324 research outputs found

    Substrate surface engineering for tailoring properties of functional ceramic thin films

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    Using oxide substrates for functional ceramic thin film deposition beyond their usual application as chemical inert, lattice-matched support for the films represents a novel concept in ceramic thin film research. The substrates are applied as a functional element in order to controllably modify the atom arrangement and the growth mode of ceramic prototype materials such as cuprate superconductors and colossal magnetoresistance manganites. One example is the use of epitaxial strain to adjust the relative positions of cations and anions in the film and thus modify their physical properties. The other makes use of vicinal cut SrTiO3 which enables the fabrication of regular nanoscale step and terrace structures. In YBa2Cu3O7-x thin films grown on vicinal cut SrTiO3 single crystals a regular array of antiphase boundaries is generated causing an anisotropic enhancement of flux-line pinning. In the case of La-Ca-Mn-O thin films grown on vicinal cut substrates it could be demonstrated that magnetic in-plane anisotropy is achieved.Comment: 6 page

    On Magnetic Interlayer Coupling and Proximity Effect in a La0.67_{0.67}Ca0.33_{0.33}MnO3_3(10 nm)/YBa2_2Cu3_3O7_7(10 nm) Superlattice

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    We present a study of interlayer coupling and proximity effects in a La0.66_{0.66}Ca0.33_{0.33}MnO3_3(10 nm)/YBa2_2Cu3_3O7_7(10 nm) superlattice. Using element-sensitive x-ray probes, the magnetic state of Mn can be probed without seeing the strong diamagnetism of the superconductor, which makes this approach ideal to study changes in the magnetic properties across the superconducting transition. By a combined experiment using {\it in situ} transport measurements during polarized soft x-ray measurements, we were able to see no noticeable influence of the superconducting state on the magnetic properties and no evidence for magnetic coupling across a 10 nm YBCO layer.Comment: 4 pages, submitted to Applied Physics Letter

    A study of the ferromagnetic transition of SrRuO3SrRuO_3 in nanometer thick bilayers with YBa2Cu3OyYBa_2Cu_3O_y, La1.88Sr0.12CuO4βˆ’yLa_{1.88}Sr_{0.12}CuO_{4-y}, Au and Cr: Signature of injected carriers in the pseudogap regime

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    The hypothesis regarding the existence of uncorrelated pre-formed pairs in the pseudogap regime of superconducting YBa2Cu3OyYBa_2Cu_3O_y is tested experimentally using bilayers of YBa2Cu3OyYBa_2Cu_3O_y and the itinerant ferromagnet SrRuO3SrRuO_3. In our study, we monitor the influence of YBa2Cu3OyYBa_2Cu_3O_y on TpT_p, the ferromagnetic ordering temperature of SrRuO3SrRuO_3. Here, TpT_p is the temperature of maximum dM/dT or dR/dT where M and R are the magnetization and resistance of SrRuO3SrRuO_3, respectively. We compare the results with similar measurements carried out on bilayers of La1.88Sr0.12CuO4βˆ’yLa_{1.88}Sr_{0.12}CuO_{4-y}, AuAu and CrCr with SrRuO3SrRuO_3. We find that in bilayers made of underdoped 10 nm YBa2Cu3OyYBa_2Cu_3O_y/5 nm SrRuO3SrRuO_3, the TpT_p values are shifted to lower temperatures by up to 6-8 K as compared to Tpβ‰ˆ140T_p\approx 140 K of the 5 nm thick reference SrRuO3SrRuO_3 film. In contrast, in the other type of bilayers, which are not in the pseudogap regime near TpT_p, only a smaller shift of up to Β±\pm2 K is observed. These differences are discussed in terms of a proximity effect, where carriers from the YBa2Cu3OyYBa_2Cu_3O_y layer are injected into the SrRuO3SrRuO_3 layer and vice versa. We suggest that correlated electrons in the pseudogap regime of YBa2Cu3OyYBa_2Cu_3O_y are responsible for the observed large TpT_p shifts.Comment: 9 figure

    Suppression of Superconductivity in YBCO/LCMO Superlattices

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    The competition of superconductivity and magnetism in superlattices composed of alternating YBa2_2Cu3_3O7βˆ’d_{7-d} and La0.67_{0.67}Ca0.33_{0.33}MnO3_{3} thin films is investigated using low-energy optical spectroscopy. The thickness of the superconducting YBCO layers is varied from 30 nm to 20 nm while the thickness of the magnetic LCMO layers is kept constant at 20 nm. We clearly observe that the superconducting condensate density in the superconducting state of superlattice is drastically reduced by the magnetic subsystem which may be connected with proximity effects that distort the gap symmetry and thus suppress superconductivity.Comment: 4 pages, 4 figure

    Enhancement of flux-line pinning in all-oxide superconductor/ferromagnet heterostructures

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    We have studied the local critical current density, jc, in the superconductor thin film of bilayer structures consisting of YBa2Cu3O7 and the ferromagnets La2/3Ca1/3MnO3 and SrRuO3, respectively, by means of quantitative magneto-optics. A pronounced hysteresis of jc was observed which is ascribed to the magnetization state of the ferromagnetic layer. The results are discussed within the frame of magnetic vortex - wall interactions.Comment: 9 page

    Dramatic role of critical current anisotropy on flux avalanches in MgB2 films

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    Anisotropic penetration of magnetic flux in MgB2 films grown on vicinal sapphire substrates is investigated using magneto-optical imaging. Regular penetration above 10 K proceeds more easily along the substrate surface steps, anisotropy of the critical current being 6%. At lower temperatures the penetration occurs via abrupt dendritic avalanches that preferentially propagate {\em perpendicular} to the surface steps. This inverse anisotropy in the penetration pattern becomes dramatic very close to 10 K where all flux avalanches propagate in the strongest-pinning direction. The observed behavior is fully explained using a thermomagnetic model of the dendritic instability.Comment: 4 pages, 5 figure
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