Hyun‐Woo Lee

Pohang University of Science and Technology

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Kyung‐Jin Lee

Korea Advanced Institute of Science and Technology

Mutsuo Nakaoka

University of Malaya

Dongwook Go

Johannes Gutenberg University Mainz

Kyoung‐Whan Kim

Korea Institute of Science and Technology

Kwang‐Ho Kwon

Korea University

Daegeun Jo

Pohang University of Science and Technology

Jisu Ryu

University of Colorado Boulder

Khairy Fathy

Kyungnam University

Eiji Hiraki

Okayama University

Kab‐Jin Kim

Korea Advanced Institute of Science and Technology

Cooperative Institutions

Seoul National University

214

Korea University

203

Korea Advanced Institute of Science and Technology

153

Yonsei University

149

Samsung (South Korea)

149

Pohang University of Science and Technology

146

Sungkyunkwan University

115

Korea Institute of Science and Technology

111

Hanyang University

104

Government of the Republic of Korea

102

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Surface Modification of Polypropylene Separators in Lithium-Ion Batteries Using Inductively Coupled Plasma Treatment

Journal of Nanoscience and Nanotechnology (2014)

Jin-Young Son Mun-Seog Kim Hyun‐Woo Lee Jong‐Sung Yu Kwang‐Ho Kwon

We describe herein an improvement in the surface wettability of plasma-treated separators for use in lithium-ion batteries. We treated the separators with an O2/Ar inductively coupled plasma to increase their surface energy. The plasma treatment on the separator and plasma diagnostic experiments were performed in an inductively coupled plasma (ICP) reactor. The fraction of Ar in the O2/Ar plasma was changed from 0% to 100%. The plasma diagnostics were performed using optical emission spectroscopy and a double Langmuir probe. To confirm the morphological change of the separator membrane by the plasma treatment, we used the scanning electron microscopy. The surface energy measurements were performed using the drop method. We found that the plasma treatment transformed the separator from a hydrophobic membrane to a hydrophilic one, thereby achieving high separator wettability. After the treatment of the separators with O2/Ar plasma, the batteries exhibited better cycle performance and rate capacity than those employing the untreated ones.

Separator (oil production)

Surface Modification

Langmuir Probe

10.1166/jnn.2014.10119

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Citations (8)

Perpendicular Spin-transfer Torque in Asymmetric Magnetic Tunnel Junctions: Material Parameter Dependence

Journal of the Korean Magnetics Society (2011)

Jae-Ho Han Hyun‐Woo Lee

스핀전달토크는 나노구조에서 자성상태를 제어하는데 유용한 수단이다. 자기터널접합에서 스핀전달토크는 자성물질층의 자화가 이루는 평면에 평행한 성분과 수직인 성분으로 나눌 수 있다. 이중 평행한 성분의 스핀전달토크의 성질은 상당히 잘 알려져 있으나, 수직인 성분의 스핀전달토크의 성질에 대해서는 여전히 이견이 많다. 비대칭 자기터널접합에서의 최근 실험에서, 수직전달토크의 전압 의존성이 전압의 이차항 성분뿐만 아니라 일차항 성분도 가짐을 보고하였다. 하지만 물질 변수에 대한 의존성은 여전히 잘 알려지지 않았다. 이 논문에서는 비대칭 자기터널접합에서의 스핀전달토크의 전압의존성을, 강자성층의 스핀 갈라짐 에너지와 일함수의 차이, 그리고 페르미 에너지를 변화시켜 가면서 체계적인 조사를 하였다. Spin-transfer torque is a useful tool to control the magnetic state in nanostructures. In magnetic tunnel junctions, the spin-transfer torque has two components, the in-plane spin torque and the perpendicular spin torque. While properties of the in-plane spin-transfer torque are relatively well understood, properties of the perpendicular spin-transfer torque still remain controversial. A recent experiment demonstrated that in asymmetric magnetic tunnel junctions, the bias voltage dependence of the perpendicular spin-transfer torque contains both linear and quadratic terms in the bias. However it still remains unexplored how the bias voltage dependence changes as a function of material parameters. In this paper, we systematically investigate the perpendicular spin-transfer torque in asymmetric magnetic tunnel junction by varying spin splitting energy, work function difference, and Fermi energy of the ferromagnetic metal leads.

