소결 첨가제 없는 고특성 페라이트 영구자석 공정 개발

유평열,김민호,강영민 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.8

Sintered M-type hexaferrites with the chemical formula of Sr0.3Ca0.4La0.3Fe9.8Co0.2-xMnxSi0.135O19-d (x = 0, 0.05, 0.1, 0.2) and Sr0.3Ca0.4La0.3Fe9.8-yCo0.2MnySi0.135O19-d (y = 0.05, 0.1, 0.2) were prepared by conventional solid station reaction routes. A high sintering density of more than 95% of the theoretical density was achieved in all hexaferrite samples when calcination was carried out at 1100 oC for 4 h, followed by sintering at 1230-1250 oC for 2 h without the use of sintering additives. High saturation magnetization and coercivity were achieved simultaneously at the x = 0.05 composition, where Mn replaces part of the Co. The secondary phase Fe2O3 generated by the initial addition of SiO2 was gradually reduced when the Fe contented was decreased in the Sr0.3Ca0.4La0.3Fe9.8-zCo0.15Mn0.05Si0.135O19-d samples, and a single M-type hexaferrite phase was confirmed in the Sr0.3Ca0.4La0.3Fe8.3Co0.15Mn0.05Si0.135O19-d (z = 1.5) sample, which also exhibited optimized hard magnetic properties, with a saturation magnetization of 4581 G and coercivity of 4771 Oe. Anisotropic sintered magnets were fabricated using the optimized composition, and showed excellent hard magnetic properties, with a remanent magnetic flux density of 4400 G and intrinsic coercivity of 4118 Oe, and a maximum energy product of 4.72 M·G·Oe. This result is very promising because high magnet performance can be achieved with a single batch process without the need for sintering additives during the process.]

Tuning of electromagnetic wave absorbing properties in Fe-deficient SrFe9.6-Co1.2Ti1.2O19 hexaferrite-epoxy composites

유평열,강영민 한국물리학회 2021 Current Applied Physics Vol.31 No.-

We report the tunable electromagnetic (EM) wave absorption properties of Fe-deficient SrFe9.6-xCo1.2Ti1.2O19 hexaferrite–epoxy composites. SrFe9.6-xCo1.2Ti1.2O19 hexaferrite powders were prepared via solid-state reaction routes. It was observed that Sr–Ti-rich second phases were formed as x increased, i.e., the Fe content decreased. The ferromagnetic resonance (FMR) frequency of the composites gradually decreased from 8.8 GHz to 4.8 GHz with increasing x, and accordingly, the EM absorption frequency range also gradually changed. The gradual FMR frequency shift was attributed to the compositional shift in the mother phase. It is predicted that the Fe deficiency caused a decrease in the magnetocrystalline anisotropy, and in turn, it shifted the FMR frequency and modified the corresponding EM absorbing properties. All the samples demonstrated a high EM absorption performance with the lowest reflection loss of < 40 dB at the optimized frequency and thickness.

Eγ=30MeV 이하에서의 ⁴He의 광핵분열 반응에 대한 이론적인 연구

김경훈,유평열 順天大學校 1994 論文集 Vol.13 No.1

□ ⁴He(Υ,p)³H and ⁴He(Υ,n)³He cross sections have been caculated for photonenergies from the (Υ,n)threshold to 30 MeV. Effects of Coulomb ineractions, nuclear Potential shape and mass differences have been taken into account using a shell-model caculation of p-³H and n-³He elastic scattering. The ratio σ(Υ,p)/σ(Υ,n)is predicted to be close to 1, expect at energies very close to the (Υ,n) threshold.

육방정 페라이트 복합상의 합성 및 GHz 대역 전자기파 흡수 특성

유평열(Pyeong-Yeol Yu),강영민(Young-Min Kang) 한국자기학회 2020 韓國磁氣學會誌 Vol.30 No.4

Multi-hexaferrites (Sr<SUB>3-x</SUB>Ca<SUB>x</SUB>Co₂Fe<SUB>24</SUB>O<SUB>41</SUB>, x = 0, 0.1, 0.2, 0.3, 0.4) with more than two types of hexaferrite phases were synthesized by solid-state reactions and substitution of Sr by Ca in the stoichiometric Z-type Sr₃Co₂ hexaferrite composition. Multi-hexaferrites consisting of Z + U + W, X + U +W, and X + W phases were formed for the samples with x = 0, x = 0.1, and x≥0.2, respectively, upon first and second calcinations at 1160 and 1210 oC. The saturation magnetization increased largely with Ca-doping (x≥0.1). The complex permeability spectra were shifted to higher frequency and the imaginary permeability peak became broader by Ca doping. In the RL maps plotted as functions of sample thickness (d) and frequency (f), the strong EM absorbing area moved to higher f and lower d direction with increasing of x. For the Ca-doped samples (x≥0.1), the minimum reflection loss (RL < -30 dB) corresponding to the maximum microwave absorption was obtained at f = 10 GHz vicinity and d = ~2 ㎜, while the undoped sample exhibited the minimum RL (-42 dB) at f = 4.6 GHz and d = 4.6 ㎜. The highest EM wave absorption performance of RL = 56.5 dB could be achieved at the sample of x = 0.3 with d = 2.2 ㎜ and f = 11.4 GHz. For the x = 0.2 samples, RL <-10 dB (EM energy absorption above 90%) is satisfied in the full X-band frequency range (8~12 GHz) with d = 2.3 ㎜. The broad-band EM absorption properties could be achieved owing to the overlaps of the hard-soft magnetic properties of the multi-hexaferrites.

