• 한국자기학회지
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• 제6권1호
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• pp.1-6
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• 1996

MR/TbCo 박막 계면의 자기교환 결합의 특성을 시뮬레이션 하기 위해서 박막내에 존재 하는 자기 에너지를 최소화 하여 자화의 방향을 구하였다. 수치해석 방법으로는 Newton법과 Gauss-Seidel 방법이 이용되었다. TbCo의 이방성 상수에 비례적으로 자기 이력곡선의 폭이 변하고, TbCo 천이영역의 두께가 얇을수록 자기이력곡선이 벌어지지 않았다. 특히 TbCo 천이영역의 두께가 $400\;\AA$ 일때 단일 곡선(보자력 10 Oe 이하)을 보였다. 또한 계면 교환 결합상수가 작을수록 천이영역의 두께가 얇을 때와 비슷한 곡선을 보였고, 완전히 결합된 상태의 1/100 정도 일때, 단일 곡선을 보였다. 제작한 박막의 자기이력곡선과 비교하여 계면교환 결합상수를 추정할 수 있었다.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1703-1707
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• 2018

Ferromagnetic ${\tau}-phase$ $Mn_{54}Al_{46}C_{2.44}$ particles were synthesized, and its composites with commercial $Sm_2Fe_{17}N_3$ and synthesized $Fe_{65}Co_{35}$ powders were fabricated. Smaller grain size than the single domain size of the $Mn_{54}Al_{46}C_{2.44}$ without obvious grain boundaries and secondary phases is the origin for the low intrinsic coercivity. It was confirmed that the magnetic properties of the $Mn_{54}Al_{46}C_{2.44}$ can be enhanced by magnetic exchange coupling with the hard magnetic $Sm_2Fe_{17}N_3$ and soft magnetic $Fe_{65}Co_{35}$. The high degrees of the exchange coupling were verified by calculating first derivative curves. Thermo-magnetic stabilities of the composites from 100 to 400 K were measured and compared. It was demonstrated that the $Mn_{54}Al_{46}C_{2.44}$ based composites containing $Sm_2Fe_{17}N_3$ and $Fe_{65}Co_{35}$ could be promising candidates for future permanent magnetic materials with the proper control of purity, magnetic properties, etc.

• Journal of Magnetics
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• 제20권4호
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• pp.336-341
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• 2015

MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-x)NdFeB/xMnBi, x = 20, 30, 40, 50, and 80 wt%. The as-milled powder mixtures of Nd-Fe-B and MnBi were aligned in a magnetic field of 18 kOe and warm-compacted to anisotropic and dense bulk magnets at 573 K by 2,000 psi for 10 min. The magnetic ordering of two hard phase components strengthened by the exchange coupling enhanced the Curie temperature ($T_c$) of the magnet in comparison to that of the powder mixture sample. The prepared hybrid magnets were highly anisotropic with the ratio $M_r/M_s$ > 0.8. The exchange coupling was high, and the coercivity $_iH_c$ of the magnets was ~11-13 kOe. The maximum value of the energy product $(BH)_{max}$ was 8.4 MGOe for the magnet with x = 30%. The preparation of MnBi alloys and hybrid magnets are discussed in details.

• Journal of Power Electronics
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• 제16권5호
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• pp.1639-1649
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• 2016

This paper presents a family of soft-switching DC-DC converters with a simple auxiliary circuit consisting of a coupled winding and a pair of auxiliary switch and diode. The auxiliary circuit is activated in a short interval and thus the circulating conduction losses are small. With the auxiliary circuit, zero-voltage-switching (ZVS) and zero-current-switching are achieved for the main and auxiliary switches respectively, over wide input voltage range and load variation. In addition, the reverse-recovery problem of diodes is significantly alleviated because of the leakage inductor. Furthermore, the coupled inductor simultaneously serves as the main and auxiliary inductors, contributing to reduced magnetic component in comparison with the conventional zero-voltage-transition (ZVT) converters. Experimental results based on a 500 W prototype buck circuit validate the advantages and effectiveness of the proposed magnetic coupling ZVS converter.

