First-principles Study Of Two Semi-metallic Materials

Half-metallic ?HM? material is a promising application material for spintronics materials. In microstructure scale, HM materials, in which metallic and semiconducting characters coexist in different spin directions, process 100% spin polarization at the Fermi level ?EF?. Up to now, many types of HM materials have been found, which can be classified according to the different properties, such as the origin of the HM nature, the crystal structure, the HM electronic state, the electronic and magnetic properties and so on. In this paper we present an attempt of First-principles study to investigate the structural, electronic and magnetic properties of CrO₂ with rutile structure and Zr₂VSn Heusler alloy within the density functional theory ?DFT? using the Vienna ab initio simulation package ?VASP? with the projector augmented-wave ?PAW? pseudopotential.For the CrO₂ with rutile structure, the calculations reveal that the F-doped CrO₂ with low F concentration keeps a high spin polarization. Due to F doping, five different Jahn-Teller structural distortions are observed for the octahedrons around five groups Cr atoms in F-doped CrO₂, this results from the 3d electron orbitals are asymmetrically occupied. Compared with pure CrO₂, the decrease of spin polarization of F-doped CrO₂ is contributed by the shift of Cr_?B 3d state towards low energy region. The impurity moment by substituting F impurities for O atoms are aligned with the host moment and the total magnetic moment increase about 1 ?B by more substituting one F impurity for one O atom, indicating that magnetic moment can be controlled by F doping. For Cr₅₄O₁₀₂F₆, Cr_?A and Cr_?B alternately arrange in a unbroken F-Cr-F zigzag chain along< 111> direction in ?110? plane, but the additional magnetic moment by substituting Fimpurity for Odoes not appear to reside on the Crion in the vicinity of the Fimpurity, but is quite diffuse due to the magnetic double-exchange interaction.For full heusler alloy, the calculations reveal that the bulk Zr₂VSn Heusler alloy with Hg₂CuTi-type are ferrimagnetic half-metallicity with equilibrium lattice constant 6.815 A and total magnetic moment-1.000 ?B/f.u., following the Slater-Pauling rule ?_t,=Z_t-18. For five different ?001? surfaces ?ZrV-, ZrSn-, VV-, ZrZr- and SnSn-terminations?, due to different atomic displacements, the surface atoms exhibit different electronic properties, but the half-metallicity which can be observed in bulk are all destroyed in five terminations. The high spin polarization 75% is observed in ZrSn-termination, in which the atomic magnetic moments in surface layer are slightly decreased relative to the bulk magnetic moments.