Enhanced High-Frequency Magnetoresistance Responses of Melt-Extracted Co-Rich Soft Ferromagnetic Microwires

Abstract

We present the relationships between the structure, magnetic properties and high-frequency magnetoresistance (MR) effect in melt-extracted Co_68.2Fe_4.3B₁₅Si_12.5 microwires subject to thermal annealing. In order to release residual stresses to improve the magnetic softness while retaining the good mechanical property of an amorphous material, microwire samples were annealed at different temperatures of 100°C, 200°C, 350°C, 400°C, and 450°C for 15 min. We have shown that relative to an as-cast amorphous microwire, annealing microwires at T _a = 100°C, 200°C, and 350°C improved both the magnetic softness and the MR effect, while an opposite trend was observed for the microwires annealed at T _a = 400°C and 450°C. We have observed a distinct difference in the frequency dependence of MR response (ξ) for dc applied magnetic fields below and above the effective anisotropy field of the microwires. While the microwire annealed at 200°C shows the largest MR ratio (~580%) at 100 MHz, the highest value of ξ (~34%/Oe) has been achieved at 400 MHz for the microwire annealed at 350°C. These results indicate that the optimally annealed Co_68.2Fe_4.3B₁₅Si_12.5 microwires are attractive candidates for high-frequency sensor applications.