PURPOSE: To improve characteristics of a patterned amorphous soft magnetic alloy layer by heat-treating the layer in the same plane as that of the layer and under the effect of an elliptic rotating magnetic field having the ratio of its principal axises different from 1.

CONSTITUTION: An amorphous soft magnetic alloy layer is heat-treated in the same plane as that of the layer under the effect of an elliptic rotating magnetic field having the ratio of its principal axises different from 1. The effect of variation in diamagnetic field coefficients is offset by elliptically varying a magnetic field applied from the external and the magnitude of the magnetic field actually applied to the soft magnetic layer is made approximately isotropic, thereby to lighten magnetic anisotropy in the patterned layer too.