• Korean Journal of Materials Research
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• v.13 no.6
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• pp.365-368
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• 2003

Small amounts of additives such as mol % 0.13 NiO and mol % 0.01 $CaCO_3$were added to Cu-Zn-Mg ferrites. Basic composition of the Cu-Zn-Mg ferrites was $Cu_{Cu}$X/$Fe_{0.054}$ /$Zn_{0.486}$$Mg_{0.407}$ $Fe_{1.946}$ $O_4$(group A) and $Cu_{0.263}$$Fe_{0.027}$ $Zn_{0.503}$ $Mg_{0.262}$ $Fe_{1.973}$ $O_4$(group B). Specimens were sintered at different temperatures (1010, 1030, $1050^{\circ}C$) for 2 hours in air followed by an air cooling. Then, effects of various composition and sintering temperatures on the microstructure and the magnetic properties such as inductions, coercive forces, and initial permeabilities of the Cu-Zn-Mg ferrites were investigated. The average grain size increased with the increase of sintering temperature. The magnetic properties obtained from the aforementioned Cu-Zn-Mg ferrite specimens were 1,724 gauss for the maximum induction, 1.0 oersted for the coercive force, and 802 for the initial permeability. These magnetic properties indicated that the specimens could be utilized as the core of IFT (intermediate frequency transformer) and antenna in the amplitude modulation.

• Journal of the Korean Magnetics Society
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• v.20 no.5
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• pp.182-186
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• 2010

Effect of cobalt substitution on the sintering behavior and magnetic properties of a NiZnCu ferrite was studied. $Ni_{0.36-x}Co_xZn_{0.44}Cu_{0.22}Fe_{1.98}O_4(0{\leq}x{\leq}0.04)$ ferrite was fabricated by a solid stat reaction method. It was proposed and experimentally verified that $Co^{2+}$ substituted NiZnCu ferrite was effective on improving the quality factor and magnetic properties of NiZnCu ferrites for multilayer chip inductors. The ferrite was sintered without sintering aids, at $880{\sim}920^{\circ}C$, for 2 h and the initial permeability, quality factor, density, shrinkage, saturation magnetization, and coercivity were also measured. The quality factor (Q) was increased linearly up to x = 0.01 and decreased rapidly over x = 0.01. As the cobalt content increased, the initial permeability and density of the ferrites decreases. The initial permeability of toroidal sample for $Ni_{0.35}Co_{0.01}Zn_{0.44}Cu_{0.22}Fe_{1.98}O_4$ ferrites sintered at $900^{\circ}C$ was 130 at 1 MHz and quality factor was 230.

• Journal of the Korean Magnetics Society
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• v.24 no.2
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• pp.46-50
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• 2014

The crystallographic properties and cationic distribution of $M_{0.2}Fe_{2.8}O_4$ (M =Mn, Ni, Cu) and $Fe_3O_4$ thin films prepared by sol-gel method have been investigated by X-ray diffraction (XRD) and conversion electron M$\ddot{o}$ssbauer spectroscopy (CEMS). The ionic valence, preferred site, and hyperfine field of Fe ions of the ferrites could be obtained by analyzing the CEMS spectra. The $M_{0.2}Fe_{2.8}O_4$ films were found to maintain cubic spinel structure as in $Fe_3O_4$ with the lattice constant slightly decreased for Ni substitution and increased for Mn and Cu substitution from that of $Fe_3O_4$. Analyses on the CEMS data indicate that $Mn^{2+}$ and $Ni^{2+}$ ions substitute octahedral $Fe^{2+}$ sites mostly, while $Cu^{2+}$ ions substitute both the octahedral and tetrahedral sites. The observed intensity ratio $A_B/A_A$ of the CEMS subspectra of the samples exhibited difference from the theoretical value. It is interpreted as due to the effect of the M substitution for A and B on the Debye temperature of the site. The relative line-broadening of the B-site CEMS subspectra can be explained by the dispersion of magnetic hyperfine fields due to random distribution of M cations in the B sites.

