Electron-γ\gamma - perturbed angular correlation studies on high-TC_{C} superconductors

Recent results on the study of high-T$_{c}$ superconductors using the e$^-\!-\gamma$ perturbed angular correlation technique are presented. The basic features of the experimental equipment and its installation at the ISOLDE facility are briefly described. Results obtained from $^{197m}$Hg implanted into high quality Y$_{1}$Ba$_{2}$Cu$_{3}$O$_{6+\delta}$ epitaxy thin films are presented and discussed

Stability studies of Hg implanted YBa2_{2}Cu3_{3}O6+x_{6+x}

High quality YBa$_{2}$Cu$_{3}$O$_{6+x}$ (YBCO) superconducting thin films were implanted with the radioactive $^{197m}$Hg (T$_{1/2}$ = 24 h) isotope to low fluences of 10$^{13}$ atoms/cm$^{2}$ and 60 keV energy. The lattice location and stability of the implanted Hg were studied combining the Perturbed Angular Correlation (PAC) and Emission Channeling (EC) techniques. We show that Hg can be introduced into the YBCO lattice by ion implantation into unique regular sites. The EC data show that Hg is located on a highly symmetric site on the YBCO lattice, while the PAC data suggests that Hg occupies the Cu(1) site. Annealing studies were performed under vacuum and O$_{2}$ atmosphere and show that Hg starts to diffuse only above 653 K

Stability and diffusion of Hg implanted YBa2_{2}Cu3_{3}O6+x_{6+x}

The radioactive isotope $^{197m}$Hg was implanted at 60 keV with low fluences (10$^{13}$ ions/cm$^{2}$ ) into YBa$_{2}$Cu$_{3}$O$_{6+x}$ (YBCO) superconducting thin films at ISOLDE/CERN. We report on the Hg dynamics and stability inside the YBCO lattice as a function of annealing temperature up to 890 K in vacuum or O$_{2}$ atmosphere. The perturbed angular correlation (PAC) technique was used for probing the Hg behavior at the atomic scale, while by monitoring the sample's activity in situ the Hg outdiffusion was studied. We found that Hg ions occupy unique lattice sites and that Hg should be bound to two apical oxygens. Hg diffusion occurs only for annealing temperatures above 653 K, in vacuum. The Hg migration energy was estimated to be EM = 1.58 $\pm$ 0.15 eV

Studies of colossal magnetoresistive oxides with radioactive isotopes

We propose to study Colossal Magnetoresistive (CMR) oxides with several nuclear techniques, which use radioactive elements at ISOLDE. Our aim is to provide local and element selective information on some of the doping mechanisms that rule electronic interactions and magnetoresistance, in a complementary way to the use of conventional characterisation techniques. Three main topics are proposed: \\ \\ a) Studies of local [charge and] structural modifications in antiferromagnetic LaMnO$_{3+ \delta}$ and La$_{1-x}$R$_{x}$MnO$_{3}$ with R=Ca and Cd, doped ferromagnetic systems with competing interactions: - research on the lattice site and electronic characterisation of the doping element. \\ \\ b) Studies of self doped La$_{x}$R$_{1-x}$MnO$_{3+\delta}$ systems, with oxygen and cation non-stoichiometry: -learning the role of defects in the optimisation of magnetoresistive properties. \\ \\ c) Probing the disorder and quenched random field effects in the vicinity of the charge or orbital Ordered/Ferromagnetic phase instability: - Investigating the local environment of ions at the Mn site, which trigger the ferromagnetic phase. Our approach to study these problems, combines complementary techniques such as Perturbed Angular Correlation, Emission Channeling and Electrical/Magnetic Measurements in pellets, single crystals and high quality thin films of CMR oxides doped with radioactive isotopes. Preliminary results obtained in La Cd MnO$_{3+x}$ pellets and thin films implanted with $^{111m}$Cd are also presented

Sur differentes lois de Cauchy dans Rn, caracterisees comme invariantes par certains groupes de transformations

SIGLECNRS T 58725 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Synthèse et caractérisation de couches minces de SrTiO3 par MOCVD à injection en vue de ses applications en microélectronique

Dans le contexte d'une miniaturisation toujours plus exigeante des composants électroniques, SrTiO3 est un matériau à forte permittivité électrique qui pourrait remplacer l'oxyde de grille dans les structures CMOS pour les générations inférieures à 1 nm. La technique de dépôt par MOCVD à injection liquide est un outil performant qui permet la synthèse de couches minces de SrTiO3 de bonne qualité, moyennant une optimisation des conditions de dépôt. Elle permet notamment l'emploi d'un précurseur bimétallique de faible volatilité. L'importance de la composition de la solution de précurseurs, en particulier le choix des précurseurs et du solvant, a été mise en évidence. SrTiO3 étant thermodynamiquement instable sur Si, les dépôts ont été réalisés sur SiO2. Dans ce cas, une couche amorphe de faible permittivité diélectrique se forme dans les premiers stades de la croissance du film, ce qui réduit sévèrement la constante diélectrique de l'ensemble. Différentes préparations de surface ou des sous-couches n'ont pas permis d'améliorer significativement les résultats électriques. Sur des substrats métalliques inertes vis-à-vis de l'oxygène, les constantes diélectriques des couches minces sont bien plus élevées. Ainsi, l'intégration à court terme de SrTiO3 en microélectronique aura probablement d'abord lieu dans des applications 'Above IC'.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

An elementary proof of the Knight-Meyer characterization of the Cauchy distribution

This paper propounds a short proof of a result previously proved by F. Knight and P. A. Meyer (1976, Z. Warsch. Verw. Gebiete 34 129-134). Let X be a random variable in n with the following property: for any matrix (ca bb) in GL(n+1) (where a is a (n, n) matrix) there exist [alpha] in GL(n) and [beta] in n so that (aX + b)/(cX + d) and ([alpha]X + [beta]) have the same distribution. Then X is necessarily Cauchy distributed.Cauchy distribution characterization type projective space

Epitaxial and polycrystalline BaFe12O19 thin films grown by chemical vapour deposition

Epitaxial and polycrystalline barium hexaferrite BaFe12O19 thin films were prepared by metalorganic chemical Vapour deposition (MOCVD). Films were grown by a liquid MOCVD technique which aim is to control precisely the precursor vapour pressures. Two kinds of substrates were used: sapphire (001) and silicon thermally oxidized. On Si/SiO2 films are polycrystalline and the magnetization is isotropic. On Al2O3 (001), structural studies reveal the films to be predominantly single phase, well crystallized without annealing procedure and with the c-axis perpendicular to the film plane; epitaxial relationships between the film and the substrate were determined. The magnetic parameters, deduced from vibrating sample magnetometer measurements, show a high dependence of the magnetization with the orientation of the field with respect to the surface of the film. (C) 1999 Elsevier Science S.A. All rights reserved

Synthèse par MOCVD et caractérisation structurale et de magnéto-transport de couches minces de manganite de terre-rare non-substituées (application des manganites à des dispositifs de type jonctions "marche")

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Possible appearance of Sm3+ ions during neutron irradiation at 21 K of samarium monosulphide doped with phosphorus impurities

Nous avons irradié à 21 K aux neutrons rapides, 4 échantillons de SmS dopés en phosphore (1 %). Nous avons observé un accroissement important de leur conductivité électrique, qui semble indiquer l'apparition d'ions Sm3+ pendant l'irradiation.Four SmS samples, doped with phosphorus (1 %), have been irradiated with fast neutrons at 21 K. A high increase of their electrical conductivity has been observed which seems to be due to an appearance of Sm3+ ions during irradiation