Browsing by Author "Tjeng, L. H."

Now showing 1 - 9 of 9

Charge-transfer energy in iridates: A hard x-ray photoelectron spectroscopy study
(2020-07-13)
Takegami, D.
;
Kasinathan, D.
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Wolff, K. K.
;
Altendorf, S. G.
;
Chang, C. F.
We have investigated the electronic structure of iridates in the double perovskite crystal structure containing either Ir4+ or Ir5+ using hard x-ray photoelectron spectroscopy. The experimental valence band spectra can be well reproduced using tight-binding calculations including only the Ir 5d, O 2p, and O 2s orbitals with parameters based on the downfolding of the density-functional band structure results. We found that, regardless of the A and B cations, the A(2)BIrO(6) iridates have essentially zero O 2p to Ir 5d charge-transfer energies. Hence double perovskite iridates turn out to be extremely covalent systems with the consequence being that the magnetic exchange interactions become very long ranged, thereby hampering the materialization of the long-sought Kitaev physics. Nevertheless, it still would be possible to realize a spin-liquid system using the iridates with a proper tuning of the various competing exchange interactions.
Floating zone growth of Ba-substituted ruthenate Sr2-xBaxRuO4
(2015-10-01)
Li, Z. W.
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Liu, C. -F.
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Skoulatos, M.
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Tjeng, L. H.
;
Komarek, A. C.
We report on the exploration to synthesize Sr2-xBaxRuO4, the large volume variant of the unconventional superconductor Sr2RuO4. We have succeeded in growing single crystals for x-values up to 0.4 by making use of the traveling solvent floating zone method. The quality of the obtained crystals is confirmed by X-ray and neutron diffraction measurements and the properties of these Ba-substituted ruthenates were studied with magnetic and electrical transport measurements. (C) 2015 Elsevier B.V. All rights reserved.
Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-like BiFeO(3)
(2011-09-29)
Zhang, J. X.
;
He, Q.
;
Trassin, M.
;
Luo, W.
;
Yi, D.
We report direct experimental evidence for a room-temperature, similar to 130 mu C/cm(2) ferroelectric polarization from the tetragonal-like BiFeO(3) phase. The physical origin of this remarkable enhancement of ferroelectric polarization has been investigated by a combination of x-ray absorption spectroscopy, scanning transmission electron microscopy, and first principles calculations. A large strain-induced Fe-ion displacement relative to the oxygen octahedra, combined with the contribution of Bi 6s lone pair electrons, is the mechanism driving the large ferroelectric polarization in this tetragonal-like phase.
Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-like BiFeO3
(2011-09-29)
Zhang, J. X.
;
He, Q.
;
Trassin, M.
;
Luo, W.
;
Yi, D.
We report direct experimental evidence for a room-temperature, similar to 130 mu C/cm(2) ferroelectric polarization from the tetragonal-like BiFeO3 phase. The physical origin of this remarkable enhancement of ferroelectric polarization has been investigated by a combination of x-ray absorption spectroscopy, scanning transmission electron microscopy, and first principles calculations. A large strain-induced Fe-ion displacement relative to the oxygen octahedra, combined with the contribution of Bi 6s lone pair electrons, is the mechanism driving the large ferroelectric polarization in this tetragonal-like phase.
Molecular beam epitaxy preparation and in situ characterization of FeTe thin films
(2020-02-28)
Pereira, V. M.
;
Wu, C. N.
;
Liu, C. E.
;
Liao, S-S
;
Chang, C. F.
We have synthesized Fe1+y Te thin films by means of molecular beam epitaxy (MBE) under Te-limited growth conditions. We found that epitaxial layer-by-layer growth is possible for a wide range of excess Fe values, wider than expected from what is known from studies on the bulk material. Using x-ray magnetic circular dichroism spectroscopy at the Fe L-2(,3) and Te M-4(,5) edges, we observed that films with high excess Fe contain ferromagnetic clusters while films with lower excess Fe remain nonmagnetic. Moreover, x-ray absorption spectroscopy showed that it is possible to obtain films with very similar electronic structure as that of a high quality bulk single crystal Fe-1.(14) Te. Our results suggest that MBE with Te-limited growth may provide an opportunity to synthesize FeTe films with smaller amounts of excess Fe as to come closer to a possible superconducting phase.