• Journal of the Korean Ceramic Society
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• v.50 no.3
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• pp.231-237
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• 2013

Thermodynamic modeling of the $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ complex ferrite system has been adopted as a rational approach to establish routes to better synthesis conditions for pure phase $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ complex ferrite. Quantitative analysis of the different reaction equilibria involved in the precipitation of $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ from aqueous solutions has been used to determine the optimum synthesis conditions. The spinel ferrites, such as magnetite and substitutes for magnetite, with the general formula $MFe_2O_4$, where M= $Fe^{2+}$, $Co^{2+}$, and $Ni^{2+}$ are prepared by coprecipitation of $Fe^{3+}$ and $M^{2+}$ ions with a stoichiometry of $M^{2+}/Fe^{3+}$= 0.5. The average particle size of the as synthesized $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$, measured by transmission electron microscopy (TEM), is 14.2 nm, with a standard deviation of 3.5 nm the size when calculated using X-ray diffraction (XRD) is 16 nm. When $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ ferrite is annealed at elevated temperature, larger grains are formed by the necking and mass transport between the $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ ferrite nanoparticles. Thus, the grain sizes of the $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ gradually increase as heat treatment temperature increases. Based on the results of Thermogravimetric Analysis (TGA) and Differential Scanning Calorimeter (DSC) analysis, it is found that the hydroxyl groups on the surface of the as synthesized ferrite nanoparticles finally decompose to $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ crystal with heat treatment. The results of XRD and TEM confirmed the nanoscale dimensions and spinel structure of the samples.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 1999.09a
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• pp.1-63
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• 1999

Generation of abnormally large grains in the microstructure of small grains has been investigated on some ferrites. Some fractions of large grains were observed in the microstructure of sintered ZnFe$_2$O$_4$, Mn-ZnFe$_2$O$_4$, Fe$_3$O$_4$(in N$_2$) and MnFe$_2$O$_4$(in air). On the other hand, the large grains were not observed in NiFe$_2$O$_4$ and CoFe$_2$O$_4$, independent of calcining and sintering conditions. The large grains seem to be generated in such ferrites that are easy to vary their compositions or valencies at high temperatures. As the sintering proceeded, the number of large grains was increasing to form a continuous structure consisting of large grains, while the size of large grains did not increase remarkably. In addition, the growth of small grains was also very slow during the generation of the large grains. The large grains appeared to be suddenly generated after some induction periods. Avrami equation could be applied to the relation between net volume of large grains and sintering time. Thus, the grain boundaries may be strongly stabilized when the large grains are generated. The large grain in generated by the local activation of the stabilized grain boundaries, which is caused by the variation of compositions or valencies during sintering. It is concluded that the essence of the abnormal grain growth is not the generation of abnormally large grains, but the abnormal stabilization and the local activation of the grain boundaries.

• Transactions of the Korean hydrogen and new energy society
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• v.12 no.3
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• pp.219-229
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• 2001

Hydrogen production by a 2-step water-splitting thermochemical cycle using metal oxides (ferrites) redox pairs and $CH_4$ have been studied in this experiment. The ferrites were reacted with $CH_4$ at $700{\sim}800^{\circ}C$ to produce CO, $H_2$ and various reduced phases (reduction step); these were then reoxidized with water vapor to generate $H_2$ in water-splitting step (oxidation step) at $600{\sim}700^{\circ}C$. The reduced ferrites, Ni-FeO and Ni-Fe alloy showed respectively different reactivity for $H_2$ formation from $H_2O$. In reduction reaction at $800^{\circ}C$, carbon was deposited on surface of Ni-ferrite due to $CH_4$ decomposition. This reduced phase containing carbon, which was taken quite different feature from other phase, produced $H_2$, CO, $CO_2$ by reacting with $H_2O$ at $600^{\circ}C$. The amount of $H_2$ evolved using reduced phase containing carbon was much higher than that of other phase.

