Development of Fe–Nb–Cr–B Glassy Alloys With Low Curie Temperature and Enhanced Soft Magnetic Properties

Fe_67.7Nb_0.3Cr₁₂B₂₀ glassy melt-spun ribbons and glass-coated microwires with T_C around 310-320 K (~35-45°C) (the lowest ever reported for metallic glasses) have been prepared by rapid solidification. Excepting the thick melt-spun ribbons of 40 μm, all samples have a glassy structure in the as-quenched state, consisting of very small Fe-Cr and boride (Fe₃B) clusters of sizes ranging from several nanometer up to several tens of nanometer, embedded within the residual amorphous matrix. The ferromagnetic behavior of the glassy materials deteriorates drastically with an increase in the temperature. The melt-spun ribbons become paramagnetic above 34-35°C, whereas the transition temperature for the glass-coated microwires is around 45°C, because of the very specific magnetic domain structure and magnetic anisotropy distribution. The observed stable behavior of low T_C Fe_67.7Nb_0.3Cr₁₂B₂₀ glassy alloys up to very high frequencies (10 GHz) is another important feature for sensing and biomedical applications. The temperature sensor based on low T_C Fe_67.7Nb_0.3Cr₁₂B₂₀ glassy melt-spun ribbons has a very good sensitivity in a narrow temperature range (about 1°C).