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Origin of asymmetry of tunneling conductance in CoFeB∕MgO∕CoFeB tunnel junction
Jang, Youngman,Lee, Kisu,Lee, Seungkyo,Yoon, Seungha,Cho, B. K.,Cho, Y. J.,Kim, K. W.,Kim, Kwang-seok American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>We investigated the top and bottom interfaces of a CoFeB/MgO/CoFeB tunnel junction using transmission electron microscope (TEM) and x-ray photoemission spectroscopy (XPS) in order to understand the origin of the asymmetry of dI/dV in terms of bias polarity. It was found, from a TEM image, that there is no clear cut at the top interface, while the bottom interface has relatively clean boundary. Furthermore, XPS data show that more hydroxides were formed at the top interface than at the bottom interface. These indicate that the hydroxides would hinder the epitaxial crystallinity at the interface in CoFeB/MgO/CoFeB tunnel junctions. Therefore, it is most likely that the asymmetry of dI/dV is caused by the disappearance of minority Bloch state, which is closely correlated with the existence of hydroxides at the top interface of a CoFeB/MgO/CoFeB tunnel junction. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3055344]</P>
Translocation of magnetic beads using patterned magnetic pathways for biosensing applications
Anandakumar, S.,Sudha Rani, V.,Jeong, J-R.,Kim, CheolGi,Kim, K. W.,Rao, B. Parvatheeswara American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>We have designed, fabricated, and demonstrated a novel system for translocation of magnetic beads at specific sites of the sensor surface on a single chip for biosensor applications. The soft NiFe elliptical (9 x 4 x 0.1 mu m(3)) elements are arranged as magnetic pathways connected to the model sensor surface. The patterned NiFe elements can generate different stray magnetic fields when they are subjected to the external rotating magnetic field. The inhomogeneity in stray magnetic fields can govern the magnetic bead motion on the pathways. We demonstrated the motion of Dynabead (R) M-280 magnetic bead on patterned pathways by controlling the external rotating magnetic field in clockwise and counterclockwise directions. The magnetic beads that were placed on the magnetic elliptical pathways are shown to be transported to the sensor surface, as well as be pulled out away from the surface. This technique enables microtranslocation of the magnetic beads coated with biomolecules to the specific binding sites of the sensor surface and as well as drive off the nonspecific binding biomolecules from the surface in performing number of sequential bead detection experiments for future integrated lab-on-a-chip systems. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3073965]</P>
Exchange bias and compositional depth profiles of annealed NiFe∕FeMn∕CoFe trilayers
Kim, Ki-Yeon,Choi, Hyeok-Cheol,You, Chun-Yeol,Lee, Jeong-Soo American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>We investigate the exchange bias fields and compositional depth profiles of the NiFe (bottom)/FeMn/CoFe (top) trilayers after a thermal treatment at different annealing temperatures. Interestingly, the magnetic hysteresis measurement revealed that the NiFe/FeMn/CoFe trilayers exhibit a contrasting variation of the exchange bias fields at the two interfaces in a completely different way to each other. High angle x-ray diffraction indicates that there is no distinguishable effect of a thermal treatment on the NiFe (111) and FeMn (111) peaks. The Ni 2p and Mn 2p x-ray photoelectron spectroscopy (XPS) spectrums near these two interfaces along with the XPS compositional depth profiles are measured. We find the asymmetric depth profiles of the Fe and Mn atoms throughout the FeMn layer and the preferential Mn diffusion into the NiFe layer compared to the CoFe layer. We believe that in situ applied fields during sample growth and ex situ cooling fields after sample growth have a different effect on the exchange bias fields of both top and bottom interfaces. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068628]</P>
Anisotropic magnetic phase diagrams of HoB4 single crystal
Kim, J. Y.,Cho, B. K.,Han, S. H. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>We have investigated the magnetic and electronic properties of a single-crystal HoB4. Antiferromagneticlike transitions were revealed by the temperature-dependent magnetization exhibiting two transition temperatures at T-N1=7.1 K and T-N2=5.7 K for an applied magnetic field along the c-axis, and showed only one transition at T=5.7 K for an applied magnetic field perpendicular to the c-axis. The isothermal magnetization with an applied magnetic field along the c-axis exhibited three distinct metamagnetic phase transitions at H-c1=2 T, H-c2=3.5 T, and H-c3=3.9 T at T=2 K. On the other hand, the isothermal magnetization with an applied magnetic field perpendicular to the c-axis showed two metamagneticlike transitions. A rapid change in the temperature and the field-dependent resistivity was found to be intimately correlated with magnetic transitions. Based on the isothermal magnetization and field-dependent resistivity for both magnetic field directions (H parallel to c and H perpendicular to c), anisotropic phase diagrams of HoB4 were constructed. From the comparison of the phase diagram of HoB4 with that of DyB4, it was deduced that HoB4 has a geometrical quadrupolar frustration of Ho3+ moment. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3075871]</P>
