Experiment research on residual magnetization of rare earth permanent magnet for cryogenic undulator

The magnetic properties of commercial polycrystalline Nd₂Fe₁₄B (N50M, N45H, N40SH, N35EH) and Sm₂Co₁₇ (XG30/20, XG26/25, XG22/20) magnets at cryogenic temperatures were tested by using a comprehensive physical properties measurement system (PPMS). The results show that spin tilt temperature T_st of Nd₂Fe₁₄B magnets is closely related to intrinsic coercivity H_ci, N50M and N45H with smaller H_ci show a residual magnetization jump at 235 K and 225 K, respectively. For Sm₂Co₁₇ magnets, in 50-300 K, with temperature decreasing, residual magnetization M_rc shows a nearly linear increase, while in 10-50 K, M_rc has little change. The research results provide a reference for cryogenic undulators and other high-precision cryogenic devices.