Bulk and nano Ni1-xMgxFe2O4 (x = 0–1) samples were synthesized via microwave double sintering and microwave assisted hydrothermal techniques respectively. The diffraction pattern confirmed the formation of cubic spinel phases in case of both the ferrites. The larger bulk densities were achieved to the bulk than that of nano. In addition, a comparative study on X-band (8.4–12 GHz) electromagnetic interference shielding properties of current bulk and nanomaterials was elucidated. The results showed that the bulk Ni0.6Mg0.4Fe2O4 composition revealed the highest total shielding efficiency (SET) of ∼17 dB. In comparison, the shielding efficiency values of all bulk contents were higher than that of nano because of larger bulk densities. Moreover, the ac-electromagnetic parameters such as electrical conductivity (σac), the respective real (ε′ &amp; μ′) and imaginary parts (ε″ &amp; μ″) of complex permittivity and permeability were investigated as a function of gigahertz frequency. The bulk ferrites of x = 0.4 &amp; 0.6 showed the high ε″ of 10.26 &amp; 6.71 and μ″ of 3.65 &amp; 3.09 respectively at 12 GHz which can work as promising microwave absorber materials. Interestingly, nanoferrites exhibited negative μ″ values at few frequencies due to geometrical effects which improves the microwave absorption. © 2016 Elsevier B.V.

Madhuri W

Department of Physics

School of Advanced Sciences

Vellore Campus

Chandra Babu Naidu K

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Materials Chemistry and Physics

One-dimensional lead hexaferrite (PbFe12O19) nanofibers are produced using electrospinning technology combined with sol–gel followed by muffle furnace heating. PVP/DMF is used as reductant to form precursor solution for lead hexaferrite nanofiber. Polycrystalline nanofibers with an average diameter of 145 nm have been prepared by electrospinning method. The structural features of the sintered nanofibers are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and EDX. The obtained PbFe12O19 nanofibers showed a hexagonal structure after sintering. The SEM image clearly shows the fibrous morphology of PbFe12O19. Vibrating sample magnetometer (VSM) revealed very low coercivity and fairly high saturation magnetization. The fiber exhibited a ferromagnetic behaviour at room temperature, which is attributed to the nanometre-size of PbFe12O19 nanofibers. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.

Applied Physics A

Evidence of magnetism in electrospun PbFe12O19 nanofibers

The effect of iron deficiency on the structural, electrical and magnetic properties of the nano PbFe12-xO19-δ (where x = 0.0, 0.25, 0.50, 0.75 and 1.0) hexaferrites prepared by sol-gel auto combustion and further processed by microwaves is presented. The structure studied using transmission electron microscope (TEM) showed hexagonal cylindrical particles with an average size of ∼20 nm. Selected area electron diffraction (SAED) reflected highly crystalline nature of these nanoparticles. From the dielectric characterizations ac-conductivity, dielectric constant and loss tangent are analysed for pure and modified PbFe12-xO19-δ hexaferrites. The magnetic analysis revealed the formation of single-domain structure. Saturation magnetization (MS) decreases from 63.2 (x = 0) to 38.2 (x = 1.0) emu/g with increasing the Fe ions deficiency. Room temperature Mössbauer spectra show five sextets for all compositions confirmed the single phase formation. The relative area of 12k (↑) site decreases and 4f2 (↓) increases drastically with increasing the Fe ions deficiency in Pb-hexaferrites. © 2018 Elsevier B.V.

Effect of non-stoichiometry in lead hexaferrites on magnetic and dielectric properties

Ferrites are magnetic semiconductors realizing an important role in electrical and electronic circuits where electrical and magnetic property coupling is required. Though ferrite materials are known for a long time, there is a large scope in the improvement of their properties (vice sintering and frequency dependence of electrical and magnetic properties) with the current technological trends. Forth coming technology is aimed at miniaturization and smart gadgets, electrical components like inductors and transformers cannot be included in integrated circuits. These components are incorporated into the circuit as surface mount devices whose fabrication involves low temperature co-firing of ceramics and microwave monolithic integrated circuits technologies. These technologies demand low temperature sinter-ability of ferrites. This article presents low temperature microwave sintered Ni–Mg ferrites of general chemical formula Ni1−xMgxFe2O4 (x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) for potential applications as transformer core materials. The series of ferrites are characterized using X-ray diffractometer, scanning electron microscopy, Fourier transform infrared and vibrating sample magnetometer for investigating structural, morphological and magnetic properties respectively. The initial permeability is studied with magnesium content, temperature and frequency in the temperature range of 308 K–873 K and 42 Hz–5 MHz. © 2016 Elsevier B.V.

Journal of Magnetism and Magnetic Materials

Microwave processed NiMg ferrite: Studies on structural and magnetic properties

Magnesium is replaced systematically by zinc in Ni0.2Mg0.8-xZnxFe2O4 (x = 0.2–0.8) prepared by microwave-assisted solid-state reaction route. The structure is confirmed by X-ray diffractograms. An improvement in initial permeability is observed with substituent in Ni0.2Mg0.8-xZnxFe2O4 due to increase in average grain size. The obtained permeability values are varying between 106 and 687 at 1 MHz. The permeability plots revealed that Curie-transition temperature (Tc) is decreasing with increase in zinc. Both x = 0.2 and 0.4 compositions show low relative loss factor of order 10−5 to 10−4, which are exhibiting required magnetic properties for transformer and inductor core applications. © 2016 The American Ceramic Society

International Journal of Applied Ceramic Technology

Effect of Nonmagnetic Zn2+Cations on Initial Permeability of Microwave-Treated NiMg Ferrites

The spinel ferrite of compositions Ni0.2Mg0.8−x ZnxFe2O4 (x = 0.2, 0.4, 0.6, 0.8) are synthesized using microwave double sintering technique. X-ray diffraction study reveals formation of single phase spinel cubic structure. The lattice parameter (a), average crystallite size (D) and bulk density (ρb) are increasing with zinc content. Fourier-transform infrared spectra are recorded to locate octahedral and tetrahedral sites. The dielectric constant (εr), loss tangent (tanδ), ac, dc-electrical conductivities (σac and σdc) are increasing while Curie transition temperature (Tc) and activation energies (Ea) are decreasing with zinc substitution. Power law fit is applied to logσ versus logω plots to evaluate dc-electrical conductivity and exponent (n) at room temperature. Electrical conduction mechanism and relaxation time (τ) are reported from impedance analysis. Hysteresis loop attributes that saturation magnetization (Ms), anisotropy constant (K1) and coercivity (Hc) are decreasing with substituent. Low coercivity of 1.96–2.89 G obtained is suitable for magnetic recording applications. © 2016 Elsevier B.V.

Journal	Data powered by TypesetMaterials Chemistry and Physics
Publisher	Data powered by TypesetElsevier BV
ISSN	0254-0584
Open Access	0