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  • 1
    Electronic Resource
    Electronic Resource
    Improved microwave performance of Ag-doped Y1Ba2Cu3O7−δ thin film microstrip resonators (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5105-5108 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microwave transmission properties of undoped and Ag-doped laser ablated thin film Y1Ba2Cu3O7−δ microstrip resonators have been studied both on 〈100(approximately-greater-than) MgO and 〈100(approximately-greater-than) LaAlO3 substrates at X-band frequencies. While the Q factor and microwave surface resistance, Rs, of undoped films showed better performance on LaAlO3 as compared to that on MgO, Ag-doped films on LaAlO3 showed far greater improvement as reflected not only by a decrease in Rs but also by a total absence of its microwave power dependence up to 13 dBm at 77 K. These results are explained as due to the influence of Ag in increasing the grain size and grain alignment and thus, significantly decreasing the density of grain boundary weak links which are known to affect the microwave transmission in high temperature superconductor films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353783
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  • 2
    Electronic Resource
    Electronic Resource
    Critical current in a spin injection device (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7502-7504 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on direct evidence of the suppression of critical current due to pair-breaking in a superconducting microbridge when the measurement is carried out by injecting spin-polarized carriers instead of normal electrons. A thin layer of La0.7Ca0.3MnO3 was used as the source of spin-polarized carriers. The microbridge was formed on the DyBa2Cu3O7−δ thin film by photolithographic techniques. The design of our spin-injection device allowed us to inject spin-polarized carriers from the La0.7Ca0.3MnO3 layer directly to the DyBa2Cu3O7−δ microbridge (without any insulating buffer layer) making it possible to measure the critical current when polarized electrons alone are injected into the superconductor. Our results confirm the role of polarized carriers in breaking the Cooper pairs in the superconductor. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1356048
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  • 3
    Electronic Resource
    Electronic Resource
    Transport and magnetic properties of laser ablated La0.7Ce0.3MnO3 films on LaAlO3 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5718-5725 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: La0.7Ce0.3MnO3 is a relatively new addition to the family of colossal magnetoresistive manganites, in which the cerium ion is believed to be in the Ce4+ state. In this article, we report the magnetotransport properties of laser ablated La0.7Ce0.3MnO3 films on LaAlO3, and the effect of varying the ambient oxygen pressure during growth and the film thickness. We observe that the transport and magnetic properties of the film depend on the oxygen pressure, surface morphology, film thickness, and epitaxial strain. The films were characterized by x-ray diffraction using a four-circle goniometer. We observe an increase in the metal-insulator transition temperature with decreasing oxygen pressure. This is in direct contrast to the oxygen pressure dependence of La0.7Ca0.3MnO3 films and suggests the electron doped nature of the La0.7Ce0.3MnO3 system. With decreasing film thickness we observe an increase in the metal-insulator transition temperature. This is associated with a compression of the unit cell in the a-b plane due to epitaxial strain. On codoping with 50% Ca at the Ce site, the system (La0.7Ca0.15Ce0.15MnO3) is driven into an insulating state suggesting that the electrons generated by Ce4+ are compensated by the holes generated by Ca2+, thus making the average valence at the rare-earth site 3+ as in the parent material LaMnO3. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371584
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  • 4
    Electronic Resource
    Electronic Resource
    Growth of epitaxial and polycrystalline thin films of the electron doped system La1−xCexMnO3 through pulsed laser deposition (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 524-530 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The polycrystalline La1−xCexMnO3 manganites do not exist in single phase in bulk under the preparation conditions so far employed, but their polycrystalline and epitaxial films deposited by the pulsed laser deposition (PLD) technique form readily in single phase. The cerium oxide (CeO2) remains partially unreacted when the bulk sample is prepared through the solid state reaction route. The resistivity of the bulk La0.7Ce0.3MnO3 sample shows a broad metal insulator transition (MIT) clearly resolved into two peaks, suggesting the presence of a second (impurity) phase, which is identified as unreacted CeO2 by the intensity analysis of the x-ray diffraction (XRD) data. However, when prepared as thin films by PLD, La0.7Ce0.3MnO3 forms in single phase, as corroborated by the uniqueness and sharpness of the MIT peak and also by the XRD patterns of the polycrystalline films. We also performed a detailed study of the epitaxial films by a high-resolution XRD system with a four-circle goniometer and did not find any impurity phase. The magnetization data shows a very sharp transition followed by a sharp MIT in resistivity at the same temperature in the epitaxial thin film. These results suggest that PLD can be used as a useful technique to synthesize unconventional compounds, which do not form easily in bulk. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331648
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  • 5
    Electronic Resource
    Electronic Resource
    Si induced size effects in ferroelectric PbTiO3 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 462-466 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Physical properties of PbTiO3 in the presence of Si are investigated in detail. Polycrystalline bulk samples with nominal composition of (Pb1−xSix) (Ti1−xSix)O3, where x varies from 0.01 to 0.25, are synthesized using the coprecipitation route. The presence of Si in the matrix leads to a reduction in coherently diffracting domain size (dXRD). The observed reduction in the ferroelectric distortion in the lattice c/a, ferroelectric transition temperature Tc and shift in Raman lines of PbTiO3 with increase in Si content are attributed to the Si induced finite size effect. However, at higher calcination temperatures, the material exhibits properties similar to pure, undoped, bulk PbTiO3. There is no evidence of change in crystal structure and ferroelectric nature of PbTiO3 due to the presence of Si. Our data suggests that Si, which is diffused out of PbTiO3 perovskite lattice, is likely to reside in the grain boundary region in an as yet unidentified chemical form. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371884
