Browsing by Author "Hsieh, C. C."

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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.
;
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.
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.
;
Luo, C. W.
;
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.
Effects of compressive epitaxial strain in the b-axis on the magnetization response of orthorhombic HoMnO(3) thin films
(2009)
Lin, T. H.
;
Hsieh, C. C.
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Shih, H. C.
;
Luo, C. W.
;
Uen, T. M.
The orthorhombic phase HoMnO(3) (o-HMO in Pbnm symmetry setting) thin films were prepared on LaAlO(3)(110) (LAO(110)) substrates by pulsed laser deposition. While for films grown on LAO(110) substrates, the compressive strain along the b-axis was resulted from the tensile strain in the a-c plane. The films provide the opportunity of investigating the effects of strain, hence lattice elasticity, on the physical properties of this material. For o-HMO films an antiferromagnetic ordering with T(N)similar to 42 K, irrespective to the direction of applied field was clearly observed. However, an additional magnetic ordering occurring around 26.4 K was observed when the field was applied along the c-axis of o-HMO. This transition, however, was absent when the field was applied along a-and b-axis. These results indicate that the second magnetic ordering observed along the c-axis could be more relevant to the Mn moments lying along the partially strained b direction of the o-HMO which has been theoretically expected to result in incommensurate-commensurate lock-in transition.
Electronic Structure and Magnetic Anisotropies in Orthorhombic Multiferroic YMnO(3) Thin Films
(2009-01-01)
Hsieh, C. C.
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Lin, T. H.
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Shih, H. C.
;
Lin, J-Y
;
Hsu, C-H
Thermodynamically YMnO(3) (YMO) can only exist with hexagonal structure at ambient conditions. In this study, we demonstrate that the stain between film and substrate can play an important role in forming orthorhombic YMO (o-YMO). o-YMO films with nearly perfect crystallographic orientation alignment were obtained on LaAlO(3)(110) substrates. These films allow us to unambiguously disclose the intrinsic magnetic property and electronic structure anisotropies along different crystallographic orientations. The antiferromagnetic (AFM) phase transition was around 42 K. Moreover, we observed a signature of spin reordering at lower temperatures when the applied field was parallel to the a- or c-axis. On the other hand, only the AFM transition was observed when the field is parallel to the b-axis. By comparing the X-ray absorption spectroscopy (XAS) results to standard manganese oxides, YMnO(3) exhibits the dominant Mn(+3) characteristics as that obtained from the standard Mn(2)O(3) powder. The polarization dependent XAS also revealed anisotropic bonding behavior along each crystalline axis.
Electronic Structure and Magnetic Anisotropies in Orthorhombic Multiferroic YMnO3 Thin Films
(2009-01-01)
Hsieh, C. C.
;
Lin, T. H.
;
Shih, H. C.
;
Lin, J-Y
;
Hsu, C-H
Thermodynamically YMnO3 (YMO) can only exist with hexagonal structure at ambient conditions. In this study, we demonstrate that the stain between film and substrate can play an important role in forming orthorhombic YMO (o-YMO). o-YMO films with nearly perfect crystallographic orientation alignment were obtained on LaAlO3(110) substrates. These films allow us to unambiguously disclose the intrinsic magnetic property and electronic structure anisotropies along different crystallographic orientations. The antiferromagnetic (AFM) phase transition was around 42 K. Moreover, we observed a signature of spin reordering at lower temperatures when the applied field was parallel to the a- or c-axis. On the other hand, only the AFM transition was observed when the field is parallel to the b-axis. By comparing the X-ray absorption spectroscopy (XAS) results to standard manganese oxides, YMnO3 exhibits the dominant Mn+3 characteristics as that obtained from the standard Mn2O3 powder. The polarization dependent XAS also revealed anisotropic bonding behavior along each crystalline axis.
Epitaxial-Strain Effects on Electronic Structure and Magnetic Properties of Hexagonal YMnO3 Thin Films Studied by Femtosecond Spectroscopy
(2013-04-01)
Wu, K. H.
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Chen, H. -J.
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Hsieh, C. C.
;
Luo, C. W.
;
Uen, T. M.
