Role of DC Joule Heating on the Fe and Co‐Based Ribbons for the Magnetoimpedance Sensor

The magnetoimpedance (MI) effect on the Joule‐annealed Fe 72 Si 10 Cu 1 Nb 2 B 15 , Co 72 Ni 5 Si 5 Cu 1 Nb 2 B 15 , and Co 77 Si 5 Cu 1 Nb 2 B 15 melt‐spun ribbons was investigated. The MI values were higher in the Joule‐annealed Fe 72 Si 10 Cu 1 Nb 2 B 15 ribbons than in the as‐quenched Fe 72 Si 10 Cu 1 Nb 2 B 15 ribbons due to the formation of nanocrystals on the ribbon surfaces. The MI values decreased in the ribbons annealed at 1.5 A compared with those annealed at 1 A due to the lower effective permeability. The MI values of Joule‐annealed Co 72 Ni 5 Si 5 Cu 1 Nb 2 B 15 and Co 77 Si 5 Cu 1 Nb 2 B 15 ribbons were higher than those of the corresponding as‐quenched Co 72 Ni 5 Si 5 Cu 1 Nb 2 B 15 and Co 77 Si 5 Cu 1 Nb 2 B 15 ribbons due to induced stress relaxation of the melt‐spun ribbons. Lower MI values were observed in the Co 72 Ni 5 Si 5 Cu 1 Nb 2 B 15 and Co 77 Si 5 Cu 1 Nb 2 B 15 ribbons annealed at 1.5 A than in those annealed at 1 A due to the formation of heated regions. The heated regions pin the magnetic moments and induce large magnetic anisotropy in the ribbons. The DC electrical resistivity values were lower for all three ribbons when annealed at 1 A due to atomic ordering and a reduction in the number of scattering events resulting from uniformly grown nanocrystals within the amorphous matrix.