# Magnetic Properties of Nanocomposites
## 4 Ceramic Nanocomposites
### Ceramic Nanocomposites Containing Ni
Applying Equation (1) to the ZFC curve of Figure 16 (top left) above 20 K (in order to exclude the low-temperature anomaly, which will be discussed in due time), one gets the Gaussian \(p(D)\) curve shown in the top right panel; a comparison with the histogram obtained from TEM image analysis indicates that the model is able to approximately predict the size distribution even in the case of interacting NPs. Figure 10: Sequence of the operations implemented in the preparation of Ni NCs. Reprinted from the work of [64] with permission from Elsevier. Figure 11: TEM **(a,b)** and HR-TEM (high resolution TEM) **(c)** images of the NiA735C—12 min sample. Instrumental magnification: 6000\(\times\), 30,000\(\times\), and 400,000\(\times\). Reprinted in modified form from the work of [14] with permission from Elsevier. **(d)** Ni particle size distribution. Figure 12: TEM **(a–c)** and HR-TEM **(d)** images collected of the NiA750C—0 min sample. Instrumental magnification: 8000\(\times\), 30,000\(\times\), 100,000\(\times\), and 400,000\(\times\). Reprinted in modified form from the work of [14] with permission from Elsevier. **(d)** Ni particle size distribution. High-field magnetic susceptibility measurements were performed on sample NiX735C--12 min to identify the non-ferromagnetic phase in these NCs. The linear behavior of the reciprocal high-field susceptibility \(\frac{1}{\chi_{HF}}=\frac{H}{M}\) plotted as a function of temperature (Figure 17, left panel) clearly indicates the existence of a pure paramagnetic phase at high T; at intermediate temperatures (50 K \(\leq\) T \(\leq\) 200 K), the experimental curve deviates from the linear behavior, showing a small downward concavity; at even lower temperatures, a broad minimum followed by a new increase of \(\frac{1}{\chi_{HF}}\) is observed. The deviations from the linear behavior observed with all the samples above 50 K indicate that an interaction exists  
Figure 14: Room temperature saturation magnetization \(M_{s}\) as a function of the total content of metallic Ni and hexagonal nickel hydride. Figure 13: TEM (**a**,**b**) and HR-TEM (**c**) images of the NiX735C—12 min sample. Instrumental magnification: 4000\(\times\), 100,000\(\times\), and 400,000\(\times\). Reprinted in modified form from the work of [14] with permission from Elsevier. (**d**) Ni particle size distribution. among paramagnetic ions in these materials. This is substantiated by plotting the product \(\chi_{H\text{F}}\)T as a function of temperature (Figure 17, right panel). Both the downward concavity of the \(\chi_{H\text{F}}\)\({}^{-1}\) versus T curve above 50 K and the shallow minimum in the \(\chi_{H\text{F}}\)T curve, followed by an increase at lower temperatures [76; 77; 78], indicate that the interaction among paramagnetic ions is basically ferrimagnetic. Figure 16: **(Top left)** FC/ZFC curves of sample NiX735C—12 min; **(top right)** NP size distribution derived from the ZFC curve analysis (blue line), superimposed to the experimental histogram (Figure 13d); **(bottom left)** magnification of the low-temperature structures of FC/ZFC curves in sample NiX735—12 min; **(bottom right)** low-temperature structures resulting after subtraction of the baseline. Figure 9:0 Hysteresis loops measured in sample NiX735C—12 min in the temperature interval 2-300 K and in the field range \(-\)70 kOe \(\leq\) H \(\leq\) 70 kOe. Upper inset: high-field magnetization as a function of temperature; lower inset: detail of the low-field region for three temperatures. Further information comes from the analysis of the low-temperature anomaly of FC/ZFC curves, as shown in Figure 16 (bottom left): a monotonic increase and a bump of the magnetization are superimposed to the featureless FC and ZFC curves, respectively.