229 research outputs found
Structure and magnetic properties of nanocrystalline PrCo3
The structure and magnetic properties of nanocrystalline PrCo prepared by
high-energy milling technique have been investigated by means of X-ray
diffraction using the Rietveld method coupled to Curie temperature and magnetic
measurements. The as-milled samples were subsequently annealed in temperature
range from 750 to 1050 {\deg}C for 30 min to optimize the extrinsic properties.
From x-ray studies of magnetic aligned samples, the magnetic anisotropy of this
compounds is found uniaxial. The Curie temperature is 349 {\deg}K and no
saturation reached at room temperature for applied field of 90 kOe. The
coercive field of 55 kOe and 12 kOe measured at 10 and 293 K respectively is
obtained after annealing at 750 {\deg}C for 30 min suggests that
nanocrystalline PrCo are interesting candidates in the field of permanent
magnets. We have completed this experimental study by simulations in the
micromagnetic framework in order to get a qualitative picture of the
microstructure effect on the macroscopic magnetization curve. From this simple
model calculation, we can suggest that the after annealing the system behaves
as magnetically hard crystallites embedded in a weakly magnetized amorphous
matrix. PACS : 75.50.Bb, 75.50.Tt, 76.80.+yComment: Published in Journal of Applied Physics, 107, 083916 (2010). To be
found at: http://jap.aip.or
Magnetic and structural properties of nanocrystalline PrCo
The structure and magnetic properties of nanocrystalline PrCo obtained
from high energy milling technique are investigated by X-ray diffraction, Curie
temperature determination and magnetic properties measurements are reported.
The as-milled samples have been annealed in a temperature range of 1023 K to
1273 K for 30 mn to optimize the extrinsic properties. The Curie temperature is
349\,K and coercive fields of 55\,kOe at 10\,K and 12\,kOe at 293\,K are
obtained on the samples annealed at 1023\,K. A simulation of the magnetic
properties in the framework of micromagnetism has been performed in order to
investigate the influence of the nanoscale structure. A composite model with
hard crystallites embedded in an amorphous matrix, corresponding to the
as-milled material, leads to satisfying agreement with the experimental
magnetization curve. [ K. Younsi, V. Russier and L. Bessais, J. Appl. Phys.
{\bf 107}, 083916 (2010)]. The microscopic scale will also be considered from
DFT based calculations of the electronic structure of Co compounds,
where = (Y, Pr) and = 2,3 and 5.Comment: To be published in J. Phys.: Conference Series in the JEMS 2010
special issue. To be found once published at
http://iopscience.iop.org/1742-659
The strain-induced magnetic anisotropy of Ni81Fe19/W90Ti10 multilayers
The magnetic anisotropy results of Ni81Fe19 multilayers, prepared by DC sputtering in ultra high vacuum, were described on the basis of existing models. It is shown that magnetoelastic anisotropy energies Kme of the Ni81Fe19/W90Ti10 multilayers which have fcc (111) perfectly flat interfaces can be expressed with biaxial modulus, magnetostriction and lattice mismatch. In the incoherent state, the residual strain gives rise to a magnetic anisotropy which is proportional to the reciprocal of the magnetic layer thickness. The influence of roughness would decrease the anisotropy contribution
Electrochemical Fabrication and Characterization of p-CuSCN/n-Fe2O3 Heterojunction Devices for Hydrogen Production
[EN] p-CuSCN/n-Fe2O3 heterojunctions were electrochemically prepared by sequentially depositing alpha-Fe2O3 and CuSCN films on FTO (SnO2:F) substrates. Both alpha-Fe2O3 and CuSCN films and alpha-Fe2O3/CuSCN heterojunctions were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Pure crystalline CuSCN films were electrochemically deposited on alpha-Fe2O3 films by fixing the SCN/Cu molar ratio in an electrolytic bath to 1:1.5 at 60 degrees C, and at a potential of -0.4 V. The photocurrent measurements showed increased intrinsic surface states or defects at the alpha-Fe2O3/CuSCN interface. The photoelectrochemical performance of the alpha-Fe2O3/CuSCN heterojunction was examined by chronoamperometry and linear sweep voltammetry techniques. The alpha-Fe2O3/CuSCN structure exhibited greater photoelectrochemical activity compared to the alpha-Fe2O3 thin films. The highest photocurrent density was obtained for the alpha-Fe2O3/CuSCN films in 1 M NaOH electrolyte. This strong photoactivity was attributed to both the large active surface area and the external applied bias, which favored the transfer and separation