http://www.recercat.cat:80/handle/2072/48860 www.ub.edu Wed, 19 Jun 2013 19:19:21 GMT 2013-06-19T19:19:21Z http://www.recercat.cat:80/bitstream/id/26444/ http://www.recercat.cat:80/handle/2072/48860 http://www.recercat.cat:80/handle/2072/206210 Sintesi i caracteritzacio dels materials multiferroics BiFeO3, La: BiFeO3 i Sr: BiFeO3 Vendrell, Xavier; Mestres i Vila, Ma. Lourdes Recentment, ha crescut un notable interès pels materials multiferroics (o materials que presenten simultàniament propietats elèctriques i magnètiques), a causa de les seves múltiples aplicacions, sobretot en el camp de l"electrònica. Aquest article pretén donar a conèixer els materials multiferroics, tant des del punt de vista de la física fonamental com de la química de l"estat sòlid. Tanmateix, es presentarà un dels materials multiferroics actualment més estudiats i s"exposaran els detalls de la seva síntesi i caracterització habituals en la química de l"estat sòlid. http://www.recercat.cat:80/handle/2072/206210 http://www.recercat.cat:80/handle/2072/206209 Highly textured Sr, Nb, co-doped BiFeO3 thin films grown on SrRuO3/Si substrates by rf-sputtering Ostos, C.; Raymond, O.; Suarez-Almodovar, N.; Bueno-Baqués, D.; Mestres i Vila, Ma. Lourdes; Siqueiros, J. M. In this study, (011)-highly oriented Sr, Nb co-doped BiFeO3 (BFO) thin films were successfully grown on SrRuO3/Si substrates by rf-magnetron sputtering. The presence of parasite magnetic phases was ruled out based on the high resolution x-ray diffraction data. BFO films exhibited a columnar-like grain growth with rms surface roughness values of 5.3 nm and average grain sizes of 65&br&70 nm for samples with different thicknesses. Remanent polarization values (2Pr) of 54 lC cm 2 at room temperature were found for the BFO films with a ferroelectric behavior characteristic of an asymmetric device structure. Analysis of the leakage mechanisms for this structure in negative bias suggests Schottky injection and a dominant Poole-Frenkel trap-limited conduction at room temperature. Oxygen vacancies and Fe3þ/Fe2þ trap centers are consistent with the surface chemical bonding states analysis from x-ray photoelectron spectroscopy data. The (011)-BFO/ SrRuO3/Si film structure exhibits a strong magnetic interaction at the interface between the multiferroic film and the substrate layer where an enhanced ferromagnetic response at 5 K was observed. Zero-field cooled (ZFC) and field cooled (FC) magnetization curves of this film system revealed a possible spin glass behavior at spin freezing temperatures below 30 K depending on the BFO film thickness. http://www.recercat.cat:80/handle/2072/206209 http://www.recercat.cat:80/handle/2072/205134 Complexes of Pd(II) and Pt(II) with 9-aminoacridine: reactions with DNA and study of their antiproliferative activity Riera, X.; Moreno Martínez, Virtudes; Ciudad i Gómez, Carlos Julián; Noé Mata, Verónica; Font Bardia, Ma. Mercedes; Solans, Xavier, 1949-2007 Four new metal complexes {M = Pd(II) or Pt(II)} containing the ligand 9-aminoacridine (9AA) were prepared. The compounds were characterized by FT-IR and 1H, 13C, and 195Pt NMR spectroscopies. Crystal structure of the palladium complex of formulae [Pd(9AA)(μ-Cl)]2 · 2DMF was determined by X-ray diffraction. Two 9-acridine molecules in the imine form bind symmetrically to the metal ions in a bidentate fashion through the imine nitrogen atom and the C(1) atom of the aminoacridine closing a new five-membered ring. By reaction with phosphine or pyridine, the Cl bridges broke and compounds with general formulae [Pd(9AA)Cl(L)] (where L = PPh3 or py) were formed. A mononuclear complex of platinum of formulae [Pt(9AA)Cl(DMSO)] was also obtained by direct reaction of 9-aminoacridine and the complex [PtCl2(DMSO)2]. The capacity of the compounds to modify the secondary and tertiary structures of DNA was evaluated by means of circular dichroism and electrophoretic mobility. Both palladium and platinum compounds proved active in the modification of both the secondary and tertiary DNA structures. AFM images showed noticeable modifications of the morphology of the plasmid pBR322 DNA by the compounds probably due to the intercalation of the complexes between base pairs of the DNA molecule. Finally, the palladium complex was tested for antiproliferative activity against three different human tumor cell lines. The results suggest that the palladium complex of formula [Pd(9AA)(μ-Cl)]2 has significant antiproliferative activity, although it is less active than cisplatin. http://www.recercat.cat:80/handle/2072/205134 