Gaston Collin

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Konrad Eisenbichler

University of Toronto

Roland Betancourt

University of California, Irvine

Clario Di Fabio

University of Genova

Elisabetta Scarton

Università degli Studi di Udine / University of Udine

Carla M Bino

Università Cattolica del Sacro Cuore (Catholic University of the Sacred Heart)

Gennaro Varriale

Universidad de Granada

ARCHIves Project

Birkbeck College, University of London

José María SALVADOR-GONZALEZ

Universidad Complutense de Madrid

Dickran Kouymjian

California State University, Fresno

Antonio Salvatore Romano

Pontificia Facoltà Teologica dell'Italia Meridionale

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Papers by Gaston Collin

ChemInform Abstract: EINIGE REIHEN STOECHIOMETRISCHER VERBINDUNGEN DER FORMEL LN6B2C2X14

Chemischer Informationsdienst, 1972

Aus den Sulfiden der einzelnen Metalle wurden die Verbindungs gruppen (I) bis (IV) erhalten.

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17O NMR comparison of zinc and nickel substituted YBa2Cu3O6.6

Physica C: Superconductivity, 1997

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NMR Study of the Magnetic and Metal-Insulator Transitions inNa0.5CoO2: A Nesting Scenario

Physical Review Letters, 2006

Co and Na NMR are used to probe the local susceptibility and charge state of the two Co sites of ... more Co and Na NMR are used to probe the local susceptibility and charge state of the two Co sites of the Naordered orthorhombic Na 0.5 CoO 2. Above 86 N T K = , both sites display a similar T-dependence of the spin shift, suggesting that there is no charge segregation into Co 3+ and Co 4+ sites. Below T N , the magnetic long range commensurate order found is only slightly affected by the metal-insulator transition (MIT) at 51 MIT T K =. Furthermore, the electric field gradient at the Co site does not change at these transitions, indicating the absence of charge ordering. All these observations can be explained by two successive SDW induced by nestings of the Fermi Surface specific to the x=0.5 Na-ordering.

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Intrinsic Susceptibility and Bond Defects in the Novel Two Dimensional Frustrated AntiferromagnetBa2Sn2ZnCr7pGa10−7pO22

Physical Review Letters, 2004

We present microscopic and macroscopic magnetic properties of the highly frustrated antiferromagn... more We present microscopic and macroscopic magnetic properties of the highly frustrated antiferromagnet Ba2Sn2ZnCr7pGa10-7pO22, respectively probed with NMR and SQUID experiments. The T -variation of the intrinsic susceptibility of the Cr 3+ frustrated kagomé bilayer, χ kag , displays a maximum around 45 K. The dilution of the magnetic lattice has been studied in detail for 0.29 ≤ p ≤ 0.97. Novel dilution independent defects, likely related with magnetic bond disorder, are evidenced and discussed. We compare our results to SrCr9pGa12-9pO19. Both bond defects and spin vacancies do not affect the average susceptibility of the kagomé bilayers.

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Correlations between crystallographic and physical properties in (Bi,Pb)2Sr2(Ca,Y)Cu2O8+Δ superconductors

Physica B: Condensed Matter, 1999

Efforts were made to synthesize pure and single-phased samples of the (Bi, Pb) Sr (Ca, Y)Cu O > s... more Efforts were made to synthesize pure and single-phased samples of the (Bi, Pb) Sr (Ca, Y)Cu O > system. Systematic X-ray incommensurate Rietveld refinements along with AC susceptibility measurements were performed. The basic yttrium substitution reveals strong internal structural changes on the modulation parameters. In the mean time, diamagnetic shielding in the samples vanishes before ¹ does, suggesting a 3D-2D crossover. It is proposed that Y> creates correlated domains in the CuO planes and localizes charges, thus diminishing the diamagnetic screening. Such a localization could be accompanied by the heavy structural changes observed. Adding lead in the structure would then restore the mobility of the charges. Indeed, without affecting ¹ (i.e. without affecting the carrier concentration), Pb substitution enhances diamagnetic shielding and even restores superconductivity in the otherwise insulating Bi Sr (Ca ,Y)Cu O > sample. We then conclude that carrier concentration is very little affected by cationic substitution (small ¹ variations) and that Y and Pb rather affect the mobility of the charges, destroying and restoring 3D correlations, respectively.

