Electronic structure and magnetic behavior ofUMn2andUFe2

The electronic structure of ${\mathrm{UMn}}_2$ and ${\mathrm{UFe}}_2$ has been determined using the first-principles self-consistent spin-polarized scalar-relativistic linear muffin-tin-orbital method. The calculations were performed at several lattice spacings for these materials in the C15 (cubic Laves phase) crystal structure. In agreement with experimental data it is found that ${\mathrm{UMn}}_2$ is almost nonmagnetic (small moments on the sites) whereas in ${\mathrm{UFe}}_2$ both U and Fe sites have appreciable moments. Furthermore, the magnetism in these systems is determined by exchange splitting and not by charge-transfer effects. The calculated moments in ${\mathrm{UFe}}_2$ are larger at the U sites than those seen experimentally. The total moment in ${\mathrm{UFe}}_2$ is somewhat insensitive to changes in lattice spacing (over the limited range determined) while the moments on individual sites are very sensitive to this variation.