Low frequency conductivity study of gallium‐substituted magnesium–copper spinel ferrite

Abstract

Mixed ferrites with the chemical formula Mg 0.5 Cu 0.5 Ga x Fe 2-x O 4 (0.0 ≤ x ≤ 0.5) were prepared by a ceramic route. X-ray diffraction results confirmed the presence of single-phase spinel structure for these samples. Electrical properties of these ferrites at various compositions were investigated from room temperature up to 550 K in the frequency range 10 2 -10 5 Hz. The obtained results revealed semiconductor behavior at high frequency and metallic behavior at low frequency in these materials. All studied compositions exhibit a transition with a change in the slope of the conductivity versus temperature curve. The obtained transition temperature T C is found to decrease linearly with increasing Ga concentration. As Ga substitutes Fe in these compounds the activation energy for electrical conduction in the ferrimagnetic region (E f ) has a small variation with frequency. In contrast, the activation energy in the paramagnetic region (E p ) shows undefined behavior reflecting the nature of this disordered state. The relation of the universal exponent s with temperature gives evidence for the presence of the large overlap polaron (LOP) hopping conduction mechanism in these compounds. The obtained results are explained in the light of the cation -anioncation and cation -cation interactions present over the octahedral B-sites in the spinel structure.

Conductivity and dielectric studies of copper–aluminate substituted spinel nickel ferrite

“…Substitution of Cu in place of Ni in this ferrite system decreases T c with Cu concentration x. This agrees with the previous studies for superexchange interaction for various oxides [18,19] …”

“…5. These changes in (s) and ln B(T) have been previously noted to occur at the transition temperature T c from the magnetic region to the paramagnetic region [17][18][19]. The values of T c determined from Fig.…”

Effect of nickel substitutions on some properties of Cu–Zn ferrites

“…In the intermediate range of frequency (6-20 kHz), a semiconductor to metallic transition is observed. In the low-frequency range (800 Hz-4 kHz), the conductivity has a slight temperature dependence and the relation of σ with temperature for this sample has remarkable change at 466 K. As Ni content increases (x = 0.4) the conductivity shows an increase with increasing the temperature, in a behavior similar to that exhibited by semiconductor materials [25]. At low temperature, the frequency dependence of the conductivity is clear but, at high temperature, the conductivity becomes frequency independent at a certain temperature.…”

“…Goodenough [27] and Kaiser and Ata-Allah [25] pointed out that, in the case of strong cation-anion-cation interactions and weak cation-cation interactions, the materials have semiconducting (or insulating) behavior. But, if cations of the same element but different valences are simultaneously present, the materials may have metallic-type σ-T character below a ferromagnetic Curie temperature [27].…”

“…σ decreases with increasing temperature). As the temperature increases, the conductivity σ becomes frequency independent at 448 K, which separates the ferrimagnetic region (where σ is frequency-dependent) and the paramagnetic region (where σ is frequency independent) [25]. An abrupt change at the temperature (448 K) is taken as the transition temperature.…”