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Interface Engineering in Quasi-Magnetic Tunnel Junctions with an Organic Barrier
Deung Jang Choi,Nyun Jong Lee,Tae Hee Kim 한국자기학회 2010 Journal of Magnetics Vol.15 No.4
Spin polarized tunneling through a hybrid tunnel barrier of a Spin filter (SF) based on a EuO ferro-magnetic semiconductor and an organic semiconductor (OSC) (rubrene in this case) was investigated. For quasi-magnetic tunnel junction (MTJ) structures, such as Co/rubrene/EuO/Al, we observed a strong spin filtering effect of the EuO layer exhibiting I-V curves with high spin polarization (P) of up to 99% measured at 4 K. However, a magnetoresistance (MR) value of 9% was obtained at 4.2 K. The low MR compared to the high P could be attributed to spin scattering caused by structural defects at the interface between the EuO and rubrene, due to nonstoichiometry in the EuO.
최등장(Deung Jang Choi),장은영(Eun Young Jang),이년종(Nyun Jong Lee),김태희(Tae Hee Kim) 한국자기학회 2007 韓國磁氣學會誌 Vol.17 No.5
Understanding the spin polarization (P) has been an ongoing research challenge. The Co<SUB>1 ? x</SUB>Mn<SUB>x</SUB> (x = 0.27, 1) and Co<SUB>1 ? x</SUB>Fe<SUB>x</SUB> (x = 0, 0.5, 1) films were prepared using UHV-MBE system. For these films, the magnetic properties and spin polarization were investigated using SQUID and Meservey-Tedrow technique, respectively. Although measured P is uncorrelated to the bulk magnetic moment (M) in Co-Fe and Ni-Fe alloy films, it correlates with M in some alloys such as Co-Mn and Ni-Cu. The results can be understood by the tunneling currents made up of the hybridized sp-d electrons near the Fermi-energy level. Our work shows the feasibility to tailor new materials with large P values.
Nanoparticle assemblies as memristors.
Kim, Tae Hee,Jang, Eun Young,Lee, Nyun Jong,Choi, Deung Jang,Lee, Kyung-Jin,Jang, Jung-tak,Choi, Jin-sil,Moon, Seung Ho,Cheon, Jinwoo American Chemical Society 2009 NANO LETTERS Vol.9 No.6
<P>Recently a memristor ( Chua, L. O. IEEE Trans. Circuit Theory 1971 , 18 , 507 ), the fourth fundamental passive circuit element, has been demonstrated as thin film device operations ( Strukov, D. B.; Snider, G. S.; Stewart, D. R.; Williams, R. S. Nature (London) 2008 , 453 , 80 ; Yang, J. J.; Pickett. M. D.; Li, X.; Ohlberg, D. A. A.; Stewart, D. R.; Williams, R. S. Nat. Nanotechnol. 2008 , 3 , 429 ). A new addition to the memristor family can be nanoparticle assemblies consisting of an infinite number of monodispersed, crystalline magnetite (Fe(3)O(4)) particles. Assembly of nanoparticles that have sizes below 10 nm, exhibits at room temperature a voltage-current hysteresis with an abrupt and large bipolar resistance switching (R(OFF)/R(ON) approximately 20). Interestingly, observed behavior could be interpreted by adopting an extended memristor model that combines both a time-dependent resistance and a time-dependent capacitance. We also observed that such behavior is not restricted to magnetites; it is a general property of nanoparticle assemblies as it was consistently observed in different types of spinel structured nanoparticles with different sizes and compositions. Further investigation into this new nanoassembly system will be of importance to the realization of the next generation nanodevices with potential advantages of simpler and inexpensive device fabrications.</P>
Single atomic spin sensing of magnetic interactions in a tunnel junction
Jinkyung Kim,Won-jun Jang,Thi Hong Bui,Deung-Jang Choi,Christoph Wolf,Fernando Delgado,Yi Chen,Denis Krylov,Soonhyeong Lee,Sangwon Yoon,Christopher P. Lutz,Andreas J. Heinrich,Yujeong Bae 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Single spins are widely regarded as a leading candidate for realizing next-generation quantum devices for sensing and quantum information processing. Detection and coherent control of single spins require to localize single spins and characterize its magnetic surroundings. Scanning tunneling microscopy in combination with electron spin resonance (ESR-STM) technique [1] enables a direct access to the quantum states of single magnetic atoms or molecules on surfaces. Using ESR-STM, we investigated spin resonance of hydrogenated Ti (TiH) atoms adsorbed on bridge binding site of MgO in a two-dimensional vector magnetic field. Here, the spin 1/2 TiH atom with no magnetic anisotropy was employed as a probe of magnetic environments at the tunnel junction. We found both ESR frequency and amplitude change as a function of the angle of vector magnetic fields. The resonance frequency varied by different vector magnetic fields indicates an anisotropy of the g-factor, resulting from the variation of angular momentum contributions due to the crystal fields. We developed a stereoscopic way to unravel the g-factor along the three principal axes. Moreover, ESR amplitude dependence on the direction of magnetic fields provides the further understanding of ESR mechanisms, which results from two factors, tunneling magnetoresistance (TMR) effect at the spin-polarized STM junction and the transverse magnetic field to drive ESR. Our results will enable to predict ESR active spin centers on different substrates as well as in other quantum-nanoscience platforms.
장은영(Eun Young Jang),이년종(Nyun Jong Lee),최등장(Deung Jang Choi),김태희(Tae Hee Kim) 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.4
Magnetite (Fe3O4) is currently one of key materials for applications in magnetic storage and many bioinspired applications because bulk Fe₃O₄ has a high Curie temperature (Tc = ~850 K) and nearly full spin polarization at room temperature (RT). In this work, Fe₃O₄ nanoparticles with different sizes of 12 to 15 ㎚ were prepared in a well-controlled manner by a nonhydrolytic synthetic method. Here, we report the significant intergrain magneto-resistance (MR) of ~2 % at RT in Fe₃O₄ nanoparticle pellets. The tunneling conductance was also investigated based on the Brinkman model, as well. Our results show clearly that the surface or interfacial property of the particles plays a crucial role in the MR effect.
