Nanocrystallization behaviour and optimized magnetoimpedance effect in FeZrBNbCu alloys

The work aims at understanding the changes in magnetic properties and the magnetoimpedance (MI) effect for the Fe84.5Zr4B8.5Nb2Cu1 (FZBNC) nanocrystalline alloys with the annealing temperature (Ta) from the microstructure point of view. The as-quenched FZBNC ribbons were annealed in a vacuum condition at selected temperatures for 20?min. The microstructures of the specimens were examined by the x-ray diffraction technique. The bcc ?-Fe phase is identified from the XRD patterns. The mean grain size of the ?-Fe phase (D1) at different annealing temperatures (Ta) was estimated using Scherrer's equation. The results show that D1 for the sample annealed at 575??C is about 20?nm, which is the smallest value among all the samples. Measurements on the MI effect reveal that the FZBNC ribbon annealed at 575??C exhibits the most drastic MI ratio of 756% at 600?kHz accompanied by the field sensitivity of 108%?Oe?1, while a large MI effect is not observed in the sample annealed at other temperatures. The origin of the excellent MI effect is investigated in this paper.