Superior high-temperature magnetic softness for Co and Ge doped nanocrystalline Fe72.7Al0.8Si17.5B5Cu1Nb3 alloys

The complex impact of partially substituting Fe and Nb by Co and Ge on the thermal, microstructural and soft magnetic characteristics was investigated for melt spun and annealed Fe72.7-xCoxAl0.8Si17.5B5Cu1Nb3-yGey (x = 4, 8; y = 0, 0.4) alloys. The onset temperatures of the primary crystalline (Tx1) and the secondary crystalline (Tx2) are both declined and the Curie temperature of amorphous phase (TCam) is enhanced when Co content increase from x = 4 to x = 8. Although the crystallization temperatures are not affected by the partial substitution of Nb with Ge for x = 8, the TCam increases with respect to the alloy without Ge. When Co content x = 4, Ge substitution is found to not only decrease the Tx1 but also enhance the TCam. Fe64.7Co8Al0.8Si17.5B5Cu1Nb2.6Ge0.4 alloy has the highest TCam about 410 °C in all investigated alloys, and exhibits excellent high-temperature magnetic properties, and its higher initial permeability μi about 5000 at 10 kHz can be held up to 475 °C, which exhibits a potential prospect for the elevated temperature application.