Sintered Sm2Co17-Based Magnets With Small Additions of Indium

In an attempt to develop anisotropic high-temperature permanent magnets consisting Of Sm-2 (Co,Fe)(17) grains separated by thin layers of a nonmagnetic phase, small amounts of Ag, C, Ga, In, and Sri were added to the Sm2Co17-based alloys and sintered magnets. Grain-boundary phase(s) with the melting temperature of 985-1070 degrees C was obtained by adding 0.5-1.5 at. % In to Sm-Co, Sm-Co-Fe, and Sm-Co-Mn alloys with the Sin content slightly enriched compared to the 2 : 17 stoichiometry. Iron, manganese and, apparently, oxygen tend to decrease the melting temperature of the grain-boundary phase(s). Due to this low-melting-temperature phase, sintering of the milled Sm2Co17-based alloys becomes possible at temperatures as low as 1025-1075 degrees C. This phase is also believed to be responsible for the coercivity of 6-8 kOe observed in the Sm-Co-Fe-Mn-In alloys. The coercivity was found to be critically sensitive to the postsintering heat treatment: it dramatically deteriorates when the magnets are annealed below the melting temperature of the grain boundary phase(s).