Yoshio Bizen

Magnetic properties of FeCuNbSiB nanocrystalline alloys with low magnetostriction

Abstract The magnetic properties of nanocrystalline Fe bal Cu 1 Nb 3 Si 13.5−19 B 5−10 alloys with low magnetostriction both before and after epoxy resin moulding were investigated in relation to the alloy composition and annealing conditions. A high permeability of about 4 × 10 4 at ƒ = 1 kHz was obtained in the composition range 5–8 at.% B and 15–17 at.% Si after epoxy resin moulding. A low core loss of about 400 kW m −3 was obtained in almost the same composition range after epoxy resin moulding. It was found that the alloy composition and annealing conditions giving the highest permeability were different before and after moulding. This relates to the microstructure of the nanocrystalline FeCuNbSiB alloys, which consist of ultrafine b.c.c. grains and amorphous grain boundaries. The nanocrystalline FeCuNbSiB alloys with low magnetostriction are suitable for cut cores in high frequency transformers used for inverters because of their low core loss and high permeability after epoxy resin moulding.