In this paper, (001)-oriented hexagonal YMnO3 (h-YMO) thin films with various nominal strain states were deposited on MgO(100), MgO(111), and YSZ(111) substrates by pulsed laser deposition. The in-plane orientation alignment and substrate-induced epitaxial strain between the h-YMO films and substrates are examined by X-ray diffraction (XRD) theta-2 theta, I broken vertical bar, and omega scans. The effects of epitaxial strain on the on-site Mn d-d transition energy E (dd) (T), and the N,el temperature (T (N)) in these thin films are investigated by wavelength-tunable ultrafast pump-probe techniques. We find that the changes of E (dd) (T) and T (N) depend on the type and magnitude of the epitaxial strain. The possible mechanisms for the observed strain effect on the electronic structure and associated magnetism are discussed.
Fabrication and low temperature thermoelectric properties of NaxCoO2 (x=0.68 and 0.75) epitaxial films by the reactive solid-phase epitaxy
(2007-02-05)
Chang, W. J.
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Hsieh, C. C.
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Chung, T. Y.
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Hsu, S. Y.
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Wu, K. H.
The authors have fabricated NaxCoO2 thin films via lateral diffusion of sodium into Co3O4 (111) epitaxial films (reactive solid-phase epitaxy [Ohta , Cryst. Growth Des. 5, 25 (2005)]). The environment of thermal diffusion is key to the control of the sodium content in thin films. From the results of x-ray diffraction and in-plane rho(ab), the epitaxial growth and the sodium contents of these films were identified. The thermoelectric measurements show a large thermoelectric power similar to that observed in single crystals. The quasiparticle scattering rate is found to approach zero at low temperatures, consistent with the small residual resistivity, indicating high quality of the NaxCoO2 thin films. (c) 2007 American Institute of Physics.
Magnetic ordering anisotropy in epitaxial orthorhombic multiferroic YMnO(3) films
(2008-11-15)
Hsieh, C. C.
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Lin, T. H.
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Shih, H. C.
;
Hsu, C. -H.
;
Luo, C. W.
Orthorhombic YMnO(3) thin films with (200), (020), and (001) orientations were, respectively, obtained by pulsed laser deposition on SrTiO(3)(110), LaAlO(3)(110), and SrTiO(3)(001) substrates. The results demonstrate that the strain between film and substrate can serve as an alternative in transforming the thermodynamically stable hexagonal YMnO(3) into the orthorhombic phase, which previously could be obtained with high-pressure high temperature syntheses and epitaxy-stabilized thin film processes. More importantly, these films allow us, for the first time, to unambiguously disclose the intrinsic magnetic property along different crystallographic orientations. Our results show that, although the antiferromagnetic (AFM) ordering remains the same, there is an additional spin reordering transition which is very much dependent on the crystallographic orientation along which the measuring field was applied and on the in-plane crystallographic alignment of the films. Detailed analyses indicate that the origin of the observed second reordering may be due to some strain-induced canted AFM state instead of the incommensurate lock-in transitions conceived previously.
Magnetic ordering anisotropy in epitaxial orthorhombic multiferroic YMnO3 films
(2008-11-15)
Hsieh, C. C.
;
Lin, T. H.
;
Shih, H. C.
;
Hsu, C. -H.
;
Luo, C. W.
Orthorhombic YMnO3 thin films with (200), (020), and (001) orientations were, respectively, obtained by pulsed laser deposition on SrTiO3(110), LaAlO3(110), and SrTiO3(001) substrates. The results demonstrate that the strain between film and substrate can serve as an alternative in transforming the thermodynamically stable hexagonal YMnO3 into the orthorhombic phase, which previously could be obtained with high-pressure high temperature syntheses and epitaxy-stabilized thin film processes. More importantly, these films allow us, for the first time, to unambiguously disclose the intrinsic magnetic property along different crystallographic orientations. Our results show that, although the antiferromagnetic (AFM) ordering remains the same, there is an additional spin reordering transition which is very much dependent on the crystallographic orientation along which the measuring field was applied and on the in-plane crystallographic alignment of the films. Detailed analyses indicate that the origin of the observed second reordering may be due to some strain-induced canted AFM state instead of the incommensurate lock-in transitions conceived previously.
Magnetism-induced ferroelectric polarization in the c-axis-oriented orthorhombic HoMnO(3) thin films
(2009-11-15)
Lin, T. H.
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Hsieh, C. C.
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Luo, C. W.
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Lin, J. -Y.
;
Sun, C. P.
The magnetism-induced ferroelectricity in the E-type orthorhombic HoMnO(3) (o-HMO) films grown on Nb-doped and undoped SrTiO(3)(001) substrates was studied. The temperature dependent magnetization in these films evidently exhibits an antiferromagnetic ordering around 44 K and an anomalous second magnetic ordering along the c-axis near 35 K. Interestingly, at this anomalous transition temperature, an associated ferroelectric polarization was probed by the P-E hysteresis measurements, indicating the intimated coupling between the ferroelectric response and the reordering of Mn spins, which has never been disclosed previously by dielectric constant measurements. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3260241]
Magnetism-induced ferroelectric polarization in the c-axis-oriented orthorhombic HoMnO3 thin films
(2009-11-15)
Lin, T. H.
