The effect of cooling rate on the thermal stability and soft magnetic properties of [(Fe0.5Co0.5)(0.75)B0.2Si0.05](100-x)Nb-x (x = 5, 6, 7, 8 at. %) system was investigated. The alloys were produced into the form of ribbon and cylindrical rod by melt-spinning and injection casting, respectively. Their structure, thermal, mechanical and soft magnetic properties were investigated by x-ray diffraction, differential scanning calorimetry, universal testing machine and vibrating sample magnetometer, respectively. All of the alloys were identified as fully amorphous by X-ray diffraction. It turned out that the rod samples had exceptionally high saturation fields reaching 3.0 kOe, which is key properties for sensor application. Also, among these Fe, Co-based samples, the Fe-35.25 Co-35.25 B-18.8 Si-4.70 Nb-6 ribbon exhibits the highest saturation magnetization with 142.1 emu/g. (C) 2015 Elsevier B.V. All rights reserved.