• Journal of Magnetics
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• 제4권1호
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• pp.26-32
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• 1999

The HDDR process can be used as an effective means of processing of the coercive Nd-Fe-B-type or the Sm2Fe17Nx materials. The HDDR (hydrogenation, disproportionation, desorption, recombination) processed materials are feartured with a very fine microstructure. The thermomagnetic characteristics of the Nd-Fe-B-type or the Sm2Fe17Nx materials with fine microstructure due to the HDDR process were investigated. It has been found that the fine-microstructured hard magnetic materials showed an unusual TMA (Thermomagnetic analysis) tracting featured with a low and constant magnetization at lower temperature range and a peak just below their Curie temperatures when a low external field is applied. This thermomagnetic characteristic was immediate particularly in the TMA with a low applied field. This thermomagnetic characteristic was interpreted in terms of the competition between two counteracting effects; the decrease in magnetication due to the thermal agitation at an elevated temperature and the increase in magnetization resulting from the rotation of magnetization of the fine grains comparable to a critical single domain size due to the decreased magnetocrystalline anisotropy at an elevated temperature.

• Journal of Magnetics
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• 제2권4호
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• pp.147-156
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• 1997

An artificially modulated magnetic Co/Pd multilayer is one of the promising candidates for high density magneto-optic (MO) recording media, due to a large Kerr rotation angle in the wavelength of a blue laser beam. However, since multilayer structure, as well as amorphous structure, is a non-equilibrium state in terms of free energy and a MO recording technology is a kind of thermal recording which is conducted around Curie temperature (Tc) of the recording media, when the Co/Pd mulilayer is used for the MO recording media, changes in the magnetic properties are occurred as the amorphous structure do. Therefore, the assessment of the magnetic properties in the Co/Pd multilayer during interdiffusion is crucially important both for basic research and applications. As the parameter of the magnetic properties in this research, saturation magnetization and perpendicular magnetic anisotropy energy of the Co/Pd multilayer are measured in terms of Ar sputtering pressure and heat treatment temperature. Form the results of the research, we find out that the magnetic exchange energy between Co and Pd sublayers strongly affects the changes in the magnetic properties of the Co/Pd multilayers during the interdiffusion in ferromagnetic state. This discovery will provide the understanding of the magnetic exchange energy in the Co/Pd multilayer structure and suggest the operating temperature range for MO recording in the Co/Pd multilayer for the basic research and applications, respectively.

• 폴리머
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• 제24권3호
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• pp.418-430
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• 2000

알칼리키토산과 프로필렌옥사이드를 반응시킴에 의해 유방성 및 열방성 액정상을 형성하는 새로운 히드록시프로필키토산(HPCTO)을 합성함과 동시에 HPCTO/메탄올의 유방성 액정용액에 glyoxal첨가하여 주형시킴에 의해 HPCTO의 가교필름들을 제조하였다. 가교필름들의 열 및 팽윤 특성을 검토하였다. 필름들은 cholesteric 액정상의 특징적인 지문조직을 나타내었으며 이들의 pitch는 온도 및 가교제의 농도가 증가할수록 증가하였다. 가교시료들은 물과 메탄을 중에서 이방성 팽윤을 나타내었으며, 이러한 사실은 HPCTO분자들간에 2차원적인 가교가 우선적으로 일어남을 시사한다. 이방성 팽윤의 정도는 용매의 종류에 크게 의존하나 검토된 가교제의 농도에는 의존하지 않았다.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.331-349
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• 2016

