Browsing by Author "Huang, Eugene"

Now showing 1 - 4 of 4

Pressure dependence of the electronic structure and spin state in Fe(1.01)Se superconductors probed by x-ray absorption and x-ray emission spectroscopy
(2011-09-09)
Chen, J. M.
;
Haw, S. C.
;
Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
Pressure dependence of electronic structures and spin states of iron-chalcogenide Fe(1.01)Se superconductors up to similar to 66 GPa has been investigated with x-ray emission spectra and x-ray absorption spectra with partial-fluorescence yield. The intensity of the pre-edge peak at energy of similar to 7112.7 eV of the Fe K-edge x-ray absorption spectrum of Fe1.01Se decreases progressively with pressure up to similar to 10 GPa. A new prepeak at energy of similar to 7113.7 eV develops for pressure above similar to 13 GPa, indicating formation of a new phase. The experimental and the calculated Fe K-edge absorption spectra of Fe(1.01)Se using the FDMNES code agree satisfactorily. The larger compression accompanied by significant distortion around the Fe atoms along the c axis in Fe(1.01)Se upon applying pressure suppresses the Fe 3d-Se 4p and Fe 4p-Se 4d hybridization. The applied pressure suppresses the nearest-neighbor ferromagnetic superexchange interaction and enhances spin fluctuations on the Fe sites in Fe(1.01)Se. A discontinuous variation of the integrated absolute difference values of the K beta emission line was observed, originating from a phase transition of Fe(1.01)Se for a pressure >12 GPa. Fe(1.01)Se shows a small net magnetic moment of Fe(2 broken vertical bar) at ambient pressure, probably arising from strong Fe-Fe spin fluctuations. The satellite line K beta' was reduced in intensity upon applying pressure and became absent for pressure >52 GPa, indicating a continuous reduction of the spin moment of Fe in Fe(1.01)Se superconductors. The experimental results provide insight into the spin state of Fe(1.01)Se superconductors under pressure.
Pressure dependence of the electronic structure and spin state in Fe1.01Se superconductors probed by x-ray absorption and x-ray emission spectroscopy
(2011-09-09)
Chen, J. M.
;
Haw, S. C.
;
Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
Pressure dependence of electronic structures and spin states of iron-chalcogenide Fe1.01Se superconductors up to similar to 66 GPa has been investigated with x-ray emission spectra and x-ray absorption spectra with partial-fluorescence yield. The intensity of the pre-edge peak at energy of similar to 7112.7 eV of the Fe K-edge x-ray absorption spectrum of Fe1.01Se decreases progressively with pressure up to similar to 10 GPa. A new prepeak at energy of similar to 7113.7 eV develops for pressure above similar to 13 GPa, indicating formation of a new phase. The experimental and the calculated Fe K-edge absorption spectra of Fe1.01Se using the FDMNES code agree satisfactorily. The larger compression accompanied by significant distortion around the Fe atoms along the c axis in Fe1.01Se upon applying pressure suppresses the Fe 3d-Se 4p and Fe 4p-Se 4d hybridization. The applied pressure suppresses the nearest-neighbor ferromagnetic superexchange interaction and enhances spin fluctuations on the Fe sites in Fe1.01Se. A discontinuous variation of the integrated absolute difference values of the K beta emission line was observed, originating from a phase transition of Fe1.01Se for a pressure >12 GPa. Fe1.01Se shows a small net magnetic moment of Fe-2 broken vertical bar at ambient pressure, probably arising from strong Fe-Fe spin fluctuations. The satellite line K beta' was reduced in intensity upon applying pressure and became absent for pressure >52 GPa, indicating a continuous reduction of the spin moment of Fe in Fe1.01Se superconductors. The experimental results provide insight into the spin state of Fe1.01Se superconductors under pressure.
Pressure-dependent electronic structures in multiferroic DyMnO(3): A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
(2010-10-21)
Chen, J. M.
;
Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
;
Huang, S. W.
Variations in the electronic structure and structural distortion in multiferroic DyMnO(3) were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO(6) octahedra in DyMnO(3) on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO(3) progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO(3) shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO(6) octahedra in compressed DyMnO(3). A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490400]
Pressure-dependent electronic structures in multiferroic DyMnO3: A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
(2010-10-21)
Chen, J. M.
;
Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
;
Huang, S. W.
Variations in the electronic structure and structural distortion in multiferroic DyMnO3 were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO6 octahedra in DyMnO3 on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO3 progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO3 shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO6 octahedra in compressed DyMnO3. A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490400]