The hyperfine field at the Sn site in the Heusler alloys ${\mathrm{Co}}_2\mathrm{Mn}{Z}_{0.98}{\mathrm{Sn}}_{0.02}$, for $Z=\mathrm{A}\mathrm{l},\mathrm{G}\mathrm{a},\mathrm{S}\mathrm{i},\mathrm{G}\mathrm{e},\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{S}\mathrm{n}$, was measured using the Mössbauer effect. Values of +40.5, +35.3, -15.6, +6.2, and + 102 kOe were obtained for the five alloys, respectively. ${\mathrm{Co}}_2$MnAl and ${\mathrm{Co}}_2$MnGa both have magnetic moments of approximately 0.5${\mathrm{\mu }}_{\mathit{B}}$/Co and 3.0${\mathrm{\mu }}_{\mathit{B}}$/Mn as well as similar lattice parameters. It is therefore reasonable that the Sn-impurity-site hyperfine fields are similar in the two alloys. The ${\mathrm{Co}}_2$Mn(Si,Ge,Sn) series of alloys all have moments of approximately 0.75${\mathrm{\mu }}_{\mathit{B}}$/Co and 3.6${\mathrm{\mu }}_{\mathit{B}}$/Mn. The large variation in field in these alloys can be attributed to differences in the lattice parameters. Theoretical predictions of Jena and Geldart, and of Blandin and Campbell, and the volume-overlap model of Stearns, are applied to these alloys. Neither the model of Jena and Geldart nor the model of Blandin and Campbell is in satisfactory agreement with our experimental results. Numerical results for the volume overlap cannot be attained because of the lack of experimental results for the Co-based Heusler alloys. Trends predicted by this model are discussed in terms of the results obtained in this study.

• Received 23 July 1982

DOI:https://doi.org/10.1103/PhysRevB.26.6013