Magnetism of (FeCo)Si alloys: Extreme sensitivity on crystal structure

Theoretical results for (FeCo)Si substitutional random alloys, obtained within the framework of the exact muffin-tin orbitals method in combination with the coherent potential approximation, are presented. For concentration range 0.1 < x < 0.9, the magnetic structure of Fe1-xCoxSi is found to be almost degenerate, which is reflected in extreme sensitivity of the local magnetic moments on the internal structure parameters and lattice constant. Results are analyzed and discussed using Stoner, covalent magnetism, and rigid band models. In Fe-rich and in Co-rich alloys, the composition dependence of the magnetic moments can be understood in terms of a simple model. It is shown that disorder has a significant effect on magnetism in (FeCo)Si alloys.