| 1. |
- Chen, HonQui, et al.
(författare)
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Determining the crystal symmetry of epitaxial Tl-2201 thin films by X-ray diffraction
- 2002
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Ingår i: Physica. C, Superconductivity. - 0921-4534. ; 371:2, s. 83-89
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal symmetry of epitaxial Tl-2201 films on LaAlO3 and SrTiO3 substrates is investigated by X-ray diffraction. In the case of Tl1.85Ba2CuO6 film, a φ-scan of the (1 1 10) reflection showed four diffraction peaks separated by 90.00±0.02°. A 2θ-scan of the same reflection exhibited a single peak. 2Θ−ω- and φ-scans of the corresponding reflection in Tl2.04Ba2CuO6 show splitting and broadening of the diffraction peaks indicating an orthorhombic distortion. The effect of errors in film alignment on the φ-scan and 2Θ−ω-scans is discussed. A periodic function, δ=a+bsin(ω−φ), was used to correct the φ-scan measurements. The influence of lattice mismatch between film and substrate on the structural symmetry of the films is discussed.
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| 2. |
- Koblischka, M. R., et al.
(författare)
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Flux distributions of an artificially granular YBa2Cu3O7- thin film observed using magneto-optic imaging
- 2000
-
Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 331, s. 113-26
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Tidskriftsartikel (refereegranskat)abstract
- Flux distributions in a YBa2Cu3O7- thin film with artificial granularity are observed by means of magneto-optic imaging. At low magnification, flux patterns generated exclusively by the intergranular currents flowing in the intergranular area (effective medium) are directly observed. The properties of this effective medium are studied by taking flux density profiles that reveal the intergranular current density. As the observations at high magnifications show the flux penetration and pinning within the individual disks, we can identify and study the different contributions of the intergranular and intragranular current densities to the flux patterns. We show that our model sample reproduces several features observed, e.g., in Ag-sheathed (Pb,Bi)2Sr2Ca2Cu3O10+ tapes
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| 3. |
- Nyholm, R., et al.
(författare)
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ELECTRONIC AND STRUCTURAL-PROPERTIES OF THE CU-BI2CASR2CU2O8 INTERFACE
- 1991
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 180:1-4, s. 120-123
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Tidskriftsartikel (refereegranskat)abstract
- The formation of the Cu-Bi2CaSr2Cu2O8 interface has been studied by photoelectron spectroscopy using synchrotron radiation. Photon energies in the range 20-1000 eV were utilized in order to probe both the valence band and to monitor chemical changes upon Cu deposition, as revealed by the core-level shifts. A strong chemical reaction between Bi2CaSr2CuO8 and Cu is manifested by the formation of metallic Bi. From the intensity variations as a function of electron emission angle it is shown that the metallic Bi segregates to the top surface layer.
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| 4. |
- Nyholm, R., et al.
(författare)
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PHOTOEMISSION-STUDY OF THE BI2CASR2CU2O8 SUPERCONDUCTOR WITH CU, AG AND AU OVERLAYERS
- 1993
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 218:1-2, s. 103-108
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a photoemission study of the interaction of Cu, Ag and Au with clean single-crystal Bi2CaSr2Cu2O8 superconductor surfaces. Both the valence-band and the Bi 5d, O 1 s and Sr 3d core levels were monitored for all overlayers. Cu, Ag and Au were deposited as consecutively thicker layers starting with a third of a monolayer and progressing in steps up to a deposition in the range of eight monolayers. Comparing the results for the different overlayers reveals the Ag overlayer to be less reactive than Au which causes the formation of metallic Bi on cleaved Bi2CaSr2Cu2O8 surface. Cu is shown to be the most reactive of the three metals. The Au and Ag overlayers display an island-growth mode, while Cu grows in a layer-by-layer fashion.
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| 5. |
- Qvarford, M., et al.
(författare)
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Polarisation-dependent X-ray absorption in high- and low-Tc Bi2Sr2Can-1CunO4+2n superconductors
- 1993
-
Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 214:1-2, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- Taking advantage of the linear polarisation of synchrotron radiation, the polarisation dependence of the O K and Cu L3 X-ray absorption edges has been compared for in situ cleaved Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 single crystals. The X-ray absorption spectra were measured by means of total electron yield detection. The spectra show for both crystals that the lowest unoccupied Cu 3d and O 2p orbitals are dominantly oriented parallel to the a-b plane, but also the presence of a small amount of unoccupied orbitals oriented perpendicular to the a-b plane can be deduced from both the O K and Cu L3 absorption spectra. A shift of the order of 0.5 eV between absorption into the in-plane and the out-of-plane Cu 3d orbitals was measured for the Bi2Sr2CaCu2O8 crystal, but no such shift was found for the Bi2Sr2CuO6 crystal.
