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Design of MgAl₂O₄ Spinel-Oxide-Based Tunnel Barriers for Advanced Spintronics Devices
Kenji Nawa,Keisuke Masuda,Shinto Ichikawa,Hiroaki Sukegawa,Tsuyoshi Suzuki,Katsuyuki Nakada,Seiji Mitani,Yoshio Miura 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
Tunnel magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) is one of the central properties to develop high-performance spintronics devices. MgO(001) with bcc-Fe or CoFe electrodes has been mostly studied as a tunnel barrier of MTJs for the last decades because of its giant TMR ratio originating from the spin-filtering effect of Δ₁-symmetric evanescent states (s, pz, d3z²-r² orbitals), as predicted in 2001. However, the TMR ratio of MgO-MTJs reduces significantly by bias voltage applications, indicating a limitation of the output voltage of the MTJ. Recent experiments show that the use of a (001)-oriented spinel-type oxide, MgAl₂O₄, as a tunnel barrier improves the robustness of the TMR ratio under bias applications, but a theoretical TMR limit in Fe/MgAl₂O₄/Fe(001) MTJs is very small compared to the MgO-MTJs. This is because the in-plane lattice periodicity of Fe electrode is half of that of MgAl₂O₄ and a band-folding effect is induced in the two-dimensional Brillouin zone of the in-plane wave vector in the Fe electrode. This effect provides additional conductive states at the Δ line in MgAl₂O₄-MTJ, contributing to the reduction of the TMR ratio. In this talk, we propose a combined trilayer tunnel barrier, MgO/MgAl₂O₄/MgO, to overcome the above issue of the small TMR limit of MgAl₂O₄-MTJs on the basis of the first-principles calculations. We performed ballistic-conductance calculations in an Fe/MgO(n)/MgAl₂O₄/MgO(n)/Fe(001) MTJ using the non-equilibrium Green’s functions method to clarify the TMR ratio under bias voltage application. Here, number of MgO layers (n-ML) is changed as n = 1, 2, 3. In the case of n = 1, a large TMR ratio of 1184% is obtained at a zero-bias voltage and this large value is almost maintained up to V = 1.2 V (see blue in Fig. 1), leading to a large voltage output. In contrast, a single barrier MgAl₂O₄ shows only a small TMR ratio (~125%), which is constant below V = 1.6 V (see orange in Fig. 1). These results indicate that both the models have a similar tendency in bias voltage dependence of TMR, except for the magnitude of a TMR ratio. Moreover, we clarified that the presence of an MgO interlayer between Fe and MgAl₂O₄ plays an important role in retaining (blocking) the Δ1 evanescent state for majority (minority) spin. The former leads to the robustness of the TMR ratio against bias voltage as observed in single MgAl₂O₄ MTJs, while the latter does to the large TMR ratio as in single MgO MTJs. 〈그림 본문참조〉
내등호남의 근대동アジアヘ의 시각 -「간도문제」에 대한 동찰-
명화열자 ( Nawa Etsuko ) 중국사학회 2003 中國史硏究 Vol.22 No.-
본고는, 20세기 초 일본의 중국문제 전문가였던 內藤湖南이 20世紀初에 발생한 淸과 韓國간의 국경문제 즉 「間島問題」에 어떻게 관여하고 어떤 입장을 보였는지를 살펴보았다. 內藤湖南이 1905년 일본 외무성의 위촉을 받아 청한 국경문제와 간도의 귀속문제를 조사하여 일본 외무성과 참모본부에 보고한 조사서를 비롯하여 그가 같은 문제를 위해 수집한 각종 자료와 그의 연구자료를 일차자료로 하여 내등의 조사보고와 의견이 1908년 청일간 체결과 청한국경획정과 간도귀속문제에 관한 조약에서 두만강을 국경으로 하고 간도에 대한 청의 영유권을 인정하는데 어떠한 영향을 미쳤는가를 검토하였다. 內藤湖南은 淸과 韓國의 역사적 배경에 근거하여 당시의 간도 사회 전체의 상황을 직시하고, 상당히 거시적인 관점으로 간도의 미래상을 제시하였음에 분명하다. 지금까지의 연구는 일본의 東北地域 資本主義化의 과정 가운데서 內藤湖南과 「間島問題」의 연관성을 주목해 왔다. 筆者는 이러한 시각이 이 문제에 대한 실증적 연구를 수행하는데 장애물이 되어왔다고 생각한다. 현재 역사연구는 질적 변화를 보이고 있고 하나의 큰 정치공동체를 대상으로 하고 있을 뿐만 아니라 地域社會史, 地域經濟史로 나뉘는 경향이 있다. 이것은 일본 뿐만 아니라 중국이나 한국에서도 80년대 이후 90년대 걸쳐 나타나고 있는 경향이다. 그런데 內藤湖南의 많은 연구 업적 가운데 「間島問題調査書』는 中國東北地域의 영토귀속문제에 관한 연구의 하나에 불과한 것이었으며 『私見』도 이 지역의 사회경제에 관한 연구의 一端에 불과한 것이었다. 따라서 그의 『間島問題調査書』와 『私見』을 재검토하는 것은 당시 일본의 이 지역에 대한 歷史像을 새로이 구축하는 일이라 할 수 있다. 本稿에서는 그가 「間島問題」에 관여한 經緯에 대해서는 구체적으로 검토하지 못하였다. 이 문제는 추후 別稿로 검토할 예정이다.
