PURPOSE: To prevent the occurrence of thin-film peeling and substrate fracturing, by selecting substrate bias voltage and substrate temp. and by regulating the internal stresses after film formation and before and after annealing to a specific value or below at the time of forming an FeAlSi-alloy thin film on a substrate.

CONSTITUTION: At the time of forming the FeAlSi-alloy film on the substrate by means of a DC three-electrode sputtering device, etc., negative bias voltage to be applied to the substrate at the time of film formation and substrate temp. are selected so that internal stresses after film formation and before and after the annealing at about 500°C necessary to recover magnetic properties are regulated to 1×109dyne/cm2 or below, respectively. In this way, peeling of thin film and fracturing of substrate due to film formation are prevented and the FeAlSi-alloy thin film having superior soft-magnetic properties can be obtained.