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Author (up) Nakamura, O.; Fullerton, E.; Guimpel, J.; Schuller, I.
Title High Tc thin films with roughness smaller than one unit cell Type Journal Article
Year 1992 Publication Applied Physics Letters Abbreviated Journal Appl. Phys. Lett.
Volume 60 Issue 1 Pages 120
Keywords High?Tc Superconductors; Thin Films; Superlattices; Epitaxy; Magnetrons; Sputtering; Roughness; Thickness
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Call Number BT @ jguimpel @ Serial 610
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Author (up) Nakamura, O.; Fullerton, E.E.; Guimpel, J.; Schuller, I.K.
Title Disorder and superconductivity in YBa2Cu3O7−δ/GdBa2Cu3O7-δ superlattices Type Journal Article
Year 1991 Publication Physica C: Superconductivity Abbreviated Journal
Volume 185-189, Part 3 Issue Pages 2069-2070
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Abstract The structure of coriented YBa2Cu3O7−δ/GdBa2Cu3O7−δ superlattices is analyzed throug refinement of the X-ray diffraction spectrum. This novel technique, similar in spirit to the well known Rietveld refinement of powder X-ray diffraction spectra, allows quantitative determination of the interfacial roughness. The results show that for these superlattices the roughness consists in step disorder of one unit cell around the average thickness of the layer and interdiffusion of 15 to 25% between the Y and Gd sites within one unit cell from the interface.
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ISSN 0921-4534 ISBN Medium
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Notes Approved no
Call Number BT @ jguimpel @ Serial 617
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Author (up) Nakamura, O.; Guimpel, J.; Sharifi, F.; Dynes, R.; Schuller, I.
Title Synthesis and properties of a-axis and b-axis oriented GdBa2Cu3O7-d high Tc thin films Type Journal Article
Year 1992 Publication Applied Physics Letters Abbreviated Journal Appl. Phys. Lett.
Volume 61 Issue 21 Pages 2598
Keywords Gadolinium Oxides; Barium Oxides; Copper Oxides; Quaternary Compounds; High?Tc Superconductors; Film Growth; Sputtering; Magnetrons; Crystal Orientation; Control; Temperature Effects; X?Ray Diffraction
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Call Number BT @ jguimpel @ Serial 609
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Author (up) Niebieskikwiat, D.; Haberkorn, N.; Guitarra, R.; Guimpel, J.
Title Magnetic properties of SrTiO3/Pr2/3Ca 1/3MnO3 multilayers Type Conference Article
Year 2010 Publication Journal of Physics: Conference Series Abbreviated Journal
Volume 200 Issue 7 Pages 072069
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Abstract Nanoscale ferromagnetic (FM) clusters embedded within insulating (I) layers of the antiferromagnetic Pr2/3Ca1/3MnO3 (PCMO) are known to improve the magnetoresistance ratio of FM-I magnetoresistive multilayers. Here, we study the magnetic properties of perovskite superlattices comprised of five PCMO layers of variable thickness t separated by 5nm-thick spacers of SrTiO3 (STO). Several multilayers (1.5 nm ≤ t ≤ 8 nm) were grown on (001) STO substrates by magnetron sputtering. We show that the magnetic moment of PCMO due to the FM inclusions presents a maximum for t ∼ 3 nm, accompanied by an abrupt increase of coercivity and exchange bias field. The nonmagnetic nature of the neighboring STO layers demonstrates that the observed behavior is not related to any interlayer exchange coupling, but the geometrical matching between layer thickness and FM domain size is the key driver for the enhancement of the FM moment and anisotropy energy. These results open a new door for the optimization of perovskite based spintronic devices.
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Call Number BT @ hernan @ Serial 602
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Author (up) Nieva, G.; Lee, B. W.; Guimpel, J.; Iwasaki, H.; Maple, M. B.; Schuller, I.K.
Title Changes in the Pr-induced TC depression of 123 compounds by chemical pressure Type Journal Article
Year 1991 Publication Physica C: Superconductivity Abbreviated Journal Physica C
Volume 185-189 Issue 1 Pages 561-562
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Abstract We present structural data refined from X-ray spectra for R1−xPrxBa2Cu3O7−δ (R=Er, Gd, Eu, Sm, Nd) systems with x=0, 0.1, and 0.4. The evolution of Tc with the ionic radius of the rare earth for different values of x can be related to the Cu2---O4 distance. The effect of chemical pressure on Tc in R1−xPrxBa2Cu3O7−δ systems is opp osite to that of hydrostatic pressure on the Y1−xPrxBa2Cu3O7−δ system.
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Call Number BT @ gnieva @ Serial 439
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Author (up) Nieva, G.; Osquiguil, E.; Guimpel, J.; Maenhoudt, M.; Wuyts, B.; Bruynseraede, Y.; Maple, M.B.; Schuller, I.K.
Title Photoinduced enhancement of superconductivity Type Journal Article
Year 1992 Publication Applied Physics Letters Abbreviated Journal Appl. Phys. Lett.
