Papers by Marwène Oumezzine
Acta Crystallographica Section A Foundations of Crystallography, 2012
We report the synthesis of polycrystalline samples with nominal compositions La 0,67 Ba 0,33 Mn 1... more We report the synthesis of polycrystalline samples with nominal compositions La 0,67 Ba 0,33 Mn 1-x Cr x O 3 (0£x£0,1) via the solid state reaction route and our study of their structural, magnetic and electrical transport properties with the variation of doping concentration of Cr. Rietveld analysis of fitted and observed XRD patterns exhibited the single-phase nature phase of all the studied materials, which crystallize in R-3C space group when . Energy Dispersive X-ray Analysis (EDAX) confirms the expected stoichiometry of all samples. Successive substitution of Cr at Mn site in La 0,67 Ba 0,33 Mn 1-x Cr x O 3 manganites makes both the Curie temperature T c and the magnetization M to diminish, which is ascribed to the reduction of the DE interaction by Cr doping. Nevertheless, Cr doping makes the saturation magnetization at 5K to decrease, which indicates that the Cr 3+ moments tend to be antiparallel to the Mn 3+ moments at low temperature. The Cr-doped manganites exhibit a large variation in resistivity values. The increase of Cr doping leads to an increase of the electrical resistivity. Below 10 at.% of Cr 3+ , the electrical resistivity shows a metallic behaviour, which is well fitted by the relation r = r0+ r2T 2 + r4.5T 4.5 , indicating the importance of the grain/domain boundary, the electron-electron scattering effects and, to a lesser extent, the electron (magnon,phonon) scattering effects in the mechanism of conduction.
Journal of Low Temperature Physics, Jan 7, 2021
A simple thermodynamic theory is proposed for the quantitative description of giant magnetocalori... more A simple thermodynamic theory is proposed for the quantitative description of giant magnetocaloric effect observed in metamagnetic shape memory alloys. Both the conventional magnetocaloric effect at the Curie temperature and the inverse magnetocaloric effect at the transition from the ferromagnetic austenite to a weakly magnetic martensite are considered. These effects are evaluated from the Landau-type free energy expression involving exchange interactions in a system of a two magnetic sublattices. The findings of the thermodynamic theory agree with first-principles calculations and experimental results from Ni-Mn-In-Co and Ni-Mn-Sn alloys, respectively. V
Journal of Applied Physics, 2013
Magnetic and magnetocaloric properties of the alloy Mn0.96Nb0.04CoGe have been investigated. Acco... more Magnetic and magnetocaloric properties of the alloy Mn0.96Nb0.04CoGe have been investigated. According to the mean-field theory prediction, the relationship between ΔSM ∝ (H/TC)2/3 has been confirmed in the temperature region near TC for that system. To investigate the nature of the magnetic phase transition, a detailed critical exponent study has been performed. The critical components, γ, β, and δ determined using the Kouvel-Fisher method, the modified Arrott plot, as well as the critical isotherm analysis agree well. Moreover, these critical exponents are confirmed by the Widom scaling law and the validity of the calculated critical exponents was also confirmed by the scaling theory. The values deduced for the critical exponents are close to the theoretical prediction of the mean-field model values, thus indicating that long range interactions dominate the critical behavior in the Mn0.96Nb0.04CoGe system. It is also speculated that the competition between the localized Mn-Mn magn...
Journal of Applied Physics, 2016
A simple thermodynamic theory is proposed for the quantitative description of giant magnetocalori... more A simple thermodynamic theory is proposed for the quantitative description of giant magnetocaloric effect observed in metamagnetic shape memory alloys. Both the conventional magnetocaloric effect at the Curie temperature and the inverse magnetocaloric effect at the transition from the ferromagnetic austenite to a weakly magnetic martensite are considered. These effects are evaluated from the Landau-type free energy expression involving exchange interactions in a system of a two magnetic sublattices. The findings of the thermodynamic theory agree with first-principles calculations and experimental results from Ni-Mn-In-Co and Ni-Mn-Sn alloys, respectively.
