The role of silicon on the microstructure and magnetic behaviour of nanostructured (Fe0.7Co0.3)100−xSix powders

Abstract Single-phase(Fe 0.7 Co 0.3 ) 100− x Si x nanostructured powders ( x =0,5, 10, 15 and 20) have been elaborated by mechanical alloying in order to investigate the effect of silicon on the microstructure and magnetic properties of these alloys. A disordered Fe(Co, Si) solid solution with body centred cubic (bcc) crystal structure is formed after 72 h of milling for all the compositions. The addition of Si gives rise to a progressive decrease of the lattice parameter, from about 2.865 A for the binary Fe 70 Co 30 compound down to 2.841 A for the powder with x =20. The sample with the uppermost Si content exhibits the lowest value for the mean grain size (≈10 nm) as well as the largest microstrain (above 1.1%). All the samples are ferromagnetic at room temperature, although the saturation magnetization value reduces almost linearly by adding Si to the composition. A similar trend is observed for the hyperfine magnetic field obtained from the analysis of the room temperature Mossbauer spectra. The hyperfine field distributions show a broad double-peak shape for x >0, which can be ascribed to multiple local environments for the Fe atoms inside a disordered solid solution.