The design of bipolar spin semiconductor based on zigzag-edge graphene nanoribbons

Using first-principle methods, we investigate the magnetism properties of zigzag-edge graphene nanoribbons (ZGNRs) with a nanopore, and find that edges of such a nanopore show important effects although the electron transport is mainly along the outer edge of ZGNR. The robust bipolar spin semiconductor can be obtained when the edges of such a nanopore are varied, where both spin states have a gap but can relatively shift. We speculate that bipolar spin semiconductor behavior is related with two factors: broken inner edge states and width of electrode. A series of models are considered: 6-ZGNRs with only one edge occupied by one triangle protrusion (TP), are connected with different width ZGNR electrodes. With the increase the electrode width along the TP edge direction, the systems show the following behavior in turn: spin metallicity, spin gapless semiconductor, and bipolar spin semiconductor. Finally, we show that the half-metallicity is realizable when electric fields are applied across the ZGNR with a nanopore, and their magnetic properties can be controlled by the external electric field. These findings suggest a new possibility for developing nanometer-scale carbon spintronic devices.