83 research outputs found

    Angular dependent vortex dynamics in superconductors with columnar defects

    Full text link
    We explore in detail the angular dependent vortex dynamics in type II superconductors with aligned columnar defects introduced by irradiation with very energetic heavy-ions. We use dc magnetization measurements deep in the vortex solid phase, and ac susceptibility near the solid-liquid transition. We show that aligned columnar defects are an excellent tool to test models for vortex dynamics, particularly if they are tilted with respect to the crystallographic axes, so their effects can be easily distinguished from those arising from mass anisotropy, sample geometry, twin boundaries and intrinsic pinning. This allows us, for instance, to use the uniaxial pinning of the columnar defects as a probe to determine the orientation of the vortices inside a bulk material, which in general is different from the orientation of the applied fields. In some aspects we have found an excellent agreement with the theoretical expectations of the Bose-glass model. The field dependence of the lock-in angle follows remarkably well the 1/H prediction over the whole temperature range of our measurements. In turn, the temperature dependence of the lock-in angle gives strong support to the concept of an effective pinning energy dominated by the entropic smearing effect. On the other hand, both our ac and dc results show that columnar defects produce effective pinning over a wide angular range, and that correlated pinning dominates the scenario for all field orientations. One consequence of this is the existence of a rich variety of vortex staircases.Comment: to be published in International Book series "Studies of High Temperature Superconductors", edited by Anant Narlikar, Nova Science Publishers, New York, Vol 49/50, (2003

    Statistical domain wall roughness analysis through correlations

    Get PDF
    The geometry and morphology of magnetic domain walls (DWs) are closely related to their dynamics when driven by external forces. Under some reliable approximations DWs can be considered self-affine interfaces, so universal laws govern their behavior. On the other hand, large-scale DW structure has been less explored so far. Recently, it has been shown that bubble-like magnetic domains can be strongly deformed on a large scale by applying alternating (ac) magnetic field pulses. In the present paper, we conduct a comprehensive analysis of DW structure at both small and large length scales in bubble-like domains present in ferromagnetic thin films with perpendicular anisotropy, focusing on its initial evolution under the application of ac magnetic pulses. Results obtained from the widely used roughness correlation function B(r) and its corresponding structure factor, are consistent with those obtained from the spatial autocorrelation function of DW fluctuations. Whereas the roughness exponent slightly increases during the ac evolution, a strong deformation is observed at a large scale, where a striking periodicity (statistically speaking) is observed. This period is probably determined by the boundary conditions and a characteristic intrinsic length.Fil: Domenichini, Pablo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; ArgentinaFil: Pasquini, Gabriela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Capeluto, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin

    Vortex dynamics in single crystals with columnar defects near the glass transition

    Get PDF
    En este trabajo investigamos la dinámica del sistema de vórtices en cristalessuperconductores de YBa2Cu3O7 con defectos columnares, a campos magnéticosbajos, en la región cercana a la transición vidrio-líquido. Intodujimos los defectos columnares por irradiación con iones pesados dealta energía en el acelerador TANDAR. La mayor parte de las mediciones fueron realizadas con la técnica desusceptibilidad alterna. Desarrollamos una serie de métodos novedosos parala interpretación de las curvas de susceptibilidad y su relación con el sistemade vórtices subyacente. Esto nos permitió construir un Diagrama Dinámico experimental cuantitativoen el plano (ha, T), en donde identificamos los distintos regímenesdinámicos y las regiones de transición entre los mismos. Pudimos extraerparámetros característicos de los potenciales de anclaje como la constante de Labusch y las energías de activación térmica. Investigamos la dependencia de la respuesta alterna con la orientacióndel campo continuo. Comparando estos resultados con los que obtuvimos enmuestras sin irradiar, identificamos los centros de anclaje preponderantes encada región angular. Haciendo un estudio detallado a diferentes ángulos, analizamos cómo semodifica el Diagrama Dinámico cuando el campo está inclinado respecto delos defectos. Por último, complementamos el estudio de la dependencia angular conmediciones de transporte en la región del líquido de vórtices. Con ambastécnicas, comprobamos que los defectos columnares siguen actuando comocentros de anclaje correlacionados hasta ángulos muy alejados de los defectos. Para los campos utilizados, el anclaje sigue siendo efectivo hasta que elmaterial llega al estado normal: no existe una región en el líquido de vorticesdonde la respuesta sea puramente óhmica.We studied the behavior of vortex dynamics in single crystals of YBa2Cu3O7with columnar defects, at low DC magnetic fields near the glass transition. The columnar defects were introduced by high energy heavy ion irradiationat the TANDAR accelerator. Most of the results were obtained by ac. susceptibility measurements. Wedeveloped some novel techniques for the analysis and interpretation of thedata and their relationship with the underlying vortex system. Through this analysis we were able to build up an experimental quantitative Dynamic Diagram in the (ha, T) plane, where we could identifydifferent dynamical regimes and the transition regions between them. Wecould extract the characteristic parameters of the pinning potentials, such asthe Labusch constant and the thermal activation energies. We studied the ac. response dependence on the direction of the DCfield. Through the comparison of the results obtained in irradiated andunirradiated samples, we could identify the main source of vortex pinningin different angular regions. Through a careful angular study, we analysed changes induced in the Dynamical Diagram by the relative orientation of the field and defects, For the sake of completeness we performed some transport measurementsof the angular dependence of the response in the liquid region of the phasediagram. With both techniques we confirm that columnar defects act ascorrelated pinning up to angles far away from the tracks. In the low field region studied, we found that pinning is effective up to thenormal state of the material: a region of pure ohmic response in the vortexliquid does not exist.Fil: Pasquini, Gabriela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

