Fig. 1. (a) XRD patterns and (b) the calculated crystallinity of raw mixture components and mechanical-alloyed FeCoNiAlCr0.9 HEA samples (P0, P20, P30, P40 and P50).

Fig. 2. SEM images of (a) P0, (b) P20, (c) P30, (d) P40 and (e) P50 FeCoNiAlCr0.9 HEA samples; (f) Statistical distribution of particle size.

Fig. 3. (a) Hysteresis loops and (b) varying curves of Ms and Hc for mechanical-alloyed FeCoNiAlCr0.9 HEA samples.

Fig. 4. Conductivity of the mechanical-alloyed FeCoNiAlCr0.9 HEA samples. The inset represents the changing curves of the mass ratios of C and O elements.

Fig. 5. Frequency dependence of (a) ε′, (b)ε″, (c) μ′ and (d)μ″ of FeCoNiAlCr0.9 HEA samples.

Fig. 6. Variation curves of calculated reflection loss (RL) with frequency under different thickness and simulations of absorber thickness and corresponding peak frequency based on λ/4 wavelength theory: (a) P0, (b) P20, (c) P30, (d) P40 and (e) P50.

Fig. 7. Frequency dependence of microwave reflection loss (RL) with 2 mm thickness for the Px (x = 0, 20, 30, 40 and 50) samples. With the increased PCA volume, the effective bandwidth (RL < - 10 dB) gets enhanced.

Fig. 8. Calculated attenuation constant α of the Px (x = 0, 20, 30, 40 and 50) samples at 1-18 GHz. Due to the existence of skin effect, the particles with larger thickness are not suitable for EM absorbent.

Fig. 9. Schematic representation of EM wave absorbing mechanism in HEA particle.