Confined growth of highly uniform and single bcc-phased FeCo/graphitic-shell nanocrystals in SBA-15

•SBA-15 with a highly ordered 2D hexagonal mesostructure has been used as a support to produce FeCo/GC nanocrystals.•The FeCo/GC nanocrystals are highly uniform and have a single bcc-phase.•The FeCo/GC nanocrystals exhibit superparamagnetism with high saturation magnetization at room temperature.

We have synthesized highly uniform and single bcc-phased FeCo/graphitic carbon shell (FeCo/GC) nanocrystals with an average diameter of 5.7 ± 0.3 nm by thermal decomposition of metal precursors in SBA-15 and subsequent methane CVD. Small-angle XRD data and N2 adsorption–desorption isotherms of the SBA-15 before and after loading with FeCo/GC nanocrystals clearly demonstrate that the structure of SBA-15 was retained during the nanocrystal growth and most of the channels of the mesoporous silica were stucked by the FeCo/GC nanocrystals. The nanocrystal sizes of 5–6 nm are consistent with the pore diameters of the SBA-15. The yield of nanocrystals in silica has been increased 6-fold and the Fe/Co ratio of the FeCo/GC nanocrystals has been improved from 34:66 to 46:54 by using SBA-15 instead of fumed silica. The FeCo/GC nanocrystals exhibit superparamagnetism with high saturation magnetization of 209 emu/g metal at room temperature.

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