Browsing by Author "Lin, J. Y."

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Antisite disorder driven spontaneous exchange bias effect in La2-xSrxCoMnO6 (0 <= x <= 1)
(2016-03-02)
Murthy, J. Krishna
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Chandrasekhar, K. D.
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Wu, H. C.
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Yang, H. D.
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Lin, J. Y.
Doping at the rare-earth site by divalent alkaline-earth ions in perovskite lattice has witnessed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report an antisite disorder driven spontaneous exchange bias effect as a result of hole carrier (Sr2+) doping in La2-xSrxCoMnO6 (0 < x < 1) double perovskites. X-ray diffraction and Raman spectroscopy have evidenced an increase in disorder with the increase of Sr content up to x = 0.5 and thereby a decrease from x = 0.5 to 1. X-ray absorption spectroscopy has revealed that only Co is present in the mixed valence of Co2+ and Co3+ states with Sr doping to compensate the charge neutrality. Magnetotransport is strongly correlated with the increase of antisite disorder. The antisite disorder at the B-site interrupts the long-range ferromagnetic order by introducing various magnetic interactions and instigates reentrant glassy dynamics, phase separation and canted type antiferromagnetic behavior with the decrease of temperature. This leads to a novel magnetic microstructure with unidirectional anisotropy that causes a spontaneous exchange bias effect that can be tuned with the amount of antisite disorder.
Bonding anisotropy in multiferroic TbMnO(3) probed by polarization dependent x-ray absorption spectroscopy
(2009-01-26)
Chen, J. M.
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Lee, J. M.
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Chen, C. K.
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Chou, T. L.
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Lu, K. T.
O K- and Mn L(2,3)-edges x-ray absorption spectra of orthorhombic TbMnO(3) single crystals show strong polarization dependence, in contrast with results of previous experiments on orthorhombic LaMnO(3) and DyMnO(3) thin films that show nearly isotropic spectral structure. First-principles calculations reveal that TbMnO(3) exhibits a zigzag e(g) orbital ordering ground state. The highly distorted MnO(6) octahedron and orbital ordering in TbMnO(3) produce highly anisotropic Mn-O bonding within the ab plane, a frustration of the magnetic ordering, and the formation of complicated incommensurate magnetic structures.
Bonding anisotropy in multiferroic TbMnO3 probed by polarization dependent x-ray absorption spectroscopy
(2009-01-26)
Chen, J. M.
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Lee, J. M.
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Chen, C. K.
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Chou, T. L.
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Lu, K. T.
O K- and Mn L-2,L-3-edges x-ray absorption spectra of orthorhombic TbMnO3 single crystals show strong polarization dependence, in contrast with results of previous experiments on orthorhombic LaMnO3 and DyMnO3 thin films that show nearly isotropic spectral structure. First-principles calculations reveal that TbMnO3 exhibits a zigzag e(g) orbital ordering ground state. The highly distorted MnO6 octahedron and orbital ordering in TbMnO3 produce highly anisotropic Mn-O bonding within the ab plane, a frustration of the magnetic ordering, and the formation of complicated incommensurate magnetic structures.
Distribution of electronic reconstruction at the n-type LaAlO(3)/SrTiO(3) interface revealed by hard x-ray photoemission spectroscopy
(2011-12-26)
Chu, Y. Y.
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Liao, Y. F.
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Tra, V. T.
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Yang, J. C.
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Liu, W. Z.
We investigated the electronic reconstruction at the n-type LaAlO(3)/SrTiO(3) interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti(4+) to Ti(3+) occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO(3) with a depth of about 48 angstrom (similar to 12 unit cells) and an estimated total charge transfer of similar to 0.24 electrons per two-dimensional unit cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672099]
Distribution of electronic reconstruction at the n-type LaAlO3/SrTiO3 interface revealed by hard x-ray photoemission spectroscopy
(2011-12-26)
Chu, Y. Y.
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Liao, Y. F.
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Tra, V. T.
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Yang, J. C.
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Liu, W. Z.
We investigated the electronic reconstruction at the n-type LaAlO3/SrTiO3 interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti4+ to Ti3+ occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO3 with a depth of about 48 angstrom (similar to 12 unit cells) and an estimated total charge transfer of similar to 0.24 electrons per two-dimensional unit cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672099]
Effects of Fe substitution on the transport properties of the superconductor MgB2
(2007-05-01)
Gahtori, Bhasker
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Lal, Ratan
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Agarwal, S. K.
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Kuo, Y. K.
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Sivakumar, K. M.
