Microwires coated by glass: A new family of soft and hard magnetic materials

The Taylor-Ulitovski technique was employed for fabrication of tiny ferroma gnetic amorphous and nanocrystalline metallic wires covered by an insulatin g glass coating with magnetic properties of great technological interest. A single and large Barkhausen jump was observed for microwires with positive magnetostriction. Negative magnetostriction microwires exhibited almost un hysteretic behavior with an easy axis transverse to the wire axis. Enhanced magnetic softness (initial permeability, mu(iota), up to 14000) and giant magneto impedance (GMI) effect (up to 140% at 10 MHz) was observed in amorp hous CoMnSiB microwires with nearly zero magnetostriction after adequate he at treatment. Large sensitivity of GMI and magnetic characteristics on exte rnal tensile stresses was observed. Upon heat treatment, FeSiBCuNb amorphou s microwires devitrificated into a nanocrystalline structure with enhanced magnetic softness. The magnetic bistability was observed even after the sec ond crystallization process (increase of switching field by more than 2 ord ers of magnitude up to 5.5 kA/m). Hard magnetic materials were obtained as a result of decomposition of metastable phases in Co-Ni-Cu and Fe-Ni-Cu mic rowires (fabricated by Taylor-Ulitovski technique when the coercivity incre ased up to 60 kA/m. A magnetic sensor based on the magnetic bistability was designed.