http://www.recercat.cat:80/handle/2072/200683 Optimización de un nuevo método de preparación de óxidos mixtos tipo perovskita con vacantes de oxígeno. Mestres i Vila, Ma. Lourdes; Martínez Sarrión, María Luisa; Lepe, F.J. Se han optimizado las condiciones para la deslitiación de compuestos de fórmula general La2/3-xLi3xTiO3 así como las de la posterior termólisis de compuestos de fórmula general La2/3-xTiO3-3x(OH)3x. En ambos procesos se mantiene la estructura perovskita cúbica Pm3m. Estudios preliminares de conductividad eléctrica indican que los compuestos La2/3-xTiO3-3x/2 obtenidos mediante química suave a partir de la perovskita de lantano y litio se comportan como semiconductores. http://www.recercat.cat:80/handle/2072/200683 http://www.recercat.cat:80/handle/2072/195815 Molecular prototypes for spin-based CNOT and SWAP quantum gates Aromí Bedmar, Guillem; Repollés Rabinad, Ana; Martínez-Pérez, María José; Aguilà Aviles, David; Roubeau, Olivier; Zueco, David; Alonso Gascón, Pablo Javier; Evangelisti, Marco; Camón Lasheras, Agustín; Sesé Monclús, Javier; Barrios Moreno, Leoni Alejandra; Luis Vitalla, Fernando We show that a chemically engineered structural asymmetry in [Tb2] molecular clusters renders the two weakly coupled Tb3+ spin qubits magnetically inequivalent. The magnetic energy level spectrum of these molecules meets then all conditions needed to realize a universal CNOT quantum gate. A proposal to realize a SWAP gate within the same molecule is also discussed. Electronic paramagnetic resonance experiments confirm that CNOT and SWAP transitions are not forbidden. http://www.recercat.cat:80/handle/2072/195815 http://www.recercat.cat:80/handle/2072/184069 Quantum energy gap in two quasi-one-dimensional S=1 Heisenberg antiferromagnets Renard, J. P.; Verdaguer, Michel; Regnault, L. P.; Erkelens, W. A. C.; Rossat-Mignod, J.; Ribas Gispert, Joan; Stirling, W. G.; Vettier, C. http://www.recercat.cat:80/handle/2072/184069 http://www.recercat.cat:80/handle/2072/182395 Applications of optically active metallacycles: new useful materials for the determination of the enantiomeric excess of Lewis bases and as resolving agents for monodentate phosphines Granell Sanvicente, Jaime Ramón; Müller Jevenois, Guillermo Es descriu la síntesi de nous compostos ciclopal·ladats derivats d'imines i amines primàries, òpticament actius, així com les seves aplicacions per a la determinació de l'excés enantiomèric i per a la resolució de bases de Lewis. També es comenta la síntesi i resolució de noves fosfines P-quirals, així com la seva aplicació a processos de catàlisi asimètrica. A més, es descriu la preparació d'algunes fosfines secundàries quirals i s'estudia la seva estabilitat configuracional. http://www.recercat.cat:80/handle/2072/182395 http://www.recercat.cat:80/handle/2072/182394 Low-dimensional polynuclear complexes and high-spin molecules: towards molecules magnets Ribas Gispert, Joan http://www.recercat.cat:80/handle/2072/182394 http://www.recercat.cat:80/handle/2072/172715 A first-principles analysis of the magnetism of CuII polynuclear coordination complexes: the case of [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5H2O Deumal i Solé, Mercè; Ribas Ariño, Jordi; Robb, Michael A.; Ribas Gispert, Joan; Novoa Vide, Juan J. The magnetic structure of the [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5 H2Ocrystal - using fractional coordinates determined at room-temperature ¿ has beenanalysed in detail. This analysis has been carried out by extending our first principlesbottom-up theoretical approach, which was initially designed to study through-spacemagnetic interactions, to handle through-bond magnetic interactions. The only input datarequired by this approach are the values of the computed JAB exchange parameters for allthe unique pairs of spin-containing centres. The results allow the magnetic structure ofthe crystal, which presents two types of isolated tetranuclear CuII clusters, to be definedin quantitative terms. Each of these clusters presents ferro and antiferromagneticinteractions, the former being stronger, although outnumbered by the latter. Thecomputed magnetic susceptibility curve shows the same qualitative features as theexperimental data. However, there are small differences that are presumed to beassociated with the use of room-temperature crystal coordinates. http://www.recercat.cat:80/handle/2072/172715 http://www.recercat.cat:80/handle/2072/67251 Magnetic long-range order induced by quantum ralaxation in single-molecule magnets