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PubMed2004

Initial observation of magnetization hysteresis and quantum tunneling in mixed manganese-lanthanide single-molecule magnets.

The preparation of a new family of mixed transition metal/lanthanide clusters is reported. The reaction of [Mn3O(O2CPh)6(py)2(H2O)] with Ln(NO3)3 (Ln = Nd, Gd, Dy, Ho, and Eu) in a 1:2 molar ratio in MeOH/MeCN (1:20 v/v) leads to dark crystals in 55-60% isolated yield of complexes all containing the [Mn11Ln4]45+ core. The Dy compound has been found to give out-of-phase AC susceptibility signals, suggesting it might be a single-molecule magnet (SMM). This was confirmed by the observation of magnetization hysteresis loops. An Arrhenius plot constructed from magnetization decay data gave a barrier to relaxation of 9.3 K and showed the temperature-independent relaxation at very low temperatures indicative of quantum tunneling of magnetization. This is the initial demonstration of hysteresis and quantum behavior in a mixed 3d/4f SMM.

Journal Article↗
PubMed2005

Magnetic anisotropy of [Mo(CN)7]4- anions and fragments of cyano-bridged magnetic networks.

Quantum chemistry calculations of CASSCF/CASPT2 level together with ligand field analysis are used for the investigation of magnetic anisotropy of [Mo(CN)7]4- complexes. We have considered three types of heptacyano environments: two ideal geometries, a pentagonal bipyramid and a capped trigonal prism, and the heptacyanomolybdate fragment of the cyano-bridged magnetic network K2[Mn(H2O)2]3[Mo(CN)7]2.6H2O. At all geometries the first excited Kramers doublet is found remarkably close to the ground one due to a small orbital energy gap in the ligand field spectrum, which ranges between a maximal value in the capped trigonal prism (800 cm(-1)) and zero in the pentagonal bipyramid. The small value of this gap explains (i) the axial form of the g tensor and (ii) the strong magnetic anisotropy even in strongly distorted complexes. Comparison with available experimental data for the g tensor of the mononuclear precursors reveals good agreement with the present calculations for the capped trigonal prismatic complex and a significant discrepancy for the pentagonal bipyramidal one. The calculations for the heptacyanomolybdate fragment of K2[Mn(H2O)2]3[Mo(CN)7]2.6H2O give g(perpendicular)/g(parallel) approximately 0.5 and the orientation of the local anisotropy axis close to the symmetry axis of an idealized pentagonal bipyramid. These findings are expected to be important for the understanding of the magnetism of anisotropic Mo(III)-Mn(II) cyano-bridged networks based on the [Mo(CN)7]4- building block.

Journal Article↗
PubMed2006

Vortices and their relation to ring currents and magnetic moments in nanographenes in high magnetic field.

Much attention has been paid to the role of vortices in the magnetic response properties of superconductors, but less so for molecular systems. Here we present a theoretical analysis on nanographenes subject to a strong homogeneous magnetic field. The analysis is based on the simple Hückel-London model, for which we derive the topological definition of vorticity. The results are confirmed by a more elaborate model that includes nonnearest neighbor interaction, the explicit presence of nuclei and all terms due to the magnetic field. We find that due to frontier orbital intersections, large changes in magnetic dipole moments occur. Orbital energy minima and maxima can be related to change of vortex patterns with flux.

Journal Article↗
PubMed2005

Rigid, superparamagnetic chains of permanently linked beads coated with magnetic nanoparticles. Synthesis and rotational dynamics under applied magnetic fields.

An inexpensive and versatile approach is reported for the synthesis of monodisperse magnetoresponsive rods of desired diameter, length, and magnetic susceptibility based on the confined alignment of magnetic beads in microchannels of selected channel height, followed by localized hydrolysis of sol-gel precursors within polyelectrolyte shells adsorbed on the beads. The layer-by-layer technique was used to coat the polystyrene beads with polyelectrolytes of alternating charge and with charged magnetic nanoparticles, and the polystyrene cores could be removed either by solvent dissolution or by calcination to form hollow-shelled chains. The reorientation dynamics of single and clustered chains following the application of an external magnetic field was evaluated theoretically, with favorable comparisons with the experimental data.

Journal Article↗
PubMed2005

Synthesis of flexible magnetic nanowires of permanently linked core-shell magnetic beads tethered to a glass surface patterned by microcontact printing.

We have developed an efficient, one-step method to create magnetic nanowires consisting of permanently linked chains of magnetic beads of varying flexibility tethered to a patterned glass surface using simple amidation chemistry. The flexibility of the nanowire was governed by the molecular weight of the molecule used to covalently link the beads and its length by the height of the microchannel in which it was synthesized. The nanowire diameter was determined both by the bead size and by the number of beads adhering to each dot in the microstamped, patterned array. Longer nanowires can form loops attached at two points on the glass surface. Both single flexible chains and flexible loops can adopt different configurations (straight, hairpin, S-shaped, etc.) when subjected to magnetic fields, the configurations depending on the directions of these fields. Shorter, less flexible nanowires align with the field always and do not exhibit the more exotic configurations seen for long, flexible chains and loops. These magnetic nanowires can have potential use in microfluidic pumping and mixing processes and in microparticle manipulation.

