Electrical control of spin polarization is very desirable in spintronics, since electric field can be easily applied locally in contrast with magnetic field. Here, we propose a new concept of bipolar magnetic semiconductor (BMS) in which completely s
pin-polarized currents with reversible spin polarization can be created and controlled simply by applying a gate voltage. This is a result of the unique electronic structure of BMS, where the valence and conduction bands possess opposite spin polarization when approaching the Fermi level. Our band structure and spin-polarized electronic transport calculations on semi-hydrogenated single-walled carbon nanotubes confirm the existence of BMS materials and demonstrate the electrical control of spin-polarization in them.
We report a first-principles electronic-structure calculation on C and BN hybrid zigzag nanoribbons. We find that half-metallicity can arise in the hybrid nanoribbons even though stand-alone C or BN nanoribbon possesses a finite band gap. This unexpe
cted half-metallicity in the hybrid nanos-tructures stems from a competition between the charge and spin polarizations, as well as from the pi orbital hybridization between C and BN. Our results point out a possibility of making spintronic devices solely based on nanoribbons and a new way of designing metal-free half metals.
