A. Dhahri

Synthesis, structural and complex impedance spectroscopy studies of Ni0.4Co0.4Mg0.2Fe2O4 spinel ferrite

ABSTRACT Spinel ferrite having composition Ni0.4Co0.4Mg0.2Fe2O4 was prepared by sol-gel method. X-ray diffraction result indicates that the ferrite sample has a cubic spinel type structure. FT-IR showed two absorption bands (ν1 and ν2) that are attributed to the stretching vibration of tetrahedral and octahedral sites. Complex impedance properties have been investigated in 200–420 K temperature range with varying frequency between 40 and 107 Hz. Frequency and temperature dependency of imaginary part of permittivity (ϵ″) and dielectric loss (tanδ) has been discussed in terms of hopping of charge carriers between Fe2+ and Fe3+ ions. Activation energy has been estimated from both temperature dependency of dc conductivity and relaxation time data, which indicates that the relaxation process and conductivity have the same origin. Nyquist plots of impedance show semicircle arcs for sample and an electrical equivalent circuit has been proposed to explain the impedance results.

Critical parameters near the phase transition temperature in La0.67-xDyxPb0.33MnO3

La0.67–xDyxPb0.33MnO3 (x=0.00 and x=0.10) were elaborated by the solid state method and checked by X-ray diffraction. Close to magnetic temperature transition, the order transition and the critical behavior were investigated by dc magnetization measurements versus x composition. The critical properties were investigated through various techniques such as modified Arrott plot (MAP), Kouvel-Fisher (KF) method and critical isotherm (CI) analysis based on the data of static magnetic measurements recorded around the Curie temperature TC. The values of critical exponents (β and γ) estimated were found to lie between those predicted for a 3D-Ising model for x=0.00 and those of 3D-Heisenberg model for x=0.10. The reliability of the critical exponents values was confirmed by the Widom scaling relation and the universal scaling hypothesis. The change in the universality class should be due to the increase of the Dy content.

Microstructural, magnetic and electrical properties of Zn0.4M0.3Co0.3Fe2O4 (M = Ni and Cu) ferrites synthesized by sol–gel method

A comparative study of microstructural, magnetic and electrical properties of Zn0.4Ni0.3Co0.3Fe2O4 (ZNCFO) and Zn0.4Cu0.3Co0.3Fe2O4 (ZCCFO) ferrites prepared using sol–gel method have been investigated in this work. X-ray diffraction results indicate that samples have cubic spinel type structure (

Effect of Sn-doping on the structural, magnetic and magnetocaloric properties of La0.67Ba0.33Mn1-xSnxO3 compounds

Fd\bar {3}m

Synthesis, structural, magnetic and electrical properties of La1−xCdxMnO3 manganites (0.1 ≤ x ≤ 0.5)

Fd3¯m space group). Lattice constant, average grain size and X-ray density are higher for ZCCFO than those of ZNCFO. The magnetic parameters such as Ms, Hc, and Mr were found to decrease with the substitution of Ni by Cu. The electrical properties of the samples have been studied using impedance measurements as a function of frequency and temperature. The substitution of Zn–Co ferrite with Cu leads to improve its conductivity that its substitution with Ni. The behaviors of imaginary part of permittivity and loss tangent have been investigated using Maxwell–Wagner’s model and Koop’s theory. The electrical modulus study reveals the presence of the non-Debye type of dielectric relaxation in our samples. Close values of activation energy for dc conduction (Edc) and for conductivity relaxation (EMʺ) were found confirming that the relaxation process and electrical conductivity are attributed to the same defect. Nyquist representations (Z″ vs. Zʹ) were plotted and their characteristic behaviors were analyzed in terms of electrical equivalent circuit.

Room temperature critical behavior and magnetocaloric properties of La0.6Nd0.1(CaSr)0.3Mn0.9V0.1O3

ABSTRACT We have investigated the effects of barium deficiency on structural, magnetic and magnetocaloric properties of La0.6Nd0.1Ba0.3−xMn0.9Cr0.1O3 (x = 0, 0.05 and 0.1) manganites prepared using the solid-state reaction. All the studied samples crystallize in the orthorhombic structure phase with Pnma space group. Magnetization versus temperature showed that the samples exhibit a second-order paramagnetic to ferromagnetic transition with a decrease of the Curie temperature (TC) from 275 K for x = 0–235 K for x = 0.1. The increase of barium deficiency leads to the decrease of the maximum magnetic entropy change and relative cooling power values from (4.40 J.kg−1 K−1 and 262.94 J.kg−1, for x = 0) to (2.78 J.kg−1 K−1 and 159.41 J.kg−1, for x = 0.1) for an applied magnetic field μ0H = 5 T. These values are compared favorably with those of some other reported manganites, making our samples promising candidates for the magnetic refrigeration technology.