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  • 6
    Electronic Resource
    Electronic Resource
    Oxidation state and superconducting properties of Y1−xPrxSr2Cu2.85Re0.15O7+δ (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6884-6887 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconductivity exists in orthorhombic Y1−xPrxSr2Cu2.85Re0.15O7+δ up to a critical concentration (xcr) of 0.65. A progressive decrease in Tc occurs as x increases from 0 to 0.65. A further increase in x leads to a tetragonal transformation and as a consequence the Tc vanishes; however, the orthorhombicity of these Sr-based compounds is much lower than that observed for the Ba analog, Y1−xPrxBa2Cu3O7−δ and, hence, the Tc. On the one hand, crystal chemistry correlations indicate that the Pr ion is in trivalent state while on the other hand, the stabilizing cation, viz., Re, is in hexavalent state which accounts for the excess oxygen (〉7.0) in the system. The high xcr value of the Sr series compared to the Ba series (xcr=0.55) is attributed to the much reduced orbital overlap of the trivalent Pr(4f ) state with the Cu(3dx2−y2)–O(2p) conduction band, via hole localization and/or pair breaking, and is not due to the much discussed hole filling by tetravalent Pr. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363758
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  • 7
    Electronic Resource
    Electronic Resource
    Silver doping and its influence on the oxygenation during in situ growth of YBa2Cu3O7−x thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1349-1351 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of Ag doping on both oxygenation and deoxygenation during growth of YBa2Cu3O7−x films at 700 °C by pulsed laser deposition has been studied. Experiments show that undoped and Ag-doped films grown at 200 mTorr oxygen pressure and quenched immediately after termination of growth have a superconducting transition temperature Tc of 61 and 86 K, respectively. The high Tc of 86 K obtained with quenched Ag-doped films is thought to be due to both enhanced oxygen incorporation and reduced deoxygenation associated with Ag doping. These results show that Ag-doped YBa2Cu3O7−x films could be crucial for realizing devices based on multilayer structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357802
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  • 8
    Electronic Resource
    Electronic Resource
    Microstructural study of yttria stabilized zirconia buffered sapphire for YBa2Cu3O7−δ thin films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 940-946 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Yttria stabilized zirconia (YSZ) buffer layers were grown by rf-magnetron sputtering on the r (11¯02) plane of sapphire for YBa2Cu3O7−δ (YBCO) thin film deposition. Microstructural changes of YSZ buffer layers grown using different sputtering conditions (5, 10, and 20 mTorr; Ar/O2 gas mix ratio of 9:1 and 1:1) were monitored by atomic force microscopy (AFM). Films grown using a lower oxygen partial pressure (5 mTorr) and a higher Ar/O2 ratio (9:1) showed smooth surface morphology and the average surface roughness increased with an increase in oxygen partial pressure. YBCO films in situ grown by pulsed laser deposition on sapphire with a YSZ buffer layer deposited using optimized sputtering parameters (5 mTorr gas pressure, 9:1 Ar/O2 ratio) yielded the highest critical density, Jc≈4.5×106 A cm−2 at 77 K. An excellent correlation between microstructure and Jc has been found and AFM has proved to be important for the study of the microstructure of films. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360876
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  • 9
    Electronic Resource
    Electronic Resource
    Pulsed laser ablation: A new route to synthesize novel superconducting compounds as oriented films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1082-1091 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report here the significance of the pulsed laser ablation technique in stabilizing strained lattices that do not form by the conventional ceramic method and show that the technique offers unique possibilities to probe the structure property relationship in complicated systems. One of such systems is LuBa2Cu3O7−δ; a systematic investigation of structural (in)stability of its superconducting phase is presented here. Our analysis suggests that the system suffers from internal strain due to lower ionic radius of Lu3+; however, the structure can be stabilized only as oriented films on 〈100〉 LaAlO3, 〈100〉 SrTiO3, and 〈100〉 MgO, with excellent superconducting properties (Jc≈5.0×106 A cm−2 at 77 K). We have also investigated similar compounds having their stability close to their crystallographic limit. The important feature of these metastable phases is that they grow only as oriented films. Free energy of epitaxial growth of strained films are investigated and a simple growth model is proposed based on our observation. Importance of this growth model in explaining the superconductor–normal-metal–superconductor type of junctions, observed in high-Tc superconductors is highlighted. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360898
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  • 10
    Electronic Resource
    Electronic Resource
    Two-dimensional growth model for laser-ablated Ag-doped YBa2Cu3O7−x thin films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5802-5808 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ag-doped YBa2Cu3O7−x (YBCO) thin films using 2–20 wt % Ag-doped YBCO targets have been grown in situ by the laser ablation technique. The improvement in properties in normal and superconducting states of Ag-doped YBCO films has been interpreted using a two-dimensional growth model. The model is simple and is based on widely accepted characteristics of Ag such as its flux action at high temperatures and its nonreactivity with YBCO phase. Experimental evidence in support of the growth model is presented by carrying out microstructural studies and measurements of room-temperature resistivity, critical current density, and microwave surface resistance in superconducting state. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359159
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