# Superparamagnetic Fe/Au Nanoparticles and Their Feasibility for Magnetic Hyperthermia
## 3 Results
In addition, comparison of coercivity and saturation magnetization with literatures is shown in Table S1. To describe the feasibility of the prepared Fe/Au nanoparticles for magnetically induced heating, in contrast to the measurements presented above, the following experiments have been performed by means of dispersed particles in an aqueous solution. The dispersions have been prepared using distilled water as a biocompatible environment that is similar to the human biological body. The particles were dispersed in a water solution using a sonicator and vortex shaker with particles concentration of 5 mg/mL. The heating effect of the dispersed particles solution in alternating magnetic fields was studied by means of a high frequency generator with water-cooled magnetic coil system. Alternating magnetic fields with a frequency range of 144-304 kHz and magnetic field strengths of 0-500 Oe were applied to the samples. The temperature of the sample was measured by a fiber-optical temperature sensor. The solution temperature versus the exposure time (\(Txt\)) was detected and recorded using a fiber-optic sensor, as shown in Figure 3. It presents time-dependent calorimetric measurements at different applied magnetic fields for all the prepared samples. A significant heating effect is observed at applied magnetic fields for  
Figure 2: M-H curves at 300 K for Fe/Au core-shell nanoparticles. both samples for both samples more prominent than 200 Oe. At the maximum applied magnetic field and frequency of 400 Oe and 304 kHz, the heating rate reached values of 4 \({}^{\circ}\)C/min for a sample of 2:1 Fe:Au ratio and size of 71 nm. The heating effect of the other Fe:Au ratios are lower than of 2:1 balance. Based on the obtained data we cannot judge whether this is due to the agglomeration of 1:1 and 3:2 Fe:Au ratios to larger magnetic agglomerates in the suspension or caused by the less amount Fe particles and a large amount of magnetite in those ratios, which result in lower magnetization and hence reduce the induced heating power by the particles. It is clear that when the applied magnetic field and frequency increase, faster rotation of the magnetic moment and nanoparticles itself are obtained in the solution releasing an expansion of the temperature of the sample. The induced heating power of the magnetic nanoparticles under applied alternating magnetic fields is usually described in terms of the specific absorption rate (SAR). The SAR expresses the heating ability of the magnetic nanoparticles and, therefore, their feasibility for application in magnetic hyperthermia for cancer treatment. The induced heating power per unit mass of the sample (SAR), was calculated from the initial slope of temperature versus time plots (Figure 4) using the following equation:  
\[SAR=\frac{C_{p}}{m_{act}}\left(\frac{dT}{dt}\right)_{t=0} \tag{1}\]  
where \(C_{p}\) is the water-specific heat (4.18 J\(\cdot\)g\({}^{-1}\cdot\)K\({}^{-1}\)), \(\mathrm{m_{act}}\) is the mass of the sample over the total mass (in our case, the total mass = sample mass + 1 mL solution of distilled water) and \((dT/dt)_{t=0}\) is the initial slope of temperature-time data obtained from the magnetic hyperthermia experiment [7]. Figure 4 shows the heating rate and specific absorption rate SAR. on the magnetic field strength for each frequency for the prepared three samples. The 2:1 Fe:Au sample with higher Ms is producing a maximum heating rate up to 4 \({}^{\circ}\)C/min (Figure 4A) and SAR up to 50 W/g (Figure 4B) under therapeutic magnetic field intensities and frequencies. The observed quadratic field dependence is in agreement with the fact that the dissipated heating power is proportional to H\({}^{2}\). Heating of magnetic nanoparticles in an  
Figure 3: Temperature vs. time at different fields and frequencies for samples with sizes of (**A**) 61 nm, (**B**) 71 nm, (**C**) 83 nm. alternating magnetic field may be understood in terms of several types of energetic barriers which must be overcome for reversal of the magnetic moments [6].