Complex permeability of Fe-deficient Ni-Cu-Zn ferrites

► Ni-Cu-Zn ferrites were studied with increase of Fe-deficiency. ► Permeability spectra of Fe-deficient Ni-Cu-Zn ferrites are discussed. ► Heating and cooling cycles are used for the various studies of Ni-Cu-Zn ferrites. ► Fe-deficiency in Ni-Cu-Zn ferrites ensures high permeability. ► Cu works as a sintering aid to the Fe-deficient Ni-Cu-Zn ferrites.