The glass formation ability and soft magnetic properties of the Fe79Si9B4.5P1.5CuNbx nanocrystalline alloys

•The GFA and magnetic properties of the Fe79Si9B4.5P1.5CuNbx alloys was studied.•Nb increases the GFA but decreases the Ms, Tc and grain size of the alloys.•The Fe79Si9B4.5P1.5CuNb2 alloys exhibit the best comprehensive properties. In this study, the Fe79Si9B4.5P1.5CuNbx alloys were prepared using the melt spinning method. Further, the microstructure, micromorphology, thermal behavior, and magnetic properties of the alloys were studied. The results denote that Nb can improve the glass formation ability from 85 to 115.5 K, reduce the grain size, decrease the coercivity from 0.22 to 0.10 Oe, and rapidly decrease the Curie temperature from 705 to 648.5 K. In addition, the unit mass loss of Fe79Si9B4.5P1.5CuNb2 is 5.84 W/kg, 19% lower than that of the Fe79Si9B4.5P1.5Cu alloys, and Ms decreased by 3%.