The effect of minor transition metals and rare earths on glass-forming ability, thermal stability and crystallization of [(Fe0.6Co0.4)0.75Si0.05B0.20]96-xNb4Mx alloys was investigated. The thermodynamic parameters traditionally used to predict the glass-forming ability have been calculated from calorimetric data and tested against mold casting. Only the addition of Zr and Mo allowed to cast 2 mm diameter rods, which does not correlate with predicted results. The microstructural evolution of the different alloys along the crystallization process has been studied by means of transmission Mössbauer spectroscopy showing for all studied compositions (FeCo)23B6 as primary phase that remains stable in the fully crystallized samples. Moreover, the Mössbauer spectra allowed the identification of some paramagnetic phases not identified by conventional x-ray diffraction. Peer Reviewed