Ferromagnetism of lightly Co-doped ZnO nanoparticles

Zn1−xCoxO ( x = 0 – 0.04 ) nanoparticles were synthesized by an auto-combustion method. X-ray diffraction and Raman scattering studies confirmed the incorporation of Co into the ZnO lattice. Hysteresis loops were observed at 300 K in the samples with x = 0.01 – 0.04 , and the coercivity decreased with increasing Co content x . Temperature dependence of magnetization showed a usual steep upturn for transition metals doped ZnO at low temperature, however a simultaneous rapid decrease of coercivity below 50 K was observed in this work. Both of the features could be associated with the localization and the low density of the carriers at low temperature.