Dielectric spectroscopy study of the Ni_0.2Zn_0.8Fe₂O₄ spinel ferrite as a function of frequency and temperature

Highlights

• The dielectric properties are strongly dependent on both temperature and frequency.

• The complex impedance plots have revealed the presence of three semicircular arcs.

• The relaxation time is strongly dependent on temperature and frequency.

• The dielectric permittivity is giant at different temperatures and various frequencies.

Abstract

The resistance and the capacitance of ${\mathrm{N}\mathrm{i}}_{0.2}{\mathrm{Z}\mathrm{n}}_{0.8}{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_4$nanocrystalline ferrite prepared by solid state method were measured as a function of frequency in the range 50 Hz–10 MHz at various temperatures (340 K–600 K). The electrical and dielectric properties of spinel ferrite were determined and studied as a function of temperature. The decrease of real impedance values with the increase in frequency is explained using the model of Maxwell–Wagner interfacial polarization. We found that the relaxation time is strongly dependent on frequency and temperature. The impedance plane plots present three semicircle arcs associated to three different relaxation phenomena. Electrical equivalent circuit was determined to explain the dielectric measurements. Activation energies determined from both dc resistance and distribution of the relaxation times are similar. Frequency and temperature dependency of the giant dielectric constant values have been discussed using the model of charge carrier hopping.

Introduction

Nickel-zinc spinel ferrites ${\mathrm{N}\mathrm{i}}_{0.2}{\mathrm{Z}\mathrm{n}}_{0.8}{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_4$ are amongst the most versatile electric and magnetic materials considering their low dielectric loss, large permeability, high electric resistivity and unique magnetic structure [1], [2], [3], [4]. Due to these properties, they are widely used in higher technology such as magnetic heads, magnetic resonance imaging [5], filters [6], biomedicine [7], catalysis [8] and gas sensors [9], [10]. In fact, the performance of spinel ferrites depends on the preparation method, the chemical composition, and the morphological parameters such as density, grain size and lattice constant [11], [12], [13]. As a result, the introduction of Ni metal ion in ${\mathrm{N}\mathrm{i}}_{0.2}{\mathrm{Z}\mathrm{n}}_{0.8}{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_4$ causes the alteration of Fe³⁺ ion distribution. In Ni-Zn system, Ni²⁺ and Fe³⁺ are distributed in octahedral sites whereas Zn²⁺ and Fe³⁺ in tetrahedral sites [9]. Several researchers covered the morphological and magnetic properties of the Ni-Zn systems [14], [15], [16], [17], [18]. Yet, the study of the electric properties is still ongoing [19].

This work aims to study the structural, dielectric and electric properties of ${\mathrm{N}\mathrm{i}}_{0.2}{\mathrm{Z}\mathrm{n}}_{0.8}{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_4$ ferrites with temperatures varying from 340 K to 600 K and in a large frequency range going from 50 Hz to 10 MHz by using X-ray diffraction and impedance spectroscopy. We used resistance and capacitance spectroscopy to characterize the synthesized ferrites materials. Then, we investigated the charge transport mechanism involved in dc and ac resistance. The giant permittivity is strongly dependent on temperature and frequency. Both relaxation time and activation energy values of our samples are determined as a function of temperature and frequency in the ${\mathrm{N}\mathrm{i}}_{0.2}{\mathrm{Z}\mathrm{n}}_{0.8}{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_4$ materials.