Search

Ab initio calculations based on density functional theory and non-equilibrium Green's function are performed to investigate the thermal spin transport properties of single-hydrogen-saturated zigzag graphene nanoribbon co-doped with non-metallic Nitrogen and Boron in parallel and anti-parallel spin configurations. The results show that the doped graphene nanoribbon is a full half-metal. The two-probe system based on the doped graphene nanoribbon exhibits various excellent spin transport properties, including the spin-filtering effect, the spin Seebeck effect, the single-spin negative differential thermal resistance effect and the sign-reversible giant magnetoresistance feature. Excellently, the spin-filtering efficiency can reach nearly 100% in the parallel configuration and the magnetoresistance ratio can be up to −1.5 × 1010% by modulating the electrode temperature and temperature gradient. Our findings indicate that the metal-free doped graphene nanoribbon would be a promising candidate for spin caloritronic applications.

The electronic and magnetic properties of novel Heusler alloys Co 2 HfZ (Z = Al, Ga, Ge, Sn) with Hg 2 CuTi- and Cu 2 MnAl-type structures are investigated by first-principles calculations. It is found that the Cu 2 MnAl-type structure is more stable than the Hg 2 CuTi-type structure for all the Co 2 HfZ alloys. The Hg 2 CuTi-type structures of Co 2 HfZ show a metallic ferrimagnetic character with a high spin polarization. The Cu 2 MnAl-type structures have half-metallic ferrimagnetic behavior with minority-spin gaps of 0.38, 0.06, 0.55 and 0.46 eV for Co 2 HfAl, Co 2 HfGa, Co 2 HfGe and Co 2 HfSn, respectively. The total magnetic moments of the Cu 2 MnAl-type alloys are 1µ B , 1µ B , 2µ B and 2µ B , which obey the Slater–Pauling rule (M tot = Z tot − 24). Analysis of the projected density of states indicates clear gaps resulting from the hybridization of Co (A) and Co (B) atoms. The half-metallicity makes Co 2 HfZ with Cu 2 MnAl-type structure promising candidates for spintronic applications.

In this paper, we study the electronic structures, magnetic properties, and half-metallicity of the bulk and (001) surface of Heusler alloy NiCoMnGa. Our first-principles calculations exhibit that, within the generalized gradient approximation (GGA) of the electronic exchange–correlation functional, the quaternary Heusler alloy NiCoMnGa is a half-metallic ferromagnet at the equilibrium lattice constant of 5.795 Ǻ with a total spin magnetic moment of 5 μ B per formula unit. The calculated total atomic magnetic moment follows the Slater–Pauling rule. At the same equilibrium lattice constant, the half-metallicity confirmed in the bulk NiCoMnGa, is destroyed at both MnGa- and NiCo-terminated (001) surfaces and subsurfaces. Based on the magnetic property calculations, the magnetic moments of Co, Mn, and Ga atoms at the NiCo- and MnGa-terminated surfaces increase with respect to the corresponding bulk values while the atomic magnetic moment of Ni at the NiCo-terminated surface decreases.

We investigate the electronic structure and magnetic properties of the twelve quaternary Heusler alloys CoFeTiZ and CoFeVZ (Z=Al, Ga, Si, Ge, As, Sb) by using the first-principles calculations. It is shown that only CoFeTiSi, CoFeTiAs and CoFeVSb are half-metallic ferromagnets with considerable half-metallic gaps of 0.31, 0.18 and 0.17 eV, respectively. CoFeTiAl and CoFeTiGa are conventional semiconductors, and other alloys exhibit nearly half-metallicity or their half-metallic gaps are almost zero eV. We also find that the half-metallicities of CoFeTiSi, CoFeTiAs and CoFeVSb can be preserved under appropriate uniform and in-plane strains. The considerable half-metallic gaps and the robust half-metallicities under uniform and in-plane strains make CoFeTiSi, CoFeTiAs and CoFeVSb promising candidates for spintronic applications.

