Epitaxie de phases métastables de fer

In this paper, Fe structures and magnetic properties in FeRu and FeIr superlattices are presented. Fe is grown on hexagonal surface lattices as Ru(0001), Ir (111), but also on rectangular or square ones as Ru (1122), and Ir (100). On hexagonal lattices, the beginning of the growth is pseudomorphic in the plane of growth but Fe relaxes in its strain bcc phase via Kurdjumov-Sachs (KS) coïncidence. The pseudomorphic phase is shown to be non-magnetic at room temperature, as a moment appears when relaxation occurs. In FeRu (1122) superlattices, no KS relaxation occurs, and again 10 non-magnetic layers are observed. On the contrary, a small moment is observed for thin Fe layers on FeIr (100) superlattices. Fe is thus synthesized with body centered tetragonal structures with a c/a ratio varying from 1,26 to 1 (bcc). A rotation of the easy axis of magnetization as well as an increase of the magnetic moment is observed from out to in plane

Upper critical field measurements in high-Tc superconducting oxides

We present upper critical field measurements on the superconducting oxides RE Ba2Cu3O7-δ (RE = Y, Gd) performed in a pulsed magnetic field up to 43 T. Values for Hc2 as high as 52 T and 77 T for Y and Gd respectively, are expected at 77 K. However, in order to observe no resistive behaviour up to 43 T the temperature must be decreased down to 50 K. In the case of oxygen deficient systems the magnetoresistance reveals two superconducting phases wich could be related to two different orders of oxygen vacancies

Structure et magnétisme de super-réseaux Ru/Mn et MnFeMn/Ru préparés par MBE

Our recent works on Fe/Ru superlattices revealed a new hexagonal structure , a reduced magnetic moment (1.7 µB) for the Fe inner layers, and two magnetic dead layers at the interface. Then we decided to insert just one plane of manganese between Fe and Ru to test the interface influence on the structural and magnetic properties in these superlattices. In this paper, we present results obtained from X-ray diffraction and absorption and from macroscopic magnetization and Mössbauer spectroscopy on MnFeMn/Ru superlattices. The Mn environment identical to that of Fe, is quantitatively described. We show that there is no solid solution at the Fe/Ru interface ; thus the four Fe magnetic dead layers do not originate in interface alloying. For the inner Fe layers, we obtain the same reduced magnetic moment as in Fe/Ru superlattices and a few tenth of µB for Mn atoms. Finally we confirm once more the quality of the interfaces in these superlattices

Études par diffraction haute résolution et réflectivité de films minces épitaxiés

The studies we present concern the general researches involved in order to understand the growth mechanisms of thin films deposited on oriented substrates. Among the different investigation technics of the thin layers, X-ray diffraction and reflectivity will be discussed through two applications. In a first step, thediffraction presented, illustrated by reciprocal space mapping, will give information about the layer state of stress and the lattice distorsion of La$_{1-x}$Sr$_x$MnO$_3$ deposited on SrTiO$_3$. The results obtained are discussed and compared to those given by electron microscopy. In a second step, we will present an application of reflectivity concerning a very roughness surface of platinum deposited on MgO showing an island growth process. We will verify that reflectivity can lead to the determination of the recovered rate of the surface, even if some problems exist in the simulation of the whole data set. Results obtained in electron microscopy will complete those issued from reflectivity.Les études que nous allons présenter sont à replacer dans le contexte général de la compréhension des mécanismes de croissance des films minces déposés sur des substrats orientés. Parmi les diverses techniques d'investigations des couches minces, la diffraction et la réflectivité des rayons X vont être abordées à travers deux applications. Nous verrons tout d'abord que la diffraction, illustrée par la cartographie en deux dimension du réseau réciproque, permet de remonter à l'état de contrainte ainsi qu'à la déformation de la maille de La$_{1-x}$Sr$_x$MnO$_3$ déposé sur SrTiO$_3$. Les résultats déduits de ces mesures seront discutés et comparés à ceux obtenus en microscopie électronique. Dans la suite de l'article, nous verrons une des applications de la réflectivité, sur une surface très perturbée de platine déposé sur MgO et présentant une croissance en îlots. Nous verrons que la réflectivité permet d'estimer le taux de recouvrement de la surface, mais que des problèmes persistent dans la simulation de l'intégralité des données expérimentales. Les résultats obtenus en MET viendront compléter ceux issus de la réflectivité

Epitaxial growth of biferroic YMnO3(0001) on platinum electrodes

Epitaxial films of the biferroic YMnO3 (YMO) oxide have been grown on platinum-coated SrTiO3(1 1 1) and Al2O3(0 0 0 1) substrates. The platinum electrodes, (1 1 1) oriented, are templates for the epitaxy of the hexagonal phase of YMO with a (0 0 0 1) out-of-plane orientation, which is of interest as this is the polarization direction of YMO. X-ray diffractometry indicates the presence of two crystal domains, 60° rotated in-plane, in the Pt(1 1 1) layers which subsequently are transferred on the upperlaying YMO. Cross-section analysis by high-resolution transmission electron microscopy (HRTEM) of YMnO3/Pt/SrTiO3(1 1 1) shows high-quality epitaxy and sharp interfaces across the structure in the observed region. We present a detailed study of the epitaxial growth of the hexagonal YMO on the electrodes

Randomized comparison of selective serotonin reuptake inhibitor (escitalopram) monotherapy and antidepressant combination pharmacotherapy for major depressive disorder with melancholic features: A CO-MED report

10.1016/j.jad.2011.04.032Journal of Affective Disorders1333467-476JADI