Soft magnetic properties of amorphous alloys based on iron can be improved by a thermal annealing at temperatures closed to the crystallization temperature. This is usually attributed to formation of nanocrystalline grains (αFe, αFe(Si)) embedded into amorphous matrix. For the Fe₈₀Nb₆B₁₄ amorphous alloy the optimization effect was attributed to annealing out of free volume without formation of nanograins. Nb atoms cause a slowing down of diffusion processes which makes possible to obtain the relaxed amorphous phase. The optimization effect without formation of nanograins is very interesting because it can give very good soft magnetic material free of embrittlement.

The aim of the paper is to study the application of the Fe₈₀Nb₆B₁₄ amorphous alloy as electromagnetic shields. The strips of as received material (thickness d=25 µm) were annealed at 700 K/1h. This optimization annealing gives material with initial magnetic permeability about 3x10⁴ and coercive field less than 1 A/m. In order to study the shielding effectiveness single shields (25x25 cm²) were made of two layers of optimized amorphous strips. Each layer was glued onto one side of double-sided scotch tape. Every shield consists of more than 50 strips forming a uniform soft magnetic plane with thickness d=50 µm.

For magnetic field (impedance<377Ω) in frequency range 0.2-10000 kHz for a single shield b decreases from 15 to 5 dB. For a quadruple shield (d=200 µm) b>20 dB in frequency range 0.2-10 kHz. The shielding effectiveness for electric field (impedance>377Ω) decreases from 50 to 20 dB (2-15 MHz) independently of shield thickness. The best result was obtained for electromagnetic field (far zone, 200-1000 MHz). In this case for a single shield in all frequency range the shielding effectiveness is better than 30 dB. For a triple (d=150 µm) and quadruple (d=200 µm) shields b>100 dB.

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