Difference between temperature dependences of both initial permeability and maximum permeability of sendust alloys

The temperature dependences (-10-50°) of the initial permeability (μ
5
), the maximum permeability (μ
max
), and the coercive force(H
c
) of Sendust alloys (Fe-9 to 10 wt% Si-5 to 7 wt% Al) continuously cooled to room temperature, were investigated. Most of the studied alloys gave at least one peak value for both μ
5
and μ
max
, in the studied temperature range. The temperature giving the peak μ
5
agreed well with that of μ
max
(an effective permeability at an alternating field): the peak temperature of μ
eff
seems to correspond to the temperature giving a zero magnetocrystalline anisotropy constant (K
1
= 0). The relationship between temperature and μ
5
was not always the same as that between temperature and μ
max
. From the compositional dependence of μ
max
at various temperatures (10-30°C), the zero polycrystalline magnetostriction constant (λs = 0) line of the ternary Sendust alloys at each temperature could be evaluated. It is clarified that μ
5
of the alloys with K
1
< 0 is determined by both K
1
and λs, whereas μ
max
is primarily determined by λs. When K
1
changes with temperature from a negative to a positive value, both μ
5
and μ
max
of the alloys markedly decrease, independently of λs.