• Journal of Magnetics
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• v.20 no.3
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• pp.201-206
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• 2015

Using the Vienna ab initio simulation package (VASP) incorporating both semiempirical and nonlocal van der Waals interaction, the structural, adsorption, and magnetic properties of Ni/BN/Co systems were investigated. We proposed that the relative spin direction of Ni and Co magnets can be easily tuned, because the total energy difference between ferromagnetic (FM) and antiferromagnetic (AFM) states is small. Despite this feature, very interestingly, both Ni and Co layers manifest half-metallic state, whereas the spacer BN layer becomes weak metal for one monolayer (ML) thickness and an insulating barrier for two ML thicknesses. The half-metallic behavior of the magnetic layers seems very robust, because it is independent of the magnetic coupling between Ni and Co. This finding indicates that the Ni/BN/Co system can be used as a potential candidate for tunneling magnetoresistance system.

• Progress in Superconductivity and Cryogenics
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• v.18 no.1
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• pp.33-36
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• 2016

Suppression of the superconducting transition temperature ($T_c$) of NbN thin films in superconductor/ferromagnet multilayers has been investigated. Both superconducting NbN and ferromagnetic FeN layers were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an $Ar-N_2$ gas mixture. The thickness of FeN films was fixed at 20 nm, while the thickness of NbN films was varied from 3 nm to 90 nm. $T_c$ suppression was clearly observed in NbN layers up to 70 nm thickness when NbN layer was in proximity with FeN layer. For a given thickness of NbN layer, the magnitude of $T_c$ suppression was increased in the order of Si/FeN/NbN, Si/NbN/FeN, and Si/FeN/NbN/FeN structure. This result can be used to design a spin switch whose operation is based on the proximity effect between superconducting and ferromagnetic layers.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.180.1-180.1
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• 2014

이중층 그래핀(graphene)의 한쪽 표면에 전하를 주입하면 반전 대칭(inversion symmetry)이 깨지며 라만-비활성 진동모드가 활성화되면서 라만 G-봉우리 부근에 새로운 봉우리가 나타난다고 알려져 있다. 삼중층 그래핀은 그래핀이 적층되는 방식에 따라 ABA (Bernal), ABC (rhombohedral) 그래핀으로 나뉘며, ABC 그래핀은 ABA와는 달리 반전 대칭성을 가지고 있다. 본 연구에서는 화학적인 방법을 이용하여 ABC 그래핀의 반전 대칭을 제어하고 그에 따른 라만 스펙트럼의 변화를 탐구하였다. ABA 그래핀과는 달리 이중층 그래핀과 ABC 그래핀에서는 저진공 열처리 또는 요오드 흡착반응을 한 후에 G-봉우리 부근에서 새로운 봉우리가 나타나는 것을 관찰하였고, 전하밀도 정도가 증가 할수록 G-봉우리와 새로운 봉우리의 위치 차이는 증가하는 것을 관찰하였다. 물과 메탄올에 의한 세척 반응으로부터 열처리는 복층 그래핀과 기판 계면에 그리고 요오드 흡착은 그래핀의 상단표면에 잉여 전하를 유발하여 반전 대칭을 깨트린다는 사실을 확인하였다. 또한 G-봉우리와 새로운 봉우리의 진동수 차이가 반전 대칭을 유발한 전하밀도의 그래디언트에 대한 척도가 될 가능성을 제시하였다.

• Progress in Superconductivity
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• v.4 no.1
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• pp.37-41
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• 2002

In this work. we have designed two different kinds of Rapid Single Flux Quantum (RSFQ) OR-gates. One was based on the already developed RSFQ cells and the other was aimed to develop a more compact version. In the first circuit, we used a combination of two D Flip-Flops and a merger and in the other circuit we used a combination of RS Flip-Flops and Confluence Buffer. We tested the circuit performance by using the simulation tools, Xic and Wrspice. We obtained the operation margins of the circuit elements by a margin calculation program, and we obtained the minimum operation margins of $\pm$30%. The circuits were laid out, aimed to fabricate by using the existing KRISS Nb process. KRISS Nb process includes the $Nb／Al_2$$O_3$／Nb trilayer fabricated by DC magnetron sputtering and the reactive ion etching technique for the definition of the features. The major tools used in the layouts were Xic and L-meter.

