Boron content dependance of magnetoimpedance in Fe_91-xZr ₅B_xNb₄ alloys

A systematic investigation of the influence of B content on the magnetoimpedance (MI) effect in melt-spun Fe_91-xZr₅B _xNb₄ (FZBN, 0 ≤ x ≤ 30) ribbons has been performed within a frequency range, f ∼ 310-1110 kHz and under a varying dc magnetic field (H_dc) up to 70 Oe. The MI effect is not observed in the sample with x ≤ 5 but within the range 8 ≤ x ≤ 30. A distinct MI effect has been observed with a maximum change of 180% at around 1.1 MHz in the sample with x = 20, coincident with a saturation magnetic field of 66 Oe and a field sensitivity of about 7%/Oe. Magnetic measurements reveal that the MI effect and B content dependence of the effect are closely related to coercivity of the FZBN alloy series, except for the sample with 20 at.%. The drastic MI ratio observed in the sample with x = 20 is ascribed to its special microstructure. The mechanism of the MI effect in FZBN alloys and of the significant MI value appearing at a B content of x = 20 is discussed in this paper.