Magnetic and Optical Properties of Ag-CoFe Nanohybrids Prepared by a Sequenced Microfluidic Process

Metal-based magnetic nanoparticles (NPs) with hybrid structures are currently attracting extensive attention due to the synergistic effects among constructing components. Their unique physicochemical properties endow them with widespread applications in catalysis, optics, magnetic separation and magnetic resonance imaging contrast agents. However, the formation of nanohybrids (NHs) is usually difficult due to the incompatibility of components, especially for NHs of core-shell structures with mismatched crystal lattices. In this study, NHs containing Ag core and CoFe alloy surface layer (Ag-CoFe NHs) with varieties of hybrid structures were successfully synthesized by a sequenced microfluidic process. The hybrid structure formation mechanism was discussed according to the crystal plane matching theory, and their related optical and magnetic properties were investigated. When compared to Ag NPs, Ag-CoFe NHs presented a distinct red shifted and broader absorption peak in visible region. This may be attributed to the changes in dielectric constant caused by different CoFe shells and the diversity of hybrid structures. Moreover, due to the interface pinning effects and magnetoelectric coupling effect between Ag cores and CoFe shells, the superparamagnetic properties of Ag-CoFe NHs still existed at room temperature although its block temperature was much higher than that of CoFe NPs. Based on these characteristics, the Ag-CoFe NHs show great potential in magneto-optics, multi-mode nanomedicines and other related fields.