키타에프 자성에 대한 간략한 소개: 전자구조계산 연구자의 관점에서

김흥식 한국물리학회 2019 새물리 Vol.69 No.10

In this short review, we will introduce Kitaev magnetism in two- or three-dimensional magnetic materials based on an electronic structure and materials physics perspective. Specifically, the focus will be on the significance of spin-orbit coupling and anisotropic magnetic exchange interactions in devising the Kitaev exchange interaction. First, the quantum mechanical aspects of magnetism on the lattice geometry will be addressed, then, the effects of spin-orbit coupling and the resulting Jackeli-Khaliullin mechanism will be discussed. An introduction to Kitaev’s exactly solvable model and its solution will be discussed later. Finally, we will review currently studied Kitaev candidates, the history of researches and various trials to realize Kitaev magnetism and measure the predicted Majorana mode. 본 리뷰에서는 2차원 및 3차원 자성체에서 나타나는 키타에프 (Kitaev) 자성에 대한 제일원리 전자구조계산 및 물성물리적 관점에서의 간략한 소개를 하고자 한다. 특별히 본 논문에서는 키타에프 자성을실현하기 위한 결정상 물리계에서의 스핀-오비탈 결합의 중요성 및 이를 통해 발생하는 비등방적인 자성상호작용에 대한 소개를 중점적으로 다룰 예정이다. 우선 결정구조 위에서의 양자역학적 효과에 의한자성의 발생, 스핀-오비탈 (Orbital) 결합 및 Jackeli-Khaliullin 메커니즘에 대한 소개를 마친 뒤, 키타에프자성 모델 및 이의 정확한 풀이 방법과 그 해에 대한 간략한 소개를 할 것이다. 그리고 2009년 이후로제안되어 온 해당 자성을 가질 수 있는 후보 물질들 및 실물질에서의 키타에프 자성 연구 및 실험적으로키타에프 자성에 의해 발생하는 스핀 액상 및 마요라나 (Majorana) 페르미온 (Fermion) 을 관찰하기위한 시도들에 대한 역사를 소개한다. 마지막으로 키타에프 자성을 구현하기 위한 방법들을 제일원리전자구조계산 방법론의 관점 하에서 소개하는 한 편 이에 대한 최신의 이론 및 실험 연구들을 소개하며 본리뷰를 마무리하고자 한다.

A small lunar swirl and its implications for the formation of the Reiner Gamma magnetic anomaly

Lee, Jung-Kyu,Maxwell, Rachel,Jin, Ho,Baek, Seul-Min,Ghassemi, Omid,Kelley, Megan,Lee, Hyojeong,Kim, Khan-Hyuk,Lee, Seongwhan,Garrick-Bethell, Ian Elsevier 2019 Icarus Vol.319 No.-

<P><B>Abstract</B></P> <P>The Moon does not currently possess a dynamo, but its crust contains numerous magnetic anomalies detected from orbit. The geologic origins of these anomalies are still unknown, including the archetypal Reiner Gamma magnetic anomaly. To gain insight, we study a small magnetic anomaly, herein called the octopus, which is possibly associated with Reiner Gamma. The octopus has curving bright albedo patterns characteristic of features known as swirls. We use high cadence 9 Hz Lunar Prospector magnetometer data, along with constraints provided by this swirl's albedo pattern, to perform inversions for the swirl's magnetic source body characteristics. We use three different inversion methods, and they all return similar results. We also estimate the depth of magnetization from characteristics of the horizontal component of the magnetic field and the albedo pattern. We find that performing inversion for source body properties at small swirls has advantages compared to larger anomalies, or anomalies without albedo markings. We find the octopus is magnetized in the same direction as the main Reiner Gamma anomaly (within 1<I>σ</I> uncertainties), suggesting they formed contemporaneously. The large spatial distance between these coeval anomalies and their inferred shallow source body depths are compatible with formation in a hot ejecta deposit that cooled in the presence of a dynamo field, as suggested by <I>Hood</I> et al. (2001). However, a key remaining enigma is why the northeastern Reiner Gamma “tail” formation has a magnetization direction ∼60° different from the main body and octopus.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We study one of the smallest lunar magnetic anomalies using 9 Hz magnetometer data. </LI> <LI> We use three different inversion methods to determine its magnetization. </LI> <LI> We find its magnetization direction is nearly equal to that of the Reiner Gamma anomaly. </LI> <LI> We infer that this anomaly and Reiner Gamma formed at the same time. </LI> <LI> We infer these anomalies likely formed as an ejecta deposit magnetized by a dynamo field. </LI> </UL> </P>

