First-principles study on structural, electronic and magnetic properties of ZnO nanotube filled with Fe, Co and Ni nanowires

The structural, electronic and magnetic properties of transition metal TMn (TM=Fe, Co or Ni and n=5, 9 or 13) nanowires encapsulated inside (8,8) zinc oxide nanotube (ZnONT) have been investigated by first-principles calculations. Due to strong interaction between inner TM13 nanowires and outer ZnONT, not only a near square cross section shape is formed for outer ZnONT but also an anticlockwise rotation about their common axis takes place for the TM13 nanowires. The combining processes of all TMn@(8,8) composites are exothermic showing that the semiconducting (8,8) ZnONT can therefore be used to shield these TM nanowires. For TM13@(8,8) composites, the charge density accumulated strongly around the O atoms implies a large charge transfer from TM atoms (as well as from Zn atom) to more electronegative O atoms and thus the ionic binding characters between them. The magnetic moment of TMn@(8,8) composites decreases with the increasing TMn nanowire thickness, and there is almost no reduction in the magnetic moments of TM5@(8,8) and TM9@(8,8) composites with respect to the corresponding freestanding TM5 and TM9 nanowires, reflecting that the TMn@(8,8) composites especially the loosely wrapped TM5@(8,8) and TM9@(8,8) composites can be utilized in high density magnetic recording devices.