# Magnetic Properties of Nanocomposites
## 4 Ceramic Nanocomposites
### Ceramic Nanocomposites Containing Ni  
The interplay between NPs containing a zerovalent TM and residual TM ions still present in the ceramic matrix has been elucidated through a detailed investigation of Ni\({}^{2+}\) exchanged A/X zeolites, which can be considered a study case for the general understanding of the magnetic behavior of this class of nanomaterials [14]. The complex sequence of operations implemented to obtain the magnetic NCs is shown in Figure 10; the NCs are the result of a variety of cation exchange procedures and thermal treatments. Three representative TEM images of the ceramic NCs are shown in Figures 11-13; these images clearly show the presence of a large fraction of Ni NPs; the corresponding particle size distributions are also reported. The nanoparticulate phase of these NCs is dominated by Ni\({}^{0}\) particles, although a little fraction of HNi\({}_{2}\) particles has also been detected (in A zeolite-derived materials only, see Figure 10). The room temperature saturation magnetization is observed to linearly increase with the total content of Ni in the nanoparticulate phase, as shown in Figure 14.  
However, a study of the magnetic response of these NCs as a function of temperature down to T = 2 K clearly indicates that a non-negligible fraction of Ni does not belong to the nanoparticulate phase. This can be easily understood by examining the changes taking place in the shape of the hysteresis loops of the entire family of NCs when the temperature is lowered; for the sake of simplicity, one representative example of a sample not containing HNi\({}_{2}\) compound (see Figure 10) (sample NiX735C--12 min) will be discussed here. The hysteresis loops are shown in Figure 15; the upper/lower insets show the high-field magnetization as a function of temperature and some loops in the low field region, respectively. A strong non-ferromagnetic signal is observed to increasingly emerge with lowering of the temperature; this signal adds to the saturating behavior of the M(H) curve that dominates above 250 K. Such an effect is reflected by the temperature behavior of the high-field magnetization M\({}_{\rm 70 kOe}\)  
Figure 9: (**Left**) sorption isotherm of simazine on (Fe,H)A800C—0 min (full circles), (Fe,H)A600C—90 min (empty circles), zeolite H–Y(full triangle), and SiO\({}_{2}\)(II)400 (full square) samples. Reprinted from the work of [62] with permission from Elsevier; (**right**) adsorption isotherm for DNA equilibrium concentration in FeA800C—0 min (circles) and FeA750C—2 h (squares) sample suspensions. Solid lines: Langmuir curve-fits. shown in the inset Figure 15. The non-saturating contribution to M(H) is linear above 30 K, but a downward curvature appears below this temperature. An accurate estimate of the non-saturating (paramagnetic) fraction is based on the analysis of the curves reported in Figure 15 and is supported by QPA (quantitative phase analysis) of powder diffraction patterns under synchrotron radiation [64]; in this material, the paramagnetic fraction turns out to be as high as 46% of the total loaded Ni. The FC/ZFC curve measured in sample NiX735C--12 min is shown in the left panel of Figure 16 (top left). The two curves become separate at exactly room temperature, indicating that the blocking temperature of zerovalent Ni NPs is well above room temperature [27]; see Table 1. The FC/ZFC curves are almost featureless over nearly the whole examined temperature range (i.e., above 20 K), with the FC curve being almost flat and the ZFC magnetization increasing almost linearly with T. The rate-equation model developed to evaluate the size distribution \(p(D)\) of a system of non-interacting NPs starting from the ZFC curve can be tentatively applied even in this case, although the density of NPs indicates that they must be somewhat interacting.