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  • 1990-1994  (23)
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  • 1
    Electronic Resource
    Electronic Resource
    Optimization of annealing parameters for the growth of epitaxial Ba2YCu3O7−x films on LaAlO3(100) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6353-6360 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The superconducting and structural properties of Ba2YCu3O7−x (BYCO) films on LaAlO3(100) substrates can be improved by carefully optimizing the post-deposition annealing parameters. Films are grown by co-deposition of BaF2, Y, and Cu in the correct stoichiometric ratio to within 1% of 2:1:3. Annealing parameters in an ex situ furnace, including the ambient, annealing temperature, oxidation temperature, and duration of anneals are systematically studied. Films are characterized for epitaxial quality (χmin), morphology, critical temperature (Tc), sharpness of the superconducting transition (ΔT), and critical current density (Jc). For example, beyond simply dissociating BaF2, the use of wet O2 appears to prevent the agglomeration of oxides during the initial heating process, and then act to thermodynamically stabilize the basic BYCO film structure at high temperatures after being formed. Comparisons are made with the best single-crystal BYCO structural and electrical data available. The optimized films have relatively smooth morphology with χmin〈3%, Tc〉90 K, ΔT〈0.5 K, and Jc〉106 A/cm2 in essentially zero magnetic field at 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346881
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  • 2
    Electronic Resource
    Electronic Resource
    Giant magnetoresistance in layered magnetic compounds (invited) (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5332-5332 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353769
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  • 3
    Electronic Resource
    Electronic Resource
    Anomalous composition dependence of anisotropy in amorphous Tb-Fe and Ho-Fe (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5466-5466 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic anisotropy Ku of magnetron cosputtered amorphous Tb-Fe has been found to drop precipitously when the composition is within several at. % of 22 at. % Tb, a composition which is the room-temperature compensation point. The samples showing this low value for Ku are magnetically saturated (fields up to 100 kOe were used) and torque curves have the expected uniaxial behavior. The unexpected decrease is correlated with a previous finding of anomalous, nonuniaxial anisotropy for films prepared with less than 22 at. % Tb when nonperpendicular incident angles are used for the deposition. We hypothesized that an undetected phase separation was occurring in these Fe-rich samples. The present study examines films prepared on rotating substrates, essentially eliminating the effect of incident angles. As previously predicted, with no incident angles the phase separation is unobservable by magnetic anisotropy, but presumably is still present and may account for the observed drop in Ku. Analogous results have been seen in amorphous Ho-Fe; the relevant composition is far from magnetic compensation, supporting the conclusion that the coincidence of compensation with the anomalies in Tb-Fe is accidental. This behavior of the anisotropy is inconsistent with simple models for the atomic structure and the source of Ku. The effect of deposition temperature will also be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348011
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Deposition and properties of NiFe2O4 thin films (abstract) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6124-6124 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the properties of NiFe2O4 thin films prepared by laser ablation of a stoichiometric NiFe2O4 target. Textured polycrystalline films were obtained on a-SiO2 as well as on various substrates with Au, Ag, Pt, and MgF2 buffer layers. Epitaxially oriented films were obtained on MgO, (11¯02)-oriented Al2O3, (112¯0)-oriented Al2O3, Y-stabilized ZrO2 (YSZ), and SrTiO3, although the crystalline quality of the films varied. Contamination by diffusion from the substrate and strains induced by both lattice constant mismatch and differential thermal expansion degraded the magnetic properties of the films, and in some cases decreased the electrical resistivity as well. By choosing the right substrate (YSZ), temperature (600 °C), and PO2 (0.01 mT), we are able to prepare epitaxial films with bulk saturation magnetization (Ms=270 G) and fairly low anisotropy (K∼105 erg/cm3) as inferred by torque magnetometry. These films and bilayers are expected to be useful in a variety of fundamental investigations as well as having the potential for technological applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355481
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  • 5
    Electronic Resource
    Electronic Resource
    Critical currents and magnetization in c-axis textured Bi-Pb-Sr-Ca-Cu-O superconductors (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 868-870 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transport critical currents and magnetization behavior in c-axis textured Bi-Pb-Sr-Ca-Cu-O superconductor ribbons have been studied. The highly oriented layer structure was achieved by a combination processing of spray coating on silver foil, cold rolling, and partial melting. Transport Jc values as high as 2.3×105 A/cm2 at 4.2 K, H=8 T (H⊥ab) have been obtained. The high Jc at H≥5 T is maintained to temperatures near 20 K but it vanishes completely at or above ∼30 K, thus showing the limitation in useful, high-field operating temperatures for the Bi-system superconductors. A comparison of Jc (transport) and Jc (magnetization) indicates that the size scale of the circulating supercurrent loop in the Bean model nearly corresponds to the whole sample dimension rather than the orders-of-magnitude-smaller grain size. This demonstrates that the a-b grain boundaries in the melt-processed ribbons are not weakly coupled. The time decay of magnetization has also been studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104490