Spin-transfer torque

Tunnel magnetoresistance

Biasing

10.4283/jkms.2011.21.2.052

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Orbitronics: Mechanism of Orbital Current Generation and Dynamics

Physics and High Technology (2020)

Dongwook Go Hyun‐Woo Lee

The orbital degree of freedom is often considered to be quenched in solids due to the potential of the crystal field. In contrast to such expectation, we showed recently that the orbital current can be electrically generated despite orbital quenching in equilibrium, leading to a phenomenon called the orbital Hall effect. In this article, we provide a pedagogical introduction to the concept of an orbital current in solids and the mechanism underlying the orbital Hall effect. We also discuss the relation between the orbital Hall effect and the spin Hall effect, as well as a way to utilize the orbital current in spin-orbitronic devices.

10.3938/phit.29.034

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Orbital torque: Torque generation by orbital current injection

Physical Review Research (2020)

Dongwook Go Hyun‐Woo Lee

We propose a mechanism of torque generation by injection of an orbital current, which we call $\textit{orbital torque}$. In a magnetic bilayer consisting of a nonmagnet (NM) and a ferromagnet (FM), we consider a situation where the spin-orbit coupling (SOC) is present only in the FM. Although the SOC is absent in the NM, the orbital Hall effect can arise in the NM. When the resulting orbital Hall current is injected to the FM, the SOC of the FM converts the orbital angular momentum into spin, which exerts torque to the magnetization of the FM. Remarkably, even for small SOC strength comparable to that of $3d$ FMs, the orbital torque can be comparable to the spin torque induced by the spin Hall effect of the NM with strong SOC. This provides a way to experimentally probe the OHE and opens a new venue to achieving spin-torque devices based on light elements that exhibit gigantic orbital response. Experimental implications are discussed.

Orbital magnetization

Spin-transfer torque

10.1103/physrevresearch.2.013177

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Citations (168)

Roles of chiral renormalization on magnetization dynamics in chiral magnets

Physical review. B./Physical review. B (2018)

Kyoung‐Whan Kim Hyun‐Woo Lee Kyung‐Jin Lee Karin Everschor‐Sitte Olena Gomonay

In metallic ferromagnets, the interaction between local magnetic moments and conduction electrons renormalizes parameters of the Landau-Lifshitz-Gilbert equation, such as the gyromagnetic ratio and the Gilbert damping, and makes them dependent on the magnetic configurations. Although the effects of the renormalization for nonchiral ferromagnets are usually minor and hardly detectable, we show that the renormalization does play a crucial role for chiral magnets. Here the renormalization is chiral, and as such we predict experimentally identifiable effects on the phenomenology of magnetization dynamics. In particular, our theory for the self-consistent magnetization dynamics of chiral magnets allows for a concise interpretation of domain-wall creep motion. We also argue that the conventional creep theory of the domain-wall motion, which assumes Markovian dynamics, needs critical reexamination since the gyromagnetic ratio makes the motion non-Markovian. The non-Markovian nature of the domain-wall dynamics is experimentally checkable by the chirality of the renormalization.

Magnetization dynamics

Gyromagnetic ratio

Effective field theory

10.1103/physrevb.97.100402

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Citations (12)

Effect of spin diffusion on current generated by spin motive force

Physical Review B (2011)

Kyoung‐Whan Kim Jung Hwan Moon Kyung‐Jin Lee Hyun‐Woo Lee

Spin motive force is a spin-dependent force on conduction electrons induced by magnetization dynamics. In order to examine its effects on magnetization dynamics, it is indispensable to take into account spin accumulation, spin diffusion, and spin-flip scattering since the spin motive force is in general nonuniform. We examine the effects of all these on the way the spin motive force generates the charge and spin currents in conventional situations, where the conduction electron spin relaxation dynamics is much faster than the magnetization dynamics. When the spin-dependent electric field is spatially localized, which is common in experimental situations, we find that the conservative part of the spin motive force is unable to generate the charge current due to the cancelation effect by the diffusion current. We also find that the spin current is a nonlocal function of the spin motive force and can be effectively expressed in terms of nonlocal Gilbert damping tensor. It turns out that any spin independent potential such as Coulomb potential does not affect our principal results. At the last part of this paper, we apply our theory to current-induced domain wall motion.

