Journal of Alloys and Compounds j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j a l l c o m Microstructure and magnetic properties of (Fe 100−x Co x) 84.5 Nb 5 B 8. a b s t r a c t Partial substitution of Fe with Co in gradually devitrified Si-free Nanoperm-type alloys improves their soft magnetic properties, increases the Curie temperature of the amorphous matrix, and allows casting in air. In the present work we report the temperature dependence of structural and magnetic properties of (Fe 100−x Co x) 84.5 Nb 5 B 8.5 P 2 (x = 20, 40, 60) alloys using differential scanning calorimetry, magnetic, thermo-magnetic and X-ray diffraction measurements, to get complementary information on the microstructure, composition of the precipitated crystalline phase and their correlation with magnetic properties. Higher Co concentrations improve the magnetic softness of the alloy, whose properties can be further opti-mized by suitable thermal treatments. Magnetic data is discussed in terms of the precipitation of a Fe–Co crystalline phase consisting of different Co content.