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| 6. |
- Selinder, T.I., et al.
(författare)
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Yttrium oxide inclusions in YBa2Cu3Ox thin films : Enhanced flux pinning and relation to copper oxide surface particles
- 1992
-
Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 202:1-2, s. 69-74
-
Tidskriftsartikel (refereegranskat)abstract
- Semi-coherent Y2O3 (yttria) inclusions are identified in high quality epitaxial YBa2Cu3Ox (YBCO) thin films by using transmission electron microscopy and energy dispersive X-ray analyses. Magnetization measurements show enhanced flux pinning in films containing an increasing number density of inclusions. The inclusions are incorporated into the films without disturbing the YBCO structure appreciably. The number density is ≈ 1017 cm-3 in films having transport critical currents of 4x106 A cm-2 at 77 K. Nucleation of the yttria inclusions is suggested to occur spontaneously during film growth. The abundance of yttria inclusions is connected to the occurrence of large Cu-rich surface particles in films that have optimum superconducting properties.
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| 7. |
- Zakharov, Alexei, et al.
(författare)
-
Photoelectron escape depth in Bi2Sr2CaCu2O8+x
- 2003
-
Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 398:1-2, s. 49-52
-
Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectra of Sr and Ca shallow core levels in Bi2Sr2CaCu2O81, (Bi2212) single crystals exhibit a strong attenuation effect because the photoelectron escape depth is very short in this material. This results may have a strong impact on the interpretation of ARPES and STM spectra near the Fermi level since it suggests the electronic states of planes other than CuO play a role in both tunneling and photoemission on the BiO terminated surface in Bi2212. (C) 2003 Elsevier B.V. All rights reserved.
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| 8. |
- Ambrosch-Draxl, C., et al.
(författare)
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First-principles study of oxygen ordering in YBa2Cu3O7-x
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 1997-1998
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed first-principles calculations considering different patterns of oxygen/vacancy ordering in the Cu-O chains of YBa2Cu3O7-x. From the total-energy values we determine the effective interactions of the oxygen atoms within the basal plane by using the cluster expansion technique. Furthermore, we discuss the effect of ordering to the density of states at the Fermi level.
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| 9. |
- Andersson, Britt M., et al.
(författare)
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Electrical transport properties of dense bulk YBa2Cu4O8 produced by hot isostatic pressing
- 1990
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 170:5-6, s. 521-531
-
Tidskriftsartikel (refereegranskat)abstract
- Highly dense sintered YBa2Cu4O8 has been produced by hot isostatic pressing (HIP). The electrical resistivity varrho of this material has been measured as a function of temperature T and pressure varrho in the range 40–650 K and 0–0.7 GPa. Both the temperature dependence and the pressure dependence of varrho are found to be well described by a model based on the standard Bloch-Grüneisen theory. It is pointed out that varrho is liner in T only under isobaric conditions, while varrho is strongly nonlinear in all high-Tc superconductors under isochoric (constant volume) conditions. The critical current density of the material is 900 A/cm2 at 4 K, while the resistivity is 630 μΩ cm at 294 K.
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| 10. |
- Andersson, Britt M., et al.
(författare)
-
Thermal conductivity of YBa2Cu4O8 under high pressure
- 1993
-
Ingår i: Physica. C, Superconductivity. - : Elsevier B.V.. - 0921-4534 .- 1873-2143. ; 216:1-2, s. 187-194
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal diffusivity a of YBa2Cu4O8 (1-2-4) has been measured as a function of pressure p and temperature T over the range 85
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| 11. |
- Andersson, Magnus, et al.
(författare)
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H-T PHASE-DIAGRAM OF DYBA2CU3O7-DELTA(Y0.45PR0.55)BA2CU3O7-DELTA MULTILAYERS IN THE MIXED-STATE
- 1994
-
Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 235, s. 2617-2618
-
Tidskriftsartikel (refereegranskat)abstract
- From measurements of I-V characteristics of DyBa2Cu3O7-delta/(Y0.45Pr0.55)Ba2Cu3O7.delta multilayers, we have experimentally determined the characteristic temperature separating the vortex liquid from the vortex solid. We suggest that the cross-over temperature is determined by the anisotropy given by the artificially layered structure of these multilayers and that the studied system can be used as a test system for vortex dynamics.
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| 12. |
- Andersson, Magnus, et al.