Design of Micro Water Supply System Using Solar Energy
Ekisha Sharma,Nawa Raj Khatiwada,Anish Ghimire 적정기술학회 2019 적정기술학회지(Journal of Appropriate Technology) Vol.5 No.1
Solar pumps, for water lift systems, is becoming popular in rural areas for supplying drinking water in dry seasons when its need is elevated. The development in technology has also made solar pumps readily available and cheap which has increased its demands. So, for scattered settlements having a limited budget for operation and maintenance costs, solar pump is preferred over grid connected electrical pumping systems. This primary objective of the study was to design a solar photovoltaic pumping drinking water supply system for a small health post which is about 45 km east from Kathmandu, the capital city of Nepal. The study also compared and verified the final design with the system’s existing design prepared by a development agency. The water source for this study was a confined aquifer 115m below the surface. The water demand was calculated to be 11m 3 per day. A 1500 kPa submersible pump attached to a motor was selected and installed. Along with that twelve solar panels, reservoir, transmission main and distribution main was designed. The outcomes conclude solar photovoltaic pumping water supply systems to be cost-effective with an estimated cost of only USD 0.84 million per MLD. Solar pumps require low maintenance and operation costs and its repairs can quickly be done by the local people. The study also shows that solar technology produces no sound, needs no fuel making it environmentally friendly.
The Role and Outcome of the Korea-Indonesia e-Government Cooperation Center
Ekisha Sharma,Nawa Raj Khatiwada,Anish Ghimire 적정기술학회 2019 적정기술학회지(Journal of Appropriate Technology) Vol.5 No.1
Solar pumps, for water lift systems, is becoming popular in rural areas for supplying drinking water in dry seasons when its need is elevated. The development in technology has also made solar pumps readily available and cheap which has increased its demands. So, for scattered settlements having a limited budget for operation and maintenance costs, solar pump is preferred over grid connected electrical pumping systems. This primary objective of the study was to design a solar photovoltaic pumping drinking water supply system for a small health post which is about 45 km east from Kathmandu, the capital city of Nepal. The study also compared and verified the final design with the system’s existing design prepared by a development agency. The water source for this study was a confined aquifer 115m below the surface. The water demand was calculated to be 11m3 per day. A 1500 kPa submersible pump attached to a motor was selected and installed. Along with that twelve solar panels, reservoir, transmission main and distribution main was designed. The outcomes conclude solar photovoltaic pumping water supply systems to be cost-effective with an estimated cost of only USD 0.84 million per MLD. Solar pumps require low maintenance and operation costs and its repairs can quickly be done by the local people. The study also shows that solar technology produces no sound, needs no fuel making it environmentally friendly.