Magnetic Properties and Interstitial Atom Effects in the R(Fe,M)₁₂ Compounds

Abstract

Permanent magnets are now widely used in motor, generator, telecommunication, and control devices, and are considered as indispensable materials in everyday life. Until now, the intermetallics composed of the rare earth and 3d elements have been mainly developed as high-performance permanent magnets, such as SmCo₅, Sm₂ (Co,Fe)₁₇ and Nd₂Fei₄B (Stmat et al., 1967; Ojima et al., 1977; Buschow, 1977; Mishra et al., 1981; Sagawa et al., 1984; Croat et al., 1984; Hadjipanayis et al., 1984; Sellmyer et al., 1984). As the main, components Sm and Co are particularly expensive, and therefore it is desirable to use the less costly iron-based Compounds in place of the cobalt-based Compounds. Despite the initial promise of the Nd₂Fe₁₄B magnet, Problems associated with its poor temperature stability and corrosion resistance have ensured that the search for even better permanent magnetic materials continues unabatedly. Since 1987, worldwide efforts have been made to investigate the magnetic properties of R(Fe_1−x M _x )₁₂ (M = Ti,V,Mo, Cr,Mn,W, AI or Si)(Yang et al., 1981; Buschow, 1988, 1991; Li and Coey, 1991; Suski, 1996, and references therein). Among them, Sm(Fe,M)₁₂ seems to be the best potential candidate for permanent magnet applications (Schultz and Katter, 1991a). Unfortunately, Sm(Fe,M)₁₂ appears to offer less practical use than Nd₂Fe₁₄B. The Curie temperature is almost the same as that of Nd₂Fe₁₄B, but its Saturation magnetization is lower than the Sm(Fe,M)₁₂, which leads to the conclusion that the theoretical maximum energy product (BH)_max of Sm(Fe,M)₁₂ is only half that of Nd₂Fe₁₄B.