Browsing by Author "Lin, J. -Y."

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A new layered triangular antiferromagnet Li4FeSbO6: spin order, field-induced transitions and anomalous critical behavior
(2013)
Zvereva, E. A.
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Savelieva, O. A.
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Titov, Ya D.
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Evstigneeva, M. A.
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Nalbandyan, V. B.
Structure, electrochemical, magnetic and resonance properties of new layered antimonate Li4FeSbO6 were comprehensively studied using powder X-ray diffraction, cyclic voltammetry, magnetic susceptibility, heat capacity, electron spin resonance and Mossbauer spectroscopy. In the crystal structure the iron ions form the triangular network within (LiFeSbO6)(3-) layers alternating with nonmagnetic lithium layers. The electrochemical activity studied implies an Fe3+/Fe4+ redox couple at 4.3 V (ox.) and 3.9 V (red.) thereby revealing that Li can be reversibly extracted. The long-range antiferromagnetic order was found to occur at the Neel temperature, T-N approximate to 3.6 K, confirmed both by the magnetic susceptibility data and specific heat ones. The effective magnetic moment is estimated to be 5.93 mu(B)/f.u. and satisfactorily agrees with theoretical estimations assuming high-spin configuration of Fe3+ (S = 5/2). In the magnetically ordered state, though, the magnetization demonstrates rather peculiar behavior. An additional anomaly on the M(T) curves appears at T-2 < T-N in moderate magnetic field. The positions of transitions at T-N and T-2 separate increasingly with increasing external field. Multiple measurements consistently demonstrated field-sensitive moving of magnetic phase boundaries constituting a unique phase diagram for the compound under study. The complex low-dimensional (2D) nature of magnetic coupling was confirmed by the dynamic magnetic properties study. Electron spin resonance from Fe3+ ions in paramagnetic phase is characterized by a temperature independent effective g-factor of 1.99 +/- 0.01. However, the distortion and broadening of the ESR line were found to take place upon approaching the magnetically ordered state from above. The divergence of the temperature-dependent linewidth is analyzed in terms of both critical behavior close to long-range magnetic order and the Berezinskii-Kosterlitz-Thouless (BKT)-type transition. Heat capacity measurements even at zero field manifested an appearance of the additional anomaly at temperatures below the Neel temperature. The temperature dependence of ESR intensity, linewidth and shift of the resonant field imply an extended region of short-range order correlations in the compound studied. The rich variety of the anomalies in magnetic and resonance properties makes this new antimonate a very interesting system to investigate the multiple phase transitions and competing exchange interaction due to the critical role of the layered structure organization accompanied by the frustration effects in triangular antiferromagnets.
Anisotropic electronic structure in single crystalline orthorhombic TbMnO(3) thin films
(2010-02-01)
Wu, K. H.
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Gou, I. C.
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Luo, C. W.
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Uen, T. M.
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Lin, J. -Y.
We have deposited the c-axis-oriented orthorhombic TbMnO(3) (o-TMO) films with well-aligned in-plane orientations on NdGaO(3) (001) substrates by using pulsed laser deposition. The distinctive orientation alignments between the film and substrate allow the study of the X-ray absorption spectroscopy (XAS) with the electric field along three major crystallographic directions, respectively. Polarization-dependent XAS spectra show significant anisotropy in the electronic Structure of o-TMO. The correlation between the electronic structure, the bonding anisotropy, and the magnetoelectric effect in the multiferroic materials is revealed. (C) 2009 Elsevier B.V. All rights reserved.
Anisotropic electronic structure in single crystalline orthorhombic TbMnO3 thin films
(2010-02-01)
Wu, K. H.
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Gou, I. C.
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Luo, C. W.
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Uen, T. M.
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Lin, J. -Y.
We have deposited the c-axis-oriented orthorhombic TbMnO3 (o-TMO) films with well-aligned in-plane orientations on NdGaO3 (001) substrates by using pulsed laser deposition. The distinctive orientation alignments between the film and substrate allow the study of the X-ray absorption spectroscopy (XAS) with the electric field along three major crystallographic directions, respectively. Polarization-dependent XAS spectra show significant anisotropy in the electronic Structure of o-TMO. The correlation between the electronic structure, the bonding anisotropy, and the magnetoelectric effect in the multiferroic materials is revealed. (C) 2009 Elsevier B.V. All rights reserved.
