High-magnetic-moment core-shell-type FeCo–Au∕Ag nanoparticles

We developed a physical technique combining an on-line sputtering/evaporation process with an integrated nanocluster deposition process to prepare core-shell-type nanoparticles. High-magnetic-moment ${\left({\mathrm{Fe}}_{60}{\mathrm{Co}}_{40}\right)}_{\text{core}}{\mathrm{Au}}_{\text{shell}}$ and ${\left({\mathrm{Fe}}_{60}{\mathrm{Co}}_{40}\right)}_{\text{core}}{\mathrm{Ag}}_{\text{shell}}$ superparamagnetic nanoparticles with controllable particle size of 10–20 nm and $\mathrm{Au}∕\mathrm{Ag}$ shell thickness of 1–3 nm were prepared by using this method. Au shell is not only functional for the potential biocompatibility but also the key to prevent the oxidation of FeCo nanoparticles. Saturation magnetization of ${\left({\mathrm{Fe}}_{60}{\mathrm{Co}}_{40}\right)}_{\text{core}}{\mathrm{Au}}_{\text{shell}}$ nanoparticles was found three times higher than that of iron oxide nanoparticles. This technique enables us to control independently the dimensions of core and shell and select individually materials for core and shell for any other core-shell-type nanoparticles.