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Author Weiden, M.; Hauptmann, R.; Richter, W.; Geibel, C.; Hellmann, P.; Koppen, M.; Steglich, F.; Fischer, M.; Lemmens, P.; Guntherodt, G.; Krimmel, A.; Nieva, G.
Title Magnetic phase diagram of CuGe1-xSixO3 Type Journal Article
Year 1997 Publication PHYSICAL REVIEW B Abbreviated Journal
Volume 55 Issue 22 Pages (down) 15067-15075
Keywords
Abstract The effect of Si doping on the magnetic properties of the spin-Peierls (SP) system CuGeO3 was found to differ strongly between polycrystals (PC's) and single crystals (SC's). In SC's, the SP state is suppressed much mon strongly, whereas the existence region of the antiferromagnetic (AF) state is enhanced. We investigated the origin of this difference by means of magnetic susceptibility, specific heat, thermal expansion, Raman scattering, elastic neutron scattering, and x-ray measurements on CuGe1-xSixO3 samples prepared under different conditions. The partial oxygen pressure and the temperature during the synthesis were found to have a profound influence on the magnetic properties: preparation under reduced oxygen pressure leads to a stabilization of the AF state, whereas heating above the melting point results in a strong decrease of T-SP in Si-doped samples. Therefore, both the AF stabilization and the TSP reduction observed in SC's are not an intrinsic effect of Si doping PC samples, which can be prepared at lower temperatures and more oxidizing conditions, reflect much better the intrinsic properties of CuGe1-xSixO3. We were able to prepare PC samples up to 50 at. % Si and found a continuous decrease of the one-dimensional character of the magnetic properties without pronounced changes in the structure.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1098-0121 ISBN Medium
Area Expedition Conference
Notes ISI:A1997XF60200055 Approved no
Call Number BT @ hernan @ Serial 240
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Author Pardo, F.; Mackenzie, A.P.; delaCruz, F.; Guimpel, J.
Title Effect of the reversibility region on the low-temperature vortex structure imaged by Bitter magnetic decoration Type Journal Article
Year 1997 Publication PHYSICAL REVIEW B Abbreviated Journal
Volume 55 Issue 21 Pages (down) 14610-14613
Keywords
Abstract We have combined magnetic measurements and imaging of the vortex lattice at low fields in Tl2Ba2CuO6-delta single crystals with different oxygen content. Those with high critical temperature T-c > 80 K have a reversible region while those with low T-c < 30 K have an irreversible magnetization in the whole range of temperatures, up to T-c. The presence of the reversible region allows the formation of ordered vortex structures, while amorphous structures are obtained when no reversible region is present below T-c. The results are discussed in terms of vortex nucleation processes in the individual pinning regime.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0163-1829 ISBN Medium
Area Expedition Conference
Notes ISI:A1997XE37100086 Approved no
Call Number BT @ hernan @ Serial 187
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Author Righi, E.F.; Grigera, S.A.; Nieva, G.; Lopez, D.; delaCruz, F.
Title Finite vortex correlation in the c direction in YBa2Cu3O7-delta above the first-order melting transition Type Journal Article
Year 1997 Publication PHYSICAL REVIEW B Abbreviated Journal
Volume 55 Issue 21 Pages (down) 14156-14159
Keywords
Abstract The in- and out-of-plane resistivities of untwinned YBa2Cu3O7-delta show that at the melting temperature of the vortex lattice T-m(H), the c-axis vortex correlation length has a finite value, demonstrating that the first-order transition is a true melting and not a decoupling transition. The vortex liquid just above T-m(H) has a correlation length in the field direction on the order of a micron. The in-plane I-V characteristics in the liquid state show non-Ohmic behavior, providing evidence that thermal fluctuations dominate the response even at the first-order transition.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0163-1829 ISBN Medium
Area Expedition Conference
Notes ISI:A1997XE37100033 Approved no
Call Number BT @ hernan @ Serial 241
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Author Righi, E.F.; Grigera, S.A.; Lopez, D.; Nieva, G.; delaCruz, F.; Civale, L.; Pasquini, G.; Levy, P.