(författare)
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MAGNETORESISTANCE MEASUREMENTS ON (CA,TH)-DOPED YBA2CU3O7-DELTA
- 1991
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 185, s. 1901-1902
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Tidskriftsartikel (refereegranskat)abstract
- Magnetoresistance measurements on sintered Y1-2xCaxThxBa2Cu3O7-delta samples with x < = 0.1 are reported. By fitting the measured data to the Hikami-Larkin theory, we obtain coherence lengths, xi-ab and xi-c’ and a phase breaking time tau-phi All these parameters are found to decrease with (Ca,Th) doping. We also conclude that magnetoresistance measurements are highly sensitive to inhomogeneities in the sample.
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| 13. |
- Andersson, Magnus, et al.
(författare)
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Neutron-diffraction studies of Ca-Pr doped YBa2Cu307-delta
- 1993
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 205:1-2, s. 105-110
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed neutron powder diffraction on samples in a series Y1-2xCaxPrxBa2Cu3O7-delta, with x=0.0, 0.1 and 0.2, and analyzed the data with the Rietveld refinement method. Small changes were observed in atomic bond distances when the amount of Ca-Pr was increased. In general, these changes could qualitatively be viewed as the sum of effects from the Ca and Pr substitutions in YBa2Cu3O7-delta samples. Analyses of the distance between the superconducting CuO2 Planes suggest that the Pr ions in the Ca-Pr substituted samples have an effective valence close to + 4.
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| 14. |
- Andersson, Magnus, et al.
(författare)
-
NEUTRON-DIFFRACTION STUDIES OF Y1-2XCAXTHXBA2CU3O7-DELTA WITH X-LESS-THAN=0.1
- 1991
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 185, s. 915-916
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Tidskriftsartikel (refereegranskat)abstract
- We have made Rietveld refinements on neutron powder diffraction data from Y1-2xCaxThxBa2Cu3O7-delta samples with x < = 0.1. Only small changes in lattice distances are detected. Most noticeable are a flattening of the CuO-planes and a possible small increase in the distance between Cu(1) and the edge oxygen O(4). A comparison with the Y1-xCaxBa2Cu3O7-delta system is made.
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| 15. |
- Andersson, Magnus, et al.
(författare)
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STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF Y1-2XCAXPRXBA2CU3O7-GAMMA
- 1992
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 190:3, s. 255-260
-
Tidskriftsartikel (refereegranskat)abstract
- Samples of the nominal composition Y1-2xCaxPrxBa2Cu3O7-delta with 0 less-than-or-equal-to x less-than-or-equal-to 0.4 have been studied by X-ray diffraction techniques, chemical analyses, and measurements of the super conducting transition temperature and the upper critical magnetic field. For x less-than-or-equal-to 0.25, the results indicate that Ca and Pr can both replace Y in agreement with the nominal composition, while for x > 0.25 only Pr enters the orthorhombic unit cell. Compared to Pr substitution in 1:2:3 we observe small changes in the depression of T(c) and strong changes in the critical field slopes. These results suggest that if Pr has a magnetic pair-breaking effect, it is close to being temperature independent.
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| 16. |
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| 17. |
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| 18. |
- Andersson, Magnus, et al.
(författare)
-
Vortex liquid properties in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 332:1-4, s. 86-92
-
Tidskriftsartikel (refereegranskat)abstract
- The electrical anisotropy, gamma = (m(c)/m(ab))(1/2), can easily be varied by changing the oxygen content in single crystals of YBa2Cu3O7-delta (YBCO); thus making this system useful as a test system For vortex dynamics in high-temperature superconductors (HTSC). Here, some recent results are reviewed. Measurements of the c-axis resistivity with the magnetic field B II ab-plane is shown to be a powerful tool in studying vortex velocity correlations both parallel and perpendicular to the applied field. In optimally doped crystals, we iind evidence that the in-plane vortex lattice melts at T-m into a disentangled vortex liquid, which looses its correlation along the c-axis at a higher temperature T-br > T-m. For weakly disordered crystals and magnetic fields B \\ c-axis, a relation between the vortex glass line and the magnetic field dependence of the characteristic energy, U*, in the pinned vortex liquid is proposed. This approach is shown to give support to our idea of describing the vortex glass resistivity in the liquid regime by a modified glass correlation Length, xi(g) = xi(0)\k(B)T/U-0 - 1\(-nu) which depends on the average pinning energy, Lr,, in the system [A. Rydh, O. Rapp, M. Andersson, Phys. Rev. Lett. 83 (1999) 1850].
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| 19. |
- Andersson, Magnus, et al.