;
Hsieh, C. C.
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Luo, C. W.
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Lin, J. -Y.
;
Sun, C. P.
The magnetism-induced ferroelectricity in the E-type orthorhombic HoMnO3 (o-HMO) films grown on Nb-doped and undoped SrTiO3(001) substrates was studied. The temperature dependent magnetization in these films evidently exhibits an antiferromagnetic ordering around 44 K and an anomalous second magnetic ordering along the c-axis near 35 K. Interestingly, at this anomalous transition temperature, an associated ferroelectric polarization was probed by the P-E hysteresis measurements, indicating the intimated coupling between the ferroelectric response and the reordering of Mn spins, which has never been disclosed previously by dielectric constant measurements. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3260241]
Marked enhancement of Neel temperature in strained YMnO(3) thin films probed by femtosecond spectroscopy
(2011-04-01)
Wu, K. H.
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Chen, H-J
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Chen, Y. T.
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Hsieh, C. C.
;
Luo, C. W.
In this paper, the (001)-oriented hexagonal YMnO(3) (h-YMO) thin films with various nominal strain states were deposited on MgO(100), MgO(111) and YSZ(111) substrates by pulsed laser deposition. The ultrafast dynamics probed by wavelength-tunable femtosecond pump-probe spectroscopy was performed to disclose the effects of the epitaxial strain on the electronic structure and associated magnetism. Analyses based on the measured transient-reflectivity-change (Delta R/R) curves revealed that while the magnitude of the on-site Mn d-d transition energy E(dd)(T) changes only slightly with the variation of the lattice constant ratio c/a, a marked shift in the antiferromagnetic (AFM) Neel temperature T(N) was observed and the direction of shift was dependent on the type of strain. The possible mechanism for the observed strain effect on the AFM ordering is discussed. Copyright (C) EPLA, 2011
Marked enhancement of Neel temperature in strained YMnO3 thin films probed by femtosecond spectroscopy
(2011-04-01)
Wu, K. H.
;
Chen, H-J
;
Chen, Y. T.
;
Hsieh, C. C.
;
Luo, C. W.
In this paper, the (001)-oriented hexagonal YMnO3 (h-YMO) thin films with various nominal strain states were deposited on MgO(100), MgO(111) and YSZ(111) substrates by pulsed laser deposition. The ultrafast dynamics probed by wavelength-tunable femtosecond pump-probe spectroscopy was performed to disclose the effects of the epitaxial strain on the electronic structure and associated magnetism. Analyses based on the measured transient-reflectivity-change (Delta R/R) curves revealed that while the magnitude of the on-site Mn d-d transition energy E-dd(T) changes only slightly with the variation of the lattice constant ratio c/a, a marked shift in the antiferromagnetic (AFM) Neel temperature T-N was observed and the direction of shift was dependent on the type of strain. The possible mechanism for the observed strain effect on the AFM ordering is discussed. Copyright (C) EPLA, 2011
Ordered YBCO sub-micron array structures induced by pulsed femtosecond laser irradiation
(2008-12-08)
Luo, C. W.
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Lee, C. C.
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Li, C. H.
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Shih, H. C.
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Chen, Y. -J.
We report on the formation of organized sub-micron YBa(2)Cu(3)O(7) (YBCO) dots induced by irradiating femtosecond laser pulses on YBCO films prepared by pulse laser deposition with fluence in the range of 0.21 similar to 0.53 J/cm(2). The morphology of the YBCO film surface depends strongly on the laser fluences irradiated. At lower laser fluence (similar to 0.21 J/cm(2)) the morphology was pattern of periodic ripples with sub-micrometer spacing. Slightly increasing the laser fluence to 0.26 J/cm(2) changes the pattern into organized sub-micron dots with diameters ranging from 100 nm to 800 nm and height of 150 nm. Further increase of the laser fluence to over 0.32 J/cm(2), however, appeared to result in massive melting and led to irregular morphology. The mechanism and the implications of the current findings will be discussed. Arrays of YBCO sub-micron dots with T(c) = 89.7 K were obtained. (C) 2008 Optical Society of America
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]
Phase separation and persistent magnetic memory effect in La0.625Ca0.375MnO3 and La0.375Pr0.25Ca0.375MnO3 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.
