Annealing effects upon magnetism, structure and alternating-current transport in Co:ZnO films were investigated. The room-temperature saturation magnetization, Ms, varied markedly for Ar and Ar/H2 annealing. By using impedance spectra, the change in grain-boundary and grain defects could be analyzed. The results demonstrated that Ar annealing produced mainly grain-boundary defects; leading to the enhancement of Ms. However, Ar/H2-annealing created not only grain-boundary defects but also grain defects; resulting in a stronger enhancement of Ms. The ferromagnetism of Co:ZnO films was influenced by both grain boundaries and by grain defects.

Role of Grain Boundary and Grain Defects on Ferromagnetism in Co:ZnO Films. H.S.Hsu, J.C.A.Huang, S.F.Chen, C.P.Liu: Applied Physics Letters, 2007, 90[10], 102506 (3pp)