Electronic Structures of Manganese-Substituted Iron-Cobalt Alloys

The substitution of manganese in the body-centered cubic iron-cobalt alloys has been shown to either decrease or increase the mean saturation moment of the ternary alloys. On the basis of a modified band model, this varying effect of Mn may be ascribed to the occupancy of the localized $d$ states of the Mn atoms. An increase in the moment is observed when Mn is added to alloys with the atom ratio of Co: Fe ≥1 in which the localized $d$ states are just half filled according to Hund's rule. At lower ratios, however, the localized $d$ states become first more than half empty and eventually nonexistent. The rates at which the substitution of Mn decreases the mean moment of the latter alloys change accordingly. The proposed electronic structures are consistent with observations that the increase of residual resistivities of Fe-Co alloys caused by 1 at.% Mn also varies sensitively with the Co: Fe ratio of the host alloy.