Magnetic hardening in iron-neodymium-boron permanent magnets

Abstract
The origin of magnetic hardening has been examined in Fe‐Nd‐B magnets by correlating the magnetic properties with the microstructure and magnetic domain structure observed with electron microscopy. Hysteresis loops and susceptibility studies show a magnetic anomaly at around 140 K. Microstructure studies reveal the presence of at least four phases with compositions Fe14R2B, Fe4NdB4, a high‐Nd‐content phase, and α‐Fe. Initial magnetization studies, magnetic viscosity data, the temperature dependence of coercivity, and magnetic domain studies all indicate domain wall pinning at grain boundaries.