Synergistic Co ₂ O ₃ /Bi ₂ O ₃ co-doping in MnZn ferrites for ultra-low magnetic noise shielding in quantum precision measurements

Abstract MnZn ferrite, characterized by the low power loss, the high electrical resistivity, and the high magnetic permeability, is a promising candidate for the low-noise magnetic shielding applications. However, as the dissipative material, MnZn ferrites inherently generate a magnetic noise, which fundamentally limits the sensitivity of the magnetometers operating in the spin-exchange relaxation-free (SERF) regime. Herein, we report a synergistic co-doping strategy using Co2O3 and Bi2O3 to effectively suppress the intrinsic magnetic noise of MnZn ferrites. By systematically tuning the concentrations of Co2O3 and Bi2O3, the power loss, complex magnetic permeability, and microstructural evolution of undoped, singly doped, and co-doped MnZn ferrites are comprehensively investigated. Notably, co-doping with 1600 ppm Co2O3 and 400 ppm Bi2O3 reduces the low-frequency magnetic noise by more than 50%, which is attributed to refined grain boundary structures and suppressed hysteresis losses. The optimized MnZn ferrite is further employed to fabricate a magnetic shield for a SERF magnetometer, achieving a single-channel sensitivity of 0.25 fT/Hz1/2. This study paves an effective materials-engineering route to minimize magnetic noise in ferrite-based shielding systems, providing a solid foundation for the development of next-generation ultra low-noise platforms for the quantum precision measurements.