Study of Dielectric Properties of Nanocrystalline Cobalt Ferrite Upto Microwave Frequencies

Abstract

Summary:The dielectric properties of cobalt ferrite, prepared by sol-gel auto combustion technique, were studied from low frequencies to microwave frequencies. The single phase cubic spinel structure has been confirmed by using X-ray diffraction (XRD). The dielectric properties of the sample were studied in the low frequency range from 100 Hz to 120 MHz as well as in the high frequency range from 3.95 GHz to 5.85 GHz at room temperature. The dielectric dispersion observed at lower frequency region is due to Maxwell-Wagner two layer model, which is in agreement with Koops phenomenological theory. There is a strong co-relation between the conduction mechanism and the dielectric behaviour of ferrites. The dielectric constant remains almost constant at microwave frequencies due to the fact that it is contributed by atomic and electronic polarization. The dielectric loss tangent shows two dielectric loss peaks at about 4.332 GHz and 4.525 GHz frequencies.

Conductivity and giant permittivity study of Zn0.5Ni0.5Fe2O4 spinel ferrite as a function of frequency and temperature

“…This leads to poor conductance resulting from weak electron hopping in the region. 26 The second region that spreads from 10 3 Hz to 10 6 Hz presents a signicant increase of conductance with rising frequency and can be described by the power law: 7…”

Effect of LaNiO3 on the impedance and dielectric properties of CoFe2O4: a high temperature study

“…When the frequency of the applied electric field is close to the hopping frequency of the charge carriers, maximum energy is absorbed by the carriers and a peak is observed in the loss. This phenomenon is called resonance which is observed earlier in nanostructured CFO [13] or CFO thick film [14] and other ferrites [53]. This resonance peak follows Arrhenius equation (equation ( 1)) which indicates thermally activated process with activation energy 0.493 eV (right inset of figure 11(b)).…”

“…The frequency dispersion of ε reveals that ε has large value at low frequency and it decreases with increasing frequency which is normal dielectric behaviour of ferrites [13,34,35]. This behaviour can be explained by Koops's phenomenological theory based on Maxwell-Wagner type two layers model [36].…”

“…The alignment of the dipoles Fe +2 -Fe +3 along the direction of the applied field occurs via the rotation which can be pictured as the hopping of charge carriers between the ions Fe +2 ↔ Fe +3 . As the resistance of the grain boundary is very high, the electrons after reaching the grain boundary by hopping between the ions, pile up there and leads to space charge polarization which causes very high value of dielectric constant at lower frequency [13,35,39]. The dielectric constant depends on the number of ions, the higher the concentration of ions (Fe +2 and Fe +3 ) the larger the dielectric constant should be [29].…”

“…CFO is one of the widely used spinel ferrites because of its properties as hard ferrimagnetic material, high electrical resistance, good chemical and thermal stability and large magnetic anisotropy [11,12]. In past, most of the impedance and dielectric studies of CFO were performed in nanocrystalline form [13] or in thick films [14] and on the composites of CFO and other ferroelectric materials for example BiFeO 3 [15,16] or BaTiO 3 [17] to produce multiferroic materials. However, the correlation between defects and impedance properties are not hitherto explored.…”