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Journal ArticleDOI

Microstructure, AC impedance and DC electrical conductivity characteristics of NiFe2-xGdxO4 (x = 0, 0.05 and 0.075)

08 Feb 2012-AIP Advances (American Institute of Physics)-Vol. 2, Iss: 1, pp 012139
TL;DR: The structure and electrical properties of Gd doped Ni ferrite materials, namely NiFe1.95Gd0.05O4 and NiFe 1.075O4, are reported to demonstrate their improved electrical properties compared to that of pure NiFe2O4 as discussed by the authors.
Abstract: The structure and electrical characteristics of Gd doped Ni ferrite materials, namely NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4, are reported to demonstrate their improved electrical properties compared to that of pure NiFe2O4. NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds crystallize in the cubic inverse spinel phase with a very small amount of GdFeO3 additional phase while pure NiFe2O4 crystallize in inverse spinel phase without any impurity phase. The back scattered electron imaging analysis indicate the primary and secondary formation in NiFe1.95Gd0.05O4 and NiFe1.925Gd0.075O4 compounds. Atomic force microscopy measurements indicate that the bulk grains are ∼2-5 micron size while the grain boundaries are thin compared to bulk grains. Impedance spectroscopic analysis at different temperature indicates the different relaxation mechanisms and their variation with temperature, bulk grain and grain-boundary contributions to the electrical conductivity (Rg) and capacitance (Cg) of these materials. The con...

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Citations
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Journal ArticleDOI
TL;DR: In this article, the authors used the modified Debye model to analyze the dielectric properties of CoFe2-xMnxO4, referred to CFMO.
Abstract: Manganese (Mn) substituted cobalt ferrites (CoFe2-xMnxO4, referred to CFMO) have been synthesized by the solid state reaction method and their dielectric properties and ac conductivity have been evaluated as a function of applied frequency and temperature. X-ray diffraction measurements indicate that CFMO crystallize in the inverse cubic spinel phase with a lattice constant ∼8.38 A. Frequency dependent dielectric measurements at room temperature obey the modified Debye model with relaxation time of 10−4 s and spreading factor of 0.35(±0.05). The frequency (20 Hz–1 MHz) and temperature (T = 300–900 K) dependent dielectric constant analyses indicate that CFMO exhibit two dielectric relaxations at lower frequencies (1–10 kHz), while completely single dielectric relaxation for higher frequencies (100 kHz–1 MHz). The dielectric constant of CFMO is T-independent up to ∼400 K, at which point increasing trend prevails. The dielectric constant increase with T > 400 K is explained through impedance spectroscopy assuming a two-layer model, where low-resistive grains separated from each other by high-resistive grain boundaries. Following this model, the two electrical responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also satisfactorily accounts for the two dielectric relaxations. The capacitance of the bulk of the grain determined from impedance analyses is ∼10 pF, which remains constant with T, while the grain-boundary capacitance increases up to ∼3.5 nF with increasing T. The tan δ (loss tangent)-T also reveals the typical behavior of relaxation losses in CFMO.

120 citations

Journal ArticleDOI
TL;DR: In this paper, the size dependent variation of magnetic properties of nickel ferrite nanoparticles was investigated by using TGA-DTA, XRD, SEM, TEM and Raman spectroscopy techniques.
Abstract: We report here the investigations on the size dependent variation of magnetic properties of nickel ferrite nanoparticles. Nickel ferrite nanoparticles of different sizes (14 to 22 nm) were prepared by the sol-gel route at different annealing temperatures. They are characterized by TGA-DTA, XRD, SEM, TEM and Raman spectroscopy techniques for the confirmation of the temperature of phase formation, thermal stability, crystallinity, morphology and structural status of the nickel ferrite nanoparticles. The magnetization studies revealed that the saturation magnetization (M-s), retentivity (M-r) increase, while coercivity (H-c) and anisotropy (K-eff) decrease as the particle size increases. The observed value of M-s is found to be relatively higher for a particle size of 22 nm. In addition, we have estimated the magnetic domain size using magnetic data and correlated to the average particle size. The calculated magnetic domain size is closely matching with the particle size estimated from XRD. Impedance spectroscopy was employed to study the samples in an equivalent circuit to understand their transport phenomena. It shows that nickel ferrite nanoparticles exhibit a non-Debye behavior with increasing particle size due to the influence of increasing disorders, surface effects, grain size and grain boundaries, etc. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

68 citations

Journal ArticleDOI
TL;DR: In this paper, the frequency and temperature dependent dielectric properties of hafnium (Hf) incorporated cobalt ferrite (CoF2−xHfxO4) were investigated.

