The role played by oxygen vacancies in determining the magnetic properties of Cu-doped ZnO was studied. The observed magnetic hysteresis and the temperature dependence (irreversibility) of magnetization behaved like super-moments blocked along random directions for a low-temperature annealed sample. The magnetic hysteresis (finite coercivity and low field saturation) and the irreversibility of temperature-dependent magnetization were destroyed upon thermal annealing. It was proposed that oxygen vacancies played an important role in inducing super-moments to explain the observations.

Destruction of Ferromagnetism in Cu-Doped ZnO upon Thermal Annealing: Role of Oxygen Vacancy. Ghosh, B., Sardar, M., Banerjee, S.: Journal of Physics D, 2013, 46[13], 135001