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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 halfmetallic 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.PACS numbers: 75.90.+w, 62.25.+g, 73.22.-f, 75.30.-m Phys Rev Lett 91, 037204 (2003) Half-metallic ferromagnets are seen as a key ingredient in future high performance spintronic devices, because they have only one electronic spin channel at the Fermi energy and, therefore, may show nearly 100 % spin polarization [1,2]. Since de Groot et al's discovery [3] in 1983, a lot of half-metallic ferromagnets have been theoretically predicted and some of them furthermore have been confirmed experimentally [4,5,6,7]. Much attention has been paid to understanding the mechanism behind the half-metallic magnetism and to studying its implication on various physical properties [8,9]. However, it is highly desirable to explore new halfmetallic ferromagnetic materials which are compatible with important III-V and II-VI semiconductors. For this purpose, effort has be made on the metastable zincblende (B3) phases such as the transition-metal pnictides [10,11,12,13,14,15,16,17,18,19,20]. Although zincblende phases of MnAs [11], CrAs [12,13] and CrSb [14] have been successfully fabricated as nanodots, ultrathin films and ultrathin layers in multilayers, it has not been possible to grow the zincblende half-metallic ferromagnetic phases as high-quality layers or thick films. This is due to the metastable zincblende phases being about 1 eV per formula unit higher in energy than the ground state nickel-arsenide (B8 1 ) phases. However, spintronic devices require thick films or layers. Therefore, it is important to explore theoretically other halfmetallic ferromagnetic materials, which on the one hand are compatible with the binary tetrahedral-coordinated semiconductors, and on the other hand are not only low in energy with respect to the corresponding ground-state structures but also mechanically stable against structural deformations.In this Letter we make use of an accurate fullpotential density-functional method to study systematically transition-metal chalcogenides in the zincblende and nickel-arsenide structures in order to find halfmetallic ferromagnetic phases which could be realized in the form of films and layers thick enough. We shall show that CrTe, CrSe, and VTe in the zincblende structure are excellent half-metallic ferromagnets with wide halfmetallic gaps. They will be proved to be mechanically stable and approximately 0.31-0.53 eV per formula unit higher in energy than the corresponding ground-state phases, and therefore would be grown epitax...

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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.

On experimental side, BaFe2As2 without doping has been made superconducting by applying appropriate pressure (2-6 GPa). Here, we use a full-potential linear augmented plane wave method within the density-functional theory to investigate the effect of pressure on its crystal structure, magnetic order, and electronic structure. Our calculations show that the striped antiferromagnetic order observed in experiment is stable against pressure up to 13 GPa. Calculated antiferromagnetic lattice parameters are in good agreements with experimental data, while calculations with nonmagnetic state underestimate Fe-As bond length and c-axis lattice constant. The effects of pressure on crystal structure and electronic structure are investigated for both the antiferromagnetic state and the nonmagnetic one. We find that the compressibility of the antiferromagnetic state is quite isotropic up to about 6.4 GPa. With increasing pressure, the FeAs4 tetrahedra is hardly distorted. We observe a transition of Fermi surface topology in the striped antiferromagnetic state when the compression of volume is beyond 8% (or pressure 6 GPa), which corresponds to a large change of c/a ratio. These first-principles results should be useful to understanding the antiferromagnetism and electronic states in the FeAs-based materials, and may have some useful implications to the superconductivity.

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