Role of Si substitution in modulating the coercivity and magnetic anisotropy in Fe3CoB2 nanocrystallites

In this work, we report the impact of Si substitution on the structural and magnetic properties of Fe3CoB2 nanocrystallites as a rare-earth-free hard-magnet candidate. X-ray diffraction confirmed the formation of the tetragonal phase with an average crystallite size of ∼40 nm, while the transmission electron microscopy image revealed nanosized crystallites embedded in an amorphous matrix. Room-temperature Mössbauer spectra exhibited two sextets and two doublets, indicating magnetically ordered Fe sites in the tetragonal phase along with high-spin paramagnetic FeIII species in disordered regions. ZFC–FC magnetization curves displayed field-dependent blocking behavior, consistent with paramagnetic Fe species. Singular point detection measurements revealed a high anisotropy field of ∼10.7 kOe in the pristine Fe3CoB2, and systematically decreased with Si substitution. Magnetization measurements revealed a monotonic decrease in saturation magnetization with Si content, while coercivity was observed to increase, likely due to microstructural refinement. These results establish Fe3CoB2 as a rare-earth-free material with strong magnetic anisotropy, ideal for hard magnets.