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Magnetic properties, phase evolution, and microstructure of melt spun Sm(Co0.97M0.03)xCy (M=Hf and Zr; x=5–9; y=0–0.15) ribbons quenched at the wheel speed of 40 m/s have been investigated. X-ray diffraction analysis show that the main phases exist in Sm(Co0.97M0.03)x ribbons are 1:5 for x=5 and 5.5, 1:5 and 1:7 for x=6 and 6.5, 1:7 for x=7 and 7.5, 1:7 and 2:17 for x=8, and 2:17 for x=8.5 and 9. The grain size of 200–500 nm for these two series of ribbons is almost unchanged when x is increased from 5 to 9. Accordingly, the magnetic properties of Sm(Co0.97M0.03)x ribbons (M=Hf and Zr) are mainly dominated by their phase constitutions. Furthermore, a slight addition of C to Sm(Co0.97M0.03)x ribbons refines the grain size down to 10–50 nm, resulting in the improvement of magnetic properties. Sm(Co0.97Hf0.03)7.5C0.1 ribbons show the optimal magnetic properties of Br=6.9 kG, Hic=9.2 kOe, and (BH)max=10.0 MGOe. For the Sm-lean Sm(Co,Hf)xCy (x=8.5–9) ribbons, higher Hf and C content are required to improve the magnetic properties. The magnetic properties of Br=6.8 kG, Hic=6.2 kOe, and (BH)max=7.2 MGOe could be obtained in Sm(Co0.94Hf0.06)9C0.15 ribbons.

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The influence of Dy substitution for Nd on magnetic properties, temperature characteristics, and microstructure of (FeCo)NdB magnets has been studied. The Dy appears mainly in the tetragonal matrix phase and in the Nd-rich phase. The Dy in the tetragonal matrix phase increases the anisotropy, and twin boundaries and convoluted grain boundaries appear. These phenomena appear to be related to the increase in coercivity. In addition to the Nd(FeCo)2 (Laves) phase in the alloys with high Co and Dy content, a new phase (NdDy)(CoFe)5.2 appears. This phase causes coercivity to decrease, but may improve the temperature coefficient of the alloys.