| 1. |
- Andersson, Magnus, et al.
(författare)
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CA AND PR SUBSTITUTION IN Y-BASED AND SM-BASED 1-2-3 COMPOUNDS
- 1993
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 48:10, s. 7590-7597
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Tidskriftsartikel (refereegranskat)abstract
- Substitution with equal amounts of Ca and Pr has been studied mainly in Y- and Sm-based 1:2:3 samples and with some results also for Nd-based samples. Structural and chemical analysis and measurements of the superconducting T(c) and the upper critical magnetic field were performed. It was found that Ca and Pr can be dissolved in the orthorhombic structure up to about 25 at. % each in both Y- and Sm-based samples while for larger concentrations, only Pr continued to enter into the 1:2:3 structure. The depression of T(c) with Ca-Pr doping was found to be linear in concentration in contrast to the accelerated decrease in samples doped with only Pr. The rate of depression of T(c) increased in the sequence Y-, Sm-, and Nd-based hosts. The results suggest that Ca-Pr doping isolates a characteristic Pr-impurity effect in 1:2:3 samples. The critical magnetic-field slopes of Y- and Sm-based samples were almost independent of Ca-Pr content in the cosolubility region while a strong decrease was observed for larger Pr content, similar to 1:2:3 samples doped with Pr only. These results suggest an almost-temperature-independent magnetic pair-breaking effect by Pr.
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| 2. |
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| 3. |
- Andersson, Magnus, et al.
(författare)
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Electronic and structural properties of Laves-phase MgZn(2) of varying chemical disorder
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:2, s. 024202-
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Tidskriftsartikel (refereegranskat)abstract
- The C14 Laves-phase MgZn(2) has been investigated from 30 to 36 at. % Mg. In this way chemical disorder can be monitored over a limited concentration range and the influence on electron properties can be investigated. Our studies include thermodynamic calculations of atomic configurations of Mg and Zn at off-stoichiometric compositions, electronic-transport measurements, and electronic band-structure calculations of MgZn(2). The disorder introduced by alloying was found to be substitutional for all C14 alloys, and to have a markedly stronger effect on resistivity and magnetoresistance, Delta rho(B)/rho(0), on the Mg-rich side due to strain introduced when Mg substitutes for Zn. rho(T) and Hall constant were characteristic for weakly disordered binary alloys. Delta rho/rho of MgZn(2) was large, reached 6 at 4.2 K and 8 T, and decreased strongly at off-stoichiometric compositions. The results are discussed in view of the band-structure results and in terms of relations between atomic order and electronic properties. Several properties were found to resemble pure Zn. An empirical correlation over more than six orders of magnitude in Delta rho/rho was found for Zn and Zn-based alloys.
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| 4. |
- Andersson, Magnus, et al.
(författare)
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Magnetoresistance and Hall effect of the complex metal alloy Mg2Al3
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:2
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Tidskriftsartikel (refereegranskat)abstract
- Unusual electronic transport properties have been found in the rhombohedral beta'-phase of the complex metallic alloy Mg2Al3. The magnetoresistance (MR) is 2 orders of magnitude larger than in the related cubic beta-Mg2Al3-phase and Kohler's rule is strongly violated in the beta'-phase at higher temperatures. Above about 100 K the Hall coefficient R-H of the beta- and beta'-phases are similar and free-electron-like, while in the beta'-phase, R-H changes sign with decreasing temperature at low fields. We have inquired into the sources of these transport anomalies, but have not been able to clearly identify the grounds. Several conventional mechanisms for a large magnetoresistance are discussed, and found not to be applicable. The different properties in the beta- and the beta'-phases are puzzling since the magnitudes of the electrical resistivities are similar and omega(c)tau (cyclotron frequencyxscattering time) is equally small in both phases. The similar temperature range in which anomalies occur in the beta'-phase in the resistivity, the Hall effect, and the magnetoresistance indicates an electronic transition or a change of the electron structure in this phase below about 100 K.
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| 5. |
- Andersson, Magnus, et al.
(författare)
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MAGNETORESISTANCE MEASUREMENTS ON (CA,TH)-DOPED YBA2CU3O7-DELTA
- 1991
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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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| 6. |
- Andersson, Magnus, et al.
(författare)
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MAGNETORESISTANCE MEASUREMENTS ON POLYCRYSTALLINE YBA2CU3O7-DELTA
- 1991
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 44:14, s. 7722-7725
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Tidskriftsartikel (refereegranskat)abstract
- The magnetoresistance of a polycrystalline sample of YBa2Cu3O7-delta has been measured by an ordinary resistive method at temperatures from about 1 to 15 K above T(c) and in magnetic fields up to 12 T. From our experimental results and the theory of Hikami and Larkin, we obtain values of the coherence lengths xi-ab = 15.6 angstrom and xi-c = 3.6 angstrom and of the phase-breaking time tau-phi = 1.8 x 10(-13) s.
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| 7. |
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| 8. |
- Andersson, Magnus, et al.
(författare)
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Neutron-diffraction studies of Ca-Pr doped YBa2Cu307-delta
- 1993
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 205:1-2, s. 105-110
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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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| 9. |
- Andersson, Magnus, et al.
(författare)
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NEUTRON-DIFFRACTION STUDIES OF Y1-2XCAXTHXBA2CU3O7-DELTA WITH X-LESS-THAN=0.1
- 1991
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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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| 10. |
- Andersson, Magnus, et al.
(författare)
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RELATION BETWEEN THE CU(1)-O(4) DISTANCE AND T(C) IN Y1-2XCAXTHXBA2CU3O7-DELTA - RAMAN-SCATTERING AND CALCULATION OF THE ELECTRON-PHONON INTERACTION
- 1992
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 46:10, s. 6501-6504
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Tidskriftsartikel (refereegranskat)abstract
- The strong depression of T(c) with Ca-Th substitution in Y1-2xCaxThxBa2Cu3O7-delta has been investigated in a model calculation of the electronic and phononic contributions from the apex oxygen, O(4), on the electron-phonon interaction, lambda. The shift with Ca-Th substitution of the characteristic O(4) vibrational mode was measured by Raman scattering. The electronic part eta of lambda has been calculated at several distances between chain Cu(1) and O(4) in the region of the observed variation with x. Eta was found to depend strongly on this distance. The results show a small increase with x of the O(4) frequency and a strong decrease of eta. Both these factors thus contribute to a decrease of lambda. We therefore find evidence that a decreasing electron-phonon interaction is associated with the depression of T(c) in Ca-Th substituted YBa2Cu3O7-delta.
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