The effect of the concentration of alloying components on the crystallization of amorphous (Fe_73Si_13B_9)_1 – _ x  _– _ y Nb_ x Cu_ y and (Co_70Si_12B_9)_1 – _ x  _– _ y Fe_ x Nb_ y alloys has been studied by X-ray diffraction and transmission electron microscopy in a wide composition region. The formation of the bcc structures in both the alloy groups is shown to be substantially dependent on the alloying component concentrations. The bcc phase is found to form in the cobalt-based alloys in the concentration region, where it was not observed before. In the cobalt-based alloys, the bcc phase appears at a niobium concentration higher than 1 at % and the average bcc nanocrystal size varies from 40 nm (at 1 at % Nb) to 14 nm (at 5 at % Nb). In the Fe-based alloys, nanocrystals with the bcc lattice form at the copper concentrations of 0.45–1 at %, and the average nanocrystal size is dependent on the alloy composition and varies in the range 16–24 nm. The causes of the concentration dependence of the formation of nanostructures in these alloys are discussed.

The structure and magnetic properties of amorphous and nanocrystalline Co56Fe16B20X8 (X = Nb, Ti) alloys have been studied by X-ray diffraction and vibrating sample magnetometry. It is shown that the saturation magnetization of the amorphous Co56Fe16B20Ti8 alloy is higher than that of the Co56Fe16B20Nb8 alloy. The temperature dependence of the saturation magnetization of amorphous alloys is measured and it is shown that the saturation magnetization of the Co56Fe16B20Ti8 alloy decreases with temperature more slowly than the magnetization of the Co56Fe16B20Nb8 alloy. Crystallization of amorphous alloys leads to a decrease in the saturation magnetization of both alloys. During crystallization, BCC nanocrystals are formed in the Co56Fe16B20Nb8 alloy and multiphase structure is formed in the Co56Fe16B20Ti8 alloy.

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