Sm₃(Fe,Co,Mo)₂₉ compounds: promising materials for permanent magnets

The outstanding hard-magnetic properties are reported of Sm_3Fe_28.1-xCo_xMo_0.9 compounds with x=12, 14, 16. In this alloy system, only a small amount of Mo is needed to stabilize the 3:29 structure so that the magnetic properties are not seriously affected by the presence of this nonmagnetic element. Substitution of Co for Fe leads to a significant increase of the magnetic anisotropy, and for x≥14 the easy magnetization direction changes from easy plane to the easy axis. In this alloy system, the compound Sm_3Fe_12.1Co_16Mo_0.9 is a very promising candidate for permanent magnet applications. Its room temperature saturation magnetization (\mu_0M_s=1.5 T) and anisotropy field (B_\rm an=6.5 T) are comparable to the values for Nd_2Fe_14B (\mu_0M_s=1.6 T and B_\rm an=7 T). However, the Curie temperature of Sm_3Fe_12.1Co_16Mo_0.9 is 1020 K, which is appreciably higher than that for Nd_2Fe_14B (T_\rm C=588 K).