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The discovery of the giant magnetoresistance effect has led to the rapid development of spintronics. Although the half-metals can provide a 100% spin polarization rate and significantly improved giant magnetoresistance, the materials with low Curie temperatures present challenges for their use at room temperature. In an attempt to identify the half-metallic material with high Curie temperatures for spintronics, this study investigates a van der Waals heterostructure with vertically integrated FeCl2/WSe2/FeCl2. The spin-polarized transport properties of the device based on the heterostructure studied by the density function theory combined with nonequilibrium Green's function reveal comprehensive spintronics functions, including giant magnetoresistance, spin filtering, and negative differential resistance effect. The mechanism of the negative differential resistance effect has further been elucidated by the band alignment of the heterostructure under different biases within the bias window. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new device of spintronics by embedding two FeN4 molecules into armchair graphene nanoribbon and sandwiching them between N-doped graphene nanoribbon electrodes. Our first-principle quantum transport calculations show that the device is a perfect spin filter with high spin-polarizations both in parallel configuration (PC) and antiparallel configuration (APC). Moreover, negative differential resistance phenomena are obtained for the spin-down current in PC, and the spin-up and spin-down currents in APC. These transport properties are explained by the bias-dependent evolution of molecular orbitals and the transmission spectra. [ABSTRACT FROM AUTHOR]

According to a first-principles study of the transport properties of two thiolated anthracene-9,10-diono molecules sandwiching ethyl, a new method to induce molecular low bias negative differential resistance with multi-peaks for strong n- or p-type molecules is proposed. The anthracene-9,10-diono molecule shows strong n-type characteristics when in contact with Au and Ag electrodes via a thiolate. The multiple negative differential resistance effect originated from the molecule-electrode couple is different between Ag and Au electrodes. Our investigations may promise potential for applications in molecular devices with low power dissipation and multifunction in the future. [ABSTRACT FROM AUTHOR]

By applying nonequilibrium Green's function combined with density functional theory, we investigate the electronic transport properties of carbon-doped p-n nanojunction based on hexagonal boron nitride armchair nanoribbons. The calculated I-V curves show that both the center and edge doping systems present obvious negative differential resistance (NDR) behavior and excellent rectifying effect. At low positive bias, the edge doping systems possess better NDR performance with larger peak-to-valley ratio (∼105), while at negative bias, the obtained peak-to-valley ratio for both of the edge and center doping systems can reach the order of 107. Meanwhile, center doping systems present better rectifying performance than the edge doping ones, and giant rectification ratio up to 106 can be obtained in a wide bias range. These outstanding transport properties are explained by the evolution of the transmission spectra and band structures with applied bias, together with molecular projected self-consistent Hamiltonian eigenvalues and eigenstates. [ABSTRACT FROM AUTHOR]

We investigate the structural, electronic, and magnetic properties of the (001) surfaces and the pure V-terminated surface with V-doping for Co2VGa with L21 structure. It is shown from the present density of states that the pure V-terminated surface preserves the bulk half-metallicity although the half-metallic character is destroyed at both Co- and VGa-terminated surfaces. We also find the atomic magnetic moments at the considered three surfaces are greatly different from the bulk values due to the well-known surface effect. Our calculated results indicate the pure V-terminated surface can be more favorable to the applications of spintronic devices. [ABSTRACT FROM AUTHOR]

Motivated by the molecular-beam epitaxial growth of zinc-blend-type CrTe thin films on ZnTe, we present a theoretical study on the spin-polarized transport properties of ZnTe/CrTe p-n junction as spin diode and CrTe/ZnTe/CrTe magnetic tunnel junction for (001) and (011) surfaces. Both ZnTe(001)/CrTe(001) and ZnTe(011)/CrTe(011) p-n junctions show excellent spin diode effect, the majority spin current of positive voltage is much larger than that of negative voltage and the minority spin current is absolutely inhibited. The ZnTe(001)/CrTe(001) p-n junction has lower 'turn off' current and higher rectification ratio (about 105) than the ZnTe(011)/CrTe(011) which shows obvious anisotropy. We also find that the tunneling magneto resistance ratio of the CrTe/ZnTe/CrTe magnetic tunnel junction is up to about 4 × 109%. [ABSTRACT FROM AUTHOR]