Title Enhancement of c-axis vortex correlation by twin boundaries and columnar defects in YBa2Cu3O7-delta Type Journal Article
Year 1997 Publication PHYSICAL REVIEW B Abbreviated Journal
Volume 55 Issue 9 Pages (down) 5663-5665
Keywords
Abstract We report on transport measurements using the flux transformer configuration in a twinned single crystal of YBa2Cu3O7-delta with columnar defects. The vortex liquid shows velocity correlation along the c axis (the direction of the applied magnetic field and the columnar defects) at temperatures that correspond to an uncorrelated liquid in unirradiated samples of the same thickness. These results and previous work about the effect of twin boundaries on vortex velocity correlation show that phase coherence in the field direction is not an intrinsic property of vortex liquids but one induced by extended defects.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0163-1829 ISBN Medium
Area Expedition Conference
Notes ISI:A1997WN21800036 Approved no
Call Number BT @ hernan @ Serial 242
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Author Sereni, J.G.; Trovarelli, O.; Schmerber, G.; Kappler, J.P.
Title Comparative study of thermal and magnetic properties of CeTyX4-y ferromagnets Type Journal Article
Year 1997 Publication Physical Review B – Condensed Matter and Materials Physics Abbreviated Journal Phys. Rev. B
Volume 56 Issue 9 Pages (down) 5380-5386
Keywords
Abstract Low-temperature thermal (specific heat, C-P) and magnetic [ac susceptibility, chi(ac), and isothermal magnetization M(B)] measurements on CeTyX4-y ferromagnets (with T = Ni, Cu, Pd, Ag, Au, and X = Ga, Al, with 0.3 < y < 0.7) are reported. With the exception of T = Ni, all compounds with X = Ga show a typical second-order ferromagnetic transition. In the case of T = Ni, magnetic correlations set in at T approximate to 3T(C), (T-C being the Curie temperature) and the C-P(T) and chi(ac)(T) maxima (at 3.3 and 4.2 K, respectively) do not coincide, while the M(B) curves reveal an antiferromagnetic character at lower temperatures. In these systems, the magnetic entropy of the ordered phase is larger than 85% of Rln2, in coincidence with the low values of the Sommerfeld coefficient gamma less than or equal to 10 mJ/mol K-2. For T = Ag and X = Al, a strong diamagnetic signal was observed at T-s = 0.63 K in chi(ac)(T), with the characteristics of a superconducting component. The thermodynamical properties of these compounds confirm the lack of hybridization when the Ce atom is in a ferromagnetic ground state.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0163-1829 ISBN Medium
Area Expedition Conference
Notes ISI:A1997XW94200062 Approved no
Call Number BT @ hernan @ Serial 89
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Author Guimpel, J.; Maiorov, B.; Osquiguil, E.; Nieva, G.; Pardo, F.
Title Interrelation between persistent photoconductivity and oxygen order in GdBa2Cu3Ox thin films Type Journal Article
Year 1997 Publication Physical Review B – Condensed Matter and Materials Physics Abbreviated Journal Phys. Rev. B Condens. Matter Mater. Phys.
Volume 56 Issue 7 Pages (down) 3552-3555
Keywords
Abstract We study the metastable states induced by photoexcitation, oxygen disorder, and both effects combined in superconducting GdBa2Cu3Ox thin films. The states are identified by the temperature dependence of the resistivity. The relaxation dynamics is characterized through the time evolution of the conductivity. The results show that photoexcitation and oxygen disorder behave as noninteracting and do not cancel each other out. However, in both cases the relaxation dynamics is related to oxygen movement .
Address Centro At
Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 01631829 (ISSN) ISBN Medium
Area Expedition Conference
Notes Cited By (since 1996): 21; Export Date: 17 April 2009; Source: Scopus; CODEN: PRBMD; Language of Original Document: English; Correspondence Address: Guimpel, J.; Centro At Approved no
Call Number BT @ osquigui @ Serial 382
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Author Bauer, E.; Hauser, R.; Keller, L.; Fischer, P.; Trovarelli, O.; Sereni, J.G.; Rieger, J.J.; Stewart, G.R.
Title Onset of magnetic order in YbCu5-xAlx Type Journal Article
Year 1997 Publication Physical Review B Abbreviated Journal Phys. Rev. B
Volume 56 Issue 2 Pages (down) 711-718
Keywords
Abstract Spectroscopic, magnetic, thermal, and transport measurements under pressure are presented which were performed on YbCu5-xAlx intermetallics. The substitution of Cu by Al in YbCu5 drives the system from an almost divalent behavior of the Yb ion in YbCu5 to a trivalent state in YbCu3Al2. A compensation between the normal thermal expansion and a valence-driven contraction was found for YbCu4Al. Antiferromagnetic order sets in for x>1.5, where an increasing Al content causes both a growing transition temperature and rising saturation moments reaching 2 K and about 2.1 mu(B), respectively, for x=2. At the critical concentration (x approximate to 1.5) the possibility of a non-Fermi-liquid state is analyzed together with its tuning by pressure.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0163-1829 ISBN Medium
Area Expedition Conference
Notes ISI:A1997XL82700035 Approved no
Call Number BT @ hernan @ Serial 91
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Author Trovarelli, O.; Weiden, M.; MullerReisener, R.; GomezBerisso, M.; Gegenwart, P.; Deppe, M.; Geibel, C.; Sereni, J.G.; Steglich, F.