    Alternate-current dynamic reorganization and nonequilibrium phase transition in driven vortex matter

    Get PDF
    Externally driven glassy systems may undergo nonequilibrium phase (NEPTs). In particular, ac-driven systems display special features, such as those observed in the vortex matter of NbSe2, where oscillatory drives reorganize the system into partially ordered vortex lattices. We provide experimental evidence for this dynamic reorganization and we show an unambiguous signature of its connection with an NEPT driven by ac forces. We perform a scaling analysis and we estimate critical exponents for this transition. Our results share similarities with some glass-to-viscous-liquid NEPTs and invite a search for similar physics in other elastic disordered media.Fil: Marziali Bermudez, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; ArgentinaFil: Cugliandolo, L.F.. Université Pierre et Marie Curie; FranciaFil: Pasquini, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

    Neural and oligodendrocyte progenitor cells: transferrin effects on cell proliferation

    Get PDF
    NSC (neural stem cells)/NPC (neural progenitor cells) are multipotent and self-renew throughout adulthood in the SVZ (subventricular zone) of the mammalian CNS (central nervous system). These cells are considered interesting targets for CNS neurodegenerative disorder cell therapies, and understanding their behaviour in vitro is crucial if they are to be cultured prior to transplantation. We cultured the SVZ tissue belonging to newborn rats under the form of NS (neurospheres) to evaluate the effects of Tf (transferrin) on cell proliferation. The NS were heterogeneous in terms of the NSC/NPC markers GFAP (glial fibrillary acidic protein), Nestin and Sox2 and the OL (oligodendrocyte) progenitor markers NG2 (nerve/glia antigen 2) and PDGFRα (platelet-derived growth factor receptor α). The results of this study indicate that aTf (apoTransferrin) is able to increase cell proliferation of SVZ-derived cells in vitro, and that these effects were mediated at least in part by the TfRc1 (Tf receptor 1). Since OPCs (oligodendrocyte progenitor cells) represent a significant proportion of the proliferating cells in the SVZ-derived primary cultures, we used the immature OL cell line N20.1 to show that Tf was able to augment the proliferation rate of OPC, either by adding aTf to the culture medium or by overexpressing rat Tf in situ. The culture medium supplemented with ferric iron, together with aTf, increased the DNA content, while ferrous iron did not. The present work provides data that could have a potential application in human cell replacement therapies for neurodegenerative disease and/or CNS injury that require the use of in vitro amplified NPCs.Fil: Silvestroff, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquimica. Departamento de Quimica Biologica. Cátedra de Química Biológica Patológica; ArgentinaFil: Franco, Paula Gabriela. Universidad de Buenos Aires. Facultad de Farmacia y Bioquimica. Departamento de Quimica Biologica. Cátedra de Química Biológica Patológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; ArgentinaFil: Pasquini, Juana Maria. Universidad de Buenos Aires. Facultad de Farmacia y Bioquimica. Departamento de Quimica Biologica. Cátedra de Química Biológica Patológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; Argentin

