Magnetic properties, microstructure and magnetization reversal in sintered Nd12.2Fe81.8B6 magnets with the addition of Tb17Fe75B8

Abstract

Abstract Nd12.2Fe81.8B6 and Tb17Fe75B8 powders were mixed to prepare sintered magnets by the powders preparation, pressing and sintering. With a small addition of Tb17Fe75B8 powders the coercivity increases largely in the Nd-Fe-B/Tb-Fe-B magnets. For the addition of 0.5 g Tb17Fe75B8 (the mass ratio 0.5:9.5 of Tb17Fe75B8 and Nd12.2Fe81.8B6), the coercivity increases to 15.8 kOe, 2.2 times of that in Nd12.2Fe81.8B6. With more amount addition of Tb17Fe75B8 powders the coercivity keeps to increase, and the increase is larger than that of the conventional dual-alloy method. The magnets consist of two main phases, but the atomic interdiffusion is evident for Nd and Tb. Via the investigation of thermal activation it shows that the domain walls size decreases for a little amount addition of Tb17Fe75B8 powders. So the magnetocrystalline anisotropy increases near grain boundary of Nd-Fe-B phase owing to Tb diffusing and substituting for Nd, which is beneficial to the enhancement of coercivity. For the addition of Tb17Fe75B8 more than 0.7 g the domain wall size doesn’t decrease evidently, suggesting that the existing of interfacial exchange coupling which also contributes to the increase of coercivity in the sintered composite magnets.