Acta Crystallographica Section A Foundations and Advances, 2021
Bulk nanocrystalline samples of La0.65 Ce0.05 Sr0.3 Mn1-x CuxO3(0 <x < 0.15) manganites are prepa... more Bulk nanocrystalline samples of La0.65 Ce0.05 Sr0.3 Mn1-x CuxO3(0 <x < 0.15) manganites are prepared by the sol-gel based Pechini method. The effect of the substitution for Mn with Cu upon the structural and magnetic properties has been investigated by means of X-ray diffraction (XRD), Raman spectroscopy and dc magnetization measurements. The structural parameters obtained using Rietveld refinement of XRD ata showed perovskite structures with rhombohedral (R-3c) symmetry without any detectable impurity phase. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing copper concentration. The analysis of the crystallographic data suggested a strong correlation between structure and magnetism, for instance a relationship between a distortion of the MnO6octahedron and the reduction in the Curie temperature, Tc. Hence, a theoretical description of the second-order magnetic transition, as well as the magnetic entropy change of La0.65 Ce0.05 Sr0.3 Mn1-x CuxO3 (x=0 and x=0.15) compounds is presented based on the Bean-Rodbell model of magneto-volume interactions. It is shown that the magnetocaloric properties obtained from initial magnetization isotherms data are in a good matching with the numerical simulations. Within the framework of this specific theoretical model, the magnitude of the spin-lattice interaction, as well as the spin value fluctuation are found to increase upon Cu-doping. These observations shall be taken in accordance with the disorder induced by Cu 2+/ Cu 3+ ions in the system.
Journal of Superconductivity and Novel Magnetism
The original version of this article unfortunately contained a mistake in the affiliation section... more The original version of this article unfortunately contained a mistake in the affiliation section. Thus, this erratum is presented to fix the errors. The original article has been corrected. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Journal of Superconductivity and Novel Magnetism, 2020
The critical bahaviour of La 0.65 Ce 0.05 Sr 0.3 Mn 1x Cu x O 3 (x = 0, x = 0.05 and x = 0.15) ma... more The critical bahaviour of La 0.65 Ce 0.05 Sr 0.3 Mn 1x Cu x O 3 (x = 0, x = 0.05 and x = 0.15) manganite prepared by the sol-gel-based Pechini method has been investigated by measuring the magnetization around the Curie temperature, T C. The obtained critical exponents (beta, gamma and delta) have been calculated using the modified Arrott plot and Kouvel-Fisher techniques, scaling hypothesis and critical isotherm analysis. The estimated results for the parent compound and x = 0.05 are in between mean-field and the 3D Heisenberg models. The values of β, γ and δ will shift gradually toward those of the 3D Heisenberg theory when x = 0.15, suggesting that the short-range FM order and magnetic inhomogeneity are favoured in Cu-doped samples. The nonmonotonous temperature variation in effective exponents (β eff (ɛ) and γ eff (ɛ)) proves the existence of a magnetic disorder in the studied compounds.
ECS Journal of Solid State Science and Technology
Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8−xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20... more Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8−xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) with average crystallite size 100 nm were synthesized by citrate-gel auto-combustion method to investigate effects of Zn2+ substitution on the structural and dielectric properties. Both X-ray diffraction (XRD) and IR spectroscopy studies confirms the formation of pure cubic spinel structure. Variation of lattice parameter infers Vegard’s law linear dependence with the addition of Zn2+ concentration. The temperature-dependent behavior of dielectric and modulus spectra has been studied within the frequency range 100 Hz-100 kHz for different temperatures between 100 K and 400 K. It was concluded that the dielectric responses of ZnxNi0.8−xCo0.2Fe2O4 are found to be frequency dependent and thermally activated. Also, In the Zn doped ferrites variations of dielectric loss (tan δ) and the imaginary part of electric modulus (M") show the presence of the non-Debye type of dielectric relaxat...
Materials
Magnetic perovskite films have promising properties for use in energy-efficient spintronic device... more Magnetic perovskite films have promising properties for use in energy-efficient spintronic devices and magnetic refrigeration. Here, an epitaxial ferromagnetic La0.67Ba0.33Mn0.95Ti0.05O3 (LBMTO-5) thin film was grown on SrTiO3(001) single crystal substrate by pulsed laser deposition. High-resolution X-ray diffraction proved the high crystallinity of the film with tetragonal symmetry. The magnetic, magnetocaloric and magnetoresistance properties at different directions of the applied magnetic field with respect to the ab plane of the film were investigated. An in-plane uni-axial magnetic anisotropy was evidenced. The LBMTO-5 epilayer exhibits a second-order ferromagnetic-paramagnetic phase transition around 234 K together with a metal–semiconductor transition close to this Curie temperature (TC). The magnetic entropy variation under 5 T induction of a magnetic field applied parallel to the film surface reaches a maximum of 17.27 mJ/cm3 K. The relative cooling power is 1400 mJ/cm3 K (...