(författare)
-
Vortex liquid resistivity in disordered YBa2Cu3O7-delta single crystals
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 1239-1240
-
Tidskriftsartikel (refereegranskat)abstract
- The vortex solid-to-liquid transition line, T-g(B) and the linear resistivity in the vortex liquid of an optimally doped disordered YBa2Cu3O7-delta Single crystal is analyzed in detail. Our previously proposed description [Rydh, Rapp and Andersson, Phys.Rev.Lett. 83 (1999) 1850] is shown to quantitatively describe both T-g(B) and the vortex liquid resistivity above T-g using the same parameters. Furthermore, a comparison with the thermally activated behaviour usually employed to account for the resistivity in the vortex liquid is reported.
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| 20. |
- Andersson, Magnus, et al.
(författare)
-
Vortex liquid-to-solid transition in underdoped YBa2Cu3O7-delta single crystals with B parallel to ab
- 2003
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 388, s. 691-692
-
Tidskriftsartikel (refereegranskat)abstract
- A nearly magnetic field independent vortex liquid-to-solid transition has been observed in both the ab-plane and in the c-axis resistivity of underdoped YBa2Cu3O7-delta single crystals for magnetic fields Bparallel toab-plane. These observations suggest that intrinsic pinning caused by the superconducting layers do neither lead to a system of completely decoupled superconducting layers nor to a smectic vortex phase at high fields. A possible explanation may include a transition driven by changes in elastic properties (e.g., the shear modulus) of the vortex system.
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| 21. |
- Ao, Ping, et al.
(författare)
-
Vortex dynamics within the BCS theory
- 1997
-
Ingår i: Physica. C, Superconductivity. - : Elsevier. - 0921-4534 .- 1873-2143. ; 282-287:Part 1, s. 367-370
-
Tidskriftsartikel (refereegranskat)abstract
- Based on the BCS theory we outline a conventional path integral derivation of the transverse force and the friction for a vortex in a superconductor. The derivation is valid in both clean and dirty limits at both zero and finite temperatures. The transverse force is found to be precisely as what has been obtained by Ao and Thouless using the Berry's phase method. The friction is essentially the same as the Bardeen and Stephen's result.
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| 22. |
- Bjornangen, T., et al.
(författare)
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In-plane anisotropy and chain contribution from the magnetoresistivity of YBa2Cu3O7-delta
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 1885-1886
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetoresistivity measurements were made in untwinned YBa2Cu3O7-delta above T-c for B\\c and B\\ab, with I\\a or b. A fluctuation theory that allows for an in-plane coherence length anisotropy (gamma = xi (b)/xi (a)) was used to determine gamma. The contribution to the magnetoconductivity from the CuO-chains was also analyzed.
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| 23. |
- Bjornangen, T., et al.
(författare)
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Vortex liquid and solid correlation in untwinned YBa2Cu3O7-delta
- 2003
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 388, s. 727-728
-
Tidskriftsartikel (refereegranskat)abstract
- Longitudinal- and inter-vortex correlations in an untwinned YBa2Cu3O7-delta single crystal were studied in the liquid and driven solid state, using a modified, symmetric pseudo-flux transformer method. The response of the flowing vortex system below T-m was significantly different along the field (Hparallel toa) and perpendicular to it (Hparallel toc), with both cases probed by an in-plane current mainly parallel to b.
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| 24. |
- Dou, S.X., et al.
(författare)
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Improvement of critical current density in the Bi-Pb-Sr-Ca-Cu-O system through hot isostatic pressing
- 1990
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 167:5-6, s. 525-528
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of hot isostatic pressing (HIPing) on densification and the superconducting properties of the Bi-Pb-Sr-Ca-O system were investigated. A relative density up to 95% and a critical current density greater than 1100 A/cm2 at 77 K were achieved through HIPing at 650°C for 2 h under 200 MPa argon. Under these conditions, the product gave a value of Jc four times that without HIPing. To was unaffected by HIPing for samples encapsulated with a combination of glass and silver tubes. However, To was suppressed from 103 K to 86 K for samples encapsulated with stainless steel and silver tubes while Jc increased from 260 A/ cm2 to 1086 A/cm2 during HIPing, indicating that the weak links were significantly improved. A new minor phase, having a composition of Bi/Pb/Sr/Ca/Cu=0.58/2.8/3.0/2.1/1.1, was observed in HIPed samples but its effect on Jc is not clear
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| 25. |
- Dou, S.X., et al.
(författare)
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Microstructure and flux pinning in superconducting Bi-Pb-Sr-Ca-Cu-O wires
- 1990
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 172:1-2, s. 63-70
-
Tidskriftsartikel (refereegranskat)abstract
- The critical current density (Jc) of Ag-clad Bi-Pb-Sr-Ca-Cu-O wire has been measured to be 1.2×104 A/cm2 at 77 K in zero field. The high Jc is attributed to a combination of elimination of the poisoning effect of Ag on superconductivity, grain alignment, and enhancement of flux pinning. Jc-H dependence was significantly improved in the Ag-clad tape, which has a Jc of 1.0×103 A /cm2 at 77 K and 4000 Oe, while the Jc of the sintered pellet drops two orders of magnitude at only 100 Oe. A pronounced anisotropy in Jc under high magnetic field is attributed to the grain alignment. Planar defects, such as heavy stacking faults parallel to the a-b plane in the rolled tape, are considered to be effective pinning centres.
