Shell-Dependent Evolution of Optical and Magnetic Properties of Co@Au Core-Shell Nanoparticles

摘要

Co@Au core shell nanoparticles (NPs) of different shell thicknesses were fabricated by a combination of the displacement process and the reduction-deposition process in a microfluidic reactor. Changes in the core sizes and the whole sizes of these Co@Au NPs with the shell formation were investigated. Effects of the shell thickness and the size change on the Co-Au interface pinning effects and the interparticle interaction were analyzed and correlated to their magnetic properties and surface plasmon resonance (SPR). Increasing the shell thickness causes an increase of the coercivity at 10 K due to the enhanced interfacial pining effect and decease of the coercivity at 300 K due to the reduced interparticle interaction. The increased core sizes and Co-Au interface pinning effects with the shell formation, and the higher interparticle interaction than that of well-dispersed species, result in significantly enhanced blocking temperature (T_b) for these Co@Au NPs. But the T_b's for these Co@Au NPs slightly decrease with an increase of the shell thicknessdue to the reduced interparticle interaction. The SPR absorbance shows a line width broadening and an enhanced line shape variation with an increase of the shell thickness and a broad size distribution. Tuning of the optical and magnetic properties of the core-shell nanoparticles via the shell thickness provides an efficient and flexible method to obtain desired magnetic and optical properties for multimode sensing technology and high efficiency solar cell.