Xiaoshan Xu
University of Nebraska–Lincoln
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Publication
Featured researches published by Xiaoshan Xu.
Physical Review Letters | 2013
Wenbin Wang; Jun Zhao; Wenbo Wang; Zheng Gai; Nina Balke; Miaofang Chi; Ho Nyung Lee; Wei Tian; Leyi Zhu; Xuemei Cheng; D. J. Keavney; Jieyu Yi; Thomas Ward; Paul C. Snijders; Hans M. Christen; Weida Wu; Jian Shen; Xiaoshan Xu
The crystal and magnetic structures of single-crystalline hexagonal LuFeO(3) films have been studied using x-ray, electron, and neutron diffraction methods. The polar structure of these films are found to persist up to 1050 K; and the switchability of the polar behavior is observed at room temperature, indicating ferroelectricity. An antiferromagnetic order was shown to occur below 440 K, followed by a spin reorientation resulting in a weak ferromagnetic order below 130 K. This observation of coexisting multiple ferroic orders demonstrates that hexagonal LuFeO(3) films are room-temperature multiferroics.
Physical Review Letters | 2011
Xiaoshan Xu; Shuangye Yin; Ramiro Moro; Liang A; John Bowlan; de Heer Wa
The cobalt and iron clusters CoN, FeN (20<N<150) measured in a cryogenic molecular beam are found to be bistable with magnetic moments per atom both {\mu}N/N 2{\mu}B in the ground states and {\mu}N */N {\mu}B in the metastable excited states (for iron clusters, {\mu}N ~3N{\mu}B and {\mu}N* N{\mu}B). This energy gap between the two states vanish for large clusters, which explains the rapid convergence of the magnetic moments to the bulk value and suggests that ground state for the bulk involves a superposition of the two, in line with the fluctuating local orders in the bulk itinerant ferromagnetism.
Applied Physics Letters | 2012
Wenbin Wang; Hongwei Wang; Xiaoying Xu; Leyi Zhu; Lixin He; Elizabeth Wills; Xuemei Cheng; D. J. Keavney; Jian Shen; Xifan Wu; Xiaoshan Xu
Hexagonal LuFeO3 films have been studied using x-ray absorption and optical spectroscopy. The crystal splitting of Fe3+ is extracted as Ee′−Ee″=0.7 eV and Ea1′−Ee′=0.9 eV, and a 2.0 eV optical bandgap is determined assuming a direct gap. First-principles calculations confirm the experiments that the relative energies of crystal field splitting states do follow Ea1′>Ee′>Ee″ with slightly underestimated values and a bandgap of 1.35 eV.
Physical Review B | 2014
Hongwei Wang; I. V. Solovyev; Wenbin Wang; Xiao Wang; Philip J. Ryan; D. J. Keavney; Jong-Woo Kim; Thomas Ward; Leyi Zhu; Jian Shen; Xuemei Cheng; Lixin He; Xiaoshan Xu; Xifan Wu
Using combined theoretical and experimental approaches, we studied the structural and electronic origin of the magnetic structure in hexagonal LuFeO
Applied Physics Letters | 2016
Xuanyuan Jiang; Haidong Lu; Yuewei Yin; Xiaozhe Zhang; Xiao Wang; Le Yu; Zahra Ahmadi; Paulo S. Costa; Anthony D. DiChiara; Xuemei Cheng; Alexei Gruverman; Axel Enders; Xiaoshan Xu
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Journal of Applied Physics | 2013
Hangwen Guo; Dali Sun; Wenbin Wang; Zheng Gai; Ivan I. Kravchenko; Jian Shao; Lu Jiang; Thomas Ward; Paul C. Snijders; Lifeng Yin; Jian Shen; Xiaoshan Xu
. Besides showing the strong exchange coupling that is consistent with the high magnetic ordering temperature, the previously observed spin reorientation transition is explained by the theoretically calculated magnetic phase diagram. The structural origin of this spin reorientation that is responsible for the appearance of spontaneous magnetization, is identified by theory and verified by x-ray diffraction and absorption experiments.
