AbstractMagnetic properties of Fe‐Cu‐Nb‐X‐B (X Si, Ge, C, Ga) and Fe‐Cu‐Nb‐Si‐B‐X (X: Ge, C, P, Ga, Al) nanocrystalline alloys were studied to improve soft magnetic properties and they were evaluated for some applications. Si was the best element for the Fe‐Cu‐Nb‐X‐B system. Substitution ofPfor B made the coercive force small in the Fe‐Cu‐Nb‐Si‐B‐X system having high saturation flux density. The cores using the Fe‐based nanocrystalline alloys showed low core loss, excellent dc superimposed characteristics and good noise attenuation characteristics. Hence, Fc‐based nanocrystalline alloys have high performance for such magnetic com