Spin filter, spin amplifier and spin diode in graphene nanodisk

Graphene nanodisk is a graphene derivative with a closed edge. The trigonal zigzag nanodisk with size N has N-fold degenerated zero-energy states. It can be interpreted as a quantum dot with an internal degree of freedom. The ground state of nanodisk is a quasi-ferromagnet, which is a ferromagnetic-like state with a finite but very long life time. We investigate spin-filter effects in the system made of nanodisks and leads. A novel feature of the nanodisk spin filter is that its spin can be controlled by the spin current. We propose some applications for spintronics, such as spin memory, spin amplifier and spin diode. It is argued that a spin current is reinforced (rectified) by feeding it into a nanodisk spin amplifier (diode). Graphene nanodisk would be a promising candidate of future electronic and spintronic nanodevices.