Precision Measurements of the Magnetic Parameters of LISA Pathfinder Test Masses

A precise characterization of the magnetic properties of LISA Pathfinder free falling test-masses is of special interest for future gravitational wave observatory in space. Magnetic forces have an important impact on the instrument sensitivity in the low frequency regime below the millihertz. In this paper we report on the magnetic injection experiments performed throughout LISA Pathfinder operations. We show how these experiments allowed a high precision estimate of the instrument magnetic parameters. The remanent magnetic moment was found to have a modulus of (0.245 +-0.081) nAm^2, the x-component of the background magnetic field within the test masses position was measured to be (414+-74) nT and its gradient had a value of (−7.4 +- 2.1) μT/m. Finally, we also measured the test mass magnetic susceptibility at 5 mHz to be (−3.3723 +- 0.0069) × 10^(−5). All results are in agreement with on-ground estimates.