Journal of Physics: Condensed Matter | 2015
Shi Cao; Tula R. Paudel; Kishan Sinha; Xuanyuan Jiang; Wenbin Wang; Evgeny Y. Tsymbal; Xiaoshan Xu; Peter A. Dowben
Ferroelectricity at room temperature has been demonstrated in nanometer-thin quasi 2D croconic acid thin films, by the polarization hysteresis loop measurements in macroscopic capacitor geometry, along with observation and manipulation of the nanoscale domain structure by piezoresponse force microscopy. The fabrication of continuous thin films of the hydrogen-bonded croconic acid was achieved by the suppression of the thermal decomposition using low evaporation temperatures in high vacuum, combined with growth conditions far from thermal equilibrium. For nominal coverages ≥20 nm, quasi 2D and polycrystalline films, with an average grain size of 50–100 nm and 3.5 nm roughness, can be obtained. Spontaneous ferroelectric domain structures of the thin films have been observed and appear to correlate with the grain patterns. The application of this solvent-free growth protocol may be a key to the development of flexible organic ferroelectric thin films for electronic applications.
Journal of Physics: Condensed Matter | 2016
Shi Cao; Xiaozhe Zhang; Tula R. Paudel; Kishan Sinha; Xiao Wang; Xuanyuan Jiang; Wenbin Wang; Stuart Brutsche; Jian Wang; Philip J. Ryan; Jong-Woo Kim; Xuemei Cheng; Evgeny Y. Tsymbal; Peter A. Dowben; Xiaoshan Xu
An experimental study was conducted on controlling the growth mode of La0.7Sr0.3MnO3 thin films on SrTiO3 substrates using pulsed laser deposition (PLD) by tuning growth temperature, pressure, and laser fluence. Different thin film morphology, crystallinity, and stoichiometry have been observed depending on growth parameters. To understand the microscopic origin, the adatom nucleation, step advance processes, and their relationship to film growth were theoretically analyzed and a growth diagram was constructed. Three boundaries between highly and poorly crystallized growth, 2D and 3D growth, stoichiometric and non-stoichiometric growth were identified in the growth diagram. A good fit of our experimental observation with the growth diagram was found. This case study demonstrates that a more comprehensive understanding of the growth mode in PLD is possible.
Physical Review B | 2017
Kishan Sinha; Yubo Zhang; Xuanyuan Jiang; Hongwei Wang; Xiao Wang; Xiaozhe Zhang; Philip J. Ryan; Jong-Woo Kim; John Bowlan; Dmitry Yarotski; Yuelin Li; Anthony D. DiChiara; Xuemei Cheng; Xifan Wu; Xiaoshan Xu
The surface termination and the nominal valence states for hexagonal LuFeO3 thin films grown on Al2O3(0 0 0 1) substrates were characterized by angle resolved x-ray photoemission spectroscopy. The Lu 4f, Fe 2p and O 1s core level spectra indicate that both the surface termination and the nominal valence depend on surface preparation, but the stable surface terminates in a Fe-O layer. This is consistent with the results of density functional calculations which predict that the Fe-O termination of LuFeO3(0 0 0 1) surface is energetically favorable and stable over a broad range of temperatures and oxygen partial pressures when it is reconstructed to eliminate surface polarity.
Journal of Physics: Condensed Matter | 2017
Xiaozhe Zhang; Yuewei Yin; Sen Yang; Zhimao Yang; Xiaoshan Xu
The electronic structure for the conduction bands of both hexagonal and orthorhombic LuFeO3 thin films have been measured using x-ray absorption spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectral features and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridizations. While the oxidation states have not changed, the spectra are sensitive to the changes in the local environments of the Fe(3+) and Lu(3+) sites in the hexagonal and orthorhombic structures. Using the crystal-field splitting and the hybridizations that are extracted from the measured electronic structures and the structural distortion information, we derived the occupancies of the spin minority states in Fe(3+), which are non-zero and uneven. The single ion anisotropy on Fe(3+) sites is found to originate from these uneven occupancies of the spin minority states via spin-orbit coupling in LuFeO3.