## 3 Results  
Patchy Fe\({}_{3}\)O\({}_{4}\)-Au nanoparticles (Fe\({}_{3}\)O\({}_{4}\)@Au pNPs) were obtained through alkaline co-precipitation of Fe\({}_{3}\)O\({}_{4}\) nanoparticles from an aqueous ferrous and ferric solution in presence of Au nanostructures which were formed before through reduction of Au\({}^{3+}\) cations by Fe\({}^{2+}\) cations in acidic solution. The Fe\({}_{3}\)O\({}_{4}\)@Au pNPs were stabilized by subsequent treatment with 3-mercaptoethanol(MPA) and 1-methyl-3-(dodecylphosphonic acid) imidazolium bromide (Imidazolium-PA). The formation of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs was confirmed by examining their composition, structure, morphology and magnetic properties using EDX, XRD, HRTEM, and SQUID. The EDX spectrum of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs indicates the content of Fe, O and Au in the nanoparticles (Figure 1a). The atomic ratio of Fe to Au is 9:1, which suggests that the Fe\({}_{3}\)O\({}_{4}\) NPs were the main component and formed the core. The powder XRD pattern in Figure 1b displays the characteristic peaks of Fe\({}_{3}\)O\({}_{4}\) in the cubic inverse spinel structure and those of the Au nanostructures in the fcc phase. The peaks at 2 \(\Theta\)= 30.52\({}^{\circ}\), 35.91\({}^{\circ}\), 43.59\({}^{\circ}\), 53.91\({}^{\circ}\), 57.43\({}^{\circ}\), and 63.13\({}^{\circ}\) are attributed to diffraction from the (220), (311), (400), (422), (511), and (440) planes of Fe\({}_{3}\)O\({}_{4}\), whereas the diffraction peaks at 38.50\({}^{\circ}\), 44.47\({}^{\circ}\), 64.75\({}^{\circ}\), 77.54\({}^{\circ}\) and 81.74\({}^{\circ}\) are assigned to the (111), (200), (220), (311), and (222) planes of gold. The relatively broad widths (FWHM\(>\) 0.8\({}^{\circ}\)) of the diffraction peaks correlate with the ultra-small sizes of the Fe\({}_{3}\)O\({}_{4}\) and Au nanostructures. The mean crystal size of the Fe\({}_{3}\)O\({}_{4}\) nanoparticles was determined from the XRD pattern using Debye-Scherrer's equation and the highest-intensity diffraction peak of the (311) facet [29]. The calculated nanoparticle diameter is 22 nm. More detailed information on the morphology and size distribution of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs were attained by conducting a TEM analysis. The NP size distribution was determined by measuring the diameters of 110 NPs. Figure 2 depicts a representative TEM image (a) and the nanoparticle-size histogram (b), the latter was fitted to a Gaussian function (red solid line). The Fe\({}_{3}\)O\({}_{4}\)@Au pNPs exhibit nearly spherical shapes and sizes between 8 and 22 nm with a mean value of 12.5 nm. High-resolution transmission electron microscopy (HRTEM) studies, completed by fast Fourier transform (FFT) analyses of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs, provided in-depth insight into the spatial distribution of the chemical composition and crystal phases. The HRTEM images of a Fe\({}_{3}\)O\({}_{4}\)@Au pNP in different magnifications (Figure 3) are depicted as a projection along the (511) direction of the Fe\({}_{3}\)O\({}_{4}\) nanocrystal (Figure 3a). The Fe\({}_{3}\)O\({}_{4}\) nanocrystal is partially covered with an Au nanostructure, as it is reflected by the \"darker\" contrast due to the higher electron density and larger electron-diffracting power of Au in comparison to that of the iron oxide core. The Au composition and structure of the crystalline surface layer were confirmed by the interatomic distance d\({}_{\text{Au}}\) = 0.29 nm, which identifies the crystallographic (111) facet of face-centered cubic gold as having a lattice constant of 0.407 nm (Figure 3b). The distance between two adjacent planes in the Fe\({}_{3}\)O\({}_{4}\) structure is 0.16 nm which is related to the (511) facets of inverse spinel structured Fe\({}_{3}\)O\({}_{4}\) (Figure 3c). These results are consistent with the FFT image analysis of  
Figure 1: (a) EDX analysis of Fe\({}_{3}\)O\({}_{4}\)@Au pNPs; (b) XRD pattern of Fe\({}_{3}\)O\({}_{4}\)@Au pNPs. Figure 2: (a) TEM image of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs, (b) and their size distribution.