Ni0.8−xZnxCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) were prepared by citrate-gel auto-combustion ... more Ni0.8−xZnxCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) were prepared by citrate-gel auto-combustion method. The structural investigation using powder X-ray diffraction (XRD) showed the formation of single-phase cubic spinel structures with Fd-3m space group for all prepared samples. As the Zn2+ concentration is increased, the values of the lattice constant, tetrahedral and octahedral bond lengths undergo significant change. The absolute experimental lattice parameters are closely to the Vegard’ s law derived ones, suggesting that the cations concentration fairly correspond with those calculated prior chemical synthesis. Fourier transform infrared (FTIR) absorption bands at 594–400 cm− 1 confirm the formation of spinel structure. The values of dielectric constant and loss tangent were reported to decline with frequency and the Zn2+composition (x). Incorporation of Zn at nickel-cobalt resulted in decrease in ac conductivity at RT. Here, we report a low loss tangent factor of the order of...
Journal of Molecular Structure, 2021
Abstract Nanoferrites having excellent electromagnetic properties, great permeability, a good ele... more Abstract Nanoferrites having excellent electromagnetic properties, great permeability, a good electromagnetic wave absorbing material, are widely used in information storage systems, the field of magnetic fluid technology and microwave devices and the like. However, it has attracted much attention, for their possibility of various substitution in lattice cell of spinel ferrite (AB2O4), can significantly improve the electromagnetic, catalytic, biologic of the ferrite properties. In this research work, we investigated the substitution of the Nickel Zinc ferrite by rare earth. we studied Ni0.4Zn0.6Fe1.9-xAl0.1GdxO4 (x = 0 and x = 0.1) afterwards named NZF-Al (NZFe-Al0.1Gdx for x = 0) and NZF-AlGd (NZFe-Al0.1Gdx for x = 0.1). These two compounds were prepared using sol-gel auto-combustion synthetic route, from precursors of metal nitrates, citric acid, ethylen-glycool and ammonia. The X-Ray patterns of the prepared powder have confirmed the structure of cubic spinel structure with a space group Fd-3 m (N° 227). The morphology of the samples was investigated by Scanning Electron Microscopy (SEM) and confirmed the nearly spherical nanoparticles with an average particle size of 63 and 41 nm, respectively, for samples with x = 0 and x = 0.1. It should be noted that the substitution of Fe3+ by Gd3+ does not change its crystal structure but increasing the Curie temperature of the sample from 339 K to 436 K. On the other hand, spinel ferrite nanoparticles have a significant photo-response in the visible light region with an excellent photochemical stability. They were also found to be very efficient in removing a wide variety of organic and inorganic contaminants. Therefore, the degradation of the reactive blue (RB-21) dye was studied in the presence of ferrite nanoparticles as a catalyst. The results demonstrated the high efficiency of ferrite nanoparticles in the degradation process. The catalyst can be easily recovered and recycled by simple magnetic separation.
Journal of Low Temperature Physics, 2020
We investigate the effect of lightly Pr 3+ doping ions on the critical behavior of (La 1-x Pr x) ... more We investigate the effect of lightly Pr 3+ doping ions on the critical behavior of (La 1-x Pr x) 0.67 Ba 0.33 MnO 3 (x = 0.15-0.22) perovskite synthesized by the modified sol-gel Pechini method. The obtained critical exponents (beta, gamma and delta) have been investigated by measuring the magnetization around the Curie temperature, T C. Based on the modified Arrott plot and Kouvel-Fisher techniques, scaling hypothesis, and critical isotherm analysis, we have determined the critical exponent values characteristic of magnetic order of (La 1-x Pr x) 0.67 Ba 0.33 MnO 3 (x = 0.15-0.22), with β = 0.55-0.49, γ = 1.06-1.01, and δ = 2.702-3.299. These values indicate that the magnetic order due to lightly Pr 3+ doping exhibits long-range ferromagnetic ordering. This fact is in good agreement with the mean-field model. In addition, the exchange interaction is obtained as J(r) ~ r 4.56 and ~ r 4.49 for 15-at. % Pr and 22-at., respectively. We argue that the range of interaction extends beyond the nearest neighbors.
RSC Advances, 2019
Bulk nanocrystalline samples of (La1−xPrx)0.67Ba0.33MnO3 (0.075 ≤ x ≤ 0.30) manganites with a fix... more Bulk nanocrystalline samples of (La1−xPrx)0.67Ba0.33MnO3 (0.075 ≤ x ≤ 0.30) manganites with a fixed carrier concentration are prepared by the sol–gel based Pechini method.
