W. Schmidbauer

University of Oxford, Oxford, England, United Kingdom

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Publications (9)7.11 Total impact

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    ABSTRACT: The paramagnetic Meissner effect (PME) in the field cooled susceptibility has been observed in superconducting single crystals of Ba_{1-x}K_xBiO_3 using magnetometers of Quantum-Design Co.. The PME is similar to that observed in cuprates and Nb superconductors. For the Ba_{0.63}K_{0.37}BiO_3 crystal, the PME is observed in cooling process under the field up to 750 Oe. The PME was not found in the virgin-charged superconducting magnet. The PME is found in a superconductor with trapped flux and may arise from a remnant field, a temperature inhomogeneity near T_c, and a potassium-concentration inhomogeneity.
    07/2002;
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    ABSTRACT: For a Ba0.63K0.37BiO3 single crystal with Tc ≈31 K, Hc1≈750 Oe at 5 K, and dimensions 3×3×1 mm3, the temperature and field dependences of magnetic hysteresis loops have been measured within 5–25 K in magnetic fields up to 6 Tesla. The critical current density is Jc(0) ≈1.5 × 105A/cm2 at zero field and 1×105A/cm2 at 1 kOe at 5 K. Jc decreases exponentially with increasing field up to 10 kOe. A linear temperature dependence of Jc is observed below 25 K, which differs from the exponential and the power-law temperature dependences in high-Tc superconductors including the BKBO. The linear temperature dependence can be regarded as an intrinsic effect in superconductors.
    Physica C-superconductivity and Its Applications - PHYSICA C. 01/2000; 341:729-730.
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    ABSTRACT: A systematic study of the anisotropic magnetic penetration depth λ for several high-Tc superconductors is presented. It is shown that the existence of the linear term in the low temperature in-plane penetration depth is independent of the number of CuO2 planes per unit cell, the carrier concentration and the anisotropy. The anisotropy, however, is found to have strong effects in the out-of-plane component. The effects of Zn substitution on λ and the importance of the CuO2 planes for dx2−y2 pairing are discussed.
    Physica C Superconductivity 08/1997; 282:145-148. · 0.72 Impact Factor
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    ABSTRACT: The paramagnetic Meissner effect (PME) in the field cooled susceptibility has been observed in superconducting single crystals of Ba1–xKxBiO3 using magnetometers of Quantum-Design Co. The PME is similar to that observed in cuprates and Nb superconductors. For the Ba0.63K0.37BiO3 crystal the PME is observed in cooling process under the field up to 750 Oe. The PME was not found in the virgin-charged superconducting magnet. The PME is found in a superconductor with trapped flux and may arise from a remnant field, a temperature inhomogeneity near Tc, and a potassium-concentration inhomogeneity.
    Journal of Low Temperature Physics 10/1996; 105(3):557-562. · 1.18 Impact Factor
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    ABSTRACT: The temperature ({ital T}) dependence of the anisotropic magnetic penetration depth λ({ital T}) of magnetically aligned powders of crystalline HgBaâCaâCuâO{sub 8+δ} is reported. Measurements were performed in the Meissner state using the ac-susceptibility technique. The temperature dependences of the in-plane, λ{sub {ital ab}}({ital T}), and out-of-plane, λ{sub {ital c}}({ital T}), penetration depths are markedly different. This is believed to arise from the large anisotropy ratio γ=[λ{sub c}(0)/λ{sub {ital ab}}(0)]â30. The behavior of λ{sub {ital ab}}({ital T}) is indicative of {ital d}-wave superconductivity while λ{sub {ital c}}({ital T}) is similar to the behavior expected for a superconductor with intrinsic Josephson coupling between the CuOâ planes. Similar measurements were performed on Ba{sub 0.6}K{sub 0.4}BiOâ powders for comparison. {copyright} {ital 1996 The American Physical Society.}
    Physical review. B, Condensed matter 03/1996; 53(6):R2999-R3002. · 3.66 Impact Factor
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    ABSTRACT: The paramagnetic Meissner effect (PME) in the field cooled susceptibility has been observed in superconducting single crystals of Ba1-xKxBiO3 using magnetometers of Quantum-Design Co. The PME is similar to that observed in cuprates and Nb superconductors. For the Ba0.63K0.37BiO3 crystal the PME is observed in cooling process under the field up to 750 Oe. The PME was not found in the virgin-charged superconducting magnet. The PME is found in a superconductor with trapped flux and may arise from a remnant field, a temperature inhomogeneity near Tc, and a potassium-concentration inhomogeneity.
    Journal of Low Temperature Physics - J LOW TEMP PHYS. 01/1996; 105(3):557-562.
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    ABSTRACT: A magnetization study using three techniques with different time scales down to 10−4 s has been performed on single crystals of the three-dimensional high-Tc superconductor Ba0.6K0.4BiO3. A fishtail effect (second peak in M(B)) is observed in a large temperature range down to the shortest time scale. At high temperature (T = 0.74 Tc) the peak is still visible for the shortest time scale but disappears with increasing waiting time showing that it is not related to flux creep phenomena. The origin of the fishtail effect in high-Tc superconductors is discussed.
    Physica C Superconductivity 01/1996; 267(3):270-278. · 0.72 Impact Factor
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    ABSTRACT: The Lattice dynamics of Ba.6K.4BiO3 was investigated by inelastic neutron scattering on a superconducting single crystal (T c =26 K (midpoint)). At low frequencies the dispersion curves are very similar to those observed in BaPb.75Bi.25O3. Differences were found in the bond bending vibrations of the BiO6 octahedra which indicate that the binding in the K-doped compound is more ionic. Rather anomalous features were observed in the high frequency Bi-O bond stretching vibrations which resemble those observed in the high T c cuprates La1.85Sr.15CuO4 and YBa2Cu3O7. The observed frequency shifts are interpreted as the consequence from a strong electron phonon coupling. The data are compared to the results obtained on non superconducting Ba.98K.02BiO3.
    Journal of Superconductivity 09/1995; 8(5):595-598.
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    ABSTRACT: The isothermal growth of non-cuprate high TC Ba1−XKXBiO3 single crystals from a KOH flux with Bi2O3 and Ba(OH)2 ∗ 8H2O added will be described. Two arrangements of electrodes were used: a) three electrodes with constant overpotential on the working electrode and b) two electrodes with constant current. The crystals were characterised by EPMA, magnetic susceptibility and X-ray powder diffraction measurements.
    Physica C Superconductivity 01/1994; · 0.72 Impact Factor