• 한국세라믹학회지
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• 제38권12호
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• pp.1155-1161
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• 2001

YIG 페라이트는 마이크로파 RF 대역 통신 시스템, 이동통신, 위성방송 등의 정보산업과 각종 계측기기 등에 없어서는 안될 중요한 전자부품인 서큘레이터/아이솔레이터의 핵심소자로서 널리 사용되고 있다. 본 연구에서는 소결온도와 치환원소에 따른 서큘레이터/아이솔레이터용 YIG 페라이트의 미세구조와 전자기적 특성을 고찰하고자 하였다. Ca, V, In을 치환시킨 YIG 페라이트를 분무건조기를 사용하여 준구형 과립상태로 만들고, 일반적인 세라믹 제조 공정에 따라 125$0^{\circ}C$, 1275$^{\circ}C$, 130$0^{\circ}C$, 13$25^{\circ}C$에서 각각 소결하였다. 소결체는 XRD를 이용하여 상분석을 실시하였고, SEM을 이용하여 미세구조를 관찰하였으며, 전자기적 특성을 측정하기 위하여 VSM을 이용한 포화자화값 (4$\pi$ $M_{s}$) 측정과 FMR(Ferromagnetic Resonance)실험을 통한 자기공명반치폭($\Delta$H) 측정을 실시하였다. $Y_{1.6}$C $a_{1.4}$F $e_4$ $V_{0.7}$I $n_{0.3}$ $O_{12}$ 조성의 YIG 페라이트에 대한 전자기적 특성 측정 결과 130$0^{\circ}C$에서 소결한 YIG 페라이트가 높은 포화자화(4$\pi$ $M_{s}$) 값과 낮은 자기공명반치폭($\Delta$H)을 지닌 우수한 전자기적 특성을 나타내었다.다.을 나타내었다.다.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.395-399
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• 1999

MgO/metal nanocomposite powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with magnesia powder. After calcined in air, these powders were reduced by hydrogen. Densified nanocomposites were successively obtained by Pulse Electric Current Sintering (PECS) process. The dispersed metal partical size depended on temperature and time in calcination and reduction processes. The phase analyses in the synthesized powders as a functioni of temperature were tracked using a dynamic high temperature X-ray diffractioni (HTXRD) system. Phase and crystallite size analyses were done using X-ray diffractioni and TEM. The MgO/metal nanocomposites were successfully fabricated, and ferromagnetic responses with enhanced coercive force were also investigated for these composites.

• 대한기계학회논문집A
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• 제28권8호
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• pp.1166-1173
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• 2004

In this paper, in order to apply magnetic fluid with superparamagnetic property as the substitute of ferromagnetic materials, physical properties of magnetic fluid are investigated. A targeted drug delivery system using a capsule filled magnetic fluid is proposed where a magnetic fluid capsule and cylinders are considered as a drug and vital organs, respectively. The dynamic governing equation of this system first is derived. Fluid viscosity, clearance between a cylinder and a magnetic fluid capsule, and levitation height with respect to different cylinder height are considered as major parameters to evaluate dynamic characteristics of the system. The experiments and simulations for the position control of the magnetic fluid capsule in various cylinders are conducted using PID controller. The results show that magnetic fluid with the superparamagnetic property can be applied to a targeted drug delivery system.

• 한국정밀공학회지
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• 제28권4호
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• pp.398-403
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• 2011

Terfenol-D is one of several magnetostrictive materials with property of converting energy into mechanical motion, and vice versa. Magnetostriction is the property that causes certain ferromagnetic materials to change shape in a magnetic field. Terfenol-D is said to produce giant magnetostriction, strain greater than any other commercially available smart material. In this paper, fundamental characteristics analysis of giant magnetostrictive materials(Terfenol-D) has been investigated. The magnetic field analysis is carried out by using finite element method simulation ANSYS. The results show 223N in force and 9.5T in maximum magnetic flux density and 7.56 $10^6A/m$ in maximum magnetic field intensity 1A current. Through the analysis, basic data of Terfenol-D for the application of mechanical system are obtained.

• Bulletin of the Korean Chemical Society
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• 제18권1호
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• pp.91-97
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• 1997

In the course of magnetic study on several perovskite-type oxides, A2Fe(Ⅲ)BO6 (A = Ca, Sr, Ba and B = Sb, Bi), we have observed a strong irreversibility in their dc-magnetizations. When the structural data and the Mossbauer spectra are considered, such an irreversibility is to be associated with some competitions between the nearest-neighbors (nn) and the next-nearest-neighbors (nnn) in their magnetic sublattices. Particularly, the Mossbauer spectra indicate that Sr2FeBiO6 of cubic perovskite-structure is apparently well ordered crystalline compound. Nontheless this antiferromagnet shows a magnetic property which resembles that of a spin-glass. The strong history dependence is observed below 91 K and the irreversible magnetic behavior is also observed from the measurement of hysteresis loops at 10 K after zero-field-cooled (zfc) and field-cooled (fc) processes. Considering the nn and the nnn superexchanges of almost same order in ordered perovskite, it is proposed that there exists a competition and cancellation of antiferromagnetic and ferromagnetic superexchange between the nearest-neighbors and the next-nearest-neighbors, thus introducing a certain degree of frustration.

