Evolution of the Magnetic and Optical Properties in CocoreAushell and (CoRh)coreAushell Core–Shell Nanoparticles

The magnetic and optical properties of CocoreAushell and (CoRh)coreAushell core–shell nanoparticles (14 shells, face centered cubic structure, 321 atoms) are investigated using spin-polarized density functional theory in the generalized gradient approximation. For CocoreAushell the properties show a clear dependence on the size of the Co core. For (CoRh)coreAushell we vary the Co:Rh composition. We show that the distribution of the magnetic moments within the nanoparticle depends on strongly/weakly on the chemical environment for the Co/Rh atoms. The optical absorption shows sensitivity to both composition and chemical arrangement. In particular, (CoRh)coreAushell nanoparticles show a blue shift for increasing Co concentration, whereas (RhCo)coreAushell nanoparticles show a red shift for increasing Co concentration. The investigated nanoparticles uniquely couple the magnetism of the core to the optical properties of the Au shell and thus pave the way to optical tracking.