정신질환자들에 동반된 기능성 위장질환에 영향을 미치는 정신사회적 요인에 관한 연구
강등현,장승호,류한승,최석채,노승호,백영석,이혜진,이상열,Kang, Deung-Hyun,Jang, Seung-Ho,Ryu, Han-Seung,Choi, Suck-Chei,Rho, Seung-Ho,Paik, Young-Suk,Lee, Hye-Jin,Lee, Sang-Yeol 한국정신신체의학회 2018 정신신체의학 Vol.26 No.1
연구목적 본 연구에서는 기능성 위장질환(Functional gastrointestinal disorder, 이하 FGID)이 동반된 정신질환자들의 정신사회적 특성을 알아보고자 하였다. 방 법 일 대학병원 정신건강의학과 외래를 방문한 환자를 대상으로 Rome III questionnaire - Korean version에 따라 FGID를 선별하여 144명의 자료를 분석하였다. 인구학적 요인을 조사하였으며, 정신사회적 요인을 평가하기 위해 Hospital Anxiety Depression Scale, Patient Health Questionnaire-15, Childhood Trauma Questionnaire-Korean, State-Trait Anger Expression Inventory를 사용하였다. 통계분석은 독립표본 t-검정(independent t-test)과 교차분석(chi-square test)을 사용하였다. 결 과 FGID에 따른 집단간 비교에서 학력에 따른 차이가 나타났다(${\chi}^2=10.139$, p=0.017). FGID 집단에 따른 정신질환의 차이에서는 과민성 대장증후군(Irritable bowel syndrome, 이하 IBS) 집단에서 유의한 차이가 있었다. (${\chi}^2=11.408$, p=0.022) IBS 집단은 불안(t=-3.106, p=0.002), 우울증상(t=-2.105, p=0.037), 신체증상(t=-3.565, p<0.001), 특성분노(t=-3.683, p<0.001), 분노-억제(t=-2.463, p=0.015), 분노-표출(t=-2.355, p=0.020)에서 높은 점수를 나타냈다. 기능성 소화불량(Functional dyspepsia) 집단에서는 불안(t=-4.893, p<0.001), 우울증상(t=-3.459, p<0.001), 신체증상(t=-7.906, p<0.001), 특성분노(t=-4.148, p<0.001), 상태분노(t=-2.181, p=0.031), 분노-억제(t=-2.684, p=0.008), 분노-표출(t=-3.005, p=0.003)지표가 유의하게 높았다. 비미란성 위식도 역류증(Nonerosive reflux disease) 집단에서는 불안(t=-4.286, p<0.001), 우울증상(t=-3.402, p<0.001), 신체증상(t=-7.162, p<0.001), 특성분노(t=-2.994, p=0.003), 상태분노(t=-2.259, p=0.025), 분노-억제(t=-2.772, p=0.006), 분노-표출(t=-2.958, p=0.004)에서 유의미하게 높은 수준을 나타냈다. 결 론 본 연구에서는 정신질환자에서 FGID의 유병률이 매우 높고, 다양한 정신사회적 변인들이 이에 영향을 미치는 것으로 나타났다. 따라서 이러한 정신의학적 접근은 FGID 환자를 더 잘 이해하고 치료하는데 있어서 도움이 될 것으로 생각된다. Objectives : This study aimed to investigate the psychosocial characteristics of functional gastrointestinal disorder (FGID) in patients with psychiatric disorders. Methods : This study was conducted with 144 outpatients visiting the psychiatric clinic at a university hospital. FGIDs were screened according to the Rome III questionnaire-Korean version. Demographic factors were investigated, and psychosocial factors were evaluated using the Hospital Anxiety Depression Scale, Patient Health Questionnaire-15, Childhood Trauma Questionnaire-Korean, and State-Trait Anger Expression Inventory. Chisquared test and student's t-test were used as statistical analysis methods. Results : There were differences in education level between two groups divided according to FGID status (${\chi}^2=10.139$, p=0.017). Comparing the psychiatric disorder by FGID group, irritable bowel syndrome (IBS) group showed significant differences (${\chi}^2=11.408$, p=0.022). According to FGID status, IBS group showed significant differences for anxiety (t=-3.106, p=0.002), depressive symptom (t=-2.105, p=0.037), somatic symptom (t=-3.565, p<0.001), trait anger (t=-3.683, p<0.001), anger-in (t=-2.463, p=0.015), and anger-out (t=-2.355, p=0.020). Functional dyspepsia group showed significant differences for anxiety (t=-4.893, p<0.001), depressive symptom (t=-3.459, p<0.001), somatic symptom (t=-7.906, p<0.001), trait-anger (t=-4.148, p<0.001), state-anger (t=-2.181, p=0.031), anger-in (t=-2.684, p=0.008), and anger-out (t=-3.005, p=0.003). Nonerosive reflux disease group showed significant differences for anxiety (t=-4.286, p<0.001), depressive symptom (t=-3.402, p<0.001), somatic symptom (t=-7.162, p<0.001), trait anger (t=-2.994, p=0.003), state anger (t=-2.259, p=0.025), anger-in (t=-2.772, p=0.006), and anger-out (t=-2.958, p=0.004). Conclusions : Patients with psychiatric disorders had a high prevalence of FGID, and various psychosocial factors contributed to such differences. Therefore, the psychiatric approach can offer better understandings and treatments to patients with FGID.