By means of the first-principles calculations, we explore comprehensively the structural, electronic, and magnetic properties of the (001) and (110) surfaces of half-metallic zinc-blende CrSe. It is found that all the surfaces of (110) and Cr- and Se-terminated (001) preserve the bulk half-metallicity of zinc-blende CrSe. The atomic magnetic moments at the (001) surface are increased greatly compared to those in the bulk due to the break of Cr–Se bond at the (001) surface, but the changes are very slight for the case of the (110) surface due to the keep of Cr–Se bond at the (110) surface. We also show for the first time from the calculated surface energy that the Se-terminated (001) surface is energetically more stable than the (110) surface and the Cr-terminated (001) surface. The present work would be useful for the realization of half-metallic zinc-blende CrSe thin films or multilayers.

The structural, electronic and magnetic properties of zinc-blende TiBi are investigated by using the first-principles full-potential linearized augmented plane-wave method. It is found that zinc-blende TiBi exhibits half-metallic ferromagnetism with the energy gap of 1.39 eV in the minority-spin channel. The calculated total magnetic moment of 1.00 µ B per formula unit mainly originates from the Ti atom. We also show that the half-metallicity of zinc-blende TiBi can be maintained up to 3% compression and 5% expansion of lattice constant with respect to the equilibrium lattice, and zinc-blende TiBi is still half-metallic when the spin–orbit coupling is considered. The robust half-metallicity and low magnetic moment make zinc-blende TiBi a potential candidate for spintronic applications.

The electronic structure and the magnetic properties of Na[NpO 2 (OH) 2 ] have been studied using the full-potential linearized augmented plane wave (FP-LAPW) method based on density-functional theory (DFT). The spin magnetic moments, the total and partial density of states (DOS) and the electronic band structure of the FM and AFM states are calculated. From the calculated results, we can see that Na[NpO 2 (OH) 2 ] has a stable ferromagnetic ground state and an antiferromagnetic metastable state. In the FM states, the calculated magnetic moments reveal that the spin magnetic moments per molecule are 2.000µ B, which mainly come from the NpO 2 + . The electronic structure shows that both the FM ground state and the AFM metastable state of the compound have semiconducting characteristics.

We have used the first-principles plane-wave pseudopotential calculations to study the electronic and optical properties of N-doped, Co-doped as well as N,Co-codoped rutile TiO2 crystals. Results show that N-doped rutile TiO2 exhibits a semiconducting characteristic with a stable antiferromagnetic ground state. Co-doped rutile TiO2 shows half-metallic ferromagnetism with a stable ferromagnetic ground state, indicating that this doped material is useful in spin injection applications. N,Co-codoped rutile TiO2 has a nearly half-metallic nature with a stable ferromagnetic ground state. In addition, the optical absorption spectrum shows that N-doped, Co-doped and N,Co-codoped rutile TiO2 all extend the optical absorption in the visible-light region, and especially, Co-doped rutile TiO2 has the best absorption character in the visible-light region. We also discuss the influence of Coulomb interactions of 3d electrons of Co and Ti on the electronic structure of the doped systems studied.

In this paper, we conduct a theoretical study of the half-metallic properties of the bulk and the (110) and (001) surfaces of rocksalt VPo with an equilibrium lattice constant of 0.59 nm. The calculations are done using the first-principles full-potential linearized augmented plane–wave method based on the density functional theory. We show that both the (110) and (001) surfaces of rocksalt VPo preserve the bulk half-metallicity, and the atomic magnetic moments at both the (110) and (001) surfaces are increased compared to those in bulk VPo. Moreover, by calculating the relaxed surface energies, we assess the surface stability, and find that both (110) and (001) surfaces are not stable in equilibrium conditions, and non-equilibrium growth techniques are required for the realization of rocksalt VPo thin films.

