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Antiferromagnetic Interlayer Exchange Coupling in Ferromagnetic GaMnAs/GaAs:Be Multilayers
Lee, Hakjoon,Lee, Sangyeop,Choi, Seonghoon,Yoo, Taehee,Lee, Sanghoon,Liu, Xinyu,Furdyna, Jacek K. IEEE 2015 IEEE transactions on magnetics Vol.51 No.11
<P>Interlayer exchange coupling (IEC) between the GaMnAs layers in GaMnAs/GaAs:Be multilayer systems has been investigated using magnetotransport experiments. The observation of a stable antiparallel magnetization alignment state from the systems indicates the presence of antiferromagnetic (AFM) IEC between the GaMnAs layers. The transitions between parallel and antiparallel alignments of GaMnAs magnetic layers in the system were carefully investigated by measuring resistance change with increasing temperature under various bias magnetic fields. From the dependence of the transition temperature on bias fields, we have estimated the magnitude of AFM IEC and its temperature behavior of our GaMnAs/GaAs:Be multilayers.</P>
Lee, Sangyeop,Lee, Hakjoon,Yoo, Taehee,Lee, Sanghoon,Liu, X.,Furdyna, J. K. American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.113 No.17
<P>Magnetic anisotropy of ferromagnetic semiconductor GaMnAs film with a low Mn concentration grown on a (001) GaAs substrate was investigated by Hall effect measurements. The presence of domains with in-plane and out-of-plane easy axes was identified in the film by analyzing hysteresis loops observed via the Hall resistance measured in various geometries. Quantitative analysis of the planar Hall resistance showed that the fraction of the sample with magnetic domains having a dominant out-of-plane easy axis was about 6 times larger than the fraction corresponding to domains with easy axis in the sample plane. (C) 2013 American Institute of Physics.</P>
Manipulation of magnetization in GaMnAs films by spin-orbit-induced magnetic fields
Lee, Sangyeop,Yoo, Taehee,Bac, Seul-Ki,Choi, Seonghoon,Lee, Hakjoon,Lee, Sanghoon,Liu, X.,Furdyna, J.K.,Dobrowolska, M. Elsevier 2017 Current Applied Physics Vol.17 No.5
<P>We have investigated the effect of spin-orbit-induced (SOI) magnetic fields on magnetization switching in GaMnAs films. The sign of such SOI fields depends on the direction of the current flowing in the film, thus providing a handle for electrically manipulating magnetization in ferromagnetic GaMnAs films. Specifically, when an applied magnetic field is swept along the current direction, magnetization reversal occurs via rotations in opposite sense (i.e., clockwise (CW) or counterclockwise (CCW)) depending on the sign of the current, thus leading to opposite signs of the planar Hall resistance (PHR) measured on the film. The effect of SOI fields also manifests itself through hysteretic behavior of PHR for two opposite currents as a fixed magnetic field is rotated in the film plane. The width of the resulting hysteresis between two current directions then allows us to estimate the magnitude of the SOI field at current density of 1.0 x 10(5) A/cm(2) as similar to 1.2 Oe in our GaMnAs film. Such switching of magnetization between two magnetic easy axes induced by switching the sign of an applied current provides a means of electronically controlling the value of film resistance (in this case of PHR), a process that can be exploited in spintronic devices. (C) 2017 Elsevier B.V. All rights reserved.</P>
Lee, Hakjoon,Chung, Sunjae,Lee, Sanghoon,Liu, X.,Furdyna, J. K. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>Magnetotransport properties of GaMnAs/InGaAs/GaMnAs trilayer structures have been investigated by Hall measurements. The samples in the series are identical except for the InGaAs spacer thickness, which varies from 5 to 50 nm. The Hall measurements revealed the systematic change of magnetic easy axes from in-plane to out-of plane with increasing InGaAs spacer thickness. Such dependence of magnetic easy axes of the trilayer systems was understood in terms of the magnetic anisotropy change with spacer thickness. In the magnetization reversal process, various configurations of magnetization between the two GaMnAs layers were observed both in in-plane and out-of plane samples by the planar and the anomalous Hall effects. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3059601]</P>
심학준(Hakjoon Sim),이승훈(Seunghoon Lee),김재광(Jaekwang Kim),이지형(Jee-Hyong Lee) 한국지능시스템학회 2009 한국지능시스템학회 학술발표 논문집 Vol.19 No.1
오늘날, 웹 페이지에서 블로그 영역이 차지하는 비중이 날로 높아져 가고 있다. 이러한 상황에서 블로그가 가지는 구조적 특징(태그, 트랙백, 댓글)들은 페이지의 평가나 검색에 있어 편리성과 유연성을 가져다 줄 수 있다. 이러한 특징중, 태그는 블로거의 주관에 따라 같은 의미를 갖지만 그 형태가 달라질 수 있어 검색이나 탐색, 또는 분류에 있어서의 어려움을 야기하기도 하는데 이를 해소하기 위한 다양한 연구가 진행되고 있다. 본 논문에서는 블로그 영역의 특징 중 하나인 태그정보에서 서로 연관성을 가지는 연관태그들을 찾기 위해 클러스터링 기법을 사용하여 이를 그룹화하는 방법을 제안하였다. 마지막으로 본 논문에서는 제안하는 방법에 대한 실험을 통하여 태그의 그룹화가 얼마나 효율적으로 이루어 지는지 검증하였다.