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

In this paper, Ni-doped ZnO (Zn_1−xNi_xO, 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 Zn_1−xNi_xO. With the increment of x, wurtzite structures degrade gradually. The magnetic properties are measured using superconducting quantum interference device at room temperature; the Zn_1−xNi_xO (x ≤ 0.02) nanoparticles show ferromagnetism. However, for the sample of Zn_0.95Ni_0.05O, paramagnetism is observed, which may be ascribed to ferromagnetic–antiferromagnetic competition.