Magnetoceramic nanocrystals from the bulk pyrolysis of novel hyperbranched polyferrocenyl(boro)carbosilanes

We report a novel strategy to synthesize nanostructured magnetoceramics via a direct bulk pyrolysis of hyperbranched polycarbosilanes without any assistance of nanoscaled templates. The hyperbranched polyferrocenyl(boro) carbosilanes (hb-PBCS) were synthesized via a convenient A₂+B ₃ strategy. After the pyrolysis of hb-PBCS under a nitrogen atmosphere at 1100 °C, iron silicide nanocrystal enriched ceramics with a grain size of 20-60 nm were formed. The regular architecture and quite higher ceramic yield of polymeric precursors are superior in retaining iron and silicon that give a possibility to aggregate into regular nanocrystals during the bulk pyrolysis in comparison to their linear counterparts. Furthermore, if the mixed precursor of hb-PBCS with regular architecture and a silylene-diacetylene polymer with high ceramic yield was employed, a hierarchical structure of uniform nanorods with diameters of 20-30 nm and aspect ratios of ∼5 together with microspheres with diameters of 4-8 μm could be obtained under the same pyrolytic conditions. A vibrating sample magnetometer measurement demonstrated that the generated iron silicide nanocrystal enriched ceramics possessed weak ferromagnetism with an ultralow hysteresis loss.