• Journal of Magnetics
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• 제3권1호
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• pp.4-8
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• 1998

Two different compositions of melt spun magnetic alloys, $ Nd_4Fe_{80}B_{16} and Nd_4Fe_{76}Co}\_3Hf_{0.5}Ga_{0.5}B_{16},$ were characterized in terms of magnetic properties and thermal behaviors. It was found that the addition of Hf and Ga effectively slow down the crystallization rate of the nanocomposite $ Nd_2Fe_{14}B/Fe_3B$ magnet. Coercivity(iHc) changes only slightly with varying the post annealing conditions confirming that iHc is not a sensitive magnetic quantity as a function of grain size and exchange coupled interaction. The experimentally observed behaviors of Mr and Hc do not vary monotonously with in-creasing grain size which is not in agreement with the numerically calculated result near the critical grain size (dc). The plot of the grain size dependence for the remanence and coercivity in isotrop!c nanocomposite magnets has been revised in this study. The maxium energy product, $(B, H)_{max}$ =15.34 MGOe, and a reduced remanence, Mr/Ms=0.84 were obtained, respectively.

• 한국자기학회지
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• 제2권2호
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• pp.145-149
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• 1992

영구자석의 착자상태는 영구자석이 사용된 기기의 특성에 큰 영향을 미친다. 따라서 영구 자석기기에서 원하는 특성을 얻기 위해서는 영구자석의 착자상태를 정밀하게 해석할 필요가 있다. 본 논문에서는 비선형과 이방성 특성이 고려된 유한요소법으로 착자기를 해석하였다. 착자전류가 변함에 따른 자화량의 분포와 그 자화량에 의하여 공극에 발생되는 저장의 값을 각도가 서로 다른 2가지 착 자요크에 대하여 구한 결과, 착자요크의 형상에 따라 과도한 착자전류는 자화량의 분포를 왜곡시키고, 이에따라 발생되는 공극에서의 자장의 값은 오히려 줄어듦을 알 수 있었다. 따라서 영구자석을 자화 시키기 위한 착자기를 설계할때 원하는 착자분포를 얻기위해서는, 착자요크의 각도에 따라 적절한 착 자전류의 값이 있음을 알 수 있다.

• 한국표면공학회지
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• 제50권2호
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• pp.119-124
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• 2017

Due to the high saturation magnetization (~2.4 T), $Fe_{16}N_2$ is interesting for the thin film application such as an actuator, data record storage and sensor etc. In this study, Fe-N thin films were deposited on Si(001) substrate with various power and deposition time by DC magnetron sputtering, in order to get high portion of $Fe_{16}N_2$ phase. Surface morphology, phase formation and magnetic properties were measured. As a result, Saturation magnetization and Remanence magnetization reach to ~2.45 T and 1.41T. But, Coercivity was not enough in this experiments. Its value lower than 100 Oe. Which is very close to theoretical value.

• 한국자기학회지
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• 제13권4호
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• pp.182-186
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• 2003

펄스자장종축성형법(pulse die press, PDP)을 이용하여 32 wt%RE-67 wt%TM-1 wt%B(RE: 희토류원소, TM: 30천이금속)조성을 갖는 소결자석을 제조함에 있어서 자장성형시 분말의 탭밀도, 성형밀도, 인가자장세기 및 인가방법의 변화에 따라 얻어지는 자석의 배향율과 감자곡선상의 각형성 변화를 조사하였다. 출발합금 제조방법으로서 strip casting process에 의하여 $\alpha$-Fe 편석없이 미세하고 균일한 조직을 갖는 합금 flake가 얻어졌고, 합금 flake를 수소처리한 후 고압가스를 이용한 건식분쇄방법(jet mill)에 의하여 평균입도, 표준편차가 각각 3.65 $\mu\textrm{m}$, 1.39인 미세하고 균일한 입도의 분말로 제조하였다. 제조된 분말은 30-50 kOe치 고펄스자장에 의하여 분말을 배향시키고 동일한 펄스자장을 인가하면서 종축성형을 실시함으로써 배향율을 향상시킬 수 있었다. 결과적으로 32 wt%RE조성의 분말을 이용하여 종전의 자장성형방법인 TDP(transverse die press)와 본 연구에서 제안된 PDP에 의하여 제조된 자석의 최대자기에너지적은 각각 42.0 MGOe 및 44.8 MGOe가 얻어져, PDP가 분말의 배향율과 감자곡선상의 각 형성을 향상시키는데 효과적인 자장성형방법임을 알 수 있었다.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 somma/kms meeting
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• pp.97-97
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• 2003

• 한국정밀공학회지
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• 제6권4호
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• pp.103-107
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• 1989

The effects of annealing temperature on the magnetic properties (maximum permeability, coercive force and remanence) and mechanical properties (hardness, tensile strength and elongation at rupture) were analyzed using the nondestructive impulsive magnetic analyzer in a medium carbon cold rolled steel sheet. This nondestructive method was very useful for the analysis of magnetic and mechanical properties of materials. As it was known in the literature, the three distinct processes that indicate the recovery, recrystallization, and grain growth of a metal were measured with the non-destructive analyzer.

