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CuO/ZnO nanocomposites with proportion of 4 at% CuO were annealed in air at various temperatures between 100℃ and 1200℃ to get Cu-doped ZnO nanocrystals.X-ray diffraction illustrates that CuO phase can be observed in the CuO/ZnO nanocompostes annealed at different temperature,but the Cu-doped ZnO nanocrystals are identified to be a wurtzite structure.The main peak (101) appears a trivial shift towards the higher diffraction angle with increasing annealing temperature from 700℃ up to 1000℃,which confirms the successful doping of Cu into ZnO lattice above 700℃.Annealing induces an increase of the grain size from 25 to 165nm.SEM indicates that most particles in CuO/ZnO nanocomposites are particle morphologies when annealing at 100-400℃,but these particles have a greater tendency to form clusters or aggregates as increasing the annealing temperature from 700℃ to 1000℃.Positron annihilation measurements reveal large number of vacancy defects in the interface region of the nanocomposites,and they are gradually recovered with increasing annealing temperature up to 1000℃.Room temperature ferromagnetism can be observed in the CuO/ZnO nanocompostes using physical properties measurement system,and the magnetization decreases continuously with increasing annealing temperature.However,the origin of ferromagnetism in the CuO/ZnO nanocomposites may have several possible sources.At low annealing temperatures,the ferromagnetism originates from the CuO nanograins,and they become antiferromanetic after subsequent higher temperature annealing which leads to the weakening of ferromagnetism.After annealing from 700℃ up to 1000℃,the ferromagnetism becomes gradually invisible.The ferromagnetism is probably induced by Cu substitution but is mediated by vacancy defects in CuO/ZnO nanocomposites.The disappearance of ferromagnetism shows good coincidence with the recovery of vacancy defects.It can be inferred that the ferromagnetism is mediated by vacancy defects which are distributed in the interface region.