• 한국분말재료학회지
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• 제23권6호
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• pp.447-452
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• 2016

Neodymium-iron-boron (Nd-Fe-B) sintered magnets have excellent magnetic properties such as the remanence, coercive force, and the maximum energy product compared to other hard magnetic materials. The coercive force of Nd-Fe-B sintered magnets is improved by the addition of heavy rare earth elements such as dysprosium and terbium instead of neodymium. Then, the magnetocrystalline anisotropy of Nd-Fe-B sintered magnets increases. However, additional elements have increased the production cost of Nd-Fe-B sintered magnets. Hence, a study on the control of the microstructure of Nd-Fe-B magnets is being conducted. As the coercive force of magnets improves, the grain size of the $Nd_2Fe_{14}B$ grain is close to 300 nm because they are nucleation-type magnets. In this study, fine particles of Nd-Fe-B are prepared with various grinding energies in the pulverization process used for preparing sintered magnets, and the microstructure and magnetic properties of the magnets are investigated.

• 전력전자학회논문지
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• 제3권1호
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• pp.53-60
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• 1998

본 논문은 비디오 카메라 및 프로젝션 TV 등 영상 기기의 요소 부품인 캠코더용 Iris Assembly에 있어서 동작원리, 구성부품의 특성, 동작특성 해석과 각 요소부품의 개발시 중요 Know-how 등을 언급한다. 저전력용으로 소형이지만 간단한 구조로 만들기 위한 자계회로를 실현하였다. 특히 잔류 자계의 영향과 동작 시간의 관계를 실험적으로 규명한다. 소형 정밀부품의 국산화 개발에 있어서 필요한, 간편한 구동 시스템 원리와 그로 인해 발생하는 비선형성 토오크의 문제점 및 개발 공정 등을 설명하고, 각 부품의 Burr 최소화를 위한 점검 요소, 소형 요소 부품의 공정 등을 다룬다.

• 한국전기전자재료학회논문지
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• 제16권8호
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• pp.744-751
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• 2003

Co-Pd alloy thin films prepared by a DC-sputter that have self-organized nano structure(SONS), are promising for high-density information storage media in information era. We prepared the samples by varying Pd contents of 0~8.1 wt% at the substrate temperatures of room temperature (RT) and 200 $^{\circ}C$, respectively Microstructure and Pd contents of the Co$_{1-x}$ Pd$_{x}$ films are probed by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and an energy dispersive spectrometer (EDS). We also investigated the saturation magnetization (Ms), remanence and coercivity of the Co$_{1-x}$ Pd$_{x}$ films. Surface roughness are measured by an atomic force microscope (AFM). We revealed that self-organized nano size Co-enriched phase and Pd-enriched phase existed with Pd contents at the substrate temperatures of RT and 20$0^{\circ}C$ through microstructure characterization. SONS helped to keep the saturation magnetization and enhance the perpendicular anisotropy with Pd contents. Out result implies that we may tune the perpendicular magnetic properties with keeping the saturation magnetization by varying substrate temperatures and Pd contents for high density magnetic recording.rding.

• Journal of Magnetics
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• 제16권3호
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• pp.300-303
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• 2011

The effect of the hot-compaction temperature on the microstructure and magnetic properties of anisotropic nanocrystalline magnets was investigated. The hot-compaction temperature was found to impact both the magnetic properties and the microstructure of die-upset magnets. The remanence of the isotropic precursor increases slightly with the improved hot-compaction temperature, and the grains start to grow on the flake boundary at higher hot-compaction temperatures. After hot deformation, it was found that the change in the magnetic properties was the inverse of that observed with the hot-compaction temperature. Microstructural investigation showed that die-upset magnets inherit the microstructural characteristics of their precursor. For the die-upset magnets, hot pressed at low temperature, scarcely any abnormal grain growth on the flake boundary can be seen. For those hot pressed at higher temperatures, however, layers with large equiaxed grains could be observed, which accounted for the poor alignment during the hot deformation, and thus the poor magnetic properties.

• 한국분말재료학회지
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• 제8권1호
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• pp.55-60
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• 2001

Mechanical alloying technique was applied to prepare hard magnetic $Sm_2Fe_{17}N_x$ compound powders. Staring from pure Fe and Sm powders, the formation process of hard magnetic $Sm_2Fe_{17}N_x$ phase by mechanical alloying and subsequent solid state reaction was studied. As milled powders were found to consist of Sm-Fe amorphous and $\alpha$-Fe phases in all compositions of $Sm_xFe_{100-x}$(x = 11, 13, 15, 17). The effects of starting composition on the formation of $Sm_2Fe_{17}$ intermetallic compound was investigated by heat treatment of mechanically-alloyed powders. When Sm content was 15 at.％, heat-treated powders consisted of nearly $Sm_2Fe_{17}$ single phase. For preparation of hard magnetic $Sm_2Fe_{17}N_x$ powders, additional nitriding treatment was performed under $N_2$ gas flow at 45$0^{\circ}C$. The increase in the coercivity and remanence was proportional to the nitrogen content which increased drastically at first and then increased gradually as the nitriding time was extended to 3 hours.

