Assessment of Directionally Solidified Eutectic SmFe(Co)Ti Alloys as Permanent Magnet Materials

Sm-Fe-Ti and Sm-Fe0.8Co0.2-Ti alloys were prepared via arc-melting and directionally solidified on a water-cooled copper hearth. The as-solidified alloys featured cells of the Sm(Fe,Co,Ti)(12)-Ti(Fe,Co)(2+delta)-(alpha-Fe) lamellar eutectic. The lamellae of Sm(Fe,Co,Ti)(12) phase with a crystal structure of the ThMn12 type were less than 0.2 mu m thick and had their [001] easy-magnetization directions oriented along the temperature gradient of the solidification. The eutectic microstructure led to an increased coercivity, especially in the Co-added alloys. Below 250 degrees C, this coercivity was found not to vary much with temperature with a temperature coefficient of -0.18%/degrees C. However, the modest absolute values, reaching only 0.7 kOe, are insufficient for the utilization of the directionally solidified alloys as anisotropic permanent magnets.