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Direct Observation of Fe-Ge ordering in Fe<SUB>5-x</SUB>GeTe₂ Crystals and Resultant Helimagnetism
Trinh Thi Ly,Jungmin Park,Kyoo Kim,Hyo-Bin Ahn,Nyun Jong Lee,Kwangsu Kim,Tae-Eon Park,Ganbat Duvjir,Nguyen Huu Lam,Kyuha Jang,Chun-Yeol You,Younghun Jo,Se Kwon Kim,Changgu Lee,Sanghoon Kim,Jungdae Kim 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
The van der Waals (vdW) ferromagnet compared to conventional ferromagnetic materials provides a unique configuration of magnetic interactions due to its quasi two-dimensional (2D) nature. The pair-exchange interaction is mainly established within the 2D plane, while magnetic coupling between interlayers is weak. Therefore, the vdW ferromagnets are ideal for 2D spintronic devices that show various emergent spin-orbit coupled phenomena with time reversal and inversion symmetry breaking. As a promising vdW ferromagnet, the Fe<sub>n</sub>GeTe<sub>2</sub> family (n = 3, 4, 5) was proposed based on its high T<sub>C</sub> (260 ~ 310 K) and large saturation magnetization. Recently, the unconventional magnetic properties of Fe<sub>5</sub>GeTe<sub>2</sub> have been explained with magnetic anisotropy or/and spin reorientation by the Fe atoms in Fe<sub>5</sub>GeTe<sub>2</sub>. However, the exact mechanism of such non-trivial magnetic behaviors is still unclear because it is also involved with the structural complexity in Fe<sub>5</sub>GeTe<sub>2</sub>. Therefore, systematic study for finding the correlation between such non-trivial magnetic behaviors and the atomistic structure of Fe<sub>5</sub>GeTe<sub>2</sub> is needed to realize room temperature spintronic devices with this new vdW ferromagnet. In this study, we explore atomistic structures of an Fe<sub>5-x</sub>GeTe<sub>2</sub> single crystal by low temperature scanning tunneling microscopy (STM) and its temperature dependent magnetic behaviors. Subset Fe layers in Fe<sub>5</sub>GeTe<sub>2</sub> are expected to play a major role in magnetic ordering. STM topography reveals √3×√3 superstructures on the cleavage surface of Fe<sub>5-x</sub>GeTe<sub>2</sub>, which are attributed to the ordering of Fe(1) layer. Intriguingly, observed √3×√3 ordering of Fe(1)-Ge pair breaks the inversion symmetry, which is an important microscopic origin of the antisymmetric exchange interaction, known as Dzyaloshinskii-Moriya interaction (DMI). The temperature dependent magnetization of Fe<sub>5-x</sub>GeTe<sub>2</sub> clearly shows commensurate-incommensurate transition, a typical helimagnetic behavior arising from the DMI, just below T<sub>C</sub> = 310 K. We also confirm that spin reorientation behaviors are observed within the ranges of 120 ~ 260 K and 20 ~ 100 K due to competition between helimagnetism and other collinear properties. Our findings suggest that the Fe<sub>5</sub>GeTe<sub>2</sub> crystal has helical magnetism with non-centrosymmetric ordering of Fe(1)-Ge pairs, which can be a source of topologically protected spin solitons to develop new types of topology-based spin devices.
