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)) x 10(-8) A center dot m(2). The measurement precision of the mr is about 0.9 nA center dot 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.