Journal Article↗
PubMed2004

Magnetic enhancement and magnetic reduction in binary clusters of transition metal atoms.

Electronic and magnetic properties of small binary clusters containing one or two transition metal atoms are investigated using ab initio calculations with a view to explain the experimentally observed magnetic enhancement/reduction in these systems. As the present investigations do not rely on spin-orbit effects, our results reveal the enhancement or reduction in the magnetic moment to depend on two main factors; namely geometry and, most importantly, the d-band filling. The results can be used as a guide in the experimental synthesis of high density magnetic grains.

Journal Article↗
PubMed1999

Static magnetic field and the inner ear. A functional study of hearing and vestibular function in man after exposure to a static magnetic field.

The sensory cells of the inner ear are vulnerable to several agents (aminoglycosides, cytostatics, ionizing irradiation). The effect of strong magnetic fields occurring in industries with production based on electrolytic processes and with medical magnetic resonance equipment is unknown. The aim of this study was to clarify the effect of strong static magnetic fields on the inner ear, by exposing 11 healthy men to a magnetic field with flux density of 2-7 mT for 9 h. No damage was found to the acoustic or vestibular system.

Adult↗
PubMed2005

Magnetic alignment experiment of fine graphite-crystals dispersed in He gas oriented to study alignment of crystalline-axes of nano-sized non-magnetic particles.

The ensemble of nano-sized crystals is expected to attain additional physical properties when preferential alignments of certain crystal-axes are achieved by a magnetic field. The reduction of temperature T may realize alignment even if the mole number of the particle N and the diamagnetic anisotropy per mole (Deltachi)(DIA) are considerably small for the nano-sized diamagnetic oxides, since alignment proceeds by the balance between the energy of rotational Brownian motion and field-induced anisotropy energy. Alignment of various basic inorganic oxides such as gypsum, quartz, forsterite, KDP or calcite, having a size of 20 nm diameter, is expected to occur by a field intensity of approximately 50 T at T = 10 K; this intensity is presently available at a high magnetic-field laboratory. It is expected that the magnetic alignment of nano-sized particles can be observed by dispersing the particles in He gas, as achieved recently for micron-sized graphite crystals; a cryogenic liquid cannot be used as a dispersing medium. Measured (Deltachi)(DIA) values accumulated for basic inorganic-oxides are explained quantitatively by assuming that individual bonding-orbital composing the material possesses a constant amount of diamagnetic anisotropy; hence the majority of diamagnetic nano-sized insulators are expected to show magnetic alignment at finite field intensity.

Journal Article↗
PubMed2004

Achieving magnet hospital recognition: chief nurse executives and magnet coordinators tell their stories.

Organizational and management characteristics found in hospitals holding magnet hospital recognition are associated with professional nurse practice environments and positive patient and staff outcomes. However, while we know what works, we need a better understanding of "how to get there.'' The authors report the stories about "how we did it'' told by chief nurse executives and magnet project coordinators from hospitals that have achieved American Nurses Credentialing Center magnet hospital recognition. This article adds to the understanding of how to pursue magnet recognition.

Accreditation↗
PubMed2006

Low frequency magnetic fields induced by car tire magnetization.

Alternating magnetic fields have been measured in a variety of different cars, the dominant contribution being from magnetized tires. Magnetic field strengths have been measured as a function of frequency directly at the tires and at different positions in rolling cars. Measurements at the tires showed field strengths up to 100 microtesla (microT). In the interior of rolling cars, close to the wheels at foot regions and at the back seat, field strengths of several microT were obtained in the 10-200 hertz (Hz) frequency domain. In some cases measured field values were considerably higher than those found in previous studies. Purposely magnetizing single tires made it possible to study the influence of various parameters. Degaussed tires retained low field values over prolonged time under conditions of normal use.

Automobiles↗
PubMed2006

Alfvénic-turbulence-heated magnetic loops: effects of lateral expansion and magnetic twist.

Using a 1.5-dimensional two-fluid magnetic loop model in which loops are heated by Alfvénic turbulence, we explore the effects on the loop parameters of the varying cross-section and the magnetic twist. The introduced magnetic twist is set to be around the kink instability threshold for a curved loop. It is found that: (i) The lateral expansion, which takes place close to footpoints, can significantly influence the heating profile, leading to a significant footpoint plasma flow. When observed on disc, the corresponding footpoint blue/red shift may be found for upper transition region lines. (ii) The effects introduced by magnetic twist are twofold. Firstly, the twist-related force may contribute to the axial force balance. Secondly, the projection effect reduces the electron and proton thermal conductivities. The former is found to be of little significance; however, the latter gives rise to considerable changes compared to the untwisted case.