Title Evolution of magnetism and superconductivity in CeCu2(Si1-xGex)(2) Type Journal Article
Year 1997 Publication Physical Review B – Condensed Matter and Materials Physics Abbreviated Journal Phys. Rev. B
Volume 56 Issue 2 Pages (down) 678-685
Keywords
Abstract We have determined the magnetic phase diagram of CeCu2(Si1-xGex)(2) using specific heat, susceptibility, and resistivity measurements and additional thermal expansion and muon spin resonance experiments. The system evolves continuously from the heavy-fermion state at x = 0 to an antiferromagnetically (AF) ordered state at x = 1, though the magnetic structure undergoes significant modifications. The results strongly suggest that the AF ordering emerges from the A phase of pure CeCu2Si2. The phase diagram can be divided into three regions: Low Ge content (x less than or equal to 0.2) leads to an enhancement of the A phase of pure CeCu2Si2 and to a moderate decrease of the Kondo temperature. Despite this increase of the magnetic character, we could observe superconductivity up to x = 0.1. At large Ge content (x > 0.5) the behavior resembles that of pure CeCu2Ge2. The intermediate region is characterized by the appearance of a second magnetic transition below T-N, which seems to be of first-order type. The appearance of this transition leads to a well-defined critical point at x = 0.3 and suggests the possibility of another critical point at x = 0.5.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0163-1829 ISBN Medium
Area Expedition Conference
Notes ISI:A1997XL82700031 Approved no
Call Number BT @ hernan @ Serial 90
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Author Sereni, J.G.; Geibel, C.; Berisso, M.G.; Hellmann, P.; Trovarelli, O.; Steglich, F.
Title Scaling of the ''C-p proportional to TlnT'' dependence in Ce systems Type Journal Article
Year 1997 Publication Physica B – Condensed Matter Abbreviated Journal Physica B
Volume 230-232 Issue Pages (down) 580-582
Keywords
Abstract We analyze the T ln T dependence of the specific heat (C-p) in several Ce binaries and ternaries. We find that these systems can be directly compared by using a scaling law of the type: C-p/t = -D log t + ET0, where t = T/T-0, with the scaling temperature T-0 similar to T-K, D = 7.2 J/(mol K) and 0 < E < 0.14 J/(mol K-2). This general function describes those systems within the 0.005 < t < 0.5 range and accounts for nearly 1/2 of the expected entropy of the Ce-doublet.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0921-4526 ISBN Medium
Area Expedition Conference
Notes ISI:A1997WW40300168 Approved no
Call Number BT @ hernan @ Serial 93
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Author Luzuriaga, J.
Title Measurements in the laminar and turbulent regime of superfluid4He by means of an oscillating sphere Type Journal Article
Year 1997 Publication Journal of Low Temperature Physics Abbreviated Journal J. Low Temp. Phys.
Volume 108 Issue 3-4 Pages (down) 267-277
Keywords Calculations; Laminar flow; Oscillations; Spheres; Turbulence; Turbulent flow; Vibrations (mechanical); Oscillating sphere; Translational oscillation; Superfluid helium
Abstract The translational oscillations of a sphere in liquid helium have been measured as a way of studying superfluid turbulence. Experiments were carried out in the laminar flow regime for reference purposes, and good agreement found between measured and calculated quantities. In the turbulent region, the dissipation is found to be proportional to the square of the velocity of the sphere, as found previously by other workers. For high vibration amplitudes there is an increase in the hydrodynamic mass. This seems to scale with the superfluid fraction in a way that strongly suggests that the superfluid component plays an important role in the turbulent regime.
Address Comisi
Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 00222291 (ISSN) ISBN Medium
Area Expedition Conference
Notes Cited By (since 1996): 2; Export Date: 28 April 2009; Source: Scopus; CODEN: JLTPA; Language of Original Document: English; Correspondence Address: Luzuriaga, J.; Comisi Approved no
Call Number BT @ luzuriag @ Serial 518
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