A systematic study has been made on the effect of Fe substitution by means of resistivity, thermal conductivity, and Seebeck coefficient of the Mg1-xFexB2 superconductor involving 0%, 0.3%, 0.6%, 1.2%, and 3.0% Fe content. The superconducting transition has been found to be very sharp (similar to 0.2 K) for a pristine sample and substitution of Fe results in the decrease of T-C with the increase in the transition width. Thermal conductivity is found to decrease with Fe content in general, such that the shoulder present in the pristine sample tends to fade away with increasing Fe. An analysis has been made on the normal state resistivity in terms of a two-band model, and of the thermal conductivity in terms of the Wiedemann-Franz law and the lattice thermal conductivity, and the information obtained on the basis of this analysis has been discussed. Besides, the electronic density of states (DOS) near the Fermi level remains nearly unaffected upon Fe substitution, as evidenced by the Seebeck coefficient measurements. When compared with Mn, Fe behaves like a nonmagnetic element with a modest variation in T-C and on the other hand, the T-C depression is much stronger when compared with other elements like Al, Cu, etc. Therefore, the observed variation in T-C for the presently investigated concentrations of Fe is attributed to the specific nature of the given substituent element (Fe) in altering the phonon frequency and/or electron-phonon coupling strength rather than spin-flip scattering or change in DOS or disorder.
Effects of rapid thermal annealing on the structural properties of TiO(2) nanotubes
(2011-10-15)
Lin, J. Y.
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Chou, Y. T.
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Shen, J. L.
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Yang, M. D.
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Wu, C. H.
The structural properties of TiO(2) nanotubes with rapid thermal annealing (RTA) and traditional thermal annealing in O(2) were studied by X-ray diffraction (XRD) and Raman scattering measurements. From analyzing the line width of XRD and the correlation length of the Raman peak, we demonstrate that RTA can be an effective tool for amorphous-anatase transformation in TiO(2) nanotubes. The Raman peak redshifts and reduces its line width after thermal annealing and RTA, which may involves the reduction of oxygen-related defects. (C) 2011 Elsevier B. V. All rights reserved.
Effects of rapid thermal annealing on the structural properties of TiO2 nanotubes
(2011-10-15)
Lin, J. Y.
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Chou, Y. T.
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Shen, J. L.
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Yang, M. D.
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Wu, C. H.
The structural properties of TiO2 nanotubes with rapid thermal annealing (RTA) and traditional thermal annealing in O-2 were studied by X-ray diffraction (XRD) and Raman scattering measurements. From analyzing the line width of XRD and the correlation length of the Raman peak, we demonstrate that RTA can be an effective tool for amorphous-anatase transformation in TiO2 nanotubes. The Raman peak redshifts and reduces its line width after thermal annealing and RTA, which may involves the reduction of oxygen-related defects. (C) 2011 Elsevier B. V. All rights reserved.
Effects of strain on the electronic structures and T-C's of the La0.67Ca0.33MnO3 and La0.8Ba0.2MnO3 thin films deposited on SrTiO3
(2006-08-21)
Chou, Hsiung
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Tsai, M. -H.
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Yuan, F. P.
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Hsu, S. K.
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Wu, C. B.
The strain effects on the electronic structures of La0.67Ca0.33MnO3 (LCMO) and La0.8Ba0.2MnO3 (LBMO) thin films have been studied by O K-edge x-ray absorption near edge structure (XANES) spectroscopy. For LCMO, the first-principles calculations reveal that the features in the XANES spectra are associated with hybridized states between O 2p and Mn minority-spin 3d t(2g) and e(g), La 5d/Ca 3d, and Mn 4s/Ca 4p states. An analysis of these features shows that the tensile strain decreases substantially La-O and Ca-O hybridization and T-C for LCMO. For LBMO, the small compressive strain enhances slightly La-O and Ba-O hybridization and T-C. (c) 2006 American Institute of Physics.
Effects of water intercalation in Na(x)CoO(2)center dot yH(2)O
(2009)
Lin, J. Y.
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Chen, Y. L.
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Hsu, Ben
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Liu, C. J.
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Tai, Y. L.
Water intercalation is necessary for the occurrence of superconductivity in NaxCoO(2) center dot yH(2)O. It is known that water insertion leads to the elongation of the c-axis. Beyond that, it remains controversial about the effects of water intercalation on the electronic structure of Na(x)CoO(2) center dot yH(2)O. In this paper, we report the Co-K edge spectroscopy on y = 0.7 and 1.4 samples, respectively. The spectra are compared with those of the reference samples. It is found that the variation of the Co valence can not be explained by the simple electron counting. These results are consistent with those of the previous chemical titration.
