Performance of Low-Noise Ferrite Shield in a K-Rb-₂₁Ne Co-Magnetometer

Spin-exchange relaxation-free (SERF) co-magnetometer is considered to be a promising nuclear spin gyroscope due to its ultrahigh rotation measurement sensitivity and magnetic field disturbance cancellation ability. Recent experiments indicate that the relaxation of the noble-gas spins would result in reduction of the magnetic field disturbance cancellation ability, which means that magnetic noise from the passive magnetic shield in a SERF co-magnetometer can cause rotation rate measurement error. In this paper, the magnetic field frequency response of a SERF atomic magnetometer is derived based on state space method and the magnetic noise of different shield materials are measured. The magnetic noise error model in a SERF co-magnetometer is then derived and the magnetic noise induced rotation rate measurement error is quantitatively evaluated. The superiority of ferrite shield is shown by the performance of a K-Rb-²¹Ne co-magnetometer. Experimental results show that ferrite shield with lower magnetic noise and better temperature stability is a more favorable choice for the inner shield of the co-magnetometer.