Temperature dependence of the effective permeability of heat treated Sendust alloys

The temperature dependence (-10°C-70°C) of the effective permeability (μ
eff
) of Sendust alloys (Fe-9-10 wt% Si-5-7 wt% Al) quenched at a room temperature from the various temperatures (400°C-700°C) was investigated at every 2°C in the temperature range of -10°C to 70°C. Most of the studied alloys gave a peak of μ
eff
in the studied temperature range. The peak temperature (Tp) giving the peak μ
eff
varied with different alloy composition. The alloys of Tp = 20°C are supposed to correspond to the alloys of the zero magnetocrystalline anisotropy constant (K
1
= 0) at 20°C. The deduced K
1
= 0 lines at various temperatures (-10°C-50°C) were obtained for an Fe-Si-Al ternary system. The values of peak μ
eff
at the same Tp were different, depending on alloy composition, This difference is due to the difference in the polycrystalline magnetostriction constant (λ s) of the alloys. The peak temperatures of the studied alloys vary with the different heat treatments. This variation is due to the variation of K
1
, induced by the change in microstructures of the alloys. The variation of the values of peak μ
eff
with heat treatments was small compared to the difference of those in the alloys of different composition. It seems that the variation of the λ s with heat treatments would be small. Both the compositional dependence of μ
eff
at 20°C and the temperature sensitivity (Δμ
eff
/ΔT) were obtained for both the alloys cooled continuously to room temperature and those quenched at room temperature from 400°C.