Effects of interactions between grains with different alignment degrees on the coercivity and its angular dependence for Nd16 (Fe0.8 Co0.2) 78 B6 sintered magnets have been studied. The experiments show that the intrinsic coercivity jHc decreases with enhancing grain alignment (decreasing alignment coefficient ó), the coercivity jHc (θ) increases with increasing angle θ between the applied field and the texture axis of the magnets and the variation ratio is larger for the magnets with better grain alignment. The coercivity of the magnets should be determined by the critical field making the moment of individual grains reverse and the interactions between the grains. For the sintered magnets composed of the grains with μm size, the magnetostatic interaction between the grains is stronger than the exchange coupling interaction and it makes the coercivity of magnet increase with increasing alignment coefficient ó. Taking into account the intergrain interactions, the starting field theory of coercivity is in good agreement with the experimental results for Nd16 (Fe0.8 Co0.2) 78 B6 sintered magnets.

The hard magnetic properties and the interactions between the grains for sintered Nd16 Fe73 Co5 B6 magnets are investigated by using δM (H) plot technique. The results show that the δM (H) plot of NdFeB sintered magnet can explain the effects of the microstructure (size, shape and orientation of the grains) and the intergrain interactions on the hard magnetic properties of the magnet. However, the value of δM (H) is positive when the applied field is not strong enough, which means that the common δM (H) plot theory is not completely consistent with the sintered NdFeB magnet.

The effect of small amount of Co and Dy addition on the magnetic properties of HDDR Jsotropic NO-Dy-Fe-Co-B bonded magnets was investigated. The experimental results show that the Jn-trinsic coercivity Hcj and the reversible temperature coefficient of remanence of (Nd0.65 Dyo 35) 12.5-(Fe0.9 Co0.1) 81 B 6.5 magnet were 1.53 MA.m-1 (19.3 kOe) and-0.059%/℃ (25-155℃), respec-tively. The high coercivity and tow temperature coefficient of the magnet are due to the enhanced anisotrepy field, increased Curie temperature and improved microetructure by Dy and Co addition.