First principles study of transition-metal substitutions in Sm–Co permanent magnets.

The microchemistry and magnetism of conventional and high-temperature Sm-Co permanent magnets are investigated by first-principles calculations. Particular emphasis is on the site preference for the substitution of Cu, Ti, and Zr in SmCo₅ and Sm2Co₁₇ compounds. Cu substitution is more favorable in the 1:5 phase, in agreement with experimental findings. Titanium and zirconium have positive solution energies for both the phases, with Ti(Zr) having slight preference for the 1:5 (2:17) phase. Some Zr may segregate to the phase boundaries because of its large solution energy. For Ti and Zr the dumbbell site of the 2:17 phase is preferred over the other three inequivalent cobalt sites. These results are used to discuss the observed cellular nanostructure of the high-temperature Sm-Co hard magnets with composition close to the 2:17 phase. [ABSTRACT FROM AUTHOR]