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  • 6
    Electronic Resource
    Electronic Resource
    Fabrication of thin-film superconductors by bulk processing (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1917-1919 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple processing technique for preparation of c-axis-oriented Bi-Pb-Sr-Ca-Cu-O thin films is reported. ∼3000-A(ring)-thick superconductor films on silver substrate have been obtained by heavy cold rolling and partial melt processing of the superconductor-silver composite structure. The films are highly textured due to the interface-induced, layer-like growth of the superconducting phase, and are essentially free of weak links. They exhibited Tc∼80 K and Jc (4.2 K) ∼104–105 A/cm2. This technique, which does not require epitaxial growth from single-crystal substrates, may be suitable for high-speed, low-cost production of large-area thin films, and points to other novel thin-film processing possibilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105047
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  • 7
    Electronic Resource
    Electronic Resource
    Critical currents in proton-irradiated single-crystal Ba2YCu3O7−δ (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2681-2683 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Irradiation with 3.5 MeV protons creates defects in Ba2YCu3O7−δ, which can act as strong pinning sites, comparable to those produced by neutron irradiation. Indeed protons as well as neutrons undergo momentum-transferring collisions that result in atomic displacements; the additional electronic proton-solid interaction does not appear to yield defects which contribute to pinning. Under optimized conditions we have obtained Jc(T→0, H=1 T)∼2×107 A/cm2 in single crystals. At 77 K the value is still Jc∼1.7×105 A/cm2, decreasing only threefold in a field of 6 T. The fluence and temperature dependence of Jc suggest a model, in which spatially uncorrelated defects pin vortex cores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103269
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  • 8
    Electronic Resource
    Electronic Resource
    Sharp angular sensitivity of pinning due to twin boundaries in Ba2YCu3O7 (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2465-2467 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the pinning force due to twin boundaries by measuring the magnetic torque produced when a field is applied perpendicular to the c axis and rotated with respect to the ab axes. At 76 K, the torque increases roughly fourfold, when the field is within 2° of the parallel to the twin boundaries. This peak is absent at 27 K. Irradiation with 5×1016 cm−2 3.5 MeV protons increases the overall critical current and eliminates the peaks observed at 76 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103257
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  • 9
    Electronic Resource
    Electronic Resource
    Enhanced giant magnetoresistance in Fe/Cr multilayer films by Cr alloying of the Fe layers (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1279-1281 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the Cr alloying addition to the Fe layers in the Fe/Cr superlattice films [Fe(15 A(ring))/Cr(tA(ring))]30), (t=8–20) on the magnetoresistance behavior has been investigated. The alloyed superlattice films exhibited significantly improved giant magnetoresistance effect (ΔR/R∼12.2% at 4.2 K) as compared to the unalloyed Fe/Cr multilayer films (ΔR/R∼6.9%). Both films exhibit ΔR/R dependence on the thickness of the Cr layer with the maximum ΔR/R occurring at ∼10 A(ring) thickness. The M-H loops indicate that antiferromagnetic coupling exists in both films, which is believed to be responsible for the observed giant magnetoresistance. The improvement in ΔR/R in the Cr-alloyed superlattice films is attributed to the stronger spin-dependent scattering of conduction electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109757
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  • 10
    Electronic Resource
    Electronic Resource
    Selective electroless copper metallization of palladium silicide on silicon substrates (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 3449-3451 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A scheme for selective electroless copper patterning of Si wafers has been developed with palladium silicide as the catalytic layer initiating copper deposition. Thermal conversion of a palladium layer to silicides on a SiO2 patterned silicon substrate, followed by an acid etching of the unreacted palladium on the SiO2 surfaces, leaves only the silicided regions at the base of the windows for electroless copper deposition. Excellent via-filling down to 0.5-μm dimensions and an aspect ratio of 6 has been demonstrated. The thin copper deposited on the Pd2Si has a resistivity of ∼2.0 μΩ cm. Contactless photocarrier decay measurements indicate virtually no degradation of Si lifetimes by these processing steps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105674
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