64 citations

Journal ArticleDOI
TL;DR: In this article, structural, Mossbauer studies and improved electrical characteristics of Sm, Gd and Dy doped Ni ferrite materials in comparison to that of pure NiFe 2 O 4 are reported.

54 citations

Journal ArticleDOI
TL;DR: In this article, shock wave induced switchable phase transition (β to α and α to β) of a potassium sulfate (K2SO4) crystal is demonstrated, where the test crystals are subjected to shock waves of...
Abstract: In this research article, shock wave induced switchable phase transition (β to α and α to β) of potassium sulfate (K2SO4) crystal is demonstrated. The test crystals are subjected to shock waves of ...

37 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the formation of layered flake-like aggregates defining a macroporous system is assumed to improve the electrolyte-electrode contact in iron-containing samples.

311 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of rare-earth ion substitutions on magnetic and electrical properties of Ni-Zn ferrite was investigated. But the authors focused on the magnetic properties and not the electrical properties.
Abstract: The effect of Fe substitutions by rare-earth ions on magnetic and electrical properties of a Ni-Zn ferrite prepared by the classical method is investigated. A set of seven compounds with formula Ni0.7Zn0.3Fe1.98R0.02O4, where R identical to Yb, Er, Dy, Tb, Gd, Sm or Ce, was prepared. Emphasis is placed on current experimental results of bulk magnetic measurements and transport phenomena. The results obtained reveal that, by introducing a relatively small amount of R2O3 instead of Fe2O3, an important modification of both the structure and the magnetic and electrical properties can be obtained. We explain the influence of the rare-earth ions as an effect of the ionic radius. This assumption is supported by the lattice constant measurements. The best results from the viewpoint of magnetic and electrical characteristic acceptable for high frequencies were obtained for R ions with a large radius and with a stable valence of 3+ such as Gd in our work.

304 citations

Journal ArticleDOI
TL;DR: In this article, the authors examine recent advances in the processing of Ba-hexaferrite (M-type) films using pulsed laser deposition (PLD), liquid phase epitaxy, and screen printing.
Abstract: Next generation magnetic microwave devices require ferrite films to be thick (>300μm), self-biased (high remanent magnetization), and low loss in the microwave and millimeter wave bands Here we examine recent advances in the processing of thick Ba-hexaferrite (M-type) films using pulsed laser deposition (PLD), liquid-phase epitaxy, and screen printing These techniques are compared and contrasted as to their suitability for microwave materials processing and industrial production Recent advances include the PLD growth of BaM on wide-band-gap semiconductor substrates and the development of thick, self-biased, low-loss BaM films by screen printing

185 citations

Journal ArticleDOI
TL;DR: In this paper, the formation of the ferrite phase was confirmed by x-ray diffraction (XRD) studies, and the room-temperature dielectric measurements showed dispersion behaviour with increasing frequency.
Abstract: Cobalt-substituted nickel–copper ferrite samples having the chemical formula Ni0.95−xCoxCu0.05Fe2O4, where x varies as 0.01, 0.02 and 0.03, were prepared by the standard double sintering ceramic technique. The formation of the ferrite phase was confirmed by x-ray diffraction (XRD) studies. Resistivity and thermo-emf variation with temperature were studied in the temperature range from room temperature to 773 K as a function of cobalt content. As the cobalt content increases, the resistivity of the ferrites decreases. AC conductivity measurements made in the frequency range 100 Hz–1 MHz show that conduction in these ferrites is due to small polaron hopping. The dielectric constant and loss tangent (tanδ) were measured at room temperature as a function of frequency in the range 20 Hz to 1 MHz. The room-temperature dielectric measurements show dispersion behaviour with increasing frequency. To understand the conduction mechanism, complex impedance measurements were carried out. The variation in saturation magnetization (Ms) with variation of cobalt content is also studied.

164 citations

Journal ArticleDOI
TL;DR: Based on ex situ XRD, SEM and XPS data, the electrochemical mechanism of CoFe 2 O 4 film with lithium upon cycling was proposed in this article, where the diffusion coefficient of Li ion was determined by ac impedance method, and the average value was estimated to be 1.1 × 10 −13 ǫ 2 /S.

163 citations