• 한국초전도ㆍ저온공학회논문지
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• 제25권3호
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• pp.22-27
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• 2023

Magnetic properties of MgB₂ superconducting powder were investigated. M(H), the magnetic field H dependence of magnetization M, was measured and analyzed using a PPMS instrument. The MgB₂ superconducting powder showed high critical current density J_c > ~ 10⁷ A/cm² and clean limit superconducting properties. The equilibrium magnetization M_eq properties of MgB₂ powders exhibiting various superconducting properties were studied. We find that the equilibrium magnetization M_eq(H) properties of MgB₂ powders showing conventional BCS properties deviate from the predictions of the standard local-London theory at temperatures below T = 19 K and are in good agreement with the generalized nonlocal-London theory. Nonlocal-London analysis was used to determine and analyze the nonlocal parameters. The temperature dependence of the London penetration depth values λ(T) was studied.

• 한국초전도ㆍ저온공학회논문지
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• 제25권3호
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• pp.28-33
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• 2023

Magnetic relaxation properties of pure MgB₂ powder samples and diluted water-treated MgB₂ powder samples were investigated. The magnetic field H-dependence, m(H), and the time t-dependence, m(t), of the magnetic moment m were measured and analyzed using the PPMS-VSM magnetometer equipment, respectively. The m(t) reduction rates of pure MgB₂ powder samples and diluted water-treated MgB₂ powder samples decreased to about 0.7 ~ 1.8% and 0.6 ~ 1.0% for about 7200 s, respectively, at temperature T = 15 K. The magnetic relaxation properties of the two types of MgB₂ powders were analyzed by calculating the magnetic relaxation rate S = -dln(M_irr)/dln(t) values according to Anderson-Kim theory. The magnetic relaxation ratio S values of the two types of MgB₂ powder samples were almost similar. As a result of the quantum creep effect, the constant magnetic relaxation rate S characteristic was confirmed at a temperature range of T = 10 K or less.

• 한국분말재료학회지
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• 제15권5호
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• pp.371-377
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• 2008

This paper deals with the phase analysis of $MgB_2$ bulk using spark plasma sintering process after ball milling. Mg and amorphous B powders were used as raw materials, and milled by planetary-mill for 9 hours at argon atmosphere. In order to confirm formation of $MgB_2$ phase, DTA and XRD were used. The milled powders were fabricated to $MgB_2$ bulk at the various temperatures by Spark Plasma Sintering. The fabricated $MgB_2$ bulk was evaluated with XRD, EDS, FE-SEM and PPMS. In the DTA result, reaction on formation of $MgB_2$ phase started at $340^{\circ}C$. This means that ball milling process improves reactivity on formation of $MgB_2$ phase. The $MgB_2$ MgO and FeB phases were characterized from XRD result. MgO and FeB were undesirable phases which affect formation of $MgB_2$ phase, and it's distribution could be confirmed from EDS mapping result. Spark Plasma Sintered sample for 5 min at $700^{\circ}C$ was relatively densified and it's density and transition temperature showing super conducting property were $1.87\;g/cm^3$ and 21K.

• 한국수소및신에너지학회논문집
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• 제25권6호
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• pp.594-601
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• 2014

Rare-earth (RE) nitrides can be used as magnetocaloric materials in low temperature. They exhibit ferromagnetism and have Curie temperature in the region from 6 to 70 K. In this study, Holmium nitride (HoN) nano particles were prepared through plasma arc discharge technique and their magnetocaloric properties were studied. Nitrogen gas ($N_2$) was employed as an active element for arc discharge between two electrodes maintained at a constant current. Also, it played an important role not only as a reducing agent but also as an inevitable source of excited nitrogen molecules and nitrogen ions for the formation of HoN phase. Partial pressure of $N_2$ was systematically varied from 0 to 28,000 Pa in order to obtain single phase of HoN with minimal impurities. Magnetic entropy change (${\Delta}S_m$) was calculated with data set measured by PPMS (Physical Property Measurement System). The as-synthesized HoN particles have shown a magnetic entropy change ${\Delta}S_m$) of 27.5 J/kgK in applied field of 50,000 Oe at 14.2 K thereby demonstrating its ability to be applied as an effective magnetic refrigerant towards the re-liquefaction of hydrogen.