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Spin dynamics in frustrated magnets: from edge- to corner-sharing geometries

Journal of Physics: Condensed Matter, 2007

Our work in the past few years has been focused on local NMR (nuclear magnetic resonance) and μSR... more Our work in the past few years has been focused on local NMR (nuclear magnetic resonance) and μSR (muon spin resonance) studies of pure Heisenberg isotropic triangular lattices with nearest neighbour couplings, a prerequisite for reaching the ideal spin liquid case. In the case of chromates, although S = 3/2, the combination of the weakness of the Cr 3+ single-ion anisotropy and that of an exchange interaction resulting from a direct overlap of the Cr 3+ orbitals allows us to tackle these properties. We were recently able to single out, in the triangular compound NaCrO 2 , an original dynamical crossover regime in a broad range of T between the peak in specific heat and a low T static ground state. Moving to the corner-sharing geometry of Kagome bilayers (Ba 2 Sn 2 ZnGa 10−7 p Cr 7 p O 22 and SrCr 9 p Ga 12−9 p O 19), we illustrate all the potential of local studies (NMR and μSR) for revealing some key aspects of the physics of these compounds, namely T → 0 fluctuations, susceptibility, the impact of dilution defects which generate an extended response of the spin lattice as well as their puzzling spin glass state. These results are compared to the case of volborthite which features S = 1/2 spins on a corner-sharing, probably anisotropic, antiferromagnetic Kagome lattice.

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Cobalt charge states in sodium cobaltates at intermediate dopings

Journal of Alloys and Compounds, 2009

A likely crucial parameter in explaining the peculiar magnetism of Na x CoO 2 cobaltates in their... more A likely crucial parameter in explaining the peculiar magnetism of Na x CoO 2 cobaltates in their paramagnetic state is their charge and spin states in the cobalt layers, responsible for the electronic properties. We examine here the situation for 0.50≤x≤0.62, for which it is shown that an increasing amount of Co 3+ ions appears among ~3.5+ ions for increasing x. Together with our previous results, this defines two regions in the phase diagram, with homogeneous Co states for x≤0.5 and heteregeneous states for x>0.5. The links with the sodium structural ordering and the nature of magnetism are discussed.

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Structure cristalline du sulfure La2Fe2S5

Bulletin de la Société française de Minéralogie et de Cristallographie

Description de la structure de La₂Fe₂S₅ orthorhombique du groupe spatial A2₁am dont les paramètre... more Description de la structure de La₂Fe₂S₅ orthorhombique du groupe spatial A2₁am dont les paramètres sont : a = 11,40 Å, b = 16,55 Å, c = 4,055 Å (Z = 4). Les atomes de terres rares occupent deux sites sensiblement équivalents de coordinence 7, alors que les atomes de fer sont répartis dans deux types de sites très différents : l'un octaédrique déformé et le second tétraédrique. Le facteur R final est de 0,068.

CCDC 1554759: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1554757: Experimental Crystal Structure Determination

CCDC 1554756: Experimental Crystal Structure Determination

Structure de La6Cu2Si2S14

Bulletin de la Société française de Minéralogie et de Cristallographie, 1971

Collin Gaston, Laruelle Pierre. Structure de La6Cu2Si2S14. In: Bulletin de la Société française d... more

Défauts planaires et non˗stœchiométrie dans les composés NiAs lacunaires

Bulletin de Minéralogie, 1980

The two compounds Fe₇S₈ (2a2a3c) and Ni₀.₉₁S are studied using the Cowley's theory. It is sho... more The two compounds Fe₇S₈ (2a2a3c) and Ni₀.₉₁S are studied using the Cowley's theory. It is shown that they are both characterized on one hand : by microtwins due to planar defects interchanging along c⃗ the M and S chains and one calculates the fault rates α, and on the other hand : by imbricated sequences with different types either 3c — 4c in Fe₇S₈ at constant stoichiometry, or 3a3a3c — 2a2a3c in Ni₀.₉₁S with different stoichiometries.