• 한국재료학회지
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• 제11권12호
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• pp.1042-1046
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• 2001

Co-22%Cr alloy films are promising for high-density perpendicular magnetic recording media with their perpendicular anisotropy and large coercivity of 3000 Oe. We observed that a self organized nano structure(SONS) of fine ferromagnetic Co-enriched phase and paramagnetic Cr-enriched phase appears inside the grain of Co-Cr magnetic alloy thin films at the elevated substrate temperature after do-sputtering. We prepared 1000 $\AA$-thick Co-22%Cr films on 2000 $\AA$- SiO$_2$/Si(100) substrates at the deposition rate of 100 $\AA$/min with substrate temperatures of 3$0^{\circ}C$, 10$0^{\circ}C$, 15$0^{\circ}C$, 20$0^{\circ}C$, 30$0^{\circ}C$, and 40$0^{\circ}C$, respectively. We employed a vibrating sample magnetometer(VSM) to measure the B-H loops showing the saturation magnetifation, coercivity, remanence in in- plane and out- of- plane modes. In- plane coercivity, perpendicular coercivity, and perpendicular remanence increased as substrate temperature increased, how-ever they decreased after 30$0^{\circ}C$ slowly. Transmission electron microscope (TEM) characterization revealed that the self organized nano structure (SONS) appears at the elevated substrate temperature, which forms fine Co-enriched phases inside a grain, then it eventually affect the perpendicular magnetic property. Our results imply that we may tune the perpendicular magnetic properties with SONS obtained at appropriate substrate temperature.

• 한국자기학회지
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• 제11권6호
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• pp.262-266
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• 2001

본 연구에서는 dc 마그네트론 스터링법으로 CoSm 박막을 제작하여 자기적 성질의 자성층 두께 의존성을 조사하였다. 고밀도 자기기록 매체의 여러 가지 성질 중 자기역전부피는 자기기록 매체에 저장된 정보의 열적 안정성, 자화반전기구 및 잡음을 이해하는 데 매우 중요한 자료가 된다. 따라서 자기화 감쇄의 시간 의존성과 직류 demagnetization remanence 곡선 측정결과로부터 각각 점성계수와 비가역 자화율을 구한 다음 최대 점성계수 및 비가역 자화율을 이용하여 최대 자기역전부피의 두께 의존성을 조사하였다. 자기역전부피와 보자력은 CoSm의 두께가 48 nm와 24 nm에서 각각 최대를 보이다가 오히려 감소하였으나 자기이방성은 계속 증가하는 경향을 보였다. 이와 같은 현상은 자성층의 두께가 증가함에 따라 결정립 또는 nanocrystallites 사이의 자기적 교환 상호작용이 증가하기 때문인 것으로 해석된다.

• 한국분말재료학회지
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• 제18권1호
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• pp.29-34
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• 2011

In order to increase the coercivity of (Nd, Dy)-Fe-B sintered magnets without much reduction of remanence, small amount of Dy compounds such as $Dy_2O_3$ and $DyF_3$ was mixed with (Nd, Dy)-Fe-B powder. After mixing, the coercivity of (Nd, Dy)-Fe-B sintered magnets apparently increased with the increase of Dy compound in the mixture. Addition of $DyF_3$ was more effective than $Dy_2O_3$ for the improvement of coercivity. Reduction of the remanence by the addition of Dy compound, however, was larger than expected mostly due to unresolved coarse Dy compound in the magnet. EPMA analysis revealed that Dy was diffused throughout the grains in the magnet mixed with $DyF_3$ whereas Dy was rather concentrated around grain boundaries in the magnet mixed with $Dy_2O_3$.

• 한국분말재료학회지
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• 제9권6호
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• pp.381-393
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• 2002

Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun $Sm(Co_{0.74}Fe_{0.1}Cu_{0.12}Zr_{0.04})_{7.5}$ ribbons were prepared, which showed coercivities of up to 0.53 T at 50$0^{\circ}C$. Partially amorphous $Nd_{60}Fe_xCo_{30-x}Al_{10}(0{\leq}x{\leq}30)$ alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The $Nd_{60}Co_{30}Al_{10}$ alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.