;
Wu, K. H.
Both La0.375Pr0.25Ca0.375MnO3 (LPCMO) and La0.625Ca0.375MnO3 (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]
Spatial dichotomy of quasiparticle dynamics in underdoped thin-film YBa2Cu3O7-delta superconductors
(2006-11-01)
Luo, C. W.
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Hsieh, C. C.
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Chen, Y. -J.
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Shih, P. T.
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Chen, M. H.
By the spatial-temporal-resolved femtosecond spectroscopy on well-textured (110)- and (100)-YBCO thin films, two distinctly temperature-dependent characteristics of quasiparticle relaxation in the nodal and antinodal directions are clearly identified. One temperature dependence associated with a high-energy gap has been observed along the ab diagonal for the whole hole-doping region and along the b axis except near optimal doping, while the other temperature dependence related to the opening of the superconducting gap appears along b axis regardless of the hole concentration. This spatial dichotomy between the nodal and antinodal quasiparticle dynamics and the evolution of gap symmetry with hole doping are discussed for enlightenment on the nature of the phase diagram of hole-doped cuprates. These strongly suggest that the two characteristics may have different physical origins and compete with each other.
Strain-induced effects on antiferromagnetic ordering and magnetocapacitance in orthorhombic HoMnO(3) thin films
(2009-01-14)
Lin, T. H.
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Shih, H. C.
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Hsieh, C. C.
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Luo, C. W.
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Lin, J-Y
We investigated the magnetic and ferroelectric properties of c-axis oriented orthorhombic phase HoMnO(3) (o-HMO in Pbnm symmetry setting) thin films grown on Nb-doped SrTiO(3)(001) substrates. The o-HMO films exhibit an antiferromagnetic ordering near 42 K, irrespective of the orientation of the applied field. However, an additional magnetic ordering occurring around 35 K was observed when the field was applied along the c-axis of o-HMO, which was absent when the field was applied in the ab-plane. The magnetocapacitance measured along the c-axis showed that although there is evidence of dielectric constant enhancement when the temperature is below 35 K the expected abrupt change in dielectric constant appears at a much lower temperature and reaches maximum around 13.5 K, indicating that the low-temperature c-axis polarization might be related to the ordering of the Ho(3+) moment. The lattice constant analyses using x-ray diffraction and the observation of a slight magnetization hysteresis suggest that the weak second magnetic transition along the c- axis at 35 K might be more relevant to the strain-induced effect on antiferromagnetism.
Strain-induced effects on antiferromagnetic ordering and magnetocapacitance in orthorhombic HoMnO3 thin films
(2009-01-14)
Lin, T. H.
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Shih, H. C.
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Hsieh, C. C.
;
Luo, C. W.
;
Lin, J-Y
We investigated the magnetic and ferroelectric properties of c-axis oriented orthorhombic phase HoMnO3 (o-HMO in Pbnm symmetry setting) thin films grown on Nb-doped SrTiO3(001) substrates. The o-HMO films exhibit an antiferromagnetic ordering near 42 K, irrespective of the orientation of the applied field. However, an additional magnetic ordering occurring around 35 K was observed when the field was applied along the c-axis of o-HMO, which was absent when the field was applied in the ab-plane. The magnetocapacitance measured along the c-axis showed that although there is evidence of dielectric constant enhancement when the temperature is below 35 K the expected abrupt change in dielectric constant appears at a much lower temperature and reaches maximum around 13.5 K, indicating that the low-temperature c-axis polarization might be related to the ordering of the Ho3+ moment. The lattice constant analyses using x-ray diffraction and the observation of a slight magnetization hysteresis suggest that the weak second magnetic transition along the c- axis at 35 K might be more relevant to the strain-induced effect on antiferromagnetism.
Ultrafast Dynamics of the Mn d-d Transition on Hexagonal HoMnO(3)
(2009)
Shih, H. C.
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Lin, T. H.
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Hsieh, C. C.
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Lee, J. M.
;
Luo, C. W.
The photoinduced changes in reflectivity (Delta R/R) at energies closed to the Mn d-d optical transition of HoMnO(3) single crystal have been systematically measured from 300K to 30 K by time-resolved optical pump-probe spectroscopy. The oscillation induced by the propagation of strain pulse was clearly observed in the Delta R/R signal with various probing wavelength. Moreover, the different relaxation processes of photoexcited carriers with in various wavelengths may be led by the blue shift of Mn(3+) d level.