Synthesis, structure, and room-temperature ferromagnetism of Ni-doped ZnO nanoparticles

In this paper, Ni-doped ZnO (Zn1–xNixO, in which 0 £ x £ 0.05) diluted magnetic semiconductors nanoparticles are prepared by an ultrasonic assisted sol–gel process. Transmission electron microscopy shows spherelike nanoparticles with an average size of about 25 nm. From the analysis of X-ray diffraction, the Ni-doped ZnO nanoparticles are identified to be a wurtzite structure, but impurity phases are observed when the Ni content x reaches 0.05. Sample structures are further studied by Raman spectra, from which a broad and strong Raman band in the range of 500–600 cm–1 is observed in Zn1–xNixO. With the increment of x, wurtzite structures degrade gradually. The magnetic properties are measured using superconducting quantum interference device at room temperature; the Zn1–xNixO (x £ 0.02) nanoparticles show ferromagnetism. However, for the sample of Zn0.95Ni0.05O, paramagnetism is observed, which may be ascribed to ferromagnetic–antiferromagnetic competition.