An interplay among the Mg²⁺ ion coordination, structural order, oxygen vacancies and magnetism of MgO thin films

Singh, Jitendra Pal,Lim, Weon Cheol,Chae, Keun Hwa Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.806 No.-

<P><B>Abstract</B></P> <P>The magnetic properties of MgO thin films were discussed as an interplay among the oxygen vacancies, Mg<SUP>2+</SUP> ion coordination and structural order deposited using radio frequency (RF) sputtering method by varying substrate temperature and deposition power followed by in-situ annealing. Rutherford backscattering spectrometry (RBS) and high resolution transmission electron microscopic (HRTEM) performed for these films showed decrease of film thickness with increase of substrate temperature. Films are thicker for higher sputtering powers at corresponding substrate temperatures. Spectral features in Mg <I>K</I>-edge near edge X-ray absorption fine structure (NEXAFS) spectra are characteristics of MgO for both sputtering powers at substrate temperature of room temperature (RT) and 350 °C. O <I>K</I>-edge NEXAFS spectra exhibited onset of oxygen vacancies as inferred from pre-edge region. Magnetization versus applied magnetic field curves for these films showed onset of <I>d</I> <SUP> <I>o</I> </SUP> ferromagnetism. This behavior ceased with increase of substrate temperature, however, become dominant with increase of sputtering power. Magnetic behavior was dominant for the films which had slightly distorted Mg<SUP>2+</SUP> ion co-ordination. The existence of oxygen vacancies was not observed to be consistent with magnetization. Thus, this study envisaged the role of Mg<SUP>2+</SUP> ion coordination, long range structural order and oxygen vacancies in order to determine magnetism in these systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> MgO thin films were grown using radio-frequency sputtering method. </LI> <LI> Oxygen vacancies and Mg<SUP>2+</SUP> ion coordination were determined using X-ray absorption spectroscopy. </LI> <LI> An inverse correlation was observed among the Mg<SUP>2+</SUP> ion co-ordination and magnetism in these oxygen deficient thin films. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

캐나다 Ontario주와 우리나라 초등학교의 전기, 자기 관련 교육 과정의 비교 연구

한무현,김종성,Han, Moo-Hyun,Kim, Jong-Seong 한국초등과학교육학회 2005 초등과학교육 Vol.24 No.5

In this study, we conducted a comparative study to investigate the curriculums on electricity and magnetism between in Korean and in Ontario elementary schools in Canada with respect to connectivity and difference among course materials with grades. We compared textbooks that contain the contents about electricity and magnetism, and connectivity in curriculums that were relevant to the science content system in each country. We report the following differences in the curriculums on electricity and magnetism in each country. First, it turns out that science is taught from the first grade in Ontario, while it is taught from the third grade in Korea. Second, Ontario covers electricity and magnetism only in science curriculum, while Korea covers the same topics both in the science and practical arts curriculum. Third, while the curriculum in Korea introduces 'a magnet' in the third grade, 'electricity' in the fourth and the fifth grade, and 'an electromagnet' in the sixth grade, while the curriculum in Ontario covers the concept of energy from the first grade. As the grades go up, the contents of electricity and magnetism tend to be more deepen. It also emphasizes enhancing students' ability that they can communicate what they learn about technology with others, and that they can apply their knowledge to other fields as well. Based on this study of the Ontario curriculum, we suggest that it is necessary for us to n Science curriculum from the first grade, so that the students can learn science from the early grade, without a need to run another subject, like practical arts. We also found that the Korean curriculum has an interesting structure for the young students to learn to apply their knowledge to the real life immediately, based on an idea that the topic of 'Manipulating the electric appliances' in practical arts curriculum moves to the Science.

