Structure and hyperfine interactions of melt-spun Fe80Mo7X1B12 (X Cu or Au) before and after transformation into nanocrystalline states

Moessbauer spectrometry (57Fe transmission and conversion-electron techniques), differential scanning calorimetry, and x-ray diffraction are employed to study the microstructure and magnetism of amorphous and nanocrystalline Fe80Mo7X1B12 (X=Cu, Au) alloys. Heat treatment of amorphous specimens below the temperature of primary crystallization causes structural relaxation that, in turn, stabilizes the amorphous arrangement. Changes observed in the topological short-range order are more pronounced for X=Au because this alloy shows a higher degree of disorder in the bulk of the as-quenched state. For both alloys, three-step crystallization behaviour is observed. Annealing performed in temperature range of the first crystallization provided different amounts of body-centred-cubic Fe nanograins. Magnetic interactions among them and their impact on the surrounding amorphous residual matrix are discussed using hyperfine-field distributions. Differences in hyperfine interactions between surface regions and bulk of the alloys are revealed from conversion-electron Moessbauer spectrometry and transmission Moessbauer effect measurements, respectively. The magnetic behaviours for X=Cu and Au are very similar after annealing at temperatures close to and beyond the end of the first crystallization peak. The impact of which element is present on the microstructure and magnetism is crucial during the commencement of the crystallization but it cannot be discerned for higher crystalline contents. (author)