광전도체의 CdS 단결정 성장과 물리적 특성

정태수,유평열,신영진,신현길,김택성,정철훈,이훈,신영신,홍광준,유기수 全北大學校 基礎科學硏究所 1994 基礎科學 Vol.16 No.-

승화방법으로 광전도체의 CdS 단결정을 성장하였고 외삽법으로 구한 a_o와 c_o 의 격자상수 값은 각각 4.1318Å과 6.7122Å임을 알았다. Hall 측정값으로 부터 상온에서의 CdS 단결정의 운반자 농도와 이동도는 각각∼10^23m^-3과 2.93×10 exp (-2)㎡/V sec 이였으며 온도에 따른 이동도 변화는 33 K에서 150 K까지는 T^1/2 에 따라 증가하는 경향이 있고 180 K 에서 상온까지는 T^-2에 따라 감소한 경향이 나타났다. 광전류 측정으로 부터 나타난 단파장대의 봉우리는 진성전이에 기인하는 봉우리였으며 이 봉우리의 에너지값은 CdS 광전도체에 에너지 밴드 갭과 동일한 값을 나타냄을 알았다. A CdS single crystal was grown by using sublimation method. Lattice constants, a_o and c_o , obtained by using extrapolation were 4.1318 Å and 6.7122 Å, respectively. The carrier density was∼10^23m^-3 and the mobility was 2.93×10 exp (-2)㎡/V-sec from measured Hall data at room temperature. The mobility has a increasing tendency in proportion to T^1/2 from 33 K to 150 K and a decreasing tendency in proportion to T^-2 from 180 K to room temperature. The short wavelength band peak measured from photocurrent was due to intrinsic transition, and the energy value of this peak was equal to the energy band gap of CdS photoconductor.

CdS1-X Se x 단결정 성장 및 특성에 관한 연구

신영진,홍광준,이충일,정태수,유평열,임종순 順天大學校 1991 論文集 Vol.10 No.1

Sublimation method로 크기가 0.02mm×15mm×19mm 정도인 판상형 CdS₁- ?? 단결정을 성장하였다. X-ray 회절실험에 의해 ?? 면으로 성장된 단결정 임을 확인하였다. Extrapolation method로 구한 격자상수 ?? 와 ?? 값은 각각 4.2213Å과 6.8665Å 이었으며 온도에 따른 에너지 밴드갭 Eg(T)의 값을 결정 하였다. 광전류 peak의 분석으로 부터 intrinsic 천이와 exciton A peak가 나타남을 알았다. Hall계수 측정으로 부터 mobility의 온도 의존성을 구했고 활성화 에너지 ?? 는 0.062eV임을 알았다. The Growth of ?? ?? single crystal platelet was carried out by sublimation method. Its size was about 0.02mm×15mm×19mm. It was verified that the crystals of CdS₁- ?? were single ones by x-ray diffrection using Laue method. The formula of Energy band gap ??(T) depending on the temperatures was studied. The intrinsic transition and the exciton A peak were investigated by the analysis of photocurrent peak. By the Hall effect experiment, the temperature dependence of the mobilit was researched, and the value of the activation energy ?? was 0.062eV.

CdSe 단결정에서 Cd Vacancy Defect가 Photoconductivity에 미치는 영향(Ⅱ)

신영진,김승곤,박병호,정태수,서영우,이재만,유평열,유기수 全北大學校 基礎科學硏究所 1991 基礎科學 Vol.14 No.2

CdSe 단결정을 진공 중에서 600℃로 1시간 동안, 공기 중에서 400℃로 30분 동안 열처리하여 광전류 스펙트럼을 가시영역에서 적외선 영역까지 측정하고 Cd 빈자리 V_Cd와 Se 빈자리 V_Se로 유효한 광전도도를 연구하였다. Van der Pauw 방법으로 Hall 효과를 측정하였다. Carrier 농도는 ∼10^17/㎤ 정도이고 이동도는 ∼3x10^2㎠/v·s 정도이다. 이동도를 온도의 함수로 측정하고 defect의 관점에서 고찰하였다. Two samples of CdSe single crystal underwent annealing, one in a vacuum at 600℃ for an hour the other in an air environment at 400℃ for a half hour. Photocurrent spectra from the samples were obtained covering a range of visible to infrared region. Effective photoconductivity was investigated in connection with the vacancies of Cd and Se. As a result of Hall effect measurements performed Van der Pauw technique on the sample we obtained 10^17/㎤ and 3x10^2㎠/v·s for carrier concentration and mobility respectively. Mobility measured as a function of temperature was discussed in terms of defect.