Stiff and light fibre reinforced composites as used in air- and space-craft applications tend to high sound emission. Therefore, the damping properties are essential for the entire structural and acoustic engineering. Viscous damping is an established and reasonably linear model of the dissipation behaviour. Commonly, it is assumed to be isotropic and constant over all modes. For anisotropic materials it depends on the fibre orientation as well as the elastic and thermal material properties. To portray the orthogonal anisotropic behaviour, a model for unidirectional fibre reinforced plastics (frp) has been developed based on the classical laminate theory by ADAMS and BACON starting in 1973. Their approach includes three damping coefficients - for longitudinal damping in fibre direction, damping transversal to the fibres and shear based dissipation. The damping of a laminate is then accumulated layer wise including the anisotropic stiffness. So far, the model has been applied mainly to thermoset matrix materials. In this study, an experimental parameter estimation for different thermoplastic frp with angle ply and cross ply layups was carried out by measuring free vibrations of cantilever beams. The results show potential and limits of the ADAMS/BACON damping criterion. In addition, a possibility of modelling the anisotropic damping is shown. The implementation in standard FEA software is used to study the influence of boundary conditions on the damping properties and numerically estimate the radiated sound power of thin-walled frp parts.

• Structural Engineering and Mechanics
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• 제72권4호
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• pp.455-468
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• 2019

The present article is aimed at studying the reflection phenomena of plane waves in a homogeneous, orthotropic, initially stressed magneto-thermoelastic rotating medium with diffusion. The enuciation is applied to generalized thermoelasticity based on Lord-Shulman theory. There exist four coupled waves, namely, quasi-longitudinal P-wave (qP), quasi-longitudinal thermal wave (qT), quasi-longitudinal mass diffusive wave (qMD) and quasi-transverse wave (qSV) in the medium. The amplitude and energy ratios for these reflected waves are derived and the numerical computations have been carried out with the help of MATLAB programming. The effects of rotation, initial stress, magnetic and diffusion parameters on the amplitude ratios are depicted graphically. The expressions of energy ratios have also been obtained in explicit form and are shown graphically as functions of angle of incidence. It has been verified that during reflection phenomena, the sum of energy ratios is equal to unity at each angle of incidence. Effect of anisotropy is also depicted on velocities of various reflected waves.

• 한국자기학회지
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• 제23권4호
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• pp.122-125
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• 2013

비정질 합금인 CoSiB과 비자성체 Pd을 이용하여 CoSiB/Pd 다층박막을 제작하고, 그 자기적인 특성을 분석하였다. $[CoSiB\;t_{CoSiB}/Pd\;1.3nm]_5$ 다층박막을 $t_{CoSiB}$ = 0.1~0.6 nm의 범위로 제작하였고, 동일한 방법으로 $[CoSiB\;0.3nm/Pd\;t_{Pd}]_5$ 다층박막을 $t_{Pd}$ = 1.0~1.6 nm의 범위로 제작하여 두께에 따른 자기이방성과 포화자화도를 측정하였다. CoSiB 두께가 증함에 따라 포화자화도가 증가하는 경향을 보였는데, 특히 CoSiB의 두께가 0.2~0.3 nm 일 때 포화자화도가 급격하게 증가하였다. 보자력은 두께 0.2 nm 에서 최대값을 보이다가 두께가 증가함에 따라 점차 감소하는 것을 확인하였다. Pd의 두께 변화 실험에서는 포화자화도는 1.1~1.2 nm 구간에서 약간 감소하다가 1.3 nm 이후 점차 증가하였으며, 보자력은 포화자화도에 비해 확연한 규칙성을 보이지 않았으나, 전체적으로 Pd의 두께가 증가함에 따라 값이 감소하는 것을 알 수 있었다.

• 한국자기학회지
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• 제26권3호
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• pp.76-80
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• 2016