Anisotropic magnetoresistance of La0.7Ca0.3MnO3 thin film biepitaxial step junctions
(2006-12-01)
Chen, S. F.
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Chang, W. J.
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Hsieh, C. C.
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Liu, S. J.
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Juang, J. Y.
The angular dependence of magnetoresistance (MR) of the La0.7Ca0.3MnO3 thin film biepitaxial step junction (BSJ) shows a simple sin(2)(theta) dependence in the in-plane high-field magnetoresistance, with theta being the angle between the applied field and current. This behavior is similar to the spin-orbit coupling-induced anisotropic magnetoresistance (AMR) commonly observed in transition ferromagnetic metals, except for two salient features. First, the maximum MR in the present case occurs at an oblique angle between the applied field (H) and electric current (I), while it is usually observed to occur when H parallel to I. Second, the AMR in the plane perpendicular to the film surface displays a remarkable value (Delta rho/rho similar to 8%), which is about an order of magnitude larger than that of the in-plane AMR. Such a large AMR cannot be solely explained by spin-orbit coupling effect. We suggest instead that the metallic and ferromagnetic inhomogeneous granules existing in the BSJ region might have acted as the source of spin-polarized scattering giving rise to the enhanced AMR when the colossal magnetoresistance was measured across the biepitaxial step boundaries. (c) 2006 American Institute of Physics.
Anisotropic spin-flip-induced multiferroic behavior in kagome Cu3Bi(SeO3)(2)O2Cl
(2017-03-15)
Wu, H. C.
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Chandrasekhar, K. Devi
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Yuan, J. K.
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Huang, J. R.
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Lin, J. -Y.
Compared to the previous report on Cu3Bi(SeO3)(2)O2X (X = Cl, Br) [V. Gnezdilov et al., (arXiv: 1604.04249)], where no dielectric anomaly was observed without magnetic field near T-N similar to 25.6K, we further present the dielectric behaviors without and with magnetic field in Cu3Bi(SeO3)(2)O2Cl. At zero field H = 0, an antiferromagnetic transition from magnetization and specific heat measurements is clearly established at T-N, while no dielectric anomaly was observed. Those results are similar to the previous report [V. Gnezdilov et al., (arXiv: 1604.04249)]. Above the critical field H-c similar to 0.8 T, a metamagnetic spin-flip transition from antiferromagnetic to ferrimagnetic order at T similar to T-N is induced anisotropically only for H broken vertical bar broken vertical bar c. Meanwhile, a ferroelectric behavior from dielectric and pyroelectric current measurements is observed below T similar to T-N; then a corresponding type-II multiferroics emerges above H-c. The key mechanism of the anisotropic spin-flip-induced multiferroicity in Cu3Bi(SeO3)(2)O2Cl can be ascribed to the breaking of magnetic twofold symmetry in the bc plane above H-c.
Anisotropic ultrafast dynamics in doped Y1-xCaxBa2Cu3O7-delta superconducting thin films
(2008)
Luo, C. W.
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Wu, K. H.
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Lin, J. -Y.
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Uen, T. M.
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Gou, Y. S.
The anisotropic dynamics of photoinduced quasiparticle in the Y1-xCaxBa2Cu3O7-delta (YCBCO) is revealed by using the orientation-resolved femtosecond reflection spectroscopy. This bulk-sensitive spectroscopy, combining with the well-textured (110)- and (100)- YCBCO thin films, serves as an effective probe to quasiparticle relaxation dynamics along different crystallographic orientations. Since the temperature at which the peak of temperature-dependent relaxation time (tau) manifested in the transient reflectance (Delta R/R) measurements is believed to intimately relate to the opening of superconducting gap, the results reported here should shed some light on the issue of the competing order scenarios for over-doped high-T-c superconductors.
Anisotropic Ultrafast Dynamics of Quasiparticles on CuO(2) Planes of Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta)
(2010-07-01)
Luo, C. W.