Applied Physics Letters, 2017
We have developed a thin film structure with a maximum magnetoresistance effect (MRE) at room tem... more We have developed a thin film structure with a maximum magnetoresistance effect (MRE) at room temperature, which is one of the operating requirements for many applications. It is shown that La0.67Ba0.33Ti0.02Mn0.98O3 epilayers obtained by pulsed laser deposition onto (001) SrTiO3 single crystal substrates exhibit the highest MRE, ΔR/R(H)≈150% or ΔR/R(0)≈60% under 5 T, at 300 K, a temperature near to the corresponding Curie temperature (TC). Both doping with a tiny amount of titanium and induced stress due to lattice mismatch between the thin film and the substrate contribute to a decrease in TC as compared to the pristine compound and therefore to the decrease in the temperature where the highest MRE is recorded.
RSC Advances, 2018
Bulk nanocrystalline samples of La0.65Ce0.05Sr0.3Mn1−xCuxO3 (0 ≤ x ≤ 0.15) manganites are prepare... more Bulk nanocrystalline samples of La0.65Ce0.05Sr0.3Mn1−xCuxO3 (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method.
Journal of Alloys and Compounds, 2017
Abstract Single-phase perovskite-type manganese oxides La 0.67 Ba 0.33 Mn 1 − x O 3 with x = 0.00... more Abstract Single-phase perovskite-type manganese oxides La 0.67 Ba 0.33 Mn 1 − x O 3 with x = 0.00–0.08 have been prepared by the modified sol–gel method (Pechini) and the influence of the vacancy concentration in the B-site on their structures and magnetic properties has systematically been investigated. The structural elucidation of the synthesized materials was carried out by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. Rietveld analysis of fitted and observed X-ray diffraction patterns exhibited the single-phase nature of all the studied materials, which crystallize in R 3 ¯ c space group. The average crystallite size was found to be around 56 nm. FTIR spectra present the prominent absorption peak of the in-phase stretching mode (B2g mode) rising from the vibration of Mn O bond length. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing B-site vacancy concentration. All the samples undergo a ferro-to paramagnetic transition, at temperatures that vary from 335 to 216 K as the manganese vacancy increases. As follows from the results of structural and magnetic analyses, creating a vacancy at the Mn site (increase of chemical disorder) induces the formation of Mn4+ ions, which results in the decrease of unit cell volume and leads to a shortage of 3d electrons of the transition metal.
RSC Advances, 2016
Nanocrystalline powders (around 100 nm) of La0.67Ba0.33CrxMn1−xO3 (x ≤ 0.17) perovskites have bee... more Nanocrystalline powders (around 100 nm) of La0.67Ba0.33CrxMn1−xO3 (x ≤ 0.17) perovskites have been synthesized by the sol–gel based Pechini method at low temperatures.
Acta Crystallographica Section A Foundations and Advances, 2015
RSC Advances, 2015
We have investigated the effect of nominal strontium deficiency on the structure, magnetic and ma... more We have investigated the effect of nominal strontium deficiency on the structure, magnetic and magnetocaloric properties of La0.65Eu0.05Sr0.3−xMnO3 (x = 0, 0.10 and 0.15) perovskites.
Acta Crystallographica Section A Foundations of Crystallography, 2011
of oxygen atom of the cations. It is interesting that the structure of inorganic part is highly i... more of oxygen atom of the cations. It is interesting that the structure of inorganic part is highly influenced by the existence of organic molecules in this type of inorganic-organic hybrid materials. We have been studying the crystal structure and chemical bonding in the material by combining the data obtained by single crystal neutron and X-ray diffraction experiments. It is difficult to decide the atomic positions of organic part in the material from only X-ray diffraction data because heavy lead atom is coexisting in the structure. Neutron diffraction is suitable way to analyze the crystal structure of this type of materials. Neutron diffraction data was collected at 120K using timeof-flight single crystal neutron diffractometer "iBIX" constructed at J-PARC. X-ray diffraction data was also collected using imaging-plate single crystal X-ray diffractometer at 120K. From the obtained crystal structure, orientation of the cations and distortion tendency of PbBr 6 octahedra suggests the existence of chemical bonding between lead and oxygen atoms. In addition, the existence of hydrogen bonding between the nitrogen atoms of the cation and bromide atoms of inorganic chain is also suggested. Electron density distribution analysis by maximum entropy method was performed to investigate the nature of chemical bondings in the material. Overlapping of electron density is seen between lead and bromide atoms because of covalent characteristic of the bonding. On the other hand, because no overlapping of electron density is seen between lead and oxygen atoms, it is expected that the bonding has ionic characteristic. Each of inorganic chains is connected by electrostatic interaction through the cations.
Uploads
Papers by Marwène Oumezzine