• Progress in Superconductivity and Cryogenics
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• v.16 no.4
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• pp.17-20
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• 2014

We have investigated the effect of temperature and bias current on the stability of the inverse spin-switch effect in Permalloy(Py)/Nb/Permalloy pseudo spin-valves. The inverse spin-switch operates between two orientations of the ferromagnetic moments of Py layers; parallel (ON) and antiparallel-domain (OFF) state. Measuring time scans of the resistance changes between the ON and OFF state, ${\Delta}R_{ON-OFF}$, while alternating magnetic fields between the two states at various temperatures and bias currents, revealed that enhancement of ${\Delta}R_{ON-OFF}$ is a key factor to achieve successful operation of superconducting spin switch.

• Fibers and Polymers
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• v.7 no.3
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• pp.217-222
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• 2006

Propargyl alcohol was coupled to 2,4-hexadiyne-1,6-diol (HDD) and crystallized in the process of ultraviolet irradiation-induced topochemical polymerization. The HDD polymer crystals were used as one component in the fabrication of organic photovoltaic cells, in combination with fullerene as the electron acceptor. The various structures of the produced photovoltaic cells included bilayer, trilayer, and bulk heterojunction structures. Their photovoltaic properties were analyzed in relation to crystal structure, electrochemical properties, and band structure of the HOD polydiacetylene polymers.

• Journal of Magnetics
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• v.5 no.3
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• pp.76-80
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• 2000

Soft x-ray standing waves produced by a multilayer interference substrate add depth-sensitivity to magnetic circular dichroism to resolve changes in Co magnetism across a 10${\AA}$ distance from the Co center to the Co-Pd interface of a Pd/Co/Pd trilayer having in-plane magnetization. Large enhancements of in-plane orbital and spin magnetic moments, as well as the number of d holes, are strongly localized in a thin interface layer. These results provide new insight into the phenomenon of magnetic anisotropy at buried interfaces, and suggest a broad applicability of such standing wave measurements to interface magnetism studies.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.123-126
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• 2003

RSFQ (Rapid Single Flux Quantum) circuits are used in many practical applications. RSFQ DFFC (Delay Flip-Flop with complementary outputs) circuits can be used in a RAM, an ALU (Arithmetic Logic Unit), a microprocessor, and many communication devices. A DFFC circuit has one input, one switch input, and two outputs (output l and output 2). DFFC circuit functions in such way that output 1 follows the input and output 2 is the complement of the input when the switch input is "0." However, when there is a switch input "1."the opposite output signals are generated. In this work, we have designed an RSFQ DFFC circuit based on 1 ㎄/$\textrm{cm}^2$ niobium trilayer technology. As circuit design tools, we used Xic, WRspice, and Lmeter After circuit optimization, we could obtain the bias current margins of the DFFC circuit to be above 32％.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.207-216
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• 2000

Soft x-ray standing waves produced by a multilayer interference substrate add depth-sensitivity to magnetic circular dichroism to resolve changes in Co magnetism across a 10 ${\AA}$ distance from the Co center to the Co-Pd interface of a Pd/Co/Pd trilayer having in-plane magnetization. Large enhancements of in-plane orbital and spin magnetic moments, as well as the number of d holes, are strongly localized in thin interface layer. These results provide new insight into the phenomenon of magnetic anisotropy at buried interfaces, and suggest a broad applicability of such standing wave measurements to interface magnetism studies.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1256-1258
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• 1993

Optical data storage offer high density storage and archival storage capability. In this study, we selected the ablation mechanism-one of an irreversible recording system-using the antireflection trilayer(ART) structure. Optical recording medium is a $(Te_{86}Se_{14})_{50}Bi_{50}$ thin films. Actually, ART structure is fabricated and compared to monolayer structure. ART structure leads to the reduction of recording power as well as an increase in the effciency compared to the monolayer structure.