Temperature-stable magnetoimpedance (MI) of current-annealed Co-based amorphous microwires

Abstract

Abstract Magnetic sensing materials with enhanced performance and low dimensions are significant for various technological and industrial applications. The temperature stability of their properties is one of the main priorities. Co-rich glass coated amorphous microwires are known to demonstrate very large and sensitive magnetoimpedance (MI) effect. However, the impedance value may change up to hundreds of percent within the industrial temperature range (−20 to 100 °C) caused by structural relaxation and temperature-dependent internal stress. Current annealing inducing a well-defined circular anisotropy was proposed to realize high temperature stability without substantial loss in the MI sensitivity. The wires of composition Co66.94Fe3.83Ni1.44Mo1.69B11.51Si14.59 after optimal annealing with a dc current of 25 mA, which corresponds to a temperature of about 190 °C, demonstrated the room-temperature MI sensitivity of 59%/Oe (as compared with 62.5%/Oe for as-prepared wires) and a temperature variation of 0.1%/Oe °C. We also investigated the effect of glass removal on the magnetic structure, MI and their temperature stability. The disappearance of large internal stress due to glass-metal interface in combination with the induced anisotropy by current annealing makes it possible to achieve the temperature-stable MI with the sensitivity of more than 193%/Oe and a temperature variation of 0.04%/Oe °C. Consequently, the investigated wires after current annealing can be employed as MI field sensors with high sensitivity and temperature stability.