CoSiB은 비정질 구조를 갖는 강자성체 물질이며, CoSiB과 Pd을 포함한 다층박막은 수직자기이방성을 갖는다. 수직자기이방성은 수평자기이방성에 비해 STT-MRAM에 적용되기에 좋은 이점이 있으며, 특히 비정질 강자성체를 포함한 다층박막은 결정질강자성체를 포함한 다층박막과 비교하여 몇 가지 이점을 지니는데, 첫째는 grain boundary가 없다는 것이며 둘째는 결정질 재료에 비교하여 열적안정성이 보다 좋다는 것이다. 이러한 이유에 따라 우리는 비정질 강자성체 $Co_{75}Si_{15}B_{10}$을 포함하는 다층박막을 제작하여 그 자기적 특성을 연구하였다. 본 연구는 [CoSiB(3, 4, 5, 6) ${\AA}$/Pd(11, 13, 15, 17, 19, 24${\AA})]_5$ 다층박막을 제작하여 VSM 측정을 통해 두께에 따른 그 자기적 특성의 변화를 살펴보았으며, 이후 일부 다층박막의 열처리를 통해 온도에 따른 자기적 특성의 변화추이를 조사하였다. 포화자화값과 보자력은 CoSiB과 Pd 각 층의 두께 변화에 따라 증가와 감소를 반복하였으며, 열처리 온도의 범위는 상온에서 $500^{\circ}C$까지로 특정 온도에서 보자력의 증대를 보였다.

• Journal of Magnetics
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• 제11권1호
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• pp.43-50
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• 2006

In this paper, the influences of microstructural and surface morphological developments on the soft magnetic properties and giant magneto-impedance (GMI) effect of the $Fe_{73.5-x}Cr_{x}Si_{13.5}B_{9}Nb_{3}Au_1$ (x = 1, 2, 3, 4, 5) alloys have been presented. It was found that the Cr addition slightly decreased the mean grain size of $\alpha-Fe(Si)$ grains. AFM results indicate a large variation of surface morphology of density and size of protrusions along the ribbon plane due to microstructural changes caused by thermal annealing with increasing Cr content. Ultrasoft magnetic properties of the nanocrystallized samples were noticeably enhanced by properly heat treatments at $T_a=540^{\circ}C$ such as an increase of the magnetic permeability and the decrease of coercivity, which is likely due to the formation of nanoscale $\alpha-Fe(Si)$ phase which reduced the magnetoelastic anisotropy of samples. Accordingly, the GMI effect was observed in the annealed samples. The correlation between the microstructure, surface morphology, and soft magnetic properties were explained by nucleation and growth model.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 D
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• pp.1252-1254
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• 1998

The characteristics of linear dichroism with temperature were investigated in normally($0^{\circ}$) and $80^{\circ}$-obliquely deposited amorphous $As_{40}Ge_{10}Se_{15}S_{35}$ thin films using low temperature equipment. The saturated dichroism($D_{sat}$) of a $80^{\circ}$-obliquely deposited film shows approximately 6% which is the larger value than 4.2 % of normally($0^{\circ}$) deposited film. The $D_{sat}$ of $80^{\circ}$-deposited film was increased to 25 % at 77 K, which is four times larger than that at room temperature. The $D_{sat}$ decreased with increasing temperature and was completely disappeared at about 335K. This could be explained as the tunneling effect due to the thermal excitation of lone-pair electrons in intimate valence alternation pairs(IVAPs) which are considered to be the origin of anisotropy. The decrease of $D_{sat}$ with increasing temperature from 77K to room temperature satisfied Gaussian approximation with a standard deviation of 158K.

• 폴리머
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• 제29권4호
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• pp.413-417
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• 2005

LCD 배향막으로 응용하기 위하여 광반응성 polyvinylcinnamate 필름 위에서 액정 분자들의 배향에 관한 연구를 수행하였다. 선편광 UV를 polyvinylcinnamate 필름에 노광하면 선택적인 광반응에 의하여 필름 내에 이방성이 형성되고, 필름 표면에 인접한 액정 분자는 고분자와 분자간 상호작용으로 고분자 배향 방향과 동일한 방향으로 늘어선다. 광배향막을 사용한 액정 셀의 열 및 빛에 대한 안정성은 배향막에 UV를 다시 노광하고 열을 가한 후 유도된 액정 배향 변화를 측정하여 조사하였다. 선편광 UV를 여러번 노광한 필름의 경우 처음 노광 방향에 관계없이 최종으로 노광한 편광 UV의 방향에 따라 액정 배향이 유도되었다.