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| 26. |
- Festin, Örjan, et al.
(författare)
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"Double superconducting transition" in YBCO thin films
- 2002
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 369:1-4, s. 295-299
-
Tidskriftsartikel (refereegranskat)abstract
- Two 150 nm thick YBCO films have been investigated using flux noise and complex conductance measurements. In both experiments thermally excited vortices are studied. The first film shows a single transition, with Tc≈88.2 K and ΔTc≈0.3 K, while the second film shows a two-step transition with Tc1≈90.1 K and ΔTc≈0.1 K, and Tc2≈89.8 K and ΔTc≈0.15 K. The experimental results obtained for the double transition sample in combination with computer simulation data in Medvedyeva et al. (in this volume) indicate that this sample can be described as two weakly coupled homogeneous superconducting layers, one on top of the other, with different critical temperatures.
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| 27. |
- Fivat, Patrice, et al.
(författare)
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Possible entanglement of the vortices in dyba2cu3O7 (y1-xprx)ba2cu3O7 coupled heterostructure
- 1994
-
Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 235, s. 2599-2600
-
Tidskriftsartikel (refereegranskat)abstract
- Thermally activated flux motion is studied in proximity coupled multilayers, containing a number N of 24 Angstrom thick DyBa2Cu3O7 layers separated by 96 Angstrom (or more) of(Y1-xPrx)Ba2Cu3O7 alloy (x=0.4, x=0.55). In contrast to ultra-thin decoupled layers, for which we find that the activation energy for flux motion U approximate to=logB (H//c), coupled samples show a cross-over to a power law behaviour U approximate to B–0.5 at magnetic field H*. This characteristic field depends on the anisotropy and decreases as N increases, a behaviour which can be understood in terms of the entanglement of the vortices, resulting in a relative increase of U due to the flux line crossing energy.
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| 28. |
- Flipse, C. F. J, et al.
(författare)
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XPS study of the new superconductor Nd-Ce-Cu-O
- 1989
-
Ingår i: Physica C: Superconductivity. - : Elsevier BV. - 0921-4534. ; 162-164:2, s. 1389-1390
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present XPS and Auger measurements on Nd1.85Ce0.15CuO3.96 and its parent material. These measurements show that electron doping, by substitution of Ce4+ in the case of Nd3+, results in a filling of the Cu 3d9 states. So the Ce doped compound will have a higher 3d10 contribution. The intensity of the Cu-2p satellite is very low for this new superconductor with respect to the high-Tc superconductors.
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| 29. |
- Ghorbani, S. R., et al.
(författare)
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An anomalous dip in thermoelectric power of Nd1-xPrxBa2Cu3O7-delta
- 2003
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 388, s. 351-352
-
Tidskriftsartikel (refereegranskat)abstract
- The thermoelectric power, S, has been studied for sintered samples of Nd1-xPrxBa2Cu3O7-delta with 0 less than or equal to x less than or equal to 0.30 in the temperature range from the superconducting T-c to room temperature. S increases with decreasing temperature,and has a broad maximum at T-max in the region around 120 K before decreasing strongly when T-e is approached. Several properties indicate a decrease of charge concentration with increasing doping, x, from S(x, 290 K), T-max, and the resistivity rho(x, 290 K). An anomaly has been observed in S(T) for x greater than or equal to 0.20 in the form of a dip at 78 K of order 15% of S. The origin of this feature is not known.
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| 30. |
- Ghorbani, Shaban Reza, et al.
(författare)
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Normal state Hall effect in Nd1-xCaxBa2Cu3O7-delta : competition between added charge and disorder
- 2003
-
Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 390:2, s. 160-166
-
Tidskriftsartikel (refereegranskat)abstract
- The transport properties of sintered samples of Nd1-xCaxBa2CU3O7-delta with 0 less than or equal to x less than or equal to 0.20 have been studied in the normal state by Hall resistivity measurements. The Hall coefficient, R-H(x, T) was well described in terms of two different models. In a phenomenological narrow band model, the conduction band width became narrower with increasing Ca concentration while the density of states band width decreased slightly. A competition between two effects (i) added charge, and (ii) disorder introduced into the CuO2 planes by doping, could be the main reason for the observed small decrease of the band widths. In the Anderson model, the temperature dependent part of the Hall angle was independent of hole concentration and disorder while the temperature independent part increased linearly with increasing Ca content. The results in both models support that Ca introduces disorder in the CuO2 planes.
