Nanoclustered Co−Au Particles Fabricated by Femtosecond Laser Fragmentation in Liquids

Heterostructured nanoparticles, consisting of Au and Co nanoclusters, have been synthesized by a two-step femtosecond laser technique. Au and Co targets were ablated and fragmented in acetone resulting in nanoparticles with an average diameter of 11 nm. Particles showed concomitant optical characteristics of Au and magnetic properties of Co. Energy dispersive X-ray scattering confirmed the presence of both material in each nanoparticle and showed that the relative concentration of Au and Co can be controlled. Unalloyed Au nanoclusters are estimated to be 1.5 nm from X-ray diffraction measurement of the 220 peak width and position. Pure Co nanoparticles have a room temperature magnetization of 28 emu/g, much lower than the bulk value of 143 emu/g, probably due to surface oxidation. In the bimetallic nanostructures, Au replaced oxidized Co and protected the core from oxidation. Nanoparticles consisting of 68% Co and 32% Au showed a magnetization of 51.3 emu/g which represents a 83% increase per Co atom compared to pure Co nanoparticles.