Evangelisti, M.; Luis, F.; Mettes, F. L.; Aliaga-Alcaide, Núria; Aromí Bedmar, Guillem; Alonso, J. J.; Christou, G.; Jongh, L. J. de Can magnetic interactions between single-molecule magnets (SMMs) in a crystal establish long-range magnetic order at low temperatures deep in the quantum regime, where the only electron spin fluctuations are due to incoherent magnetic quantum tunneling (MQT)? Put inversely: can MQT provide the temperature dependent fluctuations needed to destroy the ordered state above some finite Tc, although it should basically itself be a T-independent process? Our experiments on two novel Mn4 SMMs provide a positive answer to the above, showing at the same time that MQT in the SMMs has to involve spin-lattice coupling at a relaxation rate equaling that predicted and observed recently for nuclear-spin-mediated quantum relaxation. http://www.recercat.cat:80/handle/2072/67251 http://www.recercat.cat:80/handle/2072/67250 Long-range ferromagnetic dipolar ordering of high-spin molecular clusters Morello, A.; Mettes, F. L.; Luis, F.; Fernández, J. F.; Krzystek, J.; Aromí Bedmar, Guillem; Christou, G.; Jongh, L. J. de We report the first example of a transition to long-range magnetic order in a purely dipolarly interacting molecular magnet. For the magnetic cluster compound Mn6O4Br4(Et2dbm)6, the anisotropy experienced by the total spin S=12 of each cluster is so small that spin-lattice relaxation remains fast down to the lowest temperatures, thus enabling dipolar order to occur within experimental times at Tc=0.16 K. In high magnetic fields, the relaxation rate becomes drastically reduced and the interplay between nuclear- and electron-spin lattice relaxation is revealed. http://www.recercat.cat:80/handle/2072/67250 http://www.recercat.cat:80/handle/2072/63232 Fluctuation-dominated kinetics under stirring Reigada Sanz, Ramon; Sagués i Mestre, Francesc; Sokolov, Igor M., 1958-; Sancho, José M.; Blumen, Alexander http://www.recercat.cat:80/handle/2072/63232 http://www.recercat.cat:80/handle/2072/49575 Theoretical approach to the magnetostructural correlations in spin-Peierls compound CuGeO3 Ruiz Sabín, Eliseo; Cano Boquera, Joan; Álvarez, Santiago (Álvarez Reverter); Alemany i Cahner, Pere; Verdaguer, Michel A theoretical density-functional study has been carried out to analyze the exchange coupling in the chains of CuGeO3 using discrete models. The results show a good agreement with the experimental exchange coupling constant (J) together with a strong dependence of J with the Cu-O-Cu angle. The calculation of the J values for a distorted model indicates a larger degree of dimerization than those reported previously. http://www.recercat.cat:80/handle/2072/49575 http://www.recercat.cat:80/handle/2072/49574 Electronic structure and bonding in skutterudite-type phosphides Llunell Marí, Miquel; Alemany i Cahner, Pere; Álvarez, Santiago (Álvarez Reverter); Zhukov, Vladlen P.; Vernes, Andreas http://www.recercat.cat:80/handle/2072/49574 http://www.recercat.cat:80/handle/2072/49573 Magnetic dipolar ordering and relaxation in the high-spin molecular cluster compound Mn6 Morello, A.; Mettes, F. L.; Bakharev, O. N.; Brom, H. B.; Jongh, L. J. de; Luis, F.; Fernández, J. F.; Aromí Bedmar, Guillem http://www.recercat.cat:80/handle/2072/49573 http://www.recercat.cat:80/handle/2072/49572 Structural and electronic properties of the one-dimensional organic metal bis(thiodimethylene)-tetrathiafulvalene tetracyanoquinodimethane Rovira, Carme; Tarrés, J.; Llorca, J.; Molins i Grau, Elies; Veciana, J.; Yang, S.; Cowan, D. O.; Garrigou-Lagrange, C.; Amiell, J.; Delhaes, Pierre; Canadell, Enric, 1950-; Pouget, J. P. http://www.recercat.cat:80/handle/2072/49572 http://www.recercat.cat:80/handle/2072/49571 Electronic structure and properties of AlN Ruiz Sabín, Eliseo; Álvarez, Santiago (Álvarez Reverter); Alemany i Cahner, Pere The electronic structure of the wurtzite-type phase of aluminum nitride has been investigated by means of periodic ab initio Hartree-Fock calculations. The binding energy, lattice parameters (a,c), and the internal coordinate (u) have been calculated. All structural parameters are in excellent agreement with the experimental data. The electronic structure and bonding in AlN are analyzed by means of density-of-states projections and electron-density maps. The calculated values of the bulk modulus, its pressure derivative, the optical-phonon frequencies at the center of the Brillouin zone, and the full set of elastic constants are in good agreement with the experimental data. http://www.recercat.cat:80/handle/2072/49571