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  • American Institute of Physics (AIP)  (7)
  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Magnetoresistance of polycrystalline layered manganites La2−2xSr1+2xMn2O7 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5420-5422 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline bulk samples of the layered manganites La2−2xSr1+2xMn2O7 showing a colossal magnetoresistance (CMR) effect were prepared for doping levels of x=0.4 and 0.5 by a solid-state reaction route. Temperature and field dependences of magnetization and of electrical resistivity have been measured between 5 K and room temperature. Ferromagnetic behavior with a Curie temperature of TC=135 K and a high value of spontaneous magnetization (64 emu g−1) was found for x=0.4. The x=0.5 compound orders antiferromagnetically near TN=215 K, showing a resistivity enhancement there. The resistivity of the x=0.4 compound shows a field dependence at low temperatures similar to that found for polycrystalline La0.7Sr0.3MnO3. The resemblance includes the presence of both a low-field and a high-field contribution to the magnetoresistance, as well as the magnitude of the low-field MR (−23% at 20 K and −15% at 77 K for H=1 kOe). The low-field MR is attributed to the effect of grain boundaries. In contrast to the grain-boundary MR of La0.7Sr0.3MnO3, it was also observed at temperatures far above the TC of the layered manganite. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369962
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  • 3
    Electronic Resource
    Electronic Resource
    Superconducting bulk magnets: Very high trapped fields and cracking (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3131-3133 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Improved trapped fields are reported for bulk melt-textured YBa2Cu3O7−δ (YBCO) material in the temperature range between 20 and 50 K. Trapped fields up to 12.2 T were obtained at 22 K on the surface of single YBCO disks (with Ag and Zn additions). In YBCO minimagnets, maximum trapped fields of 16 T (at 24 K) and of 11,2 T (at 47 K) were achieved using (Zn+Ag) and Zn additions, respectively. In all cases, the YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process and to avoid cracking. We observed cracking not only during the magnetizing process, but also as a consequence of flux jumps due to thermomagnetic instabilities in the temperature range betweeen 20 and 30 K. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413502
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  • 4
    Electronic Resource
    Electronic Resource
    Enhanced flux pinning in (Nd0.33Sm0.67)Ba2Cu3O7−δ melt-processed superconductors by Ar postannealing (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 259-261 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality binary (Nd0.33Sm0.67)Ba2Cu3O7−δ monodomain superconductors were fabricated by the combination of a compositional-controlled melt-processing technique in air and postannealing in Ar. Critical current densities over the whole field range were observed strongly dependent on Ar postannealing while holding superconducting transition temperatures as high as 96 K. The suppressed chemical variation between the rare-earth element (RE: Nd, Sm) and Ba associated with disperse RE2BaCuOy (RE211) precipitate due to the decomposition occurring in Ar postannealing was attributed to the modified flux pinning. This makes Ar postannealing promising to process superconductors with desired properties for various applications. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124341
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  • 5
    Electronic Resource
    Electronic Resource
    Trapped magnetic fields larger than 14 T in bulk YBa2Cu3O7−x (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2107-2109 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High trapped fields were found in zinc-doped, bulk melt-textured YBa2Cu3O7−x (YBCO) material showing a pronounced peak effect in the field dependence of the critical current density. Trapped fields up to 1.1 T were found at 77 K at the surface of a YBCO disk (diameter 26 mm, height 12 mm). Very high trapped fields up to 14.35 T were achieved at 22.5 K for a YBCO disk pair (diameter 26 mm, height 24 mm) by the addition of silver and using a bandage made of stainless steel. The pinning forces and trapped fields obtained in bulk YBCO material are compared with results reported for melt-processed NdBa2Cu3O7−x and SmBa2Cu3O7−x.© 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126278
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic behavior of the low-dimensional compounds Ba2Cu3O4Cl2 and Ba3Cu2O4Cl2 : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7240-7242 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Orthorhombic Ba3Cu2O4Cl2 contains folded Cu2O4 chains along the crystallographic a direction with two different Cu sites. In single crystals of this compound the magnetization measured for a field applied parallel to the a axis shows a spin-flop transition at a threshold field of 2.6 T for temperatures below TN(approximate)20 K. Above TN a Curie–Weiss behavior is found with a paramagnetic moment of 2.0 μB per Cu atom. Parallel to the b or c axis the magnetization increases linearly with the field strength, and no metamagnetic transition was detected for these directions. It is concluded that Ba3Cu2O4Cl2 has localized magnetic moments which, at low temperatures, order antiferromagnetically parallel to the a axis. The bulklike magnetic behavior of this compound is probably caused by a strong coupling between the Cu2O4 chains. Tetragonal Ba2Cu3O4Cl2 is built up of Cu3O4 planes, also with two types of copper atoms (CuA,CuB). Its magnetization increases nearly linearly with the field. Below TNA=337 K single-crystalline Ba2Cu3O4Cl2 shows a spontaneous magnetization and ferromagnetic hysteresis for fields applied parallel to the tetragonal [100] or [110] directions. For T〈TNB(approximate)33 K, the coercive field is more than one order of magnitude larger compared to that measured in the temperature range TNB〈T〈TNA. The spontaneous magnetization observed in TNB〈T〈TNA may be attributed to weak ferromagnetism of the Dzyaloshinsky–Moriya type. The behavior of Ba2Cu3O4Cl2 at lower temperatures, T≤TNB, is not yet understood. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367613
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  • 7
    Electronic Resource
    Electronic Resource
    High trapped fields in bulk YBa2Cu3O7−δ samples at temperatures around 50 K (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 117-119 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bulk melt textured YBa2Cu3O7−δ samples with single grains of about 24 mm diameter were obtained by use of SmBa2Cu3O7−x seed crystals. The maximum trapped field B0 in the gap between two samples was investigated as function of temperature. B0 increased from 1 T at 77 K to 8.5 T at 51.5 K, which is the highest trapped field achieved in nonirradiated samples. At low temperatures, cracking of the samples was observed under magnetic pressure. In this temperature range, the trapped field is limited by the mechanical strength of the samples, for which a value of 25 MPa was estimated. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119280
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