• Journal of the Korean Magnetics Society
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• v.13 no.1
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• pp.1-5
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• 2003

Magnetic and structural properties of $(CoFe_2O_4)_{1-x}(Y_3Fe_5O_{12})_x$ powders (0 $\leq$ x $\leq$ 1) grown by a conventional ceramic method were investigated using X-ray diffractormeter (XRD), scanning electron microscopy (SEM), Mossbauer spectroscopy and vibrating sample magnetometer (VSM). The XRD results for the powders annealed at 120$0^{\circ}C$ indicated that no other peak was observed except for the ones from cobalt ferrite and the garnet powder. SEM micrographs indicated that cobalt ferrite and garnet powders were aggregated and completely formed together. It was hard to identify which part of the powders was the garnet or the cobalt ferrite. Mossbauer spectra for powders grown separately and mixed mechanically consisted of sub-spectra of cobalt ferrite and garnet, however, powders annealed together had an extra sub-spectrum, which was related with the interaction between iron ions at the grain surfaces of cobalt ferrite and the garnet: cobalt ferrite and garnet particles were located very closely. The value of the saturation magnetization measured by a VSM as a function of composition ratio agreed very well with the ones based on the theoretical calculation.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.611-616
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• 2011

Red-orange phosphors $Gd_{1-x}PO_4:{Eu_x}^{3+}$ (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized with changing the concentration of $Eu^{3+}$ ions using a solid-state reaction method. The crystal structures, surface morphology, and optical properties of the ceramic phosphors were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectrophotometry. The XRD results were in accordance with JCPDS (32-0386), and the crystal structures of all the red-orange phosphors were found to be a monoclinic system. The SEM results showed that the size of grains increases and then decreases as the concentration of $Eu^{3+}$ ionincreases. As for the PL properties, all of the ceramic phosphors, irrespective of $Eu^{3+}$ ion concentration, had orange and red emissions peaks at 594 nm and 613 nm, respectively. The maximum excitation and emission spectra were observed at 0.10 mol of $Eu^{3+}$ ion concentration, just like the grain size. An orange color stronger than the red means that $^5D_0{\rightarrow}^7F_1$ (magnetic dipole transition) is dominant over the $^5D_0{\rightarrow}^7F_2$ (electric dipole transition), and $Eu^{3+}$ is located at the center of the inversion symmetry. These properties contrasted with those of a red phosphor $Y_{1-x}PO_4:{Eu_x}^{3+}$, which has a tetragonal system. Therefore, we confirm that the crystal structure of the host material has a major effect on the resulting color.

• Korean Chemical Engineering Research
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• v.54 no.5
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• pp.636-647
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• 2016

Magnetite nanoparticles ($Fe_3O_4$ NPs) were synthesized by co-precipitating method under optimized condition. The $Fe_3O_4$ NPs coated with sodium dodecyl sulfate-thenoyltrifluoroacetone ($Fe_3O_4$ NPs-SDS-TTFA) were then exerted as the magnetic solid phase extraction (MSPE) adsorbent for the extraction process prior to introducing to a flame atomic adsorption spectrometry (FAAS). The synthesized $Fe_3O_4$ NPs-SDS-TTFA were applied for the extraction of Pb(II) ions from different water samples. The characterization studies of nanoparticles were performed via scanning electron microscopy-energy dispersive micro-analysis (SEM-EDAX), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) techniques. The substantial parameters affecting the extraction efficiency were surveyed and optimized. A dynamic linear range (DLR) of $10-400{\mu}g\;L^{-1}$ was obtained and the limit of detection (LOD, n=7) and relative standard deviation (RSD%, n= 6, $C=20{\mu}g\;L^{-1}$) were found to be $2.3{\mu}g\;L^{-1}$ and 1.9%, respectively. According to the results, the proposed method successfully applied for the extraction of Pb(II) ions from different environmental water samples and satisfactory results achieved.

