Measurements of Magnetic Properties of Kilogram-Level Test Masses for Gravitational-Wave Detection Using a Torsion Pendulum

In spaceborne gravitational-wave detectors, the stringent requirements on the magnetic cleanliness of the test masses (TMs) make the development of ground-based characterization techniques of their magnetic properties important. An electrostatically controlled torsion pendulum has been built to measure the magnetic properties of TianQin-like solid TMs. The remanent magnetization mᵣ and the magnetic susceptibility χ of TMs can be measured at the level of 1 nA m² and 8×10^-7, respectively. The precisions of measurements are mainly limited by the mechanical sensitivity of silicon fiber. The experimental results from a solid tungsten TM as an example show that the apparatus provides a feasible way to investigate the bulk effect of a full-size TM for the TianQin mission with enough resolution.