Wenhui Xie

Half-Metallic Ferromagnetism and Structural Stability of Zincblende Phases of the Transition-Metal Chalcogenides

An accurate density-functional method is used to study systematically half-metallic ferromagnetism and stability of zincblende phases of 3d-transition-metal chalcogenides. The zincblende CrTe, CrSe, and VTe phases are found to be excellent half-metallic ferromagnets with large half-metallic gaps (up to 0.88 eV). They are mechanically stable and approximately 0.31-0.53 eV per formula unit higher in total energy than the corresponding nickel-arsenide ground-state phases, and therefore would be grown epitaxially in the form of films and layers thick enough for spintronic applications.

Half-metallic ferromagnetism in ternary transition-metal compounds based on ZnTe and CdTe semiconductors

Electronic structures and magnetic properties of various possible ternary transition-metal compounds based on zincblende ZnTe and CdTe semiconductors are systematically explored by using an accurate density-functional method. Half-metallic (HM) ferromagnetism is found in the ZnTe and CdTe heavily doped with Cr, V, and Mn. Quite high Curie temperatures would be expected in most of these HM ferromagnets. These HM ferromagnetic phases, structurally stable and compatible with the two semiconductors, would be useful in spintronics.

Electronic and magnetic properties of La2NiMnO6 and La2CoMnO6 with cationic ordering

Employing first‐principles electronic structure calculations, the electronic and magnetic properties of La2NiMnO6 and La2CoMnO6 with Ni/Mn and Co/Mn ordering in (001), (110), and (111) directions are investigated. The ground states of La2NiMnO6 and La2CoMnO6 are ferromagnetic semiconducting with alternative Ni/Mn and Co/Mn ordering along the (111) direction. Furthermore, it is found that La2NiMnO6 and La2CoMnO6 are half‐metal with Ni/Mn or Co/Mn ordering along (001) and (110) after considering the effect of electronic correlation. Our results would be helpful in exploring more spintronics materials.

Half-metallic ferromagnets based on the rock-salt IV?VI semiconductor GeTe

Using an accurate density-functional method, we study a series of ternary transition-metal compounds based on the rock-salt IV-VI semiconductor GeTe for potential use as half-metallic ferromagnets, because some of such materials have already been fabricated and proved experimentally to be ferromagnetic. We find four half-metallic ferromagnets in ternary Cr- and V-substituted compounds and study their electronic structures and charge and spin density to clarify their bonding properties. The half-metallic ferromagnetic order is stable against possible antiferromagnetic orders. The half-metallic ferromagnetism is formed because the exchange splitting of the transition-metal d states is large enough to cause ferromagnetism and keep the minority-spin gap at the Fermi level open. These half-metallic ferromagnets could be useful in spintronics because of their relationship with the semiconductor GeTe.

Crystal structure and electronic structure of quaternary semiconductors Cu2ZnTiSe4 and Cu2ZnTiS4 for solar cell absorber

We design two new I2-II-IV-VI4 quaternary semiconductors Cu2ZnTiSe4 and Cu2ZnTiS4, and study the crystal and electronic structure by employing first-principles electronic structure calculations. Among the considered crystal structures, it is confirmed that the band gaps of Cu2ZnTiSe4 and Cu2ZnTiS4 originate from the full occupied Cu 3d valence band and unoccupied Ti 3d conducting band, and kesterite structure should be the ground state. Furthermore, our calculations indicate that Cu2ZnTiSe4 and Cu2ZnTiS4 have comparable band gaps with Cu2ZnTSe4 and Cu2ZnTS4, but almost twice larger absorption coefficient α(ω). Thus, the materials are expected to be candidate materials for solar cell absorber.

