(Fe_(2)O_(3))_(5)-(Al_(2)O_(3))_(3.4)-(Ga_(2)O_(3))_(0.6)-(SiO)의 결정구조 및 자기적 특성연구

최승한 慶山大學校 2000 論文集 Vol.18 No.1

The crystal structure and magnetic properties of Ga_(2)O_(3) substituted ferrite (Fe_(2)O_(3))_(5)-(Al_(2)O_(3))_(3.4)-(Ga_(2)O_(3))_(0.6)-(SiO) has been studied using X-ray diffraction method and M ssbauer spectroscopy. The M ssbauer spectrum at room temperature shows the superpositions of two Zeeman patterns and a strong doublet. The doublet seems to be originated from the superparamagnetic clusters, It shows significant departures from the Neel's collinear model and seems to be the diluted ferrites. The M ssbauer spectra below R.T show various and complicated patterns, which can be explained by freezing of the superparamagnetic clusters. On cooling, magnetic states of the system may be various and multicritical.

치환형 Ferrite (Fe-Al-Ga-Si)의 특성 연구

최승한,Choi, Seung-Han 한국재료학회 2011 한국재료학회지 Vol.21 No.8

The crystal structure and magnetic properties of a new solid solution type ferrite $(Fe_2O_3)_5-(Al_2O_3)_{3.4}-(Ga_2O_3)_{0.6}-SiO$ were investigated using X-ray diffraction and M$\"{o}$ssbauer spectroscopy. The results of the X-ray diffraction pattern indicated that the crystal structure of the sample appears to be a cubic spinel type structure. The lattice constant (a = 8.317 ${\AA}$) decreases slightly with the substitution of $Ga_2O_3$ even though the ionic radii of the Ga ions are larger than that of the Al ions. The results can be attributed to a higher degree of covalency in the Ga-O bonds than in the Al-O and Fe-O bonds, which can also be explained using the observed M$\"{o}$ssbauer parameters, which are the magnetic hyperfine field, isomer shift, and quadrupole splitting. The drastic change in the magnetic structure according to the Ga ion substitution in the $ (Fe_2O_3)_5(Al_2O_3)_{4-x}(Ga_2O_3)_xSiO$ system and the low temperature variation have been studied through a M$\"{o}$ssbauer spectroscopy. The M$\"{o}$ssbauer spectrum at room temperature shows the superpositions of two Zeeman patterns and a strong doublet. It shows significant departures from the prototypical ferrite and is comparable with the diluted ferrite. The doublet of spectrum at room temperature appears to originate from superparamagnetic clusters and also the asymmetry of the doublet appears to be caused by the preferred orientation of the crystallites. The M$\"{o}$ssbauer spectra below room temperature show various complicated patterns, which can be explained by the freezing of the superparamagnetic clusters. On cooling, the magnetic states of the sample were various and multi critical.

몰입형 기가미디어 서비스 플랫폼 기술 개발 동향

최승한,박노삼,이훈기,고은진,한미경,장종현,Choi, S.H.,Park, N.S.,Lee, H.K.,Ko, E.J.,Han, M.K.,Jang, J.H. 한국전자통신연구원 2017 전자통신동향분석 Vol.32 No.5

This study focuses on the ongoing immersive Giga Media service platform technology developed by the Electronics and Telecommunications Research Institute(ETRI) for various projects of the Giga KOREA Foundation[1] to achieve a smart ICT environment including wireless-based Giga service by 2020. This technology enables an immersive realistic Tele-Experience service that supports immersive real-world interaction as if sharing one's surroundings in a particular location through a high-speed network among remote users. It is expected to contribute greatly to the activation of smart ICT.

In^(3+)으로 치환된 YIG계의 자기적 특성연구

최승한 慶山大學校 1999 論文集 Vol.17 No.1

The In^(3+) substituted yttrium iron garnet system Y_(3-x)In_(x)Fe_(3)O_(12)(x= 0.18,0.33, 0.5, 0.6) have been investigated by means of M ssbauer spectroscopy and SQUID. In the systems of Y_(3-x)In_(x)Fe_(3)O_(12), the M ssbauer spectra for x=0.0 at room temperature consist of two Zeeman sextets, one due to the Fe^(3+) ion on the octahedral(a-) sites and the other due to the Fe^(3+) ions on thetetrahedral(d-) sites, respectively. However the spectrum shows four Zeeman sextets in the range from X=0.18 to 0.60 due to two octahedral a-, a'-sites and two tetrahedral d-, d'-sites with different hyperfine parameters, as the substituted Fe^(3+) and In^(3+) ions occupy the c-sites. From the hysteresis loop measured by means of SQUID over the whole composition range, the saturation magnetization M_(s) and magnetic moments μ_(B) Per unit cell have been obtained. The increment of In-ion content doesn't cause M_(s) and μ_(B) decrease.

