STRUCTURE AND MAGNETIC-ANISOTROPY OF SM2FE17-XALXC (X=2-8) COMPOUNDS PREPARED BY ARC MELTING

In previous work it was discovered that the 2:17-type rare-earth-iron compounds with high carbon concentration could be formed by the substitution of Ga, Si, or Al, etc., for Fe in R2Fe17Cx. The effect of Al substitution for Fe on the structure and magnetic anisotropy of Sm2Fe17C has been investigated. Alloys with the composition of Sm2Fe17-xAlxC (x=2, 3, 4, 5, 6, 7, and 8) were prepared by arc melting. The carbides are single phase with rhombohedral Th2Zn17-type structure except for Sm 2Fe17C which contains a small amount of α-Fe. The addition of Al results in an approximately linear increase in the lattice constants and the unit-cell volumes. The Curie temperature Tc is found to increase slightly when x≤3, then decrease rapidly with increasing Al concentration, while the room-temperature saturation magnetization decreases monotonically with the addition of aluminum. X-ray-diffraction and magnetization measurement studies of magnetic-field-oriented powders demonstrate that the samples with x≤6 exhibit an easy c-axis anisotropy at room temperature and the room-temperature anisotropy field increases from 5.3 T for x=0 to about 11 T for x=2. Further substitution decreases the anisotropy field. For the sample with x=2, the room-temperature anisotropy field is higher than that of Nd 2Fe14B, and the saturation magnetization is about 110 emu/g. In this alloy, the substitution of a small amount of other elements, such as Co, Ni, etc., may yield a further improvement in its magnetic properties. Thus, it is possible that these carbides can be used as the starting materials for producing high-performance 2:17-type sintered permanent magnets.