Low-temperature specific heat of superconductors - I. Historical perspective prior to 1986
(2019-10-01)
Ho, J. C.
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Lin, J. G.
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Lin, J. Y.
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Yang, H. D.
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交大名義發表
Specific heat is a fundamental thermodynamic quantity closely related to internal energy and entropy of a system. In superconductivity research, it has been playing important roles ever since the intriguing critical phenomenon was discovered. Looking back, though, calorimetric measurements, along with the relevant low-temperature techniques, improved slowly over decades. Erroneous conclusions were reached often in the beginning, but eventually several calorimetrically-derived key features formed part of the basis in the microscopic BCS theory and its extended versions. While unable to predict whether or when a given material would become superconducting, theories helped data analysis and guided new superconductors search. Many elements, alloys and compounds joined the long list of known superconductors over the 75-year period between 1911 and 1986. Specific heat data yielded characteristic parameters, and ascertained whether an observed transition was a bulk effect. In the later years, theoretical models or experimental results also revealed a few classes of unconventional superconductors, mostly involving the interplay between superconductivity and magnetism. This article is purposely focused, as historical perspective, on how such activities progressed. Only initial findings and some related reports are cited, leaving out much more detailed and better executed work published later. For the same reason, only select figures and discussions of cited articles, but not their full extent, are included.
Memory characteristics of Co nanocrystal memory device with HfO(2) as blocking oxide
(2007-03-26)
Yang, F. M.
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Chang, T. C.
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Liu, P. T.
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Yeh, P. H.
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Yu, Y. C.
In this letter, the Co nanocrystals using SiO(2) and HfO(2) as the tunneling and the control dielectric with memory effect has been fabricated. A significant memory effect was observed through the electrical measurements. Under the low voltage operation of 5 V, the memory window was estimated to similar to 1 V. The retention characteristics were tested to be robust. Also, the endurance of the memory device was not degraded up to 10(6) write/erase cycles. The processing of the structure is compatible with the current manufacturing technology of semiconductor industry. (c) 2007 American Institute of Physics.
Memory characteristics of Co nanocrystal memory device with HfO2 as blocking oxide
(2007-03-26)
Yang, F. M.
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Chang, T. C.
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Liu, P. T.
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Yeh, P. H.
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Yu, Y. C.
In this letter, the Co nanocrystals using SiO2 and HfO2 as the tunneling and the control dielectric with memory effect has been fabricated. A significant memory effect was observed through the electrical measurements. Under the low voltage operation of 5 V, the memory window was estimated to similar to 1 V. The retention characteristics were tested to be robust. Also, the endurance of the memory device was not degraded up to 10(6) write/erase cycles. The processing of the structure is compatible with the current manufacturing technology of semiconductor industry. (c) 2007 American Institute of Physics.
Metamagnetic behaviour and effect of field cooling on sharp magnetization jumps in multiferroic Y2CoMnO6
(2014-10-01)
Murthy, J. Krishna
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Chandrasekhar, K. D.
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Wu, H. C.
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Yang, H. D.
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Lin, J. Y.
We present sharp magnetization jumps and field-induced irreversibility in magnetization in multiferroic Y2CoMnO6. The appearance of magnetic relaxation and field sweep rate dependence of magnetization jumps resembles the martensite-like scenario and suggests the coexistence of E*-type antiferromagnetic and ferromagnetic phases at low temperatures. In Y2CoMnO6, the critical field required for the sharp jump can be increased or decreased depending on the magnitude and direction of the cooling field; this is remarkably different from manganites or other metamagnetic materials where the critical field increases irrespective of the direction of the applied field cooling. The cooling field dependence on the sharp magnetization jumps has been described by considering exchange pinning mechanism at the interface, like in the exchange bias model. Copyright (C) EPLA, 2014
Nickel nanocrystals with HfO2 blocking oxide for nonvolatile memory application
(2007-05-28)
Yang, F. M.
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Chang, T. C.
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Liu, P. T.
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Chen, U. S.
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Yeh, P. H.
A distributed charge storage with Ni nanocrystals embedded in the SiO2 and HfO2 layer has been fabricated in this study. The mean size and aerial density of the Ni nanocrystals are estimated to be about 5 nm and 3.9x10(12)/cm(2), respectively. The nonvolatile memory device with Ni nanocrystals exhibits 1 V threshold voltage shift under 4 V write operation. The device has a long retention time with a small charge lose rate. Besides, the endurance of the memory device is not degraded up to 10(6) write/erase cycles. (C) 2007 American Institute of Physics.
Nickel silicide nanocrystals embedded in SiO2 and HfO2 for nonvolatile memory application
(2007-12-03)
Yang, F. M.
