Effect of Ge on soft magnetic properties at elevated temperature for Si-rich Finemet-type alloy

•The effect of Ge doping on the soft magnetic properties is investigated for Si-rich Finement-type alloy.•The Curie temperature is enhanced by doping Ge in Si-rich Finemet-type alloy.•The initial permeability μi of 540 °C-annealed Fe72Ge2.5Cu1Nb3Si17.5B5 alloy possesses a relatively large value of 5000 until 600 °C. The results obtained by partially substituting Ge for Fe in the Fe-based nanocrystalline alloy for improving the magnetic properties at high temperatures are presented in this work. These studies were performed on the Fe74.5-xGexCu1Nb2Si17.5B5(x = 2.5, 5, 7.5) alloys. The nanocrystallization and the Curie temperature are dependent on the Ge concentration. The onset temperature of primary crystallization decreases with the increase of Ge, indicating that the dual-phase nanocrystalline structure could be formed at a relatively lower temperature compared with the Ge-free alloy. For the alloy with x = 2.5at%, the Curie temperature of the amorphous alloy is enhanced to 405 °C. The initial permeability μi of 540 °C-annealed alloy possesses a relatively large value of 5000 until 600 °C. Such a magnetic softness at elevated temperature is superior to that of Finemet-type Fe-based nanocrystalline alloys ever reported. [Display omitted]