Inspired by metallic alloys in atomic solids, we used two distinct metallic nanoparticles, considered as “artificial metal atoms”, to engineer ordered binary nanoparticle alloys at the mesoscale, called binary supracrystals. Here, ferromagnetic 7.2-nm Co nanoparticles are used as large “A” site particles, while either ferromagnetic 4.6-nm Co or non-magnetic 4.0-nm Ag nanoparticles are used as small ‘B’ site particles to fabricate long-range ordered binary supracrystals with a stoichiometry of AB2 and AB13. The interparticle distances between 7.2-nm Co nanoparticles within the Co/Ag binary supracrystals can be tuned by a control of crystal structure from AB2 (CoAg2) to AB13 (CoAg13). A decrease of magnetic coupling between Co nanoparticles was observed as the Co-Co interparticle distance increases. Furthermore, by alloying 7.2-nm and 4.6-nm Co nanoparticles to form AB2 (CoCo2) binary supracrystals, a collective magnetic behavior of these two particle types, due to the dipolar interaction, was evidenced by observing a single peak in the Zero Field Cooling (ZFC) magnetization curve. Compared with the CoAg2 binary supracrystals, a spin orientation effect in sublattice that reduces the dipolar interactions in the supracrystals was uncovered in CoCo2 binary supracrystals.
Source : Engineering the magnetic dipolar interactions in three-dimensional binary supracrystals via mesoscale alloying.
Z. Yang, J. Wei, P. Bonville, M.P. Pileni Adv. Funct.Mater.,2015, 25, 4908.