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M형 Ba-Ferrite에서 Fe 이온의 열 진동에 관한 연구
서정철(Jung Chul Sur),김진수(Jin Soo Ghim),최정완(Choi Jong Wan) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.1
Mossbauer and Raman spectrum studies have been carried out on the 2b-site Fe ion in the Ba-ferrite (M-type). The thermal dynamics of Fe ion was analyzed by Mossbauer spectra at different angles between the γ-ray direction and c-axis. The vibration on the 2b-site was more active compare to other direction and had very strong intensity in the Raman spectrum.
Al₂O₃을 하지층으로 하는 Ba - ferrite 박막의 제조 및 자기적 특성에 관한 연구
서정철(Jung Chul Sur),박철진(Chul Jin Park),최정완(Jung Wan Choi) 한국자기학회 2005 韓國磁氣學會誌 Vol.15 No.2
Ba-Ferrite thin films were prepared on Al₂O₃ substrate by a pulsed laser deposition system and characterized by SEM, Mossbauer spectroscopy and VSM. The appropriate conditions of pulsation in Ba-ferrite was the oxygen pressure of 0.1 Torr at a substrate temperature of 400℃ and the thickness was variable with the deposition time. Ba-ferrite crystals had the forms of hexagonal plate in the 5 minute deposited film and the needle grains coexisted with the increasing film thickness. Mossbauer spectroscopy assured that the direction of atomic spin in Fe ion tends to normal to the substrate in the hexagonal plate. The VSM curves have the two types hysteresis of hexagonal and needle phase.
α-Fe₂O₃ 나노 입자에서 Spin - Flop에 관한 연구
서정철(Jung Chul Sur),박철진(Chul Jin Park),최정완(Jung Wan Choi),S. H. Gee(S. H. Gee),Y. K. Hong(Y. K. Hong) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.5
We have synthesized monodispersed α-Fe₂O₃ nano particles to investigate the spin change during the Morin transition temperature(T_M). The particle size was founded to have a very uniform distribution of 80 ㎚ by x-ray diffraction and size dispersion analyzer. The Mossbauer spectra between the 4.2 K and the room temperature show that T_M was shifted and the spin states of Fe ion were changed with the particle size. The Morin transition temperature of bulk usually quoted in literature is 265 K but, it decreases with the size and no transition was found at the critical size down to 4.2K. The spin direction of 80 ㎚ sized particles are normal to the hexagonal c-axis above the TM and are tilted about 28-29°below T_M, which is the [110] direction of rombohedral structure.
Ba - ferrite 박막의 제조 및 자기적 특성에 관한 연구
서정철(Jung Chul Sur),김대성(Dae Sung Kim),하태양(Tae Yang Ha),이재광(Jae Gwang Lee) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.2
Ba-ferrite thin films were prepared on Si substrate with α-Fe₂O₃ underlayer by a pulsed laser deposition system and characterized by X-ray, SEM, Mossbauer spectroscopy and VSM. The appropriate conditions of pulsation in α-Fe₂O₃ and Ba-ferrite were the oxygen pressure of 0.1 Torr at a substrate temperature of 400℃. Ba-ferrite crystals had the forms of ellipsoidal or needle and the grains shaped the more lumps with increasing the film thickness. Mossbauer spectroscopy assured that the direction of atomic spin in Fe ion was not random but had the tendency of arrangement normal to the substrate. The coercive force and squareness of hysteresis were larger in normal than in plane to the substrate but, the magnetic saturation moment was contrary to them. The spin arrangement was strongly affected by α-Fe₂O₃ underlayer and the high coercive force and squareness were influenced by this. The crystal structure was conformed to be a Magntoplumbite symmetry with the hexagonal unit cell and the lattice constant of a increased with increasing film thickness, while c decreased.
서정철(Jung Chul Sur),이호선(Ho Seon Lee) 한국자기학회 2001 韓國磁氣學會誌 Vol.11 No.1
α-Fe₂O₃thin films were prepared on Si substrate by a pulsed laser deposition system and characterized by X-ray and Mossbauer spectroscopy. The appropriate conditions of pulsation was the power of 5.128 W/㎠ at on oxygen pressure of 0.1 Torr at a substrate temperature of 300℃. After that the film was heated at 800℃ for 1 day. The particles shape deposited on the film was ellipsoidal and the average length and width were 200~300 ㎚, 70~150 ㎚ respectively. The crystal structure was conformed to be of corundums symmetry with the hexagonal unit cell having a lattice constant of α=5.03±0.05 Å, c=13.735±0.05 Å. The average angles between the atomic spin and the magnetic hyperfine field of Fe ion were 38° and 48°at above and blow the Morin transition temperature respectively. The Morin transition was found to occur at the temperature ranges from 200 K to room temperature and atomic spin direction was assumed to change from 48° to 80° in respect to the c-axis.
