Nanostructured Bimetallic Block Copolymers as Precursors to Magnetic FePt Nanoparticles

Phase-separated block copolymers (BCPs) that function as precursors to arrays of FePt nanoparticles (NPs) are of potential interest for the creation of media for the next-generation high-density magnetic data storage devices. A series of bimetallic BCPs has been synthesized by incorporating a complex containing Fe and Pt centers into the coordinating block of four different poly(styrene-b-4-vinylpyridine)s (PS-b-P4VPs, P1-P4). To facilitate phase separation for the resulting metalated BCPs (PM1-PM4), a loading of the FePt-bimetallic complex corresponding to ca. 20% was used. The bulk and thin-film self-assembly of these BCPs was studied by transmission electron microscopy (TEM) and atomic force microscopy, respectively. The spherical and cylindrical morphologies observed for the metalated BCPs corresponded to those observed for the metal-free BCPs. The products from the pyrolysis of the BCPs in bulk were also characterized by TEM, powder X-ray diffraction, and energy-dispersive X-ray spectroscopy, which indicated that the FePt NPs formed exist in an fct phase with average particle sizes of ca. 4-8 nm within a carbonaceous matrix. A comparison of the pyrolysis behavior of the metalated BCP (PM3), the metalated P4VP homopolymer (PM5), and the molecular model organometallic complex revealed the importance of using a nanostructured BCP approach for the synthesis of ferromagnetic FePt NPs with a smaller average NP size and a close to 1:1 Fe/Pt stoichiometric ratio.