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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Dependence on film thickness of grain boundary low-field magnetoresistance in thin films of La0.7Ca0.3MnO3 (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6970-6972 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetoresistance of grain boundaries in the perovskite manganites is being studied, both in polycrystalline materials, and thin films grown on bicrystal substrates, because of interest in low-field applications. In this article we show that epitaxial films grown on SrTiO3 bicrystal substrates of 45° misorientation show magnetoresistance behavior which is strongly dependent on the thickness of the film. Thin films, e.g., 40 nm, can show a large low-field magnetoresistance at low temperatures, with very sharp switching between distinct high and low resistance states for fields applied in plane and parallel to the boundary. Thicker films show a more complex behavior of resistance as a function of field, and the dependence on the angle between the applied field and the grain boundary is altered. These changes in magnetoresistance behavior are linked to the variation in morphology of the films. Thin films are coherently strained, due to the mismatch with the substrate, and very smooth. Thicker films relax, with the formation of defects, and hence different micromagnetic behavior. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1362648
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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
    Investigation of dc Josephson current distribution in double-barrier three-terminal devices with a thin middle superconducting layer (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2321-2326 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nb/Al–AlOx–Nb/Al–AlOx–Nb double-barrier three-terminal Josephson devices with a thin middle Nb/Al bilayer, which have potential for use as switching and amplifying elements in superconducting electronics, have been investigated in the stationary state by means of low-temperature scanning electron microscopy. For the devices with lateral sizes comparable with the effective Josephson penetration depth, we observed nearly homogeneous current distribution over the region common to the top and bottom junctions when the devices were biased across both the barriers in the absence of an external magnetic field. When the two junctions are biased separately, the current is concentrated at the junction edges in accordance with the behavior characteristic of distributed junctions. In an applied magnetic field, the vortex structure is confined to the area shared by both junctions when the device is biased as a whole. The experiment gives an indication that in the stationary state the spatial phase difference distribution of the two junctions coincides in the shared region at least in some interval of the external magnetic field. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363064
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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    High conductance small area magnetoresistive tunnel junctions (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 384-386 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe–Al2O3–CoFe mesa junctions with micron scale areas have been fabricated from dc sputtered whole wafer heterostructures by standard photolithographic processing. The junctions showed magnetoresistances (JMRs) of 6.2% at room temperature and 9.2% at 77 K. Resistance-area (RA) products as small as 9.6×10−10 Ω m2, suitable for device applications, were obtained. A JMR/RA ratio of 6.5×109% Ω−1 m−2 was also achieved. The fabrication processes we used provide a useful basis for manufacturing ferromagnetic tunnel devices for MR sensor applications. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121842
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