Off-stoichiometry, epitaxial $\mathrm{F}{\mathrm{e}}_x\mathrm{S}{\mathrm{i}}_{1-x}$ thin films $(0.5<x<1.0)$ exhibit $D{0}_3$ or $B2$ chemical order, even far from stoichiometry. Theoretical calculations show the magnetic moment is strongly enhanced in the fully chemically disordered $A2$ phase, while both theoretical and experimental results show that the magnetization is nearly the same in the $B2$ and $D{0}_3$ phases, meaning partial chemical disorder does not influence the magnetism. The dependencies of the magnetic moments are directly and nonlinearly linked to the number of Si atoms, primarily nearest neighbor but also to a lesser extent (up to 10%) next nearest neighbor, surrounding Fe, explaining the similarities between $B2$ and $D{0}_3$ and the strong enhancement for the $A2$ structure. The calculated electronic density of states shows many similarities in both structure and spin polarization between the $D{0}_3$ and $B2$ structures, while the $A2$ structure exhibits disorder broadening and a reduced spin polarization.

• Received 20 April 2014

DOI:https://doi.org/10.1103/PhysRevB.91.144402