Co-metal clustering as the origin of ferromagnetism in Co-doped ZnO thin films

Park, Jung H.; Kim, Min G.; Jang, Hyun M.; Sangwoo Ryu, Hyun M.; Kim, Young M.
February 2004
Applied Physics Letters;2/23/2004, Vol. 84 Issue 8, p1338
Academic Journal
The origin of ferromagnetism in ZnO-based systems was investigated using Co-doped ZnO thin films as prototypical examples of II–VI-based diluted magnetic semiconductors. In spite of the atomic-scale dissolution of Co ions in wurtzite ZnO, both the magnetization-temperature curve and the magnetization-field curve demonstrated that Zn[sub 1-x]Co[sub x]O thin films were paramagnetic for x≤0.12. On the other hand, Zn[sub 1-x]Co[sub x]O films with x greater than 0.12 were characterized by the Co-metal clustering and apparently showed room-temperature ferromagnetism. The discrepancy between the zero-field cooling and the field cooling curves further indicates that Co-doped ZnO films (for x>0.12) are superparamagnetic and the observed ferromagnetism originates from the nanometer-sized Co clusters. © 2004 American Institute of Physics.


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