Electronic and magnetic properties of zigzag graphene nanoribbons with periodic protruded edges

The electronic and magnetic properties of zigzag graphene nanoribbons with protruded steps along their edges (ZS-GNRs) are investigated by extensive density-functional theory calculations. We show that the electronic and magnetic properties are determined by an interesting interplay between the length of the protruded step and the distance of two adjacent steps along the ribbon edge. With a small length of the protruded steps along the edge, the system can be converted from a nonmagnetic semiconductor to metal and then to a magnetic semiconductor by increasing the step-to-step distance. In particular, the energy gap decreases first toward a zero minimum and then gradually increases as the step length increases, accompanying with the rapid increase in the edge magnetization. When the step length exceeds a critical value, the ZS-GNR will be always a magnetic semiconductor regardless of the step-to-step distance. We also reveal that the applied transverse electric field can enlarge the energy gap of nonmagnetic ZS-GNRs, due to the breaking of band degeneration; whereas the field-induced gap change in the magnetic ZS-GNRs is spin dependent, leading to the emergence of amazing half metallicity under certain field strengths. These findings suggest that the ZS-GNRs are promising for designing versatile graphene-based devices and can find novel applications in both electronics and spintronics.