Room-temperature ferromagnetic properties of Ni-doped ZnO rod arrays

Ni-doped ZnO rod arrays have grown on zinc foils by a hydrothermal method at 180 °C. The doping Ni content could be controlled by varying the reaction time. The characterization of the rod array with X-ray diffraction and X-ray photoelectron spectroscopy indicated that Ni2+ ions were incorporated into the ZnO lattices. Photoluminescence peak of the rod arrays shifts to a little longer wavelength and its intensity decreases with the increase in Ni content. The green light emission as a result of oxygen vacancies was observed when excessive Ni ions were doped in ZnO. The rod arrays have exhibited room-temperature ferromagnetic behavior with the remanence of 0.454, 0.605 and 0.526 emu/cm3 for the Ni concentration of 2.38, 4.35 and 5.54 at%, respectively. The exchange interaction between local spin-polarized electrons and conductive electrons was proposed as a cause of the room-temperature ferromagnetism.