We extend the recent study on above-room-temperature half-metallic ferromagnetism in bulk rocksalt CrTe [Y. Liu, S. K. Bose, and J. J. Kudrnovský, Phys. Rev. B 82, 094435 (2010)] to the (001) and (111) surfaces by using the first-principles calculations. We show that the Te-terminated (111) surface is energetically more stable than both the (001) and the Cr-terminated (111) surfaces over the whole effective Cr chemical potential, and the surface stability of the Te-terminated (111) surface of rocksalt CrTe is comparable with that of the Te-terminated (001) surface of experimental zinc-blende CrTe. In addition, both the (001) and (111) surfaces of rocksalt CrTe retain the bulk half-metallicity. The atomic magnetic moments at the (111) surfaces are greatly different from those in the bulk rocksalt CrTe due to the breakdown of Cr-Te bond at the (111) surface, but the differences are very small for the case of the (001) surface due to the existence of Cr-Te bond at the (001) surface. These results indicate that it is feasible to fabricate the half-metallic CrTe thin films with rocksalt structure other than zinc-blende one. [ABSTRACT FROM AUTHOR]

Based on the half-metallicity confirmed experimentally in bulk Heusler alloy Co2VGa, we use the first-principles calculations to extend our previous studies on the Co2VGa (111) surfacial properties to the interfaces of Co2VGa/PbS (111) heterostructures in which four possible interfacial structures are considered between the V- and Ga-terminated (111) surfaces of Co2VGa and S- and Pb-terminated (111) surfaces of PbS. From the atomic density of states, it is shown that the half-metallicity of the bulk system is destroyed at Ga-S and Ga-Pb configurations while V-S and V-Pb configurations exhibit 100% spin polarization and nearly 100% spin polarization, respectively. Furthermore, the structure relaxation and the calculated interfacial adhesion energies indicate that V-S configuration is the most stable structure among them. In addition, we also discuss the changes of the atom magnetic moments at interface and subinterface layers with respect to the corresponding bulk values. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two kinds of junctions based on doped graphene nanoribbons (GNRs) are designed and studied in this article. One is the N-doped armchair GNR (AGNR) joined directly by B-doped AGNRs, and another is similar, but there is an undoped AGNR between them. The transport properties are calculated using the full self-consistent ab initio nonequilibrium Green's function and density-functional theory methods under external bias. We find that the I-V curves for both junctions have a striking nonlinear feature and show large negative differential resistance properties, not only at the positive bias but also at the negative one. The results also indicate that the diode-like properties are kept and the rectification coefficient is very high within a wide bias region. Our calculations reveal that the formation of these peculiar transport behaviors is due to the great changes of the transmission spectra and the projected self-consistent Hamiltonian eigenvalues with the applied bias voltage. These findings suggest that the doped AGNRs may offer unique opportunities for the future development of nanoscale electronics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We have theoretically investigated surface properties of the (001) surface in cubic barium manganese (BaMnO3) 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 BaMnO3 with BaO- and MnO2-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 MnO2-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 MnO2-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 BaMnO3. 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 MnO2-terminated surface. [ABSTRACT FROM AUTHOR]

For molecule-scale transport systems, a mechanism that the charge distribution of molecule under the various bias voltages can induce strong effect of rectification and negative differential resistance is proposed. Based on nonequilibrium Green’s function combined with density functional theory, the proposal is testified by performing the first-principles calculations of transport characteristics of 2-(4′-thiolate-butyl)-6-thiol-anthrecene molecule sandwiched in two gold electrodes. The strong effect of rectification and negative differential resistance is obtained. The rectification effect is as large as 16. [ABSTRACT FROM AUTHOR]