철, 구리 스피넬 CuFe₂O₄의 Jahn - Teller 효과에 관한 연구
서정철(Jung Chul Sur),이민용(Min Yong Lee) 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.2
CuFe₂O₄ was accomplished by chemical method and the crystallographic and magnetic properties have been studied by Mobauer spectroscopy and X-ray diffraction. The slowly cooled sample is found to have a tetragonal spinel structure with the lattice constant α=8.26±0.05Å, c=8.75±0.05Å. The Mobauer spectra between the room temperature to the Curie temperature show that the Cu²+ ions at octahedral site have the Jahn-Teller effect and the sample exhibits a structural phase transition near 630 K due to the Jahn-Teller effect. The Curie temperature is found to be 690K and it is lower than that of ceramic method.
유화 Spinel Co0.95Fe0.05Cr₂S₄에서 Jahn - Teller Distortion에 의한 Mossbauer 공명 흡수선의 변화에 관한 연구
서정철(Jung Chul Sur),이민용(Min Yong Lee),고영복(Young Bok Ko) 한국자기학회 1997 韓國磁氣學會誌 Vol.7 No.5
Sulphur Spinel Co_(0.95)Fe_(0.05)Cr₂S₄ has been studied with Mossbauer Spectroscopy between 4.2 K and room temperature. The Fe²+ ion in a tetrahedral site is the Jahn-Teller active and the dynamic Jahn-Teller distorts below the magnetic ordering temperature. The distortion cause a quadrupole shift to appear which increases with decreasing temperature. The magnetic hyperfine field has a maximum at 100 K and then decreases with decreasing temperature. The magnitude of the interaction ratio R between the electric quadrupole and magnetic dipole interaction increases from 0 near the magnetic ordering temperature to 5.4 at 4.2 K. The optimum values of θ, the polar angle of the magnetic hyperfine field with respect to the principle axis of the electric field gradient (EFG) remains zero and the asymmetry of the EFG η is about 0.25. The simulations of Mossbauer spectra coincidence with the experimental results.
α-Fe₂O₃ 미세입자의 크기분포에 관한 Mossbauer 분광학적 연구
이민용(Min Yong Lee),김시정(Sea Jung Kim),고영복(Young Bok Ko),서정철(Jung Chul Sur),이충섭(Choong-Sub Lee) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.1
α-Fe₂O₃ was accomplished by chemical method as low temperature as possible and the crystallographic and magnetic properties have been studied by Mossbauer spectroscopy and X-ray diffraction. The sample heated at 150 ℃ is found to have a Corundums symmetry with the hexagonal lattice constant a=8.26±0.05Å, c=8.75±0.05Å. The Mossbauer spectra between the 4.2K and the room temperature show that the α-Fe₂O₃ crystalized with a single phase and fine sizes. The particle size distribution has the Gaussian distribution center at 98Å and the half width of 32Å.
Perovskite Gd₁-xSrxFeO₃-y(x = 0.0, 0.5)의 Mossbauer 연구
엄영랑(Young Rang Uhm),김철성(Chul Sung Kim),서정철(Jung Chul Sur),오영제(Young-Jei Oh) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.2
Crystallographic and magnetic properties of perovskite Gd_(1-x)Sr_xFeO_(3-y) (x = 0.0, 0.5) substituted Sr²+ having larger ionic radius than Gd³+ at GdFeO₃ have been studied by x-ray diffraction, Mossbauer spectroscopy, and VSM. The crystal structures are found to be orthorhombic with the lattice parameters : a_0 = 5.53 Å, b_0=5.608 Å, c_0=7.724 Å for Gd_(0.5)Sr_(0.5)FeO_(3-y), Gd_(1-x)Sr_xFeO_(3-y) (x=0.0, 0.5) have been investigated over temperature range from 4.2 to 690 K using the Mossbauer technique. The Neel temperature of Gd_(1-x)Sr_xFeO_(3-y) system is 690 K with x value of 0.0 and 515 K with x value of 0.5. Analysis of Mossbauer spectra and Mohr's salt analysis for Gd_(1-x)Sr_xFeO_(3-y) demonstrated the existence of the mixed valence states of iron and the coordination state of Fe³+ and Fe⁴+ ions. The Corresponding hyperfine parameters for GdFeO₃ are compatible with S = 5/2 Fe³+ in octahedral coordination.
Al - Ferrite의 Mossbauer 분광학적 연구
이충섭(Choong-Sub Lee),주한식(Han-Sik Joo),이찬영(Chan-Young Lee),서정철(Jung-Chul Sur) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.4
We have studied Al_xFe_(3-x)O₄ produced by direct composition method using X-ray diffraction and Mssbauer spectroscopy. The cation distribution for Al_xFe_(3-x)O₄ was determined by the ratio of sub-spectra absorption area. The charge state of Fe atoms in octahedral site(B-site) is Fe^(2.5+) based on electron hopping, Fe²+ ↔ (Fe³+, Al³+) without dependency of substituted Al amounts.