• Journal of Nutrition and Health
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• 제15권4호
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• pp.258-267
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• 1982

This study was performed to investigate the effect of different levels of protein and iron in the diet upon Fe, Cu and Zn metabolism in rat during four weeks of growing period. Forty-five male weanling rats of Sprague-Dawley strain weighing $68.5{\pm}1.1g$ were divided into 9 groups and each group was given with one of the 9 different kinds of diets for four weeks. The three dietary protein levels used were 5, 20 and 40% and Fe levels 0, 35, and 350 ppms. The results obtained were summarized as following ; 1) Food intake and body weight gain in 20%(SP) and 40%(HP) dietary protein groups tended to be significantly higher than 5%(LP) protein groups. Protein efficiency ratio (PER) was higher in LP groups than in HP and SP groups. With dietary Fe levels, there were no significant differences among groups in food intake, body weight gain, and PER. 2) In LP groups, the Fe concentrations in liver, kidney, and hind limb muscle were higher than in SP and HP groups. Regarding with dietary protein levels, the liver Cu concentrations in LP groups were slightly higher, but the liver Zn concentrations were lower in LP groups. The Fe concentrations in liver and kidney tended to decrease with decrease in dietary Fe levels, but Cu and Zn concentrations showed no consistent tendency with dietary Fe levels. 3) The Fe, Cu and Zn concentrations in serum were not different from dietary treatments except that the serum Fe concentrations increased slightly in LP groups. 4) The Fe and Cu concentrations in urine tended to be higher in HP groups. Fecal Cu and Zn concentrations showed no significant differences in dietary protein or Fe levels, but the Fe concentrations tended to increase with increase in dietary Fe levels.

• 청정기술
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• 제3권1호
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• pp.9-26
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• 1997

공해 유발형 산업기술/제품의 폐기 요구 점증, 배출된 오염 물질 제거를 위한 후처리기술(EOP 기술) 활용의 한계, Green Round에 의한 국제 무역 규제 및 환경 부담금 문제 가시화(PPMs 규제) 및 지속 가능한 환경조화형 산업기술 확보(Sustainable Development)요구 등에 능동적 대처를 위해 산업활동에서의 환경오염 발생을 원천 억제 또는 제거하는 미래형 청정기술개발에 대한 요구가 급증하고 있다. 미래청정기술은 산업활동에서의 환경오염 발생을 원천 억제 또는 제거하는 미래형 환경오염 방지 기술로 정의될 수 있다. 선진국에 비해 청정기술 개발이 늦은 국내 현실에서 청정기술의 예속화를 피하고 기술 자립을 위해서는 원천 기술의 확보가 필수 불가결하며, 이의 달성을 위한 효과적인 청정기술의 개발 전략이 요구된다. 현재 국내 외에서 진행 중인 연구개발 프로그램을 비교 분석하고, 원천 기술인 미래형 청정기술의 성격을 규명한 뒤 효과적인 연구 수행을 위한 전략을 소개한다.

• 한국초전도ㆍ저온공학회논문지
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• 제15권3호
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• pp.5-8
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• 2013