First-principles full-potential linearized augmented plane-wave method is used to investigate the electronic structure and magnetic properties of hypothetical zinc-blende and rocksalt LiS, NaS and KS. We find that all the compounds except rocksalt LiS exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 mu(B) per formula unit. The ferromagnetism results from the spin-polarization of p states of anion S. Total energies calculations indicate the rocksalt phase is lower in energy than the zinc-blende one. The total energy differences are about 0.38, 0.36 and 0.32 eV per formula unit for LiS, NaS and KS, respectively. Meanwhile, it is shown that rocksalt NaS and KS have the half-metallic gaps of 0.22 and 0.41 eV, respectively, and the half-metallic gaps are 0.03, 0.46 and 0.65 eV for zinc-blende LiS, NaS and KS, respectively. We also find the half-metallicity is robust against the lattice contraction up to 7% and 13% for rocksalt NaS and KS, respectively. Although rocksalt LiS is nonmagnetic and metallic at the equilibrium lattice constant, it shows half-metallic ferromagnetism when the lattice constant is larger than 5.40 angstrom. (C) 2011 Elsevier B.V. All rights reserved.

By means of the first-principles full potential linearized augmented plane-wave method within the local density approximation for the exchange-correlation functional, we have investigated the magnetism and electronic structure of Mn- and V-doped zinc blende ZnTe. Total energy calculations show that, for high doping concentration (12.5%), ZnTe:Mn has an antiferromagnetic ground state while the ferromagnetic state is more favorable than the antiferromagnetic state for ZnTe:V. Furthermore, ZnTe with a low doping of Mn (6.25%) has a stable ferromagnetic ground state, which is in agreement with the experimental results. The calculated magnetic moment of ZnTe doped with Mn (V) mainly originates from transition metal Mn (V) atom with a little contribution from Te atom due to the hybridization between Mn (V) 3d and Te 5p electrons. Electronic structure indicates that Mn-doped ZnTe is a semiconductor, but V-doped ZnTe shows a half-metallic characteristic. We also discuss the difference between electronic and magnetic properties for ZnTe doped with 12.5% and 6.25% Mn.

The first principles within the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) approach were applied to study the new mixed valence compound Ba(2)F(2)Fe(1.5)S(3). The density of states, the electronic band structure and the spin magnetic moment are calculated. The calculations reveal that the compound has an antiferromagnetic interaction between the Fe(III) and Fe(II) ions arising from the bridging S atoms, which validate the experimental assumptions that there is a low-dimensional antiferromagnetic interaction in Ba(2)F(2)Fe(1.5)S(3). The spin magnetic moment mainly comes from the Fe(III) and Fe(II) ions with smaller contribution from S anion. By analysis of the band structure, we find that the compound has half-metallic property. (C) 2008 Elsevier B.V. All rights reserved.

We present first-principles study on the magnetic properties of the 3D metal-ligand coordination polymer [Cu(mal)(DMF)]n within the framework of density functional theory ( DFT) by using the full-potential linearized augmented plane-wave (FP-LAPW) method. The total and partial density of states ( DOS), the band structure, and the atomic spin magnetic moment of [ Cu( mal)( DMF)] n are calculated. The calculation reveals that [ Cu( mal)( DMF)] n is a ferromagnetic semiconductor. The calculated spin magnetic moment is about 1.000 mu B per molecule, which is in agreement with experimental value. (c) 2007 Elsevier B.V. All rights reserved.

The magnetism and the electronic structure of Cr-doped rutile TiO2 are investigated using the first-principles full potential linearized augmented plane-wave (FP-LAPW) method. It is found that Cr-doped rutile TiO, has a stable ferromagnetic ground state, and it is shown to be a half-metal within the LDA (local density approximation) while a semiconductor within the LDA + U (Hubbard coefficient). We also find that the oxygen vacancy has large effect on the electronic structure and the ferromagnetism. (C) 2007 Elsevier B.V. All rights reserved.

Magnetic properties of the non-uniform quantum Heisenberg spin chains with S = 1/2 are investigated using the transfer matrix renormalization group method. By analyzing the spin alignment in the two spin chains, we show the magnetic interaction mechanism for the dominant ferromagnetic behavior. For the moderate ferromagnetic coupling of the spin-1/2 ferromagnetic-ferromagnetic-antiferromagnetic Heisenberg chain, two maximums are found in the magnetic susceptibility from spin frustration. (c) 2005 Elsevier B.V. All rights reserved.