of the photogenerated charge carriers in the alpha-Fe2O3/CuSCN heterojunction devices. The flatband potential and donor density were maximal for the heterojunction. These results suggest a substantial potential to achieve heterojunction thin films in photoelectrochemical water splitting applications. (c) 2017 The Electrochemical Society. All rights reserved.This work was supported by the Ministry of High Education and Scientific Research (Tunisia), Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Ullah, S.; Mollar García, MA.; Marí, B.; Bessais, B. (2017). Electrochemical Fabrication and Characterization of p-CuSCN/n-Fe2O3 Heterojunction Devices for Hydrogen Production. Journal of The Electrochemical Society. 164(13):936-945. https://doi.org/10.1149/2.1431713jes9369451641
Hydrothermal synthesis of nanostructured Cr-doped hematite with enhanced photoelectrochemical activity
[EN] Using the easily applicable hydrothermal method Cr-doped hematite thin films have been deposited polycrystalline on conductive glass substrates. The hydrothermal bath consisted of an aqueous solution containing a mixture of FeCl3.6H(2)O and NaNO3 at pH = 1.5. The samples were introduced in an autoclave and heated for a fixed time at a fixed temperature and then annealed in air at 550 degrees C. The concentration of the incorporated Cr atoms (Cr4+ ions) was controlled by varying the concentration of the Cr(ClO4)(3) precursor solution, varied from 0% to 20%. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Cr-doped hematite films exhibited higher photoelectrochemical activity than the undoped films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 16 at.% Cr-doped films. This high photoactivity can be attributed to both the large active surface area and increased donor density caused by Cr-doping in the alpha-Fe2O3 films. All samples reached their best IPCE at 400 nm. IPCE values for 16 at.% Cr-doped hematite films were thirty times higher than that of undoped samples. This high photoelectrochemical performance of Cr-doped hematite films is mainly attributed to an improvement in charge carrier properties. (C) 2017 Elsevier Ltd. All rights reserved.This work was supported by the Ministry of Higher Education and Scientific Research, Tunisia and Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Mollar García, MA.; Chourou, M.; Marí, B.; Bessais, B. (2018). Hydrothermal synthesis of nanostructured Cr-doped hematite with enhanced photoelectrochemical activity. Electrochimica Acta. 260:838-846. https://doi.org/10.1016/j.electacta.2017.12.049S83884626
Influence of a Compact Fe2O3 Layer on the Photovoltaic Performance of Perovskite-Based Solar Cells
[EN] In this study, uniform and dense iron oxide ¿-Fe2O3 thin films were used as an electron-transport layer (ETL) in CH3NH3PbI3-based
perovskite solar cells (PSCs), replacing the Titanium dioxide (TiO2) ETL conventionally used in planar heterojunction perovskite
solar cells. The ¿-Fe2O3 films were synthesized using an electrodeposition method for the blocking layer and a hydrothermal
method for the overlaying layer, while 2,2¿,7,7¿-tetrakis (N, N¿-di-p-methoxyphenylamine)-9,9¿ spirobifluorene (spiro-OMeTAD)
was employed as a hole conductor in the solar cells. Based on the above synthesized ¿-Fe2O3 films the photovoltaic performance of
the PSCs was studied. The ¿-Fe2O3 layers were found to have a significant impact on the photovoltaic conversion efficiency (PCE)
of the PSCs. This was attributed to an efficient charge separation and transport due to a better coverage of the perovskite on the
¿-Fe2O3 films. As a result, the PCE measured under standard solar conditions (AM 1.5G, 100 mW cm¿2) reached 5.7%.This work was supported by the Ministry of High Education and Scientific Research, Tunisia and Ministerio de Economia y Competitividad (ENE2013-46624-C4-4-R) and Generalitatvalenciana (Prometeus 2014/044).Bouhjar, F.; Mollar García, MA.; Ullah, S.; Marí, B.; Bessais, B. (2018). Influence of a Compact Fe2O3 Layer on the Photovoltaic Performance of Perovskite-Based Solar Cells. Journal of The Electrochemical Society. 165(2):30-38. https://doi.org/10.1149/2.1131802jesS3038165
Nanostructured exchange coupled hard / soft composites: from the local magnetization profile to an extended 3D simple model
In nanocomposite magnetic materials the exchange coupling between phases
plays a central role in the determination of the extrinsic magnetic properties
of the material: coercive field, remanence magnetization. Exchange coupling is
therefore of crucial importance in composite systems made of magnetically hard
