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  • 1
    Electronic Resource
    Electronic Resource
    Large low-field magnetoresistance in La 0.7 Ca 0.3 MnO 3 induced by artificial grain boundaries (1997)
    [s.l.] : Nature Publishing Group
    Nature 387 (1997), S. 266-268 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In doped perovskite manganites of the form Rj _ xAJVlnC)3, where R and A are rare-earth and alkaline-earth elements respectively, a marked polarization of charge carriers due to strong intra-atomic Hund interactions on the manganese sites leads to a dependence of the electrical resistivity on the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/387266a0
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  • 2
    Electronic Resource
    Electronic Resource
    Surface pinning and Lorentz force dependence of transport critical current in NbTa thin films and heterostructures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2361-2367 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical current densities of NbTa and Ta/NbTa/Ta thin films have been measured as a function of the orientation of an applied magnetic field with respect to both the current and the film surface. It is shown that appropriate control of the deposition conditions and the film composition allow the surface pinning and Lorentz force dependence to be reliably and reproducibly altered. Comparison of the results with those reported elsewhere for high Tc films shows broadly similar behavior in the two systems. In particular, we show that surface pinning results in a (sin φ)−1/2 dependence of Jc(φ) for B perpendicular to current, similar to the dependence attributed to intrinsic pinning in high Tc systems. The results also confirm that a lack of Lorentz force dependence of transport critical current is a characteristic of a two dimensional pinning system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357582
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  • 3
    Electronic Resource
    Electronic Resource
    Electron-beam damaged high-temperature superconductor Josephson junctions (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 5612-5632 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are presented on the fabrication and characterization of high critical temperature Josephson junctions in thin films of YBa2Cu3O7−δ produced by the process of focused electron-beam irradiation using 350 keV electrons. The junctions so produced have uniform spatial current densities, can be described in terms of the resistive shunted junction model, and their current densities can be tailored for a given operating temperature. The physical properties of the damaged barrier can be described as a superconducting material of either reduced or zero critical temperature (Tc), which has a length of ∼15 nm. The Tc reduction is caused primarily by oxygen Frenkel defects in the Cu–O planes. The large beam currents used in the fabrication of the junctions mean that the extent of the barrier is limited by the incident electron-beam diameter, rather than by scattering within the film. The properties of the barrier can be calculated using a superconductor/normal/superconductor (SNS) junction model with no boundary resistance. From the SNS model, we can predict the scaling of the critical current–resistance (IcRn) product and gain insight into the factors controlling the junction properties, Tc, and reproducibility. From the measured IcRn scaling data, we can predict the IcRn product of a junction at a given operating temperature with a given current density. IcRn products of ∼2 mV can be achieved at 4.2 K. The reproducibility of several junctions in a number of samples can be characterized by the ratio of the maximum-to-minimum critical currents on the same substrate of less than 1.4. Stability over several months has been demonstrated at room and refrigerator temperatures (297 and 281 K) for junctions that have been initially over damaged and then annealed at temperatures ∼380 K. Junctions manufactured using conventional lithography (0.5 μm wide) and which are suitable for digital electronics (Ic=500 μA at 40 K) can achieve IcRn products of 650 μV at 40 K. The production of 100 of these stabilized junctions could be accomplished in ∼4 h of irradiation time. The IcRn scaling also indicates that junctions suitable for high sensitivity superconducting quantum interference devices (Ic∼100 μA) can be made with IcRn products of ∼120 μV at 77 K. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366422
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  • 4
    Electronic Resource
    Electronic Resource
    Quasiparticle trapping and the density of states in superconducting proximity structures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2368-2375 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental study of quasiparticle trapping in epitaxial and polycrystalline Ta films on epitaxial Nb is presented using three-terminal double tunnel junction devices. It is shown that polycrystalline Ta is a more effective trap than epitaxial Ta. The experimentally measured tunneling density of states is used to calculate the inelastic quasiparticle scattering rates in the two types of Ta using the standard theory of Kaplan et al. [Phys. Rev. B 14, 4854 (1976)]. The agreement of this calculation with the experimental results shows that the tunneling density of states may be used to determine scattering rates in proximitized superconducting films whose thickness is greater than the coherence length. This result is important since no existing theory satisfactorily describes the density of states in such proximity structures, which are currently being developed for use in high-resolution particle spectrometers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357583
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  • 5
    Electronic Resource
    Electronic Resource
    Electronic transport processes and the transition from double to single barrier tunnel junctions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5171-5176 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nb/AlOx/Al/AlOx/Nb devices have been fabricated with Al interlayer thicknesses which range from a few nm to zero. Low temperature measurements of the current versus voltage characteristics show the coexistence of both a direct tunneling channel via a double thickness barrier, and a two stage process via the interlayer. Despite a considerably higher specific conductance, we show that the latter dominates the low voltage electrical properties only when a continuous interlayer exists, and that for discontinuous layers the low voltage conductance is controlled by Coulomb blockade.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355764
