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We performed first-principles calculations to investigate the formation energy, geometry structure, and electronic property of Fe-doped Bi2Ti2O7 systems with different Fe doping content. The calculated formation energies indicate that the substitutional configurations of Fe-doping Bi2Ti2O7 are easy to obtain under O-rich growth condition, but their thermodynamic stability decreases with the increase of Fe content. The calculated spin-resolved density of states and band structures indicate that the introduction of Fe into Bi2Ti2O7 brings high spin polarization. The spin-down impurity levels in FexBi2−xTi2O7 and spin-up impurity levels in FexBi2Ti2−xO7 systems locate in the bottom of conduction band and narrow the band gap significantly, thus leading to the absorption of visible light. Interestingly, the impurity states in FexBi2−xTi2O7 are the efficient separation center of photogenerated electron and hole, and less affected by Fe doping content, in comparison, the levels of impurity band in FexBi2Ti2−xO7 systems are largely effected by the Fe doping content, and high Fe doping content is the key factor to improve the separating rate of photogenerated electron and hole. [ABSTRACT FROM AUTHOR]

Gate-tunable spin-resolved scattering through a Rashba spin–orbit (SO) coupling graphene barrier is considered theoretically by using a mode-matching method. In this structure, we investigate the dependence of the tunnelling transmission probability on the spin orientation of the incident electron. It is found that the difference of the transmission probability for opposite spin orientations exhibits considerable incident-angle-dependent features when both gate voltage and Rashba SO coupling in the barrier region are present. The difference is adjustable by the gate voltage. More specifically, we find that the sign of spin polarisation of conductance can switch from positive to negative by adjusting the electric potential at any Rashba SO coupling. These results can provide an efficient way to design graphene spintronic devices without the need for ferromagnets. [ABSTRACT FROM AUTHOR]

We report on the electronic and optical properties of two theoretically predicted stable spinel compounds of the form ZnBO, where B = Ni or Cu; neither compound has been previously synthesized, so we compare them to the previously studied p-type ZnCoO spinel. These new materials exhibit spin polarization, which is useful for spintronics applications, and broad conductivity maxima near the valence band edge that indicate good p-type dopability. We show that electrons on the octahedrally coordinated Zn atom fall deep within the valence band and do not contribute significantly to the electronic structure near the band edge of the material, while the O and tetrahedrally coordinated B electrons hybridize broadly in the shallow valence states, resulting in increasing curvature (i.e., decreased electron effective mass) of valence bands near the band edge. In particular, ZnCuO exhibits high electrical conductivities in the p-doping region near the valence band edge that, at , are twice the maximum found for ZnCoO , a previously synthesized compound in this class of materials. This material also exhibits ferromagnetism in all of its most stable structures, which makes it a good candidate for further study as a dilute magnetic semiconductor. [ABSTRACT FROM AUTHOR]