and gradient echo images as well as three-dimensional MR angiograms were obtained to study the effects of flow, magnetic susceptibility, and radiofrequency-induced eddy currents. Susceptibility artifacts were restricted to the stents' direct environment and were mildest at short echo times and with the stents aligned with the main magnetic field. Nitinol stents showed less artifacts than steel stents did. Radiofrequency artifacts obscuring the stent lumen and flow-related lumen displacement were seen in all stents. The extent to which these occurred depended on strut geometry and orientation. For low-artifact stents, the material the stent is made of is not the only important factor in the process of artifact formation. Susceptibility artifacts, radiofrequency eddy currents and flow-related artifacts all contribute to the image distortion, and are dependent on the geometry and orientation of the struts and on the orientation of the stent in the main magnetic field.

Dimensional Crossover of Magnetic Transition in Diluted Ising Spin Nets Probed by Muon Spin Relaxation

The magnetic ordering process of Ising spins on diluted square lattice was studied by muon spin relaxation using model compounds Rb2Co c Mg1−c F4. Muon relaxation shows an anomaly at a remarkably higher temperature T N μSR than the transition temperature determined by neutron Bragg scattering T N ND near the percolation threshold for square lattice (c p=0.593). The difference between the two temperatures amounts to 50% of T N ND just above c p. The field cooling effect of DC magnetic susceptibility is appreciable below T N ND while the temperature of the anomaly in AC susceptibility approaches to T N μSR as the frequency is increased. It was concluded that there is a crossover from two-dimensional ordering at T N μSR to three-dimensional ordering at T N ND but the two-dimensional order between T N μSR and T N ND has slow fluctuations due to the fractal structure with a plenty of weak links.

Point-wise measurements of MRS volume selection performance are insensitive to magnetic susceptibility effects of phantom materials

The purpose was to analyse magnetic susceptibility effects on accuracy of point-wise measurements of signal profiles in the assessment of MRS volume selection performance. An existing phantom design consisting of a sphere with a movable signal source was used for the investigation. The influence from the phantom on magnetic field homogeneity was measured with phase sensitive 1H imaging and 31P spectroscopy on a 1.5 T whole body MR system. The susceptibility effects for such a phantom design can be separated in 1/ A variation in the background magnetic field, which is caused by the stationary structures and has a significant influence on spatial accuracy. 2/ A magnetic field distortion, which is caused by the movable signal source and has very little influence on accuracy. The spatial inaccuracy due to susceptibility effects in this phantom, was 0.03 mm for positions of the signal source covering a 40-mm VOI. Susceptibility effects from the movable signal source were substantial but had very little influence on spatial accuracy. Still, improvements of this phantom design are possible. Point-wise measurements using a phantom with a movable signal source is inherently insensitive to susceptibility effects from the signal source and permits accurate signal profile measurements of high spatial (sub-mm) resolution.

Iron oxide-enhanced MR lymphography: initial experience

The detection of nodal metastases is of utmost importance in oncologic imaging. Ultrasmall superparamagnetic iron oxide particles (USPIO) are novel contrast agents specifically developed for MR lymphography. After intravenous administration, they are taken up by the macrophages of the lymph nodes, where they accumulate. They reduce the signal intensity (SI) of normally functioning nodes on postcontrast T2-and T2*-weighted images through the magnetic susceptibility effects on iron oxide. Metastatic nodes, in which macrophages are replaced by tumor cells, show no significant change in SI on postcontrast T2-and T2*-weighted images. Early clinical experience suggests that USPIO-enhanced MR lymphography improves the sensitivity and specificity for the detection of nodal metastases. It also suggests that micrometastases could be detected in normal-sized nodes. This article reviews the physiochemical properties of USPIO contrast agents, their enhancement patterns, and early clinical experience.