and soft grains or in partially crystallized media including nanosized
crystallites in a soft matrix. It has been shown also to be a key point in the
control of stratified hard / soft media coercive field in the research for
optimized recording media. A signature of the exchange coupling due to the
nanostructure is generally obtained on the magnetization curve with a
plateau characteristic of the domain wall compression at the hard/soft
interface ending at the depinning of the wall inside the hard phase. This
compression / depinning behavior is clearly evidenced through one dimensional
description of the interface, which is rigorously possible only in stratified
media. Starting from a local description of the hard/soft interface in a model
for nanocomposite system we show that one can extend this kind of behavior for
system of hard crystallites embedded in a soft matrix.Comment: 18 pages, 8 figures. To be published in the Journal of Magnetism and
Magnetic Materials. (To be found at
http://www.sciencedirect.com/science/journal/03048853
Study of the first paramagnetic to ferromagnetic transition in as prepared samples of Mn-Fe-P-Si magnetocaloric compounds prepared by different synthesis routes
International audienceMagnetocaloric materials with composition of Mn 1.3 Fe 0.65 P 0.5 Si 0.5 have been prepared by ball milling and solid-state reaction methods and consolidated using powder annealing, and conventional and spark plasma sintering. Magnetic and calorimetric measurements show remarkable differences upon first cooling, and slight differences on second and further coolings between the samples prepared by different synthesis routes. Further measurements using Hall probe imaging in high magnetic field have been also carried out. As-prepared samples have been cooled down just above the critical temperature, and the first phase transition has been induced by application of a magnetic field. Bulk samples show staircase isothermal magnetization curves whereas powders show smoother transition curves
Enhanced light trapping using plasmonic nanoparticles
International audiencePlasmonics is a new light trapping method used in photovoltaic (PV) solar cells. A significant enhancement of the scattered and absorbed incident light due to the use of silver nanoparticles (Ag-NPs) was observed, which yield to the exaltation of the electromagnetic field in the vicinity of these NPs. In this context, we investigate optically and morphologically the effect of the NPs size dependence on the localized surface plasmon resonance. Extinction, absorption and scattering cross sections are calculated using Mie theory
Differently shaped nanocrystalline (Fe, Y)3O4 and its adsorption efficiency toward inorganic arsenic species
Herein we report effects of partial substitution of Fe3+ by Y3+ in magnetite (Fe3O4) on morphology and inorganic arsenic species adsorption efficiency of the Fe3−x Y x O4 nanoparticles formed. The series of Fe3−x Y x O4 (x = 0.00, 0.042 and 0.084, labeled as Y00, Y05 and Y10, respectively) was synthesized using co-precipitation followed by microwave-hydrothermal treatment (MW) at 200 °C. With increase of yttrium content (x value), both the morphological inhomogeneity of the samples and the fraction of spinel nanorods as compared to spinel pseudospherical particles increased. By both transmission electron microscopy and x-ray powder diffraction analyses, it was determined that the direction of growth of the spinel nanorods is along the [110] crystallographic direction. The Fe3−x Y x O4 affinities of adsorption toward the inorganic arsenic species, As(III) (arsenite, AsO3 3−) and As(V) (arsenate, AsO4 3−), were investigated. Increased Y3+ content related to changes in sample morphology was followed by a decrease of As(III) removal efficiency and vice versa for As(V). The increase in Y3+ content, in addition to increasing the adsorption capacity for As(V), significantly expanded the optimum pH range for the maximum removal and decreased the contact time for necessary 50% removal (t 1/2) of As(V) (Y00: pH 2–3, t 1/2 = 3.12 min; Y05: pH 2–6, t 1/2 = 2.12 min and Y10: pH 2–10, t 1/2 = 1.12 min). The results point to incorporation of Y3+ in the crystal lattice of magnetite, inducing nanorod spinel structure formation with significant changes in sorption properties important for the removal of inorganic arsenic from waters.This is the peer-reviewed version of the article: Nanotechnology, 2019, 30, 47, 475702, [https://dx.doi.org/10.1088/1361-6528/ab3ca2]Published version: [http://cer.ihtm.bg.ac.rs/handle/123456789/3243
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