CFD를 활용한 축류형 혈액펌프의 펌프 특성 해석

최승한,김동욱 한국산학기술학회 2003 한국산학기술학회 학술대회 Vol.- No.-

Artificial heart is divided by pulsation flow type and continuous flow type according to blood circulation pattern. Axial flow blood pump is a kind of continuous flow type artificial heart. Axial flow blood pump would be different pump performance according to impeller’s shape and rotating velocity. Pump performance be able to compare by flow rate according to differential pressure and Impeller’s rotating velocity. It confirms Impeller model of better efficiency according to compare Pump performance of axial flow blood pump using CFD with actual experiment result.

치환된 YIG계의 구조적 및 자기적 특성

최승한,이영배,Choi, Seung-Han,Lee, Young-Bae 한국재료학회 2003 한국재료학회지 Vol.13 No.1

The substituted yttrium iron garnet systems $Y_{ 3-x}$/Gd$_{x}$X$0.2_{0.2}$ $Fe_{4.8}$ $O _{12}$ (x = 0.2, 0.4, 0.6) have been investigated by means of X-ray diffraction, Mossbauer spectroscopy and SQUID. The X-ray diffraction patterns at room temperature confirm the samples to have a single phase of the garnet structure over the whole composition range. The lattice constants of all the samples linearly change with increasing x due to the size of substituted ions in the dodecahedral sites. $Y_{3-x}$ $Gd_{x}$ X$Fe_{4.8}$ $In_{0.2}$ $O_{12}$ system which $Y_{3-x}$ ions are substituted with Gd$^{ 3+}$ ions, the Mossbauer spectrum consists of three Zeeman sextets at room temperature, one due to the $Fe^{3+}$ ions on the octahedral(a-) sites and the others due to the $Fe^{3+}$ ions on the tetrahedral(d-, d'-) sites, respectively. From the hysteresis loop measured by means of SQUID over the whole composition range, the saturation magnetization $M_{s}$ and magnetic moments $\mu_{ B}$ per unit cell have been obtained. The increment of Gd-ion content causes $M_{s}$ and $\mu_{B}$ decrease while the increment of In-ion content does not.

YIG Ferrite계의 결정구조 연구

최승한 慶山大學校 基礎科學硏究所 2000 基礎科學 Vol.4 No.2

Yttruim iron garnet(YIG)인 Y₃Fe_5O_12에서 Yttruim 이온을 다양한 금속으로 치환시킨 Y_3-xFe_5+xO_12(x=0.0, 0.18, 0.33, 0.6), Y_3-xIn_xFe_5O_12(x=0.0, 0.18, 0.33, 0.6), Y_3-xGd_xIn_0.2Fe_4.8O_12(x=0.2, 0.4, 0.6)의 결정구조 및 결정학적 특성을 X-선 회절법을 통해 연구하였다. 실온에서 측정된 X-선 회절상을 분석한 결과 전체 조성비 영역에서 단일상의 garnet 구조를 가지며 Y_3-xFe_5+xO_12에서는 전반적으로 치환량이 증가함에 따라 격자상수가 감소하는 경향을 나타냈다. 그러나 Y_3-xGd_xIn_0.2Fe_4.8O_12와 Y_3-xIn_xFe_5O_12계에서는 치환량 증가에 따라 격자상수가 증가함을 알 수 있었다. 격자상수값들이 조성비가 증가함에 따라 선형적으로 변화된 것은 치환된 이온의 반경에 따른 것이며 Vegard's law로 인해 나타나는 결과로 해석할 수 있었다. The substituted yttrium iron garnet systems Y_3-xFe_5+xO_12(x=0.0, 0.18, 0.33, 0.6), Y_3-xIn_xFe_5O_12(x=0.0, 0.18, 0.33, 0.6), Y_3-xGd_xIn_0.2Fe_4.8O_12(x=0.2, 0.4, 0.6) have been investigated by means of X-ray diffraction method. The X-ray diffraction patterns at room temperature confirm the samples to have a single phase of the garnet structure over the whole composition range. The lattice constants of all the sample linearly change with increasing x due to the size of substituted ions in the dodecahedral sites, which is attributed to Vegard's law.

