The frequency and field dependence of permeability, the differential maximum permeability, and coercive field of a‐Fe81B13.5Si3.5C2 alloys are studied as‐received and under heat treated conditions. The sample is heat treated with infrared heat pulse and current pulse. The magnetic properties are improved when the sample is treated for a short duration heat pulse. Copyright © 1987 WILEY‐VCH Verlag GmbH & Co. KGaA