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Huang, T. C.
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Chiang, M. T.
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Wu, K. H.
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Juang, J. Y.
The orientation-resolved femtosecond spectroscopy, combined with the well-textured (110)- and (001)Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta) thin films, serves as an effective probe to quasiparticle relaxation dynamics on the ab planes and along the diagonal orientations. The significant divergences in the temperature-dependent relaxation time (tau) associated with the opening of superconducting gap were observed along the nodal directions and on the CuO(2) planes which are dominated by the a axis and b axis in the over-doped region. Moreover, the divergence in the temperature-dependent served along the nodal direction disappears around optimal doped region. This implies that the superconducting gap evolves from the dominant s-wave symmetry in over-doped region into the dominant d-wave symmetry in optimal doped region.
Anisotropic Ultrafast Dynamics of Quasiparticles on CuO2 Planes of Y0.7Ca0.3Ba2Cu3O7-delta
(2010-07-01)
Luo, C. W.
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Huang, T. C.
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Chiang, M. T.
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Wu, K. H.
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Juang, J. Y.
The orientation-resolved femtosecond spectroscopy, combined with the well-textured (110)- and (001)Y0.7Ca0.3Ba2Cu3O7-delta thin films, serves as an effective probe to quasiparticle relaxation dynamics on the ab planes and along the diagonal orientations. The significant divergences in the temperature-dependent relaxation time (tau) associated with the opening of superconducting gap were observed along the nodal directions and on the CuO2 planes which are dominated by the a axis and b axis in the over-doped region. Moreover, the divergence in the temperature-dependent served along the nodal direction disappears around optimal doped region. This implies that the superconducting gap evolves from the dominant s-wave symmetry in over-doped region into the dominant d-wave symmetry in optimal doped region.
Anomalous magnetic ordering in b-axis-oriented orthorhombic HoMnO(3) thin films
(2008-03-31)
Lin, T. H.
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Hsieh, C. C.
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Shih, H. C.
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Luo, C. W.
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Uen, T. M.
Orthorhombic HoMnO(3) films with well-aligned crystallographic orientations were deposited on LaAlO(3)(110) single crystal substrates by using pulsed laser deposition. The nearly perfect b-axis-oriented films provide the opportunity of investigating the orientation-dependent physical property of this material. The temperature dependent magnetization evidently displays an antiferromagnetic ordering near 42 K, irrespective to the direction of applied field. Furthermore, the theoretically expected lock-in transition was clearly observed at around 30 K when field was applied along the c axis and was undetectable along the a and b axes. The 30 K transition was suppressed to 26 K when the applied field increased from 100 to 500 Oe. (C) 2008 American Institute of Physics.
Antiferroelectric antiferromagnetic type-I multiferroic Cu9O2(SeO3)(4)Cl-6
(2019-12-11)
Wu, H. C.
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Denisova, K. N.
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Menzel, D.
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Kakarla, D. Chandrasekhar
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Maximova, O. V.
We report that Cu9O2(SeO3)(4)Cl-6 is a new multiferroic compound. Comprehensive studies of this compound have been carried out on single crystals as well as polycrystalline samples. Magnetic susceptibility chi and specific heat C with H parallel to c axis both reveal an anomaly at T-N = 37 K associated with the long-range antiferromagnetic order. However, no signature of this phase transition is seen with the H parallel to b axis, providing evidence of the anisotropic nature of its magnetic properties. The results of chi measurements are consistent with the temperature evolution of the intensity of magnetic reflections from the neutron diffraction experiments. The magnetic structure derived from neutron scattering measurements shows that half of the Cu(5) ions carry no moments. Furthermore, an anomaly in the dielectric constant near T-N and observable magnetoelectric coupling below T-N are found. At high temperatures, a dielectric peak at T-E = 267 K is identified with no measurable spontaneous polarization below T-E, thereby suggesting an antiferroelectric order. A steplike anomaly seen in chi(T) at T-E hints the weak spin-lattice coupling. Concomitantly, high-resolution temperature-dependent synchrotron x-ray diffraction experiments elucidate a local structural distortion at T-E.
