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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>
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>
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>
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>
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>
So, S.,Fan, S.-Q.,Choi, H.,Kim, C.,Cho, N.,Song, K.,Ko, J. AMERICAN INSTITUTE OF PHYSICS 2010 APPLIED PHYSICS LETTERS Vol.97 No.26
<P>An organic dye (JK218) with thiol moiety as an anchoring group was synthesized and explored to assemble a cosensitized TiO2 electrode in combination with an inorganic CdS quantum-dot. Due to the selective adsorption of JK218 on the surface of CdS through thiol group, the developed cosensitized electrode demonstrates cascade architecture with CdS coating on TiO2 while JK218 functions as a covering on CdS. Most importantly, the energy levels of the TiO2-CdS-JK218 electrode were also found to be stepwise aligned, which accordingly makes electrons efficiently inject from JK218 to CdS under illumination and finally collect to TiO2. This constructed cosensitized electrode with an organic sensitizer (JK218) and an inorganic quantum-dot (CdS) being selectively bonded together is expected to be valuable for the interface design of next generation solar cells. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3533906]</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>
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>
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>
Magnetic properties of heavy fermion system Ce1−xGdxCoSi3
Hong, J. B.,Oh, H. J.,Kwon, Y. S. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>We have investigated magnetic properties of the heavy fermion system Ce1-xGdxCoSi3 (0 <= x <= 1) via specific heat and electrical resistivity measurements. The specific heat shows antiferromagnetism at 9 K for GdCoSi3 (x = 1.0). With increasing Ce concentration, T-N linearly decreases and is suppressed at x = 0.1. An anomalous hump in specific heat was found below the ordering temperature for x >= 0.4. For x = 0.1, non-Fermi-liquid behavior was found in electrical resistivity and -ln T divergence in C/T below 3 K. Our results indicate that x = 0.1 is a quantum critical point. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3076604]</P>