Composés hexagonaux L6B2C2X14 lacunaires ordonnés

Bulletin de la Société française de Minéralogie et de Cristallographie, 1973

Plusieurs séries de composés L₆(B₂₋ₓ ⃞ₓ) C₂X₁₄ sont préparées. La mise en ordre des lacunes appar... more Plusieurs séries de composés L₆(B₂₋ₓ ⃞ₓ) C₂X₁₄ sont préparées. La mise en ordre des lacunes apparaît quand le rapport lacune sur cation sur le site B est supérieur à 1. Les mailles de sur-structure ont pour paramètres a₀√3 et 2 c₀ pour les composés L₆ (B₁/₂ ⃞₃/₂) C₂X₁₄, a₀√3 et 3 c₀ pour les composés L₆ (B₂/₃ ⃞₄/₃) C₂X₁₄. Les répartitions des lacunes et des cations sur les sites B sont déterminées pour les deux types de sur-structure.

ChemInform Abstract: Untersuchung physikalischer Eigenschaften der Phasen Ni3B2S2 und Ni3Pb2Se2 (B: Pb, Tl, Bi, Sn)

Chemischer Informationsdienst, 1984

Die für die Titelverbindungen beobachteten spezifischen Widerstände, Hall‐Konstanten und magnetis... more

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The crystal structure of Ni3Sn2S2 and related compounds

Journal of the Less Common Metals, 1976

Abstract Ni3Sn2S2 is monoclinic, space group B2 m(C 3 2h ) with a = 9.331(3), b = 5.403(2), c = 5... more Abstract Ni3Sn2S2 is monoclinic, space group B2 m(C 3 2h ) with a = 9.331(3), b = 5.403(2), c = 5.458(2) A , γ = 124.55°(2) . This compound is a nickel sulfostannide with each Ni atom surrounded by four Sn and two S atoms. Other compounds with this type of structure are Ni3B2S2 (B = Pb, Tl, In) and Ni3Pb2Se2. Ni3Bi2S2 presents a different crystal symmetry.

The alpha transition in Fe1-xMxS materials (M = Mn, Cr): Physical and structural aspects

J Phys Chem Solids, 1985

Étude de quelques propriétés physiques des phases Ni3B2S2 et Ni3Pb2Se2 (B ≡; Pb, Tl, Bi, Sn)

Journal of the Less Common Metals, 1984

ont et6 determinces. Les proprietes physiques observees sont celles d'un &at metallique. La valeu... more

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Unusual spin dynamics in the doped antiferromagnetic phase of YBa2(Cu0.98Zn0.02)3O6.39

Physica B: Condensed Matter, 1995

PflYSICA Unusual spin dynamics in the doped antiferromagnetic phase of YBa2 (Cu0.98 Zno.o2)3 06.39

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Nasicon : Amorphous to crystalline compounds

Solid State Ionics, 1986

Abstract According to previous studies, there are, at least, three fundamental problems for Nasic... more Abstract According to previous studies, there are, at least, three fundamental problems for Nasicon compounds: 1. i) structural transitions are generally observed above the room temperature. The order of these transitions and associated thermal effects are depending on the fabrication process of NASICON compounds. 2. ii) Zr deficient compositions only exhibits slight changes of ionic conductivity in comparison with the stoichiometric one. 3. iii) There are two possible conduction pathways in the NASICON type structure jumping between Na(2) positions and jumping from Na(2) to Na(1) to Na(2). In this paper, we show that these problems are related to the great ability for NASICON compositions to give amorphous compounds by a tetrahedra orientational disorder mechanism.

ChemInform Abstract: EINIGE REIHEN STOECHIOMETRISCHER VERBINDUNGEN DER FORMEL LN6B2C2X14

Chemischer Informationsdienst, 1972

Aus den Sulfiden der einzelnen Metalle wurden die Verbindungs gruppen (I) bis (IV) erhalten.

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17O NMR comparison of zinc and nickel substituted YBa2Cu3O6.6

Physica C: Superconductivity, 1997

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NMR Study of the Magnetic and Metal-Insulator Transitions inNa0.5CoO2: A Nesting Scenario

Physical Review Letters, 2006

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Intrinsic Susceptibility and Bond Defects in the Novel Two Dimensional Frustrated AntiferromagnetBa2Sn2ZnCr7pGa10−7pO22

Physical Review Letters, 2004