Soft Magnetic Properties and Electromagnetic Shielding Performance of Fe₄₀Ni₄₀B₂₀ Microfibers

Fe₄₀Ni₄₀B₂₀ metallic glass is a key material among the many amorphous systems investigated thus far, owing to its high strength and appealing soft magnetic properties that make it suitable for use as transformer cores. In this study, Fe₄₀Ni₄₀B₂₀ microfibers are fabricated down to 5 µm diameter. Three different melt–spinning wheel velocities: ≈51 m s⁻¹, ≈59 m s⁻¹, and ≈63 m s⁻¹ (MG1, MG2, MG3) are used. Their fully amorphous structure is confirmed using X–ray diffraction, and differential scanning calorimetry (DSC) traces reveal a larger relaxation profile for the higher–quenched microfiber. Vibrating sample magnetometer measurements showed a higher saturation magnetization of 136 emug⁻¹ for annealed metallic glass microfibers with a wheel velocity of 59.66 ms⁻¹. Cylindrical magnetic field shields are obtained by aligning and wrapping the fibers around a cast. The observed anisotropic static field shielding behavior is in accordance with the microfibers' anisotropic nature. Composite samples are also produced by embedding the microfibers in an epoxy matrix to investigate their electromagnetic properties at GHz frequencies. Inclusion of the microfibers increase the composite's attenuation constant by 20 to 25 times, making it an ideal candidate for applications in the communications frequency range.