The electronic structures of Na0.5CoO2 and other NaxCoO2 compounds (with x=1, 1/3, and 2/3) have been calculated by first-principle calculations based on density-functional theory. The result shows that state disproportion between Co3+ (S∼0) and Co4+ (S∼1/2) in them is determined by the neighboring environments of cobalt ions and the doping level x. Further analysis reveals that state disproportion plays an important role in the physical features of NaxCoO2 compounds, such as metal-insulator transition or magnetic behavior. From these, we can get a further under-standing on the phase diagram of NaxCoO2 compounds [ABSTRACT FROM AUTHOR]

We theoretically investigate the electron density of states, band structure, spin polarization, spin filter effect, and current-voltage curve of Fe(thiazole)2Cl2 nanocrystal. The results show that Fe(thiazole)2Cl2 is a metallic antiferromagnet with half-metallic ferromagnetic metastable state. The spin current for the ferromagnetic metastable state shows that Fe(thiazole)2Cl2 has spin-filter property. Moreover, the current-voltage curve exhibits negative differential resistance, which is due to the narrow feature in the density of states of Fe(thiazole)2Cl2. The perfect negative magnetoresistance is also obtained. [ABSTRACT FROM AUTHOR]

We theoretically investigate the electron density of states, band structure, spin polarization, spin filter effect, and current-voltage curve of Fe(thiazole)2Cl2 nanocrystal. The results show that Fe(thiazole)2Cl2 is a metallic antiferromagnet with half-metallic ferromagnetic metastable state. The spin current for the ferromagnetic metastable state shows that Fe(thiazole)2Cl2 has spin-filter property. Moreover, the current-voltage curve exhibits negative differential resistance, which is due to the narrow feature in the density of states of Fe(thiazole)2Cl2. The perfect negative magnetoresistance is also obtained. [ABSTRACT FROM AUTHOR]

Using the full potential linearized augmented plane wave method based on the spin density functional theory, we investigate the ferromagnetic properties, the electronic structure, and the formation energy of Ga0.9375M0.0625N (M=vacancy, Ca). The calculations indicate that both cases prefer ferromagnetic ground state. The magnetic moments mainly come from the N atoms surrounding the defect centers, which are different from the conventional diluted magnetic semiconductor. High formation energy for the Ga vacancy suggests that the defect concentration is too low to result in the ferromagnetic GaN. The formation energy for the two substitutional (CaGa,CaN) and two interstitial sites (tetrahedral T, Cai-T and octahedral O, Cai-O) doped configurations indicates that Ca prefers the substitutional Ga in GaN. The defect concentrations for the Ga0.9375Ca0.0625N under thermal equilibrium N-rich and N-realistic growth conditions are also discussed, respectively. The calculations show that defect concentration under N-rich condition can readily reach 7%, while under N-realistic growth condition, the maximum defect concentration is as low as 1.71% when the growth temperature increases to 1100 K (melting point of GaN). These results suggest that it would be a little difficult to achieve ferromagnetic state for Ga0.9375Ca0.0625N using the chemical-equilibrium fabrication method, such as chemical precipitation. Using the same method as that for Cu-doped ZnO [L. H. Ye et al., Phys. Rev. B 73, 033203 (2006)], the transition temperature of Ga0.9375Ca0.0625N may be close to room temperature. [ABSTRACT FROM AUTHOR]

The ferromagnetic phenyl nitronyl nitroxide derivate α-phase 2-(2′,5′-dihydroxyphenyl)- 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide has been studied by the electronic structure calculation based on the density functional theory. The result shows that the spin delocalization due to hyperconjugation effect plays an important role in the spin distribution and ferromagnetic coupling of the crystal. [ABSTRACT FROM AUTHOR]