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  • 1
    Electronic Resource
    Electronic Resource
    Low-noise dc superconducting quantum interference devices in Bi2Sr2CaCu2O8+x thin films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6703-6709 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-noise dc superconducting quantum interference devices (SQUIDs) were fabricated by thin film deposition of Bi2Sr2Ca Cu2O8+x (BSCCO) on bicrystalline substrates of SrTiO3 with misorientation angles aitch-theta from 24° to 45°. An optimized dc SQUID design (βL=1) was developed for aitch-theta=24°. Therein the SQUID inductance was varied between 7 and 80 pH. Fabricated dc SQUIDs operated at 77 K as well as high-quality YBa2Cu3O7−y (YBCO) SQUIDs, especially the 1/f and white noise levels were in the lowest range of data reported so far for YBCO SQUIDs and are two orders of magnitude better than noise data published this far for BSCCO SQUIDs at 77 K. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359084
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  • 2
    Electronic Resource
    Electronic Resource
    Formation of amorphous Zr-Al-Cu-Ni with a large supercooled liquid region by mechanical alloying (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5446-5448 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous Zr65.0Al7.5Cu17.5Ni10.0 powder has been prepared by mechanical alloying from crystalline elemental powders. The powders are characterized by x-ray diffraction and differential scanning calorimetry (DSC). The amorphous phase forms after about 50 h of milling, and exhibits a wide supercooled liquid region of up to 87 K before crystallization. The transformation to the crystalline state and the melting behavior of the crystalline alloy have been followed by isothermal and constant-rate heating DSC. The results are compared with data for melt-spun and water-quenched amorphous material. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359239
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructure and magnetic properties of mechanically alloyed anisotropic Nd-Fe-B : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6238-6240 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mechanically alloyed Nd-Fe-B powders with additions of Dy, Co, and Ga were hot compacted to magnetically isotropic materials and then deformed by die upsetting to obtain anisotropic magnets. Magnets can be processed either with a medium coercivity Hci of 7.8 kA/cm but with a high-energy product (BH)max of 330 kJ/m3 or with a coercivity of 21.2 kA/cm and a lower (BH)max of 192 kJ/m3. Plane-view transmission electron microscopy (TEM) pictures show nearly equiaxed Nd2Fe14B grains. In cross section, the grains display the typical platelet form known from MQ 3-type magnets with a length of about 300 nm and a height of 100 nm. Characteristic for mechanically alloyed materials are up to 500 nm large globular NdOx particles distributed regularly throughout the microstructure which inhibit the anisotropic grain growth. In addition 5–20 nm small NdOx precipitates are found within some Nd2Fe14B grains. X-ray diffraction studies also indicate that the degree of texturing after die upsetting is smaller for mechanically alloyed than for melt-spun materials. High-resolution TEM experiments did not show any grain boundary phase usually found in melt-spun materials; however, this needs to be confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358292
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  • 4
    Electronic Resource
    Electronic Resource
    The effective microwave surface impedance of high Tc thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6940-6945 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of the effective surface impedance Zeff=Reff+iXeff of superconducting thin films on the film thickness d, on the magnetic field penetration depth λ, and on the dielectric properties of the substrate material is investigated theoretically by means of impedance transformations. It was found that the effective surface resistance Reff can be expressed by RSf(d/λ)+Rtrans where RS is the intrinsic surface resistance of the superconductor. The function f(d/λ) describes the altered current density distribution in the film. Rtrans arises from power transmission through the film. It depends on d and λ as well as on the dielectric properties of the substrate material and is significantly altered in the case of a resonant background. The effective surface reactance Xeff of a superconducting thin film can be expressed by XS cosh(d/λ) where XS=ωμ0λ is the intrinsic surface reactance. Measurements of Zeff at 87 GHz have been performed for YBa2Cu3O7−δ thin films grown epitaxially by laser ablation on SrTiO3, MgO, and LaAlO3. With the best films, Reff (77 K) values of 21 mΩ and RS (77 K) values of 8 mΩ were achieved. The temperature dependence of λ was found to be in good agreement to both weak-coupling BCS theory in the clean limit and the empirical two-fluid model relation with λ (0 K) values ranging from 140 to 170 nm and 205 to 250 nm, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345037
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  • 5
    Electronic Resource
    Electronic Resource
    Glass-forming range in mechanically alloyed Ni-Zr and the influence of the milling intensity (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3224-3228 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous Ni-Zr powders have been prepared by mechanical alloying from crystalline elemental powders. The glass-forming range has been determined by x-ray diffraction, differential scanning calorimetry and saturation magnetization measurements. From 27 to 83 at. % Ni the powders become amorphous. This shows that deep eutectics do not play any role, contrary to amorphization by melt spinning. Crystallization temperatures, crystallization enthalpies, and wave numbers Qp, obtained from x-ray diffraction investigations, are compared with the data received for rapidly quenched samples. In addition, the effect of the milling intensity on the glass formation has been studied for the first time. If the intensity is too high, crystalline intermetallic phases are formed. On the other hand, the powder needs an extended milling time to become completely amorphous if the milling intensity is too low. Conclusions on the actual temperature of the individual particle during mechanical alloying and on the glass-forming process are drawn from these results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341540
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  • 6
    Electronic Resource
    Electronic Resource
