Increasing cut-off frequency of permeability in FeNi soft magnetic composites

An increasing cut-off frequency (COF) of permeability in Fe50Ni50-resin soft magnetic composites (SMCs) is studied for meeting the demand at MHz in power electronic devices. The results showed that a lower volume fraction of Fe50Ni50 particles leads to a higher COF of permeability suggesting that COF does not directly correlate with the resonance frequency of intrinsic displacement of domain walls or coherent rotation of domains. Analysis of particle ferromagnetic resonance indicated that COF is a manifestation frequency resulting from the permeability of coherent rotation of domains modulated by eddy currents rather than the displacement of domain walls. Through the reduction in particle size and the height of the SMC to mitigate the effect of eddy currents, the COF was successfully increased from 17 MHz to 117 MHz (increased by 6.8 times). Furthermore, the mitigating of the eddy current effect is benefit to the decreases of loss, with a loss of 606 mW/cm3 at 3 MHz under 10 mT magnetic flux achieved when the height of Fe50Ni50 SMC is 1.54 mm. The finding, which achieved a high permeability of 60 and a high COF of 117 MHz, provides valuable insights for overcoming the limitations of conventional SMCs.