PURPOSE: To improve the soft magnetic characteristics and the saturation magnetic flux density of a soft magnetic thin film of single-crystal iron.

CONSTITUTION: On a single-crystal sapphire substrate 1, an epitaxial buffer layer 2, which is formed of one of the metals M, which are V, Nb, Mo, Ta and W, or body-centered cubic crystal alloy composed of at least two kinds of metal selected from the metals M or Fe or body-centered cubic crystal alloy composed of Cr and M, or a double layer structure buffer layer, which has the epitaxial buffer layer as a bottom layer 2' and Cr as a top layer 2", is formed. Then, a single-crystal Fe film 3 is epitaxially grown on the epitaxial buffer layer 2 or on the double layer structure buffer layer. Fe-base material which has a purity of 99.995 or more is used and single-crystal Fe is grown in super vacuum under lower pressure than 10-8 Torr.