• Journal of Magnetics
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• 제18권2호
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• pp.130-134
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• 2013

Most electrical machines like motor, generator and transformer are symmetric in terms of magnetic field distribution and mechanical structure. In order to analyze these problems effectively, many coupling techniques have been introduced. This paper deals with a coupling scheme for open boundary problem of symmetric and periodic structure. It couples an analytical solution of Fourier series expansion with the standard finite element method. The analytical solution is derived for the magnetic field in the outside of the boundary, and the finite element method is for the magnetic field in the inside with source current and magnetic materials. The main advantage of the proposed method is that it retains sparsity and symmetry of system matrix like the standard FEM and it can also be easily applied to symmetric and periodic problems. Also, unknowns of finite elements at the boundary are coupled with Fourier series coefficients. The boundary conditions are used to derive a coupled system equation expressed in matrix form. The proposed algorithm is validated using a test model of a bush bar for the power supply. And the each result is compared with analytical solution respectively.

• 한국자기공명학회논문지
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• 제1권2호
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• pp.95-102
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• 1997

Deuterium quadrupole coupling constant (e2qzzQ/h) of ($\mu$3-C2H)[Co(CO)3]3 was determined by using solid-state deuterium MAS NMR spectroscopy. The small quadrupole coupling constant of bridging methyne unit relative to sp-acethylene in propyne is discussed in terms of the C-H bond length and the negative charge on the carbon.

• 한국자기공명학회논문지
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• 제8권2호
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• pp.70-76
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• 2004

ZORA-DFT calculations of $^{11}$B EFG (electric field gradient) tensors for lithium borates, LiB$_3O_5$ (LBO) and Li$_2B_4O_7$ (LTB), were performed. The calculated values of 11B quadrupole coupling constant and asymmetry parameter are in good agreement with the experimental values. The sign of the quadrupole coupling constant for the tetrahedral boron site was deduced from the distortion from the ideal tetrahedral symmetry.

• Bulletin of the Korean Chemical Society
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• 제4권1호
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• pp.48-54
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• 1983

A magnetic nucleus located on an internal rotor can interact with magnetic fields arising from end-over-end molecular rotation as well as internal rotation. In this paper the expressions for spin-rotational relaxation times, $T_{1.SR}\;and\;T_{2.SR}$, are derived for such nucleus with the anisotropy of molecular rotation explicitly taken into consideration. The derived expressions are shown to be composed of two parts, the contribution from spin-overall-rotation coupling and that from spin-internal-rotation coupling. Some remarks on the use of derived expressions are also provided.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2007년도 추계학술대회 논문집
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• pp.213-216
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• 2007

The computer simulation for the fault current limiting characteristics of the superconducting fault current limiter (SFCL) using the magnetic coupling of two coils was performed. The magnetic fluxes generated from two coils were canceled out during a normal time. However, the resistance generation of high-$T_c$ superconducting (HTSC) element after a fault occurrence keeps up the magnetic fluxes of two coils and contributes to the fault current limiting operation. Through the computer simulation for the fault current limiting characteristics based on its electrical equivalent circuit, its operational current and the limiting impedance could be improved by adjusting the inductance ratio between two coils.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.742-743
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• 2015

Magnetic couplings are do not require any mechanical contact with the power transmitted to the secondary side according to the primary side. For this reason, well-suited for isolated systems such as vacuums or high pressure. So, this paper presents the force characteristic analysis of the permanent magnet (PM) linear coupling with vertical magnetized using an analytical magnetic field calculations. Based on the definition of governing equations and magnetic vector potential, we obtained the analytical solutions according to the boundary condition for each of the regions. Also, we derived from the force generated in the permanent magnet surface using the Maxwell stress tensor. The analytical results are proved the validity by comparing to the finite element method (FEM).