• Journal of Magnetics
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• v.21 no.3
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• pp.315-321
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• 2016

M-Zn (M = Sb, V, Nb) substituted M-type strontium hexaferrites were prepared by a ceramic method. The phase composition, morphology and magnetic properties were studied by x-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Saturation magnetization increases with a substitution up to 75.0 emu/g (2.5 % higher compared to unsubstituted hexaferrite) and then decreases with a further substitution. A coercive field of substituted hexaferrite powders with highest saturation magnetization is more than 3 kOe. Substituted strontium hexaferrite powders prepared in this work are a rare example of high $M_S$ compositions without doping rare-earth elements and would be a promising candidate for a permanent magnet application.

• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.101-105
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• 1990

A DC thermal plasma system has been designed and constructed to obtain diamond films from a mixture of CH4 and H2. The effects of the deposition conditions such as substrate temperature ($850^{\circ}C-1050^{\circ}C$), gas mixing ratio (0.5-1.5% CH4 in H2), chamber pressure (50 - 200 Torr), axial magnetic field (0 - 900 Gauss) on the diamond film properties such as morphology, purity of the film and deposition rate, etc. have been examined with the aids of Scanning Electron Microscopy, X-Ray Diffraction and Raman Spectroscopy. Under optimum conditions, high quality diamond films can be obtained with high deposition rate (>$1{\mu}m/min$). Both of the growth rate and' particle size increased with the substrate temperature but the morphology changed from the faceted to unshaped when the temperature deviates its proper range. Furthermore, higher growth rates of $1.5{\mu}m/min$ can be obtained by applying an axial magnetic field to plasma torch. The observed values of interplanar spacings of diamond were in a good agreement with the values reported in ASTM data and all deposits have the diamond peak of $1332.5\;cm^{-1}$ in the Raman Spectra.

• Journal of Magnetics
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• v.15 no.1
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• pp.25-28
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• 2010

This study examined the crystallographic and magnetic properties of vanadium-substituted lithium cobalt titanium ferrite, $Li_{0.7}Co_{0.2}Ti_{0.2}V_{0.2}Fe_{1.7}O_4$. Ferrite was synthesized using a conventional ceramic method. The samples annealed below $1040^{\circ}C$ showed X-ray diffraction peaks for spinel and other phases. However, the sample annealed above $1040^{\circ}C$ showed a single spinel phase. The lattice constant of the sample was $8.351\;{\AA}$, which was relatively unaffected by vanadium-substitution. The average grain size after vanadium-substitution was $13.90\;{\mu}m$, as determined by scanning electron microscopy. The M$\ddot{o}$ssbauer spectrum could be fitted to two Zeeman sextets, which is the typical spinel ferrite spectra of $Fe^{3+}$ with A and B sites, and one doublet. From the absorption area ratio of the M$\ddot{o}$ssbauer spectrum, the cation distribution was found to be ($Co_{0.2}V_{0.2}Fe_{0.6})[Li_{0.7}Ti_{0.2}Fe_{1.1}]O_4$. Vibrating sample magnetometry revealed a saturation magnetization and coercivity of 36.9 emu/g and 88.6 Oe, respectively, which were decreased by vanadium-substitution.

• Journal of Magnetics
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• v.10 no.4
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• pp.145-148
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• 2005

Effect of vacuum annealing on the microstructures and magnetic properties of $Fe_{84}Si_6B_{10}$ films has been investigated as a function of annealing temperature. X-ray diffraction and transmission electron microscopy were employed to analyze crystallization behavior of the films. Permeability of the films was measured at various frequencies by one-turn coil method. When the films were annealed below 673 K, the coercivity of the films did not change a lot (${\~}$1500 A/m) although the grain size of a crystalline phase in the partially crystallized films increased gradually up to about 16 nm. It then increased rapidly as the films became almost fully crystalline mostly with $\alpha$-(Fe,Si) phase at and above 723 K. On the other hand, the electrical resistivity of the films decreased monotonically with the increase of annealing temperature. The permeabilities of the films annealed at 473${\~}$673 K were all over 1000, showing the optimum value of 3500 at 523 K, and almost constant up to 300 MHz. However, those of the as-deposited and fully crystallized films were lower than 1000 and unstable at the same frequency range.

• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.167-173
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• 2011

Nickel cobalt ferrite($Ni_{0.5}Co_{0.5}Fe_2O_4$) powder was prepared through the ceramic route by the calcination of a stoichiometric mixture of NiO, CoO and $Fe_2O_3$ at $1100^{\circ}C$. The pressed pellets of $Ni_{0.5}Co_{0.5}Fe_2O_4$ were isothermally reduced in pure hydrogen at $800{\sim}1100^{\circ}C$. Based on the thermogravimetric analysis, the reduction behavior and the kinetic reaction mechanisms of the synthesized ferrite were studied. The initial ferrite powder and the various reduction products were characterized by X-ray diffraction, scanning electron microscopy, reflected light microscope and vibrating sample magnetometer to reveal the effect of hydrogen reduction on the composition, microstructure and magnetic properties of the produced Fe-Ni-Co alloy. The arrhenius equation with the approved mathematical formulations for the gas solid reaction was applied to calculate the activation energy($E_a$) and detect the controlling reaction mechanisms. In the initial stage of hydrogen reduction, the reduction rate was controlled by the gas diffusion and the interfacial chemical reaction. However, in later stages, the rate was controlled by the interfacial chemical reaction. The nature of the hydrogen reduction and the magnetic property changes for nickel cobalt ferrite were compared with the previous result for nickel ferrite. The microstructural development of the synthesized Fe-Ni-Co alloy with an increase in the reduction temperature improved its soft magnetic properties by increasing the saturation magnetization($M_s$) and by decreasing the coercivity($H_c$). The Fe-Ni-Co alloy showed higher saturation magnetization compared to Fe-Ni alloy.

• Progress in Superconductivity and Cryogenics
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• v.8 no.4
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• pp.15-18
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• 2006

REBCO coated conductors (RE: rare earth elements) have recently drawn great attention since they are known to possess stronger flux pinning centers in high magnetic fields compared with YBCO coated conductors. In this study, $GdBa_2Cu_3O_{7-d}(GdBCO)$ was selected to investigate the influence of the distance between target and substrate and substrate temperature on the superconducting properties of GdBCO films on the $SrTiO_3(100)$ substrate. Samples were fabricated by pulsed laser deposition (PLD) with a Nd:YAG laser (355nm). Under a given oxygen pressure of 800mTorr, we changed the distance between target and substrate from 5.5cm to 7.0cm and the substrate temperature from $750^{\circ}C\;to\;850^{\circ}C$. The crystallinity and texture of GdBCO films were analyzed by X-ray diffraction (XRD), and the surface morphology was observed by the scanning electron microscopy (SEM). Tc and Jc values were measured by the four point probe method. High quality GdBCO films with Tc of 89.7K and Jc over $1MA/cm^2$ at 77 K in self field were successfully fabricated by optimizing processing parameters. The detailed processing conditions, microstructure and superconducting properties will be presented for a discussion.

• Journal of the Korean Chemical Society
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• v.60 no.1
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• pp.34-38
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• 2016

In this paper, zinc oxide nanoparticles (ZnO NPs) were synthesized using the sonochemical method, where equimolar amounts of zinc acetate dehydrate and sodium hydroxide were separately dissolved in deionized water, and then mixed for 30 min under magnetic stirring. The resultant white gel was sonicated for 60, 120, 180, 240, and 360 min with magnetic stirring. The obtained precipitates were centrifuged, repeatedly washed with ethanol to remove ionic impurities, and dried at 50 ℃ for 24 h. The formation of pure NPs was confirmed by X-ray diffraction, and their crystallinity and crystal phases were analyzed as well. Structural investigation was carried out by field-emission scanning electron microscopy (FE-SEM). The photocatalysis behavior of the ZnO NPs was investigated in a dark room under UV irradiation, using Rhodamine B. Spherical, rod, and flower-like ZnO NPs could be obtained by adjusting the sonication time, as observed by FE-SEM. The flower-like ZnO NPs exhibited excellent photocatalytic activity.