Room-temperature metal-free ferromagnetism, stability, and spin transport properties in topologically fluorinated silicon carbide nanotubes†
A new topologically fluorinated armchair single-walled silicon carbide nanotube ((n,n)SWSiCNT) with one fluorine per unit cell adsorbed on (n,n)SWSiCNT (F–Si-(n,n)SWSiCNT), where the F atoms are adsorbed on top of the Si atoms to form an infinitely straight line of F atoms (F-Line) along the tube axis, has been predicted via first principles density functional theory (DFT) and nonequilibrium Green’s function method, as well as ab initio molecular dynamic (MD) simulations. The DFT calculations demonstrate that the F–Si-(n,n)SWSiCNT structures can be spontaneously formed. Ab initio molecular dynamics (MD) show that the F–Si-(n,n)SWSiCNT structures are stable at room temperature. It was found that except for F–Si-(2,2)SWSiCNT, which is a nonmagnetic metal, all F–Si-(n,n)SWSiCNTs are spin-semiconductors with long-ranged ferromagnetic spin ordering along the tube axis. Even more excitingly, the ferromagnetism of the F-(n,n)SWSiCNT survives at room temperature. This is to say, the F–Si-(n,n)SWSiCNT is a room-temperature metal-free ferromagnetic spin-semiconductor. Moreover, the simulations of F–Si-(n,n)SWSiCNT as a field-effect transistor (FET) show that the F–Si-(n,n)SWSiCNT FET can provide completely spin-polarized currents with reversible spin-polarization direction by applying a gate voltage. Thus, F–Si-(n,n)SWSiCNTs may open new routes towards practical nanoelectronics and optoelectronics as well as spintronic devices based on SWSiCNT-based materials. In addition, it was demonstrated that F atoms topologically adsorbed on (n,n)SWSiCNT bisect sp2-like bonding networks of (n,n)SWSiCNT, creating Klein and zigzag π-edge states at each side of the F-Line. It is such Klein and zigzag π-edge states that lead to the unexpected room-temperature ferromagnetism.