• 열처리공학회지
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• 제4권2호
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• pp.9-18
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• 1991

Among the many maunfactured processes of producing multi filamentary composites, in situ process is widely used owing tv its simplicity and easyness of mass production. In this study, the mechanical and electromagnetic properties of Cu-Fe composite materials was investigated. The tensile strength of the Cu-Fe wires increased as the Fe content and reduction ratio were increased. The Cu-30 wt%Fe composites had the best properties in terms of figure merits compared to the other Cu-Fe composites made in this study or the commercially manufactured 6/1 ACSR cables of Cu cable. The coercivity was decreased by increasing Fe content, but the squareness was increased greatly. As increasing reduction ratio, the coercivity and squareness increased up to the maximum points, and then decreased. For example, the maximum values were obtained at $0.09mm{\phi}$ for Cu-30 wt%Fe composites and at $0.066mm{\phi}$ for Cu-45 wt%Fe composites. The magnetic property of Cu-Fe wires produced by precipitation treatment was higher than that of Cu-Fe wires produced by thermomechanical treatment. By annealing Cu-Fe wires after drawing process, the coercivity, remanence and squareness were improved.

• Advances in nano research
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• 제5권2호
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• pp.171-178
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• 2017

Superparamagnetic Zinc ferrite submicropheres are firstly synthesized via a one-pot solvothermal approach at $200-215^{\circ}C$ for 4-8 hours. $ZnCl_2$, $FeCl_3$ and NaAc are used as precursors with ethylene glycol solvent. The X-ray diffraction (XRD) data indicate that $ZnFe_2O_4$ nanoparticles with the grain size around $15{\pm}3nm$ can be successfully synthesized via the one-pot method. The scanning/transmission electronic microscope (SEM/TEM) images further show the samples are submicrospheres self-assembled by nanoparticles with size about 375-500 nm changed with reaction conditions. Room-temperature vibration magnetic strength measurements (VMS) demonstrates the as-obtained $ZnFe_2O_4$ submicrospheres show prefect superparamagnetism, whose coercivity force and remanence are practically nil. The reaction temperature and time influence on the crystallinity, diameter, saturated magnetic intensity and morphology of the particles.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2010년도 학술대회 초록집
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• pp.43-45
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• 2010

열잔류자화획득은 통계학적 현상으로 해당 개별 광물의 열역학적 반응시간에 좌우되는데, 냉각이 짧은 시간에 완료되는 경우 반응시간이 상대적으로 줄어들게 된다. 따라서 긴 시간에 걸쳐 냉각이 발생하는 경우에 비해 상대적으로 약한 자화를 획득하게 된다는 이론이 제시되었다. 금번 연구에서는 자철석이나 티탄철석을 함유하는 해양지각 암석의 경우, 냉각률이 커지며 자화가 감소하는 경향을 보여준다. 실제 자연산의 해양지각 암석을 사용한 경우, 입자가 미세한 특수한 경우 자화 강도의 10% 정도가 냉각률에 좌우되는 것으로 판단된다. 그러나 평균적인 입도에서는 냉각률이 자화에 미치는 영향이 3%이내이다. 일부 입자 크기가 미세한 해양지각 시료의 경우 냉각률의 자화 기여도가 10%에 이르므로 자화 해석에 주의를 요한다.

• Journal of Magnetics
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• 제7권4호
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• pp.138-142
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• 2002

Magnetic properties, microstructure and texture of NdFeB magnets fabricated by a modified hot working process from commercial melt-spun powders (Magnequench; MQPA, MQPB and MQPB＋) have been investigated. The hot-pressed isotropic magnet made from MQPA powder, which contains higher Nd content than that of MQPB or MQPB＋, shows higher coercivity. The magnet also shows homogenous and fine grains with higher coercivity for higher consolidation pressure. The hot-deformed MQPA magnet shows a strong anisotropy along the press direction with homogeneous platelet Nd$_2$Fe$_{14}$B grains of 50∼100nm in thickness and 200∼500nm in length. The hot-deformed MQPB＋ magnet, however, shows low remanence and low coercivity. The microstructure of the magnet consists of two areas; undeformed Nd$_2$Fe$_{14}$B grains and well-aligned but large grains with 3∼4 $\mu$m in length. Low Nd content attributes to the formation of the two different area.

• Journal of Magnetics
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• 제6권2호
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• pp.57-60
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• 2001

Mechanically alloyed $TbCu_7 -type \;Sm_{12.5}Fe_{87.5-x}Ti_x$(x=0, 2.5, 5, 7.5),and their nitrides have been studied systematically by X-ray diffraction, A.C. initial susceptibility, and pulsed magnetization measurement. In this series, the volume expansion by nitriding is 5.6%~7.3%, and the increment of the Curie temperature is in the range of 21$0^{\circ}C$~35$0^{\circ}C$. With increasing Ti content, the remanence decreases linearly due to the substitution of non-magnetic Ti, and the coercivity decreases rapidly from 34.6 kA/cm (43.5 kOe) for $\chi$=0 to 14.3 kA/cm (18 kOe) for $\chi$=7.5. In the $Sm_{12.5}Fe_{87.5-x}Ti_xN_y$ series, the best magnetic properties were obtained from .7Ti7Ny series, the best magnetic properties were obtained from $Sm_{12.5}Fe_{87.5}N_y$($\chi$=0) with $_iH_c$=34.6 kA/cm (43.5 kOe), $B_r=0.75 \;T, \;and (BH)_{max}=113.8 kJ/m^3$(10.9 MGOe).