G. Y. Gao

Half-metallic sp-electron ferromagnets in rocksalt structure: The case of SrC and BaC

First-principles calculations are employed to study the structural and magnetic properties of SrC and BaC in four different phases: rocksalt, CsCl, zinc blende, and NiAs. The obtained results indicate that both compounds show half-metallic behavior in all phases except the CsCl-type structure. Among them the rocksalt structure is found to be the most stable one with a robust half-metallic characteristic with respect to the lattice compression and expansion. The magnetic phase transition temperature Tc of the rocksalt phase is calculated employing both the mean-field approximation and the random-phase approximation. The predicted Tc values of both compounds are considerably above room temperature.

Preserving the half-metallicity at the surfaces of rocksalt CaN and SrN and the interfaces of CaN/InN and SrN/GaP: a density functional study.

Recent theoretical studies indicate that metastable rocksalt CaN, SrN, and BaN exhibit half-metallic ferromagnetism (Volnianska and Boguslawski 2007 Phys. Rev. B 75 224418; Gao et al 2008 Phys. Lett. A 372 1512), and further experiments confirm the existence of self-assembled metastable CaN nanostructures (Liu et al 2008 Surf. Sci. 602 1844). We here use the first-principles method based on density functional theory to investigate the structural, electronic, and magnetic properties of the (111) surfaces of CaN and SrN and the interfaces of CaN/InN(111) and SrN/GaP(111). The surface stability from the calculated surface energy indicates that the N-terminated (111) surface is more stable than the Ca (Sr)-terminated (111) surface in the N-rich environment. For CaN and SrN, both anion- and cation-terminated (111) surfaces preserve the half-metallic characteristics of the bulk. Interfacial studies indicate that the half-metallicity of bulk CaN is retained in two of the four possible configurations of the CaN/InN(111) interface, while for the interface of SrN/GaP(111) only one interfacial configuration shows half-metallicity. Furthermore, we assess the interfacial adhesive strength for all the possible different configurations of the interfaces studied here by calculating the interface adhesion energies.

Search for new half-metallic ferromagnets in zinc blende CaSi and CaGe by first-principles calculations.

We present an investigation on the electronic structure and ferromagnetism for the hypothetical zinc blende (ZB) CaSi and CaGe by using first-principles full-potential linearized augmented plane-wave (FP-LAPW) calculations. It is found that ZB CaSi and CaGe are half-metallic (HM) ferromagnets without any transition-metal component; they have a magnetic moment of 2.000xa0µ(B) per formula unit. Analysis of the density of states and magnetic moment indicates that their magnetism mainly originates from the spin polarization of anion p states and the hybridization between the anion p states and the Ca d states. We also find that the half-metallicity can be maintained even when the lattice constant of ZB CaSi and CaGe is compressed up to 8% and 5%, respectively. The absence of the transition-metal atoms makes ZB CaSi and CaGe attractive not only as materials for possible spintronics devices but also as model objects for the study of new mechanisms of the formation of half-metallic ferromagnetism in s-p electron systems.

Examining the thermal conductivity of the half-Heusler alloy TiNiSn by first-principles calculations

The thermoelectric properties of the half-Heusler alloy TiNiSn have been studied for a decade, however, a theoretical report on its thermal conductivity is still relatively unknown, because it is difficult to effectively estimate the lattice thermal conductivity. In this work, we use the ShengBTE code developed recently to examine the lattice thermal conductivity of TiNiSn. The calculated lattice thermal conductivity at room temperature is 7.6 W m −1 K −1 , which is close to the experimental value of 8 W m −1 K −1 . We also find that the total and lattice thermal conductivities dependent on temperature are in good agreement with available experiments, and the total thermal conductivity is dominated by the lattice contribution. The present work is useful for the theoretical prediction of lattice thermal conductivity and the optimization of thermoelectric performance.

Effect of carbon/hydrogen species incorporation on electronic structure of anatase-TiO2

The energy band structure and optical properties of C-doped and C/H-codoped anatase TiO2 are investigated using the first-principles based on density-functional theory. The obtained results indicate that the structure of C/H-codoping is more stable than that of C-doping. For C-doped anatase TiO2, the band gap narrowing is small, and the high visible-light catalytic ability originates from the isolated C 2p states above the valence-band maximum. With the same carbon doping level, the C/H-codoping produces significant bandgap narrowing, which leads to higher visible-light photocatalytic efficiency than the C-doping does.

