| 1. |
- 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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| 2. |
- 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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| 3. |
- Andersson, Magnus, et al.
(författare)
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Scaling of the vortex-liquid resistivity in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:18, s. 1845111-1845119
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Tidskriftsartikel (refereegranskat)abstract
- The consequences of a recently proposed model [A. Rydh. O. Rapp. and M. Andersson. Phys. Rev. Lett. 83. 1850 (1999)] for the vortex-liquid resistivity close to a vortex liquid-to-glass transition are anal-zed in detail. We find a detailed quantitative agreement between the model and resistivity measurements on disordered, optimally doped YBa2Cu3O7-delta single crystals. For temperatures below the superconducting transition temperature. a scaling of all measured resistivity curves in magnetic field (0
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| 4. |
- Bjornangen, T., et al.
(författare)
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Multiterminal transport measurements : In-plane anisotropy and vortex liquid correlation in YBa2Cu3O7-delta
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 64:22
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Tidskriftsartikel (refereegranskat)abstract
- Using a modified pseudoflux transformer geometry, the in-plane anisotropy and vortex-liquid correlation of an untwinned YBa2Cu3O7-delta single crystal have been studied. The square-shaped, multiterminal sample design allows comparative studies of a- and b-axis properties for arbitrarily oriented magnetic fields. We compare the in-plane resistivity in the case of intrinsic pinning with the longitudinal resistivity, i.e., with the resistivity in absence of a macroscopic Lorentz force. The relative ratio between resistivities rho (a) and rho (b) in the vortex state can be made to vary over a wide range by controlling the direction of the applied magnetic field. Evidence is found for almost isotropic fluctuations corresponding to a fluctuation anisotropy gamma (A)(ab)approximate to1.1, noted to be clearly lower than the anisotropy gamma (ab)=1.27 obtained from the vortex phase diagram.
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| 5. |
- Ghorbani, Shaban Reza, et al.
(författare)
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Neutron diffraction studies of Nd1-xPrxBa2Cu3O7-delta : Evidence for hole localization
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:1, s. 145031-
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Tidskriftsartikel (refereegranskat)abstract
- Sintered samples of Nd1-xPrxBa2Cu3O7-delta with x=0, 0.05, 0.10, 0.15, 0.20, and 0.30 have been studied by neutron diffraction, x-ray diffraction, and resistivity measurements. Sample stoichiometry was carefully checked. Atomic distances within the unit cell and the oxygen content were shown to be almost independent of Pr doping. Bond valence sums (BVSs) were calculated from the neutron diffraction data assuming either a constant valence or a mixed valence for Cu and Pr ions. The planar Cu2 valence is independent of Pr doping and the chain Cu1 valence is roughly constant, while the hole concentration in the planes and chains decrease with increasing Pr doping for both BVS calculation methods. All together, this indicates that hole localization on the Nd(Pr) site is a main reason for the decrease of the hole concentration in the planes. A consistent relation between the hole concentration in the planes calculated from the constant valence method and the depression of the critical temperature is also obtained, both for Pr-doped Nd-123 and for Y(Pr)-123 studied previously.
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| 6. |
- Han, S. H., et al.
(författare)
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Three-dimensional XY critical fluctuations of the dc electrical conductivity in Bi2Sr2CaCu2O8+delta single crystals
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:17, s. 11776-11779
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented to analyze the dc critical fluctuation conductivity Delta sigma of Bi2Sr2CaCu2O8+delta single crystals in zero magnetic field. Two crossovers are obtained upon approaching T-c; first the Ginzburg crossover from the mean-held region to the initial critical regime, where the critical exponent a of Delta sigma changes from -1/2 to -2/3, and then, closer to T-c, a crossover of alpha form -2/3 to 1/3 in the critical region. Good agreement is found with the expectations from the three-dimensional XY model.
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| 7. |
- Karkin, A. E., et al.
(författare)
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Monitoring an insulator-metal transition in icosahedral AlPdRe by neutron irradiation
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:9
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Tidskriftsartikel (refereegranskat)abstract
- The intrinsic disorder effect on the electrical resistivity and magnetoresistance (MR) of icosahedral AlPdRe is studied by use of high-energy neutron irradiation. The icosahedral phase is preserved under irradiation with a decrease of x-ray peak intensity and volume of the coherent icosahedral phase. An insulator-metal transition, as observed in the MR, can be driven by the irradiation and is monitored by the resistance ratio R[=rho(4.2 K)/rho(295 K)]. The relation of MR vs R was found to be similar for samples of a widely different history.
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| 8. |
- Lundqvist, Björn, et al.
(författare)
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Cutoff of the vortex-glass behavior in Tl(2)Ba(2)CaCu(2)O(8+delta) superconducting thin films
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 58:10, s. 6580-6584
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Tidskriftsartikel (refereegranskat)abstract
- The vortex dynamics of a Tl(2)Ba(2)CaCu(2)O(8+delta) thin film has been measured by electrical resistivity and I-V characteristics. The temperature T*(B) defined from a vortex-glass analysis of the resistivity in the vortex liquid state using the Vogel-Fulcher relation is shown to be consistent with a vortex-glass-like scaling of the I-V characteristics in the high dissipation regime. Below T*, there is however a significant temperature range in which the flux creep does not vanish at low currents. This suggests that the transition into a glassy vortex state is cut off at some length scale.
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| 9. |
- Lundqvist, Björn, et al.
(författare)
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Empirical scaling of the vortex glass line above 1T for high-T(c) superconductors of varying anisotropy
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:22, s. 14064-14067
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Tidskriftsartikel (refereegranskat)abstract
- The resistive transition into a glassy vortex state in oxygen-deficient YBa(2)CU(3)O(7-delta) twinned single crystals of varying anisotropy gamma (8.7 less than or equal to gamma less than or equal to 35) has been studied with an applied magnetic field along the crystallographic c axis. For B greater than or similar to 1T, the glass. line is well described by the empirical relation B(g)=B(o)[(1 -T/T(c))/(T/T(c))](alpha), where alpha approximate to 1 and B(o) approximate to 1.85 Phi(o)/(gamma d)(2). The successful fit to this relation both below and above an alleged crossover in the solid vortex state has important consequences for the H-T phase diagram of high-temperature superconductors.
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| 10. |
- Poon, S. J., et al.
(författare)
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Comment on "Extrinsic origin of the insulating behavior of polygrain icosahedral Al-Pd-Re quasicrystals"
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:21, s. 216201-
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper, Dolinšek [Phys. Rev. B 74, 134201 (2006)] suggested that the insulating behavior of icosahedral (i) Al-Pd-Re is of extrinsic origin. Large resistivities and insulatinglike properties of high resistivity samples were conjectured to result from the porous structure and the observed enhanced oxygen concentration in between the quasicrystal grains in some i-Al-Pd-Re samples. We point out that these hypotheses are incompatible with published work on the structure and properties of i-Al-Pd-Re.
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