Abstract
This paper reviews our study of developing a sintering technique of thermally degradable Sm – Fe – N powders. The Sm – Fe – N coarse powder in the flake form was sintered using a low-thermal-load process of high pressure current sintering. By using cyclic compaction and optimum sintering temperature, this process produced dense isotropic bulk magnets without thermal decomposition that exhibited the high maximum energy product of 17.1 MGOe. Meanwhile, the Sm – Fe – N fine powder was also sintered by the same sintering technique. The coercivity of the sintered compacts considerably decreased regardless of sintering temperatures under the thermal decomposition temperature. TEM and XPS analyses on the grain boundaries led to estimation of the mechanism of coercivity decrease: the oxidation-reduction reaction between the initial iron oxides and the primary Sm – Fe – N phase generated α – Fe phases which might act as reverse magnetic domain nucleation sites.