Volume 60 Issue 17 Pages 2159-2161
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Abstract We show clear and conclusive experimental evidence for the enhancement of superconductivity in GdBa2Cu3Ox and YBa 2Cu3Ox thin films by photoexcitation. Upon laser illumination the critical temperature increases while the resistivity of the material decreases. The relaxation back to the original state is very slow, of the order of days at room temperature. The existence of this effect opens the possibility of fabricating weak-link devices with in situ tunable superconducting characteristics.
Address Laboratorium voor Vaste Stof-Fysika en Magnetisme, Katholieke Universiteit Leuven, B3001 Leuven, Belgium
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ISSN 00036951 (ISSN) ISBN Medium
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Notes Cited By (since 1996): 61; Export Date: 17 April 2009; Source: Scopus; doi: 10.1063/1.107069; Language of Original Document: English; Correspondence Address: Nieva, G.; Physics Department-0319; University of California-San Diego San Diego, CA 92093-0319, United States Approved no
Call Number BT @ osquigui @ Serial 404
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Author (up) Nieva, G.; Osquiguil, E.; Guimpel, J.; Maenhoudt, M.; Wuyts, B.; Bruynseraede, Y.; Maple, M.B.; Schuller, I.K.
Title Photoinduced changes in the transport properties of oxygen-deficient YBa2Cu3Ox Type Journal Article
Year 1992 Publication Physical Review B Abbreviated Journal
Volume 46 Issue 21 Pages 14249-14252
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Abstract We show that illumination of oxygen-deficient metallic YBa2Cu3Ox films produces a change in the Hall coefficient, an increase in the critical temperature, and a decrease in the electrical resistivity. These changes relax to equilibrium with characteristic times of the order of days, and are due to variations in both the carrier density and mobility. The relaxation times are of the same order of magnitude as the ones measured in nonilluminated oxygen-deficient films immediately after quenching.
Address Laboratory for Solid State Physics and Magnetism, University of Leuven, B3001 Leuven, Belgium
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ISSN 01631829 (ISSN) ISBN Medium
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Notes Cited By (since 1996): 62; Export Date: 17 April 2009; Source: Scopus; doi: 10.1103/PhysRevB.46.14249; Language of Original Document: English; Correspondence Address: Nieva, G.; Physics Department; University of California(enSan Diego San Diego, CA 92093-0319, United States Approved no
Call Number BT @ osquigui @ Serial 407
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Author (up) Osquiguil, E.; Maenhoudt, M.; Wuyts, B.; Bruynseraede, Y.; Lederman, D.; Nieva, G.; Guimpel, J.; Schuller, I.K.
Title Photoexcitation effects in YBa2Cu3Ox Type Journal Article
Year 1993 Publication Journal of Alloys and Compounds Abbreviated Journal J Alloys Compd
Volume 195 Issue C Pages 667-670
Keywords Barium compounds; Ceramic materials; Copper oxides; High temperature superconductors; Oxides; Photoelectricity; Yttrium compounds; C-axis oriented films; Photoexcitation effects; Photoinduced phenomena; Yttrium barium cuprates; Superconducting films
Abstract We show through photoexcitation experiments carried out on YBa2Cu3Ox c-axis oriented films that photoinduced phenomena are not restricted to insulating samples. Superconducting films with critical temperatures varying between 2 K and 40 K show a clear enhancement of the superconducting transition after illumination. The increase in Tc is accompanied by a corresponding decrease in the resistivity ?, and an increase in the Hall coefficient RH, indicative of an increased carrier density. Furthermore, the carrier mobility is also affected by illumination.
Address Physics Department – 0319, University of California – San Diego, La Jolla, CA 92093-0319, United States
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ISSN 09258388 (ISSN) ISBN Medium
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Notes Cited By (since 1996): 4; Export Date: 17 April 2009; Source: Scopus; CODEN: JALCE; Language of Original Document: English; Correspondence Address: Osquiguil, E.; Laboratorium voor Vaste Stof-Fysika en Magnetisme; Katholieke Universiteit Leuven B-3001 Leuven, Belgium Approved no
Call Number BT @ osquigui @ Serial 401
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Author (up) Pardo, F.; Burmeister, G.; Guimpel, J.
Title Substrate heater design for film deposition in oxidizing atmosphere Type Journal Article
Year 1996 Publication REVIEW OF SCIENTIFIC INSTRUMENTS Abbreviated Journal
Volume 67 Issue 6 Pages 2370-2371
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Abstract A simple substrate heater for oxide film deposition is presented. Its main features are (a) good thermal contact between temperature sensor, heater, and substrate and (b) compatibility with oxidizing atmosphere at high temperatures. The system shows a good response for the deposition conditions necessary in high-T-c cuprate materials. (C) 1996 American Institute of Physics.
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ISSN 0034-6748 ISBN Medium
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Notes ISI:A1996UR22200052 Approved no
Call Number BT @ hernan @ Serial 188
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Author (up) 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 14610-14613
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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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ISSN 0163-1829 ISBN Medium
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Notes ISI:A1997XE37100086 Approved no
Call Number BT @ hernan @ Serial 187
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