Synthesis and properties of Bi1.6Pb2-xSr2-xCa2Cu3Oy

Bi1.6Pb0.4Sr2-xCa2Cu3Oy (x = 0, 0.2, 0.4) high-Tc materials were prepared from oxide-carbonate mixtures and presynthesized mixed oxides. The 2223 superconducting phase was found to be formed most rapidly in thex = 0.4 sample if the Pb-and Ca-containing starting reagents were separated in the initial stage of synthesis. The highest superconducting transition temperature, Tc(R = 0) = 104.3 K, was attained in the stoichiometric 2223 material. The materials were characterized by electrical resistivity, magnetic susceptibility, and Hall effect measurements. The Hall data were used to evaluate carrier concentration and mobility. The 77-K resistivity of the materials was measured as a function of magnetic field.

Toroid Cavity Detectors for High-Resolution NMR Spectroscopy and Rotating Frame Imaging: Capabilities and Limitations

The capabilities of toroid cavity detectors for simultaneous rotating frame imaging and NMR spectroscopy have been investigated by means of experiments and computer simulations. The following problems are described: (a) magnetic field inhomogeneity and subsequent loss of chemical shift resolution resulting from bulk magnetic susceptibility effects, (b) image distortions resulting from off-resonance excitation and saturation effects, and (c) distortion of lineshapes and images resulting from radiation damping. Also, special features of signal analysis including truncation effects and the propagation of noise are discussed. B0 inhomogeneity resulting from susceptibility mismatch is a serious problem for applications requiring high spectral resolution. Image distortions resulting from off-resonance excitation are not serious within the rather narrow spectral range permitted by the RF pulse lengths required to read out the image. Incomplete relaxation effects are easily recognized and can be avoided. Also, radiation damping produces unexpectedly small effects because of self-cancellation of magnetization and short free induction decay times. The results are encouraging, but with present designs only modest spectral resolution can be achieved.

The Effect of Magnetic Susceptibility on The Motion of Particles in A Ferrohydrostatic Separator

Separation in magnetic fluids is a sink‐and‐float technique based on the generalised Archimedes law whereby, in addition to the conventional force of gravity, a magnetically induced force acts on the fluid. Since this density‐based process takes place in a nonuniform magnetic field, magnetic properties of the material to be separated also play a role. The objective of this study is to derive an equation of motion of a non‐magnetic particle in a magnetised magnetic fluid and to solve this equation analytically so that particle trajectories could be derived. Furthermore, the magnetic susceptibility of magnetisable particles is taken into account by means of the effective density of the particle. This effective density is the sum of the physical (true) density of the particle and the density associated with the interaction of the particle with the external non‐homogeneous magnetic field. A criterion for the accuracy of separation in the form of threshold mass magnetic susceptibility is obtained. This criterion is then verified experimentally.

Structure, magnetic properties and epoxidation activity of iron(III) salicylaldimine complexes

Two new iron(III) complexes with salicylaldimine ligands, [Fe(L1)Cl]·CH3CN (1) and [Fe(L2)Cl(H2O)]·1/3CH3Cl (2) [H2L1 = N,N′-(1,1-dimethylethylene)bis(salicylaldimine), H2L2 = N,N′-(1,1-dimethylethylene)bis(3-methoxysalicylaldimine)], have been prepared and characterized. The X-ray crystal structure analysis shows that the iron(III) ion in complex 1 is in a distorted square pyramidal environment, while in 2, the iron(III) center is six-coordinate with distorted octahedral geometry. The Schiff base ligands L1 and L2 occupied the basal sites, with chloride and water occupying the apical sites. Magnetic susceptibility and Mossbauer effect measurements showed a high-spin configuration (S = 5/2) for Fe(III) in 1 and 2. The temperature dependence of the magnetic data for complexes 1 and 2 is analyzed in terms of the spin-Hamiltonian formalism, which gives an accurate estimate of the zero-field splitting of the ground state of the iron(III) ions as D = 10.2 cm−1 (E = 3.4 cm−1) and D = 7.2 cm−1 (E = 2.4 cm−1, zJ′ = −0.5 cm−1), respectively, in the above two complexes. It has been found for the first time that complexes 1 and 2 activate the epoxidation of cis-stilbene by NaOCl. With 1, the epoxides were produced in 40% yield with cis∶trans = 20∶80, and with 2, the epoxides were produced in 90% yield with cis∶trans = 40∶60.

