Pyrolysis of Highly Metallized Polymers: Ceramic Thin Films Containing Magnetic CoFe Alloy Nanoparticles from a Polyferrocenylsilane with Pendant Cobalt Clusters

We describe the pyrolysis of a highly metallized polymer precursor comprised of a polyferrocenylsilane with pendant cobalt clusters under a reductive atmosphere (N 2 /H 2 = 92%/8%) leading to CoFe magnetic alloy nanoparticle-containing ceramic thin films. Variation of the pyrolysis conditions leads to changes in the nanoparticle size, size distribution, and composition, as well as the ceramic film structure, all of which influence the magnetic properties of the material. When pyrolyzed at 500 °C, the nucleation and growth afford uniform size, larger CoFe nanoparticles on the film surface, and smaller nanoparticles in the underlying layer of the ceramic films. We found that the SiC/C ceramic matrix prevents oxidation of fully embedded nanoparticles, whereas the surface nanoparticles are oxidized on exposure to air. The nanoparticle-containing films are superparamagnetic when pyrolyzed at 600 °C and are ferromagnetic at higher pyrolysis temperatures. The CoFe nanoparticle-containing ceramic thin films have been characterized by a variety of techniques, which include scanning electron microscopy, transmission electron microscopy, atomic force microscopy, energy-dispersive X-ray analysis, selected-area electron diffraction, X-ray photoelectron spectroscopy, and the magneto-optical Kerr effect.