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 sphere- like 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-xNix O( x £ 0.02) nanoparti- cles show ferromagnetism. However, for the sample of Zn0.95Ni0.05O, paramagnetism is observed, which may be ascribed to ferromagnetic-antiferromagnetic competition.