Investigations of the magnetic properties and demagnetization processes of an extremely high coercive Sm (Co, Cu, Fe, Zr)7.6 permanent magnet II. The coercivity mechanism

The magnetic hysteresis loops for sintered multiphase Sm(Co0.68Cu0.08–Fe0.22Zr0.02)7.6 permanent magnets are investigated in the whole ferromagnetic temperature range between 10 K and Tc=1070 K. The measured temperature and field dependence of the coercive field is analysed within the framework of theoretical results for pinning fields of different magnetic phases. The influence of annealing treatments on the coercive field is compared with the intrinsic magnetic properties of the appearing ferromagnetic phases of 2:17 and 1:5 type. It is concluded that in the whole ferromagnetic temperature range nucleation of reversed domains and pinning of domain walls simultaneously occurs in the 1:5 type precipitation structure. For a quantitative interpretation of the coercive field a consideration of gradients of the magnetic material parameters inside coherent phase boundaries is necessary. A phenomenological model for phase boundaries is presented which qualitatively explains the measured hysteresis loops and coercive fields.