General Properties of Low-frequency Power Losses in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency f and amplitude flux density Bm have been investigated for the three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys in the ranges of 10 Hz< f <1000 Hz and 0.4 T< Bm <1.0 T. The total loss P is decomposed into the sum of the hysteresis loss Physt, the classical eddy current loss P(el) and the excess loss P(exc). Physt has been found to be proportional to B^2(m) and f. The behavior of P(exc)/f vs f being equivalent to P/f vs f clearly exhibits nonlinearity in the range not more than about 120 Hz, whereas the behavior of P/f vs f roughly shows linearity in the range far above 100 Hz and not more than 1000 Hz. In the range up to 1000 Hz, Physt is dominant in the original high permeability state and the state of low residual flux density, whereas Pexc in the state of high residual flux density is dominant in the wider range above about 100 Hz. The framework of the statistical theory of power loss has been used for representing the behavior of P(exc)/f vs f. It has been found that the number n of the simultaneously active "Magnetic Objects" linearly varies as n = n0+H(exc)/H0 as a function of the dynamic field H(exc) in the range below about 120 Hz, whereas n approximately follows a law of the form n= n0+ (Hexc/H0)^m with 1 < m < 2 in the range far above 100 Hz and not more than 1000 Hz. The values of the field H0 in principle related to the microstructure and the domain structure have been calculated for the three states.