Orthorhombic BiFeO3
(2012-12-14)
Yang, J. C.
;
He, Q.
;
Suresha, S. J.
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Kuo, C. Y.
;
Peng, C. Y.
A new orthorhombic phase of the multiferroic BiFeO3 has been created via strain engineering by growing it on a NdScO3(110)(o) substrate. The tensile-strained orthorhombic BiFeO3 phase is ferroelectric and antiferromagnetic at room temperature. A combination of nonlinear optical second harmonic generation and piezoresponse force microscopy revealed that the ferroelectric polarization in the orthorhombic phase is along the in-plane < 110 >(pc) directions. In addition, the corresponding rotation of the antiferromagnetic axis in this new phase was observed using x-ray linear dichroism. DOI: 10.1103/PhysRevLett.109.247606
Single-domain multiferroic BiFeO3 films
(2016-09-01)
Kuo, C. -Y.
;
Hu, Z.
;
Yang, J. C.
;
Liao, S. -C.
;
Huang, Y. L.
The strong coupling between antiferromagnetism and ferroelectricity at room temperature found in BiFeO3 generates high expectations for the design and development of technological devices with novel functionalities. However, the multi-domain nature of the material tends to nullify the properties of interest and complicates the thorough understanding of the mechanisms that are responsible for those properties. Here we report the realization of a BiFeO3 material in thin film form with single-domain behaviour in both its magnetism and ferroelectricity: the entire film shows its antiferromagnetic axis aligned along the crystallographic b axis and its ferroelectric polarization along the c axis. With this we are able to reveal that the canted ferromagnetic moment due to the Dzyaloshinskii-Moriya interaction is parallel to the a axis. Furthermore, by fabricating a Co/BiFeO3 heterostructure, we demonstrate that the ferromagnetic moment of the Co film does couple directly to the canted moment of BiFeO3.
Strong orbital polarization in orthorhombic DyMnO(3): A combined x-ray linear dichroism and ab initio electronic structure study
(2010-05-15)
Chen, J. M.
;
Hu, Z.
;
Jeng, H. T.
;
Chin, Y. Y.
;
Lee, J. M.
We present a combined experimental and theoretical study on the Mn 3d orbital occupation in orthorhombic DyMnO(3) single crystals. We have observed a very strong polarization dependence in the Mn L(2,3) x-ray absorption spectra, indicative for a distinct anisotropic orbital occupation. Ab initio electronic-structure calculations clearly infer the existence of a strong orbital polarization in the e(g) band with a staggered d(3x2-r2)/d(3y2-r2)-type ordering pattern in the ab plane. This finding is in excellent agreement with a quantitative analyis of the spectra using the atomic multiplet cluster approach.
Strong orbital polarization in orthorhombic DyMnO3: A combined x-ray linear dichroism and ab initio electronic structure study
(2010-05-15)
Chen, J. M.
;
Hu, Z.
;
Jeng, H. T.
;
Chin, Y. Y.
;
Lee, J. M.
We present a combined experimental and theoretical study on the Mn 3d orbital occupation in orthorhombic DyMnO3 single crystals. We have observed a very strong polarization dependence in the Mn L-2,L-3 x-ray absorption spectra, indicative for a distinct anisotropic orbital occupation. Ab initio electronic-structure calculations clearly infer the existence of a strong orbital polarization in the e(g) band with a staggered d(3x2-r2)/d(3y2-r2)-type ordering pattern in the ab plane. This finding is in excellent agreement with a quantitative analyis of the spectra using the atomic multiplet cluster approach.