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A new type of ferromagnetic amorphous alloy with a two‐phase structure was found in cosputtered Fe‐B‐N films. The microstructure was identified to be composed of two amorphous phases with about 50 A or less in size; one is a ferromagnetic amorphous phase of Fe‐B‐N alloy and the other is a nonmagnetic and high resistive amorphous phase of boron nitride. The homogeneous mixture of these two phases in the films resulted in unique features for magnetic and electrical properties. In comparison to sputtered Fe‐B films, the Fe‐B‐N films exhibit higher saturation magnetizations and the electrical resistivity is about 3–103 times higher. The compositional dependence of Curie and crystallization temperatures also differs from those of the sputtered amorphous Fe‐B films. Furthermore, the corrosion resistance of the films is improved in the presence of nitrogen.

A new type of high‐resistivity soft magnetic amorphous alloy film with a very fine two‐phase heterostructure was found in cosputtered Fe‐B‐C films. These amorphous films are found to have a number of superior properties in the high‐frequency range (over∼10 MHz) over not only regular amorphous films, but also sendust film cores, which have already been applied to high‐density recording media having high coercivity. They were found to exhibit unique isotropic soft magnetic B‐H curves with high Bs (∼15 000 G), low Hc (∼0.3 Oe), and high ρ (∼400 μΩ cm), and the reduced magnetization versus reduced temperature curve was almost the same as the j=∞ curve of the Brillouin function. A very high permeability with less core loss, especially in the high‐frequency range, was also experimentally observed in those amorphous films.