Internal-Field Variations with Temperature for the Two Sublattices of OrderedFe3Al andFe3Si

Abstract

Using the Mössbauer technique, the variation of the internal magnetic field with temperature from 4.2°K to about $0.9T_c$ was measured for each sublattice of ordered ${\mathrm{Fe}}_3$Al and ${\mathrm{Fe}}_3$Si structures. The variation of the reduced internal field with reduced temperature was observed to be almost identical on all the sublattices. In these alloys, it is expected that the reduced internal field varies in the same manner as the reduced magnetization for each sublattice. Thus, we can compare these measurements with the magnetization curves calculated from molecular-field theory. In this way, we obtain the exchange energies for each sublattice and for the interaction between the two sublattices. The values for the ${\mathrm{Fe}}_3$Al structure are $J_{\mathrm{AD}}=120\mathrm{}\pm 15°$K, $J_{\mathrm{AA}}=70\mathrm{}\mp 20°$K, and $J_{\mathrm{DD}}=7\mathrm{}\mp 5°$K. These values of the exchange energies are very reasonable, indicating that the molecular-field treatment satisfactorily describes the behavior of these alloys. The success of molecular-field theory is consistent with the view that the ferromagnetic behavior of Fe and these alloys is due to the long-range coupling of the atomic spins by the itinerant $d$ electrons.