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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6240-6242 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have observed giant magnetoresistance (GMR) in unannealed NiFe/Ag multilayer thin-film stripes. Rectangular stripes having constant thickness and a constant 11:1 length-to-width aspect ratio, but varying widths down to 0.5 μm, were measured. Two types of multilayer configurations were tested, a system of five NiFe/Ag bilayers with 5.5-nm-thick Ag spacer layers, and a system of nine bilayers with 4.4-nm-thick Ag layers. In contrast to the characteristic of annealed NiFe/Ag multilayer stripes, the unnannealed stripes produced increasing GMR ratios for decreasing stripe sizes, with the 0.5-μm-wide stripe of the five-bilayer system exhibiting a ΔR/R of 2.5%. Barkhausen noise and response broadening also increased with decreasing stripe size, however. The results are discussed in terms of magnetostatic coupling of the NiFe layers within the stripes.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The magnetic properties of high density recording media have been shown to be very sensitive to the film microstructure. We have investigated the influences of different sputter gases (Ar, Xe, Kr) and different sputter pressures (3 to 24 mTorr) on the microstructures and magnetic properties of CoPtCr/Cr thin films. The magnetic properties of the films (coercive field, Hc, coercive squareness, S*, and remanant moment, Mr) were determined using a vibrating sample magnetometer. The microstructures were examined by transmission electron microscopy and x-ray diffraction. For all three gases studied the microstructures and properties of the CoPtCr films were found to change with sputter pressure in similar manners. Films deposited at the lowest pressure consisted of well connected, equiaxed grains. With only a slight increase in pressure, the grains formed chains separated by small gaps. As the gas pressure increased further, the chains became better defined and the gaps between them widened. The coercive squareness and coercive field correlate with the film microstructures. S* decreased with increasing sputter gas pressure, and Hc first increased and then decreased. For all three sputter gases, Hc reached a maximum around 12 mTorr.Likewise, S* decreased quite slowly with increasing pressure up to 12 mTorr and then exhibited a sharp drop between 12 and 18 mTorr. From these results it appears that the sputter pressure, rather than the mass of the sputter gas, is most important for the microstructural development of the film. Likewise, the values of S* were found to be independent of the sputter gas. However, in spite of the similar microstructures, films deposited with Ar had higher values of Hc than films deposited with Xe or Kr, for all sputter pressures examined. The role of the sputter gas mass will be discussed. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5263-5272 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The nucleation and growth kinetics of epitaxial Ba2YCu3O7−x thin films prepared on (001) SrTiO3 by postdeposition annealing of a chemically derived intermediate layer were investigated in specimens quenched from the growth anneal. The films were produced by spin-on deposition of a metal-organic precursor solution at room temperature and ambient pressure, and subsequent postdeposition annealing to form Ba2YCu3O7−x (BYC). Integrated x-ray intensities of reflections from the majority, c-axis-normal epitaxial BYC in the films were analyzed as a function of time at annealing temperature. Data collected from specimens annealed at 730 and 750 °C were consistent with upward growth of the BYC from nuclei at the substrate surface with a constant growth rate. The linear transformation kinetics suggest the growth process is controlled by molecular processes at the BYC/intermediate interface, and is not rate limited by diffusion. The activation energy for film growth along its [001] axis was estimated to be ∼5 eV. The microstructure of fully annealed films grown on (001) SrTiO3 was, in general, similar to that of films prepared on (001) LaAlO3 using the same metal-organic deposition technique. The volume fraction of the c-axis in-plane epitaxial orientation in films on (001) SrTiO3 was, however, much smaller than in films prepared identically on (001) LaAlO3. Vicinal polishing of the SrTiO3 by as much as 2.5° off [001] in the direction of [101] increased the volume fraction of c-axis in-plane domains in the films somewhat. These domains were preferentially oriented so that their (001) planes were parallel to the steps in the SrTiO3 surface. The fraction of the films on vicinal SrTiO3 occupied by c-axis in-plane domains was, however, still significantly less than that present in BYC films prepared on nominally on-axis (001) LaAlO3. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3710-3716 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The composition of grain boundaries in La2−x Srx CuO4−y has been mapped as a function of bulk composition and annealing temperature. It is found that the predominant composition change is an enrichment of Sr, that this segregation occurs primarily on the La sublattice, and that the segregation energy (0.03 to 0.1 eV) agrees with an elastic misfit strain energy estimate for Sr as a solute. Grain boundary segregation is shown to persist at annealing temperatures as high as 1000 °C, and to be relatively uniform from grain boundary to grain boundary in these untextured polycrystals. Compositional disorder is thus intrinsic to grain boundaries in La2−x Srx CuO4−y and must be considered along with structural disorder in understanding the nature of the weak links. While prospects for high-polycrystalline critical-current densities in this material appear poor based on these results, the ability to predict and control grain boundary segregation may conversely prove to be useful in applications that require specific grain boundary junction properties.