Kim, Hyun,Han, Gang Hee,Yun, Seok Joon,Zhao, Jiong,Keum, Dong Hoon,Jeong, Hye Yun,Ly, Thuc Hue,Jin, Youngjo,Park, Ji-Hoon,Moon, Byoung Hee,Kim, Sung-Wng,Lee, Young Hee IOP 2017 Nanotechnology Vol.28 No.36
<P>Synthesis of monolayer transition metal dichalcogenides (TMDs) via chemical vapor deposition relies on several factors such as precursor, promoter, substrate, and surface treatment of substrate. Among them, the use of promoter is crucial for obtaining uniform and large-area monolayer TMDs. Although promoters have been speculated to enhance adhesion of precursors to the substrate, their precise role in the growth mechanism has rarely been discussed. Here, we report the role of alkali metal promoter in growing monolayer TMDs. The growth occurred via the formation of sodium metal oxides which prevent the evaporation of metal precursor. Furthermore, the silicon oxide substrate helped to decrease the Gibbs free energy by forming sodium silicon oxide compounds. The resulting sodium metal oxide was anchored within such concavities created by corrosion of silicon oxide. Consequently, the wettability of the precursors to silicon oxide was improved, leading to enhance lateral growth of monolayer TMDs.</P>
Ly Kim Ha 경북대학교 자연과학대학 수학과 2023 Kyungpook mathematical journal Vol.63 No.3
The main purpose of this paper is to show that over a large class of bounded domains Ω ⊂ C2, for 1 < p < ∞, the Bergman projection P is bounded from Lp(Ω, dV ) to the Bergman space Ap(Ω); from L∞(Ω) to the holomorphic Bloch space BlHol(Ω); and from L1(Ω, P(z, z)dV ) to the holomorphic Besov space Besov(Ω), where P(ζ, z) is the Bergman kernel for Ω.
Detecting gold by voltammetric handhold systems
Kim, Nack-Joo,Choi, Dal-Woong,Yoo, Hai-Soo,Lee, Kyung,Lee, Chang-Hyun,Ly, Suw-Young,Kim, Tae-Yun The Korean Society of Applied Science and Technolo 2014 한국응용과학기술학회지 Vol.31 No.3
A voltammetric investigation of Au assay was conducted at a low cost, using Nafion and DNA immobilized on a graphite Pencil working electrode (NDP) with a black lead counter and reference. The following optimal parameters were found: 0.4 V amplitude, 500 Hz frequency, -0.7 V initial potential, and 0.015 V increment potential. These optimal conditions were also applied to sand obtained from the river site. The aforementioned technique is simpler and less costly compared to the common voltammetry and spectrophotometric methods.
Fast pyrolysis of Saccharina japonica alga in a fixed-bed reactor for bio-oil production
Ly, H.V.,Kim, S.S.,Choi, J.H.,Woo, H.C.,Kim, J. Pergamon ; Elsevier Science Ltd 2016 Energy conversion and management Vol.122 No.-
Macro-algae are recognized as a potential feedstock for renewable energy and fuel production. Saccharina japonica is a kind of macro-algae that has been extensively cultivated in Korea. Through pyrolysis, S. japonica can be converted into bio-oil, gas, and char. In this study, we investigated the fast pyrolysis of S. japonica in a fixed-bed reactor at different temperatures from 350 to 550<SUP>o</SUP>C with sweeping-gas flow rates of 100, 300, and 500ml/min. As the pyrolysis temperature was increased from 350<SUP>o</SUP>C to 500<SUP>o</SUP>C, the bio-oil yields decreased while the gas yields increased. The highest liquid yield (40.91wt%) was obtained at a pyrolysis temperature of 350<SUP>o</SUP>C with a sweeping-gas velocity of 300ml/min. The major compositions in the bio-oil were di-anhydromannitol (34.45%), iso-sorbide (19.84%), and 2-methyl furyl ketone (8.43%). The gas products (including CO, CO<SUB>2</SUB>, H<SUB>2</SUB>, and hydrocarbon gases from C<SUB>1</SUB> to C<SUB>4</SUB>), were analyzed by gas chromatography with an FID and a TCD. The bio-chars contained a high carbonaceous content can be used as a pollution-free solid fuel or for the production of activated carbon and other chemicals.
A note on zeros of bounded holomorphic functions in weakly pseudoconvex domains in C2
Ly Kim Ha 대한수학회 2017 대한수학회보 Vol.54 No.3
Let $\Omega$ be a bounded, uniformly totally pseudoconvex domain in $\mathbb{C}^2$ with the smooth boundary $b\Omega$. Assuming that $\Omega$ satisfies the negative $\bar\partial$ property. Let $M$ be a positive, finite area divisor of $\Omega$. In this paper, we will prove that: if $\Omega$ admits a maximal type $F$ and the $\rm \check{C}$eck cohomology class of the second order vanishes in $\Omega$, there is a bounded holomorphic function in $\Omega$ such that its zero set is $M$. The proof is based on the method given by Shaw \cite{Sha89}.