Iron-based amorphous powder attracts increasing attention because of its excellent soft magnetic properties and low iron loss at high frequencies. The development of an insulating layer on the surface of the amorphous soft magnetic powder is important for minimizing the eddy current loss and enhancing the energy efficiency of highfrequency devices by further increasing the electrical resistivity of the cores. In this study, a hybrid insulating coating layer is investigated to compensate for the limitations of monolithic organic or inorganic coating layers. Fe2O3 nanoparticles are added to the flexible silicon-based epoxy layer to prevent magnetic dilution; in addition TiO2 nanoparticles are added to enhance the mechanical durability of the coating layer. In the hybrid coating layer with optimal composition, the decrease in magnetic permeability and saturation magnetization is suppressed.

We investigate the microstructural and magnetic property changes of DyH2, Cu + DyH2, and Al + DyH2 diffusion-treated NdFeB sintered magnets with the post annealing (PA) temperature. The coercivity of all the diffusiontreated magnets increases with increasing heat treatment temperature except at 910oC, where it decreases slightly. Moreover, at 880oC, the coercivity increases by 3.8 kOe in Cu and 4.7 kOe in Al-mixed DyH2-coated magnets, whereas this increase is relatively low (3.0 kOe) in the magnet coated with only DyH2. Both Cu and Al have an almost similar effect on the coercivity improvement, particularly over the heat treatment temperature range of 790-880oC. The diffusivity and diffusion depth of Dy increases in those magnets that are treated with Cu or Al-mixed DyH2, mainly because of the comparatively easy diffusion path provided by Cu and Al owing to their solubility in the Nd-rich grain boundary phase. The formation of a highly anisotropic (Nd, Dy)2Fe14B phase layer, which acts as the shell in the core-shell-type structure so as to prevent the reverse domain movement, is the cause of enhanced coercivity of diffusion-treated Nd-Fe-B magnets.

Effect of Cu and powder mixing with Cu-free (Nd, Dy)-Fe-B jet-milled powder on the magnetic properties of sintered magnets was investigated. The coercivity of a magnet prepared from the Cu-free (Nd, Dy)-Fe-B powder was about 10 kOe even though the alloy powder already contained some Dy (3.5 wt%). When small copper powder was blended, however, the coercivity of the magnet increased almost 100%, exhibiting about 20 kOe. On the contrary, the coercivity enhancement was moderate, about 4 kOe, when dysprosium content in the sintered magnet was simply increased to 4.9 wt% by the addition of small 3 powder.

In order to improve the remanence of (Nd, Dy)-Fe-B sintered magnets, we investigated the influence of compaction conditions such as packing density, applied field and green density on the magnetic properties. While the remanence decreased with increasing the packing density and green density, it increased with the increase of the applied field. In addition, XRD analysis revealed that the remanence was enhanced as the degree of powder alignment was improved. The green density was more influential on the remanence than the packing density and applied field.

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 and 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 was more effective than 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 whereas Dy was rather concentrated around grain boundaries in the magnet mixed with .

Effect of Cu content on microstructural and magnetic properties of a (wt.%), (x = 0.2, 0.3, 0.4, 0.5) strip-cast was studied. The average inter-lamellar spacing in the free surface and wheel side of the strip cast increased as the Cu content increases. The grain uniformity, the grain alignment, and (00L) texture of the strip cast increased with Cu contents up to 0.4 wt.%. These microstructural changes were attributed to the decrease of the effective cooling rate of the melted alloy caused by the decrease of the melting temperature of resulting from Cu addition. Coercivity and remanence were increased because of the grain alignment and (00L) texture improvement with Cu contents up to 0.4 wt.%.

In an attempt to optimize the magnetic properties of (Nd, Dy)-Fe-B sintered magnets, hydrogenation and post-sintering heat treatment processes were investigated at various hydrogenation temperatures and heat treatment temperatures. The coercivity of (Nd, Dy)-Fe-B sintered magnets hydrogenated at increased to about 1.2 kOe without any detrimental effect on the remanence. Moreover, the coercivity of the magnets was enhanced further by a consecutive and step heat treatment. These results eventually leaded to the reduction of the Dy content in a high coercive (> 30 kOe) (Nd, Dy)-Fe-B sintered magnets, as much as 10%.

Ordered to FePt nanoparticles are strong candidates for high density magnetic data storage media because the phase FePt has a very high magnetocrystalline anisotropy , high coercivity and chemical stability. In this study, the ordered FePt nanoparticles were successfully fabricated by chemical vapor condensation process without a post-annealing process which causes severe particle growth and agglomeration. The nanopowder was obtained when the mixing ratio of Fe(acac) and Pt(arac) was 2.5 : 1. And the synthesized FePt nanoparticles were very fine and spherical shape with a narrow size distribution. The average particle size of the powder tended to increase from 5 nm to 10 nm with increasing reaction temperature from to . Characterisitcs of FePt nanopowder were investigated in terms of process parameters and microstructures.

