Excellent Magnetic Softness at Room and High Temperatures for Si-Rich Fe-Based Nanocrystalline Alloy With a Small Amount of Al

The temperature dependence of the initial permeability μ_i for Fe_73.5-xAl_xSi_17.5B₅Cu₁Nb₃ alloys (x = 0.6, 0.8, and 1) during successive heating-cooling cycles from room temperature up to 700°C was investigated. An excellent magnetic softness at high temperatures was observed in the alloy with x = 0.8. The as-quenched Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ alloy exhibits a lower onset crystallization temperature (T_x1) of 491°C and a higher second crystallization temperature (T_x2) of 720 °C compared with Al-free Fe_73.5Si_17.5B₅Cu₁Nb₃ alloy. The correlation between the initial permeability and temperature (μi-T curve) for Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ alloy annealed at 460 °C-650 °C shows that, although the optimum room-temperature soft magnetic properties with a very low coercivity of 0.013 Oe and higher μi of 50000 were obtained by annealing at 550 °C, the μi quickly drops at high temperatures; however, for 650 °C annealed alloy, the higher μi over 10000 at f = 10 KHz can keep up to 400 °C and a lower coercivity of 0.024 Oe is also obtained, which is superior to other Fe-based Finemet alloys reported.