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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2934-2940 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nanocomposites of Al-In, Al-Pb, and Zn-Pb have been prepared and characterized using rapid quenching techniques and the nature of superconducting transitions in them has been studied by resistivity measurements. The precipitated second phases (In and Pb) have particle sizes (d) of a few tens of nanometers such that ξ0≥d≥dmin, where ξ0 is the superconducting zero temperature coherence length and dmin is the minimum particle size that supports superconductivity. The onset of superconductivity generally starts in samples with d∼ξ0 and progressively other grains with d≤ξ0 become superconducting. We suggest that the proximity effect of the matrix plays a significant role. In an Al-In system, even with 40 wt.% In, the zero resistivity state is obtained at T∼1.33 times the Tc of Al. But in Al-Pb and Zn-Pb, the zero resistivity state is obtained at T∼4 and 5 times the Tc of Al and Zn with only 10–15 wt % Pb, respectively.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7478-7483 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the effect of surface treatments on the dynamic conductance curves (G=dI/dV-V) of Au-Bi2Sr2CaCu2O8+δ (single crystal) point contact junctions of variable junction conductances (100 mS(approximately-greater-than)G(approximately-greater-than)100 μS). We find that if the crystal surface is cleaved freshly just prior to making contacts, all irreproducible sharp multiple features often observed in tunneling data of Bi(2212) oxide superconductors disappear. If the cleaved crystal surfaces are left under ambient conditions for a few days and the tunneling experiments are repeated, these multiple features reappear. We also find that if the current in the junction is made to pass predominantly through the bulk (and not along the surface), gap features are sharper. The observed conductance curves are fitted to a modified model [G. E. Blonder et al., Phys. Rev. B 25, 4515 (1982)] and estimated gap values are Δ(approximately-equal-to)28 to 30 meV corresponding to the ratio 2Δ/kBTc (approximately-equal-to) 7.5 with lifetime broadening Γ/Δ(approximately-equal-to)0.2. We conclude that the sharp multiple features observed in Bi(2212) tunneling curves has no intrinsic origin in the bulk and they arise from the surface only.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3071-3072 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A linear magnetic field sensor for low temperature (T≤60 K) use based on magnetoresistance of the perovskite oxide material La0.7Sr0.3CoO3 is reported. The magnetoresistance is negative and is linear in field up to at least 7 T. It is temperature independent for T≤60 K and has a small anisotropy (20%) with respect to the direction of the measuring field. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4519-4522 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Scanning tunneling microscopy was used to study the surface nanostructure of the epitaxial film Nd2/3Sr1/3MnO3 that shows giant magnetoresistance. The surface morphology of the film consists of a number of overlapping platelets of about 30–35 A(ring) diameter that grow at an angle of 35°–45° to the surface normal. The peak to peak height of the platelets are multiples of the c-axis lattice parameter of 7.85 A(ring) showing that the growth of the platelets takes place by the layer by layer addition of one formula unit. The mean surface roughness is about 10 A(ring). In the range of a few microns the film exhibits no defects or dislocations. The film is unstable in ambient atmosphere and tends to get covered by an adsorbate layer. Tip-surface interactions cause the adsorbate to be dislodged exposing the surface nanostructure. The degradation of the film in real time when imaged in air was recorded. The adsorbates increase the surface roughness of the film. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2291-2293 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Effect of particle size on the electron transport and magnetic properties of La0.7Ca0.3MnO3 has been investigated. While the ferromagnetic Tc, low field magnetic susceptibility, and insulator-metal transition are markedly affected by the particle size, the maximum magnetoresistance exhibited by the samples near Tc is not sensitive to the particle size. However, the magnetoresistance at 4.2 K increases with decrease in particle size, suggesting a substantial contribution by the grain boundaries. Preliminary measurements on La0.7Sr0.3MnO3 samples of different particle sizes also corroborate the above conclusions. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3797-3807 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this article we report the results of the scanning tunneling microscope study of the surface morphology of copper films grown by metalorganic chemical vapor deposition from the precursor Cu(tbaoac)2. Films (approximate)100 nm in thickness were grown by varying the reactor pressure. The images reveal the crucial role of the reactor pressure and growth rate on the morphology and grain growth of the films. Films grown at a low growth rate have a smooth surface with small well connected grains of (approximate)10–40 nm diameter with relatively lower resistivity, while films grown at higher growth rates have rougher surfaces and larger grain sizes of (approximate)10–100 nm diameter with poor connectivity that leads to higher resistivity. The correlation of the morphology with resistivity (ρ) and the temperature dependence of ρ in the range 300–4.2 K was investigated. Comparison with the ρ of pure bulk copper shows that these films have much higher resistivities. A large part of the high resistivity at room temperature arises from an enhanced temperature dependent part of ρ and is not due to an enhancement of the residual resistivity alone. The films exhibit deviations from Matthiessen's rule. From a semi-quantitative analysis of the data using existing theories we could assign the large ρ as well as the temperature dependence of ρ to grain boundary scattering and surface scattering. However, for T〉50 K we find that an extra temperature dependent ρ term which may be related to enhancement of electron-phonon interactions by the rough film surface is required. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 233-235 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this letter we report large magnetoresistance (MR) in ceramic samples of La1−xSrxMnO3 (0.1≤x≤0.4) in the temperature range 4.2 K≤T≤350 K in fields up to 6 T. We find that a large negative and isotopic MR exists for the whole composition range studied and the absolute value of resistivity change on application of magnetic field is more for samples with lower x which have higher resistivity. We find that the large MR occurs in the ferromagnetic state only and MR has a close relation with the magnetization M. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report measurements of 1/f electrical noise in two hole doped manganite perovskite oxides, La0.67Ca0.33MnO3 and Pr0.67Sr0.33MnO3, which exhibit colossal magnetoresistance. The noise magnitude represented by the Hooge parameter is nearly 8 orders of magnitude larger than that observed in ordinary metals (and semiconductors) and nearly 5–6 orders of magnitude larger than that observed in epitaxial films of the perovskite oxide YBa2Cu3O7 in the normal state. The normalized noise spectral density increases with decreasing temperature below the resistivity peak, suggestive of the presence of additional low energy noise processes in the ferromagnetic metallic state. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3381-3383 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Measurements of the dc transport properties and the low-frequency conductivity noise in films of charge-ordered Nd0.5Ca0.5MnO3 grown on Si substrate reveal the existence of a threshold field in the charge-ordered regime beyond which strong nonlinear conduction sets in along with a large broad band conductivity noise. Threshold-dependent conduction disappears as T→TCO, the charge-ordering temperature. This observation suggests that the charge-ordered state gets depinned at the onset of the nonlinear conduction. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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