Amorphous ferromagnetic materials in the form of microwires are of interest for the development of various sensors. This paper analyzes and argues for the use of microwires of two basic compositions of Co₇₁Fe₅B₁₁Si₁₀Cr₃ and Fe_3.9(4.9)Co_64.82B_10.2Si₁₂Cr₉₍₈₎Mo_0.08 as stress/strain and temperature sensors, respectively. The following properties make them suitable for innovative applications: miniature dimensions, small coercivity, low anisotropy and magnetostriction, tunable magnetic structure, magnetic anisotropy, and Curie temperature by annealing. For example, these sensors can be used for testing the internal stress/strain condition of polymer composite materials and controlling the temperature of hypothermia treatments. The sensing operation is based on the two fundamental effects: the generation of higher frequency harmonics of the voltage pulse induced during remagnetization in wires demonstrating magnetic bistability, and magnetoimpedance.

Miniaturization of material’s size is the key feature in many technological applications, in particular, in sensor systems. To achieve this goal, Taylor-Ulitovski technique was employed to produce microwires with very small (from 0.2 up to 100 µm) diameters. Ferromagnetic amorphous microwires exhibit giant magnetoimpedance effect (GMI) which is useful to develop high performance magnetic sensors. Since the discovery of GMI, a considerable amount of interest was devoted to enhancing sensitivity with respect to various external stimuli (magnetic field, stress, temperature). On the other hand, GMI sensing elements should have high environment stability. In the present work, a comprehensive study of the temperature effects on the magnetoimpedance behavior in amorphous microwires is conducted. The wires under investigations of the composition Co60.51Fe3.99Cr12.13B13.53Si9.84 have a relatively high Curie temperature (>300 ℃) but may demonstrate considerable temperature dependence in the intermediate temperature range (<100 ℃) of dc and ac magnetic properties. We showed that the as-casted wires exhibited a notable change in magnetic anisotropy, from circumferential to an axial anisotropy, owing to the internal stress relaxation. This is accompanied by huge variation in the magnetoimpedance behavior: the impedance vs magnetic- field plots change shape: from two symmetrical peaks to a single central peak. Current annealing (dc current of 25 mA magnitude for 60 min) was proposed to achieve a thermal stabilization of the magnetization processes and magnetoimpedance in glass-coated amorphous wires.