Hydration Effect on the Intrinsic Magnetism of Natural Deoxyribonucleic Acid as Studied by EMR Spectroscopy and SQUID Measurements

Young-Wan Kwon,Chang Hoon Lee,Eui-Doo Do,최동훈,진정일,Jun Sung Kang,Eui-Kwan Koh 대한화학회 2008 Bulletin of the Korean Chemical Society Vol.29 No.6

The hydration effect on the intrinsic magnetism of natural salmon double-strand DNA was explored using electron magnetic resonance (EMR) spectroscopy and superconducting quantum interference device (SQUID) magnetic measurements. We learned from this study that the magnetic properties of DNA are roughly classified into two distinct groups depending on their water content: One group is of higher water content in the range of 2.6-24 water molecules per nucleotide (wpn), where all the EMR parameters and SQUID susceptibilities are dominated by spin species experiencing quasi one-dimensional diffusive motion and are independent of the water content. The other group is of lower water content in the range of 1.4-0.5 wpn. In this group, the magnetic properties are most probably dominated by cyclotron motion of spin species along the helical π -way, which is possible when the momentum scattering time (τ k) is long enough not only to satisfy the cyclotron resonance condition (ωcτ k > 1) but also to induce a constructive interference between the neighboring double helices. The same effect is reflected in the S-shaped magnetization-magnetic field strength (M-H) curves superimposed with the linear background obtained by SQUID measurements, which leads to larger susceptibilities at 1000 G when compared with the values at 10,000 G. In particular, we propose that the spin-orbital coupling and Faraday's mutual inductive effect can be utilized to interpret the dimensional crossover of spin motions from quasi 1D in the hydrate state to 3D in the dry state of dsDNA.

A first principle study on the magnetic properties of Cu2O surfaces

Xiaohu Yu,Xuemei Zhang,Shengguang Wang,Gang Feng 한국물리학회 2015 Current Applied Physics Vol.15 No.11

Spin-polarized density functional theory calculations were performed to investigate the magnetism of bulk and Cu2O surfaces. It is found that bulk Cu2O, Cu/O-terminated Cu2O(111) and (110) surfaces have no magnetic moment, while, the O-terminated Cu2O(100) and polar O-terminated Cu2O(111) surfaces have magnetism. For low index surfaces with cation and anion vacancy, we only found that the Cu vacancy on the Cu2O(110) Cu/O-terminated surface can induce magnetism. For atomic and molecular oxygen adsorption on the low index surfaces, we found that atomic and molecular oxygen adsorption on the Cuterminated Cu2O(110) surface is much stronger than on the Cu/O-terminated Cu2O(111) and Cuterminated Cu2O(100) surfaces. More interesting, O and O2 adsorption on the surface of Cu/O terminated Cu2O(111) and O2 adsorption on the Cu-terminated Cu2O(110) surface can induce weak ferromagnetism. In addition, we analysis origin of Cu2O surfaces with magnetism from density of state, the surface ferromagnetism possibly due to the increased 2p-3d hybridization of surface Cu and O atoms. This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.

Hydration Effect on the Intrinsic Magnetism of Natural Deoxyribonucleic Acid as Studied by EMR Spectroscopy and SQUID Measurements

Kwon, Young-Wan,Lee, Chang-Hoon,Do, Eui-Doo,Choi, Dong-Hoon,Jin, Jung-Il,Kang, Jun-Sung,Koh, Eui-Kwan Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.6

The hydration effect on the intrinsic magnetism of natural salmon double-strand DNA was explored using electron magnetic resonance (EMR) spectroscopy and superconducting quantum interference device (SQUID) magnetic measurements. We learned from this study that the magnetic properties of DNA are roughly classified into two distinct groups depending on their water content: One group is of higher water content in the range of 2.6-24 water molecules per nucleotide (wpn), where all the EMR parameters and SQUID susceptibilities are dominated by spin species experiencing quasi one-dimensional diffusive motion and are independent of the water content. The other group is of lower water content in the range of 1.4-0.5 wpn. In this group, the magnetic properties are most probably dominated by cyclotron motion of spin species along the helical π -way, which is possible when the momentum scattering time (${\tau}_k$) is long enough not only to satisfy the cyclotron resonance condition (${\omega}_c{\tau}_k$ > 1) but also to induce a constructive interference between the neighboring double helices. The same effect is reflected in the S-shaped magnetization-magnetic field strength (M-H) curves superimposed with the linear background obtained by SQUID measurements, which leads to larger susceptibilities at 1000 G when compared with the values at 10,000 G. In particular, we propose that the spin-orbital coupling and Faraday's mutual inductive effect can be utilized to interpret the dimensional crossover of spin motions from quasi 1D in the hydrate state to 3D in the dry state of dsDNA.

