# Superparamagnetic Fe/Au Nanoparticles and Their Feasibility for Magnetic Hyperthermia
## 3 Results  
The crystal structures of the synthesized Fe/Au samples have been characterized using XRD, as shown in Figure 1b. The majority of X-ray patterns show a face centered cubic (fcc structure for Fe and Au (Ref. J.C.P.D.S. 4-784) with the presence of magnetite (Fe\({}_{3}\)O\({}_{4}\)) peaks as a minor phase. The Rietveld refinement of the corresponding powder diffraction pattern was performed, and it was found that 31 wt% Fe, 17 wt% Au and 52 wt% magnetite were present in samples prepared at 1:1 Fe:Au ratio, and 38 wt% Fe, 41 wt% Au and 21 wt% magnetite in the sample prepared at 3:2 Fe:Au ratio. However, for the sample prepared at a 2:1 ratio, the XRD peaks confirmed the formation of pure bcc Fe coated with Au with 78 wt% Fe and 22 wt% Au. The crystalline size of the samples was calculated using the Scherer equation revealing crystalline sizes of 31, 38, 36 nm for all samples synthesized at Fe:Au precursor's ratio of 1:1, 2:1, and 3:2, respectively. To investigate the morphology and the size distribution of the produced nanoparticles, high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) have been used, respectively. Figure 1c,d shows HRTEM image and size distribution determined from SEM images of the prepared Fe/Au core/shell nanoparticles. HRTEM image displays the formation of spherical-like shape and shows the construction of the core/shell of the Fe/Au nanoparticles (Figure 1c). Note that the Fe/Au system is magnetic which reduces the resolution of the images. The size distribution was determined from the scanning electron microscope images that show homogenous distribution of the particles with average size close to 71 \(\pm\) 15 for the 2:1 Fe:Au sample (Figure 1d). The size distribution for the other 1:1 and 3:2 Fe:Au ratios averages 61 \(\pm\) 21 and 83 \(\pm\) 22 respectively. The field dependence of magnetization (hysteresis loops) of the samples has been measured at 300 K, as shown in Figure 2. The samples show hysteresis loops with nearly zero coercivity (Hc), revealing superparamagnetic-like behavior at room temperature. The results yield high values of saturation magnetization (M\({}_{\text{s}}\)) of 79, 165, 89 emu/g for samples prepared at \begin{table}
\begin{tabular}{c c c} \hline  & **Reagents** & **Concentration** \\ \hline
**1** & Ethanol & absolute \\ \hline
**2** & Tween & 2 mL (1 M) \\ \hline
**3** & Potassium ferricyanide & 2 mmol \\ \hline
**4** & Gold chloride & 0.7 mmol \\ \hline \end{tabular}
\end{table} 
Table 1: Used reagent’s concentrations. Fe:Au ratios of 1:1, 2:1, and 3:2, respectively. The sample of 2:1 Fe:Au ratio show high magnetization of 165 emu/g which proves the formation of pure Fe core in the sample and in good agreement with XRD data that revealed pure Fe for the 2:1 sample. Since the size distribution is approximately the same for all samples, one can assume that the magnetization is independent of particle size. Herein, the Fe content ratio in each sample can be the reason for the observed change in magnetization values for the samples. Based on the magnetization results, the mass ratio of the magnetic core (Fe) in the Fe/Au samples can be determined by comparing their M\({}_{\text{s}}\) value to M\({}_{\text{s}}\) of their related bulk Fe yielding 34, 72, 39 wt% of the magnetic Fe in the 61 \(\pm\) 21, 71 \(\pm\) 7, 83 \(\pm\) 21 Fe/Au samples respectively [29]. The results are consistent with the phase structural data obtained from XRD and TEM The sample with a 2:1 ratio shows a high magnetization of 165 emu/g that confirms the presence of Fe core nanoparticles. In contrast, the lower magnetization of samples with 1:1 and 3:2 ratios confirms the presence of a mixture of Fe (primary phase) and Fe\({}_{3}\)O\({}_{4}\) (minor phase). The presence of Fe\({}_{3}\)O\({}_{4}\) nanoparticles is sufficient to reduce the net magnetization of the samples. The novelty of this work is that the magnetization of our samples is higher than all the previous trials made in this system [31, 32, 33, 34].