The role of alloying elements in Cu-free nanocrystalline Fe-Nb-B soft magnetic alloys

In order to clarify the role of alloying elements in Cu-free nanocrystalline Fe-Nb-B soft magnetic alloys, we have examined the kinetics of primary crystallization, the microstructure after primary crystallization, the changes in Curie temperature (Tc) and the hyperfine interactions of the amorphous phase upon primary crystallization in Fe86 − xNbxB14(x = 0, 2, 4, 5, 6 and 8) alloys. The mean grain size after primary crystallization decreased drastically in the x range 4–6 at.%. The kinetic analysis of the primary crystallization reaction showed that the decrease in the grain size can be attributed to the commencement of homogeneous nucleation. Tc of the amorphous phase increased with the B enrichment during primary crystallization. Tc decreased with Nb content and the hyperfine field distribution of the residual amorphous phase after primary crystallization for the x = 6 sample showed the presence of a non-magnetic component. These results suggest that Nb plays a role in the formation of the nanostructure by accelerating nucleation, as does B in the generation of a strong intergranular magnetic coupling, through increasing the Tc of the residual amorphous phase.