Room-temperature ferromagnetic Co-doped ZnO nanoneedle array prepared by pulsed laser deposition

A Co-doped ZnO nanoneedle array with room-temperature ferromagnetic properties was successfully fabricated by pulsed laser deposition (PLD) method. Detailed nanostructures were studied by transmission electron microscopy (TEM) and x-ray diffraction (XRD). High resolution TEM images and selected area electron diffraction (SAD) patterns showed nanoneedles grew along c-axis of ZnO with a preferential growth perpendicular to Si (100) substrate, which is also confirmed by XRD. Uneven surface and stacking faults along the nanoneedles were observed, which implies lattice distortion due to the Co doping. Electron energy loss spectroscopy (EELS) analysis of different positions along the growth direction of nanoneedles shows homogeneous distribution of the Co dopant. No segregated clusters of impurity phase were detected by TEM. Superconducting quantum interference device (SQUID) magnetometer measurements show room temperature ferromagnetic ordering, which is attributed to the Co substitution for Zn in the ZnO nanoneedle.