Fine-grained NdFeB magnets prepared by low temperature pre-sintering and subsequent hot pressing**Project supported by the National Natural Science Foundation of China (Grant No. 51101167), the National Science and Technology Major Project, China (Grant No. 2012ZX02702006-005), the Local Cooperation Project of Chinese Academy of Sciences (Grant No. DBSH-2011-013), the Natural Science Foundation of Zhejiang Province, China (Grant No. LQ14E010007), and the

Abstract

Fine-grained Nd10.79Pr2.8Al0.4B7.72Fe78.29 magnets were prepared by low temperature pre-sintering and subsequent hot pressing. The grain size of the magnets is just about 1–3 μm because the low sintering temperature results in no grain growth. The orientation degree, microstructure, and magnetic properties were studied. Some grains’ easy axes deviate from the orientation direction, possibly due to grain rotation during the hot pressing. By subsequent annealing, the magnetic properties were significantly enhanced. Especially, the squareness of the demagnetization curve was improved greatly. The enhancement of coercivity by annealing can be explained by an improvement of both grain boundaries and magnetic isolation, which decouples the exchange interaction between neighboring grains.