# Magnetic Properties of NiZn Ferrite Nanofibers Prepared by Electrospinning
## 3 Results  
For the heat treatment process, Figure 1 shows the pyrolysis behavior graphs of the PVP/metal nitrate composite nanofiber sheet that were obtained by TGA. In the curve representing the weight to temperature, the weight of about 15 wt% sharply decreased until the temperature of the sample reached about 73 \({}^{\circ}\)C. This was due to the loss of moisture absorbed during the process. From this fact, the required temperature of the drying process was calculated at 80 \({}^{\circ}\)C immediately after the electrospinning process. The gradual loss curve from 150 \({}^{\circ}\)C to 420 \({}^{\circ}\)C indicates a range corresponding to the decomposition of PVP and the volatilization of the residual solvent. The mass loss range of pure PVP is 300-600 \({}^{\circ}\)C, but the decomposition temperature range of the metal salt and hybrid electro-spun nanofiber sheets shifted to a slightly lower temperature [37]. It is generally considered that the high thermal conductivity of the metal ions between the polymer chains promotes thermal decomposition. At 420 \({}^{\circ}\) C, the mass reduction decreases and then begins to decrease again at 570 \({}^{\circ}\)C, which is the point where the NiZn ferrite fiber begins to crystallize into the spinel structure [38]. The reaction ends \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Precursors** & **Ni(NO3)2\(\cdot\)6H2O** & **Zn(NO3)2\(\cdot\)6H2O** & **Fe(NO3)2\(\cdot\)9H2O** & **PVP** & **DMF** \\  & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** \\ \hline Precursor A & & & & 18 & \\ Precursor B & 1.45 & 1.48 & 4.04 & 20 & 100 \\ Precursor C & & & & 22 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The composition and content of the precursor solution. PVP: Polyvinyl pyrrolidone; DMF: N,N-dimethylmethanamide. at 685 \({}^{\circ}\)C with a final mass loss of 88 wt%. Regarding these experimental results, the heat treatment temperature of the nanofibers used in the analysis was determined to be 750 \({}^{\circ}\)C.  
The electro-spun samples from precursors A, B, and C were labeled and analyzed as samples A, B, and C. XRD analysis was used to identify the crystalized structure of the final samples. Figure 2 shows the diffraction patterns of samples A, B, and C calcined at 750 \({}^{\circ}\)C for 4 h. Despite the differences in polymer content, the diffraction pattern for the crystalized structure was the same for all three samples. The significant diffraction peaks indexed as (202), (131), (040), (242), (151), (404), and (444), which confirmed that the spinel structure was properly formed. The diffraction pattern was indexed by comparing with the 900-9920 entry of the Crystallography Open Database. Table 2 shows the results obtained by calculating the XRD diffraction pattern using the Scherrer formula (d = 0.94\(\lambda\) / B cos \(\theta\)). In this formula, \(d\) represents the crystallite size, B is the full width at half maximum (FWHM) of each XRD peak, and \(\lambda\) is the Cu K\({}_{\alpha}\) wavelength (0.15478 nm). The table shows the average crystallite size obtained using the peak intensities at (131), (151), and (404) diffraction planes per sample. The crystallite size calculated by the Scherer formula tends to decrease with an increasing PVP content of the precursor solution. According to [PERSON] et al., nanofibers with high polymer content in the calcination process increase the size and number of pores and cracks. These defects prevent the growth of a nuclear crystal and make the diffusion in the boundary of primary crystallites difficult [39]. The difference in crystallinity can also be confirmed by the width of the FWHM. Figure 1: TGA curve of PVP/metal nitrate composite nanofibers. Figure 2: X-ray diffraction patterns of the PVP/metal nitrate composite nanofibers calcined at 750 \({}^{\circ}\)C.  
Once all the components except for the metallic element are volatilized during calcination, the fibrous structure may not be maintained even if a suitable crystallized structure is formed.