• 한국자기학회지
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• 제23권2호
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• pp.54-61
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• 2013

강자성체는 자구들의 상호작용으로 인해 잔류 자화가 남게 되는데, 전자전기 산업 및 국방 피탐지 분야에서는 이러한 잔류 자화량을 정밀하게 0으로 만드는 탈자기법이 요구된다. 하지만 현재 수행되는 탈자기법들은 경험과 실험에 의존한 방법들로, 새로운 재료의 개발에 따른 효율적인 탈자를 위해서는 강자성체의 히스테리시스 곡선을 반영한 탈자기법이 필요하다. 본 논문에서는 자성체의 물성적인 성질을 기반으로 정립된 Preisach 모델링 기법을 이용하여 Anhysteretic Deperm, Deperm-ME, Flash-Deperm에 따른 2차원 유한요소해석을 수행하였다. 탈자 전류에 의한 자기이력궤적의 분석을 통해 강자성체의 히스테리시스 곡선과 탈자 변수의 관계를 고찰하였으며, 이로써 탈자에 효율적인 전류 감소 형태를 제시하였다.

• Current Applied Physics
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• 제18권11호
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• pp.1248-1254
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• 2018

Magnetization versus temperature and magnetic-field measurements, M(T, $H_a$), have been carried out to study the magnetic and critical properties of polycrystalline $La_{1-x}Ba_xCoO_3$ (x = 0.3 and 0.5) cobaltites. These compounds with the density of ${\sim}6.2g/cm^3$ crystallized in the $R{\bar{3}}c$ rhombohedral and $Pm{\bar{3}}m$ cubic structures, respectively. With an applied field $H_a=200Oe$, M(T) data have revealed that the samples with x = 0.3 and 0.5 exhibit the ferromagnetic-paramagnetic (FM-PM) phase transition at the Curie temperature points $T_C=202$ and 157 K, respectively. At 4.2 K, the saturation magnetization ($M_{sat}$) decreases from 35.9 emu/g for x = 0.3-26.1 emu/g for x = 0.5. Particularly, the critical-behavior analyses in the vicinity of $T_C$ reveal all samples undergoing a second-order phase transition, with critical exponent values (${\beta}=0.328$ and ${\gamma}=1.251$ for x = 0.3, and ${\beta}=0.331$ and ${\gamma}=1.246$ for x = 0.5) close to those expected for the 3D Ising model. This proves short-range magnetic order existing in $La_{1-x}Ba_xCoO_3$. We believe that magnetic inhomogeneities due to the mixture of hole-rich FM regions (confined in the trivalent-cobalt hole-poor anti-FM matrix) and uniaxial anisotropy prevent long-range order in $La_{1-x}Ba_xCoO_3$.

• 한국초전도ㆍ저온공학회논문지
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• 제24권3호
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• pp.41-46
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• 2022

The superconducting properties of high temperature superconducting (HTS) GdBCO coated conductor (CC) tape (Ag/GdBCO/Buffer-layers/Stainless Steel) were investigated, specifically a series of samples prepared by vacuum heat treatment (200℃ to 600℃), using a Quantum Design PPMS-14. The critical current density J_c value was obtained by applying the modified Bean model to the irreversible magnetization ∆M_irr(H) data which was estimated from the magnetization M(H) loop. The reduction rates of lnJ_c and T_c values according to the increase of the vacuum annealing temperature T_an were d(lnJ_c)/dT_an = - 0.016 A/(cm²∙℃) and dT_c/dT_an = - 0.24, respectively. We examined the effect of recovery temperature T_re (475℃ to 700℃) and recovery duration time t (0.5 h to 24 h) on the restoration of previously completely lost superconductivity in samples that subsequently received heat treatment in an O₂ gas flow space. All samples were fully restored to superconductivity by heat treatment in an O₂ gas flow space. The recovery temperatures T_re (475℃ to 700℃) and recovery duration times t (0.5 h to 24 h) were both independent of the superconductivity recovery characteristics.

• 한국자기학회지
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• 제23권1호
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• pp.12-17
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• 2013

금속 분말 니켈(Ni)을 HCl용액에 용해시킨 후 $H_3BO_3$, KOH을 첨가하여 Chloride 도금용액을 제조 후 Ni plate 기판에 도금하였다. 도금두께는 $3{\mu}m$로 일정하게 유지하였다. 전류밀도를 $1{\sim}30mA/cm^2$ 변화를 준 결과 전류밀도를 증가시킬수록 Ni 후막표면이 거칠어졌다. $25mA/cm^2$와 $30mA/cm^2$에서는 균열된 표면형상을 관찰하였다. 또한 XRD patterns 변화를 관찰한 결과 전류밀도가 증가할수록 FCC(111)과 FCC(220) 및 FCC(311)상의 강도는 증가한 반면 FCC(200)상의 강도는 감소하는 것을 관찰하였다. 전기도금된 Ni의 수평 및 수직 자화 값을 측정하였는데 기판에 의한 수평자화 값이 크게 나왔고, 코팅층 두께가 증가할수록 수직자화 값이 커지는 것을 확인하였다.