Half-metallic ferromagnetism in vanadium chalcogenides

Using an accurate density-functional method, we systematically explore vanadium chalcogenides in various crystal structures in order to find halfmetallic (HM) ferromagnets which could possibly be fabricated as thin films with a thickness sufficient for real spintronic applications. The zincblende and wurzite (WZ) phases of VTe and the WZ phase of VSe are found to be HM ferromagnets with a magnetic moment of 3.000 µB/formula unit. Their HM gaps of, respectively, 0.31, 0.60, and 0.25 eV are 0.53, 0.56, and 0.52 eV higher in total energy/formula unit than the ground-state NiAs phase of VTe and therefore could possibly be realized in the form of films with great enough thickness. Their HM ferromagnetism persists even when the volume is compressed by 10, 20, and 5%. As they are compatible with the wellknown binary semiconductors, these HM ferromagnetic phases, when realized experimentally, may be useful in spintronic applications.

Pressure-induced structural and magnetic transitions in the infinite-chains iron oxide Sr2FeO3: a first-principle investigation

The pressure-induced transition of Sr2FeO3 was studied by first-principle calculation using density functional theory with the generalized gradient approximation plus on-site coulomb repulsion method. It shows that Sr2FeO3 exhibits a structure transition from Immm to Ammm and at about 35 GPa and then a spin transition from high spin S = 2 to intermediate spin S = 1. And it is also revealed that the pressure leads to a change in the Fe three-dimensional electronic configuration from ()1()1()1()1()1 ()1 under ambient conditions to ()1()1()1()1 () δ ()1 () σ at high pressure, where δ plus σ equals 1.

Structure and magnetic properties of the perovskite YCo0.5Fe0.5O3

Y Co0.5Fe0.5O3, in a structure of perovskite, has been successfully prepared with citrate precursors at 950-1100 °C in air by the sol-gel method. The X-ray diffraction patterns show that the samples are orthorhombic within the space group Pnma, where the Co and Fe ions are disordered at the 4b crystallographic sites. The crystal structure refinement undertaken by the Rietveld method has shown that the distortion of Co(Fe)O6 octahedra are large, where the ratio of Co/Fe-O bonding length along a axis to that in the bc plane is about 1.07. Such a large crystal lattice distortion implies a strong lattice-magnetism coupling, which may be utilized in the magnetoelectric devices. Magnetic measurement indicates that the Y Co0.5Fe0.5O3 is antiferromagnetic but showing weak ferromagnetism. We find that Fe3+ ions are in high-spin states, while Co3+ ions are in low-spin states which do not contribute to the magnetism. Both Fe3+ and Co3+ ions are not Jahn-Teller activated although the lattice distortion is large.

Magnetic and optical properties in the 1D TM–O chain compounds Sr2TMO3 (TM = Ni, Co): A first-principle investigation

In this paper, we have calculated the structural, electronic, magnetic and optical properties of Sr2NiO3 and Sr2CoO3 using density functional theory (DFT) within generalized gradient approximation (GGA). The crystal structure of both materials is well described with Immm (No. 71) symmetry which are isostructural with Sr2CuO3 and both are quasi-one-dimensional (1D) rectangular lattice G-type antiferromagnets, in consistent with the experimental data. Due to a distortion, Sr2CoO3 lifts the near-degeneracy dxz and dyz states of the local Co electronic configuration, which demonstrates a strong coupling between the structural lattice and the electronic configuration. The calculated band structure shows a band gap of 1.376 eV for Sr2NiO3 and a band gap of 1.735 eV for Sr2CoO3. Ni and Co ions are in the high-spin S = 1 and S = 3/2 configurations with the magnetic moments of 1.585 μB and 2.587 μB, respectively. Based on the Heisenberg Hamiltonian model, we conclude that the superexchange intrachain TM–O–TM superexchange interaction is predominant and interaction between the 1D chains is weak. According to the calculated dielectric function, absorption spectrum and electron energy loss spectrum, the optical responses suggest that Sr2NiO3 shows the unique anisotropic structure and interaction of the application in optoelectronics.

Anisotropies in insulating La2-xSrxCuO4 : Angle-resolved photoemission and optical absorption

Due to the orthorhombic distortion of the lattice, the electronic hopping integrals along the