Magnetic Properties of Transition Metal Monolayers on Ta(001) Surfaces

S. J. Youn,S. C. Hong 한국자기학회 2008 Journal of Magnetics Vol.13 No.4

The magnetic and structural properties of transition metal (Mn, Fe, Co) monolayers on Ta(001) surfaces are investigated theoretically by using the first principles full-potential linearized augmented plane wave method. Mn and Fe monolayers become ferromagnetic on Ta(001) surfaces while Co monolayers becomes non-magnetic. The paramagnetism of Co monolayers is explained by the Stoner theory of magnetism. The magnetic coupling of a transition metal overlayer with a substrate is ascribed to the orbital hybridization between the s and d orbitals of the transition metal.

Enhancing the coercivity of Nd-Fe-B sintered magnets by consecutive heat treatment–induced formation of Tb-diffused microstructures

Kim, Sumin,Ko, Dong-Su,Lee, Hyun-Sook,Kim, Donghwan,Roh, Jong Wook,Lee, Wooyoung Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.780 No.-

<P><B>Abstract</B></P> <P>Herein, we probed the microstructure of Tb-diffused Nd-Fe-B magnets to investigate the relationship between Tb-diffused area and coercivity enhancement, employing prolonged stepwise heat treatment to ensure sufficient diffusion of Tb in relatively large-size magnets and revealing that this stepwise annealing generated core-shell structures. Quantitative compositional changes pertaining to individual phases of the multiphase system in each heat treatment process were analyzed by constructing ternary diagrams based on electron probe microanalysis compositional maps. During the grain boundary diffusion process, coercivity increased from 15.28 to 24.86 kOe, while only negligible remanence and energy product decreases were concomitantly observed. Microstructure analysis suggested that coercivity was closely related to the concentration and distribution of Tb; more precisely, the abovementioned core-shell structures successfully suppressed the nucleation of reverse domains at Nd-rich phase/main phase interfaces and therefore enhanced magnet coercivity without decreasing remanence and energy product.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We employed grain boundary diffusion to enhance the coercivity using TbH in large-sized magnets. </LI> <LI> The stepwise annealing for large-sized magnets were introduced for enhancing the coercivity. </LI> <LI> The relationship between Tb-diffused area and coercivity was revealed by probing microstructure. </LI> <LI> EPMA investigations including ternary diagram confirmed with the XRD analysis. </LI> <LI> We enhanced coercivity without decreasing their remanence and energy product. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

중학교 과학 교과서 <전기와 자기> 단원에 제시된 설명에 대한 과학사적 관점에서의 분석

조헌국 한국물리학회 2015 새물리 Vol.65 No.10

This study aims to analyze the explanations about electricity and magnetism in secondary science textbooks from the perspective of the history of science and to suggest implications for students’ learning of electricity and magnetism. In this study, three kinds of science textbooks were analyzed with a focus on the appropriateness of the activities, the inferential process of the activities and the teaching sequence of concepts in electricity and magnetism. The results showed that a few of experiments might have the results irrelevant to the principles and that textbooks missed some reasoning steps to reach the appropriate conclusions. In terms of the sequence of contents, science concepts were not sufficiently connected with each other, and some of them were defined in a circular way. To resolve such problems, textbooks should provide students with activities based on empirical ways and well-structured teaching methods. 본 연구는 전기와 자기의 과학사적 발달 과정에 근거하여 중학교 과학 교과서의 전기와 자기 단원에 나타난 설명 방식을 분석함으로써 관련된 학생들의 어려움을 해소할 방안을 제시하였다. 이에 2009 개정 교육과정에 따른 중학교 3학년 과학 교과서 3종을 분석 대상으로 선정하였으며, 제시된 실험과 활동의 적절성, 활동 및 결과로부터의 추론 과정, 여러 개념 간의 설명 순서를 중심으로 살펴보았다. 연구 결과 교과서에 제시된 실험과 활동이 실제 수행 결과와 일치하지 않는 경우가 있었고, 관찰된 결과로부터 결론에 이르는 추론 과정이 생략되어 있거나 충분히 제시되지 않기도 하였다. 특히 개념 전개 순서에서는 정전기와 동전기가 서로 유기적으로 연결되지 않고 여러 개념들이 순환적으로 정의되는 경우가 발견되었다. 이에 본 연구에서는 이러한 문제점을 극복할 수 있는 방안을 시사점으로 제시하였다.