In order to prevent the oxide formation on the surface of nano-size iron particles and thereby to improve the oxidation resistance, iron nanoparticles synthesized by a chemical vapor condensation method were directly soaked in hexadecanethiol solution to coat them with a polymer layer. Oxygen content in the polymer-coated iron nanoparticles was significantly lower than that in air-passivated particles possessing iron-core/oxide-shell structure. Accordingly, oxidation resistance of the polymer-coated particles at an elevated temperature below in air was times higher than that of the air- passivated particles.

급속응고법으로 Fe-Nd-C 합금을 제조하여 합금의 조성 및 제조 조건의 변화에 따른 상변화와 자기특성의 변화를 조사하였다. 강자성 Fe14Nd2Cx가 초정으로 정출할 수 있는지를 알아보기 위하여 냉각속도의 변화에 따른 as-spun 합금에서의 상변화를 조사해 본 결과，10m/s로 제조한 Fe-Nd-C 리본합금은 α-Fe가 일차상, Fe17Nd2Cx가 이차상으로 존재하는 결정질이었으며. 20m/s에서는 α-Fe의 정출이 억제되거나 비정질화하여, Fe14Nd2Cx가 일차상, α-Fe가 이차상으로서 비정질상과 함께 존재하였다. 냉각속도의 증가에 따라 비정질화가 증가하여 30m/s에서는 대부분 비정질화되었으며，40m/s에서 비정질화가 완료되었다. 따라서 Fe14Nd2C는 as-spun 상태에서는 얻어지지 않고 주조합금의 경우와 마찬가지로 열처리를 통한 고상변태에 의해서만 얻을 수 있었다. Fe14Nd2C를 얻을 수 있는 유효온도구역은 주조합금의 경우보다 넓은 700~900˚C였고，비정질화가 완벽한 합금보다 다소 덜 완벽하거나 Fe17Nd2Cx와 비정질상이 혼합된 합금에서 열처리에 의한 보자력의 향상이 더욱 현저하였다. Fe를 다량 함유한 Fe-Nd-C 조성 중에서 높은 보자력이 기대되는 조성 범위는 극히 제한되어, 750~800˚C에서 몇 분간의 열처리로 10kOe 이상의 높은 보자력을 얻을 수 있는 조성은 77~78 Fe, 7~8 C (at.%) 정도였다.

목적: 본 연구는 안구운동 민감소실 재처리 기법(EMDR)이 운동선수의 경쟁상태불안에 미치는 영향을 알아보기 위해 fNIRS를 활용해 전전두엽 피질의 활성화 차이를 비교해 효과를 검증하는 것이다. 방법: 이 연구의 목적을 달성하기 위해 불안요소면담, 경쟁상태불안검사지(CSAI-2), 스포츠심상능력질문지(SIAQ)를 활용하여 대학부 운동 선수 9명을 선정하였으며, 실험을 위해 OBELAB fNIRS장비와 Matlab 소프트웨어를 사용하여 분석하였다. 연구는 시간 순서대로 전전두엽의 활성화를 측정하였으며, 기저선, 사전심상, 양측성안구운동프로그램, 사후심상 순으로 진행하였다. 결과: 첫째, 경쟁불안을 유발하기 위해 심상을 활용한 결과, 전반적인 전전두엽의 활성화가 낮아졌다. 둘째, 양측성 안구운동 프로그램 적용 결과, 사전심상과 사후심상에서 우측 전전두엽의 활성이 낮아졌다. 셋째, 양측성 안구운동 회기별 측정 결과, 양측성 안구운동 중 우측 전전두엽이 활성화되었다. 결론: EMDR이 운동선수의 경쟁불안과 관련된 기억으로 인한 부정적인 정서상태를 긍정적으로 빠르게 재처리 할 수 있다는 것을 보여준다. 본 연구는 스포츠라는 특수한 상황에서 발생하는 예기치 못한 경쟁불안을 빠르게 조절하는 데에 EMDR을 적용할 수 있는 가능성을 제시한다.

목적: 본 연구는 시-공간적인 작업기억 과제 수행 시 국가대표, 선수, 비선수의 행동학적 특성과 전전두엽의 뇌 연결성을 파악하여 우수한 경기력을 지닌 선수가 가지는 작업기억 능력의 차이를 규명하는 것이 목적이다. 방법: 이를 위하여 라켓종목 선수 국가대표 선수 12명, 선수 12명, 비선수 12명씩 총 36명이 연구에 참여하였다. 실험 과제는 시-공간적 N-back 과제를 난이도에 따라 1-back, 2-back으로 나눠서 60회씩 3회기 총 180회씩 총 360회를 수행하였고, 차이를 규명하기 위해 근적외선분광분석기(fNIRS)와 반응키를 활용하여 전전두엽의 연결성과 반응시 간을 측정하였다. 결과: 과제 수행에서 국가대표가 다른 두 집단보다 반응시간에서 통계적으로 유의한 차이가 나타났으며, 전전두엽의 연결성에서도 국가대표 집단이 강한 연결성을 나타냈다. 결론: 세계적인 경기력 수준을 가진 국가대표 선수들은 경기와 관련된 인지적 요소뿐만 아니라 일반적인 작업기억 능력 또한 우수하다고 판단할 수 있다.