CdSe 단결정에서 Cd Vacancy Defect가 Photoconductivity에 미치는 영향(Ⅰ)

신영진,김승곤,박병호,정태수,서영우,이재만,유평열 全北大學校 基礎科學硏究所 1991 基礎科學 Vol.14 No.1

육방정의 CdSe를 적당한 크기로 잘라 Ga, Cd, Se 및 Cu 증기에서 각각 열처리 하였다. 이와 같이 열처리한 시료들의 광전류를 400nm에서 1800nm까지 온도의 함수로 측정하고 V_cd의 역할을 비교 연구하였다. Van der Pauw 방법을 사용해서 이동도를 온도의 함수로 측정하였다. 그결과 150 K에서 300 K까지 사이에서는 ∼T^(-3/2)에 따라 감소하고 30 K에서 150 K 사이는 이동도가 약간 증가의 경향임을 알게 되었다. A hexagonal CdSe crystal was cut into four portions, each to be annealed in a different vapor of Ga, Cd, Se or Cu at a temperature of 100℃, 750℃, 900℃, or 900℃, respectively. Photocurrents were measured as a function of temperature on the annealed samples in the wavelength range of 400 nm to 1800 nm. The role of V_Cd in the four samples was compared and studied. Mobility measurement was performed as a function of temperature using Van der Pauw's method. As a result of this, it was found that mobility decreases as T^(-3/2)in the temperature range of 150 K to 300 K, whereas having a slope of slight increase in the range of 30K to 150K.

CdSe 단결정에서 Cd Vacancy Defect가 Photoconductivity에 미치는 영향(II)

신영진,김승곤,민한기,정태수,서영우,박병호,이재만,유평열 순천대학교 기초과학연구소 1990 基礎科學硏究誌 Vol.1 No.-

육방정의 단결정 CdS를 같은 크기로 잘라 진공중과 공기중에서 각각 하나씩 열처리 하였다. 열처리된 시료의 광전류를 400㎚에서 1800㎚까지 측정하였다. 그 결과 적외선 소광효과로부터 모체의 결합인 이온화된 V_Cd 준위와 V_Se 준위를 알게 되었다. 온도에 따른 이동도를 Van der Pauw 방법으로 측정한 결과 150K에서 300K사이에서는 이동도가 polar 산란에 따라 감소하고 30K에서 120K사이에서는 piezoelectric 산란에 따라 감소함을 알게 되었다. A hexagonal CdS crystal was cut in half, each to be annealed either in a vacuum or air. Photocurrents were measures on the annealed samples in the wavelength range of 400㎚ to 1800㎚. From the IR quenching effect, energy levels of ionized V_Cd and V_Se due to native defect were identified. Mobility measurement as a function of temperature using van der Pauw's method shows that in the temperature range of 150K to 300K it deceases due to polar scattering, whereas in the range of 30K to 120K decreasing due to piezoelectric scattering.

Iodine을 촉매로 하여 화학적 수송방법으로 성장한 CdS 단결정의 전기-광학적 특성 연구(Ⅰ)

신영진,김영기,정태수,서영우,유기수,김택성,강석일,유평열 全北大學校 基礎科學硏究所 1991 基礎科學 Vol.14 No.2

Iodine을 촉매제로 하는 화학적 수송방법으로 성장한 CdS 단결정의 전기-광학적 특성을 연구하였다. 가시영역의 광전류 스펙트럼, 적외선소광 스펙트럼과 광발광 스펙트럼을 측정하여 defect로 고찰하였다. Van der Pauw 방법으로 측정한 Hall 효과로부터 이동도가 20K에서 100K 사이에서는 ∼T^(3/2)에 따라 증가하고 100K에서 실온 사이에서는 이동도가 ∼T^(-3/2)에 따라 감소함을 알게되었다. CdS single crystal grown by chemical vapor transport method using iodine as a transport ag?? were studied; The spectrum of photocurrent in visible range, Infrared quenching effects and photoluminescence were measured and studied in terms of defect. The result of Hall effect by Van der Pauw method was found that the mobility increased along to∼T^(3/2) from the temperature of 20K to 100K and decreased along to∼T^(3/2)from the temperature of 100K to 300K.