Mark W. Meisel

Superparamagnetic Fe3O4/SiO2 Nanocomposites: Enabling the Tuning of Both the Iron Oxide Load and the Size of the Nanoparticles

Using a water-in-oil microemulsion system, silica nanoparticles containing superparamagnetic iron oxide (SPIO) crystals have been prepared and characterized. With this method, the loading of iron oxide crystals, the thickness of the silica shells, and the overall particle sizes are tunable. Moving from low to high water concentration, within the microemulsion region, resulted in a gradual shift from larger particles, ca. 100 nm and fully loaded with SPIOs, to smaller particles, ca. 30 nm containing only one or a few SPIOs. By varying the amount of silica precursor, the thickness of the silica shell was altered. Field dependent magnetization measurements showed the magnetic properties of the SPIOs were preserved after the synthesis.

Magnetic Spin Ladder (C5H12N)2CuBr4: High Field Magnetization and Scaling Near Quantum Criticality

The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an effective XXZ chain. The data exhibit universal scaling behavior in the vicinity of H(c1) and H(c2), indicating that the system is near a quantum critical point.

Photoinduced Magnetism in Core/Shell Prussian Blue Analogue Heterostructures of KjNik[Cr(CN)6]l·nH2O with RbaCob[Fe(CN)6]c·mH2O

Core/shell and core/shell/shell particles comprised of the Prussian blue analogues K(j)Ni(k)[Cr(CN)(6)](l)·nH(2)O (A) and Rb(a)Co(b)[Fe(CN)(6)](c)·mH(2)O (B) have been prepared for the purpose of studying persistent photoinduced magnetization in the heterostructures. Synthetic procedures have been refined to allow controlled growth of relatively thick (50-100 nm) consecutive layers of the Prussian blue analogues while minimizing the mixing of materials at the interfaces. Through changes in the order in which the two components are added, particles with AB, ABA, BA, and BAB sequences have been prepared. The two Prussian blue analogues were chosen because B is photoswitchable, and A is ferromagnetic with a relatively high magnetic ordering temperature, ~70 K, although it is not known to exhibit photoinduced changes in its magnetic properties. Magnetization measurements on the heterostructured particles performed prior to irradiation show behavior characteristic of the individual components. On the other hand, after irradiation with visible light, the heterostructures undergo persistent photoinduced changes in magnetization associated with both the B and A analogues. The results suggest that structural changes in the photoactive B component distort the normally photoinactive A component, leading to a change in its magnetization.

Preparation, crystal structure and magnetic properties of Cu(en)2Pd(CN)4

The compound Cu(en) 2 Pd(CN) 4 was prepared and characterized. Its crystal structure is constructed of chains running along the body diagonal to the unit cell. The building elements are [Cu(en) 2 ] 2+ cations and square-planar [Pd(CN) 4 ] 2− anions, which are linked by the bridging μ 2 -CN − groups. These bridging cyano groups are in trans positions in the cation as well as in the anion. The axial CuN(C) coordination bonds are rather long (2.544(2) A). The chains are connected through weak hydrogen bonds of the type NH⋯N(C), thereby forming an infinite plane-like arrangement. Susceptibility and magnetization studies revealed the presence of a weak antiferromagnetic exchange coupling in the studied material.

Supersolid 4He: an overview of past searches and future possibilities

This paper reviews the theoretical and experimental work that has addressed the question of the possibility of Bose-Einstein condensation in solid 4He. Due to its expected superfluid-like properties, this state of matter is called a supersolid. To date, no unambiguous supersolid 4He state has been observed. Potential future extensions of the experiments are discussed.

Size dependence of the photoinduced magnetism and long-range ordering in Prussian blue analogue nanoparticles of rubidium cobalt hexacyanoferrate

Nanoparticles of rubidium cobalt hexacyanoferrate (RbjCok[Fe(CN)6]l?nH2O) were synthesized using different concentrations of polyvinylpyrrolidone (PVP) to produce four different batches of particles with characteristic diameters ranging from 3 to 13?nm. Upon illumination with white light at 5?K, the magnetization of these particles increases. The long-range ferrimagnetic ordering temperatures and the coercive fields evolve with nanoparticle size. At 2?K, particles with diameters less than approximately 10?nm provide a Curie-like magnetic signal.

