Magnetic hyperfine interactions and compositional short range order in the Heusler alloys Cu2MnIn1-xSnx

A comprehensive study of the magnetic hyperfine interactions and the processes of crystallographic ordering in the Heusler alloy system Cu₂MnIn_1-xSn_x has been made. We report the results of Mössbauer effect experiments, X-ray diffraction studies, electrical transport, and Curie temperature measurements. By a rapid quenching, low temperature annealing technique we have been able to extend the ordered L2₁ structure to high Sn concentration. Observations of inequivalent Sn sites and nonunique ¹¹⁹Sn hyperfine field values in these alloys are shown to be due to difficulties in ordering the L2₁ structure and a basic instability of this phase for high Sn concentrations. The compositional variation of ¹¹⁹Sn hyperfine fields in the ordered L2₁ phase of the Cu₂MnIn_1-xSn_x system reveals a systematic increase with Sn composition. Calculations of these fields based on a homogeneously spin polarized electron gas model reproduce the observed field systematics quite well. The implications of these results on the nature of magnetic interactions in Heusler alloys are discussed.