A magnetic noise-free environment is essential for ultra-high sensitivity atomic magnetometry operating in a spin exchange relaxation-free regime. The critical limitation to achieving theoretical sensitivity arises from the magnetic noise of the innermost MnZn ferrite, which includes magnetization noise (related to ferrite hysteresis loss) and Johnson current noise (associated with ferrite resistivity). To address the issue, MnZn ferrites with high resistivity and permeability were designed and fabricated in this work. A series of MnZn ferrites with varying Fe₂O₃ content were synthesized using the solid-phase reaction method. The experimental samples were denoted as Mn_0.678-xZn_0.4Fe_1.922+xO₄ (x=0-0.208, 0.026/step). All samples exhibited a uniform single spinel structure. As Fe₂O₃ content increased, the grain size grew, and the pores migrated from the intragranular regions to grain boundaries. Saturation magnetization and permeability of samples initially increased followed by a subsequent decrease, whereas coercivity demonstrated an inverse trend. The resistivity decreased from approximately 2.40×10⁵Ω·mm to 2.62×10²Ω·mm. The ferrite sample with x=0.078 exhibited optimal electromagnetic performance, with a resistivity of 4.86×10² Ω·mm, permeability of 1536, and an $A$$A$ value of 6.058×10^-8 (associated magnetization noise, $A=\tan \delta /\omega \mu \prime$$A=\tan \delta /\omega \mu \prime$, 100 Hz, 25°C). The optimized composition was employed to fabricate large-sized ferrite ceramic plates measuring 150 mm × 150 mm × 3 mm using the cold isostatic pressing process. A ferrite shielding chamber was subsequently constructed. The application of the ferrite shield reduced the magnetic noise of the experimental device from 73.7 fT/Hz^1/2 to 20 fT/Hz^1/2.

中文翻译：

---

MnZn 铁氧体的 Fe2O3 成分优化及其在低频磁屏蔽应用中的磁噪声评估

无磁噪声环境对于在无自旋交换弛豫状态下运行的超高灵敏度原子磁力测量至关重要。实现理论灵敏度的关键限制来自最内层 MnZn 铁氧体的磁噪声，其中包括磁化噪声（与铁氧体磁滞损耗有关）和约翰逊电流噪声（与铁氧体电阻率有关）。为了解决这个问题，本工作设计并制备了具有高电阻率和磁导率的 MnZn 铁氧体。采用固相反应法合成了一系列不同 Fe ₂ O ₃ 含量的 MnZn 铁氧体。实验样品表示为 Mn _0.678-x Zn _0.4 Fe _1.922+x O ₄ （x=0-0.208， 0.026/step）。所有样品均呈现均匀的单尖晶石结构。随着 Fe ₂ O ₃ 含量的增加，晶粒尺寸增大，孔隙从晶内区域迁移到晶界。样品的饱和磁化和磁导率最初增加，随后降低，而矫顽力则表现出相反的趋势。电阻率从大约 2.40×10 ⁵ Ω·mm 下降到 2.62×10 ² Ω·mm。x=0.078 的铁氧体样品表现出最佳的电磁性能，电阻率为 4.86×10 ² Ω·mm，磁导率为 1536， $A$ 磁导率为 6.058×10 ^-8 （伴磁化噪声， $A=\tan \delta /\omega \mu \prime$ 100 Hz，25°C）。采用优化的成分，使用冷等静压工艺制造尺寸为 150 mm × 150 mm × 3 mm 的大型铁氧体陶瓷板。随后建造了一个铁氧体屏蔽室。 铁氧体屏蔽层的应用将实验装置的磁噪声从 73.7 fT/Hz ^1/2 降低到 20 fT/Hz ^1/2 。