Temperature-Based Magnetic Viscosity Parameter for Evaluating Long-Term Magnetization Stability of Permanent Magnets

Time-dependent polarization losses are critical for assessing the long-term stability of permanent magnets. Conventional determination of the magnetic viscosity parameter Sv, typically obtained using vibrating sample magnetometry (VSM), requires precise control of temperature and magnetic fields. This work introduces a simplified temperature-based approach using a heatable rotating sample in a Helmholtz measurement coil to determine a temperature-based magnetic viscosity parameter SvT, comparable to the traditional field-based Sv. Applied to common NdFeB permanent magnet grades, SvT increases with material coercivity and shows close agreement with Sv results. The concept of a fluctuation temperature further allows direct assessment of time-dependent polarization losses and quantitative implementation in numerical calculations such as finite element analysis (FEA). These results suggest the proposed method as a robust and experimentally simplified alternative for magnetic viscosity characterization and prediction of future magnetization states.