Mössbauer and magnetic studies of FeCoNiCuNbSiB nanocrystalline alloys

Nanocrystalline Fe_80-x-yCo_xNi_yCu₁Nb₃Si₄B₁₂ alloys were prepared by the annealing of amorphous ribbons. Primary crystallization of the alloys annealed at temperatures of between 500 and 550°C was studied by X-ray diffraction and Mössbauer spectroscopy. Magnetic properties of the alloys were investigated using a hysteresis loop tracer and vibrating sample magnetometer. The annealed ribbons are composed of a two-phase nanostructure consisting of bcc Fe-based grains embedded in an amorphous matrix. Conversion electron Mössbauer spectroscopy (CEMS) measurements reveal a more advanced crystallization process in the surface layers when compared with the volume of the ribbons. The degree of saturation magnetization of the nanocrystalline alloys is of about 1.5 T. The coercive field varies from 1.0 to 6.5 A/m and peaks at an annealing temperature of 525°C. Magnetic softening of the nanocrystalline alloys observed after annealing at 550°C is correlated with a volume fraction of the nanocrystalline bcc phase.