Magnetic properties of Sm3Fe28.1ÀxCoxMo0.9 „xÄ0,4,8,12,14,16... compounds

A series of Sm3Fe28.12xCoxMo0.9 compounds (x50,4,8,12,14,16) have been synthesized and their magnetic properties and structures investigated by means of x-ray diffraction and magnetic measurements. It is found that substitution of Co for Fe leads to a significant increase of the Curie temperature and saturation magnetization. Even more important, for x>14 the easy magnetization direction changes from easy plane to easy axis. In this compound system, Sm3Fe12.1Co16Mo0.9 is a very promising candidate for rare-earth permanent magnetic materials. Its room temperature saturation magnetization (m0M s51.50 T) and anisotropy field (Ba56.5 T) are comparable to those of Nd2Fe14B (m0M s51.60 T and Ba57.0 T). However, its Curie temperature is 1020 K, which is substantially higher than that of Nd2Fe14B (TC5588 K). The lattice inversion method has been employed to calculate the site occupancies of Mo and Co in the quaternary 3:29 type Sm3Fe282xCoxMo compounds (x50, 4, 8, 12, 16!. The results show that Co preferentially occupies Fe1, Fe8, and Fe11 sites, whereas Mo occupies Fe3, Fe2, and Fe6 sites. As Co atoms preferentially occupy Fe1, Fe8, and Fe11 sites, the negative exchange interactions of Fe-Fe pairs associated with the sites are modified into positive and strong interactions of Fe-Co or Co-Co, which leads to the rise of Curie temperature. The bond lengths between various atoms obtained by computer simulation are used to calculate the Curie temperatures of Sm3Fe292xMox (x50 and 1!. The calculated Curie temperature of Sm3Fe28Mo is close to the experimental value.