Atomic-scale evolution of modulated phases at the ferroelectric-antiferroelectric morphotropic phase boundary controlled by flexoelectric interaction
(2012-04-01)
Borisevich, A. Y.
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Eliseev, E. A.
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Morozovska, A. N.
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Cheng, C. -J.
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Lin, J. -Y.
Physical and structural origins of morphotropic phase boundaries (MPBs) in ferroics remain elusive despite decades of study. The leading competing theories employ either low-symmetry bridging phases or adaptive phases with nanoscale textures to describe different subsets of the macroscopic data, while the decisive atomic-scale information has so far been missing. Here we report direct atomically resolved mapping of polarization and structure order parameter fields in a Sm-doped BiFeO3 system and their evolution as the system approaches a MPB. We further show that both the experimental phase diagram and the observed phase evolution can be explained by taking into account the flexoelectric interaction, which renders the effective domain wall energy negative, thus stabilizing modulated phases in the vicinity of the MPB. Our study highlights the importance of local order-parameter mapping at the atomic scale and establishes a hitherto unobserved physical origin of spatially modulated phases existing in the vicinity of the MPB.
Coexistence of isotropic and extended s-wave order parameters in FeSe as revealed by low-temperature specific heat
(2011-12-27)
Lin, J. -Y.
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Hsieh, Y. S.
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Chareev, D. A.
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Vasiliev, A. N.
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Parsons, Y.
The comprehensive low-temperature specific-heat C(T) data identify both an isotropic s-wave and extended s-wave order parameters coexisting in a superconducting single-crystal FeSe with T-c = 8.11 K. The isotropic gap Delta(0) = 1.33 meV on the hole Fermi sheets and the extended s-wave gap Delta = Delta(e)(1+ alpha cos2 phi) with Delta(e) = 1.13 meV and alpha = 0.78 on the electron Fermi sheets. The extended s wave is rather anisotropic, but the low-energy quasiparticle excitations demonstrate no sign of the accidental nodes. The coefficient gamma(H) manifesting the quasiparticle contribution to C is a nonlinear function of the applied magnetic field H in the mixed state in accord with the anisotropic multiorder parameters.
Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr(2)S(4)
(2010-03-22)
Sun, C. P.
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Huang, C. L.
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Lin, C. C.
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Her, J. L.
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Ho, C. J.
Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr(2)S(4) are reported. It is found that a metal-insulator transition in CdCr(2)S(4) is triggered by the electrical field. In magnetic fields, the resistivity rho of CdCr(2)S(4) responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr(2)S(4) the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.
Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4
(2010-03-22)
Sun, C. P.
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Huang, C. L.
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Lin, C. C.
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Her, J. L.
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Ho, C. J.
Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity rho of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.
Disrupted long-range spin-spiral ordering and electric polarization in the Zn-substituted quantum helimagnet LiCu(2-x)Zn(x)O(2)
(2010-06-18)
Hsu, H. C.
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Lee, W. L.
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Lin, J. -Y.
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Liu, H. L.
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Chou, F. C.
Long-range spin-spiral ordering in quantum quasi-two-dimensional helimagnet LiCu(2)O(2) is destroyed by similar to 8% Zn(2+) substitution and a magnetic anomaly near similar to 14 K of different character emerges. Zn substitution may have introduced either a magnetic ground state of spin glass in nature, antiferromagnetic ordering with complex easy-plane anisotropy, or a gapped phase which is phase separated and proportional to the Zn substitution level on a short-range ordered background. The magnetic ground state is modified at the same time that the electric polarization disappears.
Disrupted long-range spin-spiral ordering and electric polarization in the Zn-substituted quantum helimagnet LiCu2-xZnxO2
(2010-06-18)
Hsu, H. C.
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Lee, W. L.
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Lin, J. -Y.
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Liu, H. L.
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Chou, F. C.
Long-range spin-spiral ordering in quantum quasi-two-dimensional helimagnet LiCu2O2 is destroyed by similar to 8% Zn2+ substitution and a magnetic anomaly near similar to 14 K of different character emerges. Zn substitution may have introduced either a magnetic ground state of spin glass in nature, antiferromagnetic ordering with complex easy-plane anisotropy, or a gapped phase which is phase separated and proportional to the Zn substitution level on a short-range ordered background. The magnetic ground state is modified at the same time that the electric polarization disappears.
