Search

Your search keyword '"Ghanbaja, J."' showing total 273 results
Start Over Author "Ghanbaja, J." Publication Type Academic Journals
273 results on '"Ghanbaja, J."'

17. Structural characteristics of Bi2O2CO3 nanosheets synthesized by nano‐pulsed discharges in water.

Author

Nomine, A. V., Ghanbaja, J., Redjaimia, A., and Belmonte, T.

Subjects
*CRYSTAL defects, *DIFFRACTION patterns, *LATTICE constants, *ELECTRON diffraction, *POINT set theory
Abstract

A comprehensive analysis of Bi2O2CO3 nanosheets, which were synthesized using nanosecond‐pulsed discharges in water between bismuth electrodes, was conducted in order to investigate the crystallographic features of this material. Electron diffraction, X‐ray diffraction and electron energy‐loss spectrometry techniques revealed the presence of a stoichiometric tetragonal Bi2O2CO3 structure, labelled BOC in this study. It crystallizes in the body‐centred tetragonal Bravais lattice and belongs to the I4/mmm space group (No. 139), with the following lattice parameters: a = 3.91, c = 13.77 Å. The nanosheets adopt square shapes. This shape is dictated by the symmetry elements of its point group (4/mmm) under the prevailing local conditions. From the energetic point of view, this shape, dictated by the 4/m2/m2/m point group and therefore a pinacoid, corresponds to an absolute extremum, an indicator of the stability of these BOC nanosheets. Most nanosheets are crossed by equal‐inclination fringes or bend contours. These bend contours reflect the fact that the BOC nanosheets contain crystal defects and/or are so thin that they bend elastically, leading to rotation of the lattice planes towards the diffracting Bragg position. The diffraction patterns corresponding to bend contours intersecting along the [001] zone axis have been studied in detail. Extra reflections are superimposed on the diffraction pattern of the BOC crystallographic structure. These extra reflections are essentially attributed to two phenomena: multiple diffraction and local disorder–order transformations of the BOC crystal structure, passing from a body‐centred tetragonal to a primitive Bravais lattice. A mechanism related to the ledge mechanism (kinks and jogs), explaining the formation of nanosheets in a metallic matrix, has been adapted and proposed for the formation of BOC nanosheets in water. When the nanosheets are removed from the water, they become carbonated once in the air, leading to the formation of BOC that inherits the nanosheet morphology. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

18. Spin injection at MgB2-superconductor/ferromagnet interface.

Author

Pfaff, C., Petit-Watelot, S., Andrieu, S., Pasquier, L., Ghanbaja, J., Mangin, S., Dumesnil, K., and Hauet, T.

Subjects
SPINTRONICS, THIN films, FERROMAGNETIC resonance, NONVOLATILE memory, BILAYERS (Solid state physics)
Abstract

There is a growing interest in mixing spintronics and superconductivity to develop original energy-efficient nonvolatile memory and logic devices. Research works conducted so far have mostly focused on superconductor with critical temperature Tc lower than 10 K. Here, we report on the growth and characterization of MgB2/Ni80Fe20 and MgB2/Co bilayers, where Tc of the MgB2 layer is of the order of 30 K. Ferromagnetic resonance was undertaken to analyze the spin pumping into MgB2. The larger magnetization at saturation in Co, as compared to Ni80Fe20, induces a smaller spin pumping contribution to the damping when MgB2 is normal. A spin pumping reduction was observed for both bilayers when MgB2 becomes superconductor and is attributed to the opening of the superconducting gap. The present results show that MgB2 thin films could be suitable to implement superconducting spintronic at 30 K, which is not only relevant for future technological development but also relaxes experimental constraints related to low-temperature investigations. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

36. Issues in growing Heusler compounds in thin films for spintronic applications.

Author

Guillemard, C., Petit-Watelot, S., Devolder, T., Pasquier, L., Boulet, P., Migot, S., Ghanbaja, J., Bertran, F., and Andrieu, S.

Subjects
THIN films, SCANNING transmission electron microscopy, MAGNETIC alloys, MOLECULAR beam epitaxy, SPIN polarization, GALLIUM antimonide, SPIN valves
Abstract

Heusler magnetic alloys offer a wide variety of electronic properties very promising for spintronics and magnonics. Some alloys exhibit a spin gap in their band structure at the Fermi energy, the so-called half-metal magnetic (HMM) behavior. This particular property leads to two very interesting properties for spintronics, i.e., fully polarized current together with ultra-low magnetic damping, two key points for spin-transfer-torque based devices. This Tutorial gives experimental details to grow and characterize Heusler Co2MnZ compounds in thin films (Z = Al, Si, Ga, Ge, Sn, Sb) by using molecular beam epitaxy in order to get the proper predicted electronic properties. A first part of this Tutorial is dedicated to control the stoichiometry as best as possible with some methods to test it. The chemical ordering within the lattice was examined by using electron diffraction during growth, regular x-ray diffraction, and scanning transmission electron microscopy. In particular, standard x-ray diffraction is carefully analyzed depending on the chemical ordering in the cubic cell and shown to be inefficient to distinguish several possible phases, on the contrary to electron microscopy. The electronic properties, i.e., magnetic moment, spin polarization, and magnetic damping were reviewed and discussed according to the stoichiometry of the films and also theoretical predictions. Polycrystalline films were also analyzed, and we show that the peculiar HMM properties are not destroyed, a good news for applications. A clear correlation between the spin polarization and the magnetic damping is experimentally demonstrated. At least, our study highlights the major role of stoichiometry on the expected properties. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results