Studies of thin microwires with enhanced magnetic softness and GMI effect

Abstract

AbstractIn this paper we studied the hysteresis loop and GMI effect (real component of impedance, Z, and the off‐diagonal impedance tensor ζϕz (Hex)) in ultra‐thin amorphous glass‐coated microwires with nearly‐zero and negative magnetostriction constant with metallic nucleus diameter ranging from 6 μm to 16 μm paying special attention to the effect of the metallic nucleus diameter on the aforementioned properties. Both GMI effect and hysteresis loops of nearly‐zero magnetostrictive Co67.1Fe3.8Ni1.4Si14.5B11.5Mo1.7 microwires exhibit strong sensitivity to the ratio, ρ, the metallic nucleus diameter, d, to the total microwire diameter, D. Selecting the right chemical composition we achieved low coercivity (generally below 15 A/m). The magnetic anisotropy field, Hk, increases when ρ decreases. The shape of the magnetic field dependence of Z is also affected by the ρ ‐ratio. The field dependence of the off‐diagonal voltage response of nearly zero magnetostrictive (λs ≈ –3 × 10–7) Co67.1Fe3.8Ni1.4Si14.5B11.5Mo1.7 microwires with metallic nucleus diameters ranging between 6.0 μm and 16.8 μm exhibits anti‐symmetrical shapes. At certain magnetic field, Hm, the off‐diagonal voltage reaches the maximum value. Between –Hm and Hm at certain field range almost linear dependence of the off‐diagonal voltage on magnetic field has been observed. This linear region of the curve depends on microwires geometry, but in any case is smaller than whole –Hm to Hm range. Joule heating significantly affects the off‐diagonal MI curves of Co67.1Fe3.8Ni1.4Si14.5B11.5Mo1.7 microwires with vanishing magnetostriction constant. Under DC current annealing the Hm decreases.The obtained results allow us to tailor the microwire magnetic properties for applications in magnetic sensors through the selection of their composition and/or thermal treatment conditions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)