Magnetic—Noble Metal Nanocomposites with Morphology‐Dependent Optical Response.

This paper describes the synthesis of noble metal−magnetic nanoparticle composites with different shapes, using a seeded-growth approach in the presence of a cationic surfactant (cetyltrimethylammonium bromide, CTAB). Hydrophobic CoPt3 and FePt nanoparticles were transferred into water using CTAB as a phase-transfer agent and were subsequently used as seeding materials for the reduction of gold and silver precursors to produce Au−CoPt3, Ag−CoPt3, and Au−FePt nanocomposites. The nanocomposites synthesized were characterized by transmission electron microscopy (TEM), UV−visible spectroscopy, and SQUID magnetometry. Through the modification of the growth conditions, Au−CoPt3 nanocomposites with various morphologies (spheres, cubes, rods) were prepared, providing an opportunity to tailor the optical response of these composite nanoparticles while maintaining the magnetic properties of the original seeds, even upon phase transfer into water.