Fe-Se-Te계의 특성 연구

최승한,Choe, Seung-Han 한국재료학회 1999 한국재료학회지 Vol.9 No.8

The properties of Fe-Se-Te system(FeSe(sub)1-xTe(sub)x, x=0.2, 0.5, 0.8) have been studied by means of the X-ray diffraction method and Mossbauer spectroscopy. The results of X-ray diffraction patterns show that three samples have the ixed structure of tetragonal PbO and a small amount of hexagonal NiAs structure respectively. For x=0.5 the lattice parameters of tetragonal PbO structure are a=3.795$\AA$, c=5.896$\AA$ and c/a=1.55. The Mossbauer spectra were obtained with the various temperature variation and than they do not exhibit magnetic hyperfine structure but show a strong doublet. The values of observed isomer shift and quadrupole splitting suggest that the irons of all samples exist in the +2 oxidation state with a major covalent contribution. The temperature dependence of isomer shift values for x=0.8 seems to be originated from the second order Doppler effect. Fe-Se-Te계(FeSe(sub)1-xTe(sub)x, x=0.2, 0.5, 0.8)의 특성을 X-선 회절법 및 Mossbauer 분광법에 의해 조사하였다. 결정구조는 세 시료 모두 주된 tetragonal PbO 구조와 hexagonal NiAs 구조가 일부 혼합된 형태를 보였으며 x=0.5의 경우 tetragonal 구조의 격자상수 값은 a=3.795$\AA$, c=5.896$\AA$ 이며 c/a=1.55로 나타났다. 다양한 온도변화에 의해 측정된 Mossbauer 스펙트럼은 전체 시료 모두 초미세 자기구조를 갖지 않는 강한 이중선(doublet)이 관측되었다. 조성 및 온도변화에 대해 뚜렷한 선형(line shape)의 변화는 관측되지 않았으나 결합상태에 약간의 변화를 보였다. 이성질체 이동(isomer shift)값과 사중극자 분열(quadrupole splitting)값 및 온도의존성을 분석한 결과 Fe는 low spin이 +2가 상태로 존재하며 강한 공유 결합상태임을 알 수 있었다. x=0.8의 경우 이성질체 이동값의 온도변화는 제2차 도플러 효과(second order Doppler effect)의 영향인 것으로 나타났다.

Nonstoichiometric Ferrite계의 결정구조 연구

최승한 慶山大學校 基礎科學硏究所 2000 基礎科學 Vol.4 No.1

Nonstoichiometric ferrite 5(Fe₂O₃)-(4-x)Al₂O₃-(x)Ga₂O₃-(SiO) (x=0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0)계에 대한 결정구조 및 특성을 X-선 회절법으로 연구조사 하였다. Ga₂O₃의 조성 변화에 따라 결정구조는 spinel 구조(x=0.2, 0.4, 0.6, 0.8, 1.0, 2.0), spinel과 orthorhombic의 혼합구조(x=3.0) 및 orthorhombic 구조(x=4.0)를 형성하였다. cubic spinel type 구조에서는 Ga 이온 치환량의 증가에 따라 격자상수가 약간씩 감소 하다가 증가 하였는데, 이러한 결과는 Ga 이온의 공유 결합성이 Al 보다 크다는 점과 Ga 이온의 증가에 따라 결정구조가 약간씩 변형된 것의 원인으로 보여진다. The crystal structure and properties of nonstoichiometric ferrite system 5(Fe₂O₃)-(4-x)Al₂O₃-(x)Ga₂O₃-(SiO) (x=0.2∼4.0) have been investigated using X-ray diffractometry. The crystal structure is transformed from a cubic spinel type(x=0.2∼2.0) to an orthorhombic phase(x=4.0) via the intervening region(x=3.0). For cubic spinel type structures the lattice constants have been slightly decreased by increasing Ga?? ion concentration even though the radii of Ga?? ions are larger than those of the Al?? ions. This can be attributed to a higher degree of covalency in Ga-O bonds than in Al-O and Fe-O bonds, which can be also explained with the help of elctronegativity.

A study on magnetic structure of (Fe_(2)O_(2))-(Al_(2)O_(2))_(0.8-x)-(Ga_(2)O_(3))x-(SiO)_(0.2) by Mo¨ssbauer spectroscopy

최승한 慶山大學校 1998 論文集 Vol.16 No.1

뫼스바우어 분광법에 의해 산화물(Fe_(2)0_(3))-(Al_(2)0_(3))o.8-x-(Ga_(2)0_(3))x-(Si0)o.₂계에 관한 연구가 수행되었다. 상온에서의 뫼스바우어 스펙트럼은 x=0.2 경우 잘 정렬된 두 개의 Zeeman 형태로 나타났으나 0.4 x 1.0의 조성영역에서는 강한 이중선과 두 개의 Zeeman 형태가 중첩되고 2.0 x 4.0 에서는 이중선 만이 관측되었다. 중앙 이중선의 출현은 상자성 clustering에 의해 발생된 것으로 나타났다. 이성질체 이동값은 철 금속 foil에 대한 상대적인 값으로 얻어졌으며 이로부터 철은 +3가 상태이며 조성비에 따른 변화는 작음을 알 수 있었다. 또한 사중극자분열값은 거의 영에 가까운 값을 보였으며 이중선의 비대칭성은 결정의 임의 방향성에 의한 것으로 나타났다. The magnetic oxide system (Fe₂0₃)-(Al₂0₃)o.8-x-(Ga₂0₃)x-(Si0)o.₂ has been investigated by means of M ssbauer spectroscopy. The M ssbauer spectrum at room temperature for x=0.2 shows well defined two Zeeman patterns but the spectra for 0.4 x 1.0 exhibit the superposition of two Zeeman patterns and a strong doublet also and the spectra for 2.0 x 4.0 show only doublet. The central line (doublet) in this system suggests that super paramagnetic behavior is caused by super paramagnetic clustering. Isomer shifts are obtained relative to natural iron-foil, It shows that Feions of this system exist in the high spin Fe³+ state. The dependence of isomer shift on x is small. The Quadrupole splittings values are near the zero. Asymmetry of doublet is caused by the preferred orientation of crystallities.