• 비파괴검사학회지
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• 제20권3호
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• pp.231-237
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• 2000

공업용 서멧 절삭공구는 다성분계 탄화물과 강자성체(ferromagnetic material)인 철족의 Co, Ni 결합상 금속으로 구성 되어 있다. 본 연구에서는 새로운 시도로서 금속 결합상 량과 소결조건에 따른 TiCN계 서멧의 자기적 특성의 측정에 의한 기계적 성질의 평가방법을 연구하였다. 실험에서는 결합상이 다른 상용 서멧조성의 합금을 분말 야금법에 의해 제조하였다. 소결된 서멧의 자기적 특성은 합금의 조직과 탄소량에 따라 크게 변화하였다. 포화자화(magnetic saturation, $4{\pi}\;{\sigma}$)와 항자력(coercive force, Hc)은 비례하였으며, 고탄소 소결합금에 있어서는 Co-Ni 결합상에서의 W, Mo, Ti등의 용매원자의 농도가 낮아짐에 따라 포화자화는 증가하였다 항자력이 높을수록 경도는 증가하였고, 서멧의 강도 및 인성은 포화자화가 증가할수록 우수하였다. 서멧공구에서 자기적 특성을 측정하여 기계적 성질을 비파괴적으로 평가할 수 있었다.

• 한국자기학회지
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• 제23권2호
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• pp.54-61
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• 2013

강자성체는 자구들의 상호작용으로 인해 잔류 자화가 남게 되는데, 전자전기 산업 및 국방 피탐지 분야에서는 이러한 잔류 자화량을 정밀하게 0으로 만드는 탈자기법이 요구된다. 하지만 현재 수행되는 탈자기법들은 경험과 실험에 의존한 방법들로, 새로운 재료의 개발에 따른 효율적인 탈자를 위해서는 강자성체의 히스테리시스 곡선을 반영한 탈자기법이 필요하다. 본 논문에서는 자성체의 물성적인 성질을 기반으로 정립된 Preisach 모델링 기법을 이용하여 Anhysteretic Deperm, Deperm-ME, Flash-Deperm에 따른 2차원 유한요소해석을 수행하였다. 탈자 전류에 의한 자기이력궤적의 분석을 통해 강자성체의 히스테리시스 곡선과 탈자 변수의 관계를 고찰하였으며, 이로써 탈자에 효율적인 전류 감소 형태를 제시하였다.

• 한국초전도ㆍ저온공학회논문지
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• 제22권2호
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• pp.21-25
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• 2020

We investigated the flux pinning property of GdBa₂Cu₃O_7-x (GdBCO) films on top of La_0.7Sr_0.3MnO₃ (LSMO) nanoparticles deposited by a surface decoration. Both GdBCO films and LSMO nano particles were deposited by pulsed laser deposition and the number of laser pulses were varied from 80 to 320 in order to control the density of the LSMO nanoparticles. The magnetization data at 77 K showed that the critical current density (J_c) was enhanced in all of the GdBCO films with LSMO nanoparticles and that the J_c enhancement was found to be inversely proportional to the LSMO nanoparticle density. Structural analyses revealed that LSMO nanoparticles induce a compressive strain in the GdBCO films resulting in a disordering in the CuO₂ plane. Therefore, the enhanced flux pinning property in the GdBCO with LSMO nanoparticles was attributed to the competing effect between the increase of pinning centers and the increase of compressive strain in the superconducting phase.

• 한국초전도ㆍ저온공학회논문지
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• 제18권2호
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• pp.14-17
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• 2016

Annealing as-grown electron-doped cuprates under a low oxygen-partial-pressure condition is a necessary step to achieve superconductivity. It has been recently found that the so-called protect annealing results in much better superconducting properties in terms of the superconducting transition temperature and volume fraction. In this article, we report on angle-resolved photoemission spectroscopy studies of a protect-annealed electron-doped cuprate $Pr_{0.9}La_{1.0}Ce_{0.1}CuO_4$ on annealing condition dependent superconducting and pseudo-gap properties. Remarkably, we found that the one showing a better superconducting property possesses almost no pseudo-gap while others have strong pseudo-gap feature due to an anti-ferromagnetic order.

• 한국재료학회지
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• 제29권8호
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• pp.477-482
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• 2019

The magnetic properties and electronic structures of the B20 crystal structure MnGe and MnSi were investigated using the density functional theory with local density approximation. The low symmetry of the B20 crystal structure plays a very important role to make electromagnetic characteristics of these materials. The important result of the calculations is that it can be observed the appearance of a pair of gaps in the density of states near the Fermi level in both compounds. These features are results from d-band splitting by the low symmetry of the crystal field from B20 crystal structure. It can be seen that there is half-metallic characteristics from the density of states in both compounds. The calculation shows that the value of magnetic moment of MnGe is 5 times bigger than that of MnSi even though they have same crystal structure. The electronic structures of paramagnetic case have a very narrow indirect gap just above the Fermi level in both compounds. These gaps acquire some significance in establishing the stability of the ferromagnetic states within the local density approximation. Calculation shows that the Mn 3d character dominates the density of states near the Fermi level in both materials.