• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2009년도 학술대회 초록집
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• pp.107-109
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• 2009

미세자기학은 분자구조 단위에서 (Micromagnetic modeling) 자성 광물의자화 획득 및 자화 소멸을 연구하는 학문으로 행성지질학적으로 흥미있는 자성 광물의 자화 상태를 수치해석으로 풀어내는 학문이다. 자기이력곡선 분석은 시료를 파괴하거나 가열하지 않고 빠르고 정확하게 자성 광물의 종류 및 크기를 식별할수 있다. 정6면체 형태의 합성자철석이 아닌 자연산에 존재하는 8면체 형태의 모델을 택해야 기존의 실험 결과를 더 잘 설명함을 알아내었다. 특히 8면체의 경우 120 nm 이상의 크기에서 magnetic coercivity와 magnetic remanence가 더욱 안정적이고 커짐을 알아냈다.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2008년도 Asian Magnetics Conference
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• pp.137.2-137.2
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• 2008

• 한국자기학회지
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• 제5권5호
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• pp.366-371
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• 1995

High performance magnetic materials are characterized by the combination of outstanding magnetic properties and optimized microstructures, e.g., nanocrystalline composites of multilayers and small particle systems. The characteristic parameters of the hysteresis loops of these materials vary over more than a factor of $10^{6}$ with optimum values for the coercive field of several Tesla and permeabilities of $10^{6}$. Within the framework of the computational micromagnetism (nanomagnetism) using the finite element method the upper and lower bounds of the coercive field of different types of grain ensembles and multilayers have been determined. For the case of nanocrystalline composites the role of grain size, exchange and dipolar coupling between grains and the degree of grain alignment will be discusses in detail. It is shown that the largest coercivities are obtained for exchange decoupled grains, whereas remanence enhancing requires exchange coupled grains below 20 nm. For composite permanent magnets based on $Nd_{2}Fe_{14}B$ with an amount of ~ 50% soft $\alpha$-Fe-phase coercivities of ${\mu}_{0}H_{c}=0.75\;T$, a remanence of 1.5 T and an energy product of $400\;kJ/m^{3}$ is expected. In nanocrystalline systems the temperature dependence of the coercivity is well described by the relation ${\mu}_{0}H_{c}=(2\;K_{1}/M_{s}){\alpha}-N_{eff}{\mu}_{0}M_{s}$, where the microstructural parameters $\alpha$ and $N_{eff}$ take care of the short-range perturbations of the anisotropy and $N_{eff}$ is related to the long-range dipolar interactions. $N_{eff}$ is found to follow a logarithmic grain size size dependence ${\mu}_{0}H_{c}=(2\;K_{1}/M_{s}){\alpha}-N_{eff}(\beta1nD){\mu}_{0}M_{s}$. Several trends how to achieve the ideal situation $\alpha$->1 and $N_{eff}$->1->0 will be discussed.

• Journal of Magnetics
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• 제1권2호
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• pp.69-74
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• 1996

Justeresos loops of melt-spun Nd13Fe77B10 cooled down at remanent state were measured at 4.2 K and 250 K. The hysteresis loops were analysed on the basis of the Stoner-Wohlfarth (S-W) model, the inter-grain exchange coupled single domain (SD) model and micromagnetism. The coercivity higher than that predicted from the S-W model and the striking shift of the thin minor loop along the H-axix observed at the fields of Hmax=4MA/m at 4.2 K indicated new evidences for the inter-grain exchange interaction . The S-W model failed in explaining the high iHc and the shift of the thin minor loop. The exchange coupled SD model was found to explain the experimental results qualitatively without difficulties associated with the S-W model. The micromagnetic calculations using a finite element technique simulated the experimental results fairly well quntitatively.