Néel Temperature ofα-Manganese Alloys with Nonmagnetic Impurities

Magnetic moments of the four sites align noncollinearly with different magnitudes. Because the magnetic structure is complex, the magnetism of α-Mn has not entirely been understood. The electrical resistivity for α-Mn takes a minimum at TN. Variations of the Neel temperature as a function of the concentration of transition metal impurities were studied by Williams and Stanford by means of resistivity measurements. The results have been explained by a spin density wave theory, as in the case of Cr alloys. In the present paper, the variations of TN as a function of the concentration of nonmagnetic impurities such as Al, Si, Ga, Ge and Sn were studied mainly by the measurements of the electrical resistivity. The measurements of magnetic susceptibility, neutron diffraction and Mossbauer effect were also performed supplementally for several specimens. Each ingot was prepared by melting together proper amounts of 4N Mn and of impurity material such as Al, Si, Ga, Ge or Sn in an Al2O3 crucible under an Ar+H2 atmosphere. The specimens for the Mossbauer experiment were made of enriched Sn material. The ingots were annealed at 500 or 550◦C in an Ar+H2 atmosphere for 4 days. The specimens were confirmed to be in the α-phase using an X-ray powder diffractometer, although small amounts of manganese oxides were found in some specimens. The electrical resistivity measurements were performed by a conventional four-terminal method. Temperature variations of magnetic susceptibility in a magnetic field of 5 kOe were measured using a vibrating sample magnetometer. Powder neutron diffraction experiments were conducted using a T-1-1 spectrometer installed at JRR-3M in JAERI. Besides temperature variations of scattering intensities for magnetic Bragg reflections, the intensities of about 10 nuclear Bragg reflections were also studied at room temperature, to determine the site preference of the impurity atoms among the four kinds of sites, site I to IV. This experiment reveals that Al and Sn prefer the site II, while Si and Ge do the site

Magnetic susceptibility shift selected imaging (MESSI) and localized (1)H(2)O spectroscopy in living plant tissues.

Maize root segments permeated with aqueous solutions of the paramagnetic agents GdDTPA(2-) or DyDTPA-BMA display two well-resolved NMR peaks corresponding to the signals from intracellular and extracellular (1)H(2)O, which arise from well-understood bulk magnetic susceptibility effects. This allows each component to be studied separately. Images obtained at each frequency with MESSI editing, and single- and multiple-voxel ('spectroscopic imaging') localized spectra, clearly indicate that the agents permeate into the interstitial spaces, and into the longitudinal (xylem/phloem) channels in the stele (core) of the root, confirming earlier assessments. We believe these are the first images of a multicellular tissue acquired in vivo exclusively from the intracellular water proton resonance. This method can be further exploited to study water transport in similar systems.

Electronic State of Fe in Double Perovskite Oxide Sr2FeWO6

The magnetic properties of double perovskite oxide Sr 2 FeWO 6 have been reported. The magnetic susceptibility and Mossbauer effect of 57 Fe show that this compound is an antiferromagnet with T N =37 K. The Mossbauer parameters below ∼20 K are the center shift of +1.2 mm/s relative to metallic iron, the quadrupole splitting of 1.9 mm/s and the hyperfine field of ∼110 kOe. The quadrupole splitting has a strong temperature dependence. From these data, we conclude that Fe in Sr 2 FeWO 6 is in the Fe 2+ high-spin state, while the hyperfine field seems to be quite small. The cell volume shows a large increase compared to other Sr 2 FeTO 6 ( T= Mo, Re, etc.), which is in the Fe 3+ high-spin state. These results suggest that these compounds have a strongly coupled charge and lattice systems.