Disorder and noncollinear magnetism in permanent-magnet materials

We report calculations of the noncollinear magnetic structures and of the magnetic anisotropies of YFe12-xMox permanent magnets with the ThMn12 structure, using a novel variant of a spin-polarized tight-binding-linear-muffin-tin-orbital technique allowing for local spin-quantization axes on each site and considering spin-orbit coupling. The ternary YFe12-xMox compounds crystallize in the tetragonal ThMn12 structure which can be stabilized only by the partial substitution of Fe by an early transition metal like Mo. We show that the substitutional disorder leads to canted spin-structures at low Mo content (x similar to 1) and to spin-glass-like behavior at higher Mo content (x similar to 3). We also find that the character of the anisotropy changes from uniaxial to planar with higher Mo content. (C) 1996 American Institute of Physics.