We have studied Hall effect for potassium (K)-doped $BaFe_2As_2$ superconducting thin films by analyzing the relation between the longitudinal resistivity (${\rho}_{xx}$) and the Hall resistivity (${\rho}_{xy}$). The thin films used in this study were fabricated on $Al_2O_3$ (000l) substrates by using an ex-situ pulsed laser deposition (PLD) technique under a high-vacuum condition of ~$10^{-6}$ Torr. The samples showed the high superconducting transition temperatures ($T_c$) of ~ 40 K. The ${\rho}_{xx}$ and the ${\rho}_{xy}$ for K-doped $BaFe_2As_2$ thin films were measured by using a physical property measurement system (PPMS) with a temperature sweep (T-sweep) mode at an applied current density of $100A/cm^2$ and at magnetic fields from 0 up to 9 T. We report the T-sweep results of the ${\rho}_{xx}$and the ${\rho}_{xy}$ to investigate Hall scaling behavior on the basis of the relation of ${\rho}_{xy}={A{\rho}_{xx}}^{\beta}$. The ${\beta}$ values are $3.0{\pm}0.2$ in the c-axis-oriented K-doped $BaFe_2As_2$ thin films, whereas the thin films with various oriented-directions like a polycrystal showed slightly lower ${\beta}$ than that of c-axis-oriented thin films. Interestingly, the ${\beta}$ value is decreased with increasing magnetic fields.

• Progress in Superconductivity
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• 제10권1호
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• pp.29-34
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• 2008

Magnesium diboride ($MgB_2$) is an inexpensive and simple superconductor. This material was first synthesized and its structure confirmed in 1953 but its superconducting properties were not discovered until 2001 when they caused great excitement. In this study, superconducting $MgB_2$ thin films on the r-$Al_{2}O_3$ substrates have been grown by the combination of radio frequency magnetron sputtering of B and thermal evaporation of Mg. The deposition conditions were varied by changing deposition rate. Before the co-deposition of Mg and B, the deposition rates of each element have been measured separately. The $MgB_2$ layers had 400nm in thickness and superconducting transition temperatures have been measured around $\sim$38.6K. Superconducting properties have been measured by PPMS, XRD, and SEM.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.436-436
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• 2011

Recently, spintronic devices with submicron structures are widely investigated to take advantage of their unique micromagnetic properties. In this work, we study the temperature dependence of exchange bias in bilayer anti-dot arrays made by depositing Co (40 nm)/Ni (5 nm) ferromagnetic bilayer on Si substrate to form anti-dot arrays with a diameter $1{\mu}m$. The anti-dot patterning was done only for the upper Co layer, while the Ni underlayer was kept unperforated. The temperature dependences of magnetoresistance (MR) and exchange bias were studied along magnetic easy and hard axes. The in-plane MR measurements were performed using a physical-property measurement system (PPMS ; Quantum Design Inc.) at various temperatures. The standard in-line four-point probe configuration was used for the electrical contacts. As temperature was varied, the MR data were obtained in which in-plane field (H=3 kOe) was applied in the directions along the hard and the easy axes with respect to the lattice plane. The temperature dependences of magnetic anisotropy and exchange bias were also studied along the magnetic easy and hard axes. As temperature decreases, the single peak splits into two peaks. While no exchange bias was observed along the magnetic easy axis, the exchange bias field steadily increased with decreasing temperature along the magnetic hard axis. These results were interpreted in connection with the magnetic anisotropy and the effect of the anti-dots in pinning domain wall motion along the respective direction.

• 한국초전도ㆍ저온공학회논문지
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• 제7권2호
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• pp.7-10
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• 2005

The magnetic properties of a series of both annealed (biaxially textured) and as-rolled (non-textured) Ni-xW alloy tapes with compositions x = 0,1,3, and 5 at.$\%$, were studied. Characterization methods included XRD analyses to investigate the biaxial cube texturing of the annealed Ni-W alloy tapes and studies of the magnetization M for both annealed and as-rolled Ni-W alloy tapes. Both the isothermal mass magnetizations M(H) of a series of samples at different fixed temperatures and M(T) in fixed field, employing a PPMS-9 (Quantum Design), were measured. The Ni-W alloys have shown much reduced ferromagnetism as W-content x increases. Both the saturation magnetization Msat and Curie temperature Tc decrease linearly with W-content x, and both Msat and Tc go to zero at critical concentration of Xc - 9.50 at. $\%$ W.