Magnetic complex permeability (imaginary part) dependence on the microstructure of a Cu-doped Ni-Zn-polycrystalline sintered ferrite

In this study, the effective complex magnetic permeability-imaginary part (mu'(eff)) of a Cu doped-NiZn poly-crystalline ferrite used as EMI suppressor has been quantitatively related to microstructural parameters. It has been observed that mu'(eff) strongly depends on average grain size (G) of the compact, but also on its relative density (phi): the higher grain size and density the higher mu'(eff). A mathematical relationship between mu'(eff) and average grain size and densification has been proposed and tested, accurately reproducing the experimental results. The use of densification concept allows to compare the wide range of microstructures tested and includes a lower value of relative density (estimated around 0,56) below which mu'(eff) is virtually zero. The grain boundary thickness (delta) has been estimated around 2 nm which is in agreement with experimental results reported in this work and with those found in literature.