We have investigated the effects of rapid thermal annealing under vacuum on the CoFe-doped ZnO [Zn1−x(Co0.5Fe0.5)xO] films grown by reactive magnetron co-sputtering. At least up to x=0.15, the films have the single phase of the same wurtzite structure as pure ZnO. Ferromagnetism was observed for the CoFe-doped ZnO films. We found that rapid thermal annealing leads to a remarkable increase in the spontaneous magnetization of the CoFe-doped ZnO as well as the electron concentration. The annealing also leads to a significant increase in the Curie temperature (TC), resulting in room temperature ferromagnetism with TC>300 K for the CoFe-doped ZnO films.

The temperature effects on the magnetic properties of transition metal clusters are investigated by computer simulations which combine the classical potential approximation with the generalization of our recently proposed tight-binding molecular-dynamics method that includes explicit incorporation of spin-orbit interactions and spin fluctuations. The efficacy of this new method is demonstrated by application to small and intermediate size Nin-clusters (n ≤ 201) for which experimental data are available for comparison. The results obtained are in good agreement with the recent experimental findings.