• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.791-796
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• 1993

The electro-magnetic properties of the Mn-Zn ferrite single crystal with small variation of Fe2O3 concentration at the high permeability composition, 53mol% Fe2O3-28.5mol% MnO-18.5mol% ZnO, have been studied for the VCR magnetic head application. With the increase of the Fe2O3 concentration, the Fe2+ concentration increased, the specific resistivity decreased, the secondary maximum permeability shifted to the lower temperature, and the initial permeability decreased. It was concluded that the small variation of $\pm$0.5mol% Fe2O3 concentration greatly affected the electro-magnetic properties of Mn-Zn ferrite single crystals. At the composition of 53mol% Fe2O3, the initial permeability was comparatively high (650 at 5MHz) and its temperature dependence was small.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.7
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• pp.756-761
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• 2003

The microwave absorption properties of silicone, chloride polyethylene(CPE), and natural lacquer which is newly suggested in this study as a binder for composite microwave absorber were investigated to develop a superior microwave absorber. MnZn ferrite composite microwave absorbers mixed with them were prepared and their absorption property was investigated. A MnZn ferrite microwave absorber mixed with natural lacquer showed an excellent microwave absorption property in expanded frequency band.

• Electrical & Electronic Materials
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• v.10 no.7
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• pp.668-673
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• 1997

A Single-crystalline Mn-Zn Ferrite (110 orientation) was masklessly etched by focused Ar laser irradiation in an H$_3$PO$_4$ solution. The depth of the etched grooves increases with increasing a laser power, decreasing a scan speed, and increasing the H$_3$PO$_4$concentration. The width of the etched grooves increases with a increasing laser power, but was relatively insensitive to the scan speed and H$_3$PO$_4$concentration. High etching rate of up to 714 ${\mu}{\textrm}{m}$/s and an aspect ratio of 6 for vertical slab structure have been obtained by the light-guiding effect of the laser bean in the H$_3$PO$_4$ solution.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.2
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• pp.61-66
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• 2003

The electromagnetic properties and thermal behavior of Mn-Zn ferrite cores used for the blocking filter in he Power Line Communication(PLC) application were investigated as the function of additives. The highest density and permeability of 4.98 g/㎤) and 8,221 respectively were obtained to the specimen with composition of MnO 24 mol%, ZnO 25 mol% and Fe$_2$O$_3$ 51 mol% added MnO$_3$ 400 ppm, SiO$_2$ 100 ppm and CaO 200 ppm since the uniform grains were organized and the microstructures were compacted through reduction of pores. The permeability was increased up to 13,904 as temperature of specimen increased to 11$0^{\circ}C$, however, it was decreased precipitously under 100 over 11$0^{\circ}C$. The exothermic behavior was observed in the frequency range from 1 kHz to 1 MHz that the maximum temperature of specimens became 102$^{\circ}C$ at 1 MHz. In the consequence, the Mn-Zn ferrite core developed by this research will maintain the stable electromagnetic properties since the temperature of ferrite core rose to 93$^{\circ}C$ in the range of 10 kHz to 450 kHz bandwidth qualified for PLC.

• Resources Recycling
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• v.7 no.4
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• pp.50-54
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• 1998

In order to obtain desired electromagnetic propertieι high initial permeability and good frequency dependance of initial p permeability, the adding effects of sevral seeds were experimented in Mn-Zn ferrite system. As adding seed grams, calcined at sintering temperature, abnormal grains were disappeared clearly but the density and the initial permcability of sintered Mn-Zn ferrite body were decreased. On the contrary, in case of adding seed rains which were calcined below the calcination temperatnre of matrix particle, abnormal grains remained but the initial permeability was increas$\xi$d with proper s$\xi$ed content. W With proper seed content, the initial permeability was increased by 10-20% but tbe $\alpha$ltoff frequency was not changed.

• Journal of Magnetics
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• v.5 no.4
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• pp.111-115
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• 2000

Ultrafine $Co_{0.9}Mn_{0.1}Fe_2O_4$ powders have been fabricated by a sol-gel method. Structural and magnetic properties of the powders were investigated by x-ray diffractometry, transmission electron microscopy (TEM), Mossbauer spectroscopy, and vibrating sample magnetometry (VSM). Co-Mn ferrite powders that were fired at and above 773 K contained only a single spinel phase and behaved ferrimagnetically. Powders fired at 673 and 723 K had a spinel structure and were mixed paramagnetic and ferrimagnetic in nature. The magnetic behavior of Co-Mn ferrite powders fired at and above 873 K showed that an increase of the firing temperature yielded a decrease in the coercivity and an increase in the saturation magnetization. The maximum saturation magnetization and coercivity of Co-Mn ferrite powders were 66.7 emu/g and 1523 Oe, respectively, Mossbauer spectra of the powder fired at 923 K were taken at various temperatures ranging from 13 to 850 K. The iron ions.at both A (tetrahedral) and B (octahedral) sites were found to be in ferric high-spin states. The Nel temperature $T_N$ was found to be 850 $\pm$ 2 K. Debye temperatures far A and B sites were found to be $\Theta_A = 757 \pm$5K and $Theta_B = 282 \pm$5 K, respectively.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.539-543
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• 1992