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5750-5758 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Although BaPb0.75Bi0.25O3 (BPB) has a comparatively large superconducting coherence length of ∼7 nm and no reported anisotropy in its superconducting parameters, polycrystalline BPB exhibits the same rapid decrease in transport critical current density (Jct) with low applied field (〈∼50 Oe) that is characteristic of grain boundary weak links in cuprate superconductors (e.g., La2−xSrxCuO4, YBa2Cu3O7−x ). We have studied the effects of processing thermal history on the formation and morphology of grain boundary phases, and on the composition of BPB boundaries with and without second phase, in order to understand the origin of these weak links. Scanning transmission electron microscopy and Auger electron spectroscopy results show the presence of a Pb-Bi-Ba-O phase that is wetting and liquid above ∼570 °C, but which retracts to three-grain junctions upon slow cooling or annealing at lower temperatures. However, weak-link behavior persists in materials with retracted secondary phase, as well as in hot isostatically pressed samples that never exceed the secondary phase melting temperature. It is found that the grain boundaries remain Bi- and Pb-rich even after the retraction of secondary phases; samples that never exceed the melting temperature of the secondary phase show absence of segregation at some but not all grain boundaries. The composition of the grain boundaries as well as Jct vs temperature measurements indicate that the boundaries act as SIS tunnel junctions.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4898-4900 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thin polycrystalline films of half-metallic ferromagnetic NiMnSb compound have been successfully prepared by simultaneous evaporation of Ni, Mn, and Sb elements onto heated glass and sapphire substrates. X-ray diffraction, Rutherford backscattering spectroscopy, energy-dispersive x-ray spectroscopy, and Auger studies confirmed the quality of the films and surface composition. Magnetization and Kerr rotation obtained for these films agree well with those made on a single crystal of NiMnSb. Using electron tunneling techniques, attempts have been made to measure the conduction electron spin polarization, which is theoretically predicted to be large.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1079-1080 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A general result valid for any compressible fluid is noted. It gives the maximum values of the flux densities of mass, momentum, and kinetic energy in steady and unsteady flows which are expanding isentropically from a reservoir.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3512-3514 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the optical constants of oxidized crystalline and low-temperature-grown (LTG) Al0.98Ga0.02As films, as determined by variable angle spectroscopic ellipsometry. Data were acquired at three angles of incidence over 240–1700 nm and fitted to a Cauchy dispersion function. For oxidized crystalline material, we observe a variation in the real index of ±0.5% for layer thickness variations of ±6%. We show that upon oxidation, LTG material can expand by 〉25% while crystalline material contracts by 〈2%. Atomic force microscopy analysis indicates thickness-dependent variations in the oxide microstructure. Additionally, an optical scattering loss of 2.1×10−4%/pass is calculated based on surface roughness measurements for a thin layer of oxidized crystalline material. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: High quality films of YBa2Cu3O7−δ on LaAlO3 have been grown by pulsed-laser deposition at oxygen pressures of 3.4–54 Pa (25–400 mTorr). X-ray diffraction reveals the coexistence of grains that align with the substrate axes (axial grains) and grains that are rotated by 0.4° from the substrate axes (diagonal grains). The axial grains are tetragonal while the diagonal grains achieve lattice parameters close to bulk YBa2Cu3O7. The relative proportion of axial grains accounts for the measured variations of normal-state conductance and superconducting critical current density from film to film, based on a simple two-dimensional model of randomly positioned, insulating axial grains. © 1994 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3649-3651 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The surface degradation of c-axis oriented YBa2Cu3O7−δ thin films due to air, CO2, N2, O2, and vacuum exposure has been studied with reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy, and contact resistivity measurements. The formation of an amorphous surface reaction layer upon exposure to air and CO2 is monitored with RHEED and correlated with an increase in contact resistivity. The contact resistivity of samples exposed to air increases with time t as ρc = (1.0 × 10−7 Ω cm2)e(square root of)t/640 min. Surfaces exposed to CO2 show a similar degradation while surfaces exposed to N2 showed a slightly different degradation mechanism. Vacuum exposed surfaces how little increase in contact resistivity, indicating no long-term surface oxygen loss.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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