Soft Magnetic Properties and Finely Crystallized Structures in Fe-Mo-B Amorphous Alloys

The soft magnetic properties of finely-crystallized Fe-Mo-B-M (additives) ribbons were studied. The microstructures with ultra-fine grains in Fe-Mo-B-M ribbons were obtained by the addition of Cu and Nb into the alloys and subsequent annealing. The effective permeabilities of Fe-Mo-B and Fe-Mo-B-Cu alloys without Nb decreased upon crystallization. Good soft magnetic properties with effective permeabilities of 5000 to 7000 at 1 kHz were obtained by annealing amorphous Fe-Mo-B-Nb and Fe-Mo-B-Cu-Nb alloys above each crystallization temperature. They were composed of bcc Fe crystals with fine grain size of 10 to 20 nm. It was observed that the Nb addition produced nano-scale bcc grains and the Cu addition was effective in homogenizing the nano-crystalline structure.