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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5332-5332 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Some stable compounds form in layered structures, in which magnetically ordered planes alternate with planes that are essentially nonmagnetic or disordered. SmMn2Ge2, for example, consists of planes of ferromagnetically aligned Mn2 separated by a SmGe2 structure (with the Sm moments disordered). Between 90 and 150 K, alternate Mn2 planes align antiferromagnetically, but can be rotated into overall ferromagnetic alignment by a moderate field (2–15 kOe). This is a classic metamagnetic behavior. A first-order structural phase transition accompanies the magnetic transition; it consists of a dilation of the c-axis lattice parameter and contraction of the a-axis lattice parameter with no discernable change in crystal symmetry. We have found that a 4%–8% change in the resistivity is associated with the magnetic transition, which may be related to band-structure effects as well as the elimination of the interlayer magnetic scattering channel. Since these are well-annealed, equilibrium compounds, they allow the study of this scattering channel in the limit of zero layer roughness (unlike thin film multilayers). The use of arc-grown single crystals allows us to measure the anisotropic response of the compounds: for example, the resistivity anisotropy of SmMn2 Ge2 is ρc/ρa∼25, and the AFM-FM transition is found to decrease ρc while it increases ρa. The study of this and similar layered structures serves as a complement to the study of artificial thin film magnetic multilayers.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5221-5224 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electronic structure calculations predict Ag3AuTe2 to be a small-band-gap semiconductor. Polycrystalline samples of the pure and doped materials have been synthesized, and the physical properties are reported. Thermoelectric power measurements indicate that pure Ag3AuTe2 is a p-type material with a very large room-temperature Seebeck coefficient of 530 μV/K. The thermal conductivity is very low, and at room temperature, is lower than that of the best thermoelectrics. The transport properties were found to be very sensitive to chemical doping and nonstoichiometry. Although samples made with excess Ag resulted in improved thermoelectric performance at higher temperatures (〉500 K), the large resistivity of these materials makes them noncompetitive with state-of-the-art thermoelectrics. © 2000 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 317-321 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermoelectric properties of the pure and doped half-Heusler compounds FeVSb and FeNbSb are reported. The electrical resistivities are between 0.2 and 20 mΩ cm at room temperature. Thermoelectric power measurements indicate that FeVSb is an n-type material with moderate Seebeck coefficients near −70 μV/K at 300 K. The thermal conductivity at room temperature is large, approximately 0.1 W/cm K, and increases with decreasing temperature. Chemical substitutions, which have a dramatic effect on the transport properties, were performed in an effort to enhance the thermoelectric performance. Band-structure calculations are presented for the pure materials. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 7231-7233 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature dependent dielectric constants in the vicinity of room temperature have been measured for bulk ceramics which are phase-mixtures of Pb2(Nb,Mg,Ti)2O6+x pyrochlores and Pb(Nb,Mg,Ti)O3 perovskites. A band of compositions is found in which the negative temperature coefficient of dielectric constant for the pyrochlore is very closely compensated by the positive temperature coefficient of dielectric constant of the perovskite. These compositions have dielectric constants near 200, with measured Q's near 200 at 100 kHz. © 1995 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5856-5856 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Copper oxides have dominated superconductivity research since 1987. The interplay between superconductivity and magnetism lies at the center of the controversy concerning the appropriate microscopic model for their superconductivity. We have recently been exploring a broad new family of materials which represent the first true quaternary intermetallic superconductors. Although their superconducting Tc's are not competitive with the copper oxides, several of the members of the family have Tc's equivalent to the highest Tc's ever reported for intermetallic compounds. The materials are especially surprising in that they are not based on niobium alloys, but rather are based on the borides of nickel, palladium, and platinum. The presence of square planes of the normally magnetic transition metals nickel and palladium suggests that magnetism might play some role in the superconducting mechanism. There are experimental results on both sides of the magnetic/conventional mechanism question, and although at this time the community is leaning largely toward a conventional mechanism, this should still be considered an open question. The presence of superconductivity for some of the magnetic rare earth analogs results in interesting phenomena, especially in the case of HoNi2B2C where the magnetic transition on the Ho sublattice is very close to the superconducting Tc. This talk will serve as an introduction to the chemistry, structure, and basic physical properties of these new materials, and will draw on the results of other groups, as well to present a summary view of these materials. © 1996 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2346-2348 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric properties of (Ta2O5)1−x(SiO2)x polycrystalline ceramics for 0.0≤x≤0.20 are reported. Measurements were made at 1 MHz and temperature between −40 and +100 °C. The dielectric properties are not very sensitive to SiO2 content. A moderate enhancement of the dielectric constant is found, from −30 for pure Ta2O5 to ∼45 at x(approximately-equal-to)0.10. The temperature coefficient of dielectric constant in the vicinity of room temperature decreases from ∼200 ppm/°C for Ta2O5 to ∼75 ppm/°C for x=0.14. © 1996 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5449-5451 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of a copper-oxide-based isotropic metallic oxide (La8−xSrxCu8O20) and superconducting heterostructures (YBa2Cu3O7/La8−xSrxCu8O20/YBa2Cu3O7) have been fabricated by 90° off-axis sputtering. La8−xSrxCu8O20 is an oxygen-deficient pseudocubic perovskite that exhibits Pauli paramagnetism. X-ray diffraction and cross-sectional transmission electron microscopy reveal the heterostructures to have high crystalline quality and clean interfaces. This material will facilitate fabrication of ideal superconductor–normal-metal–superconductor Josephson junctions with low boundary resistance due to its excellent chemical compatibility and lattice match with cuprate superconductors and will be useful for determining the source of interface resistance in such heterostructures. © 1995 American Institute of Physics.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated and studied the structure and magnetic properties of high quality single crystalline (Mn,Zn)Fe2O4, NiFe2O4, and CoFe2O4 films. Although (Mn,Zn)Fe2O4 and NiFe2O4 films grown directly on SrTiO3 and MgAl2O4 show mediocre structural and magnetic properties, these same films grown on SrTiO3 and MgAl2O4 buffered with CoCr2O4 or NiMn2O4 exhibit excellent crystallinity and bulk saturation magnetization values, thus indicating the importance of lattice match and structural similarity between the film and the underlying layer. X ray, Rutherford backscattering spectroscopy, atomic force microscopy, and transmission electron microscopy analysis provide a consistent picture of the structural properties of these ferrite films. © 1996 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1914-1916 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Mössbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in BaBi1−xSbxO3 with x=0.2, 0.4, and 0.5. A single resonance absorption line is observed. The isomer shift changes slightly with Sb content and falls in the region corresponding to an Sb(V) valence state. The isomer shift of 7.6 mm/s is significantly depressed (∼1 mm/s) relative to its value in a typical Sb(V)O6 chromophore and indicates a high degree of covalency, corresponding to significant 5sm5pn hybridization.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2848-2850 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Mössbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in perovskite superconducting materials. The isomer shift (IS) changes with Sb content and falls in the region of the Sb(V) valence state. The IS increases from 7.00 mm/s for BaPb0.75Sb0.25O3 to 7.25 mm/s for BaPb0.75Bi0.25O3 and to 7.70 mm/s for (Ba0.6K0.4)BiO3 compounds, indicating a high degree of covalency, corresponding to changes in the 5sm5pn hybridization.
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