▎ 摘　　要

In this paper, by using the density functional theory, we have comprehensively investigated the magnetic properties of an armchair graphene nanoribbon (AGNR) passivated by hydrogen atoms and doped with transition metal elements such as Fe, Co and Mn in different substitution positions and various densities of impurity atoms. Magnetic properties such as spin polarization and magnetic moments of AGNR have been investigated versus the distance of dopants from the ribbon's edge and the number of dopants. The results show that the values of spin band gap, spin polarization and magnetic moment can considerably vary depending on the type, position and the number of dopants. By comparing all three impurity atoms, we conclude that the substitution of the Mn instead of carbon produces higher magnetization than Fe and Co substitutions. Also, our results show that the spin filter efficiency of Mn-doped ribbon is higher those doped of Fe- and Co-doped. We expect that obtained results will have potential applications in spintronic devices.