| 1. |
- 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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| 2. |
- Ghorbani, Shaban Reza, et al.
(författare)
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Disorder Driven Localization in Charge Neutrally Doped 123 Superconductors
- 2006
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Ingår i: Low Temperature Physics. - : AIP. ; , s. 439-440
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Konferensbidrag (refereegranskat)abstract
- Charge neutral dopings with equal amounts of CaTh or CaPr on rare earth site in Nd-123 have been investigated by studies of the normal state electrical resistivity, p, the Seebeck coefficient S, and the Hall coefficient R-H. In spite of comparable rates of depression of the superconducting T, significant differences are observed in the doping concentration dependence of p, S, and RH between the two dopings. These results are discussed in terms of disorder induced localization.
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| 3. |
- 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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| 4. |
- Rapp, Östen, et al.
(författare)
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Anomalous transport in rhombohedral MgM2Al3
- 2009
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Ingår i: 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 2. - : IOP Publishing.
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Konferensbidrag (refereegranskat)abstract
- The cubic (beta) and the rhombohedral- (beta') phases of Mg2Al3 are complex metallic alloys of related structure and more then 800 atoms in their unit cells. The electronic transport properties of these phases are remarkably different. We report and discuss some aspects of the magnetoresistance of these phases.
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| 5. |
- Rapp, Östen., et al.
(författare)
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Critical exponents at the metal-insulator transition in AlPdRe quasicrystals
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:1
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Tidskriftsartikel (refereegranskat)abstract
- Insulating icosahedral AlPdRe with resistance ratios R[=rho(4.2 K)/rho(295 K)] from 40 to 220 has been studied by magnetoresistance and conductivity measurements. Consistent results for the localization length xi and the characteristic temperature T-o were determined. (R-R-c) increases from the metal insulator transition (MIT) into the insulator as the inverse of the shrinking volume of the electron wave functions similar toxi(-3). Localization is driven by disorder. Evidence is discussed that the MITs in i-AlPdRe and doped semiconductors belong to the same universality class.
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| 6. |
- Rapp, Östen, et al.
(författare)
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Electronic and atomic disorder in icosahedral AlPdRe
- 2008
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:11, s. 114120-
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Tidskriftsartikel (refereegranskat)abstract
- Relations between electronic and atomic disorder of i-AlPdRe have been investigated by studies of neutron irradiated and annealed samples. The advantage with this technique is that a single sample can be monitored over a significant range of varying electronic properties, without concern for any influence of varying impurities. X-ray diffraction, the electrical resistivity and its temperature dependence, and the magnetoresistance are studied. The results show that annealings of an irradiated sample lead to improvement of the atomic order, as reflected in increased intensities of the x-ray diffraction peaks, while electronic properties change in the direction of increasing electronic disorder towards a metal-insulator transition. The observed relation in quasicrystals that improved atomic structure is associated with stronger anomalies in transport properties is thus also seen in i-AlPdRe. In particular, the variation of the diffusion constant in the region of small values of the resistivity is found to be similar for annealed polygrain samples and for single grain samples with varying Pd concentration, as evaluated from literature data, indicating a similar development of electronic disorder in both sets of samples. However, the problem remains as to why the resistivity is small in single grain samples which are atomically well-ordered. The possibility of a strong sensitivity to concentration differences is pointed out.
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| 7. |
- Rapp, Östen
(författare)
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Electronic properties of alloys
- 2008
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Ingår i: Basics of thermodynamics and phase transitions in complex metallic alloys. - New Jersey : World Scientific. - 9789812790583 - 9812790586 ; , s. 259-318
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Electronic proprties of alloys consisting of metals are reviewed starting from the level of an undergraduate curriculum in solid state physics. These alloys occur in three different forms of solid matter, viz. crystalline alloys, amorphous alloys, and quasicrystals. A selection of electronic properties of these materials will be discussed, including examples from conduction in good metals to electron transport in insulators. The presentation is intended as a background to complex metallic alloys, the main theme of the School.
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| 8. |
- Rapp, Östen, et al.
(författare)
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Neutron irradiation and annealing recovery in the AlPdRe quasicrystal
- 2006
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Ingår i: Low Temperature Physics, Pts A and B. - MELVILLE, NY : AMER INST PHYSICS. - 9780735403475 ; , s. 1307-1308
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Konferensbidrag (refereegranskat)abstract
- The effect of high energy neutron irradiation and subsequent low temperature annealings of icosahedral AlPdRe has been studied. For an insulating sample, brought into a metallic state by irradiation, the resistivity rho, at 4.2 K was found to increase with increased annealing temperature T-a, while the resistance ratio R=rho(4.2 K)/rho(295 K) increased according to a previously established general relation for as prepared samples. The intensity of X-ray diffraction peaks were found to increase with increasing T-a, thus indicating improved icosahedral order. It is concluded that irradiation and annealing offers a method to reversibly tune a single icosahedral AlPdRe sample over a range of R-values, that R is therefore not sensitive to external impurities, and is a useful parameter to tune the metal-insulator transition.
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| 9. |
- Rapp, Östen, et al.
(författare)
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Recent results at the metal-insulator transition of icosahedral AIPdRe
- 2006
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Ingår i: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; 86:05-mar, s. 655-661
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Tidskriftsartikel (refereegranskat)abstract
- The metal-insulator transition, MIT, in icosahedral AlPdRe has been studied from measurements of magnetoresistance and conductivity. Results for the localisation length xi, the characteristic hopping temperature To and their relations at the MIT are discussed. The results indicate important similarities between i-AlPdRe and doped semiconductors.
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