Journal Article↗
PubMed2001

Self-magnetized effects in relativistic cold plasmas due to ponderomotive forces: application to relativistic magnetic guiding of light.

Nonlinear equations are derived relevant to describe the propagation of powerful electromagnetic fields launched within a plasma. The nonlinear generation of self-induced collective electromagnetic perturbations are obtained with matter lying in the relativistic regime. Our main result is the self-consistent treatment of the coupled equations between the pump and its self-induced fields. In particular, a mechanism is pointed out for self-generation of quasistatic magnetic field that is due to the relativistic ponderomotive force. This process is found to be more efficient to produce quasistatic magnetic fields, as confirmed by recent experiments, as compared to known effects such as the inverse Faraday effect. As an application, we investigate conditions for relativistic magnetic guiding of light to occur under the combined action of the self-induced density and magnetic field.

Journal Article↗
PubMed2003

Magnetic line trapping and effective transport in stochastic magnetic fields.

The transport of collisional particles in stochastic magnetic fields is studied using the decorrelation trajectory method. The nonlinear effect of magnetic line trapping is considered together with particle collisions. The running diffusion coefficient is determined for arbitrary values of the statistical parameters of the stochastic magnetic field and of the collisional velocity. The effect of the magnetic line trapping is determined. New anomalous diffusion regimes are found.

Journal Article↗
PubMed2003

Calorimetric study of magnetic fluids under a magnetic field.

In our past study, it was found that the strong magneto-optical effect of a magnetic fluid (MF) under a magnetic field is due to the second-order phase transition from colloidal particles' monodispersed phase to the particles' anisotropically agglomerated microclusters phase. These results, however, contradicted the Landau criterion. In the present study, in order to clarify whether the transition is of first order or second order, we performed differential scanning calorimetry (DSC) experiments on three different MFs to look for the existence of a phase transition latent heat. The DSC measurement was performed in the temperature range 22-150 degrees C with zero magnetic field and under approximately 10 kA/m magnetic field, respectively. No phase transition heat was observed within an experimental error of 0.03 kJ/kg for all the samples whether or not the field was applied.

Journal Article↗
PubMed2005

Particle size and magnetic field-induced optical properties of magnetic fluid nanoparticles.

Magnetite nanoparticles with diameters of 7, 9, and 12 nm have been prepared by a chemical coprecipitation method. The transmission of light through magnetic fluid containing these nanoparticles has been investigated as a function of film thickness with wavelength between 400 and 750 nm, and applied magnetic fields up to 275 Oe. The transmission threshold shifts to the lower wavelength side with decreasing magnetic fluid film thickness as well as the particle size. For a given film thickness, the transmittance increases with increasing magnetic field for films with a particle size of 7 and 9 nm, but decreases in the 12-nm film. This is attributed to the competition between the van der Waals and dipole-dipole interaction.

Journal Article↗
PubMed2001

Element-selective nanosecond magnetization dynamics in magnetic heterostructures.

We have developed a new original technique to study the magnetization reversal dynamics of thin films with element selectivity in the nanosecond time scale. X-ray magnetic circular dichroism measurements in pump-probe mode are carried out taking advantage of the time structure of synchrotron radiation. The dynamics of the magnetization reversal of each of the layers of complex heterostructures (like spin valves or tunnel junctions) can be probed independently. The interlayer coupling in the studied systems has been shown to play a key role in the determination of the magnetization reversal of each individual layer.

Journal Article↗
PubMed2001

Direct determination of interfacial magnetic moments with a magnetic phase transition in Co nanoclusters on Au(111).

The spin, in-plane and out-of-plane orbital and magnetic dipole moments of almost purely interfacial Co atoms were directly determined for Au/2-monolayer Co nanoclusters/Au(111) by angle-dependent magnetic circular x-ray dichroism (MCXD) measurements. The field- and temperature-dependent MCXD evidences a ferromagnetic(FM)-to-superparamagnetic phase transition in single-domain clusters with decreasing size. The interfacial moments are remarkably enhanced as compared with bulk values, verifying theoretical predictions. The FM clusters show strong perpendicular magnetic anisotropy, providing promise of applications for nanoscale magnetic bits.

Journal Article↗
PubMed2002

Evidence for magnetic field induced changes of the phase of tunneling states: spontaneous echoes in (KBr)(1-x)(KCN)(x) in magnetic fields.

Recently it was discovered that, in contrast to expectations, the low-temperature dielectric properties of some multicomponent glasses depend strongly on magnetic fields. The low-temperature dielectric response of these materials is governed by atomic tunneling systems. We now have investigated the influence of magnetic fields on the coherent properties of atomic tunneling states in a crystalline host in two-pulse echo experiments. As in glasses, we observe a very strong magnetic field dependence of the echo amplitude. Moreover, for the first time we have direct evidence that the magnetic fields change the phase of coherent tunneling systems.

Journal Article↗