Doping dependence of the ultrafast electronic dynamics of Y(1-x)Pr(x)Ba(2)Cu(3)O(7-delta) thin-film superconductors from femtosecond optical spectroscopy
(2010-09-17)
Luo, C. W.
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Lo, H. P.
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Su, C. H.
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Wu, I. H.
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Chen, Y. -J.
Time-domain spectroscopy, which probes the dynamics of the electronic states near Fermi surface that are associated with superconductivity, has proven to be a powerful method for providing insights into the fundamental nature of both pseudogap and superconducting gap. This study shows that the unique T-x phase diagram with the time-evolving ultrafast dynamics of Y(1-x)Pr(x)Ba(2)Cu(3)O(7-delta) can be used to identify clearly the Nernst, pseudogap, and superconducting regions. All of the orders appear together at a specific delay time, such as 1.2-3 ps, after pumping by an ultrashort pulse. These discoveries suggest that the Nernst effect, the pseudogap and even superconductivity may have the same physical origin.
Doping dependence of the ultrafast electronic dynamics of Y1-xPrxBa2Cu3O7-delta thin-film superconductors from femtosecond optical spectroscopy
(2010-09-17)
Luo, C. W.
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Lo, H. P.
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Su, C. H.
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Wu, I. H.
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Chen, Y. -J.
Time-domain spectroscopy, which probes the dynamics of the electronic states near Fermi surface that are associated with superconductivity, has proven to be a powerful method for providing insights into the fundamental nature of both pseudogap and superconducting gap. This study shows that the unique T-x phase diagram with the time-evolving ultrafast dynamics of Y1-xPrxBa2Cu3O7-delta can be used to identify clearly the Nernst, pseudogap, and superconducting regions. All of the orders appear together at a specific delay time, such as 1.2-3 ps, after pumping by an ultrashort pulse. These discoveries suggest that the Nernst effect, the pseudogap and even superconductivity may have the same physical origin.
Doping evolution of Zhang-Rice singlet spectral weight: A comprehensive examination by x-ray absorption spectroscopy
(2013-10-31)
Chen, Y. -J.
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Jiang, M. G.
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Luo, C. W.
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Lin, J. -Y.
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Wu, K. H.
The total spectral weight S of the emergent low-energy quasiparticles in high-temperature superconductors (HTSCs) is explored by x-ray absorption spectroscopy. In order to examine the applicability of the Hubbard model, regimes that cover from zero doping to overdoping are investigated. In contrast to results of mean-field theory, we found that S deviates from linear dependence on the doping level p. The slope of S versus p changes continuously throughout the whole doping range with no sign of saturation up to p = 0.23. Therefore, the picture of the Zhang-Rice singlet remains intact within the most prominent doping regimes of HTSCs.
Doping-Dependent Phase Diagram of Ca-Doped YBCO Observed by Femtosecond Spectroscopy
(2011-01-01)
Chen, Y. -J.
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Wu, K. H.
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Luo, C. W.
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Lin, J. -Y.
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Juang, J. Y.
The quasiparticle relaxation dynamics in a single (001) Ca-doped YBCO (Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta) ) superconducting thin film was probed by using the femtosecond time-resolved spectroscopy. The (001) Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta) thin film was prepared on a (100)STO substrate by pulsed laser deposition. Through controlling the oxygen pressure and the annealing temperature within quartz tube, the doping level (0.08 < p < 0.22) in the phase diagram could be widely tuned from the overdoped region to the underdoped region with varying the hole concentration (p) in a single sample. In the overdoped region, two different components (positive/negative) were obviously identified in the transient reflectivity curves (Delta R/R). The negative component in Delta R/R emerges at T < T (c) and quickly defeated by the development of the positive component. The dramatic change in the positive component of Delta R/R arises well below T (c). However, this anomaly change does not appear in the underdoped region. Only the positive Delta R/R was clearly observed at whole temperatures. These results indicate that the scenario of high-T (c) superconductivity in the overdoped region would be different from the underdoped region.