    ApoTransferrin: Dual Role on Adult Subventricular Zone-Derived Neurospheres

    Get PDF
    Neural stem and progenitor cells (NSC/NPCs) are multipotent self-renewing cells that are able to generate neurons, astrocytes and oligodendrocytes (OLs) within the adult central nervous system. We cultured NSC/NPCs from the rat subventricular zone as neurospheres (NS) and studied apoTransferrin (aTf) effects on oligodendroglial specification and maturation. Our findings suggest that aTf acts at different stages during progression from NSC to mature oligodendrocytes. On the one hand, an early event associated with the activation of NSC/NPCs proliferation and commitment toward the oligodendroglial fate, as indicated by increased BrdU incorporation, larger neurospheres production, and higher ability to generate OL precursors (OPCs) from undifferentiated cultures. On the other hand, aTf exposure during differentiating conditions favours OL maturation from OPCs by promoting OL morphological development. This evidence supports a key role of Tf on the generation of OL from NSC/NPCs and highlights its potential in demyelinating disorder treatment

    Factores y Processos de Formacion de Suelos en el Piedemonte Oriental de la Sierra Chica, Cordoba, Republica Argentina

    Get PDF
    This contribution deals with the characteristics and distribution of soils developed over six landscape units in a sector of the eastern Sierra Chica piedmont (Córdoba, Argentina). The relationship between environmental factors and pedogenetic processes have been examined. The area exhibits a significant soil variability as a consequence of geomorphic and lithologic diversity, inherent to this environment. Parental material, relief, and climate have shown influence over soil development and the differentiation of horizons. They control, as well, the intensity of melanization, decalcification-calcification and eluviation-illuviation of clays and organic matter. The most developed soils are derived from loess, loess-like and fine alluvial sediments. These soils are found in areas of intermediate to low relief, concave and flat surfaces, and long-smooth slopes. Fluvial and coarse alluvial sediments are the parental material of less developed soils, which are characteristic of reliefs dominated by rolling shapes and steep slopes.

    Carbon nanotubes effects on the relaxation properties and critical current densities of MgB2 superconductor

    Get PDF
    Addition of nonsuperconducting phases, such as carbon nanotubes, can modify the superconducting properties of MgB2 samples, improving the critical current density and upper critical field. A full understanding of the flux creep mechanism involved is crucial to the development of superconducting magnets in persistent mode, one of the main thrusts for the development of MgB2 wires. In this paper we present a creep study in bulk MgB2 samples, pure and with different amounts of carbon nanotubes additions. We conclude that the most consistent picture at low temperatures is a single vortex pinning regime, where the correlation length is limited by the grain size. We introduce a novel analysis that allows us to identify the region where the Anderson-Kim model is validFil: Pasquini, Gabriela. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales; Argentina;Fil: Serquis, Adriana Cristina. Comision Nacional de Energia Atomica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina;Fil: Moreno, Alejandro Javier. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales; Argentina;Fil: Serrano, German Dario. Comision Nacional de Energia Atomica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Patagonia Norte; Argentina;Fil: L. Civale. Los Alamos National Laboratory, Estados Unidos de América

    Curvature-driven ac-assisted creep dynamics of magnetic domain walls

    Get PDF
    The dynamics of micrometer-sized magnetic domains in ultrathin ferromagnetic films is so dramatically slowed down by quenched disorder that the spontaneous elastic tension collapse becomes unobservable at ambient temperature. By magneto-optical imaging we show that a weak zero-bias ac magnetic field can assist such curvature-driven collapse, making the area of a bubble to reduce at a measurable rate, in spite of the negligible effect that the same curvature has on the average creep motion driven by a comparable dc field. An analytical model explains this phenomenon quantitatively.Fil: Domenichini, Pablo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Paris, F.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Capeluto, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Granada, Mara. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; ArgentinaFil: George, J. M.. Université Paris Sud; FranciaFil: Pasquini, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Kolton, Alejandro Benedykt. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentin
    corecore