Local structure changes of Ga during nanocrystalline formation from melt-quenched Fe73Ga4Nb3Si11B9 alloys

XAFS measurements of the Ga K edge and the Nb K edge have been carried out for amorphous Fe73Ga4Nb3Si11B9 alloy after annealing at various temperatures in order to reveal the roles of Ga and Nb in the nanocrystalline formation. XAFS results show that: there is no definite Ga segregation, unlike Cu in Fe73Ga4Nb3Si11B9 (FINEMET) XAFS spectra of Ga for the samples annealed above the α -iron precipitation temperature, Tx1, indicate that Ga atoms sit substitutionally at bcc iron sites. Curve fitting analyses of the XAFS of Ga show that coordination number after annealing drops at Tx1 but it rises again above Tx1, which suggests that at the beginning of α -iron precipitation, Ga atoms are inclined to be excluded toward the boundary where B and Si are much more abundant than other atoms. Such a transient exclusion effect of Ga can be attributed to the nanocrystalline formation of these alloys. Nb in Fe73Ga4Nb3Si11B9 seems to play the same role as that in FINEMET, i.e. retarding crystal growth of α -iron and suppressing Fe-B compound formation. (author)