High-Frequency Magnetic Impedance in (CoFeNi)BSi and (CoFeCrMo)BSi Amorphous Microwires in a Glass Sheath near the Curie Temperature

Abstract

The temperature behavior of high-frequency magnetoimpedance (MI) in amorphous microwires in a glass sheath has been studied in the temperature range up to the Curie temperature TC. Two alloy samples with compositions of Co27.4Fe5B12.26Si12.26Ni43.08 (TC ≈ 48°C) and Co64.82Fe3.9B10.2Si12Cr9Mo0.08 (TC ≈ 61°C) with different signs of magnetostriction constant λs and with different types of magnetic anisotropy were used. For the first alloy sample, λs 0, which leads to circular anisotropy. For the second alloy sample, λs 0, and easy axis anisotropy is formed along the wire axis. A substantial decrease in the impedance is observed at elevated frequencies with an increase in the temperature in microwires with easy axis anisotropy, regardless of the application of a magnetic field, while the change in the impedance in wires with circular anisotropy is more substantial in the presence of an external field. Moreover, the change in the impedance with an increase in the temperature from room temperature to TC can reach 200–300% in the frequency range of 0.5–0.9 GHz in a magnetic field of about 10 Oe. These results may be of interest for the development of miniature temperature sensors.