Synthesis and characterization of bracelet-like magnetic nanorings consisting of Ag-Fe_3O_4 bi-component nanoparticles

摘要

Stable bracelet-like magnetic nanorings, formed by Ag-Fe_3O _4 nanoparticles with an average size around 40 nm, have been successfully prepared in large scale by means of reducing Ag~+ and Fe~(3+) simultaneously under mild conditions. In the reaction, tiny grains of silver are used as seeds to prompt small Fe_3O_4 nanoparticles to grow larger, which is essential to enhance the magnetic dipole-dipole interactions, while only superparamagnetic Fe_3O _4 nanoparticles (about 10 nm in size) can be obtained in the absence of Ag seeds. The XRD, TEM, SAED and the EDS line scan data reveal that these nanoparticles are in the core-shell structure. These magnetic Ag-Fe _3O_4 nanoparticles assembled into nanorings by magnetic dipole-dipole interactions with a diameter of 100-200 nm. The saturation magnetization of the nanorings is 39.5 emu g~(-1) at room temperature. The MRI images indicate that these kind of nanorings have the potential application in diagnostics as a T_2 MRI contrast agent.