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| 2. |
- MAGNUSSON, J, et al.
(författare)
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FLUX PINNING IN YBA2CU3O7 THIN-FILMS GROWN BY DC MAGNETRON SPUTTERING
- 1992
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Ingår i: Cryogenics (Guildford). - : Elsevier BV. - 0011-2275 .- 1879-2235. ; 32, s. 1084-1088
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of YBa2Cu3O7 (YBCO) were deposited on single crystalline LaAlO3 substrates using d.c. magnetron sputtering. The quality of the films has been assessed by X-ray diffraction; YBa2Cu3O7 grows epitaxially with the c-axis parallel to the substrate normal. For some choices of the deposition parameters in the sputtering process, it was found that secondary phases were precipitated in the films. By a deliberate choice of deposition parameters, semi-coherently grown Y2O3 (yttria) inclusions could be obtained. They had square platelet or cubical shapes with sizes from 5 - 20 nm and thickness approximately 10 nm. The superconducting properties of the YBa2Cu3O7 films were investigated using SQUID magnetometry. Magnetization measurements on films with different densities of semicoherent Y2O3 inclusions indicate an enhanced flux pinning capability with increasing inclusion density.
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| 3. |
- NISKANEN, K, et al.
(författare)
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ANGULAR DEPENDENT MAGNETIC-PROPERTIES OF SINGLE-CRYSTAL BI-SR-CA-CU-O
- 1991
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 185, s. 2207-2208
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Tidskriftsartikel (refereegranskat)abstract
- The field, time and temperature dependence of the longitudinal component of the magnetization of a single crystal of BiSrCaCuO has been investigated by SQUID-magnetometry as a function of the tilt angle between the crystallographic c-axis and the applied magnetic field. We here discuss the results on the field and angular dependence of the magnetic response in zero field cooled magnetization experiments at low fields.
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| 4. |
- NISKANEN, K, et al.
(författare)
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ANISOTROPY IN SINGLE CRYSTALLINE BISRCACUO
- 1992
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Ingår i: Superconductors Science and Technology. - 0953-2048 .- 1361-6668. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- The longitudinal component of the magnetization of a single crystal of Bi2.2Sr1.7CaCu2O8 has been investigated by SQUID-magnetometry when the magnetic field is applied at different angles 0-degrees-90-degrees with respect to the crystallographic c-axis. The anisotropy of the system, deduced from the magnetization and relaxation rate data, indicates a mass anisotropy m(c)/m(ab) of order 20, a strikingly low value compared to what has been found from torque and magnetoresistance measurements m(c)/m(ab) almost-equal-to 3000.
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| 5. |
- NISKANEN, K, et al.
(författare)
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NONLOGARITHMIC MAGNETIC-RELAXATION IN BI-SR-CA-CU-O SINGLE-CRYSTALS
- 1991
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Ingår i: Superconductors Science and Technology. - 0953-2048 .- 1361-6668. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The time dependence of the low field susceptibility of a Bi2.2Sr1.7CaCu2O8 single crystal has been investigated in the field range 0.1-300 gauss and at temperatures 0.25 less-than-or-equal-to T/T(c) less-than-or-equal-to 0.9. The relaxation of the magnetization is found to change from a logarithmic to a non-logarithmic form as the applied field is increased, implying that a conventional flux creep model cannot sufficiently describe the behaviour.
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| 6. |
- NORLING, P, et al.
(författare)
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MAGNETIC-RELAXATION OF INTERGRANULAR CRITICAL-STATE IN SINTERED YBA2CU3O7-DELTA
- 1994
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 221, s. 169-176
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Tidskriftsartikel (refereegranskat)abstract
- The relaxation of the zero-field-cooled magnetisation of three sintered samples of YBa2Cu3O7-delta has been measured at low fields. Special attention was paid to the low-field regime where the motion of intergranular vortices is dominating the decay of the magnetisation. From the measured data the apparent activation energy for flux jumps, U0, was calculated. The extracted values fall in the range 0.6-2 eV, considerably higher than what has been found for the intragranular flux creep but in the same range as reported by others for intergranular creep. The samples showed somewhat different behaviours and the sample with the most homogeneous morphology had the lowest value of U0. This can be explained within theories for pinning in granular superconductors.
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| 7. |
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| 8. |
- SVEDLINDH, P, et al.
(författare)
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MAGNETIC-RELAXATION IN AN ISOTROPIC EXTREME TYPE-II SUPERCONDUCTOR
- 1991
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 43, s. 2735-2741
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Tidskriftsartikel (refereegranskat)abstract
- The time dependence of the zero-field-cooled and thermoremanent magnetization of the isotropic extreme type-II superconductor PbMo6S8 has been measured at temperatures 0.7 less-than-or-equal-to T/T(c) less-than-or-equal-to 0.95 and for fields 1 less-than-or-equal-to H less-than-or-equal-to 300 G. The results show that the time dependence of the decay can be divided into three different field regimes: (1) A low-field regime with a closely logarithmic decay and a well-established critical state. The relaxation rate [partial M/partial ln(t)] increases as H-5 for the zero-field-cooled magnetization and as H-2.4 for the thermoremanent magnetization. The reduction in magnetization over 5 decades in time (0.3-3 X 10(4) s) is, at most, a few percent. (2) A crossover-field regime with a change from a logarithmic to a nonlogarithmic decay. (3) A high-field regime where the time dependence of the decay is well described by the expression delta-M approximately [ln(t/tau-0)]-alpha. The reduction in magnetization in the crossover- and high-field regimes is as large as 25-30% in the measured time interval. The results in the high-field regime are interpreted within the theory of collective flux creep. Comparisons are made with the magnetic relaxation found in anisotropic high-T(c) superconductors.
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| 9. |
- SVEDLINDH, P, et al.
(författare)
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NONLOGARITHMIC MAGNETIC-RELAXATION IN BI2.2SR1.7CACU2O8 SINGLE-CRYSTALS - EVIDENCE FOR COLLECTIVE FLUX PINNING
- 1991
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 176, s. 336-346
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Tidskriftsartikel (refereegranskat)abstract
- High precision magnetic relaxation measurements have been performed on BiSrCaCuO single crystals with the field H applied parallel to the c-axis. At temperatures T/T(c) > 0.5, the data exhibit two different field regimes. One for H < H* (H* corresponds to the field where full flux penetration of the sample is achieved) where the ZFC and RM magnetization relaxes logarithmically with time in agreement with the conventional flux creep model; a second one for H > H* where the relaxation follows a [ln(t/t0)]-alpha dependence. This relaxation law is predicted in the collective flux creep theory for J << J(c) as well as in the vortex-glass model. In the temperature range 0.25 < T/T(c) < 0.4, there is a change in character of the measured decay of the magnetization. This change in character is interpreted to arise from thermal fluctuations of the flux-line lattice giving rise to a considerable reduction in the pinning strength above the depinning temperature.
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| 10. |
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