Spinplasmonics

Spin diffusion

Magnetization dynamics

10.1103/physrevb.84.054462

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Citations (10)

Inter-Shell Hopping And Resonant Transport In Double-Wall Carbon Nanotube

AIP conference proceedings (2006)

Jinhee Kim Jong Wan Park Nam Soo Kim Joon Sung Lee Pil Sun Na

Electrical transport properties of individual double‐wall carbon nanotube (DWNT) are studied. Negative differential conductance (NDC) was observed for the DWNT with a defected outer shell. Such NDC was explained in terms of the resonant tunneling through multiple quantum dots. Also observed is the Fano resonance for the low‐resistance samples. The Fano resonance was manifested by asymmetric peaks in the gate modulation and also by the zero‐bias peak in the differential conductance curve. Both NDC and Fano resonance in DWNT demonstrates the interplay of inner and outer shells via the inter‐shell hopping of electrons.

Fano resonance

Nanobiotechnology

10.1063/1.2355260

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Anthracene Derivatives Containing the Various Heterocyclic Moiety as the Efficient Emitting Materials for Organic Light-Emitting Diodes

Journal of Nanoscience and Nanotechnology (2015)

Jwajin Kim Young Seok Kim Hyun‐Woo Lee Ho Won Lee Young Kwan Kim

We have designed and synthesized three emitters based on anthracene derivatives (1-3) containing various heterocyclic compounds via the Suzuki cross coupling reaction. Among those, a material showed efficient blue electroluminescent properties with a luminous, a power, and an external quantum efficiencies of 1.99 cd/A, 0.70 lm/W, and 1.17% at 20 mA/cm2, respectively.

Moiety

Quantum Efficiency

Suzuki reaction

10.1166/jnn.2016.1200

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Chiral magnetoresistance in Pt/Co/Pt zigzag wires

Applied Physics Letters (2017)

Yuxiang Yin Dong‐Soo Han June-Seo Kim Reinoud Lavrijsen Kyung‐Jin Lee

The Rashba effect leads to a chiral precession of the spins of moving electrons while the Dzyaloshinskii-Moriya interaction (DMI) generates preference towards a chiral profile of local spins. We predict that the exchange interaction between these two spin systems results in a 'chiral' magnetoresistance depending on the chirality of the local spin texture. We observe this magnetoresistance by measuring the domain wall (DW) resistance in a uniquely designed Pt/Co/Pt zigzag wire, and by changing the chirality of the DW with applying an in-plane magnetic field. A chirality-dependent DW resistance is found, and a quantitative analysis shows a good agreement with a theory based on the Rashba model. Moreover, the DW resistance measurement allows us to independently determine the strength of the Rashba effect and the DMI simultaneously, and the result implies a possible correlation between the Rashba effect, the DMI, and the symmetric Heisenberg exchange.

Zigzag

Chirality

Rashba effect

10.1063/1.4979031

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Citations (16)

Novel Soft-Switching DC-DC Converter of High Efficiency

International Conference on Performance Engineering (1995)

Dong-Kurl Kwak Kyung‐Jin Lee Ki‐Young Suh Soon-Kurl Kwon Hyun‐Woo Lee

In this paper, the authors propose a novel soft switching DC-DC converter of a high efficiency. The switching devices in a proposed circuit are operated with soft switching by the partial resonant method. The partial resonant circuit makes use of a inductor using step up and a condenser of loss-less snubber. The result is that switching loss is very low and efficiency of system is high. Also the proposed converter is deemed the most suitable for high power applications where the power switching devices are used. Some simulative results on computer and experimental results are included to confirm the validity of the analytical results.

Snubber

Source

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Citations (2)