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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]