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SINGLE-MOLECULE-MAGNET (SMM) BEHAVIOUR IN URANIUM COMPOUNDS

G6 6

Uranium complexes are unique counterparts to the lanthanides in order to understand single ion magnet behaviour and possible applications in quantum computing and spintronics. Aiming at contributing to a better description of the magnetic ground state and to separating the role of uranium and the radical ligands in the SMM behaviour of these systems, different approaches using spectroscopic (FIR and HF-EPR) and theoretical investigations have been employed. An X-ray magnetic circular dichroism (XMCD) study at ESRF beamline ID12 was performed for six uranium compounds, 3 based on hydrotris (3,5-dimethylpyrazolyl)borate (TpMe2) and other 3 based on trisamido-1,4,7-triazacyclononane [(SiMe2NPh)3-tacn]. Low temperature experiments at the M4,5-edge of uranium made possible to test and confirm the existing magnetic results and successfully deducing the spin and the orbital magnetic moment carried by the U-5f states. This separation of contribution is of paramount importance to understand the SMM behaviour of these compounds.

NEW THERMOELECTRIC MATERIALS

G6 10

The substitution of Te for Se was explored in the well-studied α-As2Te3 in order to study the changes in the electronic band structure and thermoelectric properties. The electrical resistivity and thermopower gradually increase with Se due to the progressive increase in the band gap. Se substitution further lowers the lattice contribution to thermal conductivity reaching 0.35 W m−1K−1 above 300 K in α- As2Te1.5Se1.5. Unfortunately Se substitution does not enable achieving higher thermoelectric performances in comparison to substitutions of Sn and Bi for As. Several compositions in the Cu-As-Te glassy system were prepared by melt quenching followed by SPS. The electrical transport properties of CuxAs55-xTe45, Cu15As85-yTey and Cu20As80-yTey compositions were probed, displaying high electrical resistivity (>10-2 Ωm) and high thermopower (>500 µVK-1), as typically observed in chalcogenide glasses. Although the thermal conductivities measured are low (<0.3 Wm-1K-1), ZT values remain below 0.1, mainly due to the too high electrical resistivity.

SPALLATION TARGETS

G6 9

The ISOL method is an efficient way to produce radioisotope ion beams of good quality. In this technique, a high-energy beam (e.g., protons) hits a target to produce the radioisotopes of interest through different nuclear reactions. However, the radioisotopes must be quickly released from the target, which can be done by optimisation of the target microstructure and increasing temperature. Uranium carbide is among the best target materials due to its high temperature stability and good thermal conductivity. Aiming at increasing the release rates, nanostructured materials are being tested. In this context, YCx nanofibers were prepared by electrospinning and studied the effects of the solution characteristics and electrospinning process parameters on the as-spun materials. It was concluded that the slowly heating (1oC/ min) of fibers up to 600oC is of fundamental importance to keep the fiber morphology upon polymer decomposition.

MÖSSBAUER SPECTROSCOPY

G6 7

Mössbauer spectroscopy has been extensively used as sensitive tool to determine oxidation state, coordination geometry and ordering of magnetic moments of iron in a variety of materials. In the specific case of a photoresponsive molecular polyanion prepared and characterized by Instituto de Ciencia Molecular (University of Valencia), Fe Mössbauer spectroscopy clearly showed that Fe(III) was reduced upon irradiation with UV light. The K salt of this material, in which two Fe(III) ions are simultaneously coordinated by two [A-α-PW9O34]9- polyoxometalate units and two oxalato ligands, when irradiated with UV light, exhibits a remarkable photocoloration effect due to the partial reduction of the POM units to give rise to a mixed-valence species. The process is reversible when UV light is switched off. The spectra show the material before (a) after irradiation (b), 24 h (c) and 5 days (d), after UV light switch off.

MAGNETISM AND STRONGLY CORRELATED ELECTRON BEHAVIOR IN INTERMETALLICS

G6 8

The study of magnetism and strongly correlated electron behaviour in intermetallic systems containing f-elements has been a continuing topic of research in the Solid State group. In this context, a novel ternary compound, UMo3B7, has been synthesized and characterized. It crystallizes in the YMo3B7-type structure, which exhibits a well-developed two-dimensional boron network and is composed of boron filled trigonal prisms as well as unfilled tetrahedra and tetragonal pyramids formed by metal atoms. Specific heat, magnetic susceptibility and electrical resistivity studies point to the inexistence of long-range magnetic order above 500 mK in UMo3B7. Rather, a spin fluctuation scenario characterizes the low temperature behavior of resistivity, magnetic susceptibility and specific heat of this compound, resulting in a moderately enlarged Sommerfeld value of g = 28 mJ/(molK2).  

IRON OXIDE NANOPARTICLES FOR HIPERTHERMIA

G6 5

Iron oxide nanoparticles (Fe3O4, SPIONs) are promising candidates for several biomedical applications such as magnetic hyperthermia and as contrast agents for magnetic resonance imaging (MRI). Organic incorporation in liposomes (magnetoliposomes) and inorganic encapsulation with silica are interesting possibilities. However, their colloidal stability in physiological conditions hinders their application requiring the use of biocompatible surfactant agents. Aiming at the design and development of new nanoparticles for enhanced theranostic techniques, namely for magnetic resonance imaging and for directed drug delivery, silica-based matrices were prepared and decorated with SPIONs . Good saturation of magnetization values for the specific size and morphology of the synthesized SPIONs were achieved for samples dried in vacuum at RT (∼64 emu/g), comparable with the literature results (∼60 emu/g). These results contribute to achieve a compromise between the use of oleic acid as a stabilizer of iron oxide colloids and its influence on their biomedical application.

  1. ER MAGNETIC AND LUMINESCENT COMPOUNDS
  2. CNB-EDT-TTF SALTS WITH CLO4; BILAYER POLYMORPHS AND DIFFERENT STOICHIOMETRIES
  3. NEW SINGLE COMPONENT MOLECULAR CONDUCTORS
  4. TWO CHAIN CONDUCTING AND MAGNETIC COMPOUNDS