Fe‐Based Nanocrystalline Magnetic Shielding Cylinder with Subfemtotesla‐Level Magnetic Noise

The precision measurement of extremely weak magnetic fields using spin-exchange relaxation-free atomic magnetometers demands magnetic shielding system with high shielding efficiency and low magnetic noise. Conventional magnetic shielding system (CMSS) based on µ-metal, however, often exhibits high magnetic noise. Herein, we propose a strategy to overcome this challenge, which is realized by using the Fe-based nanocrystalline (Fe-Nano) magnetic shielding cylinder (MSC) as the innermost magnetic shield of CMSS. The Fe-based nanocrystals (Fe-Nanos) prepared via the melt-spinning method followed by a three-step annealing process exhibit excellent soft magnetic properties with the permeability of 64 000, indicating superior magnetic shielding performance. The average loss factor of the Fe-Nanos is only 2.4 × 10^-7, which is significantly lower than that of µ-metal and indicates that Fe-Nanos has lower intrinsic magnetization noise. The Fe-Nano MSC with different thicknesses significantly suppresses magnetic noise when used as the innermost magnetic shield of CMSS. In particular, the ten-layer Fe-Nano MSC achieves an average magnetic noise of 0.84 fT Hz^-1/2 in the frequency range of 20-100 Hz. This work provides a lightweight, easily processable, and cost-effective strategy for the magnetic shielding system with ultra-low magnetic noise, which will promote its large-scale application in emerging fields such as biomagnetism and fundamental physics.