E. Dhahri

Bio: E. Dhahri is an academic researcher from University of Sfax. The author has contributed to research in topics: Magnetization & Magnetic refrigeration. The author has an hindex of 37, co-authored 349 publications receiving 4899 citations. Previous affiliations of E. Dhahri include Johns Hopkins University Applied Physics Laboratory & École Normale Supérieure.

Conduction mechanism, impedance spectroscopic investigation and dielectric behavior of La0.5Ca0.5-xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 0.2).

Abstract: This study presents the electrical properties, complex impedance analysis and dielectrical behavior of La05Ca05−xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 02) Transport measurements indicate that all the samples have a semiconductor-like behavior The metal-semiconductor transition is not observed across the whole temperature range explored [80 K–700 K] At a specific temperature, a saturation region was marked in the σ (T) curves We obtained a maximum σdc value at ambient temperature with the introduction of 20% Ag content Two hopping models were applied to study the conduction mechanism We found that activation energy (Ea) related to ac-conductivity is lower than the Ea implicated in dc-conductivity Complex impedance analysis confirms the contribution of grain boundary to conductivity and permits the attribution of grain boundary capacitance evolution to the temperature dependence of the barrier layer width From the temperature dependence of the average normalized change (ANC), we deduce the temperature at which the available density of trapped charge states vanishes Such a temperature is close to the temperature at which the saturation region appears in σ(T) curves Moreover, complex impedance analysis (CIA) indicates the presence of electrical relaxation in materials It is noteworthy that relaxation species such as defects may be responsible for electrical conduction The dielectric behavior of La05Ca05−xAgxMnO3 manganites has a Debye-like relaxation with a sharp decrease in the real part of permittivity at a frequency where the imaginary part of permittivity (e′′) and tg δ plots versus frequency demonstrate a relaxation peak The Debye-like relaxation is explained by Maxwell–Wagner (MW) polarization Experimental results are found to be in good agreement with the Smit and Wijn theory

Magnetic and spectroscopic properties of Ni–Zn–Al ferrite spinel: from the nanoscale to microscale

Abstract: This article presents the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni0.6Zn0.4Fe1.5Al0.5O4 (NZFAO) nanoparticles (NPs). The samples were successfully synthesized by the sol–gel method followed by annealing of the as-synthesized at 600, 800, 900, 1050, and 1200 °C. This approach yielded the formation of a highly crystalline structure with crystallite size ranging from 17 nm to 40 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques, as well as energy disperse spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman spectroscopy, were used in order to determine the structural and morphological properties of the prepared samples. Rietveld XRD refinement reveals that Ni–Zn–Al ferrite nanoparticles crystallize in inverse cubic (Fdm) spinel structure. Using FTIR spectra, the elastic and thermodynamic properties were estimated. It was observed that the particle size had a pronounced effect on elastic and thermodynamic properties. Magnetic measurements were performed up to 700 K. The prepared ferrite samples present the highest Curie temperature, which decreases with increasing particle size and which is consistent with finite-size scaling. The thickness of the surface shell of about 1 nm was estimated from size-dependent magnetization measurements using the core–shell model. Besides, spin resonance, magnetostriction, temperature coefficient of resistance (TCR), and electrical resistivity properties have been scientifically studied and appear to be different according to their size. The optical properties of synthesized NZFAO nanoparticles were investigated, and the differences caused by the particle sizes are discussed on the basis of the phonon confinement effect. This effect was also inspected by the Raman analysis. Tuning of the physical properties suggests that the Ni–Zn–Al ferrite samples may be promising for multifunctional diverse applications.

Electrical conductivity and dielectric behaviour of nanocrystalline La0.6Gd0.1Sr0.3Mn0.75Si0.25O3

Abstract: An La0.6Gd0.1Sr0.3Mn0.75Si0.25O3 ceramic was prepared via a solution-based chemical technique. X-ray diffraction study confirms the formation of the compound in the orthorhombic structure with the Pnma group space. Dielectric properties have been investigated in the temperature range of 85–290 K with the frequency range 40 Hz to 2 MHz. The conductivity spectra have been investigated by the Jonscher universal power law: σ(ω) = σdc + Aωn, where ω is the frequency of the ac field, and n is the exponent. The deduced exponent ‘n’ values prove that a hopping model is the dominating mechanism in the material. Based on dc-electrical resistivity study, the conduction process is found to be dominated by a thermally activated small polaron hopping (SPH) mechanism. Complex impedance analysis (CIA) indicates the presence of a relaxation phenomenon and allows us to modelize the sample in terms of an electrical equivalent circuit. Moreover, the impedance study confirms the contribution of grain boundaries to the electrical properties.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.