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| 31. |
- Ghorbani, Shaban Reza, et al.
(författare)
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Thermoelectric power and resistivity of Nd1-xCaxBa2Cu3Oy and Nd1-xLaxBa2Cu3Oy
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 339:4, s. 245-252
-
Tidskriftsartikel (refereegranskat)abstract
- The structural and transport properties of Nd1-xCaxBa2Cu3Oy (x = 0.0, 0.03, 0.06, and 0.10) and Nd1-xLax- Ba2Cu3Oy. (x nominally 0.0, 0.05, 0.10, and 0.15) have been studied by X-ray powder diffraction, electrical resistivity, and thermoelectric power measurements. In both series, the a- and b-axis lattice parameters decrease with increasing doping while the c-axis lattice parameter increases. The transport properties suggest improved metallic behaviour with increasing Ca doping in contrast to La doping. An anomalous sharp peak in the thermoelectric power close to T-c was observed, which depended on the doping content. We analysed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained.
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| 32. |
- Ghorbani, Shaban Reza, et al.
(författare)
-
Thermoelectric power and resistivity of Nd1-xPrxBa2Cu3O7-delta
- 2001
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 353:1-2, s. 77-84
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Tidskriftsartikel (refereegranskat)abstract
- The structural and transport properties of Nd1-xPrxBa2Cu3O7-delta (x = 0.0, 0.05, 0.10, and 0.15), have been studied by X-ray powder diffraction, electrical resistivity measurements, and thermoelectric power measurements. The decrease of the superconducting critical temperature with doping is described by a parabolic term and a linear term. The c-axis lattice parameter and the cell volume decrease with doping up to x = 0.10. Analyses of the thermoelectric power, critical temperature, c-axis lattice parameter, and the cell volume suggest that the Pr ions have a valence close to +4 at low doping concentration. The room temperature resistivity indicates that hole concentration decreases with increasing Pr doping. The room temperature thermoelectric power is positive for all samples and increases with increasing Pr doping due to a decrease in the carrier concentration. We analyzed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained. The band width of the narrow band increases and its peak position moves away from the Fermi energy with increasing doping concentration.
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| 33. |
- Grivel, Jean-Claude, et al.
(författare)
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First-order melting transition observed from resistivity measurements in ultra-pure YBa2Cu3O7-delta single crystals with high twin boundary density
- 1999
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 322:3-4, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- R(T) measurements have been performed on optimally and overdoped heavily twinned high-purity YBa2Cu3O7-delta single crystals, under a magnetic field B oriented parallel to the twin boundary planes (B parallel to c). The characteristic feature attributed to the flux line lattice melting transition has been observed in the overdoped case for B greater than or equal to 5 T. The first-order transition was not found in the optimally doped sample, even when B was tilted with respect to the c-axis. Differences between these samples are discussed.
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| 34. |
- Han, S. H., et al.
(författare)
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Studies of dynamic critical behaviour in YBa2Cu3O7-delta single crystals
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 1855-1856
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Tidskriftsartikel (refereegranskat)abstract
- Up to now, the value of the dynamic critical exponent z is still an open question. We have studied this exponent in the intermediate (XY) critical regime in zero field for a set of high quality YBa2Cu3O7-delta Single crystals in terms of Fisher-Fisher-Huse (FFH) dynamic scaling, and using previously obtained values for the critical exponents cu of the de critical conductivity fluctuations. In this regime (i.e. the absence of Coulomb interactions), one would expect model-E dynamics (z = 1.5) to apply with the conserved charge-density conjugate to the phase fluctuations. However, we find the dynamic critical exponent to be z = 2, which is in agreement with the suggestion of FFH that due to plasma fluctuations, fully relaxational dynamics, model A (z = 2), should be appropriate.
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| 35. |
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| 36. |
- Haviland, David B., et al.
(författare)
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Quantum phase transition in one-dimensional Josephson junction arrays
- 2001
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 352:04-jan, s. 55-60
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Tidskriftsartikel (refereegranskat)abstract
- We describe experiments on one-dimensional arrays of small capacitance Josephson junctions which show how the Coulomb blockade of Cooper pair tunneling is influenced by changing the Josephson coupling energy in situ with an externally applied magnetic flux. We show how the zero bias resistance of the array is affected by the length of the array, and we use the length scaling of this resistance to infer that a quantum phase transition occurs as the Josephson coupling energy is changed. The data are qualitatively analyzed in terms of a theoretical model of the quantum phase transition which uses a mapping to the two-dimensional XY model.