• 조명전기설비학회논문지
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• 제28권9호
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• pp.67-72
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• 2014

Inflow or outflow from the water treatment plant and the sewage water has potential energy. If this potential energy can be converted into electrical energy by water turbine generator, it can help to save energy because of the high capacity utilization. So recently, micro hydro power plant is reviewed in the water treatment facility. If generation capacity is low, induction generator is primarily used. If output capacity is low, generated power is supplied to the inside load. Induction generator can cause voltage drop by the inrush current at a start-up and requires reactive power for magnetization. In this study, we analyzed the flow of power and voltage variation against inrush current that occurs when the induction generator starts under the terms that loads of linear and non-linear of the water purification plant are used. Analysis results are that the voltage drop is within an allowable range and the power factor is slightly reduced by the need of reactive power.

• 한국자기학회지
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• 제3권1호
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• pp.29-33
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• 1993

$1{\times}10^{-6}$Torr의 진공에서 열저항 가열식 진공증착 방법으로 제작한 $Permalloy/Al_{2}O_{3}/Co$ 강자성 터널집합의 자기저항 효과를 조사하였다. 이 논문에서는 제작한 강자성 터널접합 시료의 전류-전압 특성과 자기 valve 효과를 측정하고, 시료진동형자기계로 측 정한 자기이력곡선을 통하여 터널저항의 히스테리시스성 자장 의존성을 조사하였다. 터널링은 전류-전압 특성을 측정함으로써 확인 되어진다. 자기저항의 히스테리시스 곡선은 자화의 히스테 리시스 곡선과 잘 대응한다. 측정한 자기저항비 ${\Delta}R/R$은 실온에서 약 0.6% 였다.

• Progress in Superconductivity
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• 제3권2호
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• pp.213-217
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• 2002

We have fabricated successfully single-filament composite $MgB_2$/SUS tapes, as an ultrarobust conductor type. The fabrication of the $MgB_2$/SUS tapes was performed by power-in-tube (PIT) process such as swaging and cold rolling. The critical transition temperatures $T_{c}$~38.5 K and ~36 K were observed for the sintered and the nonsintered $MgB_2$/SUS tapes, respectively In addition, the isothermal magnetization M(H) of the sintered $MgB_2$/SUS tapes was measured at temperatures T (between 5 and 50 K) in fields up to 6 T, employing a PPMS-9 (Quantum Design). The persistent current density (J$T_{P}$) values were obtained from the M(H) data, using Bean model, fur the sintered $MgB_2$/SUS tapes. The estimated values were higher than ~ 6$\times$ $10^{5}$ $A/\textrm{cm}^2$ at T = 5 K, with H : 0 G. We also investigated the cross section of the sintered tapes, by using SEM and EDX. An evidence of weak reaction on boundary between $MgB_2$ and SUS tube is found in the SEM and EDX.X.X.X.

• Progress in Superconductivity
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• 제3권1호
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• pp.45-48
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• 2001

We have fabricated $MgB_2$thin films on (1 1 02)$ A1_2$$O_3$substrates by using a two-step method. Amorphous B thin films were deposited by a pulsed laser deposition technique and sintered in Mg vapor at various temperatures from 800 to $950^{\circ}C$. Superconducting properties of the thin films were investigated by temperature dependences of magnetization and critical current density. Structural studies were carried out by an x-ray diffraction and a scanning electron microscope. The films fabricated at $900^{\circ}C$ showed the highest transition temperature of 39 K and critical current density of ~$10^{7}$ A/$\textrm{cm}^2$ at 15 K.

• 한국초전도ㆍ저온공학회논문지
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• 제17권1호
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• pp.14-16
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• 2015

Due to the considerable development of the technology of second generation high-temperature superconductors and a significant improvement in their mechanical and transport properties in the last few years it is possible to use HTS tapes in the magnetic levitation systems. The advantages of tapes on a metal substrate as compared with bulk YBCO material primarily in the strength, and the possibility of optimizing the convenience of manufacturing elements of levitation systems. In the present report presents the results of the magnetic levitation force measurements between the stack of HTS tapes containing $n=2{\div}200$ of tapes $12mm{\times}12mm$ and NdFeB permanent magnet in the FC and ZFC regimes. It was found a non- linear dependence of the levitation force from the height of the array of stack in both modes: linear growth at small thickness gives way to flattening and constant at large number of tapes in the stack. Established that the levitation force of stacks comparable to that of bulk samples. The numerical calculations using finite element method showed that without the screening of the applied field the levitation force of the bulk superconductor and the layered superconductor stack with a critical current of tapes increased by the filling factor is exactly the same, and taking into account the screening force slightly different.

• 한국초전도ㆍ저온공학회논문지
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• 제16권4호
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• pp.57-61
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• 2014

Output fluctuation which is generated in wind power farm can hinder stability of total power system. The electric energy storage (EES) reduces unstable output, and superconducting magnetic energy storage (SMES) of various EESs has the proper performance for output compensation of wind power farm since it charges and discharges large scale power quickly with high efficiency. However, because of the change of current within SMES, the electromagnetic losses occur in the process of output compensation. In this paper, the thermal effect of the losses that occur in SMES system while compensating in wind power farm is analyzed. The output analysis of wind power farm is processed by numerical analysis, and the losses of SMES system is analyzed by 3D finite element analysis (FEA) simulation tool.