Microstructure and phase dependence of magnetic softness of FeSiGaB nanocrystalline alloys

•Free electrons transference from Fe to Ga was confirmed by X-ray photoelectron spectroscopy tests.•The key of improving saturation magnetization for Fe-based nanocrystalline alloys containing Si by alloying optimum content of Ga, was to prevent Ga and Si coexisting in the nearest neighbour position of Fe atoms.•Concerning the magnetic moment of Fe, the transfer of free electrons between Fe, Si and Ga atoms in primary crystallization has been discussed.