The fabrication of CoPt nanowire and nanotube arrays by alternating magnetic field during deposition

Ordered CoPt nanowire (NWs) and nanotube (NTs) arrays were fabricated in anodic aluminum oxide template, their crystallographic structure and magnetic properties, during the progress of electrodeposition in applied external magnetic field, were investigated by X ray diffraction (XRD) and vibrating sample magnetometer (VSM). The XRD result shows that the CoPt face centered cubic (fcc) phase was dominant for all samples, while, the preferred crystal growth was influenced by external magnetic field. For CoPt NWs, with the increase of external magnetic field, coercivity (Hc∥ and Hc⊥) increased and the easy axis kept parallel with nanowire axis. On the other hand, for CoPt NTs, with increase of external magnetic field, Hc∥ increased and Hc⊥ decreased. When the NTs were electrodeposited in external magnetic field parallel to template, the easy axis kept perpendicular to nanotube axis; However when external magnetic field was perpendicular to template, the easy axis of magneto-electrodeposited NTs changed from being perpendicular to tube axis to being parallel with tube axis. The change of effective magnetic anisotropy was explained by the competition between magnetocrystalline anisotropy and shape anisotropy.