Structural evolution and magnetic properties of nanocrystalline 50 Permalloy powders prepared by mechanical alloying
TL;DR: In this article, the evolution of the microstructure and magnetic properties during the milling process were studied by the X-ray diffraction technique, the scanning electron microscope, the transmission electron microscope and the vibrating sample magnetometer.
About: This article is published in Journal of Alloys and Compounds.The article was published on 2013-10-15. It has received 32 citations till now. The article focuses on the topics: Nanocrystalline material & Coercivity.
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TL;DR: In this article, the microwave shielding properties of Ni and its Fe alloy NPs were investigated in the Ku band and the results showed that Ni NPs are good candidates for EMI shielding having the ability to attenuate 99.9% of electromagnetic radiation.
Abstract: Ni and NiFe alloys with different compositions have been successfully synthesized using a simple, surfactant-free polyol method. The morphological analysis demonstrated a uniform spherical nature of the alloys, with size range ∼10–30 nm. A very thin oxide layer was found to form over the alloy nanoparticles (NPs) which is weakly visible in TEM and later confirmed by XPS analysis. The magnetic properties of the Ni and NiFe NPs were measured using a vibrating sample magnetometer (VSM) at room temperature. The saturation magnetization value was found to be lowest in Ni and keeps on increasing with increasing Fe content in the composition. The resistivity, as revealed from I–V characteristics, was shown to be lowest for the permalloy (Ni80Fe20) phase, while the values increase with further increment in the Fe content. The microwave shielding properties of the Ni and its Fe alloy NPs were investigated in the Ku band range. The lower EM wave transmittance with good reflection and absorption coefficients is responsible for the high shielding values. All of the alloys tested in this investigation showed excellent microwave shielding properties ranging from −21 to −41 dB in the entire Ku band, for ∼1 mm thick samples. The lowest EMI shielding range (−21 to −29 dB) was noted for Ni NPs while the highest was observed in the case of permalloy (−30 to −41 dB). The rest of the NiFe combinations show intermediate shielding effectiveness as compared to Ni and permalloy. Certainly, all of the NiFe alloy combinations we tested showed excellent EMI shielding above −30 dB, with significant enhancements in the absorption shielding efficiency. These alloys are good candidates for EMI shielding having the ability to attenuate 99.9% of electromagnetic radiation.
59 citations
TL;DR: In this paper, the authors describe new findings of an investigation of the morphology and composition of NiFe alloy nanoparticles synthesized under controlled conditions, showing that the NiFe nanoparticles exhibit remarkable resistance to air oxidation in comparison with Ni or Fe particles.
42 citations
TL;DR: In this article, the authors reviewed the key role of these parameters on the structure and magnetic behaviors of soft magnetic materials and highlighted the mechanism of mechanical alloying and effect of diffusivity.
Abstract: Soft magnetic materials are widely used in electrical and electronic industries due to their desirable electromagnetic features, i.e. relatively high electrical resistivity and low eddy current loss at high frequencies. From industrial point of view, once the size of grains is reduced to micron scale regimes, their performance is only narrowed to a few megahertz frequencies, due to their higher conductivity and domain wall resonance. Thus, one way to resolve this issue and utilize these materials at high frequency applications, is to reduce the size of grains from micron to sub or nanoscale before they are being compacted for sintering. In this aspect, however, several methods are employed to synthesize these nanoparticles, a mechanical alloying is found to be a proven route to produce a vast variety of materials with both non-equilibrium and equilibrium phases in a controlled size and shape of powder particles at desired tonnages. Mechanical alloying (MA) is a solid-state powder metallurgy route which involves a repeated action of fracturing and re-welding of powder particles in a high-energy ball mill. The final products characteristics are strongly dependent on the variable parameters of the process, i.e. milling time, ball-to-powder weight ratio, rotation speed, grinding media and milling atmosphere. Thus, this work reviews the key role of these parameters on the structure and magnetic behaviors of soft magnetic materials. Eventually, the mechanism of mechanical alloying and effect of diffusivity are also highlighted.
40 citations
TL;DR: In this article, the effect of urea-to-nitrate molar ratio on the synthesis and properties of Mn0.5Zn0.4 ferrite prepared by microwave-induced combustion method has been studied.
Abstract: In this work, the effect of urea-to-nitrate molar ratio on the synthesis and properties of Mn0.5Zn0.5Fe2O4 ferrite prepared by microwave-induced combustion method has been studied. The product powders synthesized at three different molar ratios of urea to nitrate (U/N ratio), varying from 0.58 to 1.08. X-ray diffraction patterns confirm formation of a spinel-type structure of ferrite and also hematite in the as-synthesized powders. The average of particle size is found to be in the range 30–80 nm. The values of saturation magnetization and permeability are increased with the increase in U/N ratio. Dielectric parameters were measured as a function of frequency. The real and imaginary parts of dielectric constant are found to decrease with the increase in frequency, while the ac conductivity is found to increase with increasing frequency. The complex impedance analysis shows only one semicircle indicating the predominant effect of grain boundary property of the material.
26 citations
TL;DR: In this paper, nanocrystalline Li-Zn ferrites with the chemical composition of Li0.5Zn and Zn 0.5−x O4 were synthesized by glycine-nitrate combustion process using glycine as a fuel, nitrate as an oxidizer, and microwave oven as a heat source.
Abstract: In this study, nanocrystalline Li–Zn ferrites with the chemical composition of Li0.5Zn
x
Fe2.5−x
O4 (where 0 ≤ x≤0.5) were synthesized by glycine–nitrate combustion process using glycine as a fuel, nitrate as an oxidizer, and microwave oven as a heat source. The as-synthesized powders were characterized using an X-ray diffraction technique. X-ray diffraction patterns show that nanocrystalline Li–Zn ferrite phase with a spinel structure has been formed successfully in all samples. Dielectric properties including dielectric constants, dielectric loss, AC conductivity, and complex dielectric impedance were measured in the frequency range 20 Hz–10 MHz using a LCR meter. Results show that dielectric constant, as well as dielectric loss, decreases with increasing frequency and then becomes roughly frequency independent at high frequencies. In contrast, AC conductivity follows an upward trend with frequency. Complex impedance spectroscopic studies show the presence of only one semicircle for all samples, suggesting the predominant effect of grain boundary property of the material. It is also found that substitution of Zn for Fe ions leads to a significant decrease in electrical conductivity due to decrease of ferrous and ferric ions available for the hopping process. Similarly, both dielectric constant and dielectric loss show reduction with the increase in Zn content as a result of the reduction of Fe2+/Fe3+ ions.
24 citations
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TL;DR: In this paper, the early days of the Rietveld method are described, along with a retrospective view of its application in various areas of physics, such as X-ray and neutron analysis.
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TL;DR: In this paper, a review of attrition as a method to produce nanocrystalline (nc) materials is presented, including ball milling of single component powders, mechanical alloying of multi-component powders and mechanical crystallization of amorphous alloys.
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