Recently, the transition metal-doped ZnO film has been receiving remarkable attention because of their application in magnetic semiconductor devices [1][2][3][4][5][6][7][8][9][10]. In particular, ZnO-based dilute magnetic semiconductors (DMSs) have been predicted to show ferromagnetic behavior with Curie temperature above room temperature and have a large magnetization [11][12][13], which makes them a promising candidate material for the next generation of spintronic devices utilizing electronically or optically controlled magnetism. To date, the origin of ferromagnetism in oxide DMSs remains a very controversial topic. Therefore, there remain a lot of open questions or controversial opinions. The origin of ferromagnetism in the Co-doped samples was attributed to Co clustering in one case [14] and to the formation of secondary phases in the other case [15]. Chakraborti et al. [16] pointed out that carrier induced exchange is not directly responsible for the magnetic properties of the Al-doped Zn(Cu)O sample. Rather, a defect mediated exchange mechanism needs to be invoked for this system [16]. However, other researchers have proposed that the ferromagnetism is due to the Ruderman-Kittel-Kasuya-Yosida indirect exchange or doubleexchange mechanism [17], or due to the percolation of bound magnetic polarons (BMPs) to produce long-range magnetic order [18]. Due to the technological importance of DMS-based devices, a full understanding of the nature of their magnetic characteristics is of greater interest. In this study, we reported that the room temperature ferromagnetic behavior is observed for Co 0.2 Al x Zn 0.8Àx O O films prepared by the sol-gel method. The relationships between aluminum content, acceptor-like defects and the magnetic properties for Co 0.2 Al x Zn 0.8Àx O films were also investigated in this study. The sol-gel technique is very attractive as it can be implemented easily in a laboratory for the deposition of DMS films.
2. Experiment
Co 0.2 Al x Zn 0.8Àx O DMSs were prepared by the sol-gel method using Zn(CH 3 COO) 2 Á2H 2 O, Al(NO 3 ) 3 Á9H 2 O and Co(CH 3 COO) 2 Á4H 2 O as starting precursors and 2-methoxyethanol and monoethanola-