Metastable amorphous and crystalline Fe1−xSix alloys and compounds were synthesized in an argon atmosphere with and without hexane, using a solid-state alloying method in a composition range of 0.1 < x < 0.4. Systems alloyed with hexane formed a single-phase amorphous structure with a composition range of 0.1 < x < 0.2. The Curie temperature of the amorphous phase decreased from 376 to 173 °C, and that of the crystalline phase from 722 to 517 °C as a function of x. The carbon content of the powder alloyed with hexane increased during the alloying time, reaching a maximum value of 8 wt% after 350 h of milling. It is concluded that carbon increases the tendency for the formation of amorphous phase. The Fe1−xSix system synthesized without hexane includes an amorphous phase together with crystalline FeSi and Fe2Si, with the composition range of 0.3 < x < 0.4. Solid solution exists in the composition range of 0.1 < x < 0.2. Curie temperatures decreased from 716 to 544 °C in crystalline phases and from 330 to 115 °C in the amorphous phases as a function of x.