    Progress of the amorphization reaction during mechanical alloying in Fe-Zr (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1408-1413 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The amorphization process in mechanically alloyed Fe-Zr powders has been investigated by optical and scanning electron microscopy, x-ray diffraction, differential scanning calorimetry, and saturation magnetization measurements. The transformation from the initially layered composite to the amorphous alloy occurs between 2 and 16 h milling time. Longer milling leads to a homogenization within the particles. Prior to amorphization the internal stress within the powder particles strongly increases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339972
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  • 7
    Electronic Resource
    Electronic Resource
    Large magnetoresistance of the polycrystalline metamagnetic layered manganite La1.2Nd0.2Sr1.6Mn2O7 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 814-816 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization and magnetotransport have been investigated for polycrystalline samples of the bilayer Ruddlesden–Popper compound La1.2Nd0.2Sr1.6Mn2O7 that shows the colossal magnetoresistance effect connected with ferromagnetic ordering at TC=74 K. At T2=38 K the compound reveals a transition from the ferromagnetic to an antiferromagnetic spin arrangement of alternating ferromagnetic bilayers, which undergoes a first order metamagnetic transition towards ferromagnetism in a magnetic field of ∼3.5 kOe at 20 K. In measurements of resistance vs magnetic field, this transition is accompanied by a large resistance drop of [R(5 kOe)−R(0)]/R(0)=−60% at 5 K. The tunneling-like magnetoresistance (MR) known for current transport perpendicular to the layers in (La, Nd)1.4Sr1.6Mn2O7 single crystals contributes to this large MR observed in a polycrystalline sample. While current is expected to mainly follow the bilayers within the grains due to the anisotropy of conductivity, the high value of resistivity of our sample (∼8 Ω cm at 5 K) suggests that current paths are partially directed perpendicular to the layers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371946
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  • 8
    Electronic Resource
    Electronic Resource
    Highly coercive SmCo5 magnets prepared by a modified hydrogenation-disproportionation-desorption-recombination process (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5666-5668 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hydrogenation-disproportionation-desorption-recombination (HDDR) process was applied to SmCo5 using extreme conditions, namely high hydrogen pressures and reactive milling under hydrogen. Investigations on the hydrogen absorption behavior of SmCo5 by differential scanning calorimetry under hydrogen pressures between 1 and 7 MPa showed absorption events due to an interstitial absorption at about 100 °C and a disproportionation reaction at about 600 °C. X-ray diffraction showed the disproportionation of SmCo5 into Sm hydride and fcc-Co. A favorable effect of high hydrogen pressures on the disproportionation reaction was observed which can be explained by a decrease of the free enthalpy of the samarium hydride for increasing hydrogen pressures. Reactively milled SmCo5 showed also the products of the disproportionation reaction. The recombination to the original SmCo5 phase on hydrogen desorption in a subsequent heat treatment in vacuum was successful for both methods. However, Sm2O3, Sm2Co17, and Sm2Co7 were detected as minor phases. Maximum coercivities μ0JHC of 2.1 and 4.7 T were achieved for high pressure and reactively milled HDDR powders, respectively. The high coercivities originate from the high anisotropy field of the SmCo5 phase in combination with the grain refinement due to the HDDR treatment. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369834
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  • 9
    Electronic Resource
    Electronic Resource
    Two-phase high-performance Nd–Fe–B powders prepared by mechanical milling (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1540-1544 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanocrystalline two-phase NdFeB+α-Fe material was prepared by milling techniques and subsequent heat treatment. These isotropic exchange-coupled powders show excellent hard magnetic properties with enhanced remanences up to 1.20 T and energy densities (BH)max around 150 kJ/m3. The performance is based on (i) the use of grain refining additions, (ii) partial substitution of Fe by Co and (iii) the use of pre-melted master alloys. The distribution of Co among the hard and soft magnetic phases upon milling and annealing is studied via Curie temperature measurements up to 10 at. % Co substitution. The effect of Co on the intrinsic properties is estimated and clarifies the extrinsic magnetic behavior. An overview of samples prepared with different milling techniques and compositions is presented. It summarizes the above listed, three different approaches to improve the magnetic performance together with the influence of the phase ratio of hard and soft magnetic phases. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1380223
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  • 10
    Electronic Resource
    Electronic Resource
    Atomic ordering and magnetic properties in Nd57Fe20B8Co5Al10 solids (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3565-3569 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nd57Fe20B8Co5Al10 bulk cylinders and ribbons were quenched from the melt at different cooling rates using copper mold casting and melt spinning, respectively. Both the melt-spun ribbons and the cast cylinders display x-ray diffraction patterns without obvious crystalline peaks. However, the ribbons show soft magnetic properties, the cylinders are hard magnetic, and the crystallized alloys are not ferromagnetic at all. On the other hand, the cylinders show different exothermic transformation behavior than the ribbons upon heating to elevated temperatures. While the ribbons are regarded as amorphous, the structure of the cylinders prepared at slower cooling rate is considered to consist of metastable ordered clusters. This structure forms in the undercooled melt most likely due to intensive generation of ordered nuclei and slow growth kinetics. The magnetic coherence length, which is equivalent to the dimension of the ordered clusters, may be larger than the exchange length. Therefore, the cylinders shows much larger coercivity than the ribbons. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288697
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