Influence of Cobalt Substitution on Hyperfine Interactions in $(Fe_{1-x}Co_x)_{76}Mo_8Cu_1B_{15}$ Alloys

The effect of cobalt substitution on structure, magnetic behaviour, magnetic arrangement, and hyperfine interactions in $(Fe_{1-x}Co_x)_{76}Mo_8Cu_1B_{15}$ (x = 0, 0.1, 0.2, 0.25, 0.5) is studied by the Mössbauer spectrometry for both as-quenched and annealed alloys. Partial substitution of Fe by Co resulted in an enhancement of the average value of hyperfine magnetic field distributions as a function of x probably due to higher magnetic moment of Co. After annealing, a two-phase nanocrystalline structure composed of amorphous matrix and bcc-FeCo nanocrystallites was observed. Mössbauer spectra were fitted with up to four six-line patterns of narrow lines assigned to different number of Co nearest neighbours inside a bcc-FeCo lattice.