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| 37. |
- Hu, Q H, et al.
(författare)
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Properties of Tl-2201 thin films
- 1997
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 282-287:Part 2, s. 1075-1076
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Tidskriftsartikel (refereegranskat)abstract
- Tl2Ba2CuO6 (Tl-2201) thin films were synthesised on single crystal LaAlO3 and SrTiO3 substrates and on bicrystal LaAlO3 by an ex-situ process. Depending on thallium content and processing conditions, the films were orthorhombic or tetragonal. Tc was in the range 30 – 92 K while Jc reached 4.106A/cm2 at 12 K. By oxygen depletion, Tc was increased by 15 – 20 K for some films.
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| 38. |
- Istomin, Sergey Ya., et al.
(författare)
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A new superconducting sulfide—'EuNb2S5'
- 1998
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Ingår i: Physica. C, Superconductivity. - : Elsewier. - 0921-4534 .- 1873-2143. ; 300, s. 67-70
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Tidskriftsartikel (refereegranskat)abstract
- A new low-temperature superconducting (Tc≈3 K) niobium sulfide ‘EuNb2S5' with a hexagonal structure (a=3.3556(8) Å, c=23.440(9) Å) was synthesized from a mixture of EuS, Nb(m) and S in evacuated and sealed silica tubes, heated at 1100°C for 48 h. This superconductor was characterized by EDX analysis, X-ray powder and electron diffraction studies. Electron diffraction revealed the presence of a supercell: asuper=bsuper=√7×a.
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| 39. |
- Jukna, A, et al.
(författare)
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Electric properties of planar Ag/HgBa2CaCu2O6+delta interface
- 1999
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 316:1-2, s. 83-88
-
Tidskriftsartikel (refereegranskat)abstract
- Silver coatings were magnetron sputtered onto the surface of highly c-axis-oriented HgBa2CaCu2O6+delta superconducting thin films exhibiting zero resistance T-c at about 120 K and the critical current density similar to 10(5) A/cm(2) at 100 K. Electrical resistance of the Ag/HgBa2CaCu2O6+delta planar interface and current-voltage dependencies were investigated in a course of post-deposition annealing of the Ag/HgBa2CaCu2O6+delta at 50-350 degrees C in both purl oxygen and oxygen-free ambient. Results of the electrical measurements are explained in terms of the insulating layer formation at the Ag/HgBa2CaCu2O6+delta interface. It is assumed this insulator is a product created by oxygen non-stoichiometry and decomposition of the superconductor at the interface between both materials. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 40. |
- Kawano, K., et al.
(författare)
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BIG films fabricated by PLD for magnetic flux visualisation of YBCO
- 2002
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 372, s. 696-699
-
Tidskriftsartikel (refereegranskat)abstract
- Bi3Fe5O12 (BIG) magneto-optic (MO) films have been grown onto (111) and (100) gadolinium gallium garnet substrates by pulsed laser deposition (PLD). X-ray and transmission electron microscopy measurements have confirmed the epitaxial growth of the BIG films oil both substrate orientations, Faraday rotation angles of both films showed linear field dependence from - 1600 to + 1600 G and the saturated Faraday rotation angle values were similar to5 deg/ pm and similar to7.8 deg/mum for the (111) and (100) oriented films, respectively. A change in the MO contrast of both films in applied magnetic field has been observed and magnetic nux distributions have been visualised in YBa2Cu3O- , (YBCO) bulk superconductor using the (001) oriented BIG film.
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| 41. |
- Koseoglu, Y, et al.
(författare)
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ESR studies on high-T-c superconductor MgB2
- 2003
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Ingår i: Physica. C, Superconductivity. - : Elsevier BV. - 0921-4534 .- 1873-2143. ; 390:3, s. 197-203
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Tidskriftsartikel (refereegranskat)abstract
- MgB2, a high-T-c superconductor, has been studied by electron spin resonance (ESR) techniques at the temperature range of 7-300 K. Polycrystalline powders consisting of MgB2, MgO and MgB4 phases were diluted and oriented in paraffin by applying an external magnetic field of 15 kG. A very narrow (2.5 G), strong, and isotropic signal that corresponded to almost free electron g-values was observed at all temperatures. Both the signal intensity and line width were observed to exhibit strong temperature dependence below T-c. The intensity of the ESR spectra, which corresponds to dc susceptibility, generally obeys the Curie law in this temperature range; However, some critical temperatures (approximately 215, 190, 150, and 39 K) were evident from both intensity and line width curves. While the ESR line is strongly broadened, the signal intensity significantly start to increase just below T = 39 K (corresponding to a transition temperature from normal to superconducting state), passes through a broad maximum around 30 K and then shows a sharp decrease as the temperature is decreased further. The origins of the minor changes both in the intensity and the line width curves at other (higher) critical temperatures are not clear yet. In fact, the change at 215 K was observed to be meta-stable. These minor changes might be taken as signs for changes of local crystalline field symmetry around weakly localized conduction electrons or holes, which are the sources of the ESR signal.
