Interface Related Ferromegnetism In Non-magnetic Composite Materials

Materials’interface and surface characteristics are at least as important as periodic structure bulk materials whether in technology applications or basic physical phenomena. Recent years, researchers have found new interface-related physical properties which is different from bulk materials in many complex systems, and interface-related ferromagnetism in composite systems of simple oxides have been also reported frequently. Although the reports have made experimental basis for these composites in spintronics and spin-electronic devices, some basic problems such as the mechanism of interface-related ferromagnetism and the way to adjust this kind of ferromagnetism through interfaces have not been solved yet. In this paper, we describe the diluted magnetic semiconductors and the research of their ferromagnetism. And then we summarized the studies of the ferromagnetism which is related to interfaces. Here is our specific work:Firstly, we prepared a group of samples by calcining CuO powders with different reaction times at a temperature of950℃. Samples changed from pure CuO to pure Cu2O with the increasing of calcination time, and the magnetic signals of the samples firstly increased and then decreased, and the biggest Ms was0.04emu/g. We believed that the ferromagnetism was related to the interfaces of CUO/Cu2O, and we observed the interfaces by high-resolution TEM images. Secondly, we used hydrothermal method to make CuO/Cu2O mixtures, and found that we could control the generation of CuO and Cu2O effectively by changing reaction temperature, reaction time or concentration of the precursor, then we could adjust the interfaces of CuO/Cu2O which made our series of samples’ferromagnetism present the same trend. Thirdly, interfaces were obtained by using ball-milled method to mixed ZnO and CuO powders together in different proportions. XRD results explained that samples were not chemically reacted; VSM results shown that number of the interfaces changed, ferromagnetism also changed accordingly; XPS and TEM tests indicated that the changes of Cu elements’oxidation state might be the origin of the ferromagnetism in ZnO/CuO composites. Ultimately, we used a simple exchange model to explain this phenomenon. According to the results, we selected jilt glue method to prepare a series of ZnO/CuO thin films in order to control the number of the interfaces in our composites. We also produced pure ZnO and pure CuO thin films, finding that the ferromagnetism was belong to body effect. After excluding the contribution of pure phases, we gained a linear relationship between ferromagnetism of the samples and the number of interface in two phases.