Field and Current Controlled Domain Wall Propagation in Twisted Glass-Coated Magnetic Microwires

The torsion effect on the field and current driven magnetization reversal and the associated domain wall velocity in cylindrical amorphous and nanocrystalline glass-coated microwires is reported. Samples from three representative compositions have been investigated: (1) amorphous Fe_77.5Si_7.5B₁₅ with positive magnetostriction, λ ≅ 25 × 10^-6, (2) amorphous Co_68.18Fe_4.32Si_12.5B₁₅ with nearly zero negative magnetostriction, λ ≅ -1 × 10^-7, and (3) nanocrystalline Fe_73.5Si_13.5B₉Cu₁Nb₃ (FINEMET) with small positive magnetostriction, λ ≅ 2.1 × 10^-6, all having the diameter of the metallic nucleus, d, of 20 µm and the glass coating thickness, t_g, of 11 µm. The results are explained through a phenomenological interpretation of the effects of applied torque on the anisotropy axes within the microwires with different characteristics. Among all the complex mechanical deformations caused by the application of torque on magnetic microwire samples, the most important are the axial compression - for axial field-driven domain wall motion, and the circumferential tension - for electrical current/circumferential field-driven domain wall motion. The Co_68.18Fe_4.32Si_12.5B₁₅ microwire, annealed at 300 °C for 1 hour and twisted at 168 Rad/m exhibits the optimum characteristics, e.g. the lowest switching current (down to 9 mA~2.9 × 10^-3 A/cm²) and the largest domain wall velocity (up to 2300 m/s).