## 6 Functional Properties and Applications of Nanocomposites
### Magnetic properties  
Concerning magnetic nanocomposites, two groups of composites can be assessed: those containing metal nanoparticles, and those containing Fe\({}_{2}\)O\({}_{3}\), Fe\({}_{3}\)O\({}_{4}\) or ferrite nanoparticles. In most cases the resulting nanocomposites are free of hysteresis, indicating a superparamagnetic material. [PERSON] _et al._[154] reported about alcohol-coated amorphous iron nanoparticles without hysteresis. They did not reach saturation, even at an applied magnetic field of 15 T. In contrast, [PERSON] _et al._[155] found saturation magnetizations ranging from 0.9 to 37.8 Am\({}^{2}\)/kg for different compositions of polymer coated iron nanoparticles. The highest values were associated to the samples with the highest iron loading. Most of their materials exhibited hysteresis at room temperature. Furthermore, they were characterized by a coercivity depending on the core diameter with a maximum at around 20 nm. [PERSON] _et al._[75; 76] measured a saturation magnetization of 15 Am\({}^{2}\)/kg for a polymer nanocomposite containing 21.8 wt % of Fe\({}_{2}\)O\({}_{3}\). Their material was free of hysteresis at room temperature, and as an additional feature, also optically transparent. Nanocomites, consisting of magnetic \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles in an electroconducting polymer matrix, were free of hysteresis and possessed a saturation magnetization around 58 Am\({}^{2}\)/kg [156]. Biocompatible ferrofluids containing between 10 and 40 wt % Fe\({}_{3}\)O\({}_{4}\) hybrid nanoparticles were also free from hysteresis [53]. A saturation magnetization around 30 Am\({}^{2}\)/kg and superparamagnetism were found for core/shell Fe\({}_{2}\)O\({}_{3}\)/polymer nanoparticles containing 15.3 wt % of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)[89]. A high saturation magnetization of 69 Am\({}^{2}\)/kg, respectively 54.9 Am\({}^{2}\)/kg was found for two different \(\epsilon\)-caprolactone-grafted Fe\({}_{3}\)O\({}_{4}\) nanocomposites [54]. Nanocomites containing between 20 and 50 wt % of Fe\({}_{2}\)O\({}_{3}\) nanoparticles in PPy exhibited saturation magnetizations around 30 - 45 Am\({}^{2}\)/kg. Additionally, an improved electrical conductivity was observed [157], compared to pure PPy. Nanocomites, containing 12.37 wt % of Fe\({}_{3}\)O\({}_{4}\) in a polyaniline matrix, were found to be superparamagnetic with a saturation magnetization of 3.88 Am\({}^{2}\)/kg [64]. Optically transparent thin films of block copolymers containing superparamagnetic  
Figure 8: Particle size dependency of the emission maxima of ZnO/PBDMA nanocomposites (Data taken from [PERSON] _et al._[132]), ZnO/m-PMMA nanocomposite particles (Data taken from [PERSON] _et al._[136]) and ZnO/Vinylester nanocomposites (Data taken from [PERSON] _et al._[131]). \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) have been developed by [PERSON] and [PERSON] [158]. They indicated a saturation magnetization of 0.5 Am\({}^{2}\)/kg for their material containing 2.6 wt % of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\). Figure 9 summarizes some literature data of different magnetic nanocomposites. As a clear trend, the saturation magnetization is, as expected, a function of the content of magnetic nanoparticles. However, not all authors give straight forward information about the content of magnetic phase. The particle size of the magnetic phase is indicated in the diagram, as far as it is available. Application potential for superparamagnetic nanocomposites was found as microwave absorbing material [64]. Very recent and advanced developments of organic coated magnetic nanoparticles show application potential mainly in biology, medicine, in biomedicine [54,159-162], and diagnostics, such as contrast agent for MRI (magnetic resonance imaging) [163,164], in cancer treatment by local hyperthermia [165-167], as drug carriers [168-170] or as biocompatible ferromagnetic fluid [53,171].