Phase equilibria and magnetic properties of iron-rich Fe-Nd-Ti and Fe-Sm-Ti alloys

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Abstract
In Fe-Nd-Ti and Fe-Sm-Ti the phase with the hexagonal structure of Co5R is stabilized by the addition of Ti and has a rare-earth content just above 12 at. %, but well below 16.7 at. %, so that it must be classified as a Cu7Tb type. It and Fe17R2 dissolve approximately 3 at. % Ti, accompanied by an increase in Curie temperature in the latter. In Fe-Nd-Ti the phase with the tetragonal Mn12Th structure is found near Fe11TiNd, and its low-anisotropy field is verified. It forms in the cast alloys and is stable only above 1000 °C. At 1000 °C and below it decomposes according to Fe11TiNd→Fe17Nd2 +Fe2Ti+Fe. In Fe-Ti-Sm the high-anisotropy phase Fe11TiSm does not undergo this decomposition down to 700 °C, but it is restricted by the coexistence of Fe17Sm2 and Fe2Ti. As a result, Fe11TiSm is found accompanied by either free Fe or easy-plane Fe17Sm2. A new phase Fe9.5Ti1.5Sm has the structure of tetragonal Ce(Mn,Ni)11 with a=0.8253 and c=0.4825 nm; it has no permanent magnetic moment at room temperature. The high-anisotropy phase near Fe70Ti10Sm20 is not observed between the melting temperature and 700 °C.