Effects of secondary particle size distribution on the magnetic properties of carbonyl iron powder cores

•Magnetic Fe cores with varied secondary particle size distributions are prepared.•Size distribution and size ratio greatly affect density and magnetic properties.•Real permeability is inversely proportional to the mean diameter of particles.•Minimum loss factor is obtained at coarse/fine particles mixing ratio of 7:3. The effects of secondary particle size distribution on the electromagnetic properties of the carbonyl iron powder cores have been investigated in this work. For preparing the cores, the iron powders were firstly undergone insulation treatments including phosphorization and organic coating. After granulation, the secondary particles with different size distributions were molded into the final shape and cured at 200 °C. The results show that for the secondary particles with unimodal size distribution, the real part of the complex magnetic permeability of the powder core is in inverse proportion to the particle size. For the cores prepared from the secondary particles with bimodal size distribution, the effects of the size ratio and volume ratio of the coarse particle/fine particle on the magnetic properties are discussed. It is found that the permeability increases with the increasing volume of fine secondary particles. The minimum magnetic loss factor value is obtained at the coarse/fine secondary particles volume ratio of 7:3. The density and magnetic properties including complex permeability and magnetic loss of the cores prepared with coarse/fine particles size ratio of ~3 and ~7 are both in inverse proportional to the volume fraction of coarse secondary particles. The present work indicates that a reasonable size distribution of the secondary particles is required to improve the magnetic properties of the soft magnetic powder cores.