Surface properties of the (001) surface of cubic BaMnO3: A density functional theory study

We have theoretically investigated surface properties of the (001) surface in cubic barium manganese (BaMnO(3)) by the full-potential linear augmented plane wave methods within the local spin-density approximation. We present and discuss the electronic properties of the (001) surface of cubic BaMnO(3) with BaO- and MnO(2)-terminations. Surface structure, Mulliken effective atomic charges, surface energies and stability, band structure, and partial density of states have been obtained. For the BaO-terminated surface, we find that all layer atoms relax inward (toward the central layer), while for the MnO(2)-terminated surface all layer atoms relax outward (toward the vacuum). The largest relaxations emerge on the first-layer atoms on the two terminations. The surface rumpling of the BaO-terminated is much larger than that of the MnO(2)-terminated surface. Based on the results of the calculated surface energies and stability, we obtain that only the BaO-terminated surface can exist in the (001) surface of cubic BaMnO(3). From the analysis of their band structure, we can see that the BaO-terminated surface has obvious half-metallic character, compared with the bulk materials and the MnO(2)-terminated surface

Surface half-metallicity of CrS thin films and perfect spin filtering and spin diode effects of CrS/ZnSe heterostructure

Recently, ferromagnetic zinc-blende Mn1−xCrxS thin films (above xu2009=u20090.5) were fabricated experimentally on ZnSe substrate, which confirmed the previous theoretical prediction of half-metallic ferromagnetism in zinc-blende CrS. Here, we theoretically reveal that both Cr- and S-terminated (001) surfaces of the CrS thin films retain the half-metallicity. The CrS/ZnSe(001) heterogeneous junction exhibits excellent spin filtering and spin diode effects, which are explained by the calculated band structure and transmission spectra. The perfect spin transport properties indicate the potential applications of half-metallic CrS in spintronic devices. All computational results are obtained by using the density functional theory combined with nonequilibrium Greens function.

The half-metallic properties and geometrical structures of cubic BaMnO3 and BaTiO3/BaMnO3 superlattice

The electronic structure and electrical transport properties of the cubic perovskite (E21) oxide barium manganese (BaMnO3) and the BaMnO3/BaTiO3 superlattice are investigated by the density-functional theory in this report. The results show that the cubic BaMnO3 exhibits half-metallic properties with an integral magnetic moment of 3.000 μB per unit cell in its metastable state, while the BaTiO3/BaMnO3 superlattice also shows a stable half-metallic ground state with an integral magnetic moment of 12.000 μB per unit cell. In conclusion, we show that the construction of a BaMnO3/BaTiO3 superlattice could stabilize the cubic metastable phase of the BaMnO3 and provide a stable half-metallic material for potential applications in spintronic devices.

Spin transport properties based on spin gapless semiconductor CoFeMnSi

Spin gapless semiconductors have been regarded as the most promising candidates for spin injection materials due to the complete (100%) spin polarization and the conductivity between half-metals and semiconductors. To explore the potential spintronic applications of the quaternary Heusler alloy CoFeMnSi (CFMS), a recently fabricated spin gapless semiconductor with a high Curie temperature of 620u2009K, we design the GaAs/CFMS heterostructure and the CFMS/GaAs/CFMS magnetic tunnel junction (MTJ). It is found from the first-principles calculations combined with nonequilibrium Greens function that the heterostructure exhibits an excellent spin filtering effect and spin diode effect and the MTJ has a large tunnel magnetoresistance ratio (up to 2u2009×u2009103), which are explained from the calculated spin-dependent band structure and transmission spectrum. These perfect spin transport characteristics make CFMS a promising candidate for spintronic applications.

Ultralow lattice thermal conductivity in topological insulator TlBiSe2

We present ab-initio calculations of the phonon thermal transport properties of topological insulator TlBiSe2. Our results point to a very low lattice thermal conductivity, comparable or lower than those of some popular good thermoelectric materials. Furthermore, we find a slight thermal anisotropy between the in-plane and cross-plane directions in TlBiSe2, markedly smaller than those of van-der-Waals topological insulators explored so far. These conclusions are confirmed and explained by comprehensive analysis of the phonon spectrum of TlBiSe2. The combination of ultralow lattice thermal conductivity and small anisotropy makes TlBiSe2 a promising candidate for thermoelectric applications.