Characteristic analysis of electrodynamic suspension device with permanent magnet Halbach array
Cho, Han-Wook,Han, Hyung-Seok,Bang, Je-Sung,Sung, Ho-Kyung,Kim, Byung-Hyun American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>This article deals with the characteristic analysis of electrodynamic suspension (EDS) device with the permanent magnet (PM) Halbach array system. On the basis of transfer relation theorem with magnetic vector potential, the magnetic field quantities were obtained and then confirmed with the corresponding two-dimensional and three-dimensional finite element analysis result. In order to validate the characteristic analysis scheme for PM-EDS device, the dynamic performance was tested by using a high-speed rotary-type dynamic test facility with linear peripheral speed up to 250 km/h. A comparison is made between the analysis and the experimental results to demonstrate the design considerations of PM-EDS device for high-speed maglev. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068425]</P>
Jalli, Jeevan,Hong, Yang-Ki,Bae, Seok,Lee, Jae-Jin,Abo, Gavin S.,Lyle, Andrew,Gee, Sung-Hoon,Lee, Hwachol,Mewes, Tim,Sur, Jeong-Chul,Lee, Sung-Ik American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>Liquid phase epitaxy technique was used to grow 144 mu m thick barium ferrite (BaFe12O19; BaM) single crystalline films on (111) Gd3Ga5O12 substrate. The growth rate of 72 mu m/h was achieved with a flux system of Fe2O3-BaCO3-Na2CO3. The grown BaM films show single crystalline (000l) orientation that was confirmed by x-ray diffraction and magnetic torque curves. The saturation magnetization (4 pi M-s) and the anisotropy field (H-k) were found to be 4.2 kG and 16.0 kOe, respectively. The ferrimagnetic resonance linewidth (Delta H) at 35 GHz was measured to be 0.1 kOe. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3062824]</P>
Gwag, Jin Seog,Bae, Kwang-Soo,Lee, You-Jin,Kim, Jae-Hoon American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>This paper proposes a liquid crystal (LC) display (LCD) mode, characterized by an azimuthally continuous nematic domain, driven by patterned electrodes with circular- and doughnut-shaped slits producing conelike fields, as a vertically aligned (VA) nematic LC mode. This proposed mode is focused on achieving a high transmittance display with omnidirectionally uniform optical characteristics by utilizing the proposed electrode structure. Consequently, the experimental results of the proposed LCD mode show high brightness and wide viewing angles that correlate well to numerical calculations. Other electro-optics characteristics of this mode correspond to the patterned VA LC mode. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3075593]</P>
Kim, Byung-Hyun,Kim, Gyubong,Park, Kihoon,Shin, Mincheol,Chung, Yong-Chae,Lee, Kwang-Ryeol American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.113 No.7
<P>A multi-scale approach connecting the atomistic process simulations to the device-level simulations has been applied to the Si(100)/SiO2 interface system. The oxidation of Si(100) surface was simulated by the atomic level molecular dynamics, the electronic structure of the resultant Si/suboxide/SiO2 interface was then obtained by the first-principles calculations, and finally, the leakage currents through the SiO2 gate dielectric were evaluated, with the obtained interface model, by the non-equilibrium Green's function method. We have found that the suboxide layers play a significant role for the electronic properties of the interface system and hence the leakage currents through the gate dielectric. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4791706]</P>
Tran, D. H.,Putri, W. B. K.,Wie, C. H.,Kang, B.,Lee, N. H.,Kang, W. N.,Lee, J. Y.,Seong, W. K. American Institute of Physics 2012 JOURNAL OF APPLIED PHYSICS - Vol.111 No.7
<P>We investigated influence of 4 wt. % BaSnO3 (BSO) addition on the thickness dependence of critical current density (J(c)) of GdBa2Cu3O7-delta (GdBCO) thin films deposited by using the pulsed laser deposition technique. The results show that J(c) measured at 77K of the GdBCO films is significantly enhanced by the addition of BSO. Thickness dependence of self-field J(c) in the BSO doped GdBCO films is reduced in comparison with that of pure GdBCO films. Improved field performance of J(c) is also observed for the BSO-doped GdBCO films up to thickness of 1.5 mu m. The enhancements are attributed to the growth of artificial pinning centers in the form of BSO nano precipitates confirmed by the cross-sectional transmission electron microscopy images. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676618]</P>
Luminescence and Raman studies of YNbO4 phosphors doped by Eu3+, Ga3+, and Al3+
Nazarov, Mihail,Kim, Young Jin,Lee, Eun Young,Min, Kyoung-In,Jeong, Mun Seok,Lee, Su Woong,Noh, Do Young American Institute of Physics 2010 JOURNAL OF APPLIED PHYSICS - Vol.107 No.10
<P>Efficient phosphors based on YNbO4 and doped by Eu3+, Ga3+, and Al3+ were synthesized with different fluxes under different thermal conditions and investigated under x-ray excitation and Raman spectroscopy. The samples codoped by Al3+ and Ga3+ show higher intensity under x-ray excitation in comparison with YNbO4:Eu3+ phosphors. The model of redistribution energy transfer from D-5(1) level to F-7(J) is proposed. Monoclinic fergusonite crystal structure and excellent luminescent properties under x-ray excitation allow recommend these phosphors as good candidates for different applications. (C) 2010 American Institute of Physics. [doi:10.1063/1.3392918]</P>