• Journal of the Korean Ceramic Society
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• v.39 no.7
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• pp.657-662
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• 2002

The reduced ferrites, reduced NiF $e_2$ $O_4$ and CuF $e_2$ $O_4$, by C $H_4$ were applied to $CO_2$ decomposition to avoid the greenhouse effects. At the reduction reaction above $700^{\circ}C$, $H_2$ and CO were generated by partial oxidation of C $H_4$ After the reduction reaction up to 80$0^{\circ}C$, the spinel structure ferrites changed to mixture of the oxygen deficient iron oxide (Fe $O_{(1-{\delta})}$(0$\leq$$\delta$$\leq$1)) and the metallic Ni or Cu. The rate and quantity of $CO_2$ decomposition with reduced CuF $e_2$ $O_4$ were larger than those with reduced NiFe $O_4$. The $CO_2$ gas was decomposed by oxidation of the oxygen deficient iron oxide. The metallic Cu and Ni were not oxidized and remained in a metallic state up to 80$0^{\circ}C$. The $CO_2$ decomposition reaction with the reduced ferrite by C $H_4$ gas is excellent process preparing useful gas such as $H_2$and CO and decomposing $CO_2$ gas.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.4
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• pp.47-53
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• 2002

In this study, two different (NiCuZn)-ferrite which were fabricated by using ultra-fine powders synthesized by the wet processing and conventionally commercialized powder, were investigated and compared each other in terms of the low temperature sintering and electromagnetic properties. Composition of x and w in $(Ni_{0.4-x}Cu_xZn_{0.6})_{1+w}(Fe_2O_4)_{1-w}$ were controlled as 0.2 and 0.03, respectively. The sintering temperature were $900^{\circ}C$ for ultra-fine powders by way of initial heat treatment and $1150^{\circ}C$ for commercialized powders. The (NiCuZn)-ferrite by ultra-fine powders showed love. sintering temperature than that of commercialized powders by over $200^{\circ}C$, and excellent electromagnetic properties such as the quality factor which is a important factor in the multi-layered chip inductor. In addition, characteristics of B-H hysteresis, crystallinity, microstructure and powder morphology were analyzed by a vibrating sample method(VSM), x-ray diffractometer(XRD), transmission electron microscope (TEM) and scanning electron microscope(SEM).

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1652-1654
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• 2000

고상반응법을 이용하여 $Ni_{0.6-x}Cu_{x}Zn_{0.4}Fe_{2}O_4$(x=0, 0.1, 0.2, 0.3) ferrite 분말을 제조하고 1200$^{\circ}C$에서 열처리하여 Cu 첨가에 따른 입자변화와 전자파흡수 특성과의 관계를 조사하였다. Ni를 Cu로 0.1 mol 치환했을 때 까지는 포화자화 및 전자파흡수능이 치환하지 않았을 때와 거의 비슷하였으나, 그 이상 첨 가시는 직선적으로 감소하였다.

• Journal of Magnetics
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• v.8 no.4
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• pp.138-141
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• 2003

$Ni_{0.65}Zn_{0.35}Fe_2O_4$thin films were prepared by using a sol-gel method. Their crystallographic, dielectric and magnetic properties were investigated as a function of Cu contents by means of an X-ray diffractometer (XRD), X-ray reflectivity, LCZ meter (NF2232), a vibrating sample magnetometer (VSM), and an atomic force microscope (AFM). From typical C-V measurements for $Ni_{0.65}Zn_{0.35}Fe_2O_4$ thin films on p-type silicon substrate, the surface charge density was calculated as 1.4 ${\mu}$C/$m^2$. The dielectric constant evaluated from the capacitance at the accumulation state was 28. The high $H_{c}$ and low $M_{sat}$ at x=0.0 and 0.1 were due to the growth of the ${\alpha}$-$Fe_2O_3$ phase having antiferromagnetic properties. The rapidly decreased $H_{c}$ and increased $M_{sat}$ at x=0.2 and 0.3 can be explained that the ${\alpha}$-$Fe_2O_3$ phases have completely disappeared at x=0.3 and so, non-magnetic defects are minimized. The $M_{sat}$ was slightly decreased and the $H_{c}$ was increased above at x=0.3 because the increase of grain boundary due to smaller grain size acts as defects during magnetization process.