Measurement of remanent magnetic moment using a torsion pendulum with single frequency modulation method

In TianQin spaceborne gravitational-wave detectors, the stringent requirements on the magnetic cleanliness of the test masses demand the high resolution ground-based characterization measurement of their magnetic properties. Here we present a single frequency modulation method based on a torsion pendulum to measure the remanent magnetic moment m _r of 1.1 kg dummy copper test mass, and the measurement result is (6.45±0.04(stat)±0.07(syst)) × 10 ⁻⁸ A⋅m ². The measurement precision of the m _r is about 0.9 nA⋅m ², well below the present measurement requirement of TianQin. The method is particularly useful for measuring extremely low magnetic properties of the materials for use in the construction of space-borne gravitational wave detection and other precision scientific apparatus.