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Park, Young S.,Kim, Yongmin,Im, Hyunsik American Institute of Physics 2010 JOURNAL OF APPLIED PHYSICS - Vol.107 No.8
<P>We report that the performance of the optical properties in multilayered GaN/Al0.5Ga0.5N quantum wells is improved by inserting an ultrathin (5 angstrom) Al0.5Ga0.5N layer in the middle of the GaN layers. A considerable redshift in the photoluminescence and the cathodoluminescence (CL) spectra is observed due to the additional strain along the growth direction resulting in piezoelectric polarization. The structural uniformity along the plane directions is investigated using two dimensional CL mapping. The results presented are useful for tuning the optical properties of multilayered heterojunction optoelectronic devices. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3386381]</P>
Ding, Z.,Li, J. X.,Zhu, J.,Ma, T. P.,Won, C.,Wu, Y. Z. American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.113 No.17
<P>The anisotropic magnetoresistance (AMR) effect with a magnetic field along arbitrary directions in single crystalline (001)-oriented Fe3O4 films was studied. A cubic symmetry term, an in-plane uniaxial term, and an out-of-plane uniaxial term could be quantitatively separated. The cubic term is independent of the current direction, and decreases with increasing temperature, but both in-plane and out-of-plane uniaxial terms are found to be strongly dependent on the current orientation. This three-dimensional magnetoresistance measurement provides a quantitative method for identifying the different contributions to the AMR effect. (C) 2013 American Institute of Physics.</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>
Dependence of the switching current density on the junction sizes in spin transfer torque
You, Chun-Yeol,Jung, Myung-Hwa American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.113 No.7
<P>We investigate the dependence of switching current density on the junction sizes in the in-plane spin transfer torque nanopillar structures by using micromagnetic simulations. While the macrospin model predicts weak dependence of switching current density on the junction sizes, we find that the switching current density is a sensitive function of the junction sizes. It can be explained with the complicated spin configurations and dynamics during the switching process. The detail spin configurations and dynamics are determined by spin wave excitation with the finite wave vector, which is related with the exchange coupling energy and junction shape. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792728]</P>
Ryu, Gi-Bong,Kim, Sung-Soo American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>With a simulation model of microstrip line attached by Fe55Al18O27 thin film of high magnetic loss, S parameters and power absorption has been analyzed by finite element method in the frequency range of available material parameters (0.1-1.5 GHz). It is demonstrated that the S parameters and power absorption are dominantly controlled by the electrical properties of the thin film. Although the film has a large value of magnetic loss resulting from ferromagnetic resonance, it is predicted that the power dissipation by magnetic loss is negligibly small. Simulation under assumption of high electrical resistivity shows that both S-11 and S-21 values approach to the value of original microstrip line. Another simulation of sheet resistance effect by film thickness control shows that higher value of power absorption is predicted in the films of small thickness mainly due to lower reflection loss. For the conductive and magnetic Fe55Al18O27 thin film, it is concluded that the dominant power loss mechanism is eddy current loss for magnetic field or Ohmic loss for electric field around the strip conductor in the frequency range investigated. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068014]</P>
Finite element analysis for cooling effect of magnetic fluid with alternating magnetic field
Lee, Se-Hee,Kim, Young-Sun American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>We present a fully coupled finite element method (FEM) for analyzing a cooling effect of magnetic fluid with an alternating magnetic field driven with the power frequency, 60 Hz. There are two different heat sources with an alternating magnetic field such as the Joule's loss in coils excited with electric input and the power dissipation corresponding to Neel and Brownian relaxation. Because the input frequency is relatively low, the Joule's loss in coil is a dominant heat source. The heat, therefore, transfers from the coil to the magnetic fluid and the natural convection phenomena arise on the coil surfaces. To consider the natural convection phenomena, the buoyant force density was considered in a magnetic fluid. Additionally, the forced convection, magnetoconvection, results from the magnetic body force density with the magnetization as a function of magnetic field intensity and temperature. These two convection phenomena play a key role for cooling effect of magnetic fluid with an alternating magnetic field. To derive the magnetic body force density, we, here, numerically employed the continuous approach of Kelvin force density, which has been derived by introducing the virtual air-gap scheme incorporating with the FEM. The Langevin function was employed to consider the nonlinear magnetic susceptibility for evaluating the Kelvin force density and the power dissipations due to the Neel relaxation and Brownian relaxation. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3062955]</P>
Kang, J.-S.,Kim, G.,Lee, H. J.,Kolesnik, S.,Dabrowski, B.,Lee, Hangil,Kim, J.-Y.,Lee, Jieun,Kim, Bongjae,Min, B. I. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>The electronic structure of ferromagnetic double-perovskite La2MnNiO6 has been investigated by employing Mn and Ni 2p -> 3d resonant photoemission spectroscopy (RPES) and soft x-ray absorption spectroscopy (XAS). The Mn and Ni 2p XAS measurements show that Mn ions are formally tetravalent (3d(3)) and that Ni ions are formally divalent (3d(8)). Mn and Ni 2p -> 3d RPES shows that the occupied Mn 3d(3) (t(2g)(3)up arrow) states are sharp and located around 2 eV below E-F, while the occupied Ni 3d(8) (t(2g)(3)up arrow t(2g)(3)up arrow e(g)(2)up arrow) states are broader than the Mn 3d states and they extend from E-F to similar to 5 eV below E-F. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3073663]</P>
Kim, Jungtaek,Yoo, Taehee,Chung, Sunjae,Lee, Sanghoon,Liu, X.,Furdyna, J. K. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>The angle dependence of the planar Hall effect has been analyzed based on the magnetic free energy including the magnetic anisotropy and the Zeeman effects. The Zeeman effect dominated the magnetic anisotropy in high field and only a single energy minimum is shown in free energy over entire field angle, which leads to the coherent rotation of the magnetization in the form of a single domain state. When the field strength is reduced below 300 Oe, multiple energy minima appear in the angle dependence of free energy due to the increase in the relative importance of magnetic anisotropy. In the low field region, reorientation of magnetization experiences abrupt transition between the free energy minima. The pinning fields obtained from the analysis showed systematic dependence on the strength of external field, which was used to rotate magnetization. We understood such pinning energy dependence in terms of the difference in the free energy density profile for the different field strengths. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3055354]</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>
Kim, Jung H.,An, Hyeun H.,Yoon, Chong S. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>Silicon oxide nanowires synthesized during carbonization of polyimide thin film on a silicon substrate exhibited marked enhancement in photoluminescence (PL) at 420 nm by prolonging the growth period. Maximum intensity was recorded when the nanowire diameter coarsened from 70 to 165 nm by extending the growth period from 1 to 3 h. The enhancement was attributed to the increase in concentration of neutral oxygen vacancies on the surface of the nanowires. It was also demonstrated that the PL peak can be shifted to 600 nm while maintaining the enhanced intensity by postannealing the nanowires in a reducing atmosphere. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3091261]</P>