Characterization of ferromagnetic saturation at 4.2K of selected bulk rare earth metals for compact high-field superconducting cyclotrons

Abstract

The saturation magnetization of the rare earth ferromagnetic metals gadolinium and holmium was investigated. Cylindrical samples were placed in a superconducting test magnet and induced magnetic field measured at various applied fields. Data was obtained with Hall sensors mounted at the tips of the cylinders, and a powerful analytical calculation was derived to allow estimation of the saturation magnetization from this surface data. If the metal is saturated in a uniform, vertical magnetic field, the measured field at the surface due to the magnetization of the cylinder is just the saturation magnetization divided by a factor of two. Results show saturation magnetization values ranging from 0.5 to 1.5 T higher than iron, establishing the candidacy of these metals for advanced superconducting cyclotron pole tips.