Magnetic Properties of Nanocrystalline Powder Cores Fabricated by Mechanically Crushed Powders

Fe73.5Cu1Nb3Si15.5B7 nanocrystalline powder cores with different particle sizes ranging from 10 to 125 mu m were fabricated by cold-pressing techniques. The cores exhibited increased core loss P-ev and decreased initial permeability mu(i), with addition of fine powders below 50 mu m in size, and the content should be less than 40 mass. It was thought to be closely related to the high coercive force H-c due to the stresses generated during the crushing process and high demagnetization fields of small powders. Furthermore, modifying the alloy compositions by adding defined amount of Ni could improve the soft magnetic properties, including superior characteristics of permeability under high direct current (DC) bias field and comparable low core loss at high frequency.