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  • 6
    Electronic Resource
    Electronic Resource
    Inelastic quasiparticle scattering and multiplication in superconductors (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1105-1110 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a theoretical and experimental study of quasiparticle multiplication in superconductors. A model of the multiplication process, based on random quasiparticle-phonon inelastic scattering, has been compared with experimental data obtained from double tunnel junction devices in which the quasiparticle injection energy can be varied by altering the bias voltage. Excellent quantitative agreement has been obtained for a variety of device structures provided that a previously unidentified quasiparticle energy enhancement process is included in the model. The existence of this energy enhancement process has implications for quasiparticle trapping and multiplication in practical energy resolving detector devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357830
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  • 7
    Electronic Resource
    Electronic Resource
    Novel hysteresis effects in Nb/AlOx/Al/AlOx/Nb tunnel junctions (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2376-2381 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements on current-biased Nb/AlOx/Al/AlOx/Nb double tunnel junction devices with very thin central Al layers show a novel double hysteretic structure in the subgap region. Similar junction structures have previously exhibited very large nonequilibrium effects; the effects reported here appear close to and above the equilibrium critical temperature of Al. A model is presented in which the hysteresis is shown to arise from a transition from finite to zero voltage across one barrier on increasing current, due to the nucleation of an inhomogeneous state in the ultrathin central Al layer in which normal and superconducting states coexist. This reverse switching effect is shown to arise from the self-shunting effect of low-gap regions. Predictions of this model are shown to agree with the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348723
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic anisotropy of thin film La0.7Ca0.3MnO3 on untwinned paramagnetic NdGaO3 (001) (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3388-3392 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe in detail a method by which to establish the magnetic anisotropy of thin ferromagnetic films on strongly paramagnetic substrates that are slightly anisotropic. The film that we consider is composed of the much studied manganite La0.7Ca0.3MnO3 and the substrate is NdGaO3, a good lattice match. Below a Curie temperature Tc of 260 K it was found, using a vibrating sample magnetometer, that 72±3 nm La0.7Ca0.3MnO3 films grown epitaxially by pulsed laser deposition on untwinned orthorhombic NdGaO3 (001) substrates exhibit uniaxial anisotropy with K=(3.6±0.1)×105 erg cm−3. The easy direction is along [110] of the pseudocubic unit cell, i.e., diagonal to the O–Mn–O bond directions and parallel to the side of the actual unit cell which is orthorhombic. We attribute an 11±4% loss of the low temperature moment to the proximity of the paramagnetic substrate rather than to stress. It is argued that stress is minimal such that the observed anisotropy must be magnetocrystalline. Both the reduction in moment and the anisotropy must be taken into account when designing thin film experiments. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1347957
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  • 9
    Electronic Resource
    Electronic Resource
    Current–voltage characteristics and electrical transport properties of grain boundaries in La1−x(Sr/Ca)xMnO3 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 7263-7266 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Grain boundaries in doped lanthanum manganites have been shown to have a large low-field magnetoresistance. However, the mechanism of electrical transport across grain boundaries, and the origin of the low-field magnetoresistance, are not well understood. Models based on scattering at domain walls, spin-polarized tunneling and depression of the Curie temperature due to strain near the grain boundary have all been proposed. This article reports detailed studies of the transport properties of artificial grain boundaries formed in a variety of thin films grown on bicrystal substrates. Resistance versus field sweeps on all grain boundary devices showed strong low-field magnetoresistance and the effect of individual domain motion at the grain boundary has been observed in single grain boundaries. In all cases, current versus voltage characteristics were highly non-ohmic, and reminiscent of an electron tunneling process. However, the magnetic dependence of the current–voltage characteristics implies that the magnetoresistance may be unrelated to tunneling. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370542
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  • 10
    Electronic Resource
    Electronic Resource
    Structure and chemistry of manganite based tunnel junctions (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6757-6759 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Half-metallic manganite (La0.7Ca0.3MnO3) based spin tunnel junctions with two barrier layers (NdGaO3 and La0.45Ca0.55MnO3) have been investigated structurally as well as chemically using high spatial resolution electron microscopy techniques. Both junctions were grown on a NdGaO3 substrate, which has better lattice match compared to a more traditional substrate such as strontium titanate (SrTiO3). Devices with a NdGaO3 barrier showed tunnel magnetoresistance (TMR) values up to 85% at 77 K, whereas the devices with a La0.45Ca0.55MnO3 barrier layer showed only 18% TMR at 77 K. The electron microscopy data show much clearer, sharper interfaces, structurally as well as chemically, for NdGaO3 than for the La0.45Ca0.55MnO3 barrier layer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357834
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