Volume magnetic susceptibility of gold–platinum alloys: possible materials to make mass standards for the watt balance experiment

In 2000, the Bureau National de Métrologie (BNM, France) decided to develop a new watt balance experiment. Among numerous design studies, the choice of the transfer mass is particularly important. Because of the proximity to a source of high magnetic intensity, this mass must have a magnetic susceptibility as weak as possible. Gold–platinum alloy seems to meet this requirement, as well as additional requirements for density and hardness values, making it a possible candidate for mass standard realization. Five different gold–platinum alloys were studied, their volume magnetic susceptibility ranging from −2.8 × 10 −5 to −2.1 × 10 −5 for two of them and from +1.1 × 10 −5 to +8.8 × 10 −5 for the other three.