Nature of room-temperature ferromagnetism from undoped ZnO nanoparticles

摘要

ZnO nanoparticles were synthesized by a solgel calcination process following being annealed in air at 400, 600, 800 and 1000℃. X-ray diffraction pattern and X-ray photoelectron spectroscopy show that all the samples present a typical wurtzite structure and no other impurity phases are observed. Room-temperature ferromagnetism from all the samples is confirmed by the vibrating sample magnetometer measurements, which shows that the RTFM decreases with the annealing temperature increasing from 400 to 800℃, and then became larger for the sample annealed at 1000℃. According to the Raman scattering spectra and electron paramagnetic resonance, the RTFM of samples annealed at 600, 800 and 1000℃ might be related to the oxygen vacancy related defects. However, the RTFM from the sample annealed at 400℃, presenting nearly the same value as that of the sample annealed at 1000℃, could originate with the interstitial zinc defects associated with XPS and photoluminescence analyses.