High magnetic field induced changes of gene expression in arabidopsis

BackgroundHigh magnetic fields are becoming increasingly prevalent components of non-invasive, biomedical imaging tools (such as MRI), thus, an understanding of the molecular impacts associated with these field strengths in biological systems is of central importance. The biological impact of magnetic field strengths up to 30 Tesla were investigated in this study through the use of transgenic Arabidopsis plants engineered with a stress response gene consisting of the alcohol dehydrogenase (Adh) gene promoter driving the β-glucuronidase (GUS) gene reporter.MethodsMagnetic field induced Adh/GUS activity was evaluated with histochemical staining to assess tissue specific expression and distribution, and with quantitative, spectrofluometric assays to measure degree of activation. The evaluation of global changes in the Arabidopsis genome in response to exposure to high magnetic fields was facilitated with Affymetrix Gene Chip microarrays. Quantitative analyses of gene expression were performed with quantitative real-time polymerase-chain-reaction (qRT-PCR).ResultsField strengths in excess of about 15 Tesla induce expression of the Adh/GUS transgene in the roots and leaves. From the microarray analyses that surveyed 8000 genes, 114 genes were differentially expressed to a degree greater than 2.5 fold over the control. These results were quantitatively corroborated by qRT-PCR examination of 4 of the 114 genes.ConclusionThe data suggest that magnetic fields in excess of 15 Tesla have far-reaching effect on the genome. The wide-spread induction of stress-related genes and transcription factors, and a depression of genes associated with cell wall metabolism, are prominent examples. The roles of magnetic field orientation of macromolecules and magnetophoretic effects are discussed as possible factors that contribute to the mounting of this response.

Structural, thermal, and magnetic properties of three transition metal-4,4′-bipyridine coordination polymers: [Ni(4,4′-bipy)3(H2O)2](ClO4)2·1.4(4,4′-bipy)·3(H2O); [Co(4,4′-bipy)3(H2O)2](ClO4)2·1.4(4,4′-bipy)·3(H2O); [Cu(4,4′-bipy)3(DMSO)2](ClO4)2·2(4,4′-bipy)

Abstract Three new transition metal coordination polymers based on 4,4′-bipyridine (4,4′-bipy) are reported. The reaction of 1 equiv. of nickel(II) perchlorate hexahydrate or cobalt(II) perchlorate hexahydrate with 3 equiv. of 4,4′-bipy under inert atmosphere, hydrothermal conditions yields [Ni(4,4′-bipy)3(H2O)2](ClO4)2·1.4(4,4′-bipy)·3(H2O) (1) and the isostructural [Co(4,4′-bipy)3(H2O)2](ClO4)2·1.4(4,4′-bipy)·3(H2O) (2), respectively, while the combination of one equivalent of copper(II) perchlorate hexahydrate with three equivalents of 4,4′-bipy under ambient laboratory conditions in dimethyl sulfoxide produces the structurally related [Cu(4,4′-bipy)3(DMSO)2](ClO4)2·2(4,4′-bipy) (3). The metal:bipy molar ratio within the framework is 1:3 for each structure. Each sample consists of coordinate covalent metal-(4,4′-bipy) chains that pack through a combination of weaker hydrogen bonding and π-stacking interactions to form two-dimensional sheets. The sheets in turn pack to form three-dimensional structures with oblique channels that extend throughout the solid and contain enclathrated guest molecules. All three samples are susceptible to loss of enclathrated guest molecules. Magnetic data indicate that each sample behaves essentially Curie-like, with only small exchange coupling (J/kB

Thick film chip resistors as millikelvin thermometers

Abstract The results of thermal and magnetic studies of commercially available thick film chip resistors are reported. Resistors with room temperature values of 1 kΩ and 500 Ω have been investigated down to 30 mK, and the magnetoresistance of a 1 Ω resistor has been studied in fields up to 8 T. In addition, the heat capacity of the 1 Ω units has been measured, and these thermometers are being utilized in small-sample calorimeters.

Magneto-structural correlations in one-dimensional Ni(en)2Pd(CN)4: magnetic properties and redetermination of the crystal structure at two temperatures

Abstract The magneto-structural correlations in Ni(en)2Pd(CN)4 (NEPC) have been studied. The crystal structure is formed by infinite electroneutral 2,2-TT type chains [Ni(en)2NCPd(CN)2CN] (en=1,2-diaminoethane) in which the paramagnetic nickel atoms are bridged by diamagnetic tetracyanopalladate anions. Contrary to the previous room temperature X-ray analysis of NEPC, the results of the current structure determinations at both 293 and 150 K showed the nickel atom to be coordinated in the form of slightly elongated octahedron with two chelate bonded and disordered en molecules in the equatorial plane (mean NiN distance of 2.096 A at both temperatures) and N-bonded bridging cyano groups in the axial positions (NiN distances of 2.117 and 2.108 A at 293 and 150 K, respectively). Consequently, the zero field splitting parameter D is finite and positive. The chains are held together by weak hydrogen bonds of the NH⋯N(C) type. Magnetisation, susceptibility and specific heat measurements indicate that NEPC represents an S=1 Heisenberg magnetic chain characterised by strong planar anisotropy, D/kB≈5 K, weak in-plane anisotropy, E/D=0.1, and by a small exchange coupling constant, J/kB≈0.25 K. These properties are similar to those exhibited by an analogous compound Ni(en)2Ni(CN)4.