Effect of Particle Size Distribution on the Magnetic Properties of Fe-Si-Al Powder Core

The Fe-Si-Al soft magnetic powder cores with five particle size distributions were prepared. The microstructure study revealed that the cores had a fairly compacted structure with a uniform insulation layer of the phosphate forming on the surface of the magnetic particles. The particle size distribution was found to have the great influence on the core’s magnetic properties. The increase of the percentage of the small particles results in the decrease of the effective permeability, the improvement of the DC-bias performance, and the deterioration of the core loss. The effects of the distributed air gap and the demagnetization field on the core’s magnetizing process were believed to be the underlying physical origins. The core losses at the frequencies lower and higher than 150 kHz were found to be mainly determined by the hysteresis loss and the eddy-current loss, respectively. The good magnetic performances of the Fe-Si-Al powder cores with the effective permeability of about 55–60 were finally achieved as follows: the percent permeability at 100 Oe is up to 52.3 %, and the lowest core loss at 50 kHz/1000 Gs is 270 mW cm−3.