The continuous growth method was developed for Mn-Zn Ferrite single crystals. It is a new process that the polycrystalline MnχZn1-χFe2O4 raw materials are supplied continuously from the powder feeding system to the crucible heated by R.F. induction and melted in the crucible, and after the single crystals seed is attached to crucible's hole, the crystals are pulled downward with rotation. Growing the crystals by using the growth method different from the conventional Bridgman or Floating Zone method, we defined the factors having effect on the crystal growing through the pre-experiments. They are temperature distribution in the crucible, melt velocity according to its height, wettability between the crucible's bottom and melt. Therefore, Mn-Zn Ferrite single crystals were to be grown by attaining the appropriate melt height in the crucible, powder feeding rate, temperature gradient between the crucible and interface, crystal growing speed, and this method was confirmed to have possibility for single crystal growing.

• Journal of the Korean Ceramic Society
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• v.16 no.2
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• pp.69-76
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• 1979

This study attempted to characterize the powder and sintered specimen of Mn-Zn ferrite that was prepared by Hot Petroleum Drying Method. The results of the experiment were as follows: 1. The mixed sulfate powder prepared by Hot Petroleum Drying Method was homogeneous and very reactive. The ferrite formation of this powder occurred at lower temperature than the one prepared by Sulfate Dry Mixing Method. 2. The calcined oxide powder prepared by Hot Petroleum Drying Method was found to be agglomerated, and therefore it was very difficult to compact this powder. 3. The sintered density was 4.95g/㎤, 97% of the theoretical density, when the specimen was prepared by Hot Petroleum Drying method, calcined at 90$0^{\circ}C$ in air for 3h, sintered at 1,30$0^{\circ}C$ in air for 3h, and then cooled in nitrogen. 4. The discontinuous grain growth occurred at lower temperature in the specimen prepared by Hot Petroleum Dyring Method than in the one prepared by Sulfate Dry Mixing Method. The discontinuous grain growth was considered to be due to the presence of liquid formed by addition of CaO and $SiO_2$.

• Journal of the Korean Ceramic Society
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• v.27 no.5
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• pp.652-660
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• 1990

Oxidation of Mn-Zn ferrite was made in air at various temperatures ranging from 400$^{\circ}C$ to 1150$^{\circ}C$. Subsequent reduction fo these oxidized samples was also made in air at 1300-1350$^{\circ}C$ where the spinel phase of Mn-Zn ferrite is stable. Morphological observation revealed that the shape of precipitated hematite was plate or lath type on the close-packed habit plane of {111} ferrite which has a definite orientation relationship. The growth of precipitates showed the behavior fo parabolic dependence of the oxidating time. An apparent activation energy for the growth was found to be 125${\pm}$3Kcal/mol. The fact that pores are observed along the precipitates illustrates the oxidation to occur dominantly by the counterdiffusion of cations and ction vacancies. For the reductio reaction pores are found to form at the site once occupied by the precipitates and at the surface. This observation illustrates that the oxygen volitalization from interior region to the surface is the dominant process for the reduction reaction.

• Korean Journal of Materials Research
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• v.6 no.12
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• pp.1221-1232
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• 1996

용접부 인성을 향상시키기 위해 Ti 산화물을 첨가한 Ti 산화물강에 대하여 용접시 최고가 열온도와 냉각속도의 변화가 용접열영향부의 미세조직에 미치는 영향을 조사하였다. 용접열영향부의 인성향상에 기여하는 acicular ferrite는 140$0^{\circ}C$ 이상의 최고가열온도와 $\Delta$t800-500가 40초보다 빠른 냉각속도에서 활발해 생성되었다. 오스테나이트 결정립내에서 개재물로부터 핵생성된 일차 acicular ferite의 생성량은 전체 aicular ferrite의 약 20% 정도로 적었으며 대부분의 acicular ferrite는 일차 acicular ferrite로부터 생성된 이차 acicular ferrite인 것으로 나타났다. 이차 acicular ferrite는 plate사이에 Fe3C층이 존재하는 것으로 보아 확산기구에 의해 생성되는 것으로 생각된다. 개재물은 TiO, TiO2, TiN, MnS, AI2O3 MnO(galaxite)등으로 구성된 복합상이었으며 개재물이 일차 acicular ferrite의 핵생성 site로 작용하기 위해서는 약 1$\mu\textrm{m}$이상의 크기가 효과적인 것으로 나타났다. Ti 산화물과 TiN는 직접적인 acicular ferrite의 핵생성 site로 작용하기보다는 MnS, galaxite 등의 석출 site로 작용하여 개재물의 크기를 증가시킴으로써 acicular ferrite의 생성을 촉진시키는 것으로 생각된다.