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| 42. |
- Langmann, Edwin, et al.
(författare)
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Mean field analysis of a model for superconductivity in an anti-ferromagnetic background
- 1998
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Ingår i: Physica. C, Superconductivity. - : Elsevier. - 0921-4534 .- 1873-2143. ; 296:1-2, s. 119-136
-
Tidskriftsartikel (refereegranskat)abstract
- We study a lattice fermion model for superconductivity in the presence of an anti-ferromagnetic background, described as a fixed external staggered magnetic field. We discuss the possibility that our model provides an effective description of coexistence of anti-ferromagnetic correlations and superconductivity, and its possible application to high-temperature superconductivity. We also argue that, under certain conditions, this model describes a variant of the periodic Anderson model for heavy fermions. Using a path integral formulation we construct mean field equations, which we study in some detail. We evaluate the superconducting critical temperature and show that it is strongly enhanced by anti-ferromagnetic order. We also evaluate the superconducting gap, the superconducting density of states, and the tunneling conductivity, and show that the most stable channel usually has a dx2-y2-wave gap.
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| 43. |
- Lundqvist, Björn, et al.
(författare)
-
Field independent vortex solid-to-liquid transition for B parallel to ab in oxygen deficient single crystals of YBa(2)Cu(3)O(7-delta)
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341:Part 3, s. 1335-1336
-
Tidskriftsartikel (refereegranskat)abstract
- Single crystals of YBa(2)Cu(3)O(7-delta) provide a suitable test system for vortex dynamics in high temperature superconductors, since the electrical anisotropy gamma = (m(c)/m(ab))(1/2) can easily be varied over a large range by changing the oxygen content. In this paper the vortex solid-to-liquid transition, as determined from a vortex-glass analysis of the resistivity, has been studied for magnetic fields 012 T parallel with the ab plane of oxygen deficient single crystals of YBCO. Strikingly for high magnetic fields a field independent vortex solid-to-liquid transition is observed. A possible explanation for this phenomenon involving a crossover to a two-dimensional (2D) system is suggested.
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| 44. |
- Lundqvist, Björn, et al.
(författare)
-
Vortex dynamics in oxygen deficient single crystals of YBa2Cu3O7-delta
- 1997
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 282, s. 1959-1960
-
Tidskriftsartikel (refereegranskat)abstract
- In YBa2Cu3O7-delta (YBCO), oxygen deficiencies in the CuO chains change the coupling between the charge carriers in adjacent superconducting CuO2 planes and thereby the electrical anisotropy, gamma=(m(c)/m(ab))(1/2). Such crystals therefore provide a simple test system for systematic studies of the influence of anisotropy on vortex dynamics. We have studied the vortex glass transition of YBCO single crystals with delta in the range of 0.07 to 0.27, corresponding to gamma between 9 and 18, for magnetic fields 0
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| 45. |
- Lundqvist, P., et al.
(författare)
-
mu SR study of charge neutrally doped Nd1-2xCaxThxBa2Cu3O7-delta
- 2000
-
Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 338:4, s. 263-268
-
Tidskriftsartikel (refereegranskat)abstract
- Equal amounts of Ca and Th were doped into the Nd1-2xCaxThxBa2Cu3O7-delta superconductor with 0 less than or equal to x less than or equal to 0.10. X-ray diffraction showed a single orthorhombic phase for all samples except at x = 0.10, suggesting a solubility limit below x = 0.10. For increasing doping concentration x the superconducting T-c and the electrical resistivity, rho at 275 K both vary strongly, with a linear decrease of T-c and an increase of rho. The muon spin relaxation rate, sigma, follows the Uemura line for large x, and deviates in the direction of increasing sigma-values for decreasing x. The approach of the data to the Uemura Line was compared between different alloy systems by plotting the normalized distance to the Uemura line as a function of doping concentration. Ca-Th doped samples were found to approach the Uemura line about three times faster than for Ca-Pr doping. The same replacements in Y-123 confirm this result. The strong doping concentration dependence of sigma in Ca-Th substituted samples is explained in terms of electronic disorder effects.
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| 46. |
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| 47. |
- NISKANEN, K, et al.
(författare)
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ANGULAR DEPENDENT MAGNETIC-PROPERTIES OF SINGLE-CRYSTAL BI-SR-CA-CU-O
- 1991
-
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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| 48. |
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| 49. |
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| 50. |
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