Transition metals doped and encapsulated ZnO nanotubes: Good materials for the spintronic applications

Among the ferromagnetic II-VI semiconductors, the (Zn, TM)O diluted magnetic semiconductors (DMSs) is the most promising for application in spintronic, since the high Curie temperature. In this work, the structural, electronic and magnetic properties of pristine armchair (5,5) and zigzag (5,0) ZnO nanotubes (ZnONTs) and doped with a single and a pair 3d transition metals (TMs) were studied based on density functional theory (DFT) method. Moreover a single TM encapsulated inside twice unit cell of (5,5) ZnONT are systematically investigated. The both doped and encapsulated systems are found exceptionally stable and their formation is exothermic. It is revealed that the TM magnetic moment increases first and then decreases, and reaches the maximum value when Mn is doped into ZnONTs. The values of magnetic moment and their variation trend versus the atomic number are similar for 3d TM-doped (5,0) and (5,5) ZnONTs, indicating they are independent of the chirality of tubes. Additionally, the Fe-doped (5,5) and Cu@(5,5) ZnONT with half-metal and thus 100% spin polarization characters seem to be good candidates for spintronic applications. Our research can provide guidance for the experiment upon DMSs and systemic investigation in 3d TMs. We suggest that ZnONTs especially armchair type, doped by TMs would have application potential as a spin polarized electron source for spintronic devices in the future. (C) 2017 Elsevier B.V. All rights reserved.