Magnetic properties of Fe-based ribbons with controlled permeability prepared by continuous pulse annealing under tensile stress

Abstract

An amorphous Fe73.5Cu1Nb3Si15.5B7 ribbon was pulse annealed continuously under tensile stress by being passed through in an infrared furnace switched on and off repeatedly for preparation of a nanocrystallized toroidal core with controlled permeability. Optimization of the duty ratio D(=Ton/T) of the furnace enabled us to obtain ribbons with low Hc(<10 A/m) and completely developed anisotropy under a high moving velocity of the ribbon, 50 cm/min. ac magnetic properties of a toroidal core, which is made from the pulse-annealed ribbon, at Bm=0.1 T were measured in the frequency range of 0.1–1 MHz. The loss of the prepared core at f=0.1 MHz is 0.50 J/m3, which is lower than those for a gapped ferrite, sendust powder, and amorphous powder core. The relative permeability of approximately 330 was constant up to 1 MHz. These results suggest that the continuous stress annealing by pulse annealing method is one of the hopeful methods for preparation of a long ribbon with excellent magnetic properties.