FIELD: metallurgy. SUBSTANCE: invention relates to an amorphous alloy based on the iron-silicon-magnesium system, which can be used as a material for magnetic cores of transformers, inductors, chokes and electric motors. The amorphous magnetic alloy comprises, in at.%: iron - 88 - 92, magnesium - 4, silicon - 4-8. Amorphousc alloy is characterized by increased magnetic induction and high thermal stability. EFFECT: alloy is easily processed in a wide temperature range, while maintaining its amorphous structure. 1 cl, 1 dwg, 1 ex.