High SnO2-doped MnZn ferrite for low-noise magnetic shielding at subzero temperatures

Manganese-zinc ferrite with high electrical resistivity is widely used for a low-noise magnetic shielding in ultra-sensitive magnetic field measurements. However, thermal magnetic noise in ferrite materials perturbs the measurement accuracy. Herein, a high SnO 2 -doped MnZn ferrite with enhanced permeability at subzero temperatures is reported. Compared to the undoped MnZn ferrite, the addition of 6000 ppm SnO 2 increases the real part permeability by 19.3% at −50 °C. Based on the experimentally measured complex permeability and the analytical model for an idealized cylindrical-shield, the calculated magnetic noise is reduced by 24.6%, yielding a calculated magnetic noise level of 4.86 fT/Hz 1/2 @20 Hz at −50 °C with a complex magnetic permeability μ′ = 4018, μ″ / μ′ 2 = 7.46 × 10 −5 . Moreover, a 26.3% calculated magnetic noise reduction is also observed at −50 °C relative to the undoped sample. This work estimates the significant potential of high-SnO 2 -doped MnZn ferrite for low-noise magnetic shielding applications at subzero temperatures. Systematic data on the evolution of magnetic permeability across the subzero temperature range have been lacking, and the correlation between the temperature-dependent shift of the magnetocrystalline anisotropy zero-crossing point and low-temperature magnetic-noise suppression has yet to be established. Clarifying this correlation provides a viable route toward understanding the underlying mechanism of magnetic-noise suppression and offers a potential strategy for optimizing ferrite compositions for low-noise magnetic shielding at subzero temperatures.