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Chang, T. C.
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Liu, Po-Tsun
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Yeh, Y. H.
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Yu, Y. C.
In this study, a nonvolatile memory device with NiSi2 nanocrystals embedded in the SiO2 and HfO2 layer has been fabricated. A significant memory effect is observed during the characterization of the electrical properties. When a low operating voltage, 4 V, is applied, a significant threshold voltage shift of 1.3 V, is observed. The processing of this structure is compatible with the current manufacturing technology of semiconductor industry. (C) 2007 Published by Elsevier B.V.
Nonlinear transport of the inhomogeneous Wigner solid in a channel geometry
(2016-11-23)
Badrutdinov, A. O.
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Smorodin, A. V.
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Rees, D. G.
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Lin, J. Y.
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Konstantinov, D.
The transport properties of an electronic Wigner solid (WS) on the surface of superfluid helium-4 are investigated in a geometry that allows WS systems of significantly different sizes to be defined. We probe and compare transport phenomena attributed to the electronic order, such as Bragg-Cherenkov scattering and the WS sliding transition, in the cases of a long homogeneous WS, a small WS island, and a long inhomogeneous WS. We find no significant WS size effects on the transport properties, in contrast to predictions of theoretical works, which indicates an absence of long-range order in the WS systems under consideration. For the inhomogeneous WS, consisting of two distinct WSs connected in series, a complex interplay of individual WS transport properties is observed, as revealed in the observation of two separate Bragg-Cherenkov plateaus and WS sliding transitions. A simple model is proposed that provides a qualitative explanation of this behavior.
Optical coupling from InGaAs subcell to InGaP subcell in InGaP/InGaAs/Ge multi-junction solar cells
(2013-01-14)
Shu, G. W.
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Lin, J. Y.
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Jian, H. T.
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Shen, J. L.
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Wang, S. C.
Spatially-resolved electroluminescence (EL) images in the triple junction InGaP/InGaAs/Ge solar cell have been investigated to demonstrate the subcell coupling effect. Upon irradiating the infrared light with an energy below bandgap of the active layer in the top subcell, but above that in the middle subcell, the EL of the top subcell quenches. By analysis of EL intensity as a function of irradiation level, it is found that the coupled p-n junction structure and the photovoltaic effect are responsible for the observed EL quenching. With optical coupling and photoswitching effects in the multi-junction diode, a concept of infrared image sensors is proposed. (C)2012 Optical Society of America
Optical properties of Na0.68CoO2 thin film
(2007)
Hsu, M. H.
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Liu, H. L.
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Chang, W. J.
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Lin, J. Y.
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電子物理學系
The optical reflectance of single-crystalline Na0.68CoO2 (thickness around 3000 angstrom) thin film has been measured over a wide frequency (40-55000 cm(-1)) and at temperatures between 20 and 300 K. The room-temperature optical conductivity spectrum displays a metallic character. In addition, one E-1u phonon mode at about 518 cm(-1) is identified, while the other four phonon peaks are due to the sapphire substrate. As the temperature is lowered, the Drude plasma frequency exhibits little temperature dependence, whereas the scattering rate monotonically decreases with decreasing temperature. Notably, the Drude scattering rate at 20 K is found to approach zero, consistent with the small residual resistivity, indicating high quality of Na0.68CoO2 thin film. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Phase separation and persistent magnetic memory effect in La(0.625)Ca(0.375)MnO(3) and La(0.375)Pr(0.25)Ca(0.375)MnO(3) films
(2009-01-01)
Tsai, Y. T.
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Chang, W. J.
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Hsieh, C. C.
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Luo, C. W.
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Wu, K. H.
Both La(0.375)Pr(0.25)Ca(0.375)MnO(3) (LPCMO) and La(0.625)Ca(0.375)MnO(3) (LCMO) were found to exhibit coexistence of competing orders (phase separation) over a wide temperature range. However, substantial hysteretic behaviors in both of the temperature-dependent resistance [R(T)] and magnetization [M(T)] also known as the persistent magnetic memory effect (PMME)] are only displayed in LPCMO. The results indicate that, in LPCMO, the size distribution of the coexisting charge-ordered insulating and metallic ferromagnetic (FM) phases plays a determinant role in the PMME effects in different temperature regimes. Moreover, due to the direct competition between the two coexisting phases, the system is most susceptible to the external applied field in the hysteretic temperature region. On the other hand, in LCMO, the phase transition between paramagnetic and FM is more like an isomorphic transition in pure materials, and thus does not show significant hysteresis. c 2009 American Institute of Physics. [DOI: 10.1063/1.3055802]