6,679 research outputs found
Electronic phase separation and the CMR effect in Pr1-xCaxMnO3 films on (001) vicinal SrTiO3 substrates
No full textOur previous work showed that Pr1-xCaxMnO3 (x=0.2-0.5) thin films reveal an electronic phase separation, in which the low-temperature phase is orbital- and charge-ordered of the Zener-polaron type [Ch. Jooss, T. Beetz, L. Wu, M. Beleggia, R. Klie, M. Schofield, Y. Zhu, S. Schramm, J. Hoffmann, submitted for publication]. Applying a magnetic field leads to a ferromagnetic and conducting phase, which gives rise to the colossal magneto resistance effect (CMR). In this article we show that the orbital- and charge-ordered state could be significantly modified by different kind of lattice defects. Quenched disorder, present after the film deposition, can suppress long-range ordering. In addition, extended defects like twin boundaries act as a nucleation center for ordered domains, i.e. the hysteretic properties depend on the density of these defects. Well-ordered artificial anti-phase boundaries (APB) can be introduced by an epitaxial growth on vicinal substrates, leading to anisotropic transport properties with respect to the orientation of the APB. (C) 2007 Elsevier B.V. All rights reserved
Straightforward field calculations for uniaxial hardmagnetic prisms: stray field distributions and dipolar coupling in regular arrays
No full textElements of hard- or moderately hardmagnetic materials may exhibit remanent states with a stable uniform magnetization distribution due to the high magnetocrystalline anisotropy energy. In this work, we present analytical calculations of magnetic field distributions arising from appropriate prismatic magnets and apply the results to the special case of hardmagnetic cuboids. The influence of the aspect ratio on the stray field distribution and its range is analysed. Based on these calculations a simple quasi-phase diagram for the emergence of dipolar coupling between individual elements with perpendicular easy axis in regular arrays is derived
Manipulating the dipolar magnetic interactions in FePt square arrays: The role of edge roughness
No full textThe high magnetocrystalline anisotropy energy in hard magnetic materials may sustain magnetization distributions in the remanent state, which exhibit a high number of magnetic surface charges and thus significant magnetic stray fields. Here, we focus onto the stray field distribution in the exterior and the demagnetization field distribution in the interior of hard magnetic FePt elements without and with artificial saw tooth edge roughness. Our experiments and calculations reveal that external stray fields and internal demagnetization fields are considerably modified by the artificial edge roughness
TACC3-ch-TOG track the growing tips of microtubules independently of clathrin and Aurora-A phosphorylation
Full text linkThe interaction between TACC3 (transforming acidic coiled coil protein 3) and the microtubule polymerase ch-TOG (colonic, hepatic tumor overexpressed gene) is evolutionarily conserved. Loading of TACC3–ch-TOG onto spindle microtubules requires the phosphorylation of TACC3 by Aurora-A kinase and the subsequent interaction of TACC3 with clathrin to form a microtubule binding surface. Whether there is a pool of TACC3–ch-TOG that is independent of clathrin in human cells, and what is the function of this pool, are open questions. Here, we report that TACC3 is recruited to the plus-ends of microtubules by its association with ch-TOG and that this pool is independent of phosphorylation and binding to clathrin. The plus-end binding of TACC3–ch-TOG persists in interphase and we propose that one cellular function of TACC3–ch-TOG is to modulate cell migration. We also describe the distinct subcellular pools of TACC3, ch-TOG and clathrin. TACC3 is often described as a centrosomal protein, but we show that there is no significant population of TACC3 at centrosomes. The delineation of distinct protein pools reveals a simplified view of how these proteins are organized and controlled by post-translational modification
Simultaneous determination of grain and grain-boundary critical currents in YBa2Cu3O7-coated conductors by magnetic measurements
No full textWe present a complete description of a noninvasive inductive methodology developed to study the magnetic granularity inherent in coated conductors. The method is based on the analysis of coated conductor hysteresis loops and enables us to identify the presence of electromagnetic granularity from the appearance of a peak in the return branch of the irreversible magnetization. Minor hysteresis loop cycles reveal the evolution of this peak and allow us to separate and analyze independently grain, grain-boundary critical current densities, and grain size of coated conductors. We have performed different tests to the developed model in order to validate the main assumptions considered and better understand the key factors involved
Magnetostatic interactions in patterned CoPt films embedded in a permalloy matrix
No full textIn order to study magnetostatic interactions in magnetic arrays, a two-dimensional pattern of hard magnetic (001) L1(0) CoPt squares embedded into a permalloy matrix was fabricated. The structural and magnetic properties of these arrays were characterized by magneto-optical measurements, atomic force and magnetic force microscopies. The hard magnetic squares are not exchange coupled to the soft magnet, yet a magnetostatic coupling was observed. This coupling modifies the domain structure of the permalloy matrix. In periodic arrays of embedded CoPt squares, the stray field interaction induces a long-range ordered domain pattern in the soft magnetic matrix and short-range correlations of edge domains in adjacent CoPt squares. (c) 2007 American Institute of Physics
Experimental confirmation of Zener-polaron-type charge and orbital ordering in Pr(1-x)Ca(x)MnO(3)
No full textPr(1-x)Ca(x)MnO(3) in the doping range between 0.3 < x < 0.5 represent an extremely interesting manganite system for the study of the interplay of different kinds of ordering (charge, orbital, lattice, and spin). While there is consensus that a charge- and orbital-ordered state develops below a transition temperature T(co)approximate to 230 K, recent controversial structural refinements resulting from neutron and x-ray diffraction studies challenged our understanding of the particular type of charge ordering (CO) and orbital ordering (OO), and consequently, the underlying mechanism of the colossal resistance effects. Here, we present a detailed high-resolution transmission electron microscopy and electron-diffraction study that, based on extinction rules, resolves the current controversy and confirms the existence of the Zener-polaron (ZP)-type CO and/or OO in Pr(1-x)Ca(x)MnO(3). The ZP-type ordering is further verified by atomic-column-resolved electron energy-loss spectroscopy revealing strong charge ordering of the in-plane oxygen-Mn bonds, while valence disproportionation at the Mn sites is less than expected. Over wide doping and temperature ranges, we observed structural phase coexistence between the ZP-CO/OO P2(1)nm and the disordered Pbnm structure
Determination of Zener-Polaron-Type Charge and Orbital Ordering in Pr1-xCaxMnO3 Manganite
No full textAchieving large acoustic and phonon band gaps in multilayered structures
No full textBand gaps in the vibrational spectrum of periodic multi layer structures offer excellent opportunities to control acoustic waves and phonons. Engineering the characteristics of the band gaps requires a careful selection of layer materials and thicknesses. This paper aims to develop general guidelines for material and geometry selection to maximize band gaps in the elastic wave spectrum of binary multilayer structures. We calculate band gaps for a wide range of layer thickness fractions and material properties using an analytical solution for plane wave propagation normal to the layers. The behavior of the maximum band gap and the midgap frequency is captured into empirical relations which allow optimal layer materials and thicknesses to be selected. Their use is demonstrated with specific promising material systems for oxide-based thermoelectric applications, which show the possibility of band gaps on the order of the midgap frequency. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimDFG [SPP-1386, SFB 1073
Reconstruction of the electric field in type-II superconducting thin films in perpendicular geometry
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