Ah. Dhahri

Correlation between magnetic and electric properties based on the critical behavior of resistivity and percolation model of La0.8Ba0.1Ca0.1MnO3 polycrystalline

We investigated the magneto-electrical properties of a La0.8Ba0.1Ca0.1MnO3 polycrystalline sample, prepared by the polymerization-complex sol–gel method. Comparison of experimental data with the theoretical models showed that in the metal-ferromagnetic region, the electrical behavior of the sample is quite well described by a theory based on electron–electron, electron–phonon and electron–magnon scattering and Kondo-like spin dependent scattering. For the high temperature paramagnetic insulating regime, the adiabatic small polaron hopping model was found to fit well with the experimental curves. The estimated critical exponents, obtained from resistivity, were (β = 0.516 ± 0.013, γ = 1.181 ± 0.005 and α = 0.004). They were very close to those predicted by the mean-field model. These results were in good agreement with the analysis of the critical exponents from magnetization measurements.

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

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.