Mossbauer study of amorphous and nanocrystalline Fe-Nb-B alloys

Curie temperature (T-c) and hyperfine interactions of the amorphous phase in melt-quenched Fe86-xNbxB14 (x=0, 2, 4 and 6) alloys in an as quenched stale and after primary crystallisation were studied by means of thermo-magnetic analysis and Fe-57 Mossbauer spectroscopy. T-c of the amorphous phase increased with the enrichment of B during primary crystallisation. The T-c decreased with the Nb content x and the hyperfine-field distribution of the residual amorphous phase for the x=6 sample after primary crystallisation showed the presence of a nonmagnetic component. These results suggest that B promotes the intergranular magnetic coupling whereas Nb reduces it. Since Nb plays an important role in the nano-structural formation, the combination of B and Nb is essential for obtaining the nano-structure with good magnetic softness.