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-x
Al
_x
Si
_17.5
B
₅
Cu
₁
Nb
₃
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
_72.7
Al
_0.8
Si
_17.5
B
₅
Cu
₁
Nb
₃
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
_73.5
Si
_17.5
B
₅
Cu
₁
Nb
₃
alloy. The correlation between the initial permeability and temperature (μi-T curve) for Fe
_72.7
Al
_0.8
Si
_17.5
B
₅
Cu
₁
Nb
₃
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.