▎ 摘　　要

The zigzag-edged hexagonal graphene quantum rings (ZHGQRs) are sandwiched between two Au electrodes to construct nanojunctions, and their electronic and magnetic properties are investigated by the first-principles method. It shows that there are always significant transmission gaps ( semiconductor behavior) for all ZHGQRs but changing in an obvious oscillating manner with variations of the edge width. The mechanism for such a feature is analyzed deeply, and it is found that the weak localization for the quantum interference correction to conductance and the parity of wave function play the crucial roles. No intrinsic magnetism is observed in the ZHGQRs, this is because there always exist local armchair-edge-like defects at its corners to weaken the spin polarization strongly. And also shown is that the magnetic field can effectively suppress the weak localization behaviors leading to a negative magnetoresistance for the ZHGQR, which is in good agreement with experimental findings in graphene. These findings are of very important for understanding the electromagnetic properties of graphene quantum ring devices. (C) 2015 Elsevier Ltd. All rights reserved.